The Norwegian aurora polaris expedition, 1902-1903

LIBRARY

UNIVERSITY OF

CALIFORNIA
SANTA CRUZ

THE NORWEGIAN

AURORA POLARIS EXPEDITION

1902-1903

VOLUME I

ON THE CAUSE OF MAGNETIC STORMS AND
THE ORIGIN OF TERRESTRIAL MAGNETISM

BY
KR. BIRKELAND

FIRST SECTION

LEIPZIG

JOHANN AMBROSIUS EARTH

CHRISTIANIA
H. ASCHEHOUG & CO.
LONDON, NEW YORK

LONGMANS, GREEN & CO.

PARIS
C. KLINCKSIECK

Of

.

CHRISTIANIA A. W. BRGGGERS PRINTING OFFICE 1908

PREFACE.

1 he knowledge gained, since 1896, in radio-activity has favoured the view to which I gave
expression in that year, namely, that magnetic disturbances on the earth, and aurora borealis, are
due to corpuscular rays emitted by the sun.

During the period from 1896 to 1903 I carried out, in all, three expeditions to the polar
regions for the purpose of procuring material that might further confirm this opinion. I have
moreover, during the last ten years, by the aid of numerous experimental investigations, endea-
voured to form a theory that should explain the origin of these phenomena. It is the results of
these investigations that are recorded in this work, the first volume of which treats of terrestrial
magnetic phenomena and earth-currents, this section forming the first two thirds of the volume.
The second volume will treat of aurora and some results of meteorological observations made at
our stations.

The leading principle that I have followed in this work has been to endeavour always to
interpret the results of the worked-up terrestrial-magnetic observations, and the observations of
aurora, upon the basis of my above-mentioned theory.

Thus the magnetic storms, for instance, have been studied in such a manner, that on the
one hand we have formed from our observation-material a field of force which gives as complete
a representation as possible of the perturbing forces existing on the earth at the times under
consideration. On the other hand, by experimental investigations with a little magnetic terrella
in a large discharge-tube, and by mathematical analysis, we have endeavoured to prove that a current
of electric corpuscles from the sun would give rise to precipitation upon the earth, the magnetic
effect of which agrees well with the magnetic field of force that was found by the observations
on the earth.

Although our observation-material of magnetic storms was, I may safely say, the largest that
has ever been dealt with at one time, it was deficient in certain points, as might well be expected.

We generally had at our disposal in 1902 — 1903, magnetic registerings from 25 observatories
scattered all over the world, among them being our 4 Norwegian stations on Iceland, Spitsbergen,
Novaja Semlja, and in Finmark.

We have moreover treated separately certain well-marked magnetic storms in 1882—1883,
from the observations in the reports of the international polar expeditions.

In addition to the deficiencies in our observation-material, there are also defects in the
experimental and mathematical investigations; but notwithstanding all this, the results are so
satisfactory that I can hardly be mistaken in my belief that we are on the right road.

IV

Besides making clear the origin of important terrestrial phenomena, the investigations give
promise of the possibility of drawing, from the energy of the corpuscular precipitation on the
earth, well-founded conclusions regarding the conditions on the sun.

The disintegration theory, which has proved of the greatest value in the explanation of the
radio-active phenomena, may possibly also afford sufficient explanation as to the origin of the
sun's heat. The energy of the corpuscular precipitation that takes place in the polar regions
during magnetic storms seems indeed to indicate a disintegration process in the sun of such
magnitude, that it may possibly clear up this most important question in solar physics.

Future researches in the paths here entered upon, which I believe will lead to the solution
of some of the most attractive scientific problems of our age, e. g. the origin of terrestrial
magnetism, and the origin of the sun's heat, may be carried out upon a far wider basis than I
have been able to employ, without making the expenses connected therewith too great a deterrent.

In 1Q02— 1903 I had the great good fortune of having twenty-five observatories with me;
but on a future occasion it will be necessary to have double the number.

We should then have to send out small expeditions with, say, ten stations suitably distributed
about each of the magnetic poles, and make sure of getting magnetic registerings for the same
period from all the observatories in the world.

As the position of the stations, within certain limits, may be chosen with tolerable freedom,
the end would be best attained by accompanying whalers, or, as I once had to do, equipping
such vessels one's self for certain places.

The mathematical investigations, which, together with my experiments, are intended to make
clear the movement of electric corpuscles from the sun to the earth, have been carried out, with
a perseverance and ingenuity worthy of all admiration, by my friend, Professor STORMER, who will
publish the complete results of his investigations in a special part of the present work. These
results, however, will be known to some extent from the papers he has already published.

In concluding this first section, I have to thank those persons who have so greatly assisted
me in my work. In Mr. L. VEOARD I have had an invaluable collaborator, whom I have to thank
for many excellent suggestions. Great merit is also due to Mr. DIETRICHSON and Mr. KROGNESS
for their share in this work; and I would further thank Messrs. RUSSELTVEDT, NORBY and IRGENS,
for their energetic labour.

The translation, which I consider very successful, has been performed by Miss JESSIE MUIR.

Christiania; October, 1Q08

Kr. Birkeland.

CONTENTS.

INTRODUCTION. Page

Art. i. The first Expedition, 1897 - ' i

„ 2. The second Aurora Expedition, 1899 — 1900 5

THE EXPEDITION OF 1902 — 1903 9

„ 4, 5. The Auroral Station in Kaafjord 10

„ 6, 7. The Auroral Station in Dyrafjord, Iceland 18

„ 8, 9. The Auroral Station in Spitsbergen - 24

„ 10, n. The Auroral Station in Novaja Semlja 31

„ 12. The Working-up of the Material 37

PART I.

MAGNETIC STORMS, 1902—1903.
INVESTIGATIONS BY MEANS OF DIURNAL REGISTERINGS FROM 25 OBSERVATORIES.

CHAPTER I.
PRELIMINARY REMARKS CONCERNING OUR MAGNETIC RESEARCHES.

„ 13. Our Aim and our Method of Working 41

„ 14. On the Calculation of the Perturbing Force 44

„ 15. On the Separation of Simultaneous Perturbations 47

CALCULATION OF THE SCALE-VALUES FOR THE REGISTERINGS AT THE NORWEGIAN STATIONS.

„ 1 6. Determination of the Scale-Values for the Declinometer 48

„ 17. Determination of the Sensibility of the Variometers for the Horizontal and Vertical Intensity 48

„ 18. Determinations of Sensibility for Kaafjord and Bossekop 5°

„ 19. Determinations of Sensibility for Dyrafjord 51

„ 20. Determinations of Sensibility for Axeleen 53

„ 21. Determinations of Sensibility for Matotchkin Schar 54

„ 22. Temperature Coefficients for the Registerings 55

„ 23. Explanation of the Charts 56

„ 24. The Copies of the Magnetic Registerings, Explanation and General Remarks . . . 58

CHAPTER II.
ELEMENTARY PERTURBATIONS.

„ 25. General Remarks 61

„ 2.6. The Equatorial Perturbations 62

„ 27. The Positive Equatorial Perturbation. The Perturbation of the 26th January 1903 . . 63

„ 28, 29. The Perturbations of the 9th December, 1902 7°

„ 30. The Perturbation of the 23rd October, 1902 7^

VI

Page

Art. 31. Concerning the Cause of the Positive Equatorial Perturbation .... .... 78

„ 32. The Negative Equatorial Storms 83

,. 33- The Polar Elementary Storms -84

„ 34. The Typical Field for the Polar Elementary Storms 85

„ 35. The Perturbation of the isth December, 1902 87

„ 36. Concerning the Cause of the Perturbation ' 95

« 37> 38- The Perturbation of the loth February, 1903 • 106

•I 39- Concerning the Cause of the Perturbation 113

„ 40 — 43. The Perturbations of the 3oth and 3151 March, 1903 115

„ 44—47. The Perturbations of the 22nd March, 1903 127

„ 48. The Perturbations of the 26th December, 1902 137

„ 49- Cyclo-Median Storms 144

» 5°> 51- The Perturbation of the 6th October, 1902 145

„ 52. Concerning the Cause of the Perturbation 149

„ 53. Further Comparison with Stormer's Mathematical Theory 158

CHAPTER III.
COMPOUND PERTURBATIONS.

„ 54. The Perturbation of the 29th and 3oth October, 1902 161

„ 55. The Perturbation of the 25th December, 1902 164

„ 56. The Perturbation of the 28th December, 1902 169

» 57> 58- The Perturbations of the I5th February, 1903 172

„ 59, 60. The Perturbations of the 7th and 8th February, 1902 187

„ 61, 62. The Perturbations of the 27th and 28th October, 1902 209

„ 63, 64. The Perturbations of the 28th and 2gth October, 1902 222

„ 65, 66. The Perturbations of the 3ist October and ist November, 1902 230

„ 67. How these Perturbations may be explained 234

„ 68. The Perturbations of the nth and I2th October, 1902 251

„ 69. Concerning the Cause of the Perturbations. Positive and negative Polar Storms . . . 268

„ 70, 71. Tht Perturbations of the 23rd and 24th November, 1902 272

" 72» 73- The Perturbations of the 26th and 27th January, 1903 286

„ 74. Further Comparison with the Terrella-Experiments 297

CHAPTER IV.

CONCERNING THE INTENSITY OF THE CORPUSCULAR PRECIPITATION
IN THE ARCTIC REGIONS OF THE EARTH.

„ 75. Development of General Formulae 303

„ 76—79. Numerical Values for Height and Strength of Current 306

„ 80. The Energy of the Corpuscular Precipitation. The Source of the Sun's Heat . . . . 311

PLATES.

PI. I. The Perturbation of the 6th October, 1902

PI. II. The Perturbations of the nth and I2th October, 1902.

PI. III. The Perturbation of the 23rd October, 1902.

PI. IV. The Perturbations of the 27th and 28th October, 1902.

PI. V. The Perturbations of the 28th and 2gth October, 1902.

PI. VI. The Perturbations of the 2gth and 3oth October, 1902.

PL VII. The Perturbations of the 3ist October and ist November, 1902.

PI. VIII. The Perturbations of the 23rd and 24th November, 1902.

PI. IX. The Perturbations of the gth December, 1902.

PI. X. The Perturbation of the isth December, 1902.

PI. XL The Perturbation of the 25th December, 1902.

PL XII. The Perturbation of the 26th December, 1902.

PL XIII. The Perturbation of the 28th December, 1902.

PL XIV. The Perturbation of the 26th January, 1903.

PL XV. The Perturbations of the 26th and 27th January, 1903.

PL XVI. The Perturbation of the 8th February, 1903.

PL XVII. The Perturbations of the 8th February, 1903.

PL XVIII. The Perturbation of the loth February, 1903.

PI. XIX. The Perturbation of the isth February, 1903.

PL XX. The Perturbations of the 22nd March, 1903,

PL XXI. The Perturbations of the sist March, 1903.

ERRATA.

Page 44, line 14 from above: For "in front of the special treatment of the separate perturbations", read
"at the end of this volume".

„ 59 : As the table shows, e, is not determined for Wilhelmshaven. By comparing the vertical curves
with those from Potsdam, we found by deduction that e, = 10 y per mm. might not be so far
from the right value. This value has been used in the calculations. On a later inquiry at the obser-
vatory, we obtained the value EV = 20 y per mm., but it was rather uncertain. This value, how-
ever, we have not made use of, for in what we had to consider it was the direction of the
vertical component and its variation that were of the most importance, and not the actual amount
of P,.

„ 67, line i from below: For "Chap. Ill", read "Part II, Chap. I".

„ 68—208, On the Charts, for "Vv", read "/>„".

„ 70, line 12 from below: For "negative", read "positive".

„ 71, lines 12 & 13 from above: For "must be of a somewhat local character", read "must belong to

another system".

» 96, ,, 7 & 6 „ below : After "positive vortices" add "of the negative rays".

» 96, „ 6 & 5 „ „ For "divergence", read "convergence", and vice versa.

„ 121, Table XVIII, Zi-ka-wei, P, line 14: For "5.83 X 10 /', read "5.8 y".

„ 128, line 3 from below: For "Chapter III", read "Part II, Chapter I".

„ 198, Table XXX, Christchurch, P, line i: For "—1.5 y", read "+i.sy".

INTRODUCTION.

'"THE EXPEDITION of which the results are here given, is the third of a series which the author,
with the aid of the Norwegian State, the University and the Scientific Society in Christiania,
and private persons, got together and led, with the object of investigating the aurora borealis and magnetic
disturbances in the polar regions.

1, The first expedition, in February and March, 1897, was a failure, partly owing to unfortunate
circumstances, but chiefly to a lack of experience. The idea was to make it a reconnoitring expedition,
in order that we might gather knowledge and prepare for a larger expedition; but it was also our special
aim to find out whether the northern lights could, as frequently asserted, come right down to the tops
of the mountains in the district between Bossekop and Kautokeino on the Finland border of Norway,
and to make atmospheric-electric and magnetic measurements high up on the mountains during the
occurrence of aurora.

The expedition has not been described before, because it was such a sad adventure; but now that
time has drawn a veil of melancholy oblivion over the misfortune that befell us, I will briefly relate
some of our experiences. An acquaintance with these may be of some interest to those who may think
at some future time of making investigations in the winter on the mountains in the far north.

Besides myself, there were two excellent students, B. HELLAND-HANSEN and K. Lows, who shared
in the investigations. They had offered themselves as assistants solely out of interest in the matters
to be dealt with.

We set off from Christiania on the and February, and by the 8th were ready to ascend the
mountain from the well-known polar station Bossekop in Finmark. We had procured reindeer to take us
and our traps, and a first-class guide in the old Finn "postvappus" (postman), CLEMET ISAKSEN H^ETTA.

After a quick run in brilliant moonlight, we arrived at the mountain hut of Gargia, 25 kilometres
south of Bossekop.

The reindeer, each with its pulk, were fastened together in a line one behind another, called a
"raide", and the pace, especially down-hill, was something tremendous.

The next morning, the gth February, there was a little wind, but we all got ready for the start,
both those who were going to Kautokeino, those who were returning to Bossekop, and we who were
going up to Lodikken Hut on Beskades, 16 kilometres from Gargia. The temperature that day was

o /-«

-25 C.

When we got up on to Beskades, the snow was drifting a little, but not at first in any alarming
degree; and we went on up the comparatively gently sloping mountain, passing cairn after cairn on the
Kautokeino road, up which we went at a walking pace for a distance of about 10 kilometres. The
wind howled a good deal in the old, weather-beaten guide-posts with their outstretched arms, that showed
that day both where the wind came from and where the road went to, as we passed them one by one;
but we did not interpret it as a warning. The storm increased, however, and we asked the vappus several
times if it were safe to proceed, and whether he was sure of the way, to which he answered "Yes".

Birkeland, The Norwegian Aurora Polaris Expedition, 1902 — 1903.

BIRKKI.AND. THF. XORWKGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

Fig. I.
Postvappus C. I. Haetta.

We then left the road with the cairns, to go up towards Lodikken on the wild mountain, having
then 5 kilometres to reach the hut. But the storm increased with frightful rapidity. The guide had to
lead the reindeer, or they would not face the wind; and it was impossible to sit in the pulk, as at that
height from the ground we were pelted with bits of ice and even small stones, which did not reach
our face when we were on our feet.

We worked our way on; but while the storm increased, our strength
diminished.

At last the vappus cried that we should have to turn back, but the next
moment said, "No, we must go on. We can't have more than 2 kilometres to
go, and perhaps it will be more difficult to go down than up."

So on we went. Progress was very slow, and I felt that I was approaching
a critical state of weariness. Immediately after, Helland-Hansen's nose and chin
were frost-bitten, but nothing could be done. Fortunately the affected parts
were soon covered with a protecting mask of ice, beneath which they gradually
thawed, whereupon the ice was removed.

Later on we were all more or less frost-bitten in the exposed parts of our
face, the vappus in particular, a large part of his face being white with frost-bite.
It was not long before some of the reindeer lay flat down, and the vnpptis
thereupon threw himself upon a pulk, declaring that he could go no farther, and
could not find the way. "You must go on by yourselves, and keep the wind
in your face," he said.

Under these circumstances there was no question of continuing our way; the only thing to be done
was to make what arrangements we could, and get into our sleeping-bags as quickly as possible. We
agreed, however, to try and build a barricade with the pulks and our baggage, and behind it to put up
a little low tent upon a piece of hard snow.

While thus engaged, Helland-Hansen
got his hands frost-bitten. It was done in
a few minutes. We then got into our
sleeping-bags with all possible speed, Lows
being the last, as he had been the toughest,
and was the least exhausted.

The twenty hours we lay thus were
a dismal time for us. We passed it partly
in lying and thinking our own thoughts,
partly in struggle, first Helland-Hansen's
desperate and vain attempts to bring life
into his fingers, and then our endeavours
to prevent our being buried in the snow;

Fig. 2. A "Raide" of Reindeer.

for wherever there was a little shelter from

the wind, the snow would heap itself up into a thick, compact drift, in which you sat as in a vice if

you let it grow.

After the long night, it at last began to grow light; but the wind was almost as strong. The vappus
had lain all the time in his Finn furs under a pulk. I shouted to him from my bag until at last he
heard and crawled up to me. I said we must try to get down to Gargia again, and asked him to take
all the baggage and instruments off the pulks. His only answer was that he was so fearfully cold; and
nothing was done until Lows crept out of his bag, and set things going. Lows was the one who had

INTRODUCTION.

kept up best, but then before he lay down he had had the good sense to rip up a bag of bread with
his knife, and take out a loaf. He divided it into two, and threw one half over to me; but I did not
hear him shout when he did this, and thus had none. He had gnawed at his half during the night, and
of course it had strengthened him; and he was the only one of us who had tasted food since we left
Gargia.

At last we started, each in our pulk, after the guide had solemnly asked us if it were really our
intention to try to get back to Gargia in this weather. We could not see more than a few yards in
front of us, but we were quite determined to try.

The couple of hours spent in the descent were the most exciting I have ever gone through. It
was now that our guide showed himself to be the adept that I had been told he was. It was wonderful
to see the way he ran to the right or to the left, to find tracks or take a course, and how he drilled

:- ' _1 . - . rffti

Fig. 3. Lodikken Hut on Beskades.

the reindeer when they became unmanageable and suddenly set off up in the face of the wind again.
The energy he developed when once he had thawed was incredible. At last we had the good fortune
to run almost up against a cairn with a sign-post on the Kautokeino road, and then we knew we
were alright.

We got back to Gargia at 4 p. m., 31 hours after we had left it. Here Helland-Hansen's hands,
which were white and stiff to the wrists, were immediately put into ice-cold water, and kept there until
they thawed; and by this means the circulation returned to his hands, except the end joints of eight
fingers. We then at last got something to eat, not having tasted food all through the terrible journey;
and then we once more turned our attention to Helland-Hansen's hands, which were in a terrible state,
and dressed them as well as in the mean time we were able. And in spite of everything, our spirits
now rose high, in our intense delight at having at any rate not lost our lives.

Next morning I went to Bossekop for a doctor, who came and bandaged Helland-Hansen's hands
properly; but he could not of course give any opinion as to how it would end. Under his aegis, Helland-
Hansen was taken to Bossekop, whence he went on as soon as possible with Lows, who took charge of

4 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

him, to Hammerfest, and went to the hospital ('). I remained at Gargia to await an opportunity of going
with the guide to look for our things, the instruments in particular. The first time we set out on the
search, the wind was so high that we had to come down again.

The journey back down the Beskades hills with fresh reindeer, was the wildest piece of driving
one can imagine. The animals flew like the wind, and galloped along in places where a horse would
have gone carefully step by step. We had five reindeer fastened together in a raide, and I sat in the
last pulk, firmly lashed to it. Occasionally the pulk was thrown over the edge of the slope, notwith-
standing that I put on all the brake that I possibly could with my elbows, which were well protected
with fur. Once indeed my reindeer itself fell, wonderfully sure-footed though it was; but after being
dragged along by the others for a few moments, it managed to struggle to its feet without assistance.
The day after this unsuccessful attempt, we once more went up. There was a little wind in the
morning, very much as it had been on the gth; but this time, instead of increasing, it gradually dropped
as we ascended; and when we began to beat up and down in the neighbourhood of the place in which
our things might be supposed to be, the sun shone out brightly, and there was no more wind than that
the Finn could light his pipe.

We found the things at last, nearly all of them buried in the snow, scarcely more than one
kilometre from Lodikken hut, where we had thought of staying.

We dug out nearly all our things, and got safely back to Gargia with them.

That evening there was bright aurora, and I therefore unpacked some instruments, and had the
good fortune to make an interesting observation, which I have described in the report of my 2nd
aurora expedition (2).

We had previously, also on our first expedition, made a very interesting observation of a rare,
but very significant, auroral phenomenon, which I will here briefly describe. To myself it is of special
interest from the fact of its being my first auroral observation of any importance. Moreover it immedi-
ately appeared to me that the observation was a confirmation of the hypothesis put forward by me in
1896 regarding the origin of the aurora, namely that the northern lights are due to cathode rays or
similar rays emitted by the sun, these rays being drawn in from space towards the earth by the terrestrial-
magnetic forces.

It was ten minutes to six on the evening of the 5th February, when we were some miles from
Hammerfest, the weather clear and the moon shining, when there appeared a sharply-defined arc of light
from east to west through the zenith. From the very first, the arc was very intense, but very narrow,
right above our heads. Notwithstanding the bright moonlight, the aurora, which soon began to pass
through various phases of development with draperies and sheaves of rays, was visible up to half past
seven, when it disappeared.

At Hammerfest the next day, the weather was just as clear; and at five minutes past six, the same
arc suddenly appeared again, though considerably fainter. Its manner of development and its disappear-
ance were so similar to those of the arc of the preceding day, that the phenomena left a decided
impression that the position of the sun or the moon in relation to the earth must play a direct part
in them.

It may, as we know, not infrequently be seen in the registering of magnetic disturbances, not only
that well-defined perturbations reappear on two or more consecutive days, which in other respects may
be fairly calm magnetically, but that these well-defined perturbations can be so wonderfully uniform in

(') HELLAND-HANSEN is now Director of the Biological Station at Bergen.

(a) Expedition Norv6gienne de 1899—1900 pour 1'etude des aurores bordales, par KR. BIRKELAND, p. 76. Videnskabs-
Selskabets Skrifter 1901, No. i.

INTRODUCTION.

character, that the impression they leave is similar to that of the above-mentioned auroral observation.
We shall return to this parallelism between aurora and magnetic disturbances later.

Fig. 4. Sukkertop and Talviktop.

2. The second aurora expedition,

from September, 1899, to April, 1900, had
stations upon the top of two mountains
about 3000 feet in height, Sukkertop
and Talviktop, situated in the moun-
tain district of Haldde, on the west side
of the Alten Fjord, between Kaafjord
and Talvik.

As long before as the autumn of
1897, after my unsuccessful first expedi-
tion, I had again been up in Finmark
to find a mountain that would do for
my auroral investigations. After ascend-
ing and examining six of the highest
mountains about Kaafjord, and the Lang

Fjord, I decided on Sukkertop and Talviktop — the latter situated at a distance of 3^4 kilometres to the
north of the first-named mountain — as most suitable for my purpose.

I then obtained a grant from the State in order to build two small mountain observatories on these
summits. They were built of stone and cement, and were finished in September, 1899; so upon those
Haldde mountains, right in the southern margin of the auroral zone, there now stand two of the best

auroral observatories in the world. In
clear weather everything that takes place
in the sky can be observed, from the
point where it begins to that where it
leaves off. The view is uninterrupted,
and from both observatories, but espe-
cially the highest and northernmost, there
is a panorama stretching from the sharp,
blue peaks of the Kvaenang mountains
in the west, to the softer outlines of the
Porsanger mountains in the east, and
from the precipitous cliffs of Lang Fjord
and Stjerne Island in the north to the
mountain plateau in the south, stretching
inland in undulating lines as far as the
eye can see, in towards the winter home
Fig. 5. On the way to Snkkertop. of the mountain Lapps. And far below

lies the fjord like a dark channel that
is continued in the Alten valley itself and its numerous branches.

The expedition of 1899 — 1900 was furnished, inter alia, with self-registering barometers, thermo-
meters, and hygrometers, and also with apparatus for the photographic registration of the three com-
ponents of terrestrial magnetism, and of the electric condition of the atmosphere. On Sukkertop we

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

Fig. 6. The Observatory on Sukkertop.

had kites, with self-registering instruments for investigations high up in the atmosphere; but the wind was
almost always very strong up on the mountain, and we very soon lost them. The members of the

expedition were myself, SEM
S^ELAND, amanuensis at the Uni-
versity Physical Institute, E.
BOYE, a student, K. KNUDSEN,
telegraphic engineer, and a cook.
The results of the expedi-
tion's magnetic investigations
and of the auroral observations
have been already published
in the above-mentioned work,
whereas the meteorological ob-
servations have unfortunately
not yet been worked up.

Many of our experiences
during our stay upon these
mountain-tops were such as
others have probably not passed
through; for as far as is known
no one has ever before passed
a winter upon the highest mountain-summits in Finmark.

It is my intention, however, not to relate here much more about our life and our difficulties in the
second and third expeditions than may serve to show the development in these undertakings, but to tell
enough to give those who may make future expeditions in the same regions, the benefit of our experience
to build upon.

The natural force with which we
especially had to battle with up in
Haldde was the wind; for it sometimes
blew fearfully. We were unable to mea-
sure the highest velocities, but once we
measured one of 46 metres per second.
For this we used two good little hand
anemometers of Richard Freres; but
they were certainly not intended for
such great wind-velocities, and what the
error may have been in these extreme
measurements, I cannot say.

We often had much greater hurri-
canes, however, than the one mentioned
which we measured. The wind some-
times roared so against the houses, that
you would have thought you were sitting

at the foot of a waterfall; and the floors trembled and everything shook. We soon got to be able to gauge
relatively the storm outside by the noise within. Our measuring apparatus, as I have said, did not allow
of our determining the greatest wind-velocities, and often we could not get out of the house ourselves for

Fig. 7. The observatory on Talviktop.

INTRODUCTION.

several days. One strong anemograph we had put up was blown to pieces in the course of a few days, and
we found pieces of it from 50 to 100 metres from the place where it had been put up. The reason of
this was probably that at the same time as the wind, the air was at times so saturated or supersaturated
with moisture, that ice formed upon everything. In nine or ten hours, ice-formations the length of one's
finger would be formed, always pointing towards the wind. Suspended telephone wires would become
as thick as a man's arm with ice. It was probably a heavy coating of ice such as this that destroyed
our very strongly built anemometer in a hurricane. In high winds it was impossible to go out, and
more than once, on Sukkertop, it took three men with a great effort to close our little door.

After storms such as
this, there were of course
many changes to be seen.
We have seen a layer of
snow a metre thick, and so
hard that you could jump
on it without sinking in,
practically disappear from
the summit in the course
of nine or ten hours. It
may be imagined then what
a whirling and drifting there
was in a wind, when the
snow was comparatively
fresh, and not pressed into
such a compact mass.

For the sake of com-
parison it may be mentioned
that the greatest wind-velo-
city observed by the Nansen

Fig. 8. Going to measure the wind-velocity.

Expedition in three years
was only 18 metres. This
is an interesting circum-
stance, for it shows that
on the ice-fields of the
polar regions in a more
restricted sense a compara-
tive stillness prevails in the
atmosphere.

As a rule the wind on
the Haldde mountains was
not especially cold, but it
could be sometimes. On the
2oth February, 1900, when
the temperature was — 33'5°
C., the wind-velocity was
about 20 metres. The
greatest wind-velocities ob-
served upon the Haldde
mountains are given below.

Temperatures of — 20° accompanied by winds with a velocity of from 20 to 30 metres were pretty
frequent both in January and February, 1900.

Wind-velocity
in metres
per second

Direction of
Wind

Temperature
C.

Nov. 17, 1899

37

NW

- T*°

Dec. 30, 1899

38

SSE

-13°

Jan. 20, 1900

38

S

-I6°

Feb. 28, 1900

35

NNE

-10°

March 3, 1900

4i

NW

- 5°

March 4, 1900

46

WNW

- 4°

No one who has not tried it can imagine what it is to be out in such weather. Knudsen, for
instance, once had one hand frost-bitten in the few minutes he was out to take a reading, although he
had on thick woollen gloves. He had neglected the precaution of having fur gloves over them. Frost-bite
such as this, however, is not serious when you can go at once into a warm house, and get ice-water
for your hands.

8

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

The wind would sometimes come like a rushing river at the one station, while it was fairly calm
at the other. On the igth January, for instance, on Sukkertop, the velocity of a wind from the SSW
was found to be 36 metres, while on Talviktop at the same time there was no wind, this being ascer-
tained by telephone. The wind was heard on Talviktop, however, as a tremendous rushing from the
south; and an hour and a half later the wind blew with tremendous force over both mountains.

In extreme cold and a high wind, it was uncomfortable on Talviktop. Water once froze there a
couple of yards from a glowing stove; and the lamp was blown out on the table in the middle of the
room, although in a general sense the house was well enough built.

The worst trouble was the repeated breaking of our telephone-wires, occasioned by the snow-
storms. At first the telephone wires between the two summits were hung upon poles in the usual
manner; but this proved to be useless. Either the wires themselves were blown to pieces, or the insulators

,\orm. pressure atO°t678 &»
Correspond to 760 nt sea-level

Fig. 9.

torn down, and the line in either case destroyed. On the other hand, the wires, when laid upon the
ground, keep fairly well, except on hills, where great snow-drifts are heaped up upon them. In such places
they often came to grief; and our first work after a fall of snow and storms used to be to get them
repaired.

In the same way we at first had a double line from Sukkertop down to Kaafjord; but here too
the wires were often broken, and we had great difficulty in repairing them.

A couple of hours before violent winds came over Haldde, great changes were generally observed
in the barometer, which sometimes went up and down at intervals of a few seconds; and when this
occurred, we knew that it would not be safe to start from one observatory to go to the other.

During the storms this vibration of the barometer, owing to dynamical causes, was very considerable,
as will be seen from the barograms, and could serve as a relative gauge for the violence of the storm.

Figure 9 shows a couple of correlated barograph and thermograph curves drawn on Sukkertop.
They show the conditions during these very January storms mentioned, which moreover were the cause
of many casualties on the coast of Norway that year.

INTRODUCTION. 9

In spite of our barograph predictions of storms, our postman, a sturdy little Finmark man, now and
again happened to come in for dangerous weather when he came with the post from Kaafjord once or
twice a week. We were often afraid for him, but he was always alright, though sometimes so covered
with ice when he arrived, that he was quite unrecognisable. I once asked him if he were never frightened
when the weather was so bad. At first he did not answer, but sat quietly down to thaw; but a little
while after he said: "I'm too stupid to be frightened".

Sad to say, our second aurora expedition was also destined not to terminate without a great mis-
fortune, which occurred just a week before we thought of packing up.

The very road that our postman traversed every week as long as the expedition lasted, was to be
the scene of the death of two clever men, an avalanche having overwhelmed in Sivertdalen five persons
who were on their way to visit the observatory in Haldde on the i6th March.

The two who perished were our good comrade, E. Boye, and Captain Lange, master of the Kaa-
fjord Mines' steamer; the other three escaped without injury. There had been an unusually heavy snow-
storm the night before, preceded by frost.

THE EXPEDITION OF 1902-1903.

3. The treatment of the observations that were collected during the 2nd aurora expedition, the results
of which have been published in the previously-mentioned work, showed with perfect clearness that in
order to solve the problem of the cause of the aurora and magnetic perturbations, it was necessary to
have at our command simultaneous magnetograms and observations from several suitable polar stations
at distances of about 1000 kilometres from one another, and also corresponding material from as many
other stations all over the world as it was possible to obtain.

I demonstrated namely, that certain well-defined magnetic perturbations that occurred over large por-
tions of the earth might be naturally explained as the effect of electric currents, which, it might be sup-
posed, in the polar regions flowed approximately parallel with the surface of the earth at heights of several
hundred kilometres, and strengths of up to a million amperes, if they could be measured by their effect
as galvanic currents. These currents in the polar regions were well defined and greatly concentrated, and
often passed for the most part between two neighbouring stations, as, for instance, Bossekop and Jan Mayen
(see "Expedition", etc., 1. c., p. 27), in such a way that Bossekop lay quite on the one side of the current,
and Jan Mayen on the other; and the magnetic effect of the currents in the polar regions was not in-
frequently as much as 20 times stronger than in Central Europe. The investigation of these phenomena
would necessarily, of course, require simultaneous registrations of the magnetic elements at several uniformly
equipped polar stations.

By such registrations, other important, unexplained phenomena that are very characteristically devel-
oped in the polar regions, might be excellently studied, e. g. the tremendous changes in the magnetic
components, which often occur at short intervals, especially during an aurora. A rapid registering of the
magnetic elements and of the earth-currents appearing simultaneously, would greatly assist the study of
these conditions.

It was with these things in my mind that from the beginning of 1901 I began to work for the sen-
ding out of a new aurora expedition, with stations in Finmark, Iceland, Spitsbergen and Novaja Semlja,
so as to obtain observations simultaneously from both sides of the auroral zone.

On this occasion also, the Norwegian Government looked upon my plans with favour, a grant of
20,000 krones being made by the Storthing towards a new expedition. The president of the Storthing,

Birkeland, The Norwegian Aurora Polaris Expedition, 1902 — 1903.

TO BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

GUNNAR KNUDSEN, J. FABRICIUS, a landed proprietor, and A. SCHIBSTED, editor of the "Aftenposten" then
contributed 6000 krones each; and the remainder, which amounted to about 30,000 krones, I have fur-
nished myself.

It may safely be said that economy is one of the virtues of Norwegians as a nation, perhaps one
may say a virtue of necessity; but the nation's idealism often turns the balance in delightful non-comfor-
mity with economy. The grants to my aurora expeditions are an instance of this. I will take this
opportunity of offering my respectful thanks to the government authorities, the scientific institutions, and
the private men who have given their support to these undertakings.

The preparations for the expedition were pushed on with the greatest energy for a year, and in
this I was ably assisted by my assistant of the 2nd expedition, Hr. S. Saeland. After a search in the
four lands mentioned above, for the purpose of finding suitable dwelling-houses with as easy access from
Christiania as possible, I fixed upon the following as my four stations: Kaafjord in Finmark, Dyrafjord
in Iceland, Axeleen in Spitsbergen, and Matotchkin Schar in Novaja Semlja.

The expedition was ready to start about the 1st July, 1902.

F

-

THE AURORAL STATION IN KAAFJORD.

4. This station was in the province of Finmark, close to the Kaafjord Copper Mines, in 69°56'N.
Lat. and 22° 58' E. Long.

The members of the expedition were RICH. KREKLING, a science graduate, and O. EGEN^S, an engineer.
The station was under my special supervision; during my absence it was managed by Krelding.

Sseland, Krekling and Egenaes set out for Kaafjord with their equipment on the zoth July, 1902,
and arrived at their destination on the I7th.

The first investigations that were made here during this expedition were simultaneous registerings
of the terrestrial-magnetic components, with two exactly similar sets of registering apparatuses. The

one set was placed in the mountain
observatory on Talviktop, the other
in a mine, 100 metres in under
the mountain. Saeland registered in
the mine, while the other two men
worked at the summit from the 26th
July to the 15th August.

The second series of investiga-
tions comprised magnetic and earth-
current observations, and in the
next place meteorological and at-
mospheric-electric measures. These
were made in Kaafjord during the
period from the i8th August, 1902,
to the 1 3th March, 1903.

The third series of investiga-

Fig. 10. The Kaafjord Station. tions- magnetic and earth-current

registering, was made, for reasons

given below, at Bossekop, during the period from the 15th March to the ist April, near the locality of
the polar station in 1882 and 1883.

bf
£

INTRODUCTION. 13

EQUIPMENT.

Magnetic Instruments.

A set of terrestrial-magnetic variation instruments with photographic registering apparatus and lamp
reflector of the Eschenhagen pattern from Otto Toepfer's, Potsdam.

An Eliott Brothers' unifilar magnetometer, belonging to the observatory in Christiania.

An inclinatorium, lent by Professor Rydberg, and previously used on the "Vega" expedition.

An earth-inductor, from G. Schulze in Potsdam, with galvanometer made by O. Pluth, Potsdam.

Earth-current Apparatuses.

Two Deprez-d'Arsonval galvanometers from Keiser & Schmidt, Berlin. As these instruments proved
to be bad, one of them afterwards had to be exchanged for one from Hartmann & Braun, Frankfort-
on-the-Main.

A registering apparatus with accessories, resistance-boxes, cables with rubber insulation, etc.

Meteorological Apparatuses.

A mercurial barometer.

A thermometer-screen with its thermometers, and spare thermometers.

A large barograph.

A large thermograph with forms, from the Meteorological Institute in Christiania.

A cloud-measuring apparatus, an anemometer from Richard Freres, Paris, etc.

Electrical Apparatuses.

An Elster & Geitel's electroscope with accessories for observations of dissipation of electricity in
the air.

A Zamboni battery, with wires, insulators and tightly-closing drum, from Gunther & Tegetmeyer,
Brunswick.

Astronomical Instruments.

The station had no permanent theodolite, as it was in telegraphic communication with the astrono-
mical observatory in Christiania. The azimuth
of the mark (the spire of Kaafjord Church) was
found by Saeland with a large theodolite in the
autumn of 1902, before he left for Iceland.

The expedition had borrowed from the
Military College in Christiania a box-chronometer,
Kessel 1390.

They also took with them books, papers,
etc., rifles, ammunition and provisions, as some
time was to be spent at the Haldde obser-
vatory. In Kaafjord, the members of the ex-
pedition put up at the Kaafjord Copper Mines.

Fig. 12. At the Astronomical Pillar.

14 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

BUILDINGS.

Upon the arrival of the expedition, the following buildings and contrivances were put up:
The terrestrial magnetic register-observatory.
The observatory for absolute determinations.
Hut for the registering of earth-currents.
Thermometer-hut.
Pillar for astronomical measurements, etc.

The Terrestrial Magnetic Register-Observatory.

This was a stone cellar, divided into two rooms, the outer of which served as an entry, the north,
inner room being the real observatory. (Plan Fig. 13). Here there were 4 stone pillars, the same as were
used in the polar year 1882 — 83, for the instruments and the registering apparatus. P, PI and PH, are
the pillars for the three instruments, PHI the one for the registering apparatus. L is the lamp reflector,
R the registering apparatus, V, D, and H the variometers for respectively the vertical intensity, declination,
and horizontal intensity, d1 and dH are the two doors.

The drawing beside the plan, on the magnetic meridian arrow, represents the position of the magnets
in the instruments in relation to the meridian. The magnets in the drawing are about one fifth of their
actual size.

The Observatory for the Absolute Determinations.

This observatory was a house of the same kind as that in Spitsbergen, the drawing of which will
therefore serve to illustrate this one. There was only one difference, namely that the stone pillar
upon which the various magnetic instruments and the earth-inductor were set when in use, was placed
in the middle of the house. The azimuth of the pillar was determined by triangulation, the pillar
forming one vertex of a triangle of which the two other vertices were the astronomical pillar (marked on
the map (i), and mentioned above under the heading 'Buildings'), and the spire of Kaafjord Church.

Hut for the Registering of Earth-Currents.

This hut was built of wood, and stood beside the magnetic register-cellar, as shown on the map.
The purpose of these earth-current investigations was to obtain photographic curves showing the varia-
tions in the earth-currents, especially during magnetic storms.

Four insulated cables of a length of 200 metres were laid down in the directions north, east, south,
and west. Their ends were connected with the earth by filling deep holes with coal-dust, which was
pressed firmly down round a bright copper wire.

In the register-house the two cables, north and south, were connected, with a suitable shunt, with
one galvanometer Deprez-d'Arsonval, and the east and west cables similarly connected with another
exactly similar galvanometer. The oscillations of the galvanometer were registered photographically.

Unfortunately these galvanometers, supplied by Reiser & Schmidt, Berlin, were very bad, so that at
last, after prolonged trial, we had to reject one and replace it with one from Hartmann & Braun, of Frank-
fort. When subsequently we succeeded in obtaining good photograph curves, an electromagnetic con-
trivance for the time-marks was arranged for all magnetic and earth-current registerings, in order to
facilitate comparison with the magnetic curves. Down in the dwelling-house, by the side of the chro-
nometer, the time could be marked on all the photograms by pressing an electric button. This, espe-
cially during the rapid march of the registering apparatuses, was of very great importance.

As it appeared that the earth-currents in Kaafjord had a predominant direction which seemed to
indicate that local conditions such as the proximity of the coast-line, etc., had something to do with it,

Kaafjord kBossekop

5 cafe

4, 5 Km..

Ground-plan

Ui* observatory in Xoo.
fjord/, Jfortaotf toUJi a diagra/n
shoving Ot£ position of th
in rtlott+x. to the ntailtftu meridian

Fig. 13-

INTRODUCTION. if

the whole auroral station, as already stated, was moved to Bossekop, in the vicinity of the polar station
of 1882 — 83, on the I3th March, 1903. Before many days had passed, all the instruments were again
in operation.

The Thermometer-Hut.

This was built like an English hut of wood, and large enough to contain the thermometer-screen
and the thermograph. The arrangement was the ordinary one. By the thermometer-hut was placed a
weather-vane, with which measurements were taken 3 times daily of the velocity of the wind, with the
aid of an anemometer Richard.

The barograph was placed in an unused room in the dwelling-house. Near it stood the cloud-
measuring apparatus, especially for use in determinations respecting polar bands and cirrus clouds.

The electric measurements with Elster and Geitel's apparatus, were also made in the vicinity of the
dwelling-house, in order that wind and weather should not have too disturbing an influence.

5. During our stay at the stations Haldde and Kaafjord, a journal was kept of the meteorological
elements, and of the aurora and cirrus-bands observed. These observations cover a period extending from
the 28th August to the end of February. For the last month, March, there are no records of this descrip-
tion, as the entire day was taken up with registering, especially rapid registering with changing of the
photographic paper on the instruments every two hours.

The meteorological observations were made regularly 3 times a day - - at 8 a. m., 2 p. m., and
8 p. m.

These observations show that the weather, as is usual in these regions at this time, has been very
variable. The sky has very seldom been quite clear, but was as a rule covered with clouds, a circum-
stance which has to some extent hindered us in our observations of aurora.

Some idea of the weather-conditions at this time may be obtained by looking at the table below,
in which the highest and lowest temperatures and barometer-readings, and the highest wind-velocity ob-
served at the above-mentioned hours are given for each month.

Month

Temperature

Barometer-reading

Wind-velocity

Max.

Min.

Max.

Min.

Max.

C°

C°

Metres per sec.

1 1 '6

6'8

766-7

q'c

September ....

14-0

— I'O

767-8

731-6

6-a

October

766-0

•700-4

9-8

November ....

6'6

-16-4

771-7

736' I

I3'3

December ....

6-7

-16-8

766-7

731-6

I5'°

6'6

— 2O"3

768-7

721-0

19-0

4-6

-I3'9

758-7

711-0

1 2-4

In August and the first half of September, the atmospheric pressure was fairly low, but with little
precipitation to speak of. The temperature remained, on an average, at about 3°C. In the latter half of
September, there was high pressure with rain. On the 27 th September, the first snow fell, the temperature
at the time being about 2'2°.

Birkeland, The Norwegian Aurora Polaris Expedition, 1002— 1903.

l8 B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

During the first half of October there was low atmospheric pressure with frequent falls of snow,
often accompanied by high wind. Throughout the latter half of the month the pressure was higher, with
sleet and snow, the latter sometimes very thick.

In November the weather was variable, without much precipitation, but sometimes with high winds.
The temperature was not very low, having kept at about o°.

During the first half of December, the sky was alternately clear and overcast, but there was little
precipitation. Towards the end of the month, the pressure was lower. High winds were frequent, though
they did not attain a higher velocity than 15 metres per second.

During the first week of January, the weather was cold and calm, the lowest temperature being
—20 '3°. Later on a lower pressure supervened, with mild weather and high wind.

From the 8th to the i5th February, we had the lowest pressures that were observed. It went right
down to 711.0 mm. and remained at about that height for several days. With the exception of a couple
of days in the middle and end of the month, the atmospheric pressure throughout February was unusually
low, with a cloudy sky and some snow.

In the course of the autumn and winter, 27 auroral phenomena, some of them very well developed
and of long duration, were observed and described. It appears that almost without exception, they make
their appearance in the afternoon and during the evening, generally disappearing soon after midnight.

They usually develope from the northern sky, but not infrequently, especially during a bright mani-
festation, they appear on the southern sky. This was observed in the cases of the bright, exceedingly
beautiful and long-lasting auroras of the nth, 24th and 3ist October, and 24th November, which took
place simultaneously with some of the very greatest magnetic storms that were observed during that period.

The aurora of the 24th November in particular was one of extreme beauty. It developed into an
auroral corona, which lasted some minutes, and then dissolved into a great number of intensely brilliant,
red streamers. These moved backwards and forwards across the heavens for some time, making the
sky glow with red.

Considering that there was so much cloudy weather in October, it must be admitted that we were
exceptionally fortunate in being able to observe these beautiful auroral phenomena. On the other hand,
it is not improbable that the overcast sky from the 8th to the I5th February may have caused some
auroral phenomena to escape our attention, as at that time, owing to magnetic conditions, bright aurora
might have been expected.

The weather on the whole must be said to have been not unfavorable. The violent storms experi-
enced on former occasions up at the mountain observatories, we that winter escaped by keeping down in
the valley at Kaafjord. The greatest wind-velocity measured was not more than 19 metres per second.

AURORAL STATION IN DYRAFJORD, ICELAND.

6. The station was situated upon a promontory, Hofdaodden, on the north side of Dyra Fjord (see
Fig. 17). Its latitude was 66° 15' N., and longitude 22° 30' W., equivalent to i hour and 30 minutes
before Greenwich time.

The members of the expedition were SEM S^ELAND (leader), amanuensis to the University Physical
Institute, and LARUS BJORNSSON (assistant). Saeland left Christiania with his equipment on the roth October,
and arrived in Iceland on the loth November, 1902. The voyage was satisfactorily accomplished, but
the vessel was delayed a fortnight by snow-storms.

INTRODUCTION. jg

EQUIPMENT.

Magnetic Instruments.

A set of terrestrial-magnetic variation instruments with photographic registering apparatus of the
Eschenhagen pattern, supplied by Otto Toepfer, Potsdam.

A universal magnetometer (travelling instrument), capable of being used for the absolute determination
of intensity, declination and inclination; supplied by L. Tesdorpf, Stuttgart.

Meteorological Apparatuses.

An aneroid barometer from the Norwegian Meteorological Institute.

A thermometer -screen with its thermometers, and spare thermometers, from the Meteorological
Institute.

A meteorograph (baro-thermo-hygrograph) from the Physical Institute.
A cloud-measuring apparatus, recently procured.

Electrical Apparatuses.

An Elster & Geitel's electroscope with accessories, for measuring the conductivity of the air.
A Zamboni battery (high-tension battery) with wires, insulator, and tightly-closing drum, for investi-
gating the radio-activity of the atmosphere; supplied by Gilnther & Tegetmeyer.
An Elster & Geitel's high-tension electroscope.

Astronomical Instruments.

A large theodolite with broken axis, borrowed from the Astronomical Observatory in Christiania.
A box-chronometer, Hohwii No. 639, and a pocket-chronometer Michelet, also from the Astronomical
Observatory.

Books were also taken, paper, forms, etc., some tools, besides rifles and ammunition. As regards
food, only some delicacies were taken, as the members of the expedition lodged at Berg's whaling-station,
which lay at the extreme end of the promontory, as shown in the sketch.

BUILDINGS.

After Saeland's arrival, the following were erected:
The magnetic variation observatory.
The observatory for absolute determinations.
Thermometer -hut.

Pillar for cloud-measuring apparatus.
The mark.

The Magnetic Register-Observatory.

The observatory was erected farthest from the other buildings, a little way from the shore (see
Fig. 1 7). It was built of wood (framework), and was completely sunk in the loose, brown sand of which
the ground consisted. The house was divided into 3 rooms, in order to obtain as even a temperature
in the north, innermost room as possible. The first room (entry) was provided with a descending flight
of stairs, and was separated from the inner room by a sliding door, 81, that room being separated
from the register-room by a similar door, (JH. In the middle room, various requisites were kept.

In the innermost room, six pillars were imbedded in the earth, two large ones for the three variation
instruments, and three smaller for the three legs of the registering apparatus. The pillars were cut from a
mast-tree, and set deep down under the floor in a large hole, which was afterwards filled up with stones.

20

HIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, I 902 — 1903.

Fig. 14. Observation-Huts at Oyrafjord Station.

Wooden pillars of this kind, buried in this
manner, and exposed to fairly constant
humidity, and, as in this case, beyond the
reach of the frost, have proved quite satis-
factory. The instruments must be placed
directly upon the end-grain.

P, PI , and PI I are the pillars for the
registering apparatus, PHI, PIY, and PV,
those for the magnetometers. //, D, and
V are the variometers for respectively hori-
zontal intensity, declination, and vertical in-
tensity, R is the registering apparatus and
L the lamp reflector.

The drawing on the right of the plan

shows how the magnets were placed in the instruments, in what direction the north pole of the magnets
pointed, and the size and shape of the magnets. The scale is about one/fifth of the actual size.

The Observatory for Absolute Determinations.

This was very well and practically made.

The drawing gives a plan and elevation, and

shows how the whole was arranged. It "will

be seen that the house was partially buried

in the sand. The part above the ground was

almost entirely of glass. A square hole was

dug in the ground, and into the corners and

sides of this were driven 12 posts, upon which

rested a frame, a similar frame connecting

their lower ends upon the earth beneath the

floor. The floor rested upon the latter frame,

and from it, and up to the surface of the

ground, were nailed boards, which thus formed the walls of the underground portion. Above the ground,

grooves were cut up the sides of the posts, into which were fitted glazed window-frames. The windows

were kept in their place by bolts. In the
drawing, one of these is marked K. The roof
was formed of three window-frames, which
were wedged into the beams of the roof in the
same way as the side windows. The roof
windows were kept in their place by two
overlapping clamped beams, one end of which
was attached by hinges, h, It1, the other end
being held fast by the clamps /, 71, which
could be unhooked, and thereby allow the
beams to be raised, and one or all of the win-
dows to be removed. The side windows could
be removed in a similar manner. Thus the
Fig. 16. View from Dyrafjord Station; by moonlight. great advantage of this observatory was that

Fig. 15. View from Dyrafjord Station; by moonlight.

Hrgiste
Observatory for abso-
lute dtierminaliens •
Thfrmomcter - house
'Pillar for cUntd - mca,-

1 .T

The t'tfiff "houses and
arntfigemerUs belong
to Jicrg's w/mfarto; • sta-
tion.

The Infuse in which
tin- ni.-rtdrcrs of tJt£
expedition lived.

t for whalers. >
(Iron steamships)

Sketch-map

of

Kofdaodden

so 100 200 300 too soo

Q

Ground -plan

of ih& register obter*

Iceland . together u-tf/i
a diagram showing
the ficsUu>n of the
magnet*.

!,'. '-,>/!. "i and filan ct' tfte observatory for the absolute- JaUrmirtm.-
Uois , on Hofdaoddtn , Jrriand. .

Fig. 17.

INTRODUCTION. 23

there was abundant light, and that the telescope could be pointed in any direction desired, as any win-
dow could be removed.

In the middle of the room was a solid wooden pillar, fixed in the same manner as those in the
register-observatory. The pillar is marked P.

The Thermometer- Hut (see the sketch).

A perfectly plain hut was erected between the observatory for absolute determinations and the
pillar for the cloud-measuring apparatus.

The Pillar for the Cloud- Measuring Apparatus was a wooden pillar sunk in the earth, with stones
round it.

The Mark was a wooden pole.

There was also here, as at the other stations, a mark at a greater distance from the station. For
this Saeland had chosen a prominent point on the other (western) side of Dyra Fjord.

No accidents occurred during the winter, either to instruments or buildings. It appeared that
Sseland in his completely closed and underground register-observatory, was no more inconvenienced
by the condensation of moisture on the instruments than was Russeltvedt in Spitsbergen, where a slow,
practical ventilation was contrived.

7. The expedition to Dyra Fjord was carried out much later than had been planned, as Saeland
had to make a journey of inspection to Novaja Semlja in September, instead of Professor Birkeland, who
had the misfortune to be bitten by a dog at Archangel under such suspicious circumstances, that he
was advised by the doctors to go to Moscow to be treated at the Pasteur Institute there. Further delay
was caused by the very stormy weather experienced on the voyage to Iceland in the latter part of
October and beginning of November.

Both in the erection of the observation-houses and in other ways, our expedition received valuable
assistance from Captain Berg's whaling-station.

The general impression of the weather during the winter was that it was much more uncertain
than it usually is in Dyra Fjord. The sky was almost constantly overcast from the beginning of November
to the end of January. Snow-storms from the NW alternated unceasingly with a south wind and deluges
of rain; and if, between whiles, the wind dropped for a day or so, we always had to be prepared for
a fresh gale. In February, however, we did get a little clearer, frosty weather, and when in March
the drift-ice came in-shore, we had clear, cold winter weather for about a fortnight.

At times the wind was exceedingly strong. On the night of the I3th November, for instance, a
large portion of the roof of the whaling-station was blown off, and a number of houses in the surrounding
district suffered more or less damage. The barometer readings were throughout extraordinarily low.
On the igth February, a reading of 693 mm. was noted on the aneroid barometer of the expedition.
The day before, according to Icelandic papers, a correspondingly low reading had been noted in
Vestmaneyarne.

It is obvious that with such weather there were comparatively few opportunities of observing aurora.
We kept regular watch in the evening; but as a rule only very small patches of sky were visible, and
what auroras were observed, were therefore usually observed piecemeal.

Opportunities of observing the typical development of auroral arcs at right angles to the magnetic
meridian, with a slow ascent from the northern horizon up towards the zenith, were rare. This may to
some extent be due to the above-mentioned conditions; but on the other hand, it was far more usual
here than, for instance, at Haldde in Alien, to see aurora in the south, and also it was our impression
that among the various forms of aurora, the corona is far more general in Iceland than at Haldde.

24 HIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

On the whole, however, the aurora in Dyra Fjord also, is seen far more frequently in the north
than in the south. In this particular, it does not quite seem to carry out the current theory as to
the position of the auroral zone being to the south of Iceland.

THE AURORAL STATION IN SPITSBERGEN.

8. The station was situated on the Axel Islands in Belsund, West Spitsbergen. The expedition was
stationed, as the map shows, (Fig. 18), at the southern end of the largest, most northerly island (Hoved-
een). The astronomical pillar near the dwelling-house has a latitude of 77° 41' 21,5" N., and a longitude of
I4°5o' E., equivalent to o hrs. 59 min. 20 sec. by Greenwich mean time.

The head of the station was NILS RUSSELTVEDT, assistant at the Meteorological Institute in Christiania;
and there was only one permanent assistant, namely, H. HAGERUP, an electrotechnicist. They went,
however, with a hunting expedition, under the command of Captain Hagerup from Tromse; and the
members of the latter expedition were bound to render ours whatever assistance they required.

EQUIPMEMT.

Magnetic Instruments.

For a continuous record of the terrestrial-magnetic elements, 2 registering apparatuses were taken,
and 2 unifilar magnetometers of the Eschenhagen pattern by Otto Toepfer, Potsdam, and a Lloyd's balance
from Charpentier, Paris.

For the absolute determination of the terrestrial-magnetic elements there was a Fox's circle, and a
Dover's inclinatorium, and also some requisites and spare parts. During his stay at the station, the
leader of the expedition made a special instrument for the determination of the declination.

Meteorological Apparatuses.

For meteorological uses there were 2 thermographs, i barograph, i mercurial barometer, i aneroid
barometer, 6 thermometers Vs0 C., 2 sling-thermometers, i large thermometer-screen, 4 minimum thermo-
meters, an anemometer Richard, and a cloud-measuring apparatus, besides books, forms, etc., some of
them placed at our disposal by the Norwegian Meteorological Institute. A thermometer and thermograph
hut was made at the place, and a weather-vane.

Electrical Apparatuses.

For measurements of the dissipation of the electricity in the air, there was an Elster & Geitel's
electroscope, with accessories.

Astronomical Instruments.

For astronomical uses we had a theodolite and a large sextant belonging to the Astronomical Ob-
servatory in Christiania. There were also 2 chronometers, a Lacklan & Son No. 512 and an Arnold No. 152.

Some instrument-maker's tools were also taken, as also guns and ammunition. To the vessel's
equipment belonged a camp forge and smith's tools, some carpenter's tools, etc.

Russeltvedt left Christiania on the 3rd July - - taking with him the instruments and the tinned
provisions that were required --to join the other members of the expedition at Tromse, and to attend
to the equipment of the ship. The ship, which was to winter in Spitsbergen, was a large coaster
called "Jasai".

When everything was arranged, the expedition started from Tromse on the 241)1 July, and arrived
in Spitsbergen on the 7th August.

Environs of the Station

at

General Plan

of the Station at

A rtUar for- AstronamtcaJ Observation*
B Obienratory I'orAtaoluU M.'./nr/i<- - ,

Ground -plan

of

Magnetic "Register Observaliirv

viith Us fiitin-i.i . mi-/ a ttioyram •
malic rc/irfsrntolu>n ffthefiasi-
tun of t/u- magnels in n-laftait
ta ttb- magnetic meridian

The

Absolute Magnetic Observatory
in Spitsbergen

Fig. 18.

1 Tl. « M „

INTRODUCTION.

Fig. 19. Dwelling-house of the Expedition.

The following buildings were repaired and erected at the station:

The magnetic register-observatory

The observatory for absolute magnetic determinations

A dwelling-house

A storehouse, to which were attached a thermometer-screen (t) and the electroscope-hut (e).

The Magnetic Register-Observatory.

The building was quite a plain
wooden house (frame-house). It was
sunk down into the earth as far as the
underlying rock would permit. (See
sketch Fig. 18). Some earth was
thrown up against the walls; but
owing to the lack of loose, light
earth, it could not be covered entirely
over with earth. Stones were laid upon
the roof to prevent its being torn off
by the wind. The observatory was
divided into two rooms. The first, more
northerly, was fitted up for developing;
the inner, more southerly, was the regis-
ter-room.
On the ground-plan are the following:

./ii Ji> J-n ./4> indicate respectively the north, east, south and west walls. The door, (5, opens
into the front room, where B is the bench upon the west wall. Upon this were kept various chemicals,
and implements for the keeping in order
of the instruments. The arrow, V^ , shows
the direction of the ventilating air. In
the north outside wall some holes were
bored, through which the air was ad-
mitted under the bench in the front room,
where the snow, etc., that accompanied
it was separated from it, and the air
could pass through the holes in the parti-
tion-wall, S, in a pure condition, free
from snow. The snow that blew in could
easily be taken away from under the
bench.

The door, (51, led into the register-
room. Here were built two solid cement

pillars upon the firm rock. They were pig. 20. Observation-huts at Axel0en Station.

of the form shown in the ground-plan

at P and P1 . Upon them were placed the registering apparatuses, which consisted of 2 photographic
registering apparatuses, R and /?', with their benzine reflectors, L and Z.1. The 3 magnetometers
(variometers), D, H, and V, are respectively the declination variometer, the horizontal intensity vario-
meter, and the vertical intensity variometer.

28 HIRKELANU. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902— 1903.

At the side of the plan, upon a line which indicates the magnetic meridian, three magnets are
drawn one third of their actual size. Their position is here shown in relation to the meridian.

t is a thermograph which registers the temperature in the observatory.

The ventilating air, which, as already said, entered the register-room through the partition-wall, S,
passed out through the draught-pipe, V, into the open air. As this ventilation was only for the purpose
of eliminating the moisture produced by the benzine lamps, and to provide fresh air for the latter, it
did not need to be particularly strong. Too strong ventilation is injurious, as with a change in the
weather it may occasion a deposit of hoar frost.

The Observatory for Absolute Magnetic Determinations.

The house was a frame-house, and, like the register-observatory, was roofed with tarred paper.

The foundations were dug down to the solid rock,
and the walls shored up with earth and stones.
As will be seen from the sketch, there is, a door
to the north, and a window in each of the other
three walls. There is only a single large pillar
cemented on to the rock ; but this was so large
that the instruments kept their place unchanged
all the year through. Their places can best be seen
in the sketch (Fig. 18). When one of the magnetic
instruments was being used for observation, the
magnets were removed from the others, and were
then kept in their cases in an empty barrel a little

Fig. ai. Hut for Absolute Magnetic Measures, .. ,. . ,~. . , ,.

to the north of the observatory. 1 he theodolite

and the Coaster Jasai .

was also removed, if it was not down at the

dwelling-house at the time. The south window was so arranged that one or more of the four panes
could be taken out when observations were being made with the theodolite or the declinator.

The Dwelling-house.

This consisted of two rooms. Of these, the south one served as a living-room and office. It had
a door leading to the north room, which not only did duty as an anteroom, but also as a workshop
and storehouse for various things. The north room had two exits, one to the east and one to the west.
The house was built of stone, with wood pannelling inside (frame-work). Between the frame and the
stone wall there was a close internal layer of birch-bark, and externally a 6-inch layer of moss. On the
roof also there was first a layer of birch-bark, then moss, and on the top of that a layer of gravel;
and finally, the whole was roofed with slates. In this way, the house was both substantial and warm.

The Storehouse.

This was a little square house with door on the north side. It served as the storeroom for the
most necessary of our things, such as food, ammunition, etc., so that, in case of fire, we should not be
left without the necessaries of life. Outside the north wall stood the thermometer-screen, (t) It was
divided into two compartments, one for the thermometers and one for the registering apparatuses. It
was also arranged so that the draught of air could be reduced to a minimum. The air was admitted
through holes in the bottom. The draught was reduced when it was snowing, in order to hinder the
snow from blowing in and filling the screen.

INTRODUCTION. 29

The electroscope-hut, (e) (Fig. 18) was a kind of cupboard on the west wall of the storehouse. In this
cupboard, which was ventilated while the observations were being made, observations could be made in
almost all kinds of weather. Observations of the electric conductivity of the air were taken three times
a day, together with the meteorological observations. If time permitted, observations were moreover
made every quarter of an hour during rapid registering.

As the observations were made, in the hut (e) and were thus not exposed to the full force of
the wind, it should be remarked that the observations cannot be directly compared with observations
made in other places in the open air. In this case, however, this was of minor importance, as the main
object was to obtain the variations in the local electric conditions. Had the observations been made in
the open air, only a small number would have been successful. As it was, it was only in the worst
weather that the observations had to be suspended.

The arrangements of the other things is best seen in the detail-map. The only remark to be
made in conclusion is that the auroral observations were made from a board that was nailed to the bottom
of an empty barrel, which was placed between the dwelling-house and the register-observatory.

9. A few adventures and occurrences of the expedition are related here.

Captain Hagerup, accompanied by the members of our expedition, left Tromse on the 24th July;
but as the wind was unfavorable, they did not get to sea until the 2yth.

On the 2nd August, Bell Sound was sighted, but also, at the same time, the ice, which appeared
to form an impenetrable barrier. On the yth, it looked as if the ice had become slacker, and at last there
was room for the ship to advance a little, though not sufficiently to allow of her getting in to the Axel
Islands. She was therefore compelled to seek a haven on the west side of the main island about
800 metres from the winter haven.

Here they remained, passing the time in hunting. On the night of the i2th, an open line was
seen in the ice between the islands. A whaling-boat was immediately lowered, and filled with building
materials. Two boat-loads were taken ashore. On the way back at 4 in the morning, they only just
managed to get the boat back. All hands, except two, were then on shore and worked the two follow-
ing days. The observatory for the registering apparatuses was set up on a rocky knoll, small enough
for the house to surround it, and thus have a splendid foundation.

This house was soon put to the proof, for on the iyth there blew such a hurricane, that it was
impossible to stand on deck. No attempt to go ashore could be made. The magnetic register-observatory
was then finished except for the stones and earth along the walls. It was blown down and broken to
splinters. The heavy boarding of which the house was built was torn from the framework, and some
of it flung to a distance of more than 100 metres.

On the 1 8th the wind had gone down, and it was possible to venture ashore. The work of restor-
ing the ruined house was started, and at n p. m. it was quite completed and literally loaded with
stones, both on the roof and along the walls. The sleepers, moreover, were cemented to the rock.

The ice had now drifted away, so that the ship could be taken into a safe harbour. On the igth,
the instruments were brought ashore, and on the 2oth the installation of the magnetic apparatuses was
begun, and was completed without any accident.

The instruments were considerably out of order, but everything was capable of being put right.
The balance for the determination of variations in the vertical intensity occasioned some trouble, but that
too was set right. On the 2gth, the registering was begun regularly, slight changes being made subse-
quently ; and the work at this comparatively poorly equipped station was executed to my entire satisfaction.

It may serve to give some idea of the peculiar difficulties with which the expedition to Spitsbergen
had to contend, if we begin by describing a stormy period such as there were a score of during the
time the expedition lasted, most of them in the winter.

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

It must be in a great measure to the tremendously varying conditions of weather, that the immense
loss of life on West Spitsbergen is due. It is no exaggeration to say that all round about our station
was one great graveyard.

It is for this reason that of late no one has ventured to winter in Spitsbergen; it is only during
the last three or four years that it has been done once more, for the polar bear hunting.

It was fine during the first few days of January. The sky was clear, and the temperature was
more or less steady at - 30° C. But then the temperature began to rise, and the weather became un-
settled, with short stormy periods, all the rest of the month. On the night of the i3th January, the
temperature was — 34° C. with a hazy atmosphere. On the morning of the i4th it had risen, however,
to --"19, and on the evening of the i5th, o'6° was recorded. The wind was fresh but tolerably steady
from the SSW. The precipitation was in the form of a rapidly varying mixture of snow, rain and soft

hail. In the night, however, the temperature
fell to — 7° again, and snow was continuous.
It may be mentioned that on the Axel Islands

• f;.( ^C^A\^1 &* ft can qufte we^ pour with rain with a tempera-

M||^V ,^J^| ture 5° or 6° below zero. The wind changed,

H^v-^B however, in the course of the i6th, through

the west to north, while the temperature slowly
mf\ sank, and at midday on the lyth, we had quite

» 9*L U ^» * a soft east-north-east wind with a temperature

of — i5'4°- Good weather had been expected
again; but the black, threatening atmosphere
that rolls in from the sea (the Gulf Stream) in
the west, when a storm is brewing, hung over
us, heavy and unchanged.

The temperature began to rise again, and we had five or six hours' storm from the east on the
night of the I7th. In the morning — 9'5°C was recorded, and by midday the temperature was about o°
again, together with a south-west wind with rain, snow and sleet.

During the i8th, igth and 2oth, the temperature sank again slowly, while the wind kept in the
south. The sky was an inky black, and it snowed and rained now and again. In the evening of the
1 9th, it rained with a temperature of — 4-8° C. By the evening of the 2oth, it had sunk to — 14'5°,
and the atmosphere was a little lighter than it had been for a long time, so that the hope of fine weather
this time was well-founded, as the wind also had gone over to NNE again. On the morning of the
2ist, however, the temperature was up to — 9°, and later in the morning the wind was due south with
a very variable temperature with an average of 0^4 °. That night there began a regular Spitsbergen storm in
all its wildness and greatness. We were awakened by the roar and noise occasioned by wind, ice and
rain. In the morning the storm reached its height. There was an average temperature of 2° C. The
wind was from the south, but its velocity varied incessantly; at one moment there was none, or a slight
breeze, the next it was blowing the wildest hurricane. It was these fearful gusts of wind, which often
occur in the stormy periods, that were dangerous to any one going out, for it is impossible to keep
one's balance in such a wind. During a storm of this kind, every condition varies by fits and starts -
wind, temperature and precipitation. You hear boom after boom, now in the distance and now so close
that you are in the very middle of it, and hear a roar as of a torrent around you; and gravel, stones
and snow are whirled about. The gusts often last only a few seconds. You can hear them coming
and then dying away in the distance. This may sometimes be followed by a heavy deluge of rain, but
the rain may also come during a lull. The sky is no longer an even black, but dark clouds of every
possible form are being driven along.

Fig. 22. Celebrating a National Festival.

INTRODUCTION. 3!

On the 5th February there began the most violent snowstorm that we had during our stay there,
and it lasted almost uninterruptedly until the gth. While it was going on. it was exceedingly difficult
to carry out the meteorological observations. The thermometer-screen stood only four or five metres
from the door, but on one occasion five vain attempts were made to get a reading of the thermometers.

It was especially during the dark season, which lasted about four months, that the storms raged
worst; but October too was a bad month. The calmest and most beautiful time was July, August, and
part of September.

It will be easily understood that weather such as this placed enormous difficulties in the way of the
observations. It was, for instance, impossible, with the few means at our disposal, to prevent even great
changes in temperature and humidity occurring in the magnetic register-room. The warm, damp air
found its way into the observatory through the ventilators, and precipitated its moisture upon the instru-
ments, dimmed the glasses, etc. Even the bases for the instruments, which were built into the rock,
were not altogether beyond the possibility of change.

THE AURORAL STATION IN NOVAJA SEMLJA.

10. The station was situated on Matotchkin Schar, on the western side of the island, in a bay in
the strait. The latitude of the place is 73° 16' 38" N, and its longitude 53° 57' i' E. No map was made,
but the accompanying sketch will make the conditions intelligible.

The members of the expedition were H. RIDDERVOLD, science graduate (chief), and H. SCHAANNING
and J. KOREN as assistants.

EQUIPMENT.

Magnetic Instruments.

For magnetic measurements we had a set of terrestrial-magnetic registering apparatuses of the
Eschenhagen pattern, made by Otto Toepfer, Potsdam. For the absolute measurements of the magnetic
elements, a unifilar magnetometer of the Kew pattern, made by Eliott Brothers, and a Dover's inclinatorium.

Meteorological Apparatuses.

For meteorological uses there were a mercurial barometer, 6 thermometers Vs0 C., 2 sling-thermo-
meters, a thermometer-screen, 4 minimum thermometers, a cloud-measuring apparatus, and an anemometer
Richard, besides forms, etc.

Electrical Apparatuses.

For electric measurements (atmospheric electricity) we had an Elster & Geitel's electroscope with
a Zamboni battery and other accessories.

Astronomical Instruments.

For astronomical uses we had a theodolite and two box-chronometers, a Poulsen No. 5 and a
Kessel No. 1280.

There were also some tools, guns and ammunition, and the necessary provisions.
On the I4th August, our instruments, baggage, coal and wood were landed and brought to the
station. The instruments had suffered little on the whole, and could be set up without much difficulty.

BUILDINGS.

Two observation-houses we had brought with us were erected, namely:
The magnetic register-observatory, and
The observatory for absolute measures.

HIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

The Magnetic Register-Observatory.

The observatory, as the sketch and accompanying plan shows (Fig. 24), was erected to the SSW of the
dwelling-house. There was no rock foundation there, so the house could be sunk some way into the
earth. As the plan shows, the observatory is quite a plain wooden house, divided into two rooms, both
dark rooms. The front, more southerly one merely forms the necessary anteroom to the inner, north room
which is the register-room.

The following is an explanation of the plan :

<JI and (JH are the two doors by which the register-room is entered. To the right of the entrance
is the vertical intensity variometer, V, then the declination variometer, D, and finally the variometer for
horizontal intensity, H. These instruments are placed upon a wooden board, T, which rests upon two
solid wooden posts, P and Pl, which are sunk far down into the earth and surrounded with stones_
Farthest in is the register, R, with the reflector, L. It stood on the ground, upon the long legs belonging
to the instrument.

The drawing beside the above is a diagrammatic representation — scale two fifths — of the position of
the magnets during the registering. The arrow through it gives the magnetic meridian. The letters on the

magnets give the direction in which the
poles pointed. A wind-rose is drawn
round the declination variometer.

The Observatory for Absolute Measures.
This was a house exactly similar
to that erected in Spitsbergen. Instead
of the cement pillar, however, there
was a solid wooden post about 35
centimetres in diameter in the middle
of the house, properly sunk into the
earth and surrounded with stones.

11. The other buildings shown
in the sketch were already there, and
were placed at our disposal with great
willingness by the Russian govern-
ment. The dwelling-house, which had

been built for the Russian painter, BORISOFF, was a good, substantial house, fully furnished and in good
condition. The Russian authorities were most kind in the assistance they gave to our expedition.
The Governor, RIMSKI KORSAKOFE, showed us his good-will in many ways. We were even carried
free of charge from Archangel to Matotchkin Schar and back, with all our baggage; and the steamer
"Wladimir" had instructions to land all our cases at Borisoffs house. We further received permission
to make use, if necessary, of the depot that is intended for shipwrecked sailors who may come ashore
there. There was also a thermometer-hut and a weather-vane there already; all we had to do was
to put in the thermometer-screen, and to put the whole thing into a state of efficiency.

The electroscope was not observed regularly, and when it was, it was done in the open without
protection. The Zamboni battery got out of order during the time of observation.

In August and part of September, it was summer in Matotchkin Schar; but it was cold and
inclement, and there was rarely more than 10 degrees of heat. It was almost always cloudy and damp,
and the sun was seldom visible.

Fig. 23. Our Station at Matotchkin Schar.

SKETCH

ttb JDtveUinq - House
ffl Jtyr4*

D Hegiftcr observatory
A D Observatory for ab.whitt deterrtri =

na/i/fn.?

C D Thermpnifter house
D © Weather- vane

Ground plan

of lltf R'-'fixtcr Observatory on Mniotfltlun
XrJini- in A'i'wjy'a S,-mifa ,ruiih a diagram,
imilir r.-prrstntatian. of the jtosktiun of

Fig. 24.
Hirkcland, The Norwegian Aurora Polaris Expedition, 1902 — 1903.

INTRODUCTION.

35

Fig. 25. Hut for Magnetic Observations.

On the 28th September, the "Wladimir" came again, bringing Saeland to inspect the station. The
vessel remained for three days, and it soon appeared that she had been none too early in getting away,
as the winter came unusually early. About a week after her departure, ice covered the sea after a
snow-storm and a week of cold weather had cooled the water.

The first part of the winter was severe. As early as November, the thermometer showed as a
rule between 20 and 30 degrees of frost. There was, however, comparatively more clear weather than
at other times of the year. But it was the same here as in other places; calm weather and from 30 to
40 degrees of cold gave no inconvenience. It was worse, however, when there were about — 20
degrees C. and a snow-storm, which might continue for a week or two at a time.

We had a great deal of aurora during
the first part of the winter. It would begin
with an arc low down in the north, which
gradually moved upwards and increased in
brightness, and at last often stood almost
magnetic east and west through the zenith.
There then sometimes developed several large
arcs, with a flaming rosette in the zenith;
now and then the entire northern heavens
seemed like a sea of fire. Sometimes the re-
flection would be so bright, that every object
upon the ground could be distinctly seen.

As the winter advanced, the days be-
came quickly shorter. From November, the
sun was always below the horizon, and in the latter half of November, in December and January, we
had to burn lamps all day long. At first there was no difficulty in doing without daylight, but as it
continues, the constant darkness has a depressing effect.

The severest part of the winter was the month of January. We then had for long periods at a
time from 30 to 40 degrees of frost. It is strange that even in this severe part of the winter, a wind

from the south could send the thermometer
up above freezing-point. The lowest tem-
perature observed was — 42° C.

On the 22nd February, a very remark-
able thing occurred. The barometer sud-
denly fell to the lowest level of the year.
In the morning, when we looked out of the
window, the whole mass of ice in the strait,
which had been fast since November, and was
very thick, was drifting westwards. Soon
after we had open water everywhere. The
wind, which otherwise is the most impor-
tant cause of changed ice-conditions, had
nothing to do with this freezing of the ice.
At the beginning of March, the weather
again became cold, the strait froze over once more, and the ice became fast as before.

In the latter half of February, the polar bear appeared. This animal, while at other seasons of
the year remaining in the north of the Kara Sea, wanders farther afield in the latter half of the winter,
Matotchkin Strait being one of its favorite haunts.

Kig. 26. Samoyed and Team.

36 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

The first two bears were seen on the i8th February; they were jogging quietly along the west
coast of the island. In a great, deep snow-drift they had dug themselves a big lair, which looked very
nice. Large bear-paths led from it in several directions, which showed that the bears must have been
living there for some time. The hunt now began, and two days later the two bears, a she-bear and a
year-old young one, were brought down.

It was not long before there was a continuation of the bear-hunting. The very next day, three
bears passed our door; we seized our rifles, and in another instant the three bears lay stretched upon
the ground, each with a well-aimed bullet in its body. (See figure 23).

The bear-hunting also brought a welcome addition to our larder. Our supply of meat, which
besides tinned things, for which one soon gets a distaste, consisted only of gulls and other sea-birds
preserved from the autumn shooting, had now become very small.

The weather as regards February, March and part of April, may be most correctly described as one
long storm, now and then broken by calm intervals. Now and then, too, the wind increased to a hurricane.
The first harbinger of spring came on the I2th May. On that day the first bird of passage arrived,
the snow bunting; and after it came gradually the others -- larks, swans, geese, etc.

Winter still held on obstinately for some time, and the snow in most places did not disappear

until June or July. Through the greater part
of June we had frost, with calm, foggy or
cloudy weather. Not until July was there any
summer warmth.

In the middle of July, after the conclusion
of the observations, the members of the ex-
pedition met with a disagreeable adventure.

They had gone out with a rowing-boat
several miles from home, and had landed on
the farther side of a little river, which at that
time could be waded without much difficulty.
The boat was moored to the bank.

When they had been there a few days,
Fig. 27. The Observer as Hunter. quite unsuspecting of danger, a fearful storm

broke; the lightning flashed and the thunder

roared --a very rare occurrence in those regions. At the same time the east wind broke loose in
earnest, with oppressive heat. The consequences were not long in being noted. When the storm had
abated, evidences were visible of the effect of the heat and the wind in the melting of snow, for the
river was changed into a foaming torrent. The entire tongue of land upon which the boat had lain, was
washed away; and the boat was nowhere to be seen; it had drifted out to sea with the east wind.

The question now was, what was to be done? With no boat, and the river, which was many
miles long and very broad, now impossible to wade. Of provisions there were none, and no matches.
Fortunately the members had brought their guns farther inland, so they set out on a hunting-expedition
and shot some birds, which were immediately skinned and eaten raw. The following day they attempted
to go along the river, in the hope that its upper part might be more easily crossed ; but after wading
for 20 or 30 miles, the attempt was abandoned. They then went back to the sea, and tried for several
days in every possible way to get across, but all in vain.

It was clear, however, that they must at all costs manage to get home. The fare was not first-
class; it still consisted of the one dish -- raw bird. With some old rope and some drift-wood they
made a kind of raft, and also found some boards that could be used as oars. It was an exceedingly

INTRODUCTION. 37

poor vessel; even when all three men rowed with all their might, it made only the slowest progress.
They nevertheless put out from the shore; but when they got into the river-current, they were carried
rapidly out to sea, and were soon several kilometres from the shore. They rowed with all their might
in order to cross the current and get into the counter-current that was formed on the border between
the current and the still water. The worst of it was that the raft began to go to pieces, so that one
man had to hold it together with his hands and feet while the others rowed.

After a hard struggle they at length reached a little iceberg that was grounded, where they at
any rate did not drift away from the shore. Once more they took to the oars, and were fortunate
enough to get into the counter-current, which carried them shorewards, while at the same time a gentle
sea-breeze also helped a little. The row in was therefore easier than they had ventured to hope, and
at last they all reached land safe and sound.

But when they were safe on terra firma they saw how great the danger had really been; for a
fog as dense as a wall came pouring down from the north. If this had come a little sooner while they
were rowing, it is highly probable that they would have gone on rowing in a circle all the time while
the stream would have driven them farther and farther out; and the result would then have been very
doubtful. But now they were on familiar ground; they had only a few miles to go, and six hours
after landing, they were all at home.

A week later, on the 2ist July, at 2 in the morning, the "Wladimir" steamed into the haven, and
the expedition broke up hastily, and on the 3rd August reached Archangel.

12. The Working-up of the Material. From the four Norwegian polar stations here described, a
quantity of material was gathered in 1902 and 1903, which has been in process of working up for a
long time; but, principally for financial reasons, the publication of the results has not been practicable
until now.

For the gain to science which our auroral expedition has brought, we owe a debt of gratitude not
only to those who guaranteed the undertaking financially, but also to others, especially the directing
heads of a large number of magnetic and meteorological observatories all over the world.

Experience from earlier work in this field had clearly shown me that if light was to be thrown
upon the phenomena that we had set ourselves to study, it would be of the greatest importance — neces-
sity, I may say --to obtain simultaneous observations from most parts of the earth. This applies to a
certain extent both to cloud-observations and to observations of aurora; but it is of special importance
in the study of the magnetic storms, for they, as is generally known, are usually of a universal character.

With the object of getting, if possible, several observatories to co-operate in these researches, I
sent out a circular, dated May, 1902, from Christiania, before the departure of the expedition, to a number
of observatories all over the world.

I will here confine myself to giving a brief extract from this circular f1).

"As leader of the expedition started by the Norwegian Government for the study of Earth-Magnetism,
Polar Aurora and Cirrus clouds, I beg to inform you that during the time from August ist 1902 until
June 30th 1903, four Norwegian Stations will be erected, viz. at Bossekop (Finmarken), at Dyrafjord
(Iceland), at Axel Island (Spitzbergenl and Matotchkin-Schar (Novaja Zemlja)."

"The above-mentioned expedition has assumed the task of determining the connection existing
between earth-magnetical perturbations, boreal lights and cirrus-clouds."

"To obtain a happy solution of this task, it is absolutely necessary to get the requisite facts from
the largest number of points of observation distributed as widely as possible over the whole earth.»"

(') Terr. Magn. and Atm. Electr. June, 1902, pp. 81.

38 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION igO2 — 1903.

"At these four Norwegian stations the three magnetic elements will be registered photographically.
To this effect registering instruments will be employed like those used by the contemporary Antarctic
Expeditions. The three elements will also be determined absolutely. The term observations stipulated
by the Antarctic Expedition will also be carried through at these stations.

The special subject prosecuted by our expedition, and for the fulfillment of which we solicit your
kind support are :

The determination of the cause and progress of different magnetic perturbations, as discussed by
me in my report: "Expedition Norvegienne de iSyy — 1900 pour I' etude des aurores borcales. Resiiltats
des recherches magnetiques" .

Some information was added as to the best way of making the observations for the purpose desired;
and the times for the rapid registerings were fixed.

As it would have been impossible to have material sent from all the observatories for the whole
of this period, it was necessary to confine ourselves to a few fixed days. As soon as we had observa-
tions from two of our stations, I sent out a new circular from Christiania, to the same observatories,
dated June, i903(1). Part of this was as follows

"After comparing photograms from Bossecop with corrresponding ones from Potsdam, I selected
thirty days, on which general magnetic disturbance was great, as those which most suited my purpose
and I have, consequently, determined to adopt these as the basis of my investigations. 1 now take the
liberty of asking all those who are in the position to do so, to give or lend me copies — photographic
preferred --of photograms of magnetic disturbances that may have occurred on those thirty days, and
urge them, in the interest of science, not to mind facing the considerable amount of trouble which must
be undertaken in order to fill such a request; and, if required, I am willing to refund any expence
necessarily incurred in connection with it. In the work that I intend to publisch, I shall reproduce so far
I can by photography, a very large number of such photograms after they have been reduced to a uni-
form scale as regards time, so that any one may be able to check the results arrived at, by me, from
my manipulation of the materials to hand. The variations of most value for my work, are those of the
two horizontal elements. In respect to the thirty days in question, when the vertical intensity shows
marked variations, it will be, likewise, very important to me to obtain copies of photograms relating to
vertical intensity."

We have in this way, in response to our request, received numerous photographic reproductions
of magnetograms and tables of magnetic observations for comparison with simultaneous observations
from our 4 stations, from each of the following 23 observatories: Honolulu, Sitka, Baldwin, Toronto,
Cheltenham, San Fernando, Stonyhurst, Kew, Val Joyeux, Uccle, Wilhelmshaven, Munich, Potsdam,
Pola, Pawlowsk, Tiflis, Jekaterinburg, Bombay, Dehra Dun, Irkutsk, Batavia, Zi-ka-wei, Christchurch.

We have further received observations of occurrences of cirrus bands -- these being made, while
the expedition lasted according to a common plan -- from the meteorological observatories at Valencia
(Ireland), Falmouth, Aberdeen, Kew, Aix-la-Chapelle, Von der Heydt-Grube (b. Saarbrucken), Bremen,
Uslad, Celle, Brocken, Christiania, Potsdam, Grunberg, Schneekappe, Neustettin, Budapest, Konigsberg.

For this extreme readiness on the part of my honoured confreres to give their assistance, I would
here offer them my warmest thanks.

It is my hope that the importance of this material to our work will be fully apparent from the
subsequent treatment of the subject.

To one man more particularly, if he had lived, this expression of gratitude would have been
addressed, namely the late Geheimrath VON BEZOLD. It was especially through his valuable aid that I
succeeded in obtaining such ready response from observatories all over the world as I finally did.

(') Terr. Magn. and Attn. Electr. June, 1903, pp. 74.

PART I.
MAGNETIC STORMS, 1902—1903.

INVESTIGATIONS BY MEANS OF DIURNAL REGISTERINGS
FROM 25 OBSERVATORIES.

CHAPTER I.

PRELIMINARY REMARKS CONCERNING OUR MAGNETIC RESEARCHES.

13. Our Aim and our Method of Working. It has, as is generally known, been ascertained
that there exists a close connection between sunspots and the magnetic conditions upon the earth. As
early as 1852, SABINE discovered, almost simultaneously with GAUTIER and WOLF, that in years when
sun spots were numerous, the magnetic storms were more frequent and more violent than in years when
there were few sun-spots. By comparison with the period of magnetic oscillations pointed out by LAMONT
in 1850, it was discovered that maxima and minima in the magnetic period coincided with maxima and
minima in the sun-spot period.

These and kindred circumstances have since been carefully investigated. It has been found that
the magnetic constants have secular variations, which, with convincing exactitude, follow the simultaneous
variations in the occurrence of sun-spots; and further, that there are periods for the frequency of
magnetic storms and for aurora, which correspond with the so-called undecennial period of the sun-spots.
From the very first, when these relations were discovered, attempts were naturally made to find
out the connecting mechanism between these phenomena, so that the physical cause might become clear;
but these have not as yet been entirely successful.

It has gradually come to be acknowledged that aurora and magnetic perturbations should be regarded
as rather moderate manifestations — at present the only ones there are for us to observe — of an un-
known cosmic agent of solar origin, and quite different from light, heat or gravitation. It has long been
supposed that this unknown agent was in some way or other of an electrical nature. The elder BECQUERF.L
even, gave expression to some very interesting ideas on this subject.

With regard to the magnetic storms in particular, it is clear that the observed changes in force
can be formally explained by an infinity of assumptions with distribution of fitting agents that generate
magnetic forces; but nevertheless it may safely be said that up to the present not one definitely
formulated hypothesis has been put forward, which explains all the phenomena so simply and naturally,
that the hypothesis becomes satisfactory.

In the following pages it will be shown how far I have succeeded in explaining the above-mentioned
and several kindred relations, starting with the assumption which, viewed from the present standpoint
of natural philosophy, is a legitimate one, namely, that the sun, and especially the spots on the sun,
send out into space cathode or kindred rays.

In order to gain definite conceptions of the effect of such rays in the vicinity of the earth, I have
again and again had recourse to analogisms from my previously-described experiment in which a magnetic
terrella is suspended in a large discharge-tube ('), and exposed to cathode rays.

The experiment, which was originally made for the purpose of finding points of support for a
hypothesis for the formation of aurora, has proved a veritable mine of wealth, in which I have constantly
made valuable discoveries.

(') Expedition Norvegienne de 1889 — 1900, etc., I. c., pp. 39 et seq.
Rirkeland, The Norwegian Aurora Polaris Expedition, 1902—1903.

42 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

The experiment in various forms has been repeated a great many times in the course of the last
few years, and I have succeeded in photographing all the light-phenomena appearing. The results of
these experiments will be fully described in a later part, and the light-phenomena illustrated by numerous
photographs.

There are light phenomena produced by the rays that beat directly down upon the terrella, and
which, in my opinion, answer most nearly to the light-phenomena and certain magnetic storms in the
auroral zone on the earth.

There are light-phenomena produced by rays made to fall upon a movable screen, for the purpose
of ascertaining how those rays behave that do not fall directly upon the terrella, but move about in its
immediate neighbourhood. I think that such rays can give a natural explanation of the cause of
certain universal magnetic disturbauces and sometimes to aurora polaris, if the ray-stream comes near
enough to the atmosphere of the earth.

Finally, there is a flat, detached bright ring round the magnetic equator of the terrella, which
immediately recalls Saturn's ring.

It seems as if this bright ring might bring us almost to the solution of other most important
terrestrial magnetic problems.

In a lecture "On the Cause of Magnetic Storms, and the Origin of Terrestrial Magnetism" , given
before the Scientific Society in Christiania, on the 25th January, 1907, I gave a sketch of the results
of the terrestrial-magnetic investigations which will be produced in the present work.

The conformity discovered by Sabine and others between sun-spots and magnetic perturbations, as
also aurora, has become apparent through observation and the summing up of a large number of single
phenomena. It must necessarily be supposed from this conformity, that also in single cases it must be
possible to prove a connection between these phenomena. This has often, especially in more recent
times, been observed in particularly marked cases.

It will therefore be an important task to endeavour to discover the course of the process which
at times takes place in the neighbourhood of the sun-spots, and gives rise subsequently to aurora and
magnetic perturbations, and thus show that these terrestrial and solar phenomena are only different
phases in a continuous process.

In order to solve this problem, one is naturally led to take one of two ways. The most rational,
if the necessary material were forthcoming, would be to start from the sun, where the process begins.
This is the way I have formerly taken. Starting with the hypothesis that the sun-spots are the source for
the emission of cathode rays, I have endeavoured to follow the process from the sun to the earth, and
by analogy with the above-mentioned experiment see how some of the rays strike the earth, and some
glance past it under the influence of terrestrial magnetism. This is moreover the way my friend, Pro-
fessor STSRMER, has taken in his mathematical investigations of the path of such rays from the sun to
the earth. He has published the complete results of his investigations in a special part of the present
work; but these results will already be to some extent known from his earlier papers. Here, for the
first time, a detailed mathematical treatment of the aurora problem and kindred problems will be found.

The other way is to start with the conditions upon the earth, study a single perturbation, seek
for the terrestrial processes that might be able to influence them directly, and follow these up until, if
possible, we are stopped at the point when the cause can no longer be sought upon the earth, but in
the arrival of something from without; and here the two ways may meet.

It is by going both ways, employing both methods, that we have thought we might have the best
prospect of solving our problem.

That which, at a certain spot on the earth, and at a given moment, characterises a magnetic per-
turbation, is the strength and direction of the perturbing force.

PART I. ON MAGNETIC STORMS. CHAPT. I. 43

In order, therefore, to obtain a clear conception of the perturbation, such as it actually appears on
the earth, there are in particular two important points upon which enlightenment is to be sought, namely,

(1) How is the force distributed upon the earth at a definite point of time during the perturbation ?

(2) How does the distribution of force change with time ?

The investigation of these two points has formed one of our principal tasks.

Our investigations were thus in the first place directed towards finding out how an individual
perturbation developes, and what course it takes. We find that for the solution of this problem it
has been particularly important to study with special exactitude the simplest phenomena, those in which
the course is simple and with no great, sudden changes, as at the outset it seems probable that we
are here face to face with elementary phenomena, which together may form the multiplicity of mag-
netic storms.

As, however, there will, as a rule — notwithstanding the many great similarities — always be many
individual peculiarities in each perturbation, which should be specially mentioned, we have decided to
treat each perturbation separately, each accompanied by a description. We have, however, tried to
arrange them together in groups according to their special character, in such a way that the various
elementary types come first, after which the more compound perturbations will be treated.

There may also be a question of finding average characteristics of a large number of perturbations
at one particular place on the earth. It appears, however, that there are several kinds of perturbations,
and in order to pick out the average characteristics, it is necessary to keep to one particular kind.
Moreover, the course of the perturbations in one place will be greatly dependent upon the time of day.
It will thus also be necessary, starting from this point of view, first to proceed to a close investigation
of the distribution and course of the perturbations.

In the treatment of the separate perturbations, we have, in accordance with the above remarks,
employed the following mode of procedure.

The horizontal and vertical components of the perturbing force are calculated for all the observa-
tories for a series of points of time within the period in which the perturbation appears, and the result
is given in tables.

In order to obtain a clear idea of the distribution of force, we have employed a synoptic repre-
sentation on charts. The direction of the horizontal component of the perturbing force, which was
originally determined in relation to the magnetic meridian, is fixed in relation to the astronomical, by
the aid of declination.

Now it might seem reasonable to pick out the perturbing forces themselves, and place them, with
their particular direction and magnitude, on the charts. We have, however, instead of the perturbing
forces themselves, to mark so-called "current-arrows". These would give the direction of the horizontal
current that would produce, above the place, a magnetic force in the direction of the perturbing force.
The size of the current-arrows is proportional in every case to the perturbing force, and gives the
force in magnetic units.

This mode of representation is specially chosen out of regard to the Norwegian stations; for there,
during a whole series of the greatest polar perturbations, the force will undoubtedly be produced by
currents that flow almost horizontally; and the current-arrow then nearly gives the direction of the
horizontal current. We have, moreover, other groups of perturbations, e. g. those which we have called
equatorial perturbations and cyclo-median perturbations, which are also best represented by current arrows.

This mode of marking also presents advantages with regard to the geometrical representation of
the vertical component of the perturbing force.

It must not, however, be assumed that the current-arrow indicates that a current is actually flowing
in the direction staled, all over the place. The perturbing force may, in the first place, be generated

44 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

by several simultaneously operating current-systems; it may moreover be the effect of far distant systems
that are not even always horizontal. The current-arrow is simply and solely a geometrical representation
of the perturbing force.

With regard to the number of charts that should be worked out for each perturbation, it will be
a matter of opinion how many should be taken in each case. We have, however, throughout made it
a rule that for perturbations in which the perturbing force undergoes slow changes, the time between
each chart shall be longer than for those in which the perturbing force oscillates.

By a comparison of the charts, a clear idea of the development of the perturbation will be obtained.

In this way we can, however, represent the perturbation only for certain separate points. In order
to obtain a representation of the connected course of the perturbation, a plate will be drawn of
each perturbation, reproducing on a somewhat reduced scale the actual registered curves for variations
in H, D, and V.

These copies of curves from all the observatories will be found all together, arranged according
to date, in front of the special treatment of the separate perturbations.

To ensure the best possible result being obtained from this method, material should be collected
from a large number of stations distributed over all parts of the world. The best material for the
purpose would include registerings of all three magnetic elements from a ring of stations round both
poles of the earth, and a number of other stations more or less evenly distributed over the rest of the
world --as many as possible.

We have no such material at our disposal. Our simultaneous observations of 1902 and 1903 are
all, with the exception of the registerings from Batavia and Christchureh, New Zealand, confined to the
northern hemisphere. In the arctic regions, moreover, we have observations only from our own four
stations; and although we think that these four stations were admirably situated for their object, yet the
material has not proved quite sufficient for a comprehension and elucidation of the perturbation-conditions
in the regions around the so-called auroral zone.

In order to throw more light upon these conditions in the auroral zone itself, we have made a
special investigation of the conditions in these regions, and for this purpose have made use of the
material from the polar year, 1882 — 83.

Our study of the universal character of the magnetic perturbations thus divides into two sections.

The first section comprises the working-up of the material from 1902 and 1903. In the course of
this, an attempt is made, by the employment of the previously-cited method, to throw light both upon
the conditions in lower latitudes, and upon the possible connection of these conditions with the storms
occurring at the same time at our four stations near the auroral zone.

The second section comprises an investigation by the same method, which is more especially
directed to the conditions in the arctic regions in and about the auroral zone. We have moreover, for
the sake of completeness, and in order to be better able to compare the results of these two sections,
also included in our investigations of the polar observations from 1882 — 83, observations from a few
stations that have a more southerly situation, namely, Christiania, Gottingen and Pawjowsk.

14. On the Calculation of the Perturbing Force. For the calculation of the perturbing force,
there are registerings of the variations in horizontal intensity and declination, and for some stations in
vertical intensity also. When there are only the first two, only the horizontal component of the per-
turbing force can be determined.

When no perturbations occur, the curves will have an even course, having only a slight bend
owing to the daily variation. If the curve has a marked divergence from this line, which must be
ascribed to the alteration in the magnetic constants, we then have a perturbation.

PART I. ON MAGNETIC STORMS. CHAPT. I. 45

It need hardly be said that instances will necessarily occur in which it will be difficult to decide
whether the curve is normal or not. No exact definition of a perturbation can therefore be given; but
we shall always try to keep to cases in which there is no doubt about the matter.

We will call the magnetic force that is actually found at a given moment, Ft, and the force we
should have had at the time, without perturbation, Fn.

The perturbing force P is the force which, together with /"„, has Ft as its resultant.

We resolve all the forces along 3 axes at right angles to one another -- one vertical, one along
the magnetic meridian, and one perpendicular to these, and we designate

the components of Ft as FUl, Fu, Flv
» /'„ » Fnh, Fnt, Fm
» P , Ph, Pd, P,.

We thus obtain

Pk = Ftk-F* =//«-//„ )

Pd = Fid~F,ld = Fu ( W

P, = Ftv- F»,= Vt - Vn,

introducing the customary denotations for the horizontal and vertical components of terrestrial magnetism.
We will call the horizontal component of the perturbing force /-*,, and we have

PI =1 Pk* + Pi* and

P = !/>, *-)-/>, a.

It appears from equations (i), that it is only necessary to know the difference between the
components of FI and F,,, and not their absolute value; and this difference is found by the curves, a
"normal line" being drawn upon the magnetogram, which gives the course of the curve, if no perturba-
tion has taken place.

If we denote the ordinate from the base-line to the curve and to the normal line at a given
moment, as Of, and On, and if a deviation of one length-unit on the magnetogram answers to a magnetic
force £, then

Ph = tk (Oft — Ort) = th 4
Pa = td (Otd — Ond) — £d ld
P, = e, (Ot, — Om) = ev /„,

the differences of the ordinate being denoted by //„ 4 and /„,

According to our definition-equations (i), we shall have Pk and P, becoming positive in the same
direction as the corresponding total forces. H is positive towards the north, and V is assumed to be
positive downwards. We hereby obtain the following rule for the sign of £;, and £,.

(i, is positive when increasing ordinate corresponds to increasing horizontal intensity.

For £„ we obtain

(1) In the northern hemisphere,

ev positive, when increasing ordinate corresponds to increasing numerical value of V.

(2) In the southern hemisphere.

e, positive, when increasing ordinate corresponds to decreasing numerical value of V.

With regard to £d it should be noted that in general it is not directly given. On the other hand,
the number of minutes of arc, (i, that the declination is altered by oscillations of one length-unit
is given.

46 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

A simple mechanical reflection then shows that

£d = - — 8 Ht = aid Hf.
180 . 60 r

If we resolve to reckon Pd positive towards the west, we obtain the following rule for the sign of fd .
ed is positive when increasing ordinate corresponds to increasing westerly, or decreasing easterly,
declination.

In taking out the ordinate-difterences, a purely graphic method has been adopted, the normal line
being drawn upon the magnetogram itself, and the ordinate-differences taken out directly by measurement.

One thing which here often causes some difficulty, is the placing of the normal line. It may
sometimes happen, especially when the perturbation is of long duration, that doubt may arise with
regard to its situation, and in this way a corresponding fault may arise in the determination of the
perturbing force.

In a series of perturbations, however, this doubtful territory is small, so that the position of the
normal line is decided almost without question.

It will immediately be seen that the strong, brief perturbations, which appear somewhat suddenly
on an otherwise calm day, will be particularly favorable in this respect. Here the normal line will be
a line that connects the calm districts before and after, in such a manner that its further course is ruled
by the curve on the nearest calm days. Perturbations such as these, in which the situation of the
normal line can be easily fixed, will be indicated as well-defined perturbations. The study of these short,
well-defined perturbations will also, as already remarked, be advantageous for the reason that we are
here possibly face to face with elementary phenomena, which together may form the multiplicity of the
perturbations.

If the perturbation is of long duration, if it extends over the whole magnetogram, which generally
represents 24 hours, there will very likely be some uncertainty. If, for instance, there is a part of the
curve that is normal, part of the normal line will thereby also be determined. Its absolute distance
from the base-line will then be ascertained, and its further course over the perturbed region must be
determined by the form of the curve on the nearest calm days. We must here notice whether, if the
temperature has varied during the period under consideration, it has approximately varied in the same
manner throughout the day; should this not be the case, we should have to find, by the aid of the tem-
perature coefficient, the form for the neighbouring curves, that corresponds to the temperature on the
day under consideration.

If there is no part of the magnetogram calm, the normal line must be determined, both as to its
form and to its absolute distance from the base-line, by the aid of the curves on the nearest calm days.
And here regard must be paid to differences in temperature. If we are to avoid corrections for tem-
perature, it will not be sufficient that the temperature-curve has the same course during the two days;
the temperature must also have the same absolute value at the same hour. As a rule, the temperature
in the observatory will be fairly constant, so that in most cases by this method there will be no need
of correction for temperature, unless it were actually to affect the sensibility.

As the curves from day to day in other respects -- presupposing the same circumstances - do
not repeat themselves altogether congruently, there is liable to be some arbitrariness in their situation.
If therefore we are to be able to count upon obtaining values for the perturbing force with a reasonable
error-percentage, these protracted perturbations must also be strong, if the calculation is to yield any
return; and it will frequently happen that in such cases the direction and strength of the perturbing
force cannot be greatly relied upon, when the magnitude of the force is small.

PART I. ON MAGNETIC STORMS. CHAPT. I.

47

This is, in the main, what can in general be said with regard to the placing of the normal line.
In certain cases special circumstances may arise which may make it necessary to take other things
into consideration, our material being somewhat imperfect for these determinations, as we have only
magnetograms for separate days from the foreign observatories, and these separate days are just some
of the perturbed ones. Fortunately, in the case of several places, there are several curves upon one
magnetogram, so that in this way the neighbouring curves accompany them, a circumstance which has
been of great importance to us.

On the Plates in which the magnetograms are reproduced, the normal line that has been employed
in the calculation is generally drawn.

15. On the Separation of Simultaneous Perturbations. The perturbing force calculated according
to the above-mentioned method, will give us the resultant of all the perturbing forces that are present
at the moment. Now it will often happen that we at any rate have one system of perturbations which
is predominant, so that the total perturbing force gives us directly the effect of this system. But it may
also frequently happen that at the same time we have to do with several perturbations, that, in other
words, we have in the actual field the superposition of fields from several current-systems. It may then
be important to find the effect of each separate one — in other words to decompose the total perturbing
force into several partial forces, each of which is the effect of an independent current-system, or is at
any rate due to relatively independent causes.

A decided rule for the permissibility of such a decomposition can in general scarcely be given.
The reasons that favour the interpretation of the total perturbation as the resultant effect of several
simultaneously acting systems, must be apparent from the single case in question.

We will here, however, draw particular attention to two circumstances, which will be of some
importance.

(1) When the perturbing force during a protracted calm perturbation suddenly changes its direction
and strength, only to return once more, after some time, to its original value, it will be natural to
conclude that a change such as this is due to an independent system appearing at the same time.

If this sudden change in P for all places on the earth is only a change in strength, there will, on
the other hand, be little reason for assuming the presence of an independent system.

(2) Another thing which may lead to the settlement of this question is the examination of those
places on the earth in which the perturbing force is greatest.

If, during a perturbation that is strongest at one particular place on the earth, a sudden change
takes place that is greatest at a spot situated at a great distance from the first-named place, this must
of necessity be regarded as two separate phenomena that work into one another.

It will thus often happen that during a perturbation that is highly developed at the equator, there
appears a change, which increases towards the north pole. Here then, we have undoubtedly to do
with two different current-systems, one with its point of departure in the polar regions, and one
equatorial current-system.

Frequently, however, the existence of independent systems may be recognised, although, with the
material at our disposal, we may not have the means wherewith to discriminate their magnetic effect.

It will often be a matter of judgement, whether to undertake a decomposition of the total perturbing
force or not.

It is very fortunate when a protracted perturbation is very quiet and uniform in direction, and
the intermediate one is relatively strong and not of very long duration. In such a case, it would be
natural to take out the effect of the intermediate storm by drawing a normal line that harmoniously
connects the curves before and after it.

48 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, lgO2 — 1903.

It should at once be remarked that it is the total force that can be calculated almost after an
objective method. The components, or partial forces, as we will call them, will as a rule be less exact.
A decomposition will nevertheless be of value in throwing light upon the development of the perturbations.

CALCULATION OF THE SCALE-VALUES FOR THE REGISTERINGS
AT THE NORWEGIAN STATIONS.

16. A. Determination of the Scale-Values for the Declinometer. The declinometer consists
principally of a magnet suspended by a quartz thread. Fixed to the magnet is a mirror. Light from a
fixed source is reflected in the mirror, and is focussed by a lens into a spot of light upon the photo-
graphic paper. If the fibre had no torsion, the turning of the mirror would give directly the change
of declination.

But the fibre has torsion, and its effect must be determined.

The effect of the torsion is found by twisting a certain angle a minutes of arc, and measuring the
corresponding deviation on the paper.

The scale-value, or the angle in absolute measurement, which answers to a length-unit in deviation,
is determined by the following formula:

-f x)

' d

where •/ is given by the equation

•/ =-

— x

r<i is the distance from the mirror of the declinometer to the cylinder with the photographic paper.
ka is the angle in radians about which the twisting is done.
.v is the deviation on paper, answering to the torsion.

When the angle in the equation for y. is measured in minutes, and .v in millimetres, we can put
for our apparatuses for the numerical calculation, approximately,

2 krd •= i, and

y. =

For the calculation of the perturbing force perpendicular to the meridian, we obtain the following
scale-value :

Ht is the horizontal component actually existing at the moment.

17. B. Determination of the Sensibility of the Variometers for the horizontal and vertical
Intensity. The main principle here consists in seeking the deflection corresponding to a known mag-
netic force /.

PART I. ON MAGNETIC STORMS. CHAPT. I. 49

If a deflection of « length-units on the photogram answers to /, then the scale-value is

* = f

n,

f is to act as the deflecting force for the horizontal variometer along the line of direction of the
horizontal component, for the variometer for vertical intensity, in a vertical direction.

/ is determined in relation to Hg, or the horizontal component of the magnetic force during the
determination of sensibility. This is done by letting the deflecting magnet, as before, deflect the decli-
nation-needle. During the determination, care must be taken that the deflecting magnet in all three
cases is at the same distance from the observation-magnet.

If the declination-needle undergoes a deflection answering to nd length-units, we obtain

If this is inserted, we obtain, employing the equation for

»d rr

ti, = -- . w d rio

»

£, = . 10 d tif,

Mc

If we do not here demand greater exactness from sk and c, than i per cent, of the amount, we
can in general, as long as the declinometer has the same thread and the same distance, consider iod as
constant, x being small in proportion to the unit. We can then generally, instead of H0, choose
a mean value, H0, of the horizontal component. This we can safely do here, as a determination of
sensibility made during a great perturbation ought not to be employed.

We then obtain

«/. = — - ' iOd HO

£v ~ ' (-Od **.Q

For slighter perturbations, we can put, with the same accuracy as before,

Ht = HO.

This assumption, which we can probably always make with more southerly stations, is not always
permissible for our Norwegian stations in the treatment of perturbations; for at the latter the horizontal
component of the magnetic force is very small, while at the same time the variations in it on account
of the perturbation may go up to 500 y or even more. We can now put

In general we have

,t TJ D [ D

A fit — J\h -f- r\ ,

where Rh is the reduction from the mean value to the normal value for the point of time under
consideration. PI, is the perturbing force in the direction of the magnetic meridian.

In the cases in which the equation will come to be employed, P/, is preponderant in relation
to /?/,, and if we put

^ = 6'

Birkelnnd, The Norwegian Aurora Polaris Expedition, 1902—1903. 7

50

we obtain

BIRKELAND. THF. NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

I'd

= -- coj

lt>d

Our calculations have been made according to these formulae.

In the determination of sensibility, the following mode of operation has been used in the main for

all the four stations:

TABLE I.

I

2

3

4

5

Torsion

Declinometer

H. I. Variometer

V. I. Variometer

Declinometer

Equilibrium

Equilibrium
Magn. W, North pole W

Equilibrium
Magn. N, North pole N

Equilibrium
Magn. Up, N. pole Up

Equilibrium
Magn. E, N. pole E

o

E

S

„ „ „ „ Down

W

- a

+ o

» E, „ „ W

„ S, „ „ N

„ Down, „ „ Up

„ W, „ „ E

a

E

„ s

„ „ „ „ Down W

Equilibrium

Equilibrium

Equilibrium

Equilibrium

Equilibrium

DETERMINATIONS OF SENSIBILITY FOR KAAFJORD AND BOSSEKOP.

18. The apparatuses were in position at Kaafjord from the igth August, 1902, up to, and
including, the i3th March, 1903. During this time they underwent no changes of any importance.

From the i5th March, 1903, to the 2nd April following, the apparatuses were set up at Bossekop.
During this time, considerable changes were made in them, a new thread having been put in on the 25th
March, in the H. I. variometer, and 6 astatising magnets placed beneath the declinometer.

On the 2gth March, another new thread was put in the H. I. variometer, and the astatising magnets
were moved higher up. These alterations were made for the purpose of increasing the sensibility.

In the table below will be found the quantities that come into the formulae, and the calculated
scale-values, for the determinations of sensibility that were made, as also the date of the determinations,
and the temperature at the beginning of each measurement.

As a unit for scale values we use iy=io-s abs. magn. units, referred to i mm. deviation on the
magnetogram. See art. 14.

TABLE II.

Scale- values for Kaafjord.
HO = 0.1248 rj = 1708 mm. •/. = 0.00465 u>dHo = 3.67

Date

nd

«A

>'v

fh

£v

Temp.

Sept. 9, 1902 . . .

37.1 mm.

22.9 mm.

28.6 mm.

5-95

4.76

+ 9-5°

26,

36.8 „

23° ,,

28.9 „

5.87

4.68

+ 8.3°

Dec. 19, „ ...

36.4 „

22.5 »

18.9 „

5-95

7.07

- 4-3°

Jan. 22, 1903 . . .

36. r „

31.6 „

17.0 „

6.13

7-83

- I.o°

March 13, „ ...

36.3 ,/

2T.7 „

(4-9?),

6.12

(27.1 ?)

- 5.0"

TART

ON MAGNETIC .STORMS. CHAPT. I.

51

The table shows that the scale-values for H and V are not constant; in the case of ee in particular
there is a considerable increase, and in the determination of the 3rd March, 1903, the balance was almost
immovable. This abnormal circumstance seems, however, to have been only of a temporary nature, as
will be seen from the curves before and after. We have not employed any smoothing formula here
for £/,, but have found the scale-values by interpolating between two successive observations.

We have employed the following formula for £„:

£„ = 4.76 -f 0.0285 *>
t indicating the number of days reckoned from the ist October.

TABLE 111.

Scale-values for Bossekop.
r<i= 1740 mm.

Date

Ho'

a

X

X

Hd

»l,

»i

n>dH0

fk

£,

March 23 ...

0.123

10800'

53-5

0.00498

37-5 mm.

25.2 mm.

38.3 mm.

3-55

5-29

3-48

April i ...

0.0667

54°°'

48.4

0.00904

68.8 „

33-5 ,,

37-5 .

1.90

3-9°

3-49

HO indicates the magnetic force, to which the declinometer-needle is actually subjected. During
the first determination of sensibility it is only terrestrial magnetism that is acting.

The force acting on the declinometer-needle, during the 2nd observation, may be determined in
two ways. We can either use the deflection by the torsion, having the same thread and the same
position in both cases; or we can employ the deflection with the deflecting magnet, the magnet having
been placed at the same distance on the deflection-rod in both cases. The two methods give about
the same result. The value given is the mean value. For the period from the 25th to the 2gth March,
we have no scale-value, a determination of sensibility that was made on the 2yth having been unsuccessful.

DETERMINATIONS OF SENSIBILITY FOR DYRAFJORD.

19. The registering at Dyrafjord was begun on the 25th November, 1902, and was continued
almost without interruption until the I5th April, 1903.

During that time, neither the declinometer nor the variometer for horizontal intensity underwent any
change, except that the torsion-head of the variometer for the horizontal intensity was a little twisted on
the ist December, 1902.

As we shall presently notice more fully, the variometer for the vertical intensity, in the course of
the above-mentioned period, underwent a few small changes, which, however, have had no perceptible
influence upon the scale-value.

As the torsion in the thread of the declinometer is slight, /. will be small. The torsion has there-
fore only been determined 3 times, namely on the 28th November, and 8th December, 1902, and the
1 6th January, 1903. As the mean of these three, it is found that

y. — 0.00164.

52

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

TABLE IV.

Scale-values for Dyrafjord.
H0= 0.120 0) rd = i734mm. iodH0 = £d = 3-47-

Date

«<;

m,

nv

£l<

«»

Tempera-
ture.

1902

Nov. 29

34-°

21.4

21.4

5.50

5-5°

4-93°

Dec. 2

39-4

24.7

28.2

5-54

4.85

4-3 °

8

45-7

28.9

33-2

5-48

4-78

5.i °

» ii

(55-6
\46.4

35-4
29.2

35-4

5-46

5-5i

4-56

6.7 '

16

/47-3
I 33-°

30.0

28.0

5-47

4.16

4-5 °

1903

Jan. 2

40.4

25-1

28.7

563

4-93

0.9 °

16

39-2

25-3

27-5

5-40

4-97

2.8 °

,, 19

40.3

25.6

29-7

5.48

4-74

2.0 °

24

40.4

25-5

29.0

5-53

4.86

2.2 °

Feb. 5

{O.fl

25.6

3°-3

5-47

4-63

14 °

„ 21

39-8

24.8

29.2

5-57

4-85

i.5 °

27

40.2

25-4

28.1

5-52

5.00

1.4 °

March II

40.5

25.8

28.2

5-51

5-03

-0.5 o

„ 24

4°-3

25.8

27.7

5-44

5-07

-0.3 °

31

40.8

25-7

27.6

5-54

5.16

o.S °

April 1 1

40.7

25-5

266

5.58

5-33

1.1 °

Note. December I, 1902, the sensibility of the variometer for V. I. made a little greater.

December 1 5, 1902, compensation for the variometer for V.I. altered.

February 23, 1903, the curve longer from the base-line for V. I. ; otherwise unaltered.

January 27, 1903, fixed new mirror for V. I. ; otherwise unaltered.

It appears from the above table that the sensibility for H has remained nearly constant all the time.
No decided variation in the temperature is noticeable, nor yet any decided variation with time.
It is therefore most natural to let Eh be constant all the time. The mean of the scale-value is

«;.= 5-51-

E, also remains fairly constant all the time. For £„ we obtain the following:
Nov. 25, 1902, to Dec. i, 1902, £„ — 5.50
Dec. i, 1902, to Dec. 15, 1902, ev = 4.73
Dec. 15, 1902, to Jan. 27, 1903, e, = 4.92
Jan. 27, 1903, to Apr. 15, 1903, «„ = 4.61 + 0.0094, <•

For this last period from the 27th January to the i5th April, we have a fairly regular increase
of £„ with time. The formula set up is calculated by the method of least squares.
/ here stands for the number of days reckoned from the 27th January.

(') It must be remarked that this value is somewhat uncertain; for owing to the illness of Saeland, whose knee became
stiff while at Dyrafjord, no complete absolute determination was made. A deflection experiment was made, and this, combined
with a knowledge of the magnetic moment of the magnet employed, gave the value here given, which moreover is in accordance
with the terrestrial-magnetic charts.

1'ART I. ON MAGNETIC STORMS. CHAPT. I.

53

DETERMINATIONS OF SENSIBILITY FOR AXEL0EN.

20. The registering apparatuses on Axeleen were in operation from the 3oth August, 1902, without
interruption until the yth June, 1903.

Neither the variometer for the horizontal intensity, the declinometer, nor the balance were changed
during that time.

No determinations of sensibility were made on Axeleen for the variometer for the vertical intensity,
as this apparatus was without deflection rods. The position of the movable parts of the magnet, and the
arrangement of the balance, were however accurately noted.

Determinations of sensibility were made at the Physical Institute, ? A

Christiania, after the return of the Expedition, the conditions
that had prevailed on Axeleen being reproduced as exactly as

possible. No alteration in the magnetic moment is to be "%?

apprehended, as the magnet was several years old. The balance- — ^^^ .. t —

magnet was of the form shown in the figure. The movable > EE? J=E ^,1

parts consist of a small weight B, which can be screwed back- ~~ — — ^*~"

wards and forwards along a small, horizontal, brass rod, and a Fig. 28.

weight A, capable of being moved in a vertical direction.

By moving B, the magnet can be adjusted horizontally. It is easy to see that a small change in B will

have no great influence upon the sensitiveness, as the centre of gravity of the system is neither raised

nor lowered thereby to any noticeable extent. By screwing A, on the other hand, the sensitiveness is

altered, as the height of the centre of gravity is thereby altered.

As the position of A is not so easy to find again accurately, two determinations were made, the
weight A being placed in the highest and lowest positions possible in the case in question.

The determinations gave the following result:

A in lower position

A in upper position

( Distance of deflecting magnet 56.4 cm. «„ = 25.6

\

47-05

£„ = 24.9

Mean = 25.25
Distance of deflecting magnet 47.05 cm. tv = 23.85

Mean = 24.6 y
As we use the mean value, the error should not exceed 4 per cent.

TABLE V.

Scale- values for Axeleen
HO =0.0941 rrf = i733mm. -/ = 0.0079

=• 2.736

Date

nt

HI,

e*

r

Sept. 12, 1902

43'9

26.2

4-59

3-0°

Nov. 1 6, „

43-75

25.9

4-63

0-5°

Dec. 12, „

44.1

26.2

4.61

Q

— 1 0.0

March i, 1903

^3-6

25.8

4.62

- 8.0°

54

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

The table shows that the scale-value for the variometer for horizontal intensity has remained constant
all the time, and has not altered perceptibly with the temperature.
We therefore employ the mean value, viz.

ei, = 4-613 y per mm. deviation.

DETERMINATIONS OF SENSIBILITY FOR MATOTCHKIN SCHAR.

21. The registering apparatuses here were in operation from the 3Oth August, 1902, to the nth March,
1903. The first month, from the 3oth August to the 3oth September, was spent in trial registering: for
it proved to be very difficult to get the balance compensated for variations in temperature. Compensation
of the balance was effected on September gth,. loth, nth, I2th and ayth, and October 6th. The sensi-
tiveness of the balance was altered on the 23rd September and the gth October, being increased
both times.

The H. I. variometer acted almost without change; it only now and then underwent small corrections
with regard to the position of the base-line. These cannot, however, be supposed to have had any
special influence upon the sensibility. The declinometer acted without alteration all the time. Astatising
magnets were not employed.

It will be seen from the diagram below, that the thread in the declinometer was very stiff, the
effect of this being that v. is very large, and therefore has to be determined very exactly. At the same
time the H. I. variometer has a sensibility, which, especially considering the violent storms that occur
here, must be characterised as disproportionately great. It seems as though the threads for the two
variometers have been interchanged.

TABLE VI.

Scale- values for Matotchkin Schar.
H0 = o.i 1 13

Date

a

X

•/.

nd

«/,

««

£;,

£,

fiiiflQ

r

Sept. 20, 1902 . .

4°

67.0

0.387

28.2

77-0

1.64

4.48

2.2°

Oct. 17, „

4°

66.1

0.380

29.9

90.9

19.0

1.47

7.02

4.46

- 4-6°

Nov. 1 6, „

4°

62.8

0-354

29-5

74-4

21. 1

i-73

6.06

4-37

- 2-4°

Dec. 22, „ . .

4°

65-5

0-375

27.7

76.6

16.8

1.61

7-33

4-44

- 5-8°

Feb. 12, „

4°

65.3

0-373

28.2

76-5

14-7

1.63

8.52

4-44

-.3-8°

It will be seen that ea and £/, keep fairly constant, and exhibit no decided variation with time and
temperature. We make use of the mean, putting

£,'i =1.62

The value of ev are found from a curve, which together with the observed values, is shown in the
following figure.

PART I. ON MAGNETIC STORMS. CHAPT. I.

55

Curve representing the scale values of the
Lloyd's balance tit Matotclikia Srliar

illiit::

Octbr.

Jfovbr.

Upclir.

Jartr.

Irhr.

Mar.

Fig. 29.

TEMPERATURE COEFFICIENTS FOR THE REGISTERINGS.

22. The temperature at our four arctic stations was registered all the time, simultaneously with
the magnetic elements. At the stations at Dyrafjord, Kaafjord, and Matotchkin Schar, the temperature was
registered upon the magnetogram itself. At Axeleen, it was registered by an ordinary thermograph.
The temperature moreover is generally given at the beginning and end of each magnetogram.

Lloyd's balance, on all stations, except at Axeleen, were compensated for changes in temperature
by means of magnets which were placed at a suitable distance under the balance. The compensation
was tried by artificial warming of the rooms by means of hot bricks.

In order to be able to correct the curve for changes in temperature, we must be acquainted with
the following particulars :

£ ( , or the number of degrees centigrade that answer to a deflection in the temperature-curve of i mm.
0;, = the number of mm. the H. I. curve is displaced in relation to the base-line per degree centigrade.
Od = the number of mm. the D curve is displaced in relation to the base-line per degree centigrade.
8e = the number of mm. the V. I. curve is displaced in relation to the base-line per degree centigrade.

We call these quantities positive, when the curve, by an increase in temperature, is sent upwards
on the magnetogram.

The values found for our four arctic stations are given in the table below.

TABLE VII.

Kaafjord

Dyrafjord

Axeloen

Matotchkin
Schar

£t

0.088

o-°55

0.062

»k

-o-57

-1.38

-1.56

-0-54

9t

1.94

1-5°

— 0.67

o.oo

0,

2.71

5-53

i-34

O.X5

£t is found by comparing the temperatures read with the ordinates to the temperature-curve.

56 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

In the case of the three other quantities, we have employed a somewhat different mode of procedure
in the calculation. For Dyrafjord they are found by the aid of the change in temperature that will
always take place during a determination of sensibility, and which can be determined by the temperature-
curves. In order to be sure that the displacement of the curve is due to the temperature, it must be
calm before and after. The diurnal variation must, moreover, be taken into consideration. The values
given are means of 10 determinations distributed over the various months.

At the other three stations, a method has been employed by which we escape having to consider
the diurnal variation. Under normal conditions, the ordinates to the curve in points lying 24 hours from
one another -- provided the temperature is the same — should be of the same length. The majority
of our magnetograms cover a period of 24 hours.

We have now selected a series of registerings for the very calmest days with a great difference
in temperature between the beginning and the end. The required temperature coefficients are then
found from the differences between the ordinates to the terminal points and the difference in temperature.
This method is very suitable, as the temperature for Axeleen is read directly, at the beginning and end
of each magnetogram. At Matotchkin Schar, it is only at the beginning. At Kaafjord, on the other
hand, the temperature in the register-house was read only a few times in the course of the winter, and
there we have had to keep to the registered temperature-curve only.

The values given in the table are in each case the mean of 12 such determinations. In the cal-
culation of the mean, we have assigned different weights to the determinations, according to the amount
of difference in temperature, and the calmness of the twenty-four hours.

The temperature-coefficients of our registerings -- with the exception of those for Matotchkin
Schar -- are not inconsiderable; and as the temperature at these temporary stations undergoes great
changes, it has been necessary for us, in our calculations, in each case to direct our attention to its effect.

EXPLANATION OF THE CHARTS.

23. Our investigations of the distribution and course of the magnetic perturbations, divide, as already
mentioned, into two sections, the one embracing the whole earth, the other more especially confined to
the regions round the North Pole.

We have here found it most practical to employ two different charts in the synoptic representation.

For the universal part we have employed a map of the world on Mercator's projection. The
advantage of this projection is that it is orthomorphic, so that angles upon the earth can be marked
directly upon the chart.

For the second section we have used a polar map in the equidistant zenithal-projection. This pro-
jection is not orthomorphic; but the angular deformation in the polar regions is very slight. For all
stations except that of Cape Thordsen we have, however, taken this deformation into account. As for
Cape Thordsen the deformation is less than the accuracy with which the angles can be determined.

The previously explained current-arrows are marked on the maps, representing geometrically the
perturbing forces calculated for a particular point of time. The time is stated at the top of the map.
The length of the arrows is proportional in each chart to the perturbing forces. At the foot of the
chart a scale is marked, by means of which the magnitude of the perturbing force can easily be taken
directly from the chart. As the unit of magnetic force we have employed i y = io~ 5 absolute units.

It has proved inexpedient to make all the arrows on one chart to the same scale, as the perturbing
forces at the northern stations are often more than 10 times as great as over the other parts of the
earth during the same period.

PART I. ON MAGNETIC STORMS. CHAP. I.

57

We have therefore in general employed different scales for the arctic regions and for the rest of
the earth. On the Mercator chart, the scale given is the one employed for the more southerly stations.
The scale for the four Norwegian stations is only a fraction — generally Vs — of that given on the chart.

In order to indicate this, we have written beside the arrow the fraction by which the scale marked
on the chart must be multiplied in order to find out the scale employed for the place. When, for instance,
the fraction Vs is found on the chart, this signifies that each length-unit of the arrow is equivalent to a
force 5 times as great as that which would be directly indicated by the scale given on the chart.

On the polar chart, on the other hand, the conditions are reversed. There we have given the
scale that is employed for the polar stations, that is to say for the places where the perturbation is
strongest; and the scale for the more southerly stations is given in the same manner by a multiplier.

In order to make the charts easy of comprehension and give a direct idea of the course of the
perturbation, the same scale has as far as possible been kept for the whole of a perturbation. On the
other hand, the scale will not be the same for all perturbations, as it must be chosen so as to give the
arrow on an average a suitable length.

As the vertical intensities are of the greatest importance for a complete determination of the character
of the perturbation, they are also placed upon the charts, in order that both their magnitude and direction
may be taken thence. They are represented by lines drawn out from the place at right angles to the
current-arrows, and are marked on the same scale as the latter. Their direction is determined in the
following manner. If we imagine ourselves to be standing on the place in question, and looking out in
the direction of the current-arrows, the vertical arrow is placed on the left if Pe is turned downwards,
on the right if it is turned upwards. Or we might express it as follows: Let P, be turned 90° with the
hands of a clock, the observer facing the direction of the current-arrow.

It appears from Ampere's law, that when the perturbation at a place is due to a horizontal current-
system above the earth, the vertical arrow will point out towards the places where the current has its
greatest density.

This law has a special application to the arctic stations.

As the current-arrow, however, very often does not give the direction for a horizontal current, but
is only a representative of the perturbing force, the vertical arrow loses this significance; but it gives,
at any rate, P, in magnitude and direction.

For the purpose of distinguishing the vertical arrow from the current-arrow, the latter is made a
little thicker and with an arrow-point.

It is only from a very few stations, however, that there are registerings of variations in vertical
intensity. As a rule, arrows will be marked for the following:

The Norwegian stations Kaafjord, Dyrafjord, Axeleen, and Matotchkin Schar;

and also

Christchurch, Tiflis,

Munich, Val Joyeux,

Pawlowsk, Wilhelmshaven,

Pola, Zi-ka-wei,
Potsdam,

and sometimes for Irkutsk and Jekaterinburg. In general, no oscillation will be noticed in the V. I. curve
for Zi-ka-wei, partly on account of the small sensibility. Upon the whole, moreover, P, will be small,
often imperceptible, in southern latitudes.

Birkeland, The Norwegian Aurora Polaris Expedition, 1902—1903.

58 niRKF.I.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

The following signs will also occur on the charts:

(?) indicates that the perturbing force cannot be determined, owing to lack of material.
(*) See note in the text. The perturbation is then often ill-defined, and so small that the perturbing

force cannot be calculated with any advantage.
(0) The perturbing force is imperceptible.
(0&O) Indicate respectively the sun and the moon, and these signs are placed where the sun and moon

respectively, in the epoch under consideration, stand in the zenith.

(©) Indicates the point in which the magnetic axis of the earth intersects the earth's surface, i. e. the
axis of the elementary magnet to which the earth approaches for infinitely great distances. At
the new year, 1903, this point was determined thus: North latitude 78° 20', West longitude 71° n'.
On the Mercator's chart, the equator line for this pole-point will also often be marked.
(©) The magnetic north pole.

To show the position of the so-called auroral zone, two curves, from FRITZ'S aurora chart, are drawn
on all the polar charts and on a few of the Mercator's charts. The most southerly gives the places of
the greatest frequency of observed aurora. The most northerly connects points where aurora is seen as
frequently in the south as in the north.

It sometimes happens, in the case of the northern stations, especially Matotchkin Schar, 1902 and
1903, that the patch of light, owing to the strength of the perturbations and the great sensitiveness of
the apparatus, passes out of the paper, returning again in a little while. We know then that the deflection
is at least as great as to the edge of the paper. This minimum value of the perturbing force, obtained
by measuring to the edge of the paper, is then placed upon the chart as a dotted arrow; and at its
point is placed an arrow, to give the direction in which the current-arrow really has its point.

In cases in which the total perturbing force is resolved into two partial forces, the corresponding
current-directions will be given with dotted arrows, while their resultant is drawn in full.

THE COPIES OF THE MAGNETIC REGISTERINGS.

EXPLANATION AND GENERAL REMARKS.

24. As already mentioned, there will be a plate belonging to each perturbation, containing copies
of the magnetograms obtained.

As it is important, when reading the descriptions, to have the curves themselves before one, it
might have been better if the latter could have been in the same place as the descriptions. The fact
that, notwithstanding this, we have considered it advisable to keep all the curves together, is mainly due
to circumstances of a purely technical nature.

The curves will follow one another in chronological order.

Upon the district in which the perturbation is found, the normal line will be drawn, according to
the previously given rules, as a dotted line.

With a knowledge of the scale-value, it will thus be possible, if desired, to find out the perturbing
force at any point of time.

The scale-value is given graphically by lines placed at the end of each curve, and giving the
length of oscillation of a particular force. At the head of the column are the signs L", L", and L", which
indicate the length of a deflection in H, D and V respectively, corresponding to magnetic force, n. y,
operating in the respective directions. In the middle of the line is an arrow-head, which gives the
direction of increasing H. I. increasing westerly declination, and increasing vertical intensity.

The scale in relation to the original magnetograms is so arranged that all the magnetograms shall
have the same time-length. The scale-value is thus increased in the same proportion as the time-length
is diminished.

PART I. ON MAGNETIC STORMS. CHAP. I.

59

Iii the table below, the scale-values appear as they were given us direct, as also the length of
one hour upon the original magnetograms.

TABLE VIII.

Observatory

£i,

n>dH0

8t

Length of
i hour

Remarks

•4- 4.61
+ 3-595— 0.0125 '•(*)
+ 3.56
+ 5-12
4 '-959- 0.03 If. —2 1)(*)
4.6
+ '3-94
+ 5-51
(') From Nov. 25, 02
•4- 2.24 4- 0.0058 h.

+ C)
+ 5-1
-f 1.62
- 50
4 5-03

- 44S

- 3-165
fi9o2= + e.a.

11903 = -f 7-4/

+ C)

+ 5-i

( ToDec. 23, 02 = — 2. 141
\From. 24,02== — 2.2 1/

4 4-5
- 8.0

4- 4.67
— 6.00

+ 2.74
4- 6.36

— 12. 0
412.3

+ 5-94
7-43
- 9.85
4- 3-47

4- 8.3

+ 3-67
+ 4.68
+ 4.44
- 7.61
- 4-6

+ 6.94
- 5-o8

- 8.2

+ 4-5i
4 5-71
- 3-7i

4- 6.02
- 8.37

4- 6. 1 1
— 5-°o

-24.6

+ 16.1
3.12

+ C)

4- C)

4- (")
- 3.78
- 7-48

+ 2.070
— 3.00

- 2.55

- C)

C)
- C)

mm.
20.06
19.97
1558
15-36
19.92

15-36
14.74
19.94

19-95
19.89
15.01
J9-94
20-35
M-99

20.00

20.48

15-4
19.98

15-24
15-58
18.22

9-94

I5-40
I5-50

(*) t. = Temp, in degrees centigrade.

(") t. = Temp, in degrees centigrade.
(*) Sign changes. Given on the plates.

(*) See table of scale-values.

(') Ih = ordinate in mm.
\Average F;, = 2.56.

(*) See table of scale-values.
(*) See table of scale-values.

1 Oct. 10 — 23, 02 =2.09
(") Exactly ( Oct. 23, 02 — Feb. 20, 03 = 2.12
( Feb. 20 — Mar. 30, 03 = 2.00

... / Oct. 10 — Dec. 19,02= 1.937 — °.i43 '•
\ Dec. 21,02 — Mar. 31, 03 = 1.76.

Oct. Nov. Dec. 1 Jan. Feb. Mar.
i'i

Christchurch *) ....

Kew . . .

Matotchkin Schar . .

Pawlowsk

Pola

San Fernando ....
Sitka

Tiflis

Val Joyeux
Wilhelmshaven . . .

8.0 9.0 10.0 11.0 9.0 9.0
(*) fe not determined.

(*) rt varies greatly. The values will be
given for each curve.

(') On Sept. soth the value was 4.38 and increased o.oi per diem up to Oct. sist, after which it was constant up to Nov. 25*.

For convenience in the Plates, the sign is here fixed as follows:

(,,, iodHu and e, are indicated by -f, when a deflection upwards answers respectively to increasing
II. I., increasing westerly declination, or increasing numerical value of V. I.

The reduction of the magnetograms has been effected by a pantograph belonging to the Geogra-
phical Survey of Norway. The reduction to equal hour-length, and also the drawings, have been
executed by a very skillful cartographer, Mr. J. NATRUD of the Geographical Survey.

As mentioned in my circular of June, 1903, it was my original intention to publish some of the
magnetic records by means of photographic reproduction. This mode of procedure, however, has
proved to be very unsuitable for the arrangement of curves from so large a number of observatories;
but I think that the method of reproduction chosen by us will be of equal value to science.

6o

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

A list of the perturbations that will be treated in the following chapter is given below in Table IX.
The great generosity and interest shown by the heads of all the previously-mentioned observatories,
without which the exceptionally valuable material relating to magnetic storms contained in these twenty-
one plates could not have been collected, would be worthy of emulation in all branches of science.

TABLE IX.

No. of
Pert.

Date

No. of Plate

Class oi Perturbation

i

Jan. 26, 1903

XIV

Equatorial

2

Dec. 9, 02

IX

— • —

3

Oct. 23, 02

III

— » —

4

Dec. 15, 02

X

Elementary polar

5

Feb. 10, 03

XVIII

_._

6

Mar. 31, 03

XXI

_»_

1

Mar. 22, 03

XX

— > —

8

Dec. 26, 02

XII

— » —

9

Oct. 6, 02

I

Cyclo-median

10

Oct. 30, 02

VI

Compound

ii

Dec. 25, 02

XI

»

12

Dec. 28, 02

XIII

X

13

Feb. 15, 03

XIX

_»_

M

Feb. 8, 03

XVI & XVII

— » —

15

Oct. 27, 02

IV

_»—

16

Oct. 28, 02

V

— • —

'7

Oct. 31, 02

VII

___ )

18

Oct. ii, 02

II

_»_

19

Nov. ff, 02

VIII

— 1 —

20

Jan. !?, 03

XV

_,_

CHAPTER II.
ELEMENTARY PERTURBATIONS.

25. It will be our endeavour, as stated in the introduction to this section, while studying the
perturbations, to find out their extent and course in each case. We consider it to be of the greatest
importance for the attainment of this object that what has taken place should be viewed as directly as
possible, at moments during the perturbation as numerous and close together as is practicable. This
then has guided us in our calculation of the perturbing force, and we considered that we arrived most
easily at the truth by placing the normal line actually on the magnetogram, in accordance with the pre-
viously mentioned rules.

In connection with this, it should be mentioned that it would be expedient, when reading the
description, to have the curves before one, as there the conditions appear as directly as it is possible
to have them.

With this object in view, our purpose is best served by dividing the perturbations into groups,
which seem to have comparatively well-defined properties.

After the experience we have gained through the treatment of this material, it is our hope that
also other natural philosophers will feel convinced that we have taken the right road, a road that leads
to a clear comprehension of the laws of perturbations.

It must not be imagined, however, that these groups stand as altogether separate phenomena.

A complete acquaintance with the nature of the perturbations will assuredly lead to the assumption
that there is a certain genetic connection between the various groups. It is moreover our opinion that
this is the case, at any rate as regards the majority of the most important groups, as the physical agents
that consitute the currents are supposed to have in the sun their common source.

The following treatment of perturbations will include the most important of those that occur in the
registerings of the thirty days(1) for which we have received material from a number of observatories —
mentioned previously - - all over the world. This choice of days is based upon observations from Kaa-
fjord and Potsdam. The qualities that have guided the selection have principally been strength and dis-
tinctness; but on the other hand, the selection was made without regard to the character of the pertur-
bation in other respects. As, however, the choice was based upon observations from one particular
region of the earth, this circumstance could not but cause the perturbations that appear especially strong
about the Norwegian stations, to receive a prominent place; but this, far from being a drawback, must,
in our opinion, be considered an advantage, as the material collected by us in our arctic expedition will
thereby be turned to best account. This one-sidedness, moreover, in the material is considerably reduced
by the circumstance that for each of the hours mentioned in the circular, we have always received regis-
terings for at least one day, and in the case of several of the observatories even for several days. We

Circular of June, 1903.

62 BIRKF.LAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903

have thus had an opportunity of studying a number of perturbations that do not belong to those spe-
cially mentioned in the circular.

It would be impossible, if we are to treat the perturbations upon the lines we have laid down, to
take notice of all the deviations that might indeed be worthy of mention. We have had to confine our-
selves to the study of the greatest and longest, or at any rate to perturbations of a universal character.

We will here mention a circumstance that confirms us in our opinion that we have succeeded in
treating a number of the most important of the perturbations that have taken place during this period.

Being aware of the one-sidedness there might possibly be in our material, we wrote on the gth
March, 1907, to the Director of the Coast and Geodetic Survey of the United States with a request
that he would send us magnetograms of some of the greatest perturbations that had occurred at Sitka
and in North America during the period from the autumn of 1902 to the spring of 1903. The Super-
intendent, Mr. O. H. Tittmann, and the Director, Mr. L. A. Bauer, were good enough to comply with
our request. The perturbations, however, which had been selected with regard to Sitka for ten days in
which "the magnetic perturbations were remarkably distinct, powerful and simple", proved to be of no
very different kind or magnitude from those we had already studied. It was principally a series of per-
turbations in January that were comparatively great in those regions. We shall go more fully into
these conditions farther on, as, with the .aid of the material from the polar stations of 1882 — 83, we
may draw important conclusions regarding the position of the storm-centres about the auroral zone at
various times of the day.

A similar request was sent to the Director of the Observatory at Christchurch (New Zealand),
whence we also once more received magnetograms for 19 days of the period observed, in which the
perturbations at that place were remarkably distinct, powerful and simple. In 16 cases, however, the
perturbations were coincident with some we had previously received and discussed.

THE EQUATORIAL PERTURBATIONS.

26. It appears that magnetic storms of any considerable strength, are most frequently of a kind
in which the force increases towards the poles. It also appears, however, that it is not unusual to find
perturbations that are best developed and most powerful at the equator. It has even been found that
these perturbations in the regions about the equator, act principally upon the horizontal intensity, in such
a manner that the current-arrows point along the magnetic parallels.

As regards the lower latitudes, the circumstances of the perturbation often exhibit symmetry both
with respect to the magnetic axis and to the equator. Such perturbations we have chosen to call equa-
torial perturbations.

Of these there are again two kinds possible, namely, such as produce an increase in the horizontal
intensity, and such as produce a diminution. Both of these occur.

The first of these we have called positive equatorial perturbations; the second kind we have called
negative equatorial perturbations.

The reason for this separation is not merely the more formal one that the force is in opposite
directions; but it goes deeper, the two perturbations having quite a different character and course. The
positive equatorial perturbation in particular is strongly characterised, so much so that if attention has
once been drawn to it, it will always be recognised with the first glance at the registered curves. Its
more detailed characterisation will come out best in the treatment of the separate typical cases.

PART I. ON MAGNETIC STORMS. CHAP. II. 63

THE POSITIVE EQUATORIAL PERTURBATION.
THE PERTURBATION OF THE 26th JANUARY, 1903.

PI. 'XIV.

27. For the study of this perturbation, there are magnetograms from all the stations. As the
curves show, only the latter half of the perturbation has been obtained at most of the European stations.
The perturbation appears quite suddenly upon a quiet day. It begins at 8h 52™, and lasts until
14'' 2Om. (The time, when not otherwise stated, is Gr. M. T., o1' = midnight).

It is particularly well developed and well defined in the equatorial regions; its effect is not con-
fined to any single district, but it appears all round the equator. If, for instance, we look at the curves
for Dehra Dun, Batavia and Honolulu, we see that at these three places the perturbation agrees down
to the smallest details. We further notice immediately that it appears only in the horizontal intensity,
and in such a way that all the time the perturbing force is directed northwards, i. e. in the direction
of the magnetic meridian.

If we pass from the equator towards the poles, we see that the character of the perturbation is
maintained, the only difference being that the deflections become a little smaller. As far south as
Christchurch, which is our most southerly station, and as far north as Toronto in America, and Stony-
hurst and Pawlowsk in Europe, the perturbation preserves in the main its character of appearing only
in the horizontal intensity. When we come, however, to our most northerly stations, we find that it
also appears in the declination, which means that here in the north the direction of the perturbing force
is no longer along the magnetic meridian. At the same time, the average deflection becomes con-
siderably less for these stations. This, together with the more disturbed course of the curve, makes it
difficult to measure the perturbing force. The perturbation here acquires to some extent the character
of marked oscillations about the mean line.

In glancing at the curves, we also notice at once their jagged character during the perturbation,
answering to a great variability in the strength of the perturbing force. If we compare the serrations
in the curves for the various stations, we find them to a great extent repeated from place to place.
We further notice that as we approach the poles, the serrations become more acute and larger, and of
a somewhat local character. A sudden change in the curve answers to a great change in the pertur-
bing force, which again must be produced by a great change in the perturbing impulses.

It might now be asked whether these perturbing impulses reach the various parts of the earth
simultaneously, or whether they require an appreciable time to be transmitted from one station to
another.

The very fact that the serrations can be distinctly identified in the different curves, makes it
natural to expect that they appear simultaneously, as it would be difficult to imagine that an impulse
of this kind during a comparatively slow motion, could preserve its character unchanged.

In order to throw light upon this circumstance, we have reckoned the times at all the stations,
for a series of points that allow of easy identification. The result is given in the Table below, where
the points are indicated by the numbers i, 2, etc., and will be found marked on the curve for Dehra Dun.

The following table shows that the time varies so little with the geographical position, that it
would be premature to draw conclusions from it.. The slight differences that appear rather irregularly,
may be ascribed to inaccuracies in the determinations of time on the magnetograms; for we see that if
a difference in time for a certain point appears between two places, this difference is maintained for all
the points, a circumstance which seems best to be explained by an inaccuracy in the statement of the
time. We may conclude from this that the serrations appear simultaneously, or rather, the differences
in time are less than the amount that can be detected by these registerings. Characteristic serrations
such as these may therefore often be of great use in controlling the time of the magnetograms.

64

RIKKF.LAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

TABLE X.

Observatory

i

2

3

4

5

6

8h 5o.'8

I oil 50.' I

nn ag.'S

12'' 29. '7

I3h49'

14!! is.'o

Baldwin (') . . .

8li 5a.'4

to'1 53-'5

8h 52/6

Cheltenham (')

8h 54-'9

ioh 54'

8h 52/6

i oh sa.'p

nh 30/4

i2»32/3

I3h 54-'9

14'' i8.'8

Wanting

I2h 29.'8

'3h5i-'7

J4h i5-'7

i

i

III" 27/1

I2h32/5

Mh n-'S

Kew

)

i

ijh 32/9

I2h 32/7

i3h55-'8

I4h i9-'5

Wilhelmshaven ....

»

•

ill) 30'

I21' 29. '9

'3h 53-'6

I4h I7.'3

•

n

12" 33/2

i3h53-'8

14!! i8.'9

8h54.'3

i

ii1' 32/5

12!' 33/6

I3h 54-'5

14^ 19.'!

Tittis

i

•

iih 31/1

iah 3i.'6

i3h5i-'7

14!' 16'

8h 52.'7

ioh 51/6

nl'3i.'4

I2'> 32'

I3h 54-'a

I4h i8.'4

8h 53-'9

io>> 53'

nh3i-'5

1 2h 33/3

I3h52.'6

I4h i9.'7

Zi-ka-wei

i oh 54-'i

"h33-'S

12" 34/9

I3h 56'

14!) 20/8

8h 54-'9

io'i 54.'9

ii"33-'9

i2h35/5

I3h 56'

I4h I9.'5

8t 54-'8

ioli 53/2

nh33/6

IS*1 33-'2

'3h55-'4

I4h 19/9

The above question, which is of great importance, cannot be definitely decided until we are in
possession of rapid registerings, as usual of 12 times the rapidity of the daily registerings. By this means
we should see if the apparent difference in time, as shown in Table X, between, for instance, Honolulu
and Batavia, is a real one.

The perturbing force is calculated for a number of hours, the results being given in the annexed
Table. It should be remarked that as the perturbation is of rather long duration, the perturbing force
will be somewhat uncertain for the middle part of the perturbation. It will be seen from the Table
that the horizontal component of the perturbing force is directed, as already mentioned, along the mag-
netic meridian, except as regards the most northerly situated stations. Further, the force decreases
somewhat in strength from the equator to the poles, as the charts very distinctly show.

If we compare the force on the two sides of the equator, we see that the course is similar, but
that the force has a smaller value at Honolulu than at Dehra Dun, Bombay and Batavia.

The curve for the magnetic equator, or rather the line of intersection of the plane perpendicular
to the magnetic axis, with the earth, is also drawn on the charts. We see that the direction of the
arrows is on the whole parallel with this line.

As compared with the horizontal component, the vertical component of the perturbing force is
exceedingly small; and this proportion continues as far as Pawlowsk, as far, indeed, as the Norwegian
stations about the auroral zone. There is, however, in the south, namely, at Christchurch, an un-
doubted deflection in the vertical-intensity curve, answering to a force-component directed downwards, and

(') The curves for Baldwin, Toronto and Cheltenham are so finely serrated as to make identification difficult

PART i. ON MAGNETIC STORMS. CFIAP. U.

not exceeding the value 2.5 -/ in magnitude. In the north, it is almost imperceptible at Pawlowsk.
Even at Tiflis, where the sensibility is very great (ev = 2.55 y), the deflections in the vertical curve
may best be characterised as small vibrations about the mean line; while at the same time, the horizon-
tal component has values going up to 24 y. The directions of the vertical components are indicated on
the charts by dotted lines, as they are too small to allow of their size being marked.

It would appear from the above that we here have a perturbation of a very characteristic and
peculiar kind, a species of perturbation with which we shall very often meet. As a rule, however, it
will appear together with other phenomena, which disturb its regular development; but here we seem
to have the perturbation almost alone, and on a quiet day.

It will often happen that during a perturbation that is powerful at the equator, great storms will
occur in the north, of which the effect makes its way southwards, but is weakened towards the equator.
Here too, there is an indication of conditions such as these, of which we shall later on have several
examples. At Sitka, for instance, a sudden change in the curves occurs between n and 12.30. It is
another phenomenon altogether that here makes its appearance, and which has its focus in the polar
regions, its effect being almost imperceptible in the vicinity of the equator. It is fairly distinct at the
Norwegian stations, and its effect may also be traced in Central Europe. On the chart for 12 o'clock,
this current direction represents the total force resolved into one that should answer to the equatorial
current; the other component, which answers to the polar current, will then be directed towards the
south-west, answering to a current towards the north-west.

While we allow this perturbation to serve as a typical example of these perturbations, the positive
equatorial perturbations may be more fully characterised as follows.

The perturbation appears with greatest strength in the regions round the equator. It is true that
for a short time the deflections may be greater at the poles than at the equator; but the force does
not remain constant for so long a time. The conditions at the poles are frequently characterised as an
oscillation about the mean line, of a somewhat local character.

The perturbing force in southern latitudes, and more especially in the neighbourhood of the
equator, is directed northwards in the direction of the magnetic meridian.

The perturbations appear simultaneously all round the equator, and with a similar course, but not
always with the same strength.

The curves for the horizontal intensity, where the perturbation mainly shows itself, present a charac-
teristically serrated appearance. The serrations may very frequently be recognised all over the earth, and
in such case occur simultaneously.

TABLE XI.
The Perturbing Forces on the 26th January, 1903.

Honolulu

Sitka(')

Baldwin

Toronto

Cheltenham

Gr. M. T.

I'h

PA

Pi,

Pd

Ph

Pd

Ph

Pd

Ph

Pd

li in

9 o

+ 6.4 •/

o

?

•>

+ 5-3 7

0

+ 4-5 /

o

+ 5-3 •/

0

IO O

+ 5-9 »

0

•)

?

+ 4.6 »

o

+ 5-4 •

0

+ 5-o •

o

II 0

-1- 4. i »

0

- 4-1 /

o

+ 4-3 •

0

+ 7-2 '

E 1.2 /

+ 5-3 •

o

12 o

+ 6.2 » 0

- 6.7 -

W 9.8 /

+ 5-3 »

W 3.2 •/

4- 8.1 »

W 4.2 .

+ 5-9 "

W 4.1 y

3°

+ 16.7 »

W 3-3 /

+ I.I »

» 13.4 »

+ 13-5 »

» 8.2 »

+ 11.3 »

• 9-4 '

+ 10.6 »

• 1-1 '

13 o

-1- 16.7 1)

o

4- 8.9 »

E 4-5 »

4 15-6 »

" 5-7 "

4- 17.1 .

» 8.5 »

+ 13-8 '

i 4.1 »

3°

+ 13.9 »

o

+ 8.3 )

W3.i »

7

•>

4- 18.0 »

> 6.7 »

+ 11.7 »

0

14 o

+ 12.9 >

0

4- 5-i •

E 8.0 »

+ 13-5 '

0

4- 24.3 •

o

4-16.1 »

E 2.4 »

(') As we have only the close of the perturbation, the choice of normal lines is somewhat difficult.
Birkeland, The Norwegian Aurora Polaris Expedition, 1902— 1903.

66

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE XI (continued).

Matotchkin Schar

Kaafjord

Pavvlowsk

Stonyhurst

Gr.M.T.

Pk

Pd

P«

Pk

Pd

A

ft

Pd

p»

ft

Pd

li m

-

9 °

•4- 10.3 7

0

+ 7-3 /

+ 3-7 7

W 2.6 7

— 5-5 7

7

7

-r 3-6 7

o

10 0

+ 4-9 '

W4-4 Y

o

7

7

7

7

7

-r 4.6 »

0

II O

-t- 0.8 >

• 1.3 >

- 5-1 »

4- 3.0 »

• 2.6 >

- 3-9 '

7

?

No pertur-

4- 8.2 »

W 2.9 7

12 0

+ 7.1 »

> 3.1 »

-t- 10.3 »

0

» 4.0 '

0

+ 5-5 "

0

bation

+ -J.6 *

0

3°

0

E ii. i >

4 13-9 «

- 3-7 *

» 7.0 •

4- 6.3 »

4- 8.0 »

W 2.3 7

4 8.5 .

* 2-3 *

13 o

-1-11.3 »

W4.9 >

-1- 5-1 »

->- 6.1 »

« 9.2 »

— 3-1 »

4- 17.0 «

• 4.6 >

4- 17.8 *

» 1.7 »

3°

+ H-5 '

» 8.9 >

0

4- 9.8 »

» 6.2 »

— 3-9 »

4- 19.1 »

» 3-2 "

+ 17.8 >

E 0.6 »

14 o

4- 22.5 »

• 9-3 »

o

+ 5-5 »

» 17.2 »

-6.3 »

-1- 22.5 »

» 2.3 »

f 15-4 '

W 5.1 »

TABLE XI (continued).

Kew

Val Joyeux

Wilhelmshaven

Potsdam

San Fernando

Gr.M.T.

Pi,

Pd

ft

Pd

ft

Pk

Pd

/'y,

Fd

P*

Pd

h m

9 o

i

7

4 6.4 /

o

No per-

7

o

7

7

4 9.6 7

Oscilla-

10 o

7

7

4- 5-6 '

0

ceptible

7

0

?

7

4 4.4 »

tions of a
duration of

II 0

+ 3-8 y

E 1.9 y

+ 6.3 »

E 5-o /

perturba-

4 4.2 7

o

7

7

+ 3-7 '

about 4

12 O

4 5-i •

» 2.8 »

4- 9.6 »

o

tion; no

4- 4.9 »

E 3.1 7

4- 4.7 /

o

4- u. I »

minutes,
but too

3°

4- 6.6 «

W 1.9 .

7

7

curve after

4- 4-7 •

» 4.9 »

+ 7-5 »

W 2.0 y

4- 17.0 »

small to

13 o

4- 16-3 »

» 1.4 »

4 16.8 »

?

12''.

+ 16.3 »

» 0.6 f

J- 17.1 »

» 6.0 »

4- 23.0 «

allow of
being mea-

3°

4 15.1 >

« 0.5 »

4- 16.8 >

o

4- 16.8 »

o

f 16.1 »

» 3.0 »

4 22.9 »

sured.

14 o

+ 163 »

• 3-3 '

4- 18.0 «

» 4.2 »

4- 17.5 »

» 3-7 »

4- 14.2 »

* 5-° «

4- 22. 0 »

TABLE XI (continued).

Munich

Pola

Tiflis

Dehra Dun

Gr. M. T.

P*

Pd

P,

PA

Pd

PA

Pd

ft

PA

Pd

li m

9 o

4- 7.0 7

W 2.3 7

V. decrea-

4- 8.5 7

W3.47

?

7

?

4- ii.8 7

10 o

4- 3.0 »

» 0.4 »

ses slightly

4- 2.5 »

» 4.8 »

?

7

?

-•- 8.3 »

No mea-

II O

+ 6.0 «

o

between

4- 3.6 »

» 4.8 >

4- 6.0 7

7

?

+ 7.9 »

surable

la o

+ 9-5 •

o

I ah ^gm
and

4- 9-4 *

o

4- 8.8 .

0

?

4- 9.8 »

deflection.

3°

4- 7.8 >

o

I3h 45m

4 9.0 »

o

4 n.o »

W 0.4 7

?

4- 12.6 »

13 o

4- 16.8 »

0 '

— 0.87

4- 19.0 »

« 1.4 »

4- 22.5 «

» 5.2 »

7

4- 23.6 »

3°

+ 15-5 »

0

— 0.8 '

4- 15.0 >

o

+ 21.6 >

• 3-3 »

0

4- 21.7 »

14 o

4- 15.0 «

o

o

4- 13.4 »

» 3-4 »

4- 19.4 >•

» 5-9 >

4- 1.8 7

4- 20. 1 »

PART I. ON MAGNETIC STORMS. CHAP. II.

67

TABLE XI (continued).

Bombay

Zi-ka-wei Batavia

1

Christchurch

Gr. M. T.

A

Pd

Pv

ft

Pd

/>„

PA

Pd

Pk

Pd

b m

9 °

+ 9-v y

4- 10.0 y

0

4- 9.6 y

o

+ 10.6 y

o

10 o

+ 8.2 >

No mea-

No visible

4- 7.8 »

o

+ 8.2 »

0

+ 10.1 »

o

II 0

+ 6.7 »

surable

distur-

+ 8.8 »

W 1.3 y

No per-

4- 7.6 »

0

+ 8.3 »

0

12 0

-1- 9.2 .

perturba-

bance.

+ 14-5 »

E 2.0 »

turbation.

4- IO.O •

E 2.4 y

4- 15.6 »

W 0.7 y

3°

+ ii. 8 »

tion.

Sensibility

4- 18.0 «

" 3.0 •

4- 2O.O »

o

+ 28.1 .

0

13 o

4- 22.5 »

small.

+ 24.8 •

> 2.O >

+ 23.1 «

0

4- 23.0 •

" 0.7 •

3°

4- 2I.O »

4- 22.8 »

» 1.3 »

4- 20.8 «

o

+ 18.4 »

* 0.7 »

14 o

+ '9-5 '

4- 21.2 •

» 1-3 »

+ 15-3 '

o

4- 15.2 »

» 3-° •

Only small oscillations about the normal line, without
any distinct deflection.

Dyrafjord.

The declination-curve not drawn here. The horizontal
intensity oscillates about the normal line.

For Wilhelmshaven and Pola P, directed upwards, for Christchurch directed downwards. In all
cases too small to allow of being measured.

Figures 30 and 31 give the position of the current-arrows corresponding to the perturbation on
the 26th January, 1903. The current-arrows are constructed in the manner explained in Art. 23, by
the aid of the values for PI,, Pd and P, given in Table XI.

With regard to the times employed, it should be said that the first is chosen immediately after the
commencement of the perturbation, and thus represents the magnitude of the perturbing forces that at
that hour suddenly make their appearance upon the earth. After this hour the oscillations diminish
somewhat - as Table XI and Plate XIV show -- until at about nh 2om in many places they have
already become 0. Between gh and I2h, the conditions at the various stations are on the whole only
slightly changed, and remain fairly constant, with small perturbing forces. For this intermediate period
therefore, no charts have been constructed. After I2h, however, the oscillations begin to increase, attain
their highest value a little before 14'', and then rapidly decrease to zero. These conditions will be found
represented on the last three charts. On Chart IV the length of the arrows in certain tracts is a little
abnormal, as the way in which the force increases towards the equator is not very clearly distinguishable.
This is partly accounted for by the fact that the force at this time varies so greatly, that a slight dis-
placement in time may cause considerable changes. Even the small polar precipitations, moreover, will
exert an influence. They will possibly assert themselves most in North America - Toronto and Sitka
(cf. the perturbation of the I5th Dec., 1882; chap. III).

68

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

Current-Arrows for 26th January, 1903; Chart I at 9h and Chart II at 12h

Fig- 3°-

PART I. ON MAGNETIC STORMS. CHAP. II.

Current-Arrows for 26th January, 1903; Chart III at 13t and Chart IV at

69

yo BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

THE PERTURBATIONS OF THE 9th DECEMBER, 1902

(PI. IX).

28. These perturbations may be briefly characterised as follows.

They begin with a lengthy perturbation, which is relatively weak, but is especially developed at
the equator, where it appears only in H, and on the whole exhibits all the properties that characterise
the positive equatorial perturbations.

It commences quite suddenly, simultaneously all over the earth, at 5h 40^6 m Greenwich mean time.
At the equator it appears only in H, and the deflection answers to an increase in H. In the vicinity
of the poles, this condition is altered, while at the same time the mean deflection becomes smaller.
From 51' 40™ on to 13 h, the deflection in H is continued in the direction mentioned, but with varying
strength. The character of the curve is somewhat quieter than usual. At the Norwegian stations there
is a particularly strong and characteristic impulse at the commencement. At Matotchkin Schar, for
instance, it is partly of an undulating form, answering to a rapid turning round of the perturbing force.
Subsequently the perturbation at the three westernmost of the Norwegian stations is chiefly characterised
by small oscillations about the normal line, interrupted by smaller, sometimes brief, impulses of a more
local polar nature. Between 15 h and i8h , the character of the perturbation-conditions is essentially
changed. It is this feature that we continually find repeated, namely, that when the equatorial storm
has lasted for some hours, polar systems appear.

It is early apparent from the curves at our Norwegian stations, that we have to do chiefly with
polar storms during this period. The system, however, is of the very simplest kind. At Dyrafjord and
Kaafjord the deflections in D and H are in a direction opposite to that usual during storms that
commence on the midnight side. When we come to Matotchkin Schar, we get the deflection that
characterises the nocturnal perturbations.

As this perturbation during several hours is of a typical equatorial character, we have preferred to
class it among such. Even the polar storm with which it concludes, is a phenomenon that often seems
allied to this equatorial type.

THE FIELD OF FORCE.
(i). The Equatorial Part.

29. The field during the period is given on two charts, Chart I for 6h om, and Chart II for gh om.
This field is of the typical form for negative equatorial perturbations. It is most powerful on the
sun-side, and becomes weaker towards the poles. On Chart II , the arrows have a direction that indicates
that they are circling round the magnetic pole.

Chart III represents the conditions at I2h 15™, and at 15 h . At the first-named hour, the perturba-
tion is still mainly equatorial in character. At Axeleen and Sitka, only small polar disturbances are
observable. At the second hour named, we are just at the transition to the polar field.

(2). The Field during the Polar Storm.

Charts IV, V and VI show the field as it appears, in the main, during the polar storm.

Chart IV shows the field at two hours, namely, i6hom and i6h45m. At the first of these, the
perturbation was especially noticeable in Europe and Asia, where it forms a considerable area of divergence.
At Dyraijord, Kaafjord and Matotchkin Schar, the force is now very small. It appears, from the form
of the field in southern latitudes^), that the storm-centre is situated to the east of our Norwegian

(') See "Polar Elementary Storms".

PART I. ON MAGNETIC STORMS. CHAP. II.

71

stations. At i6h 45'", the perturbation on the whole has greatly increased in strength. We now have
very powerful perturbations at our Norwegian stations. We recognise the form of field as the typical
one for the polar elementary storms. The current-arrow in the storm-centre is now directed eastwards
along the auroral zone; and in the district of Europe and North America, the field forms an area of
divergence.

Chart V; 77* om .

The field in southern latitudes has mainly the same character as at i6h 45m; but at the Norwegian
stations the conditions have changed.

At Dyrafjord and Kaafjord we still have a current-arrow directed eastwards along the auroral
zone; but as regards Kaafjord, the force is considerably less. At Axeleen, where we now have registerings,
the conditions are of a character altogether different from those of the two first-named stations. The
current-arrow at Axeleen points almost due west. This indicates that the perturbations here must be
of a somewhat local character. At Matotchkin Schar the direction of the arrow is reversed, and is now
almost exactly opposite to that at Kaafjord. This indicates the existence of a new storm-centre, which
is advancing from the east. These districts to the east of Matotchkin Schar are now upon the night
side, and we find moreover that the current-arrow about the storm-centre af this system is directed
westwards along the auroral zone.

Chart VI.

In lower latitudes the field is almost unchanged, except at Sitka, where a remarkable difference
occurs. The conditions at Dyrafjord and Kaafjord are much the same as before; while at Axeleen
and Matotchkin Schar the force has turned.

We see that this storm has a tendency to form a field similar to that described for the polar
elementary storms. The circumstances are not, however, of the simplest. There is no doubt that we
have to do with several simultaneous polar precipitations of electric corpuscles.

TABLE XII.
The Perturbing Forces on the gth December, 1902.

Gr. M. T.

Honolulu

Sitka

Baldwin

Toronto

Cheltenham

• A

Pd

Pk

Pd

Pi,

Pd

Pi,

Pd

Pk

Pd

h m

6 o

+ 7.1 /

o

+ 3-5 /

W 3.2 •/

+ 5-3 y

o

+ 5-4 y

O

+ 3-4 /

O

1 45

+ 6.3 >

0

+ 2.8 •

O

+ 2.5 »

o

+ 3.6 »

0

f i-3 •

o

9 o

+ 7-4 »

o

4- 4.1 *

» 1.8 »

+ 4.6 »

0

+ 6.3 »

o

+ 2.6 »

o

12 15

+ 6.6 »

0

+ 3-° "

E 15.8 .

+ 9.2 »

W 3.8 y

-f 8.1 »

W4.8 7

+ 3-9 "

W 4.1 ;/

15 o

+ 3.8 »

0

— ii. a •

W9-5 '

+ 4-9 »

• 5-7 "

+ 6.3 .

» 3.6 »

-4- 2.5 »

» 4.1 •

16 o

- 3-i •

o

— 3.0 »

> 1.8 *

- 3-5 '

0

- 1.8 »

» 4.8 «

- 1-5 »

0

45

+ 3-1 •

W 5.0 /

— 12-3 "

.29.4 »

- 9.6 »

» 12. I »

- 9.9 »

» 15.0 •

- 8.5 •

» 11.3 »

17 o

+ 5-6 »

• 3-3 '

+ 6.5 »

» 5-4 *

- 0.7 »

> 18.4 >

- 6.3 »

» 21.6 »

- 4.2 •

» 16.0 »

15

+ 3-3 »

» 2.5 »

+ 3-7 •

E 9-5 •

0

* 15-3 '

o

» 19.3 >

o

» 16.0 »

UIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

TABLE XII (continued).

Or. M. T.

Dyrafjord

Axeleen

Matotchkin Schar

Ph

Pd

P.

A

Pd

ft

Pk

Pd

P.

h m

6 o

4 3.7 /

E 3-1 7

+ 3-3 y

o

E 3.8 v

4 9.87

+ 5-6/

O

4 5-87

7 45

-I- 2.7 »

* 6.2 »

- 3-7 »

0

W 12.3 •

- 17.2 »

+ 4-5'

W 7.5 y

- IO.2 »

9 °

+ 3-8 »

» 1.3 »

- 3-3 »

0

» 7.4 «

0

-t 7.1 »

» 10.6 »

— 2.9 »

12 15

9

9

7

4- 20.7 Y

0

4 2.4 »

7

7

9

'5 °
16 o

-t- 13.01

o

4- 9.8 t

7

» 7.4 >

9

9

-f 20. o >

' 7-5 »

+ 5-' '
4 14.6 «

45

+ 136.0 »

E 17.0 »

— 37-5 •

7

?

9

4 27.6 »

» 60.0 »

-175.0.

17 o

4-127.0 »

» 31.0 >

— 14.2 »

-i 54-° »

W 42.2 «

-I77.0.

- 41.2 »

£ 29.6 »

— 46.8 »

15

4 73.0 >

• 8.3 »

- 17.8 »

5-i •

» 27.3 »

— 160.0 » I 4 41.7 *

' 5i-5 •

4 41.0 »

TABLE XII (continued).

Gr. M. T.

Kaafjord

Pawlowsk

Stonyhurst

Wilhelmshaven

PA

Pd

P,

Ph

Pd

P,

PA

P<i

PA

Pd

P»

li m

6 o

4 -|.i y

E 2.2 y

o

7

7

7

4- 6.1 y

o

+ 5-6/

E 2.47

o

7 45

+ 3-5 "

W 4.8.

0

9

7

7

4 5.6.

0

4 7.4 >

• 2.4 >

o

9 o

4 1.2 »

> 4.8 >

0

7

?

9

+ M-3>

0

4 9.8.

» 1.2 »

o

12 IS

o

. 6.2 »

o

4 6.07

W 6.07

o

4 13 2 .

o

4 7.9.

0

o

15 °

o

. 1.4 *

4 7.77

0

. 0.9 »

o

4 4.0 >

E 1.27

+ 3-7 '

» 1.8 •

o

16 o

o

» 8.0 »

+ 15.5 »

- 7.0 »

. 1.8 „

0

- 2.5 »

W 2.8 .

- 6.1 >

W 3.7"

o

45

4i55-o«

. 64.0 .

4- 11.3 «

- 13-1 »

E 7.3.

-(- 3-07

- 17.8 »

» 4.0 »

— 20.5 «

0

4 4-°7

17 o

4 57.0 .

« 19.8 .

+ 19.0 «

4 36.2 .

» 5-5'

4 5.2 «

- M-3 »

» 15-4 »

— 27.5 • » 26.3 >

4 4.0 »

15

4 32-° "

0

4- 20.4 .

4 22.6 »

• 5-5 »

4 6.0 .

- 14-3 »

' 9-7 •

— 24.2 »

« 10.4 >

0

TABLE XII (continued).

Gr. M. T.

Kew

Potsdam

Val Joyeux

Munich

San Fernando

PA

Pd

PA

Pd

/';«

Pd

P«

PA

Pd

PA

Pd

h m

6 o

7

9

7

9

7

?

7

7

7

+ 8.37

E 4.17

7 45

?

?

9

7

?

?

9

7

7

4 7.0 »

0

9 o

7

7

7

7

4 9.67

o

O

+ 8.57

W 2.37

+ '4-7 '

0

12 15

4 9-77

o

4 6.67

7

4 9.6 •

0

O

+ 7-5 •

» i-5 •

+ 5-7 »

o

15 o

4 2.5 »

E 1.87

4 3.1 »

E 1.07

4 8.0 «

E 2.57

4 3.0 7

+ 3-5 »

E 1.5.

+ 5-i »

* 4-9 >

16 o

— 2.0 »

W 1.4 .

— 4-7 »

W 3.0.

- 1.6 »

o

4- 4.0 »

— 4.0 >

W 1.5.

- 5-7 »

o

45

— 17.8 «

» 2.8 «

— 17.0 »

o

- 16.8 »

Wo.8 .

4 5.0 »

— 16.0 »

o

- 14.1 »

W 4.9.

17 o

— 16.3 »

> 12.2 >

— 26.5 »

» 13.0 »

— 17.6 »

» 12.5 »

4 4.0 »

— '9-5 '

» 1 1.4 »

— 14.1 »

» 7-3 •

15

- 13-3 '

> 10-3 »

— 17.0 »

• 4-5 •

- 13-6 •

» 8.3 .

4 3.0 «

- 14-5 •

> 8.4 >

- 8.9 •

" 5-7 »

PART I. ON MAGNETIC STORMS. CHAP. II.

73

TABLE XII (continued).

Gr. M. T.

Tiflis

Dehra Dun

Zi-ka-wei

Batavia

Christchurch

Pk

ft

P,

A

Pd

P*

ft

ft

Pd

Pk

Pd

li m

6 o

?

?

•)

+ 15-47

W4.97

+ 13.27

E 4.0 y

+ 14.27

0

+ u-sy

0

7 45

o

9

•j

+ n.o »

• 9.8 »

+ 7-3 •

» 2.O »

+ 7-5-

E 6.07

+ 4.1 »

o

9 °

•p

?

•)

4- 15.8.

» 6.9 »

+ 14.4 »

» 1.0 »

+ I I.O »

» 2.4 »

j 4- 14.2 •

o

12 15

+ 6.9 x

o

-"- °-5y

+ 10.6 »

o

4- 8.4 >

0

+ 7.8 »

0

, + 9.6 »

W 5.27

15 °

-r 3.0 »

E 2.97

0

+ 2.7 «

0

+ 1.2 >

0

+ 3-9 »

o

o

O

16 o

- 9.2 »

> 3.7 »

+ 2.3 »

— IO.3 » O

- 7.2 »

o

- 7.8.

0

- 87.

E 1.5.

45

- '5-4 "

> 11.9 »

-1- 3.0 »

— IO.2 »

E 7.91

O

» 7.0 »

- 4-3 •

W 2.4 »

+ 10.6 »

» 3-° "

17 o

— 23.0 >

> 12.2 »

+ 5-3 •

- 18.1 «

» n.8 »

- 6.0 »

» 5.0 »

- 8.9.

• 3-6 »

4- i i.o i

W4.5.

15

-178'

• 8.5 »

-t-3-o"

- 13-4 '

» 6.9 »

- ,.a.

t 4.0 »

- 7.8.

» 1.2 » -t- 6.O »

» 3-° *

Current-Arrows for the 9th December, 1902; Chart I at 6'> .

Fig. 32.
Birkeland, The Norwegian Aurora Polaris Expedition, 1902 — 1903.

10

74 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQOZ — 1903.

Current-Arrows for the 9th December, 1902; Chart II at 9'), and Chart III at 12'i 15m, and 15h.

33-

PART I. ON MAGNETIC STORMS. CHAP. II.

Current-Arrows for the 9th December, 1902; Chart IV at 16h and 16h 45m, and Chart V at

75

HIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

Current-Arrows for the 9th December, 1902; Chart VI at 17k 15m.

Fig- 35-

THE PERTURBATION OF THE 23rd OCTOBER 1902.

(PI. III).

30. This perturbation does not belong to those mentioned in the circular, and is therefore from
only a small number of stations.

It is especially developed about the equator, and is there characterised as a positive equatorial
perturbation. It commences suddenly at igh um, simultaneously all over the earth. The curve is
serrated in character, and appears only in H, in which it occasions an increase.

About iV2 hours later, a polar storm, not, indeed, violent, but characteristic, simple and well-
defined, appears around the Norwegian stations. It is especially distinct at Matotchkin Schar. This
storm has at the same time the properties that characterise the polar elementary storms. The current-
arrow points westward along the auroral zone, indicating that the storm-centre, which is situated in the
region about Matotchkin Schar, now lies on the midnight side.

The field of force is shown on a chart, which represents the conditions at 19 h i6m and 22 h

22 n 22.5 '

At the first-named hour, the field exhibits a typical equatorial character; at the last-named, it is
the effect of the polar system, which, at any rate in somewhat more northerly latitudes, is most conspicuous
(see the polar elementary storms).

TART I. ON MAGNETIC STORMS. CHAP. II.

77

TABLE XIII.
The Perturbing Forces on the 23rd October, 1902.

Toronto

Axelcen

Matotchkin Schar.

Gr M T

Ph

PA

P*

Pd

Pv

PA

Pd

P,

h m

19 16

4- 20.0 7

W 6.0 /

O

Wca. 12 7

o

+ 10.3 7

W 14. ay

0

22 22.5

+ 8.5.

0

+ 5-5J'

* 21-5 »

-4- 242.0 y

— IIO.O «

E 27.6 *

- 37-° y

TABLE XIII (continued).

Kaaijord

Munich

Pola

Gr M T

Ph

ft

P»

Ph

Pd

Ph

Pd

P,

h m

19 16

+ 9-6 y

W 6.7 y

ca. — loy

4- 17.07

W 3.8^

+ 14.8 j-

W 3.5 y

+ 0.87

22 22.5

— 57-0'

E 33.0 .

- 138.0 »

+ 13-5 »

E 8.3.

+ 13-9 »

E 8.3.

o

TABLE XIII (continued).

San Fernando

Dehra Dun

Bombay

Christchtirch

Gr M T

Pk

Pd

P*

Pd

F/,

Pd

A

Pd

h m

19 16

+ I54X

E 3.07

+ 17.07

0

+ 14 7

•)

?

?

22 22.5

+ 8.3»

» 6.4 »

-f 16.2 »

o

+ 13-3'

•>

+ 5.5?

o

UIRKELAND. THE NORWEGIAN AURORA POLARIS

Current-Arrows for the 23rd October, 1902, at

EXPEDITION, 1902 — 1903.

19h 16m and 22h 22.5m.

Fig. 36.

CONCERNING THE CAUSE OF THE POSITIVE EQUATORIAL PERTURBATION.

31. The fact that this type of perturbation exhibits such great simplicity with regard to the distri-
bution of the force, and also that it shows such a tendency to repeat itself from time to time, indicates
that these perturbations might have a simple explanation.

As already remarked in the introduction, it will always be possible, in a purely formal manner, to
satisfy the properties of the field in several ways. It is our intention here to mention some of the
possibilities that might perhaps explain these perturbations, and we will in the first place find out what
magnetic systems might be assumed to have produced the field.

(1) We cannot assume a variation in the terrestrial-magnetic field itself, which would explain the
field about the equator; for as we go north, the perturbing force is no longer directed along the total
intensity. P is directed horizontally almost everywhere; in the south its direction is somewhat down-
wards, in the north often upwards. In the far north, moreover, P, (see p. 45) is no longer directed
along the magnetic meridian.

(2) As we shall subsequently see, current systems will undoubtedly appear in the polar regions
during a series of polar perturbations. It might then be reasonable to try whether this equatorial

PART I. ON MAGNETIC STORMS. CHAP. II.

79

perturbation might not also be explained by a polar current-system. Considering that the perturbation
may be due to currents of a cosmic nature that approach the earth under the influence of terrestrial
magnetism, there would be a possibility of the existence of current-systems that consisted of current-
spirals, which stretched down at the poles, and in this way acted as though magnet poles were put down.
Poles such as these, however, though they might explain the principal features in the form of the field,
would not be reconcilable with the fact that the force increases towards the equator.

We are therefore of necessity led to seek the explanation in currents that have their greatest den-
sity in low latitudes near the magnetic equator. We thus naturally come to consider the two possi-
bilities -- the perturbation either has its direct cause in currents at the surface of the earth, or in cur-
rents above the earth.

It seems hardly likely that the phenomenon is due to earth-currents. These currents, it is true,
would explain the small vertical intensity as regards magnitude, as it might be assumed that the current
was distributed over a large portion of the earth's surface; but a wide-spread system of earth-currents
such as this would hardly explain the other properties of the perturbation. The direction of the earth-
currents must, in such a case, be from east to west, the reverse of the direction of the current-arrows
marked; and it would then be difficult to explain how the force P has a component directed upwards
north of the equator, and downwards south of the equator. Such earth-currents, if, as independent pheno-
mena, they are to be able to explain the perturbations, cannot be induced currents, but must depend
upon conditions in the earth itself. As, however, the direct cause must be sought in processes in the
earth itself, it is incomprehensible how these currents can have so universal a character, and main-
tain so constant a direction with so singular a form. It seems especially impossible to explain the
simultaneous serrations; for the perturbing force would then at each place principally be determined
by that part of the current that passed beneath the place. From a physical point of view there are
greater difficulties in assuming that different parts of a wide-spread current-system such as this, which
should have its direct cause in the earth itself, should act rhythmically, and that the alteration of current-
density with the latitude at each point of time should take place so regularly and connectedly. The
question might, indeed, be settled, if they were surface-currents, by looking at the registerings for the
earth-current. If the perturbation were conditioned by surface-currents on the earth, the curve of the
earth-current should exhibit a course similar to that of the curve on the magnetograms. If, on the other
hand, the perturbation is due to currents lying outside the earth, the curve for the earth-current will
look like vibrations about the normal line, as the rapid changing in the perturbing force would produce
corresponding induced alternating impulses.

We have no complete set of earth-current registerings, however, for any station except Kaafjord.

Here, indeed, we do find that the earth-current curves are of the character described. They are
undoubtedly for the most part induced currents, but their direction is mainly determined by the local
conditions, as for instance the conductivity of the soil in the various directions.

When the great perturbations show maximal deviation, the earth-currents usually pass a 0 value.

As we shall see later on, it is easy to reconcile the existence of such conditions in the polar
regions with the fact that certain magnetic disturbances in southern latitudes, far away from the storm-
centre, may often in great part be caused by earth-currents.

The earth-currents will be treated in a subsequent part of this work.

We have already mentioned that this equatorial perturbation often comes as a precursor of polar
storms; and indeed, we have really never met with an entire perturbation of this kind with which there
have not, within the same period, been polar storms. The necessary consequence of this must be that
these two kinds of perturbations should be closely connected with one another. Now there is no doubt,

8o

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

as will be shown later on, that the polar storms are due to currents above the earth ; if so, this should
also be the case with the equatorial perturbations now under consideration.

According to this, we must necessarily seek the cause of the perturbations in currents above the
surface of the earth. If the current is to be sought at a distance from the surface of the earth that is
small in comparison to the earth's dimensions, we must, in order to explain the field, have a wide-
spread plane current circulating round the earth. Our being obliged to have a wide-spread plane
system is a consequence of the fact that otherwise the fields would be limited more rapidly. If, as is
the case, the effect is extended to all parts of the earth, there must also be currents in those regions.
A system of this kind, however, if it is to satisfy the actual conditions, is inadmissible; for we meet
here with difficulties similar to some of those in the way of the acceptance of the earth-current theory.
The first of these is that the relative strength of the current in the various districts of the earth
should remain fairly constant throughout long periods, notwithstanding that the field, as already men-
tioned, is remarkable for great variableness in strength : the variations take place in all districts in about
the same proportion. It seems, moreover, impossible, if we are not to have recourse to the mysterious,
but keep to the well-known possibilities of physics for the production of cosmic currents, to have the

stability of the current explained; for the
current, as we know, if composed of free
portions, is deflected by terrestrial magne-
tism, the separate bearers of the electric
charge — whatever the physical nature of the
latter — moving in spirals about the magnetic
lines of force, or being carried out into
space, if the corpuscular current-rays arc
stiffer.

The only possibility then left is that the
positive equatorial perturbations are due to
the effect of a current-system, whose distance
from the earth is of the same order as the
dimensions of the earth. Owing to the distri-
bution of force in the field, and the symmetry
that is found, as a rule, with regard to the equator, this current, as already mentioned, must have its
greatest effect about the plane of the equator; and on account of the direction of the perturbing force,
the current-lines, at any rate in the region nearest the earth, must lie in planes that are approximately
parallel with the plane of the magnetic equator.

There are still two essentially different cases possible here,

(1) that the current passes round the earth, and

(2) that the earth is quite outside the system that in the main conditions the perturbation.
When, on account of the field, the currents must be sought at so considerable a distance from

the earth, we are compelled, with the knowledge we at present have of the physical qualities, to assume
that these currents are corpuscular in constitution. The systems that may then be formed must be such
as may arise when a magnet is subjected to corpuscular electric radiation of some kind or other.

In order to become better acquainted with the systems that may arise under these conditions, a
little attention should be given to the experiments I have made, in which a magnetic terrella is ex-
posed to cathode rays. These will be fully treated in Volume II, and illustrated by numerous photographs;
but even here we will draw attention to a few important circumstances.

In addition to the polar precipitations there are still in particular two characteristic phenomena.

Fig- 37-

PART I. ON MAGNETIC STORMS. CHAP. II.

8r

(1) Under certain circumstances there is formed round the terrella a very steady, luminous ring.
As the system itself is confined within the form of a flat torus, the trajectories of the corpuscles in
consequence form approximately entire circles (see fig. 37). Owing to terrestrial magnetism, such nega-
tive corpuscles in space, coming from the sun, must then move from west to east round the earth.

(2) At some height above the terrella, and on the side turned towards the cathode, we shall be
able to get very well characterised systems. The existence of these systems may be shown by a
phosphorescent screen, as illustrated in fig. 38 a, b, c, where the terrella is placed in three different
positions in relation to the screen, as indicated by the diagram below the images.

The precipitations appear only on one side of this screen, and their inner border is sharply
defined. The system is of considerable breadth. It does not remain in the neighbourhood of the
equator, but extends on both sides, and fades away towards the poles, or unites with the polar system.

a. b. c.

Fig. 38.

The three figures, 38 a, b and c, show how cathode rays are drawn in towards a highly magnetic
terrella. Both terrella and fixed screen are covered with phosphorescent substances. In position a, the
screen points straight towards the cathode, that is to say, the plane of the screen is perpendicular to
that of the cathode. In position b, the planes make an angle of 45° with one another; and in position
c, the screen is parallel with the cathode-surface.

We can see how the rays are drawn in in rings or zones round the magnetic poles on the terrella
itself; but the phenomenon to which we shall here pay special attention, is the strong light that is found
only on the east side of the screen, and which is due to cathode rays that turned back before reaching
the terrella. They are caught by the screen, however, and rendered visible. It will be seen that the
mass of the rays turn back and come into contact with the screen in position b, answering to the after-
noon side of the terrella. Professor STORMER has calculated the trajectories of electrically charged cor-
puscles sent by the sun towards the earth, and has, amongst other things, studied the course of the
trajectories at the earth's magnetic equator.

Birkeland, The Norwegian Aurora Polaris Expedition, 1902— 1903. 11

82

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Fig. 39 is taken from his paper, "Sur les trajectoires des corpuscules electrises dans 1'espace sous
1'action du magnetisme terrestre'^1). It will here be seen that rays answering to y — — 0.5 and — 0.7
fall in towards the earth very much as do the greater number of the rays in the experiment with the
terrella in position b. There will also certainly be rays coming in towards the terrella, that answer to
the other mathematically possible paths; but it is not so easy to demonstrate them with this experimental
arrangement with a screen.

The phenomenon re-
presented in fig. 37, of the
ring of light round the equa-
tor, should answer to paths
where y = about — i. The
stronger the magnetism, the
larger will the ring be. In
the experiments shown in
fig. 38, the magnetism is so
strong that the equator-ring
is not formed, owing to the
glass walls of the discharge-
tube. By the experiment with
the terrella, it is also easy
to show a phenomenon that
is most easily explained by
the presence of rays answer-
ing to the calculated paths
for y = between — 0.5 and
- i. I have mentioned in
a former work(2) that, just
within the equator-ring, the
terrella sometimes has a
clearly phosphorescent line
along the equator. 1 had
formerly to have recourse to

Fig. 39-

the assumption of secondary rays in order to explain this phenomenon; but it is now explained most
naturally by rays answering to Stermer's calculated trajectories.

What we have to notice, however, is that the bulk of the rays in the experiment turn round in
front of the terrella on the afternoon side. The mathematical treatment has hitherto given only the
mathematically possible trajectories, but has not stated where the bulk of the rays pass the earth, partly
because the nature of the rays emitted by the sun is not sufficiently known.

As the current-arrows during our perturbations are directed towards the east, the perturbation
cannot be explained by a ring such as this round the earth. If, on the other hand, we assumed the per-
manent existence of such a ring, we might imagine the perturbation to be explained by a diminution in
the strength of this current. This explanation is very improbable and unnecessary. It seems necessary,
owing to the connection of these perturbations with the polar storms, to suppose that the equatorial

(') Archives des Sciences Physiques et Naturelles. Geneva. Vol. XXIV, 1907, chap. IV.
(*) Expedition Norvegienne de 1899—1900, 1. c., p. 46.

PART I. ON MAGNETIC STORMS. CHAP. II. 83

perturbations under consideration are also due to the rising of new, independent systems, and do not
merely indicate a weakening of that which may already exist.

On the other hand, it is our opinion that the positive equatorial perturbations find their natural
explanation in the second of the two systems mentioned. At the place in which the earth is found, the
system will have a force directed towards the north. If the system is far off in proportion to the
earth's dimensions, the force round the equator can be almost constant. If the system is nearer, there
will be a stronger effect upon the evening side. This is also what we find in reality, as the effect
about Dehra Dun is somewhat stronger than at Honolulu. It must be remembered, however, that the
observed force is also dependent upon the magnetic induction in the earth.

It would be useless to attempt here a more detailed description of these current-systems. It seems
probable that at times they may have a somewhat different character, being at one time fairly symmet-
rical about the equator, and at another pushed out more towards the north or the south.

The experiment shows that the system may extend considerably in directions north and south.
This, together with the effect of the magnetic induction of the earth, will account for the smallness of
the vertical components.

We have observed certain impulses in the north that appear to be of a local character, as the
force about the auroral zone might diverge greatly in direction at two adjacent stations, and receive
a marked, opposite twist. The equatorial perturbation of the 22nd March, 1903, is an instance.
This agrees very well with our view, as at times radial impulses may come right down to the earth
about the poles. In the experiment, moreover, we see that the equatorial system finally unites with the
polar; and we shall often have great polar precipitations of corpuscles. For this reason, a number of
these perturbations will be found described under the polar storms.

THE NEGATIVE EQUATORIAL STORMS.

32. On several occasions in the course of our investigations of the -composite magnetic storms, we
shall meet with conditions in the field of force, which naturally lead to the assumption that the per-
turbing force in the polar regions, on account of its independence of the polar systems, must be due
to systems that have their greatest strength in the equatorial regions. They differ, however, distinctly
from the previously-described equatorial perturbations in two very important respects, namely:

(1) The perturbing force is directed southwards, answering to a current-arrow towards the
west, and

(2) The curve has not the characteristic, serrated appearance that marks the positive equatorial
perturbations. The latter generally appear very suddenly, whereas those now under consideration
appear more gradually.

We have not succeeded, however, in finding in our material of this kind of perturbation, suffi-
ciently distinct types to enable us to class them under any elementary form. In the treatment of the
composite perturbations, we shall repeatedly have opportunities of examining more closely the reasons
that determine the assumption of such perturbations. We may here mention as instances the perturba-
tions of the 3ist October, 1902, and the 8th February, 1903.

These, like the positive equatorial perturbations, have a very wide distribution, as the conditions
of perturbation alter slowly from place to place. This, together with the quiet character of the curve,
shows that the systems that are to condition the perturbation, must be sought at a considerable height
above the earth. While we are thus led to suppose them to be corpuscular currents, we shall naturally
be obliged to connect this perturbation with the circular systems, which, according to the theoretical
investigations of the trajectories of electric corpuscles, can exist, and the possibility of which we have
also proved experimentally by the previously-mentioned ring (see fig. 37).

84 ISIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

THE POLAR ELEMENTARY STORMS.

33. One cannot look long at the curves for the registered magnetic elements without observing a
regularity in a number of details, especially in the behaviour of the great storms. This, strange to
say, is not least apparent at the stations round about the auroral zone, and especially in the storms
that have occurred at our Norwegian stations during the period in which the magnetic conditions have
been observed by us. In the first place, it appears that the great majority of storms of short duration
are at their height at our stations at about midnight by local time; and when they make their appearance
at that time, it is found that they nearly always cause oscillations in the same direction for the horizontal in-
tensity and declination. We further find that the direction of the oscillation in the vertical curve, espe-
cially in the case of Axel Island and of Kaafjord, is also repeated time after time. We get a direct
impression that, notwithstanding little accidental circumstances, the magnetic storms, in their formation
and course, are controlled by very limited conditions, and that these conditions are pre-eminently fulfilled
in very limited areas in the polar regions. This impression is opposed to the theory upheld by Ad.
SCHMIDT (l) and other terrestrial-magnetists — that the magnetic storms are produced by free cyclonic
electric current-systems.

In the well-known paper mentioned below, Professor SCHMIDT says:

"Electric currents have hitherto principally been accepted as the cause of perturbations, either currents
in the ground or in the air, especially in the upper, probably better conducting strata of the atmosphere.
Although no great clearness prevails as to the physical conditions under which such currents may occur,
yet we shall venture to maintain this hypothesis, notwithstanding the objections raised against it by
BIGELOW, the rather that no doubt can any longer exist as to the reference of the diurnal variation to
such currents. Regarded from this point of view, these centres of action can hardly be anything else
but current-phenomena that stand out with a certain distinctness from the current-system of the whole
earth, on account of their intensity and individual limitation, in fact wandering current- vortices that, in
the simplicity of the elementary perturbation, we may also expect as the normal, like the cyclones and
anti-cyclones of the atmosphere".

The violent storms in the north are always accompanied by simultaneous perturbations, that are
observable right to the equator; and as a rule we shall find, by direct study of the curves, that in
general the effect becomes slighter towards the equator.

The important question now presents itself: In what way are the perturbations in southern lati-
tudes connected with the perturbations in the north? Is there any simple connection at all?

In order to throw light upon these questions, we have made a careful investigation of a number
of very simple storms. At the outset it is only natural to suppose that when we have a perturbation
that runs the simplest possible course, this phenomenon will be particularly well adapted for throwing
light upon the laws of the perturbation.

The next section will deal with a number of simple polar storms such as this, which we have
picked out and called polar elementary storms. These, independently of any hypothesis, can be charac-
terised as follows:

(1) They are comparatively strong at the poles. The simultaneously perturbing forces, even as
far north as the 6oth parallel, have already sunk to about a tenth of their strength in the auroral zone.

(2) They are of short duration, frequently lasting not more than two or three hours.

(') Ueber die Ursache der magnetischen Sturme. Meteorologische Zeitschrift, Sept., 1899.

PART I. ON MAGNETIC STORMS. CHAP. II. gcr

(3) The conditions before and after are comparatively quiet.

(4) The oscillations at the polar stations, especially the more southern ones, run a simple course.
At the poles, they are often characterised by a simple increase to a maximum, and decrease to zero.
We may sometimes, even at the northern stations, have to some extent an undulating form, answering
to a slow turning of the perturbing force.

It follows from this, that these perturbations must be well-defined, and thus afford an opportunity
for an exact determination of the perturbing force.

THE TYPICAL FIELD FOR THE POLAR ELEMENTARY STORMS.

34. It proves — as the aggregate treatment of these elementary types of perturbations shows —
that the same field of force is repeated almost exactly from perturbation to perturbation. It will there-
fore be most convenient for its description, to note, even at this point, its typical form, in order
thereby to avoid too many repetitions. We shall then keep principally to the horizontal perturbing
force, and the field that it forms upon the earth's surface.

In the auroral zone we have very great perturbing force, and we will call the regions about those
places where the perturbation is strongest, the perturbation-centre or storm-centre. If we imagine our-
selves moving along the surface of the earth, so as always to follow the direction of the horizontal
component of the perturbing force, we should be moving along some curve or other upon the earth,
which we will call a line of force.

Supposing we were to move in such a way as always to advance in the direction of the current-
arrows, we should get another set of curves, which we will call current-lines. The one set of curves
will intersect the other at right angles.

We will now suppose that we project these two sets of curves upon the earth's surface, upon a
plane by some kind of zenithal projection, which at the same time is conform, and in such a way that
the plane of projection is tangent to the earth in the storm-centre. The two sets of curves will thus
be projected orthogonally.

If we imagine this done for the field of the various polar elementary storms, we shall obtain a
system of lines, which, in the main, is of the form represented in figure 40 (p. 86). The continuous
lines are the lines of force, the broken lines are the current-lines. C is the projection of the
storm-centre, and the figure is symmetrical round it, as also on both sides of two axes, A and B, at
right angles to one another. The former we will call the principal axis of the system, the latter the
transverse axis. On the transverse axis, and symmetrical as regards the principal axis, are two points,
from one of which the lines of force issue, while in the other they terminate. We will call the point
from which they issue the point of divergence, and that to which they converge the point of conver-
gence. The immediate surroundings of these points we will call respectively the field of divergence and
the field of convergence. We find that the current-lines in these two fields form respectively positive
and negative vortices. The field of force has some formal resemblance to the field induced by two
opposite poles; but this resemblance disappears when we consider the strength of the force. At the two
points in which the lines of force here meet, the horizontal force equals 0. In the neighbourhood of
these points we have a neutral area. The perturbing force, then, should stand, at these points, perpen-
dicular to the surface of the earth.

With regard to the vertical component, it may generally be said that except in the regions,
nearest to the centre, it is exceedingly small in proportion to the horizontal. It is only in the points of
divergence and convergence that Pv will predominate, athough it is generally comparatively small.

In order to obtain an idea of the conditions for Pv, we will consider the values along the trans-
verse axis B. In the centre, C, P, will equal 0. Starting from this point, P, will rapidly rise to a

86

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

maximum. On the side on which the point of convergence lies, the direction of Pv will be upwards,
and on the other side downwards. After reaching the maximum, P, again drops quite rapidly to a
trifling value (see lower diagram, fig. 40).

With regard to the position of the point of convergence, we may note the following.

If we imagine an observer swimming out from the centre in the direction of the current-arrows,
and with face turned towards the earth, the point of convergence will be to his left.

Fig. 40.

PART I. ON MAGNETIC STORMS. CHAP. II. 87

This then, in an idealised form, is the appearance of the field which has a tendency to develope
during the polar elementary storms. It is not founded upon any sort of hypothesis, but is merely a
collocation of what almost invariably takes place, and of which demonstration will be given in the treat-
ment of the separate storms, when we shall also have an opportunity of going into the question of
the forms of current that may be assumed to have produced a field such as this.

In comparing the above with the charts, we must remember that we there employ current-arrows.
We must then compare these with the current-lines in fig. 40.

THE PERTURBATION OF THE 15th DECEMBER 1902.

35. This magnetic disturbance makes its appearance upon an otherwise very calm day. It begins, as
the copies of the curves show, without any preceding equatorial perturbation, with a great storm in the
north, about Dyrafjord and Axeleen, and is accompanied by a perturbation, small indeed, but well-
defined, which is observed in northern America and Europe. The effect increases as we approach the
above-named Norwegian stations. It is only just perceptible at Dehra Dun, and not at all at Zi-ka-wei,
Batavia and Honolulu. There are unfortunately no magnetograms for that day from Christchurch.

The perturbation is of rather short duration. It is first observed at Dyrafjord about oh iom,
and reaches its maximum at i1' 8m with a perturbing force of 386 y. At about 3'' 15™ the storm is
over; but for a little while there are still slight oscillations to the opposite quarter.

On Axeleen the storm does not make its appearance until about 35 minutes later than at Dyra-
fjord, reaches its maximum at ih 46™ with a perturbing force of 193 y, and is over at about 3'' 45™.

The strange thing is that the oscillations at Kaafjord and Matotchkin Schar are comparatively so
small. At the first-named station, the perturbation begins at about the same time as on Axeleen, and
reaches its maximum at ih 4511 with a perturbing force of only 39.6 y. At Matotchkin Schar it
begins at about oh 5im. The perturbing force reaches its maximum at about ib 9™, with 27 y.

At the stations Toronto, Baldwin and Cheltenham, a peculiarity is apparent, in that the perturba-
tion is not of equal duration in the horizontal intensity and the declination. In the horizontal intensity
it takes place between o'1 40™ and 3h 3™, a period which coincides almost exactly with the time of the
storm in the north. In the declination, on the other hand, the oscillation is of shorter duration, as it
begins at oh 55.5™, but is well-defined and by no means inconsiderable. The oscillation in declination
thus takes place at the time when the storm in the north is at its height.

In Europe, on the other hand, it begins rather suddenly at o1' 45"°, and simultaneously in the
horizontal intensity and the declination. It lasts about 3 hours, but the time of its termination cannot
be exactly fixed, as the oscillations decrease little by little.

This perturbation, as will appear from the above, has its origin in the northern regions. Its sphere
of action, which is rather limited, is concentrated about the neighbourhood of Dyrafjord and Axeleen.
The shortness of its duration, as also the comparatively calm character of the curves even during the
perturbation, seems to indicate that this is a polar-elementary storm of the most typical nature; it
appears to be produced by a coherent impulse, which increases to a certain size, and then again decreases
to 0 during the course of the perturbation. At the same time, as the perturbation does not make its
appearance at all places simultaneously, the perturbing cause must be supposed to move with a some-
what continuous motion.

The perturbing forces for the various places are calculated for a series of times (see the table),
and there is a series of charts representing current-arrows answering to simultaneous perturbing forces.
In studying the charts, the significance of the multiplier beside the current-arrows must always be kept
in mind (see Art. 23).

88

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

TABLE XIV.
The Perturbing Forces on the I5th December, 1902.

Gr. M. T.

Sitka

Baldwin

Toronto Cheltenham

ft

Pd

Pi,

Pd

ft

ft

ft

Pd

h in

I O

- 7-0 y

E -|.o y

- 5-T/

E 7.6 y

- 9.97

E 10.6 y

- 7-iy

E 8.3 y

15

- 9.0.

• 0.4 >

- 7.1 «

» 7.6 »

- 9.9 •

« 16.4 «

- 6.8 «

> 14.2 *

3°

— 10.6 »

o

- 7-4 »

» 10. i »

— 90 >

» 18.4 »

— 6.2 «

• 15-3 '

45

- 9-7 »

W 3.7 »

-6.3.

. 4.4 »

- 7.0 »

» 10.9 »

— 6.2 1

• 9-4 •

2 0

- 7-9'

• 3-6 •

-6.3.

> 0.6 •

- 8.1 »

» 0.9 »

- 7-4 "

» 2.4 »

15

- 5-8.

o

— .4.6 » o

- 4-7 '

o

-5-6.

» 1.3 >

3°

- 5-3 '

o - 5-7 '

» 1.9 •

- 5-9'

0

- 5-° »

O

45

- 3-9 •

o — 4.6 »

0

- 6-3 »

o

- 5-3"

0

TABLE XIV (continued).

Gr. M. T.

Dyrafjord

Axe]0en

Matotchkin Schar

ft

Pi

P*

ft

Pd

ft

ft

Pd

ft

h m

12 30

— 56.9/

O

-H 19.1 y

- 7-8 ?•

E 8.7 y

+ 46-7 y

- 4-9/

E 6.6 y

0

45

-141.5 »

W5o.3y

+ 35-8 »

7.8.

• 13-6 •

-t- 66.3 «

— 2. 1 »

. 3.1 .

o

I O

-345-7 •

> 19.1 >

-*- ia-5 •

- aj.8 »

» 23.1 •

-i- 103.0 .

- 16.8 »

0

- 10.7 y

15

-273-5 •

« 6.9 »

- 1.7 •

— 37.6 «

• 42.3 '

+ 135-0 •

— 18.7 «

• 4-4 »

- 4-3 '

3°

— 206.2 »

« 8.7 «

— 22.5 •

- 7°-4 •

. 69.9 «

-t- 184.0 .

— 20.4 •

» 2.7 »

- 2.8 .

45

-237-4 »

E 33.0 »

- 61.6 .

-158.2 »

. 109.1 .

+ 159-5 >

- !3-4 •

» 3-1 *

- 9.9.

2 O

— 171.2 »

> 17.4 »

- 75-7 '

-158.7.

' 79-4 «

•+• 137-5 •

- 6.8 »

> 8.9 >

— 17.8 »

15

-i 14.9 »

» 17-4 *

- 63.6 .

— IOI.2 »

» 68.3 .

-t- 132.5 «

- 4-7 •

• 12.0 »

— 24.1 »

3°

— 70.0 >

• 7.9.

- 34-9 •

- 78.2 .

. 49.0 »

+ 122.6 «

0

. 7.1 .

— 21.3 »

45

- 58.0 »

» 9.7 »

— 3i. a »

- 59-3 •

• 32-1 »

+ 98.5 »

-1- 2. 1 »

' 3-5 •

— 24.1 »

3 o

- 35-0 »

» 7.9.

— 30.8 •

- 396 .

> 28.8 >

-t- 63.0 «

-*- 7-3 '

» 2.7 »

— 22. 0 »

TABLE XIV (continued).

Gr. M. T.

Kaafjord

Pawlowsk

Stonyhurst

Ph

Pd

ft

A

Pd

P.

P*

Pd

h m

12 30

- 4-2 y

E 2.6 y

The balance has

45

— 7.1 «

. 1.8 »

I O

- 23.8 »

W 15.41

probably stuck, or

- 5-0 Y

Wi5.6y

o

+ 7.7 y

Wi6.8y

has been out of

15

- 33-3 •

» 15.0 »

- 2.5 .

> 15-2 "

0

+ IO.2 »

. 9.4 .

3°

— 38-1 »

» 9-5 »

order in some other

0

• 14-3 »

- °-7 y

-1- IO.7 »

« 6.3 «

45

— 39.8 »

E 9.5 .

way, as there is

•+ 5-o »

» 6.4 »

- 1-5 »

4- 8.2 «

E 1.7 »

2 O

— 21.4 »

> 18.4 »

only a very slight

-H 6.O »

o

- 4..i >

4- 4.1 »

» 6.3 »

15

— 11.9 »

• 19.1 >

perturbation in V.

+ 4.0 »

E 3.7.

- 4.1 »

o

" 4-3 »

3°

• 7-7 '

» 17.6 •

-1- i.S »

» 3-7 »

- 3-4 »

- 3-i •

» 2.9 .

45

o

. 1 1.4 *

0

» 3-2 »

— 1.9 •

— 5-i »

o

3 o

-1- 2.4 .

» II.O «

PART I. ON MAGNETIC STORMS. CHAP. II.

TABLE XIV (continued).

Cr. M. T.

Kew

Val Joyeux

Wilhelmshaven

Pk

Pd

f*

Pd

p.

Ph

Pi

/',

li m

to 4-8.37

W 13.6 7

4- n. ay

W 12.3 •/

- 4-0 y

+ 4-37

W ao.a y

Small ne-

15 -1- 8.9 »

» II.o » 4- ii. 6 «

• 10.5 •

- 5-o«

+ 8.9 • » 15.3 »

gative de-

30 -1- 9.2 » » 6.5 »

+ la.o * ' « 5.8 »

- 4-5 •

+ 13.1* * 10.4 «

flection.

45 4- 6.6 » ; o

4- 8.8 » o — 4.0 »

4- 13.6 » o

2 o ; 4- 4. i ' E 6. i »

4- 5.6 » E 4.6 »

- 3-5 "

4- ii. 7 » E 7.0 »

15 — 0.5 » » 5.6 »

o » 3.4 » | — a.o *

+ 5-6 • ! « 5-5 "

45 — 3-1 • °

- 1.6*

0 — 1.0 »

- 0.9 »

^•^ •
o

TABLE XIV (continued).

(,r. M. T.

Potsdam

San Fernando

Munich Dehra Dun

Pi,

Pd

2

Pd

ft

Pd

A

Pd

h m

I 0

4- 3.a Y

W 16.87

4- 6.4 y

W 2.0 /

4- 6.0 y

W 7.67

— 2.8 7

W4.97

15

+ 6.6 »

> 12.4 a

4- 13.4 »

" 3-3'

+ 8.5.

* 13-0 >

! — 2.0 »

» 3-9 "

3°

4- 9.1 *

> 8.6 »

4- ia.1 »

» 2-5 *

4- 9.0 »

> 9.9 .

- 0.8 >

» 3-9 >

45

4- 9. i »

» I.O »

4- 11.5 >

0

4- 9.0 >

» 4.9 » 4- 2.0 »

), 3.4 »

2 O

4- 7.9 »

E 4.1 »

4- 8.3.

E 5-7 »

+ 7-5'

E 1.9 •

4- 3-5 »

» 3.0 »

15
30

4- 2.2 »

- i-3 »

» 3.6 »

> 2.O »

+ 4-5 •
o

» 3-3 •
• 3-3 •

+ 3-5'

0

» 3-° '

« i-5 »

| +3.*»
4- 1.6 »

» 3.0 »
» 3-o *

45

— 2.2 »

0

- 1.9 «

0

— 2.3 »

» 0.8 »

o » 3.0 s

TABLE XIV (continued).

Gr. M. T.

Ekaterinburg

Ph

Pd

P,

h m

I 0

-4.07 W9.57

o

15

- 2.4 » 1 « 9.5 >

o

3°

4- 2.0 »

» 7.0 »

— 1.07

45

4- 4.5 »

» 4.2 »

- 1.8 >

2 0

4- 5-o i

» i.i * | — a.o »

15

4- 5.0 i

0

- i.B i

3°

•+. 5.0 *

o

— I.O >

From Pola and Christchurch no magnetograms were received.

At Batavia, Zi-ka-wei, and Honolulu, the perturbation was so slight that the perturbing force cannot
be determined. On the charts it is marked 0.

For Bombay and Tiflis there is no declination-curve. In the case of Tiflis there is a noticeable
perturbation in the horizontal intensity.

Birkclund. The Norwegian Aurora Polaris Expedition, 1902 — 1903.

B1RKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

Current-Arrows for the 15th December, 19O2; Chart 1 at lh, Chart II at lh 15m.

Fig, 41.

PART I. ON MAGNETIC STORMS. CHAP. II.

Current Arrows for the 15th December. 1902; Chart III at li> 30»>, Chart IV at li> 45m.

Fig. 42.

9? BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

Current-Arrows for the 15th December, 1902; Chart V at 2b, Chart VI at 2ii 15™.

Fig- 43-

PART 1. ON MAGNETIC STORMS. CHAP. II.

Current-Arrows for the 15th December, 1902; Chart VII at 2h 45"",

93

Fig. 44.

Chart I shows the conditions at i'1, or about the time when the perturbing force for Dyraijord
has its maximum ; and we see that it has a direction characteristic of this place, namely south of west.
At the other Norwegian stations, the perturbing force is small at the same time, notwithstanding that
these stations are situated about the line of direction of the current-arrow at Dyrafjord. We notice
further that the current-arrows at these three stations converge towards one point.

Taking the European stations, the current-arrows show that the perturbing force for San Fernando
at this hour has a north-westerly direction, while farther north it goes almost due west. As far north
as Pawlowsk, its direction is WSW, and at Bossekop SW.

The perturbing force at Toronto, Cheltenham and Baldwin, is directed towards the SE, as is
usual during those polar storms which are especially violent at the Norwegian stations. At Sitka, its
direction is S. We notice that the arrows for these four places appear to issue from the same spot at
the south point of Greenland.

Chart II. Time /h //m.

The conditions as a whole are the same as in Chart 1. The force has increased in strength at
Axeleen, and decreased at Dyrafjord, while the directions are the same. In the mean time P, at
Dyrafjord has changed its direction.

The arrows for Sitka and Baldwin, and still more for the European stations, have turned a little
in direction from the left towards the right. This direction we will designate as the positive direction.

94 BIRKELAND. T1IK NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

Chart III. Time /'' jom,

The arrow at Axeleen has increased and assumed a direction more in accordance with Dyratjord,
where the force has decreased in strength, but is unchanged in direction. P, for Dyrafjord is directed
upwards, for Axeleen downwards.

The conditions in America are very much like those at ih 15™. In Europe, the arrows have
turned farther in the same direction.

Chart IV. Time /h .//m.

The perturbing force at Axeleen is now of about the same magnitude as at Dyrafjord. The
condition of the vertical components is the same. The arrow for Kaafjord has turned a little in direction,
so that it is more in accordance with Dyrafjord and Axeleen; but the force is still small.

The conditions in America are almost unchanged, except that the forces have diminished in strength.
In Europe, the turning is continued in a positive direction. At Dehra Dun, where the horizontal com-
ponent of the perturbing force has been directed towards SW, the force has now also taken part in
the turning. The direction is now WNW.

Chart V. Time 2h .

The force at Axeleen is now greater than at Dyrafjord. The condition of the vertical components
is the same as before. At Kaafjord and Matotchkin Schar, the direction of Pl is now in accordance
with the two first-named stations, and Pc for both is directed upwards.

In the rest of Europe, the turning of PI is continued in the same direction. In America also,
the horizontal forces are turned a little in the positive direction.

Chart VI. Time 2h //m.

The distribution of force is the same, but the intensity is less. The turning in Europe is
continued a little.

Chart VII. Time 2h v/m.

The force on the whole weaker, except in America, where it seems to be somewhat greater
than it was at 2h 15™. Otherwise the distribution of force the same.

We see, on the whole, that at each separate point of time, the field presents in its main features
the typical form mentioned in the introduction to this chapter. The position of this field is determined
in the following manner.

The principal axis is tangent to the auroral zone, and the current-arrow is directed towards WSW.
As we have seen, the spot of the greatest effect moves in the direction from Dyrafjord and Axeleen,
or, in other words, the centre moves eastwards along the auroral zone, but in such a manner that the
principal axis always keeps its direction. While this strong impulse in the north is moving, the field
in lower latitudes moves with it.

I he district of Central Europe here comes in the area of convergence, and outside the point oi
convergence. The regular turning of the force, both in this district and at Kaafjord, has its simple
explanation in the actual circumstance that the field in its entirety is moving forwards.

PART I. ON MAGNETIC STORMS. CHAP. II.

CONCERNING THE CAUSE OF THE PERTURBATION.

36. The cause of the great magnetic disturbance at Dyrafjord, and subsequently at Axeleen also,
must mainly be sought in the effect of a horizontal current. This follows from the fact that the places
of the greatest effect are found for a long distance in the direction of the current- arrow, while in the
direction perpendicular to it, the effect very quickly diminishes. At ih 45"", for instance, the perturbing
force at Dyrafjord is 240 •/, at Axeleen 193 y, and the direction about the same, reckoned from the
meridian of the place. At the same time, the strength at Kaafjord and Matotchkin Schar is respectively
39.6 / and 20.6 y, and the distance between Dyrafjord and Axeleen is 1809 kilometres, while between
Axeleen and Kaafjord it is only 896 kilometres (see fig. n).

In the district between Dyrafjord and Axeleen we must assume a horizontal current, which ought to
flow fairly close to the earth for a long distance; for, owing to the rapid diminution in the effect out
towards the sides, the current must flow rather low in relation to the earth's dimensions. We shall
return to this later on.

We may conclude from the vertical intensities that it must be a current above the earth's surface,
This is proved in the case of similar storms (see February roth and March 3ist, 1903), also by a
consideration of the earth-current curve; but this is unfortunately wanting for the day under discussion.

With regard to the further course of the current, there are two possibilities that may be considered.

(1) The entire current-system belongs to the earth. The current-lines are really lines where the
current flows upon the earth's surface, or rather at some height above it.

(2) The current is maintained by a constant supply of electricity from without. The current
will consist principally of vertical portions. At some distance from the earth's surface, the current
from above will turn oft" and continue for some time in an almost horizontal direction, and then either
once more leave the earth, or become partially absorbed by its atmosphere.

According to the first assumption, the total current-volume at Dyrafjord and Axeleen should be
squeezed together so that the greater part of it must pass through a comparatively small section, while
the electricity, both before and after, should be spread over a wider section. In this case the current-
lines drawn on fig. 40 would possess a physical reality, as there should actually be currents above the
earth, somewhat in the direction of the current-arrow, answering to these current-lines.

It is true that systems of plane currents can always be arranged for a given field, which, from a
purely mathematical point of view, would be able to explain the field; but when we consider the physical
conditions for the formation of such a system, we meet with great difficulties, for it is not easy
to comprehend what terrestrial processes would be able to maintain a current with this peculiar form,
which moreover remains constant for several hours.

In my report of the 2nd Aurora Expedition -- "Expedition Norvegienne de 1899 — 1900", etc. -
I assumed such a system of horizontal currents in order to explain the magnetic perturbations. But the
currents there are imagined as having come into existence mainly as a secondary effect of the electric
corpuscles from the sun drawn in out of space, and thus far come under the second of the possibilities
mentioned above. With observations from Pawlowsk, Copenhagen, Potsdam, Paris, Greenwich and
Toronto as a foundation, 1 have drawn up a chart of the ordinary current-directions at midnight, Green-
wich mean time, which is reproduced in fig. 45. It will be seen how well these current-directions fit
into the current-lines in the idealised diagram, fig. 40.

There does not appear, however, to be any special reason why a current-system upon the earth
should maintain such fixed directions and such a motion. If this were only a single case, one might per-
haps regard it as a freak ot nature. Among all the phenomena that occur from time to time, some will

96

RIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

Current-Lines at Midnight.

Fig. 45-

assume strange forms. But this is not an isolated case; as the entire treatment of these great polar storms
will show, we shall always, in them, find again the same direction for the current about the Norwegian
stations. We know, however, no circumstances connected with the earth itself and its immediate sur-
roundings, that are sufficient to explain why one direction should so persistently predominate. A current
such as this, moreover, which is a surface-current, would have to keep in the higher strata of the earth's
atmosphere. It would have to be a corpuscular current in a medium in which these corpuscles can freely
move out to the sides. The direction of the current would thereby be compelled to conform to the
laws for the deflection of such currents in the terrestrial-magnetic field. But with an acquaintance with
the laws for these movements, it is immediately evident that quite different forms would then be produced.

If such plane currents were possible at all, one would have to assume that the corpuscles, on account
of some properties belonging to the upper strata of the atmosphere, would be obliged to move within a
spherical shell situated at some distance above the earth's surface; for if the electric rays are at all
pliable, they will in the main follow the lines of force, and from the polar regions these issue quite
vertically. The rays might either go out into space, or back to the south pole of the earth. If the
rays were very stiff, they would certainly for a time be able to keep approximately horizontal, but would
at last have to run out into space, so that no entire circle of the above-mentioned kind would be formed.

Those rays, moreover, that move approximately horizontally at the poles, would have to turn
off to the same side; or, in other words, on the northern hemisphere there would only be positive vor-
tices, or areas of divergence for the perturbing force. But, as we see, we also have areas of con-
vergence of a very simple form.

This brings us to the necessity of considering more closely the second possibility, namely, that
the current is fed by a fairly constant supply from without, lasting for several hours. The supply
must then, in the first place, be given in the regions in which the perturbation is strongest; and the
strong perturbations in the north ought to be a direct effect of the descending current, which acts as

PART I. ON MAGNETIC STORMS. CHAP. II.

97

<i. b. c.

Fig. 46.

a horizontal current for a long distance between Dyrafjord and Axeleen. This would satisfactorily ex-
plain the constant direction that the perturbation in this and other similar cases shows.

In order to obtain a clear conception of the conditions, we will once more have recourse to my
experiments with the terrella. The experiments shown in fig. 46, a, b and c, follow directly on to
those in fig. 38, a, b and c. In fig. 46 a, the terrella is so turned that the screen forms an angle of
135° with its first position (fig. 38 a}. In
the next experiment (fig. 46 b), the angle
is 1 80°. The angles are here measured from
west to east. Fig. 46 c shows how the ca-
thode rays strike the terrella; when the lat-
ter is not magnetic, but is in the same
position as in the experiment given in
fig. 46 b, only the half that is turned towards
the cathode becomes luminous with phos-
phorescence.

It will be seen from figs. 46 a & b how
the cathode rays behave when the terrella is
very powerfully magnetised.

We will here especially direct our at-
tention to the luminous wedge that is thrown
upon the screen at about the 7oth parallel
of latitude north.

In figs. 47 a & b, we have a confirma-

tion of the way in which the rays whirl round

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903.

fig. 47-

13

98 BIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

the terrella in the above-mentioned wedge-shaped spaces about the poles. The screen here forms in
both cases an angle of 270° with its original position (fig. 38 a), and the photographs are now taken from
directions that form angles of respectively 120° and 240° with the plane of the screen in its original
position, and not, as all the previous ones, from a direction making an angle of 90° with the screen in
its original position.

The way in which the photographs were generally taken was to first expose the plate for about
five seconds during the cathode-light experiment, and then, in order to obtain a picture of the terrella
itself, to expose the latter for several minutes, illuminated by lamplight.

These experiments clearly show by analogy how, for instance, cathode rays from the sun will force
their way towards the earth in the auroral zone, in such a manner, however, that the bulk of the rays are
inclined to slip past it on the night side. The magnetic effect of the rays upon the earth would then
be comparable to an ordinary electric current above the earth, whose direction is the reverse of that
of the rays, thus approximately from east to west.

In order to find out whether currents of rays such as these are actually capable of explaining the
multiplicity of magnetic perturbations, we must first try to obtain an idea of the exact course of the
rays in the vicinity of the earth, and of the relative strength of the bundles of rays.

Owing to its deflection by terrestrial magnetism, the current from without can, as we have seen,
only enter very limited districts, which will alter according as the magnetic axis assumes various
positions in relation to the point on the sun that is the source of the rays.

We must therefore expect to find constant conditions for the current, which, when circumstances
are favorable, can force its way down to the earth; at any rate, it will be easy to understand that
distinct directions may thereby occur, as the electric rays, in order to come in, must follow paths whose
initial direction lies within narrow limits.

Further, if the rays come from bodies lying outside the earth, the variation in the position of the
points of radiation in relation to the magnetic axis, which is occasioned by the rotation of the earth,
could give an explanation of the entire movement of the system, as the initial conditions are thereby
continually varied.

If we assume, as, from a physical point of view, we might legitimately do, that the current is of
a cosmic nature, and consists of negatively or positively charged corpuscles, the trajectories of the
separate corpuscles must, as already stated, more or less approximately follow the magnetic lines of
force, moving in spirals about them.

This will at any rate be the case with the hitherto known rays of this kind, such as ordinary
cathode rays, ji rays and a rays, and within a distance from the earth a few times greater than the
diameter of the earth.

We should then, in this perturbation of the isth December, have to consider the effect of a long
vertical current, which, in the case of negative corpuscles, must come near to the earth at about Dyra-
fjord, or somewhat west of it, answering to an ascending galvanic current. A little above the surface
of the earth it turns eastwards, or rather the aggregate effect of the cosmic current relative to the earth
is as that of a galvanic current that is directed westwards, or more accurately towards the south-west.

In this descent of electric corpuscles, some will occasionally come so near the earth that they will be
partially absorbed by its atmosphere, and will then eventually give rise to aurora. If the earth were able to
retain an electric charge, we should have approximately horizontal currents, which would be necessary
for the production of electrical equilibrium. But secondary electric radiation ought also to begin,
and then, as it is still influenced by terrestrial magnetism, give rise to vertical ' ray-currents. The
bulk of the corpuscles, however, must be imagined, as shown by experimental and theoretical investigations,
as able to return, owing solely to this very influence of terrestrial magnetism, and give rise to reversed

PART I. ON MAGNETIC STORMS. CHAP. II.

99

electric currents. Starting from physical considerations, we are thus naturally led to seek to explain the
field by a system, which, in its average effects, has the character of two vertical currents in opposite
directions, connected by a horizontal part.

In their main features, the conditions for such ray-currents can approximately be settled, as there
is a long series of experimental and theoretical investigations on the course of cathode rays in a magne-
tic field. It will be sufficient for our purpose to refer to papers by POINCARE(I), myself(2),
and ViLLARD(4).

In accordance with the facts learned from the above-men-
tioned papers, I have here put forward a hypothesis regarding
the course of the rays in the vicinity of the earth, by which,
as it will be seen, the magnetic fields of force observed during
magnetic storms are explained in a simple manner.

Figure 48 illustrates by diagram this hypothesis, which
is to the effect that the rays — which are drawn in towards
the earth in the sharply wedge-shaped space in the polar regions,
always whirling around the magnetic lines of force, (fig. 48 a) —
either, as generally happens, pass the earth with an average
curvature such as is shown by the curve b, or, less frequently,
with a loop such as curve c shows.

In those regions of the earth in the auroral zone, that
lie close beneath the rays, the rays in the lowest bend of the
curves b and c will mainly condition the magnetic disturbances;
and the perturbing forces produced will be in reverse direc-
tions in the two cases. This will mean that the current-arrows
for this area will generally point from east to west along the
auroral zone (answering to the form of curve b), while less
frequently the reverse direction may occur (corresponding to the
form of curve c).

In the equatorial perturbation of the gth December, 1902,
it is mentioned that the direction of the polar storm that finally
supervenes, is the reverse of our ordinary polar night storms.
We thus have before us a field that can be explained by a
current-system, the effect of which is the same as that produced
by a linear current of about the same form as the loop in fig. 48 c.

We shall farther on meet again and again with these reversed polar storms. Fields similar to that
of the gth December will often be formed, principally on the noon and afternoon side, frequently breaking
suddenly in upon an ordinary polar storm, only to disappear again as suddenly, when the first storm
once more resumes its course.

In reality, the violent deflections that are found in nearly all magnetograms from the polar regions
during a storm, are probably due to "loops" appearing locally, and repeatedly coming and going nearly
over the place of observation.

Fig. 48.

0) POINCARE, Remarque sur une experience de M. BIRKELAND. Comptes Rendus 123, p. 930, 1896.

(a) KR. BIRKELAND. Archives des Sciences Phys. et Nat. Geneva (4) p. 497, 1896; and September, 1898.

(3) C. ST0RMER, Snr le Mouvement d'un Point, etc. Videnskabsselsk. skrifter i Mathem.. Naturvidensk. Cl. No. 3. 1904.

(4) Comptes Rendus, June 11 & July 9, 1906.

100 BIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

At great distances from the polar regions, e. g. in the south of Europe, only the mean magnetic
effect of the precipitation in those regions will make itself felt.

The question that now presents itself for closer consideration is, Will a galvanic current such as
this give rise to a field such as we have found for the storm now under discussion?

By the aid of the elementary law for the effects of electric currents, it will be easy to see that
such will be the case.

At great distances it will be mainly the two long vertical parts of the current that will be of
decisive effect. In the vicinity of the storm-centre, the effect on P, of the vertical parts will be opposite to
that of the horizontal part; but as the latter lies nearest the earth, it will predominate in these regions.
If, however, we come out along the transverse axis of the system, we shall reach a point at which the
horizontal component will equal 0, and farther out its direction will be reversed.

As approximately the long vertical portions of the current are a necessity for the appearance of
these polar storms in the auroral zone, and as it is they which should especially give rise to the
universal part of the perturbation, this explains in a simple manner the fact that the polar storms are
always accompanied by perturbations in lower latitudes. It also gives an explanation of a circumstance
which is especially distinct in this perturbation, namely, that the variations in the field with time are
called forth by the motion of a field with a constant form.

This current-system further explains the following typical properties of the polar storms:

(1) That during the storm the curves for the arctic stations undergo great and sudden changes
with time and place, in accordance with our supposition that the current in these regions really comes
near the earth.

(2) That the curves in lower latitudes, during the great polar elementary storms, exhibit a very
even course, that the form of the curve may be preserved over comparatively large regions of the earth,
and that the transitions take place very gradually. The explanation of this is simple, namely that the magnetic
disturbances are the effect of a comparatively distant system. The variations that will appear in certain
parts of the current-system, and which give to the curves their very jagged character around the storm-
centre, are not observable at great distances, as we then only get the average effect outwards of that
which takes place within the current-space.

(3) It explains the peculiarity which these elementary polar storms exhibit, in appearing with such
comparatively great strength around the auroral zone, while we find, as a rule, that southwards the strength
suddenly drops to a small fraction of what it is at the centre.

(4) It explains an exceedingly characteristic quality of the magnetic storms, namely, that it is
only around the storm-centre that the vertical component of the perturbing force has a magnitude of
the same order as the horizontal component; while in lower latitudes, it will, as a rule, even during
the greatest storms, be only just perceptible with the apparatuses generally employed. Its value in
Central Europe seldom exceeds 8y. The only place where Pe may have a greater value in relation to
Pj (see Art. 14) is near the points of convergence and divergence, where P^ equals 0.

It is easy to see that our current-system must give rise to a condition such as this. In the
neighbourhood of the storm-centre, the effect will be mainly determined by the horizontal part. If we
consider the effect of this portion of the current out, for instance, along the transverse axis, the direc-
tion of the magnetic force, which was horizontal immediately beneath the current, gradually becomes
more vertical. At the two points, one on each side of the principal axis, in which the tangential plane
through the horizontal current touches the surface of the earth, the force will be exactly perpendicular
to that surface, and thus the horizontal component = 0.

Farther along the transverse axis, the effect in the horizontal plane will be the reverse of those
previously found, and Pt, as those points are passed, turns round to the opposite direction.

PART I. ON MAGNETIC STORMS. CHAP. II. IOI

If we assume the two other portions of the current to be perfectly vertical, they will only give rise
to a magnetic force that is perpendicular to them, and thus everywhere horizontal, if the earth is con-
sidered as a homogeneous sphere.

In the storm-centre and its immediate surroundings, these vertical currents will counteract the hori-
zontal portion of the current. Farther out along the transverse axis, we shall reach two points situated
symmetrically in relation to the principal axis, at which the effect of the horizontal portion in a hori-
zontal direction will be neutralised by those of the vertical currents. These two points then, answer to
those that we have previously designated as the points of convergence and divergence. Still farther
away from the storm-centre, from the moment of passing the points of tangency already mentioned, the
horizontal and the resultant of the two vertical portions will act in the same direction, and thus strengthen
one another.

From the points of convergence and divergence then, Pt will increase rapidly; at a certain dis-
tance it will attain a maximum, and then once more decrease.

With regard to Pv, we find that it is only the horizontal portion that can produce a force such
as this. One would expect, moreover, to find the vertical components strongest along the transverse
axis, at two points situated one on each side of the principal axis, and not far from the storm-centre.
At the point of convergence, P, should be directed upwards, at the point of divergence downwards.

Along the principal axis, it will be chiefly the horizontal current that acts, at any rate in the district
that comes between the two vertical currents. In this district, the vertical currents will act contrary to
the horizontal. As we pass the points in which the vertical currents produced will meet the principal
axis, the nearest vertical portion will act in the same direction as the horizontal.

In the quadrants enclosed between these axes, the effect of the nearest vertical portion at rather
greater distances will predominate ; and the distribution of force will be as shown in fig. 40.

We have thus seen that the chief features of the form of the field in such a system, answer com-
pletely to those that are typical of an elementary polar storm.

We cannot, however, without more ado, draw any conclusion as to the distribution of intensity;
it is possible that these fields corresponded only qualitatively, not quantitatively. I have therefore made
a calculation of the effect along the transverse axis of some systems such as this. This is sufficient, as
the form of the field is thereby given accurately enough. The actual current-conditions do not answer
so exactly to these assumed linear currents with two vertical portions and one horizontal, as to make
it worth while going into details.

If we consider, in the first place, the magnetic effect of an infinitely narrow rectilinear piece of

current on a magnetic mass i cm* g* sec , we find that

f / tis . i f

K =•= I — • - • sin a = -
Jio /- 10)

b

yds

a

b

y being the distance from the point under consideration to the current, and r and a respectively the
distance of the point from the current-element under consideration, and the angle made by the element
with the direction to the pole. The direction of the force is found by Ampere's rule, and as limits,
must be inserted the distances of the terminal points from the perpendicular that can be dropped from
the point under consideration to the current-line.

102

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

Here / is assumed to be expressed in amperes, therefore K in dynes. This we will apply to a
current-system of the form mentioned above, assuming that the horizontal portion of the current lies at
a height h above the storm-centre, and has a length of 2 /.

The distance from the storm-centre in degrees along the transverse axis, we will designate ip, the
horizontal magnetic force-component, produced by the portions of current /, //and ///along the transverse

axis, respectively P/y, Piiy and Puiy, and the
other magnitudes as given in fig. 49. We will call
the force positive when it is directed towards the
storm-centre, if we are on the same side as the
point of convergence, and negative if we are on the
opposite side.

We then obtain

+J

pu = i_ s

lay \lyt _l_ s»

cos

cos

Fig. 49-

n sm

Here y = R -r

sin

where R is the radius of the earth, (i is determined by the equation

4- //

tan (f + ft) =

The equation can thus be written in the form

p i sin ft

$R sin ty i

In the storm-centre itself we have

• tan

2

cos

//o

We further obtain

where

and

Pl</'

If C is determined by the equation

tan C =

= 2

IOJ'

n = . - R cos 6,
sin a

y = R sin 0,

sin a
sm y = -1—51

sin 0

cos 6 = cos a • cos (>.

• sm y
a

R sin

/? sin 9 sin a

I n I — R cos 0 sin a

-T— - R cos 6
sin a

we obtain

sn

r 1 '

" cos^ J ==;

,- 2sin Of • sin2 -

sn

PART I. ON MAGNETIC STORMS. CHAP. II.

103

The calculation has been made in three cases, and the result is given in the tables below.

/<• = 6366 km.
is employed as the mean radius of the earth.

The following values, given in the table, correspond to a current-strength of io6 amperes, and the
values of the force are expressed in y.

TABLE XV

// = 200 km. ; 2 / = 1600 km.

*

P//V'

P J. P

/v my

1

0°

- 97° 13

+ 166.78

- 803.35

10°

7.08

4- 61.69

+ 54-6i

30°

+ 2.81

+ 9-74

+ 12.55

45°

4- 2.24

4- 4.29

+ 6.53

= 300 km.; 2 / = 2500 km.

0

" II V

P + P! j

i

P*

0°

— 648.26

4- 100.77

- 547-49

10°

- 2 1 .00

+ 58.57

+ 37-57

30°

+ 3-59

4- 13.08

4- 16.67

45°

4- 3.22

•4- 6.07

4- 9.29

// = 300 km.; 2 / = 5000 km.

V

"ay

Pty + Pmv

/v

0°

— 661.91

+ 48-30

— 613.61

10°

- 26.08

4- 40.36

+ 14.28

3o°

+ 6.15

+ 17.23

-*- 23-38

0

45

-"- 5-93

+ 9-43

+ 15-36

// = 200 km. ; / = oo

P

0° 10°

3°°

45°

pv

— looo.oo — 12.32

•T 12.09

+ 14.05

ifj — o

2l

h PH y

PI ,/• + "my

P*

I OOO

300

- 571-66

•+ 177-55

- 394-11

400

200

- 706.94 + 353-99

- 353-95

2OO

2OO

- 447-21

4- 204.24

— 242-97

104 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

It will be seen from the above that there is also a quantitative correspondence between the actual
field and that which is produced by the calculated systems.

The first answers to a system in which the horizontal portion of the current lies at a height of
200 kilometres, its length being a little less than double the distance between Kaafjord and Axeleen,
or than the distance from these two stations to Dyrafjord; it is thus a comparatively low, compressed
system. It appears that the force here diminishes a little more quickly than it is found to do during
our most typical elementary storms.

In the second system, on the other hand - - in which the horizontal portion of the current is at a
height of 300 kilometres, its length being 2500 kilometres - the distribution of force shows a great
resemblance to that found during the polar elementary storms. The length of the horizontal portion is
here a little less than the distance between Dyrafjord and Matotchkin Schar, which is roughly 3000
kilometres.

For the value if) = 10°, we have passed, as the table shows, the point of convergence or diver-
gence, and the perturbing force is about y1- of what we find at the storm-centre. At greater distances
from this, the force varies in a manner corresponding fairly well with that found during the polar elemen-
tary storms.

In the third system the horizontal portion of the current is 5000 kilometres in length, and at the
same height above the storm-centre as in the preceding case. The points of convergence and diver-
gence are now situated at a rather greater distance from the storm-centre; and for greater values of ip,
the forces are now of a comparatively greater strength than before.

On the whole, the fields produced by the last two current-systems correspond fairly exactly with
those found during the polar elementary storms.

In order, in the next place, to investigate the effect of the horizontal part, if that part became very
long, we have calculated the effect for / = oo . We then see distinctly how the directions change at
the above-mentioned points of tangency.

On a closer examination, it will be easily seen that Pm/> at the storm-centre, and its immediate sur-
roundings, will always be greater than Piy -\- Puiy- In order to inquire into the manner in which the
latter change in relation to one another, we have, in the next place, calculated the effect at the storm-
centre of some systems of various forms, where the horizontal portion of the current is made compara-
tively short.

We see, that for the small values of /, i.e. 2 / = 400 and 200 km., with the horizontal part lying
at a height of 200 km. above the storm-centre, the proportion between P^, -\- Puiy and Pn,/, is about
i : 2. For the third system, 2 /= 1000 and h = 300 km., the proportion is somewhat less.

Finally, we have calculated some forces along the principal axis, in order to obtain a general idea
of the way in which the forces change here. The formulae that will be employed are developed in a
manner exactly similar to the previous ones; all that has to be done is to insert in the general formula
some other values for distance and limits.

There is no need for a more careful investigation here, and we have therefore contented ourselves
with calculating a few values for the system 2 / = 1600, // = 200. We have chosen this especially, in
order that the changes might be more noticeable.

For this system we have found « = 6° 56'. 8.

In the storm-centre, and at the distances 2° 30' and 5° from it, we have found the respective values

-803.35, - 756-J3 and -603.06.

Here too, then, the change is not so great when we keep between the two vertical currents. If
we withdraw farther to the other side of one vertical current, however, the force will diminish more
rapidly.

PART 1. ON MAGNETIC STORMS. CHAP. II.

105

If we look specially at the perturbation under discussion, we see, true enough, that the vertical
components at the Norwegian stations have about the same magnitude as the horizontal component.

The conditions at these stations at i a.m. have already been mentioned. From these it appears
that the total perturbing force at Kaafjord, Axeleen and Matotchkin Schar may be explained as the effect
of a galvanic current, which drops at a certain angle towards the earth in a direction from Axeleen towards
Dyrafjord. The current here is so near the stations, that the nearest part will be the important part.
We make use of the law that when we approach an infinitely thin conductor, in which a stationary
current is flowing, the effect will be approximately that which would be obtained if the system were
replaced by an infinitely long current of the same strength, which passed through the nearest point on
the conductor.

The conditions which we have educed from our current-system for the vertical components in more
southerly latitudes, are corroborated in a striking manner by comparing the conditions at the few other
stations from which we have received the vertical curves for this perturbation. In accordance with our
hypothesis, the vertical components in these latitudes are very small in comparison with the horizontal.
For instance, at i1' and ih 15™, Pt for Pawlowsk and Ekaterinburg is imperceptible, whereas at the
same time, in the case of Val Joyeux, which is situated nearer the point of convergence, the oscil-
lation in the vertical curve is distinct, although faint, and answers to a perturbing force directed
upwards.

Now when the current-system moves towards ENE, we should expect that the vertical intensity
would also become noticeable at the two first-named stations, since, by the movement, they would be
brought into the area in which vertical components might be expected. This is confirmed by the actual
circumstances.

In the following charts, we find a noticeable vertical component for Pawlowsk and Ekaterinburg,
while at the same time it diminishes in the case of Val Joyeux, but is directed upwards in all three.
As the effect is so limited, and the vertical components so great, the width of the current must
be small in proportion to, for instance, 1000 kilometres. I have supposed a maximal width of 500 km.
in my report, "Expedition Norvegienne", etc., 1. c., p. 26, although it is probable that the boundary is
not sharply defined. It must therefore be understood that it is the main body of the current that has
this narrow width.

It follows from the cosmic constitution of the whole current, that the form we have assumed for
the current-system that shall be able to explain the field, is only an ideal form, which in its main
features characterises the system; and further it is to be understood that it is the total effect outwards
that in its principal features is explained by a system such as this. It does not follow from this,
of course, that the trajectories of the separate corpuscles must coincide with the direction of the as-
sumed system.

The field at each place is in reality the sum of
the magnetic effect of the separate corpuscles at each
moment.

It is evident, both from my experiments and
Stermer's calculations, that a drawing-in of rays generally
takes place over areas of greater or less extent; and
we will here only suggest that the effect of a bundle
of rays in which the course of the rays is, as shown
in fig. 50 a & b, very near, will be the same as that of
a linear current consisting of two vertical currents con-
nected by a horizontal one. Fig. 50.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903. 14

IO6 BIRKKLAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

In the more central parts it is evident that the downward and upward-going rays destroy each the
others' effect, so that only the effect of the outer parts is left. In the figure, we have made the direc-
tion of the arrow indicate the direction in which the . negatively-charged corpuscles should move; and the
galvanic currents must be imagined flowing in the opposite direction.

The paths of the separate corpuscles do not, indeed, coincide with those here indicated ; but on
the whole a system of rays such as this might not be so far removed from those that actually produce the
magnetic storms.

We have hereby only wished to prove that these two systems of rays fully explain the principal
features in the two typical fields found in the polar elementary storms. Fig. 50 a represents those in
which the current-directions at the storm-centre are directed westwards, and 50 b those in which the
currents move eastwards.

Such cosmic current-systems in the polar regions as are here assumed, will of course induce a
very complicated system of currents all over the earth itself, this being a conducting sphere composed
of sea and land.

In a later part of this work we shall deal with this question, and see how such earth-currents would
affect the magnetic instruments in different places.

THE PERTURBATION OF THE 10th FEBRUARY, 1903.

(PI. XVIII.)

37. This magnetic disturbance is brief, and commences without any previous equatorial perturbation
on an otherwise very quiet day. First a small disturbance appears rather suddenly at about 21 h 6m.
This precursor of the real storm partakes on the whole of the latter's character. It is most powerful
at the northern stations, especially at Matotchkin Schar, but is also perceptible in Europe and North
America. After about 30 minutes, the conditions are once more almost normal; but disquiet still prevails
at the northern stations, and at the other European stations a slight deflection is noticeable, especially in
the declination.

The powerful perturbation, with which we are especially concerned,and which we shall now follow,
does not commence until 23h.

As the copies of the curves show, it is very powerful, and especially so at the four arctic stations ;
while southwards, in Europe and America, there are simultaneous relatively powerful, violent pertur-
bations.

After about an hour and three quarters, the storm is over. At most of the stations, the con-
ditions have now become quite normal, the arctic ones only being still somewhat disturbed. At 2h 30™
on the nth February, another short, slight perturbation appears, which is especially remarkable for the
sharply-defined northern limits of its sphere of action (cf. perturbation of I5th Dec., 1902). Thus
while fairly powerful at Axeleen and Dyrafjord, it is almost imperceptible at Matotchkin Schar and
Kaafjord; while it is tolerably distinct in America, and less powerful on the continent of Europe.

This storm belongs to the class of perturbations that we have called elementary storms, and has
a peculiar resemblance to the perturbations of the I5th December, 1902, and the 3131 March, 1903; but
the curves for the northern stations in this perturbation are of a more disturbed character than those
of the perturbation of the I5th December.

It is difficult to say exactly when the powerful perturbation begins; but we shall see from the curves
that in the case of most of the stations, the time when the perturbation begins to be very powerful

PART I. ON MAGNETIC STORMS. CHAP. II.

I07

can be approximately given. The time when the perturbation is at its height can also be determined
with tolerable accuracy; but as in so many other cases, that of its cessation is difficult to decide.

In the table below is given the hour at which the perturbation commences, as also the time at
which the horizontal component of the perturbing force has its highest value, and the magnitude of its
maximal strength, and further the time at which the perturbing force has sunk to about five per cent,
of its maximal amount, this hour being given as the time when the perturbation ceases. This deter-
mination cannot lay claim to any great accuracy, and is therefore found by an estimate.

TABLE XVI.

Observatory

Begins

Reaches
Max.

p
*<max )

Ends

I

Matotchkin Schar. .

Dyrafjord . .

h m
23 o

» 8

li m
33 -15

373 y

h m
o 36

Axel0en

> 16

i J6

Kaafjord

> 8

a-j j.8

Wi I helm shaven . . .
Stonyhurst . .

» °-5

• 17
» 16

47-4 •

I O

Potsdam

Kew

» 16

qr R »

i | 8

Pawlowsk

• 15

Pola .

» 18

San Fernando . . .
Munich

» 0

» 18
• 30

27-5'

I 0

Toronto

* 1

» ai

IQ.4 *

o 8

Cheltenham ....

» 22

18.0 »

Baldwin .

o 16

Tiflis

» o

» -S

17. q »

o 48

Sitka .

•> 18

Dehra Dun

> 48

iq.c »

Christchurch ....
Honolulu

» 2

» ao

* 19

13.O »
7.6 »

Zi-ka-wei

7 c »

Batavia

<T s.o >

It appears from the Table, as also directly from the curves, that at the northern stations the per-
turbation occupies a peculiar position in relation to the other stations.

The times of the commencement and of the maximum of the perturbation, it will be seen, are
very different at our four Norwegian stations. At Axeleen the perturbation commences about a quarter
of an hour, and at Dyrafjord and Kaafjord about eight minutes, later than at Matotchkin Schar, although
the distance between the stations is only from 900 to 1800 kilometres. It should also be mentioned in
this connection, that at the arctic stations the curves exhibit great variableness from place to place.

In marked contrast to this, we find that at all the other stations scattered over the northern
hemisphere, the perturbation commences simultaneously. The slight differences in time, which do not
exceed three minutes, need not imply an actual difference in time, but may be ascribed to inaccuracy
in determining the time on the magnetograms. The hour for the maximum is also the same for wide
districts of the earth ; and the form of the curve is repeated almost without change from station to station,

:o8

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

the variation in form being gradual. All the stations of Central and Southern Europe have the same cha-
racteristic form of curve. The //-curve at Tiflis forms the transition to that at Dehra Dun. The com-
paratively high value at Wilhelmshaven seems to have been due to local conditions, as this station
always shows a greater force than the surrounding stations.

The conditions at Pawlowsk do not appear to allow of a similar explanation, the comparatively
small force there being accounted for by the peculiar nature of the perturbation in question, a circum-
stance to which we shall return later on.

We must here mention one more peculiarity. Although at Batavia the perturbation is almost im-
perceptible, we find, on coming as far south as Christchurch, that there is a distinct perturbation in the
horizontal intensity, appearing simultaneously with that in the northern hemisphere, and resembling in its
course the perturbations at the American stations.

It is usual for Christchurch to occupy a peculiar position such as this, and frequently the forms
appearing in these southern districts are quite different. This may be explained by the fact that the
perturbation in the arctic regions is often accompanied by simultaneous perturbations in the antarctic
regions, and it is the effect of these latter that is noticed in Christchurch. Our material does not,
however, allow of certain conclusions being drawn in this matter.

THE PERTURBING FORCES.

38. This perturbation, as we have said, has a great resemblance to the previously-described per-
turbation of the 1 5th December, 1902. This resemblance is also apparent in the perturbing forces.
If we compare the charts of the two perturbations, we find a great similarity, as for instance in the
direction of the horizontal and vertical components of the perturbing force. The chief difference is that
the force at Kaafjord and Axeleen on the 151)1 December was very small in proportion to that at the
other places.

The perturbing force elsewhere in Europe moreover exhibits a similar though smaller turn clock-
wise. The smaller extent of the turn seems undoubtedly to be connected with the circumstance that at
the commencement of this perturbation, the direction of the perturbing forces coincides with that at
2 a. m. on the I5th December, at which time, on that occasion, the perturbation was far past its maximum.

As the force in these perturbations does not seem to continue to turn after the current-arrows
in Europe have become almost uniform in direction with those at the arctic stations, it is evident that
the perturbing force in this perturbation of the loth February must have a smaller area to turn in.

For this perturbation four charts have been drawn, at intervals of a quarter of an hour. They
give a clear idea of the distribution of the force, and its changes during the progress of the perturbation.

TABLE XVII.
The Perturbing Forces on the loth February, 1903.

Gr. M. T.

Honolulu

Sitka

Baldwin

Toronto

Cheltenham

PA

Pd

Pk

Pd

Pk

Pd

Ph

Pd

Pk

«

h m

33 o

- 0.5 y

o

o

0

o

0

o

0

0

O

15

-7.6.

o

- 9-4 y

o

- 10-57

o

- n-3/

o - 14.77

0

3°

— 6.6 1,

W 2.9 y

- 13-7 •

w 5.9 y

— 15-6 "

o

- 17-5 »

E i. a y

- 15-4 *

E i&y

45

— 6.0 »

« 2.9 •

- 15-0 »

* 5-9 '

— 13-6 •

o

- 13-5 »

> 1.8 i

— 11.3 »

• 2.4 »

24 o

- 3-9'

» 0.8 '

— 6.9 »

» 1.8 »

- 7.0 »

E 2.5 y

- 6.8 .

» 6.7 >

- 1-7 '

• 4-5 •

0 15

- i-3 »

0

+ 3.2 »

o

1.4 »

0

o

o

O

o

30

o

o

+ 3.4 »

0

0

o

0

0

o

o

PART I. ON MAGNETIC STORMS. CHAP. II.

TABLE XVII (continued).

109

(ir. M. T.

Dyraljord

Axeleen

Matotclikin Schar

Pi,

ft

ft

Ph

Pd

•*

Pk

Pd

p.

Ii m

23 o

- 24.77

W 8.77

- 30.8 7

16.17

E 15.27

- 24.67 - 96 2 7

E 49-7 Y

- 59-5 y

7-5

— 172.0 »

. 39.8 •

- 16. i »

18.4 »

• 74-8 •

9.8 » — 244.0 »

» 1OO.O »

— 161.0 »

15

— 273.0 »

» 1OI.O •

• 73-5 •

- 69.0 » • 77.3 »

4- 81.0 » — 321.0 "

» 113.0 »

— 244.0 >-

22.5

- 370.0 »

• 68.0 » ! - 96.5 »

— 186.0 » » 74.0 «

4 150.0 » — 359.0 >-

>' 10O.O »

— 191.0 i.

3°

37-5

— 3°4-° »
— 1 06.0 »

» 32.6 »
» 2.4 »

- 28.0 »
• 78.0 »

— 202. o » » 76.7 »
— 298.0 » » 76.4 •

4 196.0 ~"
+ 164.0 »

— 311.0 »
— 292.0 >'

>' 106.0 »

86.5.

- 156.0 »
- 131.0 »

45

— 1 22. 0 »

E 13.2 »

- 149.0 » 1 — 345.0 » » 76.4 »

4- 158.0 >

— 196.0 >-

>. 29.3 >' i - 85.0 ).

52.5

— 128.0 »

» 23.2 »

- 93-5 " ; — 232.0 » » 78.9 »

4- 208.0 »

— 141.0 »

» 48.4 »

47.6

24 o

— H5.0 »

» 33-a •

- 32.8-

— 138.0 » « 46.2 »

4- 172.0 > ii - 65.0 »

» 28.8 1

- 21.6 »

0 15

- 88.0 »

0

9.2 »

- 85.0.

» 76.2 »

Pd somewhat
uncertain be-

4 49.2 »

- 18.0 »

> 17.8 »

14-5'

h m
23 6

— 141.0 «
— 240.0 >'

W n.8»
» 81.2 >.

4- 89.2 „
— 164.0 »

tween
23" 22.511
and 23 '* 45m,
owing to the
indistinctness
of the curve.

TABLE XVII (continued).

Gr. M. T.

Kaafjord

P.

Ph

Pd

h m

23 o

- 58-07

E 28.6 y

49-9 /

7-5

- 73-2 "

0

— IOI.O »

15

- 154.0 .

w 5.5 »

- 195-0 »

22.5

— 233.0 »

E 29.4 >

— 229.0 i

3°

— 232.0 >

» 48.4 i

— 230.0 »

37-5

l89.O >'

» 66.1 »

- 253.0 »

45

— I76.O »

>. 64.2 »

— 258.0 "

52-5

- !34.o

» 62.4

— 217.0

24 o

- 94.6 >

» 73-4

- 1 68.0 I

° 15

- 15-3"

» 57-a "

— 113.0 t

TABLE XVII (continued).

Gr. M. T.

Pawlowsk Stonyhurst

Kew

Val Joyeux

Ph

Pd

ft Ph

Pd

P*

Pd

Pk

Pd

P,

h m

23 0

4- l.o 7

E 5-57

• 1-5 y - 3-67

E 10.8 y

- 2.07

E 6.87

- 3-27

E 5-9;'

The devia-

15

4- 22.6 1

W 18.4 »

- 3.7 1 -t- 27.5 ,

i 30.8 »

+ 25.4 »

» 25.0 »

-1- 2O.O «

» 27.7 »

tion very

3°

4- 21.2 »

• 2.8 »

— 1 1.6 » 4- 19.9 •

» 34.8»

4- 16.8 »

» 28.2 »

4- 21.6 »

» 26.8 >

small,

45 4- 12.6 »

K 3-7 •

— 15.7 » -*- 1O.2 »

» 36-5 •

-t- 7.1 » > 30.8 '

4- 10.0 »

» 3 '-9'

about

24 o

° '5

+ 2.5 »

- 5.°-

• 20.2 »
» 21.6 »

- 16.4 » - 5.6 »
— 12. 0 » — 17.9 '

» 28.5 »

» i 7.2 »

- 10.7 •
- M-3 '

» 28.2 >
)• 16.4 •

- 6.4 »

— I 2.8 »

t 24.3 »
• 13-4'

+ 5- 5 V at
nb 1503.

3°

- 4.5 » 1 » 10.6 i

- 6.7 » - 7-7 •

* 8.0 •

- 7-1 •

> 8.0 >

7.2 »

* 5-5 •

I 10

I'.IKKI.I.AM'. 1111 NoK\Vl-.r,I.\N Al ROKA I'nJ.AKIS KXPKDITIO.V, I 902 '903.

TABU-; XVII Icontinuedl.

\Yilhclmshnveii

2-3 '•' I'- °. ' '/

+ 4^-° " » -'-'•» "

-•- 28.0 » » 23.8 »

4- 16.8 » • 20.3 •

\ . I. variometer
-(lowing little sensi-
tiveness. There is,
however, a slight
deflection in the
positive direction,
\vitli maximum at
i 1 1" 20"'.

San Fernando

TABU-; X\'I1 (continued).

<,r. M. T.

Munich

/'I: /',/ /Y Pi,

i'ohi

Ph

Pd

ft

h in

23 o

3.0 y K 5.0 y \'ery - 2.2 •/

K 7.6 y ~ 0.4 y

i.Sy E

i.gy

+ 0.5 y

15

4- 22. 0 " » 1 3-Q " sma''i a'" 4- 21.1 »

» 18.2 . o

4- 12.4 • ' \V

7-4 "

- 2.6 »

30

4 2 I .0 >l » 1 ^.O » 4- 20. 2 '>

» 18.8 » o

4- 10.8 » »

4.8 »

- 3-1 '

percep.

45

4- ,4.0- 22.5. (ib|e + [3.4 .

» 22.2 l> 2. 1 »

4- 14.1 » »

i . I »

- 2.8 »

24 o

- -'-5 » ' >K-° " The lorce °

. i8.8 » 1.7 .

4- 4.9 . E

4.6.

— I.O »

0 '5

- to.o )' » 15.) » is directed 6.3"

» I.T-6 » 2.5 J>

i .8 » ' »

7-4 »

o

3n

7.0 » » 0.4 » ItfiMll'fls. .^ ] ,

» O.Q » - 2.3 »

- 3-3 ' »

2.8 »

4- 0.5 .

TABU-; XVII (continued).

Dehra I Inn

•* /'d

The de-
2.9 y o

flection in
S.o » \V 7.8 v ,. .

' II is not

8-3 " 7-y " measur-

7.0 » » 5.9 » ! able here.
2.8 . . 2.q » 'There- are

i however
i . 5 » o

small irrc-
o

gulanties.

7-5
4.0

1 1.0 ')

8.3 .

6.4 »
3.2 »
o

o
E i .9 y

I Q »

» l .8 »

>' 1 .O »
1 .5 »

1 lie only niagnctoo-raiiis In. in Bombay arc for //. Tin- conditions of tin- ix-rturbation are similar
to those at Dehra Dun.

At Batavia the perturbation is noticeable, but very faint and ill-delincd, so that no perturbing force
can be determined.

PARTI. ON MAGNETIC STORMS. CHAP. II. Iri

Current-Arrows for the 10th February. 19O3; Chart I at 231' 15,,,, and Chart II at 231" 30m.

Fig. Si-

112 HIRKKI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1$O2 — 1903.

Current Arrows for the 10th February, 1903; Chart III at 23>> 45'", and Chart IV at 24i> .

fig. 52

PART I. ON MAGNETIC STORMS. CHAP. It. Iig

Chart. I. Time 2jh ijm.

The field of perturbation here shows itself to be of the typical form that is always to be found
during the polar elementary storms. The principal axis of the system falls, as shown by the chart,
along the auroral zone; and the storm-centre seems to lie a little nearer to Matotchkin Schar than to
the other Norwegian stations, though its position cannot be given more exactly. The rest of Europe
is in the vicinity of the system's area of convergence. Judging from the force at Pawlowsk, the point
of convergence itself should be situated a little to the north of that place. In America we again find
the usual directions for the current-arrows, namely, west at the three more easterly stations, and north-
west at Sitka.

Chart. II. Time 2jh jom.

The conditions are not essentially different from those of the preceding chart. The principal
axis of the system is more conspicuous in the forces at the Norwegian stations, where they are now
more or less of the same strength. It still lies along the auroral zone between Kaafjord and Axel-
een, and a little to the north of Dyrafjord and Matotchkin Schar, judging from the vertical intensities.
In the southern European stations, the forces are more or less uniform in direction with those to be
found on Chart I, except that at Pawlowsk there is a slight turn clockwise. The point of convergence
still lies a little to the north of the last-named station.

Chart III. Time a/1 45™.

The storm-centre seems to have moved eastwards, the force at Dyrafjord being considerably smaller
than before. At the same time the forces at the southern stations in Europe have turned considerably,
clockwise.

Chart IV. Time 24* om.

The forces have diminished considerably everywhere, as the close of the perturbation is now ap-
proaching. At the southern European stations, the turning is continued in the same direction as before,
so that the current-arrow is now directed distinctly southwards. In other respects, the form of the field
is in all essentials the same as before.

CONCERNING THE CAUSE OF THE PERTURBATION.

39. By reasoning as in the case of the perturbation of the I5th December, 1902, we here too arrive
at the conclusion that the perturbation at the four arctic stations is mainly due to the effect of a hori-
zontal current-system, which keeps fairly close to the surface of the earth in the area over which the
storm is most violent. In this case therefore, it should be mainly a horizontal current from Matotchkin
Schar to Dyrafjord. As it is more or less horizontal in this district, the direction of the current must
in a large measure coincide with that of the current-arrows drawn on the chart. It follows from the
vertical components, that the main volume of the current must flow north of Matotchkin Schar, passing
in a WSW direction between Kaafjord and Axeleen, and on to the north of Dyrafjord. This is in the
main the same course as that taken by the current on the i5th December.

We should mention, in this connection, that the earth-currents during this perturbation have been
very beautifully registered (see Part III, Earth-Currents). This is most fortunate, as this perturbation is
so simple in its course, increasing to a maximum and decreasing to zero. The earth-current, on the
other hand, as the curve shows, takes the following course. While the magnetic storm is increasing to
its maximum, the current flows in the same direction, increasing to a maximum and decreasing to zero;
during the second part of the perturbation, while decreasing, the direction of the earth-current is reversed,

Birkeland, The Norwegian Aurora Polaris Expedition, 1902 — 1903. 15

114 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

its volume increasing to a maximum and decreasing to zero. This furnishes a direct proof that the
primary cause of the perturbation is to be found in currents above the earth, since the current in the
earth is evidently an induced current produced by the magnetic storm. The latter must therefore have
its cause in a current-system above the surface of the earth, if, as may be considered certain in the
case of these perturbations, it is conditioned by electric currents at all.

Owing to the rapid weakening of the effect southwards, these horizontal currents must lie at a com-
paratively little height above the earth. The perturbations must be of a local character in the north, a
fact that is immediately apparent from the already-mentioned great variation in the nature of the per-
turbation from place to place. The perturbations in the southern districts are in strong contrast to
this, as they there show a slow, continuous change in their character.

The perturbations in the southern districts are not of such a character that they can be regarded
as the effect of adjacent systems; their cause must necessarily be sought in the average effect of that
which takes place in the more distant systems, a circumstance which explains the quiet, regular character
of the curve.

In discussing the perturbation of the I5th December from to some extent other points of view, we
arrived at the same result, as the explanation of the effect of the force outwards at great distances from
the arctic regions, must be sought in that of vertical currents in an opposite direction, connected with
the low-lying, horizontal portion of the current, which gave rise to the powerful perturbations in the north.

By a generally continuous movement of this system, the turning of the perturbing force is precisely
explained. On that day, the sphere of action in the north being more than ordinarily local, this move-
ment may be clearly proved by the fact that the perturbation made its appearance much later at Axeleen
than at Dyrafjord.

This perturbation is greater, and its influence is almost equally strong at all the four stations. It
commences quite as early in the regions about Matotchkin Schar as at Dyrafjord.

Thus, although we cannot prove, from the times at which the perturbation began in the north,
that there was any movement eastwards along the auroral zone, the current-arrows on Charts II and III
at Dyrafjord indicate that such a movement really took place there, as already mentioned in the descrip-
tion of the charts. Outwards there is also the same distribution of force and turning of the perturbing
force, as in the perturbation of the I5th December.

As we have said, the distribution of force at a'1 on that day answers to that at 23** 15™ on this
loth February. If we now imagine the system to be moving on eastwards, it will be easily seen that
the European stations would be passed by the magnetic field in a district in which the direction of the
perturbing force alters only slightly, and the turning would be with the hands of a clock.

In this perturbation the current-system may be assumed on the whole to have a more easterly
position than in that of the previous I5th December, in accordance with the fact that the latter appeared
later in the day.

The field of force on the surface of the earth indicates that our current-system should generally
have two symmetrically-situated points, the points of convergence and divergence, one on each side of
the horizontal portion of the current, for the horizontal component, two neutral districts in which the
horizontal component was very small.

We have not yet seen both these points during the same perturbation; for when one of them
is in Europe, e. g. in the neighbourhood of Pawlowsk, as we shall generally find it during the polar
elementary storms that have their storm-centre near our Norwegian stations, the other should be situated
symmetrically on the other side of the auroral zone, or in the most northern parts of Greenland.

During the perturbations of the i5th December and the loth February, we have found the area
of convergence, and during that of the gth December we have found the area of divergence. In our

PART I. ON MAGNETIC STORMS. CHAP. II. 115

researches on the storms of 1882—83 in the polar regions (Part II), we shall also sometimes find a field
on the other side of the auroral zone, that appears to indicate an area of divergence, at the same time
as the forces in the southern parts of Europe form an area of convergence.

This fully explains a circumstance mentioned in the description of the first part of the perturbation,
namely that Pawlowsk has a very small horizontal component considering the northerly situation of the
place. During the beginning of the perturbation, the direction of the current-arrow is almost the reverse
of that of the horizontal portion of the current. During that time therefore, the station ought to lie
nearer to the neutral district than later, when, owing to the movement of the system, the perturbing
force is turned more in accordance with the conditions in Central Europe.

In this perturbation also, the vertical components are very small in the regions outside the arctic
district, a circumstance that accords perfectly, as we have already said, with our explanation of the
perturbation, as those components should mainly be conditioned by the horizontal portion of the current.
In the vicinity of the neutral district, P, only should be of considerable size in proportion to /*,. At
Pawlowsk there is actually a considerable vertical component directed upwards all the time. In the
cases of Potsdam and Pola, it is much smaller, but directed upwards; and at Val Joyeux it is almost im-
perceptible.

THE PERTURBATIONS OF THE 30th & 31st MARCH, 1903.

(PI. XXI).

40. For the study of these perturbations, we have magnetograms for the horizontal intensity and
declination from all the stations marked on the chart with the exception of Matotchkin Schar, where, on
that day, the registering apparatuses were not acting. The declination-curve for Bombay is also wanting.
The observations from Ekaterinburg and Irkutsk are only for every hour; and as the perturbation is
short, there will here be little use in taking out intermediate values.

At Bossekop, the needle in the variometer for horizontal intensity during the perturbation was
deflected out of the field, and did not return. The perturbing force here can only be taken for the first
part of the perturbation.

In addition to the horizontal intensity and declination curves, there are also vertical intensity curves
for the Norwegian and some other stations.

The time during which this violent perturbation is acting at the Norwegian stations is very short.'
The deflections, moreover, are uniform in direction. The character of the curve in the north is as usual
very disturbed, and varies greatly from place to place, indicating that the current-systems that condition
the phenomenon here, must come comparatively near the earth.

Simultaneously with this exceedingly powerful, brief storm round the Norwegian stations, distinct
perturbations are noticed at all the observatories from which observations have been received. The
curves immediately show that the perturbations outside the arctic district are of a universal character, as
the form of the curve remains very nearly constant over large districts, and the transition takes place
gradually - - conditions with which we meet in most of the polar storms.

It will be seen from the magnetograms from the districts visited by this perturbation, that in advance
of this elementary storm in the north, there is a long perturbation that is especially powerful and distinct
at the stations near the equator, and occurs chiefly in H. We also note the jagged character of the
curve, and that the serrations occur simultaneously all over the earth. That the perturbation between
24'' and 2h is connected with that in the north is probable from the fact that it then rather suddenly
becomes comparatively powerful in D, and also that the horizontal intensity curve oscillates greatly at
this time. The perturbation moreover becomes more powerful with an approach to the northern stations.

n6

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

The perturbation in H which precedes this, is on the contrary, as already stated, well developed and
powerful southwards towards the equator.

We may therefore safely assume that we here have two phenomena to be dealt with, one connec-
ted with the storm in the north, and before it an equatorial perturbation of a kind similar to that of the
26th January, 1903.

The placing of the normal line on the magnetograms has occasioned no special difficulty. The
storms are fairly powerful and well-defined at all the stations with the exception of Christchurch and
Honolulu ; the perturbing force can therefore be taken out with very satisfactory accuracy. The following
circumstances are taken into consideration in the drawing of the normal line. In declination the condi-
tions are simple, as there the perturbation is of short duration. The quiet parts before and after the
perturbation are connected in such a manner that the form of the curve corresponds with that at the
same hour on the nearest calm days. The conditions in the horizontal intensity are somewhat more
difficult, as there, as we have said, there is a long perturbation in front of the one under consideration.
In this, judging from things in general, the curve for most of the stations is normal at about 3h, and
for an hour afterwards. The absolute distance of the normal line from the base-line on the magneto-
gram will thereby be determined; and its further course is regulated by the nearest calm days.

THE EQUATORIAL PERTURBATION.

41. As early as I9h, those little, sudden, very variable perturbations are noticed, which occur simul-
taneously all over the earth, and symmetrically as regards the magnetic axis. It will be seen from the
copies of the //-curve that the conditions at Dehra Dun, Batavia and Honolulu entirely correspond with
one another. The force is mainly directed northwards. The perturbation appears to be over at about
23h i2m. From 2ih 28m to 23'', the force remains almost constant both in magnitude and direction. The
perturbing forces are calculated for 22h, and the corresponding current-arrows are marked upon the chart.

Current-Arrows for the 30th March, 1903, at 22h .

Fig- 53-

PART I. ON MAGNETIC STORMS. CHAP. II. 117

We here distinctly see that except as regards the arctic stations, one circumstance is very conspi-
cuous, namely, that the perturbing force is strongest in the equatorial regions, and decreases towards
the poles. Honolulu is an exception to this; but, as mentioned under the perturbation of the 26th
January, this may be ascribed to local conditions. The arrows point along the magnetic parallels from
west to east.

In the arctic regions, especially at Dyrafjord, the conditions are different, owing to polar distur-
bances. In these regions, indeed, there is hardly ever calm. The distribution of force, and the pertur-
bation as a whole, are of exactly the same character as that of the 26th January; we therefore refer
the reader to the description of the latter, for its most probable explanation.

At about 23h I2m, after this equatorial perturbation has ceased, comparatively normal conditions
appear to supervene, at any rate in latitudes lower than 60°; and these are maintained for three quarters
of an hour. At the stations nearest to the equator, however, there is now a distinct deflection in H to
the opposite side. There is thus now for a time a slight equatorial perturbation, corresponding to a
current-system resembling the previous one, but in the opposite direction.

THE POLAR PERTURBATION.

42. The storm about the auroral zone is very powerful and well-defined, especially at Dyrafjord,
where it appears very suddenly at oh 24™, and concludes almost as suddenly at 2h i6m.

At Axeleen the perturbation is observed a little earlier, but the really powerful storm nevertheless
commences later here than at the other arctic stations.

At Kaafjord the perturbation begins very much earlier than at the two previously-mentioned stations,
especially in H. As early as 23h, the deflections in H begin to increase continuously. At oh 24™,
that is to say at the same time as the storm at Dyrafjord begins, the point of light swings out of the
field, to return no more. The reason of this great deflection must partly be that at this hour the sen-
sibility was made very great, the magnet being suspended by a thread with small moment of torsion.
But if otherwise, on this occasion, the apparatus acted properly, it would at any rate appear that the
perturbation began with a low-lying current about Kaafjord, which then developed further into a more
extended system, at the same time moving northwards. That the system really moves in a northerly
direction seems also to be shown by the very interesting vertical intensity curve at Kaafjord; for at
about oh 36™, Pv, from being directed downwards, turns upwards, corresponding to the flowing of the
horizontal portion of the current past the place from south to north. The curve exactly resembles that
in the lower diagram in fig. 40.

The fact that the point of light does not return - i. e. that the magnet goes round to another
position of equilibrium prevents our concluding very much from this circumstance; for it is not

impossible that the enormous deflection is partly due to the almost neutral equilibrium of the apparatus
over a large area.

At about 23h 50™, the effect of the polar perturbation is noticed at all the southern stations
throughout the world. At 2h iom, the normal conditions have reappeared in these latitudes.

In this, as in so many other instances, Christchurch occupies a peculiar position, inasmuch as con-
ditions appear there, which have no parallel in the northern hemisphere. A distinct perturbation is also
observable there, however, which to some extent coincides with the perturbation in the northern hemi-
sphere, which it also resembles in its course. At the three American stations, Toronto, Cheltenham
and Baldwin, a peculiarity is observable, namely, that the perturbation apparently lasts longer in H
than in D.

u8

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

In declination there is a brief, well-defined, powerful perturbation, which takes place at the time
when the storm about the auroral zone is at its height. In this case it lasts from oh 12™ to i1' i6m.
In reality this only means that the perturbing force has turned. A similar condition was observed on
the I5th December. These two perturbations on the whole resemble one another in a striking degree,
a circumstance that is undoubtedly connected with the fact that they both occur at about the same time
of day.

Observatory

Time of Max.

/', (max.)

Observatory

Time of Max.

l\ (max.)

li in

h in

Uyrafjord . . .

o 58

546 /

Pawlowsk .

o 30

41.1 •/

Axeleen

o 50

380 »

Val Joveux

o 30

38.4.

Toronto . . .

0 39

65-5 »

Munich ....
Pola

o 37
o ^o

33-4 *
^O.T »

Baldwin . . .

° 39

39-7 '

San Fernando

o 37-5

26.6 »

Sitka ....

° 45

22.O »

Io 23

I6.5 •

Honolulu . . .
Wilhelmshaven .

o 58
o 30

12. 1 »
63.0 •

Tiflis ....

°45\
i of

16.3 «

Stonyhurst
Potsdam . . .

o 30
o 30

47.8 »
45.8 »

Dehra Dun . .

j° 3°
I i IS

16.5.
16.3 »

Kew ....

o 30

41-5 •

Zi-ka-wei .

I O

15.1 »

Batavia ....

o 30

IO.S »

THE DISTRIBUTION OF FORCE.

43. In the above table the time of the maximum of the horizontal perturbing force is given as
the value of Pt (max.) at that time.

The maximum occurs, strangely enough, earliest at the European mainland stations, where it is
very distinct and well defined. At Tiflis and the Asiatic stations, the force remains for some time almost
constant in magnitude. At oh 39™ the maximum occurs at the three American stations; and last of all
it occurs at the northern stations, together with Honolulu and the Asiatic stations.

The earlier occurrence of the maximum on the continent of Europe and in North America than at
the source itself round the auroral zone, is a peculiar circumstance that, regarded superficially, might
lead to the belief that the phenomena in the arctic regions were separate from those in more south-lying
districts. We shall return to this subject later.

The maximal force, as we see, is strongest at Dyrafjord, where it attains the rather unusually large
value of 546 y. The table clearly shows that the force increases with proximity to the district about
this station, independently of the direction of its approach.

After the arctic district, the force is greatest at Toronto, where it attains the comparatively large
value, 65.5 y. On the whole, this perturbation is stronger at Toronto and the two stations in the United
States than at the European stations, as will best be seen from the charts.

Next to Toronto comes Wilhelmshaven, which thus, on this occasion also, occupies a comparatively
prominent place, a circumstance to be accounted for by local conditions (see the zoth February, 1903).

The perturbing forces are calculated for a series of times, given in the table, and are synopti-
cally represented by a number of charts. As the reasons which led us, on the 15th December, to our
assumption of the current-system, are also present in this case, we will, in describing each separate chart,
compare the field of force with our current-system.

PART I. ON MAGNETIC STORMS. CHAP. 11.

TABLE XVIII.
The Perturbing Forces on the 3oth & 3ist March, 1903.

Gr. M. T.

Honolulu

Sitka

Baldwin

Toronto

Cheltenham

ft

Pd

ft

Pd

ft

Prf

P*

Pd

Pk

Pd

li m

22 O

+ 9-2 7

+ 5-° 7

0

+ '3-97

0

+ 9.07

o

4- 12.07

o

0 0

— 2.42 »

+ 5-3 •

W 9.00 7

- 7-3 »

0

- 8.5.

W 4.87

- 6.5.

W 1.777

7-5

- 5-33 »

- 6.5.

» 1.80 »

— 12.2 »

0

- 10.8 •

» 6.7 »

- 9-9 •

• 4-i3"

19

- 7.50 »

+ 3-5 '

» 7.20 »

• 7.8»

E 3.78 7

- 6.7.

E 1.2 »

- 6.4.

E 4-'3 •

22.5

— 6.29 »

No per-

4- 8.1 »

« 9.90 »

- g.O •

• 17.01 »

— 12.6 »

» 30.3 •

- 1.9 »

> 34.19 >

3°

- 6.05 •

turbation j " 5-3 *

• 5.85 »

— 16.4 »

» 30.24 »

- 17.1 »

• 55-8 •

- 2.8 »

» 46.61 »

37-5

- 8.95 »

observable 1 — 19.4 »

E 0.90 * ' ' — 19.8 » » 34.65 «

- 18.4 »

» 63.0 »

- 7-5'

" 49-56 »

45

— 10. 16 »

in de-

— 21.0 • ; W 1.35 > — 24.0 » » 28.98 »

— 22.9 »

» 5i-5»

— 12.2 »

• 42.48

52.5 —10.89 >

clinatio.

- 18.8 »

» 4.50 » '; — 21.9 i

• 30.87 »

— 18.0 >

• 46.3 »

- 14.2 •

" 37-76 »

1 0 i — 12. IO »

— 22.1 »

' 1-35 »

— 19.2 »

« 17.01 •

- 18.4 »

» 3i-5 »

— 9.9 »

» 23.60 •

15 - 6.78 »

II — 19.2 »

W r.89 »

— 18.9 »

W 3.0.

- 19-9 '

o

30 - 2.66 »

From ih to ah ,
the curves have

- 17.1 »

' 5-°4i >

— 19.8 »

» 6.1 *

— 19.6 »

W 2.36 »

45 °

not been drawn.

» 5.04 »

- 15-3 "

• 5-5*

— 14.6 >

' 3-54 •

20 0

- 8.7,,

» 2.52 »|| — n.i »

o

— ii. a »

» 0.59 »

TABLE XVIII (continued).

Gr. M. T.

Dyraljord

Gr. M. T.

Axel0en

Bossekop

Ph

Pd

P,

Fh

Pd

Pt

Ph

Pd

P,

h m

h in

22 O

- 25-07

W 8.57

- 7-77

22 O

+ 9-47

o

o

9

?

9

00 0

o

+ 38.3 »

O O

4- 20.7 >

W 9-07

0

- 3527

O

- 34-97

15

+ 8.3.

o

+ 45-4 •

7-5

+ II.O »

o

o

- 343"

0

- 4°-5 "

30

- 99-7 •

E 45-i »

4- 46.4 »

15

4.6 »

E 5-4 »

o

- 477 •

E 7-57

- 53-4 »

45

- 443-2 »

» 208.2 »

+ I55-I »

22.5

- 16.1 »

» 28.3 »

+ 12.37

9

» 38.1 i

- 24.4 •

52-5

— 482.0 »

» 65.9 >

+ 258.0 •

27

?

• 45-9 '

+ 19-9 •

I O

- 565-1 "

• iai. 5 »

+ 337.4 »

3°

— 21 I »

55-8 »

+ 36.8 .

9

» 18.8 »

0

7-5

- 515-2 •

• 31.2 •

4-263.2 t

37-5

- 3r-3 •

> 108.8 »

4-110.5 »

9

W 23.4 .

- 309.4 '

15

- 398.9 •

» 27.8 »

•4- 160.0 »

39

9

> 48.8 >

— 302.4 •

22.5

— 382-3 •

W 12. 1 »

4- 72.2 «

45

- 75-o »

» >i63.2 »

4-187.0 »

?

E 4'-3 »

— 172.8 •

3»

— 243.8 »

O

-t- 23.2 •

52.5

— 186.0 »

• >i63.2 »

?

» 76.9 »

— 150.1 •

45

- 138.5 •

» 15.6 »

+ 5-2 »

54-7

— 223.0 »

• 163.2 »

4-162.0 "

?

2 O

— 72.0 »

o

+ 4i-3«

I O

— 163.0 »

» 121.3 "

+ 157-0'

?

• 93-8 '

— 134-3 •

° 59

- 637.1 •

K 104.1 »

4-242.5 »

7-5

— 189.0 »

84.3 »

4-127.5 •

9

• 91-3 »

- i IS-2 »

o 42.7

- 382.3 »

• 255.0 »

+ 2II.6 »

15

— 169.0 »

» 87.0 •

4- 157.0 •

9

• 66.6 »

— 136.1 »

22-5

— 150.0 »

• 125.1 »

4-127.5 .

?

» 51.0 »

-147-5 "

3°

— 115.0 *

» 68.0 »

4-II0.5 »

9

. 43.1 .

— 1 29. 1 •

45

- 80.5 •

» 42.2 >

+ 73-5 »

?

• 34-7 •

— 89.0 »

2 O

- 47-9 »

• 43.4 »

+ 73-5 »

?

> 28.1 >

- 75-° *

15

- 3°-8 »

» 35-4 »

-t- 49-2 •

30 - 11.5 »

» 28.8 »

+ 39-3 •

I!

There are no observations from Matotchkin Schar for this date.

120

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE XVIII (continued).

Cr M T

Pawlowsk

Stonyhurst

Kew

Val Joyeux

\jf. Wl. 1 .

ft

ft

ft

ft

ft

ft

ft

Pd

ft

b in

22 O

+ 7-87

o

+ 8.77

o

- 6.6/

o

412.07

0

0

O O

- 5-5 »

E 2.3 /

0

E 4-3 /

- 3-1 •

E 4-5 y

- 3-2 «

o

4 1.87

7-5

- 7.0 »

» 6.9 >

- 7-7 »

» 8.8 »

— IO.2 «

* 8.7 »

- 8.0 »

E 5-97

•+- 2.3 >

15

— IO.I >

3 4'6 *

- 8.4.

» 8.6 »

— IO.2 »

» 2.3 »

- 9-7 •

» 8.4 »

4 1.8 »

22.5

— 25.2 »

W 11.51

— 2.6 »

W 19.7 »

- 3-" •

W 23.7 «

— 10.5 »

W n.8 »

4 1.4 >

3°

— 32.2 •

• 25.3 .

4- 6.6 >

» 47.9 >

4- 7.4 »

» 41.0 »

o

« 38.6 »

o

37-5

— 9.0 •

• 33-1 "

4- 14.31

» 35-4 "

4 13.8 »

, 30.9 »

+ 9-7 •

• 35-7 »

- 1.8 »

45

+ 7-5'

» 23.0 >

4-13.8.

» 11.4 »
F fi o »

+ I5-3 '

> 8.2 »

E 8.2 »

4-i6.a *

» 17.1 »

- 4-5 »

52-5

I 0

+ 7-5 '

E i.o »

4 9*2 *
o

C. "'O

» 12.5 »

~r 1 2.*y "

4 4.6.

» 15.9 >

4-12.2 »

E 8.6.

5.0 »

- 3-6 '

ID

4 S-o »

» 21.2 »

- 5-6 »

• 17-7 •

- 4-i »

» 16.8 «

4- 3.2 »

» 16.7 «

- 2.7 »

3°

4 i-5 »

» 16.1 »

- 5-6 >

» 12.0 »

- 5-1 »

» 12.3 »

- 4-i •

> 12.2 »

- 2.7 .

45

- 1-5 '

» 12.9 >

- 5-i '

» 6.6 »

- 6.4.

» 7.3 >

- 3-2 »

» 8.4 »

- 1.8 »

;

2 0

-(- I.O »

» 9-2 »

- 3-6 »

» 6.3 •

— 5-- »

• 6.4 »

- 1.6 »

« 6.7 »

- 1.4 »

TABLE XVIII (continued).

Gr. M. T.

Wilhelmshaven

Potsdam

San Fernando

ft

Pd

ft

Pi,

Pd

ft

P*

Pd

b m

22 0

4 7.97

o

0

+ 12.6 V

0

o

+ 13-77

0

o o

- 3-3 >

E 1.27

- 2.5 y

- 3-48 »

E 2.54 7

4 2.7 »

— 10.4 t

O

7-5

- 9-3 »

» 7.2 »

— 3.0 »

— 9.0 »

» 5-6 »

4 2.7 »

— 14.8 »

O

15

- 7-9 '

» 9-°5 *

— 2.0 •

- 8.22 »

• 3-56 »

4 2.7 »

— 16.2 »

o

32.5

— 19.6 •

W 25.9 »

— 2.0 «

— l6.I2 r

W 20.3 »

+ 4-5 «

- 6.6 »

W 13.37

3°

— 22.5 »

. 59.1 »

- 3-o »

-15.48 »

• 43.2 »

4- S-2 •

4 16.2 »

» 15 '

37-5

o

» 44.6 »

- 5-° "

4 5-69 »

» 34-o »

- 1-5 »

423.7 "

» 14.9 »

45

416.4 "

» 13.9 »

— 2.O »

421.5 *

» 13.7 »

- 5-9 •

+ 25-5 *

» 7-5 '

52-5

421.5 "

E 6.03 »

- 4.0 »

4 24.96 t

E 4-5 »

— 6.0 »

422.2 »

E 5.0 »

I 0

415.4 »

» 18.7 •

— 3-° »

418.64 »

» 1 1. 2 »

- 3-4 »

4 14.1 »

• 5-8 »

IS

4 1.4.

» 24.1 »

— 4.0 »

4 6.32 »

» 17.8 »

- 3-3 *

4 3.7.

» 6.3 »

3°

- 5-i »

1 15-7 *

— 4.0 y>

0

» 10.2 »

— 2.1 »

- 3-°'

?

45

- 6.5.

» 7.85 »

- 4-5 »

O

» 6.4 »

- i-7 '

- 3-7 •

?

2 O

- 5-i '

» 6.6 »

- 4-5 •

o

• 5-6 »

- i-5 »

— 2.2 »

•p

t>ART I. ON MAGNETIC STORMS. CHAP,

121

TABLE XVIII (continued).

Gr. M. T.

Munich

Pola

Tiflis

Pi:

Pd

/',

£

Pd

/',

Pk

ft

Ft

h in

20 o

+ 9.87

0

o

+ 7.67

o

o

4- 9-5 /

o

0

0 0

- 5.0 »

E 3.87

4- i.i 7

- 4-5"

E 3-4 /

4- 1.7 7

— 8.6 »

E 1.87

+ 3-87

7-5
i ^

- 8 s »

• 4-5*
» 6.8 »

+ i-5*

— 9.0 »

— Q r »

• 5-5 »

+ 2.5 »

-13-3 •

» 5.6 »

4- 3.8 »

1 D
22.5

°o

- 7-5 *

W 3.8»

4- 1.7 »
4- 2.3 »

°-3 *

- 7.6 »

W20.8 •„

- 4-2 »

— '5-9»

» 4-4 •

+ 3.6 »
4- 3.6 »

3"

— 3.0 »

» 27.8 »

+ 2.8 >

0

" 3°-5 •

- 4.0 l

— 11.3 s

W 4.1 »

+ 3-3 »

37-5

-+• 6.0 »

» 33-o »

+ 2.3 •

+ 5-8 »

» 22.2 •

- 0.8 »

- 7.1 »

» 12.2 »

4- 2.3 »

45

+ 16.5 •

» 23.2 •

4- 0.8 »

4-14.8 »

» 7.6 »

4- 1.9 '

o

» 16.3 >

- 0.5 »

52-5

+ 18.5 »

» 5-3 •

0

4 14.8 »

O

4- 3-6 »

4- 6.6 i

> '3-9 >

— 1.9 »

I 0

+ 14-5 •

F- 4-5 •

0

4- II. 2 >

E 1 1. 1 »

-1- 3-1 '"

+ 11. 1 »

» 10.4 >

- 2.8 »

15

4 6.0 »

» 14.2 »

0

4- 4.0 »

» 13-9 >

•4 1.9 »

+ 10.6 »

E i.i »

- 2.8 »

3°

4- 1.7 »

* 1 1.3 »

o

0

> 9.0 »

0

+ 5-3 »

» 4.8 »

- 1.3 »

45

o

7-9 »

o

o

» 4.1 »

o

4- 2.2 »

» 4.1 »

0

2 0

o

» 5-2 "

0

0

» 3-4 '

0

+ 0.9 »

8 3-3 »

0

TABLE XVIII (continued).

Gr. M. T.

Dehra Dun

Bombay

Zi-ka-wei

Batavia

Christchurch

PA

Pd

/'/,

Pd

P,

Pi,

ft

Pk

Pd

h m

22 O

+ I3-4/'

o

+ '7-37

°

+ 16.07

0

+ 4.17

O 0

— 12.6 »

0

There is

- 5-4 •

W 2.07

From _ 8 9 „

E 4-87

- 8.7 »

7-5

-15.4 »

0

only Pi,
for this

- 6.6»

• 5-5 »

10 a. m. to
2 p.m.,

— 12.8 »

> 3-6 »

— 10.6 >

:5

-15-7 "

0

date, but

— 9.0 •

• 5-° *

there is ] — n.o »

» i. a >

- 11.5 »

22.5
3°

— 16.5 »
-15.7 »

W 1.57
» 4.9 «

in that the
perturba-
tion is dis-

— 9.6 »

- 7.8 :-

» 4.5 .

• 4-5 »

little in-
crease in
vertical

— 10.7 »
— 10.7 "

o

(o?)

- 1 1-5 »
— 11.5 "

No per-
ceptible

37-5

— 9.0 »

• 9-3 •

tinct,

- 7.2 »

• 70 .

intensity.

7

9

- 16.1 »

perturba-
tion.

with a

Its maxi-

45

- 3-9 "

» 12.3 »

course si-

- 3-6 »

" 7-5 "

mum at

- 8.9 i

» 2.4 >

- 17-5 >

52.5 4- 2.0 * > 14.7 »

milar to

o j » 10.5 »

noon

- 3-6 »

» 4.8 >

— 17.2 »

I 0

4- «.!!

» 12.8 »

that at

+ 10.2 >'

» 1 1 .0 »

amounted

- a-5 »

» 2.4 »

- :6.6 >

Dehra

to

15

+ II-4 »

» n.8 »

Dun.

+ IO.-8 »

• 7-5 »

5-83X107

+ 5-7 '

» 2.4 »

- 7-4 »

3°

4- 7.9 •

» 8.9 >

+ 10.8 »

» 6.0 i

+ 4.6 »

» 1.8 »

— 1.4 »

45

-+- 4-3 "

» 6.9 1

+ 10.3 »

» i-5 "

+ 3.8 »

> 1.2 »

+ 3.2 »

2 0

4- 2.8 »

» 4.9 »

+ 8-4 »

o

0

+ 7.8 »

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903.

1C.

122 BIRKELAND. THE NORWEGIAN AURORA 1'OLARIS EXPEDITION, 1902 — 1903.

.Current- Arrows for the 31st March, 1903; Chart I at Oh 15m, and Chart II at Oh 30"'.

Fig- 54-

PART I. ON MAGNETIC STORMS. CHAP. II.

Current-Arrows for the 31st March. 19O3; Chart III at Oh 45'", and Chart IV at I1' Om.

123

Fig- 55-

124 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Current-Arrows for the 31st March, 1903; Chart V at I1' 15'", and Chart VI at I1' 30m.

Fig. 56-

PART I. ON MAGNETIC STORMS. CHAP. II. 125

Chart I. Time o1' //'" .

In the regions nearest to the equator, the current-arrow points from E to W, while in Central and
Southern Europe it has a more southerly direction.

The northernmost stations differ greatly in this respect, the conditions at Kaafjord, in particular,
being quite peculiar. If the perturbation really has attained to such magnitude by this time, it must be
the result of purely local occurrences, or rather, the effect must be so strong on account of the proximity
to the currents that bring about the phenomenon.

Leaving the most northerly stations out of consideration, the force is strongest at the equator.
From this we may conclude that we still, at this hour, have to a great extent the effect of the previ-
ously-mentioned equatorial perturbation, which commenced at 23** I2m, and which had a current-system
the reverse of that shown on the chart for 22h om.

In the period under consideration, what we are concerned with is thus a slight equatorial pertur-
bation together with the incipient polar storm.

Chart II. Time oh jom.

The effect of the polar storm is now altogether predominant. In Europe the current-arrows have
already reached their maximum by this time. The directions of the arrows in Europe and the United
States show distinctly that the field of force for the horizontal component has a point of convergence
that is situated somewhere in the North Atlantic, probably a little south of the point of Greenland.
There, according to our assumption with regard to the cause of these perturbations, the horizontal force
should equal 0. We notice also the direction of the current-arrows at Toronto and in the United States,
converging as they do to a point in the north of Labrador.

On the whole we may say that outwards the field is explained by the assumption that the current
with negative particles descends towards the earth in the direction of the north of Labrador. It then
turns off almost along the auroral zone, and leaves the earth in the district between the southern point
of Greenland and Iceland. Judging from the form of the outer field of force, the current-system should
have its centre at the southern point of Greenland, or a little to the west of it.

If we look at the conditions in the vertical intensity, we should expect, if this were the only
system, to find P, negative at all the stations in Europe and Asia, or possibly zero at certain places.
On the contrary, however, we find that at several places there are positive values of Pv, e. g. at Pots-
dam, Val Joyeux and Tiflis; while at Pola and Wilhelmshaven they are in the opposite direction. The
conditions at Bossekop, moreover, at these hours, are rather peculiar in the two components that we
have ; for just before, these two turn round in the opposite direction, and Pd remains for a time in a
westerly direction, and P, for a shorter time positive. This opposite deflection takes place slightly
* earlier in the vertical intensity than in the declination. The forces otherwise are so strong that they can
hardly be explained by this system alone. Other perturbing causes seem to assert themselves, but of
what kind it is impossible to determine, as nothing can be concluded as to the conditions in the horizon-
tal intensity. It is possible that these two circumstances are connected with one another ; but as we have
said, the data necessary for the determination of this question are wanting.

Chart III. Time oh 45™.

The storm has now also become powerful at Axeleen, in fact it is at its height. The arrows in
the western hemisphere are about the same in direction and size as in the preceding chart. The arrows in
Europe, on the other hand, have made quite a considerable turn clockwise. The perturbing forces at
Dyrafjord and at the stations in England, Germany and France, have the reverse direction, and point
downwards towards the same point. The central point of the system must thus be situated somewhere

126 B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

to the south-east of Dyrafjord, almost in the south-east of Iceland. The point of convergence must lie
somewhere in the regions between Iceland and Stonyhurst, probably nearer the latter station, as the
force there is so small.

Taking for granted the point of convergence, the horizontal force should first increase along
the transverse axis of the system from 0, and then slowly decrease; and we do indeed find that the
force increases from Stonyhurst towards Munich, Val Joyeux and San Fernando, and then becomes
smaller towards Tiflis and Dehra Dun. The change, moreover, corresponds fairly well with that which
we find in the two calculated systems in Table XV, where the horizontal part of the current lies at
a height of 300 km.

The vertical components at Val Joyeux, Wilhelmshaven, Potsdam and Pawlowsk are all directed
upwards, just as we should expect. At Pola there was earlier a fairly considerable vertical component
directed upwards; but it now about equals 0.

Chart IV. Time /'' om.

The arrows in Europe and Asia have continued to turn. In the United States also, the arrows
have now turned a little. The alteration in the field is fully explained by the assumption that our
current-system has moved a little farther in the direction from Dyrafjord to Axeleen.

The directions of the arrows in Europe show that the point of convergence of the horizontal
components ought now to be found a little to the north of Pawlowsk. At Pawlowsk, as we should
expect from its lying near the point of convergence, PI, is exceedingly small, only 7.5 y; but on the
other hand Pv = 14 y, and is directed upwards.

At Tiflis and Potsdam, P, is directed upwards, but is rather small. At Wilhelmshaven, Pt = o.
At Pola, a small force is directed downwards.

It is in harmony with our assumption that we also find a larger horizontal force south of Pawlowsk
than at that station itself. It is greater even at Dehra Dun, Irkutsk and Zi-ka-wei. At the last-named
station, Pt = o. It appears from the vertical forces at our stations, that the principal axis of our
system should lie to the south-east of Dyrafjord and Axeleen, as P, is there directed downwards. At
Kaafjord, however, we find Pv directed upwards, which also indicates that the axis lies between the two
first-named stations and the latter.

Chart V. Time ih 15™.

The current-arrows in the United States are turned so that their direction is now about west,
answering to a southward direction of PI,.

In Europe, PI, is turned farther in the same direction, and is now directed eastwards. The field
during this period resembles that at the conclusion of the perturbation of the isth December, or those
of the 22nd March and loth February.

At Pawlowsk there is still a considerable vertical component directed upwards. The point of
convergence should now have moved farther east.

Chart VI. Time ik jom.

The distribution of force is as in the preceding chart, but the forces are much smaller. In the
case of the European stations, the turning is continued a little.

During this great but gradual alteration in the outer field, the conditions at Dyrafjord and Axel-
een, notwithstanding small local irregularities, have remained very constant. At both stations the current-
arrows have been directed all the time south-west; and the vertical component all the time has been
directed downwards. At Kaafjord, on the contrary, the vertical force has been directed upwards all the
time, with the exception of a short time at about oh 28™, and attains a magnitude of 209 y.

PART 1. ON MAGNETIC STORMS. CHAP. II.

I27

This circumstance, together with the fact that the effect at the side, at right angles to the current-
arrows, ceases before very long, can only be explained by the assumption of a comparatively low-lying
horizontal part of the current, which passed between Axeleen and Kaafjord, and a little to the south of
Dyrafjord. This horizontal part of the current forms the connection between the upward and downward
flowing vertical currents. Perhaps at about oh 28m, the current has passed south of Kaafjord, but has
then turned off over this place to take up the above-named position. The curve for P, at Kaafjord seems
to indicate the transverse passage of the current over this place at the beginning of the polar perturba-
tion. We have seen, moreover, that the field may always be assumed to have been produced by a
system such as this, which, in order to explain the variation of the field with time, must be supposed
to be moving eastwards along the auroral zone (see the perturbation of the I5th December).

We have mentioned the remarkable fact of the maximum occurring earlier in Central and Western
Europe and the United States than at the arctic stations. This is a necessary consequence of our
assumption, At oh 30™, when the perturbation is at its height on the continent of Europe, these stations
lie considerably to the east of the point of convergence, which, on account of the direction of the forces,
must be looked for in the region of the North Atlantic. Owing, however, to the movement of the system,
the stations on the mainland of Europe, at the time the perturbation in the north is at its height, will be
situated in the neighbourhood of the neutral area. This same movement of the system will also cause
it to withdraw farther and farther from the American stations. This again will cause the maximum of the
perturbing force at these stations to occur before the time at which the current-strength of the system
has reached its maximum. This displacement must be greatest at those stations which lie nearest to
the current-system; and this we also find to be the case. The displacement, as will be seen from the
table, is less at Sitka than at Toronto ; and at Honolulu it is imperceptible, as the time of the maximum
coincides with that at the northern stations.

While this perturbation was going on, remarkable aurora was observed, and earth-currents were
registered at Kaafjord. These will be discussed under the special treatment of these phenomena.

THE PERTURBATIONS OF THE 22nd MARCH, 1903.

(PI. XX.)

44. The perturbation of the 22nd March is in reality, like that of the 3151 March, composed of two
principal phenomena, an equatorial perturbation and a short, well-defined, comparatively powerful elemen-
tary polar storm. As the equatorial one is rather slight, it will not have a greatly disturbing effect
upon the polar storm, of which the properties can therefore be fairly accurately determined. As it is
the polar storm to which, on account of its simple course, we have especially turned our attention, we
have thought it best to class it among the polar elementary storms.

THE EQUATORIAL PERTURBATION.

45. This perturbation begins quite suddenly at 12'' 58™, with an oscillation that is noticed simultane-
ously all over the world. In the equatorial regions, this sharp deflection is uniform in direction, and
appears principally in H. About the auroral zone the curve oscillates, and the perturbation is notice-
able both in D and H. This first oscillation is shown on

Chart I, at ijh 4™,

which is the time when it reaches its maximum. About the equator the arrows are comparatively large,
and run about parallel with the magnetic equator. In the south and centre of Europe, the current-arrow
points considerably towards the north, as compared with what is generally the case during these

128 BIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

equatorial perturbations. At Kaafjord also, the direction of the arrow is in accordance with the rest of
Europe, but the force is somewhat greater. At Dyrafjord and Axeleen we find a peculiar circumstance,
namely, that in the course of a few minutes the force oscillates very violently. A number of arrows
are placed upon the chart, answering to various hours, the scale being the same for the southern stations
as for the northern. At Dyrafjord, the current-arrow makes a negative turn of about 180° from SW
to NE. At i3h 4'", the direction of the force is uniform with that of the arrows in the south of Europe.
At the same time, the arrows on Axeleen turn from S in a positive direction, until at 13'' 7™ they
point NE as at the other European stations.

We will not here attempt to give an explanation of this peculiar circumstance, but will only say
that this turning in different directions at two places so near to one another, must necessarily lead to
the conclusion that in the north at any rate, the perturbation is to some extent of a local character.

We thus see that while there is a current that acts powerfully and almost symmetrically on both
sides of the equator, there will be exactly simultaneous perturbations of a local character in the north.
These currents in the north, which are very slight, cannot, on account of the extent of the perturbation,
be the cause of the perturbation as a whole; for, as we see, the force diminishes from the poles south-
wards as far as Tiflis and San Fernando, whereupon it increases, and even at Christchurch is great.
In the vertical intensity this first oscillation is noticed, in southern latitudes, only at Tiflis, where it
indicates a force directed upwards. The reason why it is not felt at Zi-ka-wei can only be that the
sensibility there is so small; but on the other hand, it seems stranger that nothing is noticed at Pawlowsk
and Pola, where the sensibility is fairly great.

After the first deflection, the equatorial perturbation continues with a small deflection in H, answer-
ing to a perturbing force directed northwards along the magnetic meridian. Judging from the character-
istically serrated appearance of the //-curve in low latitudes, the perturbation seems to last until the
polar storm is over, or from about iau 57"" until midnight.

The distribution of force, as it is on the whole maintained on account of this equatorial perturba-
tion, is shown on

Charts II and III, for //* om and /p* /om .

The current-arrows in somewhat more southern latitudes lie, as we see, almost parallel with the
magnetic parallels, and the force there is comparatively great. We notice that the force at the Central
European stations varies greatly in magnitude. We must not, however, immediately draw conclusions
from this circumstance; for it may be accounted for partly by the difficulty there is in determining the
normal line for so long an interval, and partly by the fact that, owing to the rapid changes in the
deflections, a mistake in the time will easily occasion a mistake in the determination of the perturbing
force, of which the percentage becomes all the larger, when the perturbing force is small.

At the arctic stations the force is comparatively great, and we see that the current-arrow bends
northwards, and indicates a circle round the magnetic pole, showing that it is not the axis of the earth,
but the magnetic axis, that determines the phenomenon. At Sitka too, the current-arrows are some-
what abnormal, as we also found them to be in previous equatorial perturbations. This must be due to
the polar precipitation that is always present during these storms. If we look at fig. 37, we see that
the light parts in the terrella's auroral zone, come more or less in the region answering to the north
of N. America. It is possible that this drawing-in of rays may also to some extent be the cause of the
abnormal smallness of the perturbing force at Baldwin on Chart I. We shall find this confirmed in the
conditions during the equatorial storm of the isth December, 1882, described in Chapter III.

In the vertical intensity, the perturbation is almost imperceptible, being only slight at Tiflis, where
it is directed upwards at the moment of observation. At Pawlowsk it is not noticeable, and at Dyra-

PART I. ON MAGNETIC STORMS. CHAP. II. 129

fjord very slight. We should notice this circumstance with regard to the vertical components. On the
whole, this perturbation is in accordance with the usual equatorial perturbations, and to these we may
refer for the explanation of its cause.

THE POLAR STORM.

46. The polar storm, as the curves show, is very well defined and brief. It is especially worthy of
notice that the deflections, which, in the Central European field, are particularly powerful in the declina-
tion, keep to one direction all the time. Even at the arctic stations, the deflections, both in H and in
D, are nearly uniform in direction, Dyrafjord alone having an oscillation in declination. In the Table
XIX will be found the times of the commencement and termination of the polar storm, as also the time
of the maximum of the horizontal component, and the value of the latter at the moment. Since, as we
have said, an equatorial perturbation appears in advance of, and presumably simultaneously with, the polar
storm, it would seem difficult to decide when the polar storm commences and terminates. In the northern
regions, however, the polar storm will make its appearance with such strength, that the effect of the
equatorial perturbation will be comparatively minimal. At the arctic stations, we have therefore taken
the times when the great storm commences and ceases. As regards the southern districts of Europe,
\\t- are aided by the circumstance that the polar storm appears mainly in the declination, while the
previous storm has kept principally to the horizontal intensity. In the United States and Honolulu, on the
other hand, they both appear in H, but there the effect of the polar storm is marked as a decided undulation.

The position of the normal line for Sitka was somewhat difficult to determine, and there is there-
fore also some difficulty in accurately determining the commencement of the perturbation. At the Asiatic
stations, both the perturbations appear in H, so that neither beginning nor end can be determined to
any advantage.

It will be seen that the perturbing force on the whole diminishes with increasing distance from the
region of the Norwegian stations. Wilhelmshaven, as usual, comes out of its order in the series, being
before Stonyhurst, and with a very much greater maximal force. At most of the stations, the storm
lasted, as we see, for about zl/z hours.

We find, as usual, that the perturbation appears first at Bossekop, then at Dyrafjord, and then at
Axeleen. In the central and southern districts of Europe, the maximum occurs at about 22'' iom; in the
United States and at Honolulu it is later— about 22h 40™. The maximum on the whole is not well
defined, but the force remains for a fairly long time almost constant. This even applies to the arctic
stations, and we have therefore set no definite point of time here.

It appears from the Table, as also from direct observation of the copies of the curves, that the
perturbations at all the places are connected with one another, as they appear simultaneously, and their
course is somewhat similar. We find again, moreover, a very characteristic feature of these polar storms,
namely, that whereas the perturbation in the arctic districts changes very much from one time to an-
other, and from one place to another, the conditions in lower latitudes vary more slowly with time and
place. This must necessarily lead to the assumption that the perturbation in lower latitudes must be due
to the same cause as that in the arctic districts. The perturbation in southern latitudes can, moreover,
only be the distant effect of the same current-systems that come nearer to the earth about the auroral zone.

The circumstances are represented on Charts IV — VII, for the hours 22h om, 22h 15™, 22h 30™,
and 23*" oln.

On the whole, the distribution of force remains constant all the time. There is the same system
of lines of force, the intensity alone varying.

This time also, however, the force in Central and Southern Europe makes a distinct, though very
slight, turn clockwise. The field is of the same typical form as that of the polar elementary storms
already described.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903. 17

130

BIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

THE PERTURBING FORCES.

47. The total of the perturbing forces is calculated for a number of hours, and marked upon charts.
As the polar perturbation is so much greater than the equatorial, the field of force shown, per-
haps with the exception of the equatorial regions, is mainly conditioned by the polar system.

TABLE XIX.

Observatory

Begins

Reaches
Max.

p

' i max i

Ends

h in

21 12

ll 111 ll M!

22 4

ca. Q^O y

h in
23 45

*

23 44

2q 4:;

Wilhelmshaven . . .
Stonyhurst

2 I 9
21 IO

22 6
22 8

52 »

47 »

4S.4 »

23 47
23 44

23 48

21 IO

23 8

4-1-7 *

Kew

22 8

2 I IO

22 9

-J2 »

Sitka

22 12

41.3 »

QQ »

Pola

04. 7 »

Baldwin .

3° *

Cheltenham
Tiflis. .

ca. 21 15

22 36

34 .

ca. 23 50

Dehra Dun

n.=> *

Zi-ka-wei

1

ca. 22 20

12.4 »

c*a. 23

Christohurch ....

»

indeterminable

indeterminable

indeterminable

TABLE XX.
The Perturbing Forces on the 22nd March, 1903.

Gr. M. T.

Honolulu Sitka

1

Baldwin Toronto

Cheltenham

Pi, Pd

PI,

Pd

/'/,

/><< Pi,

Pd

P*

Pd

h m '

.

II

'3 4

+ 6.6 y

0

+ 9.07

W IQ.O y

+ 4.27

?(^) ? ?

?(*)

?<3)

15 o

+ 7.1 »

0

+ 3-5 '

0

?(2)

? ?

?

7

?

18 10

+ 3-8 •

o

+ 6.2 •

E 4-5 »

9

? | + ii.a y

0

?

?

19 50

+ 3.2 »

o

o

W 10.0 »

?

? -t- 14.0 t

0

?

V

21 45

— 0.9 »

o

— 2O 2 »

> 9.5 »

- 10.5 »

W 3.2 y - 11.3 »

?

— 1 6.2 y

w 5.97

32 0 — 7.0 »

W3.37

— 32.2 »

« 14.4 »

— 2O.O *

" 5-7 " — 20.7 »

?

— 21.2 »

» 6-5 »

15 ( - II.9 •

• 3-3 *

- 38.3 '

» 16.7 »

— 21. 1 »

» 7.0 » - 24.3 »

?

— 25.2 *

o

3°

— 14.4 »

a 4.2 >

- 31.7 *

i 34.8 »

— 21.4 »

• 2.5 » — 20.3 >

?

— 24.4 »

F. 2.4 »

45 - 14-9 »

• 3-3 "

- 34-2 »

» 31.2 »

?

? - 24.8 »

— 35.8 •

W 1.8 .

23 o

- 14.4 »

o

- 23.7 •

' 32.5 "

— 19.0 »

» 4-5 » j - 20.7 »

?

— 22.7 »

» 3.4 »

15

- 13.0 »

0

- 19.7 »

» 23.8 »

- 14.0 »

» 1.9 » — 18.9 »

?

- 14.7 »

0

I1) The value of Pi,, there being no declination curve.
(2/ The normal line somewhat uncertain.

PART I. ON MAGNETIC STORMS. CHAP. II.

TABLE XX (continued}.

Gr. M. T.

Dyratjord

Gr.M.T.

Axeleen

Kaafjord

Ph

Prf

A

PK

Pd

A

Ph

Pd

/>,

h in

h m

|

13 56 9.97

E 1.4 / I o ;, la 57 o E 13.5 y

59 9.9 » i » 12.2 •

+ 2-°y 59 - 37-5 / W 4.2 •

Slightly

13 o

' 12. 2 >

2.6 » 13 3

4- I2.O i<

» 18.0 »

negative

3

+ 10.3 •

» 13. 1 »

1.5.,! 4

+ 20.5 7

w 15.5 y

?

4 |+ 15.4 " " 9-2 » - 4.6 . 7

4- 31.7 » » 16.7 »

6

+ 18.4 » o 6.1 » 15 o • 12.5 » .

8

4- 30.7 » W 3.6 »

6. i » 15 o 4- 38.0 » » 26.0 » Slightly neg.

4- 23.5 » o(?)

?

II

4- 15.4 • E 3.1 • 4.6 » 1810+ 19.0 »

» 17.0 »

0

4- 3.8 . o

?

16 4- 8.0 » o 2.6 » 19 50

+ 12.7 »

> 16.5 »

4- 24.67

4- 10.0 » E 25.0 »

?

'5 o + 49-5 " W 7-8 » i Possibly 2r 45 - 83.0 » ' E 30.0*

+ 334-0 »

- iSS-O"

• 75-0 •

149.07

18 10

4- 22. o » » 6.o(?)i slightly 22 o — 265.0 » » 171.0 »

4- 408.0 »

— 182.0 »

* 99.0 »

205.0 »

'9 5°

+ 24.5 »

0 (?)

negative

15

— 327.0 » • 177.0 »

4- 492.0 i>

— 185.0 »

« IOI.O »

— 5-205.0 »

21 45

- 6i.o»

• 35-° ?

4- 31-07

3°

- 133-° »

» 84.0 »

4- 484.0 »

— 200. o »

• 93.5 •

— > 205.0 »

22 O — 26l.O »

E 87.0 »

- 115-° •

45

— 140.0 •

» 49.0 »

4- 396.0 »

- 1 25.0 »

» 47.0 .

— >205-0 "

15 - 3II.O »

W 104.0 .

— 184.0 » 23 o — 136.0 »

» IOI.O »

4- 266.0 »

- 91.0 *

• 33.0 »

— >205.0 »

30 — 286.O •

» 158.0 •

o

15 - 78.0 » ; » 74.0 » j 4- 2O2.O > | - 38.0 •

• 16.0 »

— <222 >205/

45 ~ 275.0 »
23 o — 1 76.0 »

• 104.0 >
» 35.0 »

4- 51.0 »
4- 77.0 »

15 — 83.0 • » 26.0 »

4- 38.0 »

TABLE XX (continued).

Gr. M. T.

Pawlowsk

Stonyhurst

Kew

Val Joyeux

Ph

Pd

P,

Pk

P*

P*

Pd

P*

Pd

P.

h in

'3 4

+ '5-17

W 9.2 7

0

+ 15-87

w 9.77

4- 12.5 7

W 7.67

4- 14.4 y

W 8.47

o(?)

15014- 15.2 »

» 4.0 »

o ] -f 20.4 »

0

+ 30.3 »

o

+ 19.5 »

0

o

18 10

+ 15-' •

» 9.2 »

o 4- 17.8 » o

4 12. 0 »

o

+ ao.o »

o

o

19 50

4- 20.0 »

. 4.6.

O ! 4- 12.2 » O

4- 13.0 >

o

-t- 33.3 »

0

o

21 45 ! 4- 20. i »

E 30.8 •

- 7-57 - 9-7'

E 38.3'

- 8.7.

E 34.6 »

- 3-a »

E 30.2 »

22 O

'5
3°

4- 20. 6 »
4- 10.6 >
4- 5.0 >

• 36.8 •
. 36.8 »
« 27.6 »

— 1 1.3 »
— 14.3 »
- 15-0 »

- 5-6 »

- 13.8 »
— IO.2 »

» 46.2 »
» 45-o »
* 35-5'

— 10.7 »

— II. 2 »

— ii. a >

» 43.8 >
» 42.8 «
» 33-7 »

+ 4.0 »

- 2.4 »

0

• 37.8 •

» 45-4 »
» 35-3 •

V
increases
a little.

45

— 2.0 •

« 19.8 »

— 15.0 » — IO.2 »

» 34-9 »

— 10.7 »

> 35-o '

0

» 33.8 »

23 o

- 8.0.

» 15-2 »

— 16.5 » 1

- II.7 »

» 37.0 »

— ii. a »

» 34- 1 »

- 5-6-

» 28.6 >

'5

- 5.0.

» ii. 5 •

— 10-5 » |

— 13.3 »

> 16.9 » — lo.a »

» 19.6 »

o

> 2I.O »

'33

BIRKFLAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE XX (continued).

Gr. M. T.

Wilhelmshaven Potsdam

1

San Fernando

Munich

Ph

Pd

ft

Ph

Pd

Ph

Pd

Ph

Pd P,

h m

'3 4

+ 16.3 y

W 9.0 y

+ 13.6 y

W 6.6 y

4- ii. i y

o(?)

4- 12.5 y

W 9.5 y

o

15 °

4- 19.6 >

o

4- 16.5 «

o

4- II. I »

0

4- 18.0 »

o(?)

0

18 10

4- 16.0 »

o

4- 15.2 »

o

4- 9.6 »

0

4- 15.0 »

o

o

19 5°

+ 18.6 »

0

4- 19.0 »

o

4- 13.3 » o

4 13.0 «

0

o

31 45

22 O

15

4- 13.1 *
+ 12.6 •

4- 2.8 »

E 47.6 .

• 49-4 "
> 48.2 »

A slight
positive
deflection.

4- 12.6 »
4- 12.3 »
4- 5.1 »

E 35.6 >

» 41.7 »
» 41.7 •

The curve for D
coincides with the
base-line, the deflec-

4- 9.0 i

4 IO.O »

4- 50 »

E 31-5 •
• 35.3 '

• 39-0 »

A slight
positive
deflection,

30 - 2.3 •

• 35-6 •

+ 4-7 '

' 3°-5 *

tion in both curves

4 5'^ *

» 30.0 »

mum

45
23 o

- 4-7 •

— II. 2 »

> 32.6 >
» 23.5 «

0

- 4-7 "

. 27.9 »
• 18.3 »

being so slight that
nothing is taken out.

4- 4.0 •
o

• 27.0 »
» 18.6 »

answering
to

15

- '3-5 »

» 15.1 »

- 4-7 •

» 14.3 >

0

• 15.0 . !P, = + i.97

TABLE XX (continued).

Gr. M. T.

Pola

Tiflis

Dehra Dun

Bombay

Ph

Prf

A

Ph

Pd

p,

Ph

Pd

Pi,

Pd

h m

1

'3 4

+ i2.oy

W 7.oy

0

+ 8.9 y

W 3.7 y

- 1.3 V ; 4- 13.4 y

0

+ lo.oy

15 °

4- I3.O »

o(?)

o

+ 9-5 »

o(Wi.sy?)

0 ' + I3.0 «

0

4- II.8 «

| '|

No curve.

18 10

4- I I.O »

0

o

4- 13.2 »

O

o ,4- 12.4 »

0

4 11.5 »

'9 5°

4- ii. o »

o

o

4- 18.8 >

o

- 2.7 »

+ 17.3 »

0

4- 16.0 »

3i 45

0

E 25.4 •

4- 5.0 y

4- 18.8 >

E 9.3 »

- 3-8»

+ 15-7 "

o

33 0

IS

o

— 2.2 »

' 33-7 »
• 33-7 •

4 5.0.
4- 2.8 »

4- 18.3 .
4- 14.1 '

" 13-4 >
» 13.0 »

- 3.8"

,

— 2.6 »

4- 15.0 »
4- 9,8 »

0

o

Nothing taken out
as Pd is wanting:

3°

O

» 26.8 «

4- 1.3 *

+ 8.8 »

» n. i « ! - 1.3 »

4- 4.7 »

o

45

— 3.2 »

> 24.0 >

4- i.o »

+ 3-3 »

* 10.8 »

o jl + 1.6 »

0

33 o

- 4-5 »

» 19.2 »

0

0

» 9.3 »

o i — 0.8 «

0

15

- 4-5 •

" '3-7 •

— I.O »

0

» 5.9 » o o o

TABLE XX (continued).

Gr. M. T.

Zi-ka-wei

Batavia Christchurch Irkutsk

'

Ph

Pd

Ph

Pd Ph

Pd

Pi,

Pd

P ,

h m

'3 4

-f lo.oy

o

+ ii. ^y

W 3.6 y

4- g.ay

0

15 o

4- I I.o »

o

+ IO.O » 0

+ 9.2 i

o

18 10

4- 6.5 > 0

4- 6.5 » 0

+ 10.4 »

0

'9 5°

+ 8.5 . o

4- 13.5 » 0

4- 13.8 .

0

2' 45

4- 10.2 » W 7.0 y

4- 13.2 « 0

23 0
15
3<>

45

*- 9.2 »
+ 2.4 »
o
o

» 7.0 »
• 5-° "
' 5-° "
» a-5 "

4- i i.o »
+ 9-5 »
+ 3-3"

+ a-5 •

0

o
o
o

Owing to the diffi-
culty in determining
the normal line,
nothing is taken out.

+ 12 y
+ to »
+ 5'

W i7y

» 15 »
» 8 »

- 3 7
- 4 »
- 4.6.

23 o

o

o

0

o

15

o

o

o

0

PART I. ON MAGNETIC STORMS. CHAP. II.

Current-Arrows for the 22nd March, 1903; Chart I at 13h 4m, and Chart II at 15h.

133

Fig. 5^•

T34 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

Current-Arrows for the 22nd March, 1903; Chart III at 19h50m, and Chart IV at 22h.

Fig- 58.

PART I. ON MAGNETIC STORMS. CHAP. II. 135

Current-Arrows for the 22nd March, 1903; Chart V at 22h 15m,and Chart VI at 22h 30m.

Fig. 59-

136

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.
Current-Arrows for the 22nd March, 1903; Chart VII at 23h.

Fig. 60.

The current-arrows indicate very decidedly two current-vortices, a positive vortex in the north 01
North America, and a negative one about the river Obi in Siberia, answering respectively to areas of
divergence and convergence of the perturbing forces.

As we have no observations from places near the points of convergence, we cannot here recognise
the characteristic perpendicular position of the total force in relation to the earth's surface.

As regards the cause, we may confine ourselves to referring to the previously-described elementary
storms. Here too it is difficult to understand how the perturbation in lower latitudes can be mainly due to
plane currents, as in that case this peculiarly formed current-system should retain its form and position
for nearly 2!/2 hours.

The slight oscillation of the force in Europe on this date, is in accordance with the fact that the
point of convergence is now far to the east, and this is certainly connected with the circumstance that
the perturbation appears so early in the night, reckoning by Greenwich time. At the Norwegian stations
about the auroral zone, the current-arrows point in the characteristic direction westwards along the zone.
On this date the vertical components at Bossekop and Axeleen are exceedingly powerful and in opposite
directions, answering to a current passing between the two stations. At Dyrafjord, P, is comparatively
smaller, indicating that the current should pass north of this station.

We have no observations for this date from Matotchkin Schar. From Potsdam no curves for V
were received. For Ekaterinburg nothing can be taken out.

PART I. ON MAGNETIC STORMS. CHAP. II.

137

THE PERTURBATIONS OF THE 26th DECEMBER, 1902.

(PI. XII).

48. The perturbations to which we have especially turned our attention are two successive, brief,
well-defined storms, that are particularly powerful at our Norwegian stations, more especially Dyrafjord
and Matotchkin Schar.

The first of these two well-characterised polar storms is especially powerful at Matotchkin Schar,
where PI attains a value of 248 y. At Axeleen there is a perturbation that is quite distinct in all three
components. At Kaafjord there is simultaneously a very distinct perturbation, but one that is very small
both in D and H, whereas in V it is considerably stronger. At Dyrafjord, the curve shows clearly
that this brief polar storm occurs simultaneously with a more lengthy perturbation. Its effect, on the
whole, at Dyrafjord, is contrary to that of the longer storm. A decomposition of the perturbing force
may here be effected.

The same conditions, although less marked, are found on the continent of Europe, where the
//-curve shows a faint, but long perturbation. There too, the course of the intermediate perturbation is
the reverse of that of the longer storm; but as the former is much more powerful, it will predominate
during the time in which it occurs.

The second storm is especially powerful between 22'' 30™ and 24''. It also occurs in the north as
a characteristic polar elementary storm, which is particularly powerful at Dyrafjord. This is in accord-
ance with the fact that it appears later.

At the stations in lower latitudes, we notice in the case of both storms simultaneous but compara-
tively slight perturbations; and the effect becomes weaker with an approach to the equator. At Sitka,
the perturbation is only of the same magnitude, and has the same course, as in the rest of America.

According to this, it is natural to consider these two storms as two successive polar elementary
storms, in which the storm-centre is situated somewhat differently. This will be still more apparent on
a closer examination of the field of force.

The field of force during the first storm is shown on Charts I and II, for the hours 2oh 45™, and
2ih respectively.

The form of the field is in the main the same in both cases, as also the relative strength. This
clearly indicates that the system in question is one that on the whole preserves its form and its posi-
tion, and only varies in strength. The arrows at Axeleen and Matotchkin Schar form exceptions in this
respect, the force at these stations being almost as great at 21 h as at 2oh 45™. This does not neces-
sarily, however, alter our view of the conditions; for, owing to the local character of the perturbations
in these regions, very slight movements of the system may here have a great effect, and thus the force
at one place may very well have its greatest value at a time other than that at which the system as a
whole is strongest.

The form of the field is that typical of the polar elementary storms. The storm-centre is situated
in the region north-east of Matotchkin Schar, and the area of convergence in north-eastern Russia. The
current-arrow about the centre is as usual directed WSW. There is an area of divergence in America,
which seems to belong to another storm-system, this being also confirmed by the arrows at Dyrafjord.

As regards the vertical intensities, we find at Pawlowsk a perturbing force directed upwards, just
as we should have expected. At Wilhelmshaven, Pola and Tiflis, on the contrary, we find positive
values for Pv. The deflections, it is true, are only slight, but still are sufficiently distinct. They cannot
be due to the system that we have assumed to be at our easterly stations, as that system can produce
only negative values of P, in the area of convergence.

It is difficult to decide what forces here play a part. The system that produced the area of diver-
gence in America, may indeed possibly be supposed to exert an influence here too; and this would also

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903. 18

138 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

of course produce positive values of P,. But it seems difficult to imagine that its effect may be traced
as far off as at Tiflis.

It seems more natural to explain the conditions by rays that come rather near to the earth in lower-
latitudes, as in the cyclo-median perturbations. The considerable strength of the current-arrows in Europe,
as shown on Chart I, seems to point in this direction, although the increased strength may possibly be
chiefly due to the fact that the two polar systems are here acting in about the same direction.

On account of the quiet character of the deflections, and the small perturbing forces, these currents
must nevertheless lie fairly high; and it is possible that they are connected with one of the polar
systems, probably that in America.

The field of force during the second storm is shown on Charts III, IV, V and VI, for the
hours 23h om, 23h 15™, 23'' 30™, and 23'' 52.5m, respectively.

Chart III shows the conditions at the beginning of the second storm. It is only at Dyrafiord that
the perturbing force has reached any magnitude. The arrows for the European stations represent a very
curious field of force; but as they are small, the determination is somewhat uncertain, owing to the
inaccuracy in the determination of the normal line.

The field in Charts IV and V shows very distinctly the form that is typical for the polar elemen-
tary storms.

At Dyrafjord, the force is exceedingly great, and is directed westwards along the auroral zone.
The storm-centre, which is presumably situated very near Dyrafjord, is now about 145° east of the sun.
The field to the south exhibits a well-marked area of convergence. There is probably, however, not
only precipitation round Dyrafjord; but it also seems as if there were local currents round the other
Norwegian stations, as the force there is also comparatively strong.

At 23'' 52. 5m, Chart VI, the strength of the field is considerably less. At Dyrafjord the direction
of the arrow is different, being now south. .

We notice a peculiar circumstance, namely, that with the turning of the arrow at Dyrafjord, the
whole field turns.

The arrow at Kaafjord, and at the more southerly European stations from Kew to Tiflis, indicates
an area of convergence. Judging from the shape of the field, the centre of this area should be about
Pawlowsk ; and in fact we find that at this moment the force there equals 0.

We thus see that the conditions in more southern latitudes are in very close connection with those
round the auroral zone. This circumstance, as we have said, may be explained in a very simple way,
the perturbations in low latitudes, in these cases, being assumed to be produced by the action, at a great
distance, of the systems that are necessary to the production of the perturbations about the auroral zone.

In all the elementary polar storms described, it will generally have been remarked (i) that all the
current-arrows in lower latitudes turn clockwise during the perturbation, and (2) that in the same lati-
tudes, the simultaneous current-arrows turn clockwise, if one moves from eastern to western stations.
These assertions I have already made in my earlier work, 'Expedition Norvegienne de 1899 — 1900', etc.,
pp. 32 & 33.

In this earlier work, I assumed that these assertions were explained by a current-system like that
in fig. 45, and by the fact that this current-system, starting in the polar regions, was there deflected
westwards during the perturbation. We have here maintained a somewhat different view, as, instead of
the horizontal current-system, we have supposed a system that, idealised, consists of two vertical
branches connected by a horizontal portion, and that this current-system has a district of precipitation
in the polar regions, with its principal axis along the auroral zone. The current-line system (see Art.
34 and fig. 40) is however even now similar to the formerly assumed real current-sytem. The turning

PART I. ON MAGNETIC STORMS. CHAP. II.

139

of the arrows in lower latitudes is then occasioned by the eastward movement of the storm-centre along
the auroral zone, with the principal axis always keeping its direction (see p. 94). When it is desired
to verify on all the charts this movement of the storm-centre during the course of the perturbation, it is
necessary, as we have said several times, to remember that the size of the current-arrows at the four
Norwegian stations, is not always a certain guide to the position of the storm-centre (see p. 137). This
travelling of the storm-centres is possibly caused by the effect of terrestrial magnetism upon the current-
system, and by the alteration in the earth's magnetic axis during the perturbation. We shall return to
this subject later on.

TABLE XXI.
The Perturbing Forces on the 26th December, 1902.

Gr. M. T.

Honolulu

Sitka Baldwin

Cheltenham

Ph

Pd

Pk

Pd

Ph

Pd '

Pk

Pd

\

h m

20 45

1.87

E 5.87

- 6.57

Disturbed

- 5-7 }'

E 2.57 - 6.27

o

21 O O

• 7-5 »

- 6.5.

vibrations,

- 4-7 *

» 2.5 »

- 4-4 »

o

23 o - 8.5 »

« 1 1.6 •

- 1.6 »

but

- 1.8 »

» 2.5 »

- 4-4 "

0

15

- 8.5 »

» IO.O »

- 6.5.

nothing

- 4-7 •

• 3-2 • || - 6.5 .

E 3-5 7

3°

— 6.2 f

• IO.O »

- 6.2 »

can be de- _ fi . ,
termined.

" 32 > - 7-9 "

" 5-9'

5a-5 - 3-4 *

» 6.6 »

o

• 1.4 »

» 1.3 »

- 0.8 •

0

TABLE XXI (continued).

Gr. M. T.

Dyrafjord

Axeloen

Matotchkin Schar

Ph

Pd

ft

Fh

Pd

p.

Ph

Pd

A

h m

20 45

+ 12.17

E 13.87

- 43-07

— 164.07

o

4- 150.07

— 202.07

E 146.2 y

— 202. o 7

21 0

4- 12. 1 »

» 25.2 •

- 44.0 »

— 191.0 »

E 12.07

4- 290.0 »

- i53-o '

» 158.0 »

— 128.0 •

23 o

- 1 54-0'

W 53-3'

+ 33-3 '

+ 2-3 •

W I2.O »

•+ 34-3 "

- 27-3 •

0

- 3i-5 "

15

— 247.0 •

• 159-0 •

+ 2'-5 »

- "-5"

• 30.7 »

+ 3-1-3 '

- 56.3 •

» 1.8 »

- 63-5 •

3°

— 225.0 »

• 74.2 »

- 35-2 • + 7-3 •

» 50.2 »

4- 86.0 »

- 54-6 •

W 2.7 »

- 41.0 »

52-5

4 48.8 »

E 18.7 »

— 17.1 • ;i O

» 10.7 »

4- 41.0 »

- 20.8 »

» 6.3 »

- 5-1 *

TABLE XXI (continued).

Kaafjord

Pawlowsk

Wilhelmshaven

Gr M T

Pk

Pd

P,

Pk

Pd

Pv

Pk

•Pd

P,

h m

20 45

- I3-2/

E 24.57

— 80.27 + 24.2 7

E 9-27

— 2.27

4 10.3 7

E 38.5X

4- 4.07

21 0

- 15-4 •

» 11.7 »

- 88.0 . 4- 7.5 .

» 3.7 .

- 3-7 •

4- 7.0 «

• 15-9 >

4- 4.0 »

23 o

— 28.9 »

0

- 38.0 » 1 - 4.0 .

W 5-5-

0

4- 1.8 •

W 3.6»

Possibly

•5

-61.31

W IO.2 »

— 45.0 »

— 3-° "

» IS-6 •

o

+ 9-3 '

» 14.6 >

a slight

30

— 61.3 »

> 8.4 »

— 86.0 •

4- 1.5 »

• 15-6 »

- 2.2 • j| 4- 15.4 •

• 3-6-

negative

52-5

- 25.3 „

E 4.3 >

- 6.2 •

0

0

- 3-7 *

4- 4.3 »

E 3.0 •

tendency.

140

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

TABLE XXI (continued).

Gr. M. T.

Kew

Potsdam

tval Toyeux Munich
:l

Pk

Pd

Pk

ft

P"

ft

A

ft

h m

1

20 45

- !2.7 y

E 22.07

+ 8.57

E 27.57 - 9'6/

E 22 5 7

4 6.07

E 19.0 7

21 O

- 5-i »

• n-3 »

+ 7.3 >

» 15.2 » |! - 3.2 »

» I7.6»

+ 2.5 »

» 10.6 >

33 o

0 0

+ 1.9 »

W i.o • j| o

» 4.3 »

+ 4.0.

o

15

4 10.7 »

W 4.6»

4 7.2 »

» 9.6 »

, -f 9.6 »

W 3.3 »

4- 13.5 »

W 6.8 .

3<>

-t- 12.2 »

> 1.4 »

+ '3-9 •

» 6.1 •

4 13.3 •

0

+ 10.5 •

» 3.0 »

52-5

O

E 6.1 »

+ 5-o »

E 3.0.

0

E 2.5 » I 4 5.5 .

E 2.3 »

TABLE XXI (continued).

Gr. M. T.

Pola

San Fernando

Tiflis

Ph

ft

p,

Ph

ft

P»

Pd

P,

h m

30 45

+ 2.3 7

E 17.37

•*- 3-17

- 8.37

E 11.47

+ 7-5 Y

E 1.87

+ 3-°y

21 O

4 3.1 »

» 9.7 »

4- i.o *

- 5-i •

» 11.4 >

+ 4.9 »

» i.i »

-+- 1.2 »

23 o

4 1.8 •

* 2.O >

o

- 2.5 »

» 2.4 »

- 2.9 »

W 3.7.

0

15

4- 8.5 »

W 6.2.

- I.O »

+ 5.1 .

> 4.1 .

o

" 9-3 *

- 0.7 .

3°

4 14.0 »

• 3-5 '

- 0.8 »

+ 12. 1 »

» 5-° »

+ 3-3"

• 10.4 »

- 1.2 »

52.5

+ 5-8.

E 2.O »

0

+ 3.2 »

» 3.4 >

•4- l.i »

• 3-7 "

- 0.1 •

TABLE XXI (continued).

Gr. M. T.

Dehra Dun Zi-ka-wei Batavia

Christchurch

Ph

ft

Pk

Pd

Ph

ft

/'/,

Pd

p.

h m

30 45

+ 5-9 7

W 6.97

43.47(1)

W 5.07

4 4.27

0

- 4-6/

0

o

31 0

+ 3-5 »

» 3.9 >

4 3.4 » (')

» 3.0 »

4 4.2 »

0 - 2.8 »

o

o

23 o

- 1.6 »

» 2.9 t

-2.4. (1)

» 3.0 »

o

W 12.0 >

- 5-5 »

0

4 2.3 7

IS

0

» 4.9 »

0

» 4.0 »

o

» 15.6 »

- 5-5 »

o

4 2.2 »

3°

+ 1.6 >

i 4.9 »

o

» 5-° *

- 1.8 »

» 15.6 »

- 7.8 »

0

4 1.9 >

53.5

+ 3.7 »

o

42.4M1)

» 2.0 »

- 3-5 »

» 18.0 »

- 2.8 »

o

+ 3-1 »

I1) Uncertain value.

PART I. ON MAGNETIC STORMS. CHAP. II.
Ciirrent-Arrows for the 26th December, 1902; Chart I at 201' 45'", and Chart II at 211'.

142 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQOZ — 1903.

Current-Arrows for the 26th December, 1902; Chart III at 23U , and Chart IV at 23h 15m.

Fig. 62.

PART I. ON MAGNETIC STORMS. CHAP. II. 143

Current-Arrows for the 26th December, 1902; Chart V at 23h 30m, and Chart VI at 23U 52.5m.

Fig. 63.

144 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

THE CYCLO-MEDIAN STORMS.

49. The idea that seems to have gained most adherents regarding the nature of the currents that
should produce the great magnetic perturbations is that the magnetic storms should be conditioned, so to
speak, by electric cyclones, wandering over the earth's surface.

This view is upheld very positively by Ad. Schmidt. We will here give a brief extract from his
previously-mentioned well-known paper, "Ueber die Ursache der magnetischen Sturme" (l).

"The most characteristic thing of all, however, is the continual change that prevails in all these
respects. Surprising similarity is followed in the course of a few minutes by a complete difference or
a decided contrast ; a great deflection in one curve answers to a scarcely perceptible jag or bend in the
other, while soon after in the one calm ensues, and in the other the liveliest motion.

"These well-known properties of magnetic storms, as especially the longer and more intense distur-
bances have aptly been called, point unmistakably to prevailing local occurrences as the likeliest cause of
these phenomena -- occurrences of varying strength and extent, which, appearing now here, now there,
perhaps also simultaneously at different places, probably exert a magnetic influence over the whole earth
at the same moment, and attain an intense influence, but for the most part only over a more or less
limited area".

This characterisation of the perturbation-conditions during great magnetic storms will do sufficiently
well as far as the arctic regions are concerned. As regards lower latitudes, on the other hand, our
impression of the conditions is very often as nearly as possible the contrary. There, at any rate during
the great storms, the circumstance that attracts most attention is the similarity that the perturbation pre-
sents at the various places. As a rule, for instance, the curve for the entire district, Stonyhurst to
Pola and Wilhelmshaven to San Fernando, exhibits in the main the same form. The conditions at Tiflis
also, often constitute a transition form to those at Dehra Dun. The difference in the forms of curve
often only depends upon a gradual turning of the field.

In conformity with this, our view of the great magnetic storms will be quite a different one, since
we assume that the storm is often only of a local nature in the regions around the auroral zone, while
the simultaneous perturbations in lower latitudes are probably, as we have seen in the treatment of the
polar elementary storms, due to the effect of distant systems. It appears, however,, that there is a class
of perturbations that are due to current-systems which appear in lower latitudes at a height above the
earth that is small in proportion to the earth's dimensions. These systems, however, seldom seem to
appear with any great strength, at any rate not in 1902—03. Whether, by following up the perturba-
tions in their smallest details, we should often find a component that must be due to current-systems of
a local character, is a question that we cannot here go into ; but it seems probable that when we come
to the very small perturbations, we shall find much to be of a local character. This follows indeed
from the fact that there are almost always more or less alternating earth-currents, and also, on account
of the current-systems during the great storms, and simultaneously with them, currents must be induced
in the earth, and this will give the perturbations in lower latitudes a local component.

In the whole of our material, we have not found more than one considerable perturbation that in
its entirety must be due to systems that come near to the earth in lower latitudes. This was on the
6th October, 1902.

It appears, however, so clearly and distinctly on an otherwise calm day, that its properties can be
all the more carefully studied; and it can also be traced over a considerable area. There is always a
possibility that such systems may also to some extent co-operate with the polar storms.

(!) Meteorologischc Zeitschrift, September, 1899.

PART I. ON MAGNETIC STORMS. CHAP. II. 145

THE PERTURBATION OF THE 6th OCTOBER, 1902.

(PI. I).

50. This perturbation appears quite suddenly upon an otherwise very calm day. As far as one can
decide from the magnetograms, it makes its appearance simultaneously in all parts of the area over
which it is observable. Only at Axeleen, and to some extent at the other Norwegian stations, has the
perturbation a somewhat peculiar character. At the other stations at which it is noticeable, its course
is as follows.

It makes its appearance at 14'' i3.5m simultaneously in both D and H. The deflection increases
suddenly, and about 5 minutes later reaches its maximum, this also occurring simultaneously in the two
curves. The deflection thereupon decreases in both, first rather suddenly, afterwards more slowly, until
about I4h 48"", when no deflection is observable.

It will be seen from the copies of the magnetograms, that the geographical distribution of the
perturbation is within fairly sharply-defined limits. The effect is greatest in Europe, especially at the
more westerly stations up to and including Wilhelmshaven and Pola; but even at Pawlowsk, where the
perturbation is distinctly perceptible, it is only slight. If we compare simultaneous perturbing forces
in Pawlowsk and Wilhelmshaven, we see that at the latter station they are about four times as great as
at the former. At Tiflis the perturbation is only just perceptible.

At Dehra Dun, Zi-ka-wei, Batavia and Christchurch, the //-curve, as the perturbation makes its
appearance, gives a little leap, which means that H receives a small, and as it appears, permanent
increase. These stations are marked (o) on the chart, as no definite perturbing force can be taken out.

At the three American stations, Toronto, Baldwin and Cheltenham, the perturbation runs nearly
the same course as in Europe, except that the deviation in declination is to the opposite side. From these
stations the effect diminishes greatly westwards. At Sitka it is almost, and at Honolulu quite, imperceptible.

At our Norwegian stations it appears as follows. At Kaafjord it is distinctly noticed, but its course
is somewhat different, especially as regards the latter half. At Matotchkin Schar a disturbance is notice-
able, but no measurable deflection. On Axeleen there is simultaneously a perturbation of about the
same duration and strength as on the continent of Europe; it takes place on the whole within the same
period, but its course is different. On the other hand it is of about the same magnitude as the pertur-
bation in the south-west of Europe, or perhaps a little smaller.

From Dyrafjord we unfortunately have no observations; but it seems likely, judging from the course
of the current-lines as shown by the charts, that this station would have been the most important.

THE FIELD OF FORCE.

51. During the perturbation the form of the field is maintained unaltered, the strength alone varying.
We have therefore found it sufficient to work out two charts, namely, for the hours I4h 22.5™ and I4h 30™.

We have made the calculation, however, for several hours, and these will be found in Table XXII.
With a view to increased accuracy, we have had all the curves enlarged photographically to five times
their original size.

Fig. 64 shows these enlarged copies of curves from Wilhelmshaven.

In the area from which we have observations, the greatest effect is in the south-west of Europe,
and the east of North America. It occurs, as we see, upon the day side. The current-arrow indicates
very distinctly a negative vortex, which should go round the North Atlantic Ocean; in reality we have
an area of convergence for the perturbing force. Whether the vortex is closed, whether — in

Birkeland. The Norwegian Aurora Polaris Expedition, 1903 — 1903.

146

BIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902-1903.

Wittielmshaven Octbr G, 1902

f

other words — the forces converge from all
directions towards some region or other in
the Atlantic, we are unable to say with
certainty, as we lack material from the more
southerly regions. A knowledge of the con-
ditions in West Africa and the east of
South America would be of special impor-
tance.

We note the fact that the effect of the
force seems to keep rather constant in the
same direction as the West European and
American current-arrows, while the strength
of the field decreases very rapidly perpen-
dicular to the direction of the arrows out-
wards from the vortex-centre. Thus in
Europe the effect decreases very rapidly
eastwards, the force being very small both
at Pawlowsk and Tiflis. At Kaafjord and
Sitka also, the force is small.

Among the other Norwegian stations,
only Axeleen can show a perturbing force
that is at all great; but there its direction
is almost due north, and it thus does not
appear to join the field of force in more
southerly latitudes.

Fig. 64.

TABLE XXII.
The Perturbing Forces on the 6th October, 1902.

Gr. M. T.

Baldwin

Cheltenham

Toronto

Axeloen

Ph

Pd

Ph

Pd

Ph

Pd

Ph

Pd

p.

h m

M 15

- 1.6 y

E 3-9 y

o

W 0.6 /

— 2.2 y

E 0.6 y

+ 8.1 y j W 0.3;-

+ 2-4 y

18.8

- 3.5 » ; » 10.2 »

- 6.0 y

E 6.5.

— 6.4 »

• 12.3 >

+ 16.5 » E 0.6 »

+ 19-7 •

22.5

- 4-4 »

• 8.7 t

— ii. i »

> 12.7 «

- 7-i '

» 14.4 »

-t- 22.5 »

> 2.O »

+ 17.2 »

26.3

- 3-4 »

» 6.5 »

- 9-7 »

« 8.6 »

— 2.6 »

» 8.5 .

+ 24-5 •

' O.I »

o

3°

— 2.O »

• 5-o »

- 7-5'

» 5-6 »

- 4-7 *

« 4.8 »

-•- 23-5 "

W i.i .

— 14.8 »

33-8

- I.I »

» 3-° »

- 5-9 '

» 5-3 »

- 3.2 »

* 2.6 »

-1- 16.4 «

» 4.6 "

- '9-7 '

37-5

— 0.6 »

• 2.5'

- 4.1 »

> 2.4 »

- 1.9.

» 1.7 »

-t- ii. a »

j> 6.4 »

- 14.8 •

4'-3

— O.I •

» i-3 »

— 3.7 »

> 0.8 »

- 0.7 •

0

-1- 7.1 * j » 4.9 >

- '2-3 •

45

o

« 0.4 »

- 1-3 *

« O.2 >

0

o

+ 4-5 •

» 2.6 »

- 9.8 »

PART I. ON MAGNETIC STORMS. CHAP. II.

147

TABLE XXII (continued).

Gr. M. T.

Kaafjord

Pawlowsk

Stonyhurst

Wilhelmshaven

PI,

Pd

P,

P*

Prf

P,

Pk

Pd

PA

Pd

ft

h m

14 '5 - 2.97

W 3.3 •/

O

- o-s y

w 5.57

- 5.6 y

W 9-4 /

0

W 1.97

O

18.8 - 3.1 •

* 5-5 »

+ 1.17

- 5-5 *

• 5-5 »

A slight

— 13-0 •

• 23-5 •

— 6.2 7

» 3r-3 »

o

22.5 - 1.9"

» 0.5 •

+ 5-° "

— 5.0 • 1 > 2.8 »

perturba-
tion;

— ii. 8 »

» 17.2 »

— 13.1 >

• 28.3 »

-3-°/

26.3 ->- 0.7 •

E 1.4 »

4- 7.3 »

— 2.O »

» 0.9 »

Pt max.

- 9.8 »

» n.8>

— 12.7 >

> 16.8 »

-5-5'

30 ! 4- I.O »

» 2.2 »

-1- 6.3 »

- i.o » > 0.5 »

= + 3-7 /

— 8.2 «

» 7.8 »

- 8.2»

> 9.6 >

—4.0 »

33-8

-1- 1.2 »

I 3.0 »

+ 6.2 »

- I.O »

o at about

- 6.7.

» 4-7 »

- 5-a »

» 4.9 >

0

37-5

4- I.O •

» 2.8 •

+ 6.2 »
4- 5 5 »

— 0.5 » i o

!^h 24™.

- 5-4 »

» 2.7 »

— 2.9 »

> 2.2 >

o

45

O

" 1-5 "

4- I.O »

O

o

- 3-9 *

> 0.8 >

— 0.6 «

0

o

TABLE XXII (continued).

Gr. M. T.

Kew

Potsdam

Val Joyeux

Ph

Pd

Ph

Pd

P,

Ph

Pd

P,

li m

14 15

0

W 16.17

— 0.6 y

W 10.4 /

— 0.6 y

- 2.1 y

W 8.27

18.8

- 4-4 y

" 24.3 "

- 4-4 •

• 25.5 .

o

- 3.2 »

i 16.2 >

Perhaps

22.5

- 7.1 »

> 17.3 »

- 5-8.

> 16.2 >

+ 0.6 >

- 3-5'

» 14.4 »

a slight

26.3 • - 7-5 »

» 11.4 »

- 5-1 •

« 9.6 »

4- 0.6 «

- 3-5'

» 7.9.

neg.

3°

- 6.a >

• 8.2 1

- 3-6.

» 4.9 »

o

- 3-3'

• 5-3 •

deflection.

The curve

33-8

-4.8»

» 5.4 • | - 2.3 »

> 2.6 »

0

- 3-1 »

• 3-4 •

somewhat

37-5

— 4-4 »

• 3.8 > - 1.7 •

» I.O »

0

— 2.5 » » 2.1 »

indistinct.

4'-3

- 4.1 »

» 2.8 » j! — i.i »

0

0

- 2.3 » ' 1 1.4 »

45

- 3-5 »

» 2. 1 » ,i — 0.7 >

o

o

— 1.8 » » 0.8 »

TABLE XXII (continued).

Gr. M. T.

Munich

Pola

San Fernando

Ph

ft

Ph

ft

'Pi

Ph

Pd

b m

14 '5

4-2.O 7

Wi5.oy

+ °-4 /

0

o

0

1 8.8

4-2.5 «

* 30.0 »

4- 1.8.

W 13.1 7

+ '0-4 y

W 27.2 7

22.5

0 t1)

» '9-5 »

+ 3-9 •

. 22.7 »

From 14'' 1 6m to

4- 10.3 »

. 25.9 »

26.3
3°

0 (>)

+ i.ioM1)

• 11.3 »
» 7-5 »

4- 3.0 «

4- 0.4 »

. 15.1 »
» 9-3*

I4h agm a slight
perturbation in V.
At 14!* 2om

+ 4-5'

+ 1.2 »

. 14.9 »
. 9-9 «

33-8

4-3.0 »(')

» 3.8 » 4- 0.2 »

» 5.2 »

Pv max. = —2.1.

4 0.5 »

» 6.2 >

37-5

o

0 2.2 » 1 O

» 2.6 «

O

» 3.2 »

41-3

0

O O

> I.O >

o

• 1.5 »

45 o oo

o

o

» 0.7 »

The curious form of the H-curve is due to work that was going on in the observatory at the time. The corresponding
values of Ph are therefore rather uncertain.

148 BIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

Current-Arrows for the 6th October, 1902; Chart I at 14h 22.5m, and Chart II at I4h 30m.

PART I. ON MAGNETIC STORMS. CHAP. II. 149

CONCERNING THE CAUSE OF THE PERTURBATION.

52. Notwithstanding its simplicity, this perturbation possesses rather peculiar properties, which make
it difficult to refer it to any of the other types. In the first place, the perturbation at Axeleen, owing to
the difference in its course, and to the direction of the force, must be ascribed to the effect of a rela-
tively independent system. In more southerly latitudes, the field forms, as we have seen, an area of
convergence. This immediately brings to mind the polar elementary storms. There are, however, strong
reasons against such a view.

On account of the form of the field, we should expect to have the storm-centre somewhere about
the south of Greenland, and the current-arrow might here be expected to be directed westwards along
the auroral zone. In the ordinary polar elementary storms, we shall then find the strongest force-effect
in this current-arrow's line of direction, around the main axis of the system, while the effect should
become less inwards towards the area of convergence. This time we come upon a peculiarity, namely
that the effect at Kaafjord and Pawlowsk is very small in proportion to that, for instance, at Val Joyeux
and San Fernando, which should lie almost at the same distance from the storm-centre, but much nearer
the area of convergence. A knowledge of the conditions at Dyrafjord would have enabled us to settle
the question; for if the perturbation should be referred to the same type as the polar elementary storms,
we should have found the effect very strong at Dyrafjord.

It might be thought, as an explanation of the smallness of the force at Kaafjord and Pawlowsk,
that the system that brought about the perturbation on Axeleen, counteracted the southern system. This
has, indeed, to some extent been the case, especially at Kaafjord. It does not, however, explain it en-
tirely; for then the counter effect of the northern system would be as great at Pawlowsk as at Axeleen.
But everything seems to indicate that the perturbation at Axeleen is of a very local character. The
vertical component, for instance, changes its direction. And at Matotchkin Schar, nothing at all is
noticeable.

It does not thus seem possible to refer this perturbation to the polar elementary storms. In favour
of this conclusion, there is also the fact that if it were so referable, it would have its storm-centre in the
sun's meridian, while the storms that have the current-arrow directed westwards along the auroral zone,
generally appear about midnight. But this is not all. From the calm conditions at the stations round
the auroral zone, it does not even seem to be of a polar nature. The cause of the perturbation in
lower latitudes must also be sought in occurrences in those lower latitudes.

The cause of the magnetic storms must however be sought in electric currents, of whose form and
kind we shall endeavour to obtain a clear idea by the aid of the experiments with the terrella.

The system with two vertical current-portions connected by a horizontal part, cannot satisfy the
field of force. It is then most natural to seek an explanation of the phenomenon in currents moving for
long distances along the surface of the earth, either on it, or at some height above it. It here seems
natural to suppose, after glancing at the chart, that we have had a current that, at any rate in the North
Atlantic region, has assumed the character of a real current-vortex.

The perturbing force in the south-west of Europe, as we see, converges greatly. If we were to
produce all the forces until they intersected one another, the district of the greatest density — the point
of intersection -- would lie only a little to the north-west of Spain. The force in North America, on
the other hand, has not such a great convergence. If we imagined ourselves moving over the earth's
surface in such a manner that we always advanced in the direction of the current-arrow, we should
describe some sort of curve, which we might call a current-line. What these current-lines are like in
our case, our material does not allow us to judge with certainty. There can be no doubt that those
from North America turn east, and unite with the conditions in the south-west of Europe, always, as
they do so, curving to the right, and always, the nearer they approach towards Europe, with a greater

150 BIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

curvature. Two things might now be possible; either the curvature might continue to increase, when
we should obtain a spiral, or it might decrease, and the lines pass westwards through the South Atlantic,
and thus form elliptical paths. We may conclude from the rapid decrease of the perturbation out
towards the sides, both eastwards in Europe and westwards in America, that the current-system must
appear both in the neighbourhood of the American stations and in that of the stations in the west of
Europe; or to speak more precisely, the bulk of the system ought to lie at a distance from the West
European stations that is small in proportion to the distance between Pola and Tiflis, or between Wil-
helmshaven and Pawlowsk, as the perturbation at Pawlowsk is only a fourth part of that at Wilhelms-
haven, and the perturbation at Tiflis is almost imperceptible.

It will be seen that the effect over the district Wilhelmshaven, San Fernando, Stonyhurst, Pola, is
of about the same magnitude. As this constitutes an area that has a section almost equal to the distance*
between Pola and Tiflis, we should be able to conclude that the current-system itself has its greatest
density in this district.

In order to draw conclusions from the vertical intensity at Pawlowsk, which is directed downwards,
they must be electric currents above the earth's surface, with which we have to do.

These currents would then have to be sought at a height that was small in proportion to the earth's
dimensions, small indeed in proportion to the distance between Pola and Tiflis.

We can draw similar conclusions for the stations in the western hemisphere.

On account of the convergence of the forces, it might perhaps be natural to seek an explanation
of the system in the effect of a south pole situated in their point of convergence. But the
effect from this point would not be able to account for the properties of the field. While this pole
should be acting strongly, both in America and in Europe, we see that the force from Pola to Tiflis
passes from a value that lies near the maximum of the values observed, to an almost imperceptible
amount. The bulk of the current itself must thus pass over the place in about the direction given by
the current-arrows.

If we assume the current to be of a cosmic nature, and consisting of electrically charged particles
in motion, we see that it is deflected in just such a manner as would result from the movement of the
current in the magnetic field, as in the northern hemisphere we must get vortices with a movement
contrary to that of the hands of a clock.

The simple course of this perturbation enables it to be very carefully studied. The form of field
also exhibits conditions of a simple nature. The perturbation cannot be referred either to the equatorial
or to the polar storms, but is of a special type. Its chief characteristics are that it is as great in medium
as in high latitudes, and that the current-lines are vortical in form. For this reason, we have called
these perturbations cydo-mcdian.

The perturbation of the type now under discussion, does not, however, appear as a free current-
vortex.

However the system may be constituted, it is almost stationary all through the time of its appear-
ance, the relative strength of the perturbation remaining constant all the time.

With the material at our disposal, it is impossible to draw any certain conclusions as to the com-
position of the current.

From the stability and immobility of the system, it must necessarily follow that it is ruled by
higher laws.

It is difficult to suppose that such a system might arise and be maintained only by means of pro-
cesses on the earth, as in that case other more variable and compound forms would be brought into
action. It is probable, on the contrary, that the current-systems in question are produced by the emission
from the sun of very stiff rays of electric corpuscles ; for then all the corpuscles that reach the earth will have

PART I. ON MAGNETIC STORMS. CHAP. II. igi

travelled nearly the same way, and in a short space of time the relative positions of the sun and the
earth, which should be decisive for the form of the system, would undergo only slight alteration.

With reference to this cyclo-median perturbation, I have made a number of experiments with my
magnetic terrella, and will here give some of the results of these.

With a suitable proportion between the stiffness of the cathode rays and the intensity of the mag-
netisation, the rays strike the terrella in lower latitudes, and form a well-defined luminous area.

Fig. 66 shows an area such as this. In making the experiments, an influence-machine was used
as the source of electricity, and a discharge-tube similar to that shown in fig. 37. The four positions
of the terrella, shown in the four photographs in fig. 66, were such that in No. i, the magnetic south
pole (answering to the terrestrial-magnetic north pole) was in such a position that, considering the cathode
as representing the sun, there was noon there. In the positions 2, 3, and 4, the terrella is so turned
that at the same south pole it is respectively 6 p. m., midnight, and 6 a. m.

Fig. 66.

The tension employed between the anode and the cathode was about 10,000 volts. The terrella
was magnetised with a current of 3.2 amperes, and the gas-pressure in the tube was 0.0011 mm.

The photographs were taken from the same position in all four cases, i. e. so that the line from
the centre of the terrella to the camera made an angle of 45° with the line from the centre to the cen-
tral point of the cathode. The characteristic changes undergone by the luminous area during the turning
of the terrella, are distinctly seen. It is especially noticeable that the strength of the light is greatest
in the polar regions, and that the luminous point towards the east near the equator moves from southern
to northern latitudes during the turning of the terrella.

By studying this phenomenon more closely, I have found out that under certain circumstances, several
such characteristic luminous areas may be obtained on the terrella.

By employing an inductorium as the source of electricity, and a very strong current for the mag-
netisation of the terrella, I have found three distinct, and possibly more, such areas, arranged one after
the other round the terrella from west to east. In order to make sure that these different luminous
areas were not due to the almost simultaneous appearance of cathode rays of various degrees of stiff-
ness, during each discharge from the inductorium I1), I have repeated all the experiments, employing as
the source of the current a high-tension direct-current machine, system Thury, Geneva. This machine,
when in regular work, can supply J/3 ampere at 15,000 volts, but with lower current strength can go
up to 20,000 volts.

It now turned out that I obtained exactly the same kind of light-figures on the terrella as I did when
employing the inductorium as the source of the current.

(!) See Birkeland, "Sur un spectre des rayons catodiques". Comptes Rendus. 28 Sept., 1896.

'5=

BIRKKLAND. THE NORWEGIAN AURORA POLAPIS EXPEDITION, 1902 — 1903.

§

6

V 2

. o

•

ft

PART I. ON MAGNETIC STORMS. CHAP. II.

'53

Fig. 68.
Birkcland. The Norwegian Aurora Polaris Expedition, 1903—1903.

20

154 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

These figures will throw considerable light upon the questions we are endeavouring to solve.
The arrangements for the experiments are made plain by fig. 67, in which a is the discharge-tube
with terrella, b-b a 2o,ooo-volt generator with motor, c a static Kelvin volt-meter up to 20,000 volts,
d, d, d are photographic apparatuses, e-e. is an oil-pump with motor, from Siemens-Schuckert, / a mer-
curial pump worked by hydraulic pressure, for measuring the gas-pressure in the discharge-tube, and
g a Gaede pump with motor from Leybold's Nachfolger, the best mercurial pump that I know of for
obtaining a high degree of exhaustion in large tubes.

The nine photographs in fig. 68 are taken with the terrella always in the same position, but under
three different electric and magnetic experimental conditions. The photographs are taken, as fig. 69

shows, simultaneously from three sides of the terrella. The photographs
i, 2, 3, fig. 68, belong to one experiment, 4, 5, 6 to another, and 7, 8, 9,
to a third. In all the experiments, it is noon at the magnetic south pole,
the cathode representing the sun.

The intention of the three experiments is to show how the descent
of rays upon the terrella alters when the stiffness is continually decreasing.
The first experiment shows the result when the stiffness of the rays is very
great in proportion to the magnetisation employed upon the terrella. The
stiffness of the rays is altered most simply by altering the pressure of the
gas in the discharge-tube. With an exceedingly low pressure, however,
the disadvantage is that so much gas is evolved from the cathode during

i- 1

the experiment, that it is not easy to photograph the phenomena, as they
change.

In the first experiment (i, 2, 3) therefore, I have been obliged, for the sake of the photographing,
to keep a comparatively high pressure in the discharge-tube, but on the other hand I have employed
a lower magnetising current upon the terrella than in the next two experiments (4, 5, 6 and 7, 8, 9). It
has, however, been proved with certainty that the light-figures will be the same if, in the first experi-
ment, the same high degree of magnetisation be employed as in the second and third experiments, when
the discharge-tube is exhausted sufficiently.

In the first experiment, the magnetising current was 15 amperes, answering to a magnetic moment
M, of the terrella, of 6200 C.G.S. The pressure in the discharge-tube was 0.018 mm., the discharge
current was 8.9 milliamperes, and the difference of potential between the electrodes was 4200 volts.

In the second experiment the magnetising current was 33 amperes, answering to about M = 10,000.
The pressure was about 0.006 mm., the current 9.5 milliamperes, and the tension 5 500 volts.

In the third experiment M — 10,000, as in the second. The pressure was 0.03 mm., the strength
of the current 8 milliamperes, and the tension 3300 volts.

As most of the experiments described in this volume were made with the same terrella, — marked
No. 5 — there may be some interest in seeing the curve for its magnetic moment at about 20° C. for
various intensities of the magnetising current. Fig. 70 shows this moment-curve.

The values for high current-intensities are not very exact, owing to the great changes of tempera-
ture during the measurements.

There are various circumstances that appear in the experiments represented in fig. 68, to which
we will pay special attention.

It should first be remarked that if the rays become still more pliant than in experiment 3, the
conditions in the fundamental experiment represented in fig. 47 can be exactly obtained. 'In that experi-
ment, three regions for the descent of the cathode rays were distinctly seen in a zone round each of
the magnetic poles.

PART I. ON MAGNETIC STORMS. CHAP. II. 155

It is easy to follow the development from experiment i up to the last-mentioned, represented in fig. 47.
In experiment i we see distinctly three characteristic light-areas round the terrella. In the succeeding
experiments these light-areas undergo several important changes. First the strength of the light dimini-
shes in the middle of the areas, so that the edges come out more distinctly. Then the edges also partly
disappear, except in the polar regions, where the
light increases in intensity.

The first figure in the three rows (i, 4 & 7)
shows the light reduced to two patches, the lower
of which, however, has coincided with a descent of
rays upon the screen, indicating rays that have been
deflected and have turned back before they reached
the terrella (see fig. 39, third example).

The second figure in the three rows illustrates
clearly the development mentioned above.

The third figure, as photograph 9 shows, changes
into polar bands that have possibly been produced
by the covering over of more light-areas than the
three mentioned. These zones of light are best seen
in fig. 47. Other light-phenomena are also seen in
photographs 3, 6 & 9, fig. 68, about the magnetic
north pole and on the screen.

These consecutive light-areas round the terrella
have some resemblance to other light-phenomena
observed by me during the study of the trajectories
of cathode rays under the influence of one magnetic
pole('). With one magnetic pole, the consecutive
figures became constantly smaller and smaller, while
here they are all nearly of the same size.

From these experiments we shall draw comparisons both now, while discussing the cyclo-median
perturbations, and subsequently in the treatment of the observations from 1882 — 83, Vol. I, Part II, where
the question of districts of precipitation in the polar regions for magnetic storm-centres is discussed, and
lastly in the treatment of the observations of aurora and of cirrus clouds (Vol. II).

The experiments described in connection with figs. 47 and 68, are of fundamental importance to
our theory of magnetic disturbances. Concluding by analogy from these, we should never expect to
have purely elementary magnetic perturbations upon the earth, as, among other things, the experiments
show that there are several districts of precipitation at the same time upon the earth for the electric
rays from the sun. In the preceding pages also, it has frequently been indicated that the magnetic cur-
rents are never purely elementary, like, for instance, the idealised polar form represented in fig. 40.

As regards polar storms, we have only been able to study those with the district of precipitation
in the neighbourhood of the four Norwegian stations.

In order to obtain a clear understanding of the circumstances, we ought to have simultaneous ob-
servations from stations right round the auroral zone, and if possible also from the antarctic regions. A
year's simultaneous observations from all the acting magnetic observatories in the world, and from, for
instance, 10 stations in a zone round the terrestrial-magnetic north pole, and from as many as far south

9000
8WO
7(1(10
6000

5000
U)00

3WO
2000
WOO

t

/'

"

/

'

/

/

/

/

/

/

/

t

/

!

Maj

*nelic
Terr

mome:
illaN?

it for

5

5 10 IS 20 25 30 amfierei
Fig. 70.

(') Archives des Sciences Physiques et Naturelles. Quatrieme periode, t. VI. Geneva, Sept., 1898.

156

B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

Fig. 71.

PART I. ON MAGNETIC STORMS. CHAP. II.

in the southern hemisphere as could practically be reached without too great expense, by accompanying
hunting-expeditions, would without doubt raise the veil that obscures the great question of the origin
of terrestrial magnetism, which has hitherto been one of the greatest mysteries of Nature.

In order to illustrate clearly the course of the rays in the case illustrated in fig. 66, Stermer has
calculated the trajectories of cathode corpuscles answering to those in this experiment, and has shown
the result in a wire model, which is photographed in three positions in fig. 71.

Stermer has added some remarks upon this model, which he kindly allows me to quote.

"This wire model (fig. 71) represents a number of trajectories of negatively -charged corpuscles,
moving under the influence of an elementary magnet.

"The trajectories are constructed on a graphic method of integration, worked out for the occasion,
which will be more fully described in the second part of this work (1).

"The model was specially made for Birkeland's experiments, and the sphere therefore repre-
sents the terrella, and the plate on the right the cathode. The elementary magnet is placed in the
centre of the sphere, with its axis parallel to the black rods, and the south pole upwards, the latter
being marked with a cross. The sphere is fitted with a rod representing the earth's axis of rotation.

"The lowest layer of rays consists of plane curves lying in the magnetic equatorial plane; they
are calculated exactly, and are a good check upon the others, which are constructed graphically. Above
this lowest layer of trajectories lie four other layers, so that the model shows more than 50 different
paths. To each path in the model, there is also a corresponding one that is symmetrical with the first
with reference to the magnetic equatorial plane; but all the trajectories thus produced are omitted so as
not to make the model too intricate.

"The ring is clearly seen that answers to the luminous ring round the terrella in Birkeland's ex-
periment. If we call the moment of the elementary magnet M, and express the characteristic constant ('-)

of the corpuscles by H(tou, then the radius of the ring equals

cm.

"On the third photograph are marked the points in which the trajectories intersect a sphere con-
centric with that in the model, and with a radius rather less than that of the ring. At the points of
intersection, the tangents to the trajectories have also been drawn.
It will be seen how the directions of the tangents form a vortex;
and symmetrical with this, there is a vortex on the other hemi-
sphere, below the magnetic equatorial plane. If arrows are marked
all over the sphere in directions the reverse of those of the above-
mentioned tangents, we obtain the accompanying figure 72 in which
the sphere is seen from without. The figure is only diagrammatic.
We see that the part upon which the corpuscles impinge has the
same form as that visible in the experiment; and above this there
are two contrary cyclonic current-vortices in the direction of the
arrows, situated symmetrically with reference to the magnetic
equatorial plane, and answering to the positive currents that might
produce cyclo-median perturbations.

"The trajectories that have been chosen in the wire model
are especially those that approach the elementary magnet, and
then once more recede to an infinite distance, and not such as Fig. 72.

(') Cf. "On the Graphic Solution of Dynamical Problems", by Carl Stormer. Videnskabsselskabets Skrifter; Christiania, 1908.
(2> Cf .Carl Stermer's "Sur les Trajectoires des Corpuscules Electrises dans 1'Espace, etc." Archives de Geneve, July— October, 1907.

158 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

come very near, or go right up to the elementary magnet. These paths will receive a special demon-
stration in other models, which will be described in the detailed treatment of the experiments with the
terrella (see also fig. 73).

"From the form of the cyclo-median perturbations, and comparison with experiment and theory, we
find that the radius of the ring is here about 1.5 that of the earth. Now since the magnetic moment
of the earth, M, is 8.52 x io'-3, this gives, for the corpuscles that cause the cyclo-median perturbations,

8.52 x io25
°?° = [^5 x 6.37 x lo^ = 93 milllons' approximately.

"In other words, the rays in these perturbations must be excessively stiff."

It thus appears from Stermer's calculations that two cyclonic vortices, symmetrical with reference to
the equator, are produced, such that if we reckon with positive current-directions, the vortex north of
the equator is counter-clockwise, that south of the equator, clockwise. This is in accordance with our
observations in as far as the cyclo-median perturbation formed a counter-clockwise vortex. Judging from
the light effects produced by the experiments with the terrella, a cyclo-median perturbation should also
have a somewhat stronger effect in the polar regions. This assumption, unfortunately, cannot be verified,
as we have no observations from Dyrafjord for the 6th October.

It should be remarked that the length of the arrows in fig. 72 has nothing to do with the inten-
sity of the current or of the magnetic effect.

I have not yet proved the existence of electric current-vortices such as these experimentally, but
shall try to do so later on. This is a case in which mathematical analysis has shown a superiority to
experimental investigations. It is generally, as we know, only after the experimental discoveries have
been made that analysis steps in to explain and enlarge the comprehension of the results obtained; and
this has hitherto also been the case here.

The discovery of the various districts of precipitation in the polar regions is experimental, and
from the results of the observations from the expeditions in 1882 — 83, we have found such simultaneous
districts of precipitation for the magnetic storms. This subject will be discussed in Part II of this -volume.
Later on, in Vol. II, a corresponding investigation of the distribution of simultaneous aurora will be
made, in which both our own collected material will be employed, and also that from the expeditions
of 1882—83.

FURTHER COMPARISON WITH ST0RMER'S MATHEMATICAL THEORY.

53. It seems as if Stermer's investigations would be of great importance in the problem of finding
theoretically also, the various districts of precipitation in the polar regions. This is apparent from the
following remarks, which Stermer allows me to quote:

"All these remarkable light-phenomena, shown in figs. 47 and 68, can doubtless be explained
theoretically by my mathematical investigations of the paths of electrically charged corpuscles in the field
of an elementary magnet. We shall return to this subject in a subsequent section of this work. At
present I will only point out that the patches of light about the poles, obtained by sufficiently strong
magnetism, are probably due to cathode corpuscles flung out into paths in the immediate proximity of
those which, theoretically, would strike the elementary magnet in the centre of the terrella, and whose
field, at great distances, represents the magnetic field of the terrella.

"As I have previously calculated a series of the simplest of such paths, all that is now necessary
for the re-finding of the districts of precipitation visible on the terrella is to employ these calculations.
Fig- 73 shows a wire model constructed for the case occurring in the experiments shown in fig. 47.

PART I. ON MAGNETIC STORMS. CHAP. II

159

Fig. 73-

Several bundles of rays are here

seen issuing from two points, one

of which is in the magnetic equa-
torial plane, and the other a little

above it, the rays being directed

towards the terrella.

"Fig. 74 shows a comparison

between the observed and the

theoretical districts of precipita-
tion ('). It will be seen that the

similarity is striking.

"In this connection I will

mention that the same calculations

may be employed as regards the

earth, for the purpose of finding

the districts of the precipitation of

electric (negative) corpuscles com-
ing from the sun. All the data

necessary for such a calculation

will be found in my Geneva paper (1. c., chap. IV).

" Let O (fig. 75) be the centre of the earth, P the north pole, OM the earth's magnetic axis, OAB the

magnetic equatorial plane, and OS the direction to the centre from which the corpuscles emanate (the

sun). OS is calculated from the
time of the phenomenon, by well-
known formulae from spherical
astronomy. The angle ifj is
thereby found, i. e. the altitude
of the sun above the magnetic
equatorial plane, or in other
words, the sun's altitude above
the horizon at the point M.

"The angle of deflection <P
(calculated positive (2) westwards)
answering to i//, is now obtained,
as regards the simplest trajec-
Fl£- 74' lories, with sufficient accuracy by

the tables given in §§ 14 & 15

of my paper. They give the following curves, in which </> is the abscissa and ip the ordinate (fig. 76).
"The continuous line is the curve for the northern hemisphere, the broken line, symmetrical with

the first, that for the southern.

"For each value of tp, we generally find that there are several values of 0 answering to various

trajectories from the same point of emanation; and this gives correspondingly various districts of

precipitation (3).

(') See "Sur les Trajectoires des Corpuscles Electrises", etc., by Carl St0rmer, § 16, Archives de Geneve, July — October,

1907; and a lecture on the same subject given at the International Mathematical Congress at Rome, April, 1908
(2) For positive rays, 0 must be calculated positive eastwards. - (3) I. c. §§ 14, 15 & 18.

160

HIKKKI.AMl. I UK NOKWIJ.IAN ATKOKA 1'OI.AKIS KXrl.DI'l IOX, TgO2 -1903.

"As regards the angle M( ).\, much will depend upon the stiffness of the
rays (see mv paper, ^ 17); will) constant stiffness, however, point \ will
approach M when t/i increases. Before tnrther data can he obtained lor the
stillness of the ravs that cause aurora and magnetic perturbations, we mav
assume, in accordance with the observations, that X is situated in the auroral
zones.

"The appearance and disappearance of the various districts of precipita-
tion, and their movements along the north and south auroral /ones, according

" o

as the altitude (/; of the sun above the magnetic equatorial plane changes with
time, can then he calculated hv the above. We shall return to this subject in
a later section ot this work."

V *

Fig. 76.

CHAPTER III.

COMPOUND PERTURBATIONS.

THE PERTURBATIONS OF THE 29th & 30th OCTOBER, 1902.

(PI. VI).

54. These storms consist of two principal phenomena, first appearing at the equator mainly as
a positiye equatorial perturbation, which commences suddenly at 16'' 52*". At what hour it ceases it
is difficult to say, as perturbations of another kind soon begin. The perturbation at the equator is
especially powerful at about ih 30™ on the 3oth October. It seems to be directly apparent from the
curves that this is really an equatorial perturbation. Unfortunately there are no observations for this
date from Honolulu and several other stations, as the time was not given in my Circular (p. 38).
Simultaneously with this perturbation, there are powerful storms round the Norwegian stations, that at
Matotchkin Schar being particularly so, and of long duration. The positive equatorial perturbations ob-
served by us are alicays accompanied by polar storms. As a rule, the polar storms do not begin until
a little while after the equatorial ; but on this occasion they begin almost simultaneously, that at Matotch-
kin Schar lasting from i6h 40™ to about midnight.

The almost simultaneous appearance of the polar storm and the positive equatorial perturbation has
been already mentioned as of frequent occurrence. The explanation of the positive equatorial perturba-
tion given in Art. 31, also at once suggests the connection. Fig. 38 b shows the descent upon the screen
of those rays that would turn back before reaching the terrella. It was these rays which we assumed
to be the cause of the positive equatorial perturbation. The figure also distinctly shows, however, that
this descent of rays upon the screen occurs simultaneously, and is connected, with the descent in the
polar regions on the terrella.

The field of force for the perturbation in question is shown in Table XXIII and in the two charts
following.

TABLE XXIII.
The Perturbing Forces on the 291)1 & 3Oth October, 1902.

Gr. M. T.

Toronto

Axeloen

Matotchkin Schar

I 'I,

Pd

Ph

Pd

P.

Ph

Pd

P,

17 3°

+ 3.17

0

— 224.0 7

E 28.57

- 300 y

- 27.77

E 3.1 y

_3

18 52.5

+ 3.6»

o

- 131.0 »

W36.7 »

+ 148 »

— 21 7.0 »

» 136.0 »

9

20 30

— 2.2 »

0

- 74-5 •

E 26.1 »

t- 205 »

1- 237.0 »

» 91.0 »

?

1-1 30

4- 1.8 »

o

4- 6.4 »

W 7.6 »

— H3.0 >

» 69.5 »

- 18.7 »

23 15

+ 9-5 »

o

3-7 »

E 7.6 >

-t- 94 »

- 41-5 "

» 46.5 '

- 18.7 »

1 0

+ 19.8 »

E 2.47

?

7

+ 37 '

+ 9-3 »

W 5.7 »

O

i 30

+ 10.8 »

» 2.4 »

?

? •

4- 118 »

4- 9.4 »

E 19.0 »

0

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903.

I 62

BIRKKI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.

TABLE XXIII (continued).

Gr. M. T.

Kaafjord

Stonyhurst

Wilhelmshaven

Pi,

Pd

ft

Ph

Pd

Ph

Pd

P.

li m

17 30

7

7

?

-f 6.17

E 5-I7

+ u-77

E 5-5 y

0

18 52.5

•3

7

?

— 10.7 »

» 8.6 »

- 4.2 »

* 19-5 »

o

20 30

?

7

?

- 5-6"

» 18.2 »

4- 4.6 »

» 21.3 «

O

-1 3°

7

7

?

+ 3.0 »

" 4-5 »

4- 2.8 »

" 4-3 "

5-° 7

23 15

- 46.07

E 24.87

- 89-3 7

+ 3-5"

» 8.6 »

-1- 10.7 »

» 10.4 »

- 5-o »

I O

- 1.2.

W 8.4 »

- 56.3 •

4- 11.7 »

W 4.5.

4- 17.2 »

W 5.5.

o

i 30

— 3-° "

K 20. 2 •

— 40.0 »

4- 4.6 •

E 10.8 «

4- 17.2 »

E 16.5.

o

TABLE XXIII (continued).

Gr. M. T.

Kew

Munich

San Fernando

Dehra Dun

Ph

Pd

Ph

Pd

Ph

Pd

P*

Pd

h m

17 30

+ 3-° 7

K 6.5 y

+ 5-5 >'

E 3-87

+ 7-67

E 6.57

-"- 5-i 7

o

"8 52-5

- 9.7 »

* 8.4 >

- 6.5.

» 13.7 «

- 3-2 •

• 6.5 »

4- 6.7 »

E 2.97

20 30

- 3-5 -,

» 14.1 »

4- 2.O »

» 16.8 •

+ 3-2 »

» 9.8 >

4- 6.7.

0

21 30

4- 3.0 »

» 3-3 •

4 2.5 »

» 6.1 •

4- 7.6 »

» 4.1 »

4- 4.7 »

o

23 '5

4 7.1 »

» 8.4 •

+ 4-5 •

» 8.4.

•+• 9.6 »

> 6.5 »

4- 13.0 >

W 2.9 »

I 0

-i- 13.7 »

W 3.7 » 4- 11.5 »

W 2.3 » II + '7-9 "

W 2.5 •

4- 26.0 >

• 9.8 »

I 30

4 7.6 »

E 12.2 »

- 8.0 »

E 12.2 »

4-II.5 *

E 9.0 »

+- 33-5 •

» 13.8 »

1

TABLE XXIII (continued).

Gr. M. T.

Zi-ka-wei

Batavia

Christchurch

Ph

Prf

Pv

PI,

Pd

Ph

Pd

P.

li m

17 30
18 52.5

+ 4-87

4- 6.2 »

O

o

c
o

1

E

7

7

7

1

9

20 30

+ 2.4 »

o

•S

7

7

7

?

?

21 30

»3 IS
I 0

4- 4.8 »
4 16.8 •
4- 24.0 »

o
E 9.07
» 9.0 »

JU

3
eg

1
g

?
4- 29.2 7

W 19.27

4- 27.2 7
4- 37.2 »

E 8.97
> 8.9 1

- S.S/

O

r 30

4- 28.8 »

* 4.0 »

o

4- 36.0 »

» 24.0 n

4- 38.6 »

» 9-7 '

o

PART I. ON MAGNETIC STORMS. CHAP. III.

1 63

rrent-Arrows for the 29th and 30th October, 1902; Chart I at IS" 52.5m and 2O1' 30"' on the 29th, and Chart II at I1' on the 30th

Fig. 77-

164 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Chart I shows the conditions at i8h 52.5'" and 2oh 3Om on the 2gth October.

At these hours, it is the polar systems that give the field its character. There is a polar system
in its centre presumably in the neighbourhood of Matotchkin Schar. The direction of the current-arrow
is westward along the auroral zone, indicating that the storm-centre is on the midnight side. In lower
latitudes there is an area of convergence. On the mainland of Europe, the field is turning counter-clock-
wise as in the polar regions.

Chart II shows the conditions at i'1 on the 3oth October.

The field is now mainly conditioned by the equatorial perturbation, which at this hour is very
powerful.

This is an example of a composite perturbation of the very simplest kind, in which there is the
simultaneous occurrence of a very simple equatorial perturbation, and a polar storm that also exhibits
very simple forms.

THE PERTURBATION OF THE 25th DECEMBER, 1902.

(PI. XI).

55. It is a brief, but powerful and well-defined perturbation, particularly marked at the observa-
tories in North America, that has here attracted attention. It commences there at 3'' 14™, increases
rapidly, and reaches a maximum at 3'' 21™, after which it decreases more slowly, and at 3'' 5ym the con-
ditions are once more almost normal.

We notice especially that the perturbation appears with much greater strength at Toronto than at
Baldwin and Cheltenham. At Toronto, the horizontal component of the perturbing force attains a value
°f 45-3 y> ar>d at Baldwin and Cheltenham values of 23 and 25.4 y respectively. At Sitka the pertur-
bation is noticed distinctly, but it is very faint. The perturbation that, on account of its course, should
be connected with the above, there attains a strength of 7.5 y.

During the time under consideration, perturbations occur all over the world. At our Norwegian
stations, there are storms of considerable magnitude, and elsewhere in Europe slight, but distinct per-
turbations.

These perturbations, however, run an altogether different course from those in America. At Dyra-
fjord, there is a perturbation of medium strength, but of much longer duration than those in America;
it has considerable strength as early as about ih, and lasts almost until 5h. There is moreover a fairly
powerful storm at about midnight.

At Axeleen, die conditions resemble those at Dyrafjord, except that the course of the perturbation
differs still more in its conditions from those in America. At Dyrafjord, during the time in which the
short perturbation in America is taking place, we can notice a distinct variation in the form of the curve,
especially that for H, which almost coincides with that for the perturbation in America. At Axeleen,
on the contrary, nothing special is noticed. There the perturbation has at that time already passed its
maximum, which occurs at 2'' 32™. At Axeleen also, there is a comparatively powerful perturbation at
about midnight, commencing later, namely at 23h 45™ on the 24th, and continuing fairly powerful right
on to 5h on the 25th.

The conditions at Kaafjord on this date are particularly interesting, in that during the time in which
powerful storms are occurring in the north, there are only very faint perturbations here, such as might
best be characterised as slightly disturbed conditions. We notice, however, a perturbation that appears
simultaneously with, and runs the same course as, the perturbation in America. Its strength is also
about the same, if anything a little less.

PART I. ON MAGNETIC STORMS. CHAP. III. 165

In Europe as a whole, the conditions are slightly disturbed from 23** on the 24th to 5*" on the
25th. There are especially distinct perturbations about midnight, and from 2'' 30"' to 4''. We thus see
that the conditions there are in the main connected with the polar storms at the Norwegian stations.
If we look at the curve for the declination, we see, moreover, that exactly at the time when the brief,
powerful perturbation is occurring in America, there is a perturbation in Europe with very much the
same course; it commences exactly at 3'' 15™, increases to a maximum, which occurs at 3h 2im, and
then slowly decreases until about 4'', when it is at an end.

At Tiflis, Dehra Dun, Batavia and Zi-ka-wei, this perturbation in the main occurs simultaneously
with, and runs a course similar to, the perturbation in America. It occurs in H only.

The field of force is shown in two charts for four different hours.

TABLE XXIV.
The Perturbing Forces on the 25th December, 1902.

Gr M. T.

Sitka

Baldwin

Toronto

Cheltenham

Pk

PA

Pk

Pd

Pk

Pd

ft

Pd

h in

3 °

- 0.8 y

W 2.2 y

- 4.6r

o - 6.7 y

o

- 3-5 y

0

15

- 3-6 «

E 3.1 »

— 4.6 »

E 8.97

- 5.8'

E 1507

+ 4.1 »

E 12.57

20

7-5 "

» 4.0 »

- 4-3 •

• 22.3 »

+ i-3 •

» 44.0 •

+ 5-8-

» 24.4 »

3°

- 7-3 »

» 7.6 »

-1- 2.8 .

• 20.3 »

*- 5-° '

• 3i-3 »

+ 3.2 »

" 15-4 "

40

- 2.1 »

» 5-4 »

+ 1-4 •

» 8.9 •

0

» 12.6 • I + 0.9 •

» 8.3 »

4 o

- 0.7 *

» 2.7 »

- 3-2 '

o

— 9.0 »

• 1.8 »

- 3-° '

» 3.3 *

TABLE XXIV (continued).

Gr. M. T.

Dyrafjord

Axeleen

Kaafjord

Pk

Pd

P,

Pi,

Pd

Pv

Ph

Pd

Pi

h m

3 0

— 1107

E 2.47

+ 23-5 7

— 105.07

E 62.5 7

+ 76.0 7

o

E 12.87

— 21.2 7

15

— 218 »

• 5.9 »

+ 53-3 »

- 96-3 »

» 64.0 »

-1- 81.0 »

- 6.77

» 5-i •

— 21.3 »

20

— 206 »

» 12. 1 •>

+ 59-9 »

- 93-° »

» 58.0 »

+ 83-5 »

-14.7 »

0

- 17-3 '

3°

-106 »

W 13.! »

- 6.4 »

- 59-8 »

» 48-6 »

+ 88.5 »

— 16.0 >

» 2.5 •

— 18.0 «

40

— 105 »

E 23.8 •

- 7.8»

- 44.2 »

» 30.4 >

+ 71.2 »

- 9.8 »

o

- '5-7 •

4 °

- 44 "

W 9.7.

3-4 "

- 34-5 »

» 27.2 »

+ 14.7 »

- 4-3 '

W 2.2 •

- 14.1 »

TABLE XXIV (continued).

Pavvlowsk

Stonyhurst

Wilhelmshaven

Kew

Gr M T

Pk

Pd

A

Ph

Pd

Ph

Pd

n

Ph

Pd

h in

3 o

o

E 3.27

- 3-° 7

E 4.07

- i.4/

E 3.07

- 3-°7

E 4.6 •

15

- 6.57

0

No no-

- 5-6 •

« 2.3 >

- 2.8 »

» 2.4 »

A slight

- 3-5 "

» 1.9 »

20

— 10. 0 »

W 3.2 »

ticeable

- 6.6 »

W 8.0 »

— 10.8 »

W 15.2 »

neg.

- 4.0 .

W 6.5.

3°

— 9.0 »

o

perturbing

- 5.6-

» 1 1.4 »

— 10.3 »

• 13-4 •

deflection.

- 6.1 »

* 9.8 »

40

- 7.0 »

' 2.3 »

forces.

o

» 8.5 »

- 5-6"

» I I.O »

— 2.0 •

» 7.0 »

4 o

4- i.o »

• 1.4.

+• 3-5 »

» 2.3 »

+ 3-7 »

» 3.0 »

4- 3.0 »

> 2.3 »

i66

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE XXIV (continued).

Gr. M. T.

Potsdam

Val Joyeux

Munich

San Fernando

Pk

Pd

Pk

Pi

ft

Pk

Pd

P*

Pd

h in

3 °

— 0.67

E 3.0 •/

- 1.6 7

E 5.0 y

- 1-5 y

E 2.3 v

- 3-2 y

O

15

— 2.2 «

W 2.5.

- 2.4 »

0

A very
slight neg.

- 5-o'

W 5.3.

- 3-8.

W 4.8 y

20

- 8.2 »

• 9.6.

- 3-2 '

W 10.0 »

deflection

- 4-5 »

» 7.6-

- 2.5 »

» 6.5

3°

- 6.9 1

» 8.6 »

- 4.8.

» 7-5 "

about

- 6.0 •

» 6.1 »

0

> 4.8 »

40

- 4-4 •

» 7.1 »

- 2.4 •

» 4.2 »

3li 30m.

- I.O »

• 5-3*

0

o

4 °

+ 3-a "

" 1-5 "

-1- 3.2 »

0

+ 2 O »

• 1.5 '

+ 1.2 »

o

TABLE XXIV (continued).

Tiflis

Dehra Dun

Zi-ka-wei

Batavia

Christchurch

Gr M T

Pk

Pd

ft

Pk

Pd

Pk

Pd

ft

Pd

Pk

Pd

h m

3 °

IS

-13.27
- i-5 »

E 1.4 y
o

Slight de-
flections

- 1.67
- 3-9'

No no-

- 3-6 y

— 9.6 »

No no-

- 3-27
— 6.4 >

No no-

- 1-37
— 4.6 »

No no-

20

- 3-9 »

o

to small to — 4.7 »

ticeable

- 9.6 »

ticeable

- 6.0 »

ticeable

- 7.8 »

tice-
able

3°

- 4-4 •

W 1.4 »

allow of

- 4-7 "

deflec-

- 7.2 .

deflec-

- 1-3 •

deflec-

- 5-5 •

deflec-

40

- 4-4 »

» 0.7 »

being
measured.

- 1.9.

tions.

- 2.4 »

tions.

o

tions.

- 2.3 »

tions.

4 o

- 0.8 »

0

o

- 2.4 «

- 1.8 »

o

Current-Arrows for the 25th December, 1902; Chart I at 3h 15m and 3h 20m.

Fig 78.

PART I. ON MAGNETIC STORMS. CHAP. III.

Current-Arrows for the 25th December, 1902; Chart II at 3h 30m and 3h 40m.

16?

Fig. ^g.

Chart I; Time jh //"' and j1' 2om.

At the first hour named, the conditions are similar to those prevailing at the time when the power-
ful perturbation in America commences. In the United States the current-arrows are directed southwards,
with some divergence; at Sitka, westwards. In Europe the direction of the arrows varies greatly from
place to place. This may certainly in a great measure be accounted for, partly by the fact that when
the arrows are small, their direction is rather liable to error, as the normal line cannot be so positively
determined, and partly that an inaccuracy in the time-determination, owing to the great variableness of
the conditions at this point of time, will result in a large error in the force.

Turning to the Norwegian stations, we find the force to be especially strong at Dyrafjord and
Axeleen, and at both these places the current-arrow, as is usual in such circumstances, is directed WSW
along the auroral zone.

At 3h 20™ the perturbation in America is at its height, and the field of force in southern latitudes
is now in the main determined by this brief perturbation.

The field of force in Europe and North America now shows a strong resemblance to that during
the cyclo-median storm of the previous 6th October, the chief difference being that the latter was more
restricted in area, its remarkable field of action being principally confined to North America and Europe.
At Dyrafjord and Axel0en the conditions are almost as at 3h 15™.

168 HIKKl I.AXD. 'I III'. NOKWKCIAX ATKOKA 1'OI.AKls IXI'IDilloN, [902-1903.

('hurt II: 7'inii ;" ;<>"' nnil ;" ./<>'".

The form of the field is on the whole unaltered, except that the strength is less.

Although it muv appear, from a glance at the curves, as if the perturbation were fairly simple, it
is in realitv of a rather composite character. In the district from Axeloen to 1 Jvrafjord, there; is polar
precipitation. Tin-re is, on the whole, a current-svslem acting as a hori/ontal current flowing almost in
tin- direction from Axeloen to 1 (yrafjord. The svstem should have its greatest density to the south of
these two stations. On account of the comparatively quiet conditions at Kaafjnrd, the powerful effect
at Dvrafjord and Axeloen must he due to the fact that the currents causing the perturbation must come
comparatively close to these stations. These currents remain in the north rather a long time with
varying strength, but in about tin- same position from about midnight until 5''.

While these currents arc acting in the north, and directlv or indircctlv producing verv faint per-
turbations southwards in Europe, a peculiar perturbation occurs, well-defined and powerful, but of short
duration, and remarkable for its universal distribution. It is the more remarkable that there is noplace
at which it seems to be accompanied bv storms of great violence, but appears to be as powerful in lower
as in higher latitudes.

We have said that the field of this perturbation resembles in its main features that of the previous
6th October. In addition to this, its course is on the whole the same. 1 he two perturbations are about
equal in duration, increase suddenly to a maximum, and then more slowly decrease to I); and their
strength is about equal. The only difference is that this perturbation is most powerful in North America,
while that of the 6th October was most powerful in Western Kurope.

This brief storm must thus, it seems, be classed with those perturbations which we have called
cvclo-niedian.

We might suppose that the held of force- in this short perturbation was produced by a descent of
ravs towards the earth, similar to that towards the terrella, which occasioned the appearance of one of
thi' areas of light that we find in fig. 68. We will examine a little more closely into the resemblance
of the field of force observed, to that which was to be expected according to the experiments and Stor-
mer's calculations. We will however draw attention to the fact that we have not yet any experiments
that are exactly suited to this perturbation as regards date and hour.

At Zi-ka-wei, Dehra Dun and Tiflis, the arrows are directed westwards, answering to the condi-
tions near the point at the eastern end of the patch of light. Fig. 79 distinctly shows the direction of
the current to be as one would expect. The north-westerly direction of the arrows in Central and
Northern luiropc, the south-westerly at Dyrafjord, and southerly in eastern America, correspond again
to the rest of the path; but there is nothing answering to Axeloen.

It is natural to look upon the whole lield of force as a composite field, imagining it to be partly
formed by polar precipitation round Axeloen and Dyrafjord, but also bv precipitation in lower latitudes
of stiffer rays, and probably chiefly conditioned bv the latter.

We may also mention the fact that some of the polar elementary storms already described, and
described only as elementary, sometimes have (ields that may be regarded as the production of cyclo-
median storms. The best example of this will be found on Chart 11 for the 3 1 si March, 1903 (p. 122!,
win-re it is ol exactly the same shape as that now under discussion.

15y assuming a composite lield such as this, we also find an explanation of the positive values of
/',, which occurred in the system's area of convergence, and which thus seem to be at variance with
the assumption ol a single polar elementary system in the auroral zone.

\\ e have al.-.o subsequently met with a similar disagreement as regards /',, e. g. on the 26th
December, where we have indicated the probability that there the rays came comparatively near to the
earth in lower latitudes. 'Ibis had special reference to the ravs that occur in cvclo-median storms.

PART I. ON MAGNETIC STORMS. CHAP. III. l6g

THE PERTURBATION OF THE 28th DECEMBER, 1902.

(PI. XIII.)

56. This perturbation is not one of those that it was originally intended to describe, and the time
is therefore not given in my circular dated June 1903. There are thus only a few more or less chance
observations besides those from the Norwegian stations. What has determined us nevertheless to describe
it is the peculiarity we find on comparing the curves for Dyrafjord with those for the American stations.
The perturbation occurrs chiefly between 4h 40™ and 61', that is to say about midnight, local time, at
the three easterly North American stations.

The well defined deflection in the curves for Dyrafjord indicates that the storm could be a polar
elementary one, of which the district of precipitation perhaps is in the vicinity of that station. The time
of the perturbation, however, differs from that generally found in the best examples of polar elementary
storms at the Norwegian stations. The conditions at Kaafjord and Matotchkin Schar also show with
sufficient distinctness that there is no field of precipitation at those stations, the perturbing forces there
being quite inconsiderable. At Axeleen, on the other hand, there are more powerful perturbing forces,
and the perturbation there is of somewhat longer duration than at Dyrafjord, as it begins earlier and
concludes at about the same time. The character of the curve too, is so different that it is difficult to
decide whether the perturbing forces at these two stations arise from two separate systems or not; but
this question is of no great actuality in our study of this storm. The main thing is to prove the con-
nection between the perturbations at Dyrafjord and the American stations. The form of the curves has
a very great resemblance to those found in Europe during the polar elementary storms occurring at
about midnight on, for instance, the I5th December. We should therefore imagine that in this instance,
the field on the midnight side was similar to that previously found at the Norwegian stations; and a
closer investigation seems to verify that so is the case.

On Chart I, for 4h 45™ and jh, there appears to be an area of convergence in the east of North
America, and adjoining part of the Atlantic, and in the west of Europe. This should indicate that in
the neighbourhood of Dyrafjord, possibly a little to the west of it, there should be a stormcentre with
current-arrows directed westwards. It is impossible to determine the size and position of the field of
precipitation more precisely with the comparatively few data that we have to go upon ; but the conditions
at Sitka indicate that it must extend comparatively far westwards in North America. Judging from the
curves for Sitka, we may suppose that the same system is at work there as at Toronto and Cheltenham.
The similarity between the curves at these places is great enough to allow such an assumption. The
centre of gravity, so to speak, of the field of precipitation may be assumed to be about the south of
Greenland. Sitka should be situated almost on the main axis.

The rest of the course of the perturbation may now be very simply explained by a westward
movement of this storm-centre. On surveying the curves closer, we see that at Toronto PI, turns from posi-
tive to negative a little earlier than Pd from E to W. In consequence of this the arrows will turn with
the hands of a clock, the current-arrow from S by W to N. Their size at this time, about 5h 20™, is
very small. In Cheltenham Pk and Pd change the sign at nearly exactly the same time, so that here
one does not get a rotation, but more a sudden change of direction from S to N of the current-arrow.
Thus in Toronto the conditions are such, as if the point of convergence passes just a trifle south of the
place, while the conditions in Cheltenham indicate that the point just passes the same. At any rate we
may conclude from this that the point of convergence will pass near these stations. But to determine its
course more exactly is difficult, as precision in the fixing of time here plays an important part.

At Sitka the directions of the arrows are at first rather constant, but then turn with a counter-
clockwise movement, showing that as the system moves westwards, the place comes into the area of

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903.

fetRkELANb. THE NORWEGIAN AURORA SOLARIS EXPEDITION, 1902 — 1903.

convergence. If we suppose that the principal axis of the system is always almost tangent to the
auroral zone, it corresponds exceedingly well with what one would expect.

Chart II for jh

jh jo'

and /'' 45'", shows the conditions as they subsequently develope.

We can here distinctly follow the movement described above.

The storm-centre now is entering North America, and at the last two hours named it is perhaps
situated a little to the west of Hudson Bay; for it may be concluded from the arrows that the transverse
axis must pass between Sitka on the one side and the eastern stations on the other.

The force at Dyrafjord in the mean while has decreased considerably, showing that the storm-
centre has moved away. At Axeleen, too, the forces are considerably less than before.

We thus have in this perturbation an instance of a polar elementary storm that occurs at a different
time of day, and has a somewhat different course, from those described previously. There may, more-
over, possibly be other perturbing forces in Europe. The declination-curve for Stonyhurst, wich we
have, points indeed in this direction; but we have not the material to enable us to study this more
closely. We have therefore not included this among the elementary storms.

The movement of the system in America that we have here met with, will be also investigated
more throughly in the material from 1882 — 83; and we shall there find similar conditions during nearly
all the perturbations that occur in this region at about this time of day.

TABLE XXV
The Perturbing Forces on the z8th December, 1902.

Gr M T

Sitka

Toronto

Cheltenham

Dyrafjord

Pk

Pd

Pk

Pd

Pk

Pd

Pk

Pd

P,

h m

4 45

— 13.9 y

E 16.37

+ 21.67

E 15.! 7

4- 17.47

E 5-9 y

- 154-3 y

E 43-7 •

- M-77

5 o

- 15-4 »

» 24.8 »

4- 11.3 »

» 18.1 >

•f 13.2 »

* 8.9 »

— 124.5 »

» 36.8 >

— 26.5 »

15

— IO.2 »

> 8.1 >

- 4-5 »

> I3.O>

o

» 7.1 »

— 71.6 »

> 31.2 »

- 36-9 *

3°

+ 25.2 »

» 26.6 »

— 6.8 »

W 33.1 »

- 1.8 «

W 19.0 »

- 63.3 »

« 19.8 »

— 26.5 »

45

+ 10.6 »

• 14.4 »

- 3-6 •

> 28.3 »

- 1.5 »

» 19.0 »

- 57.8 '

> 9.0 »

- 36-9 »

6 o

— 2.2 »

» 7.7 »

+ 5-9 »

» 6.0 »

•+• 5-3 »

» 4.8 »

o

• 4-5 *

- 47-2 •

15

- 7-5 »

> 8.6 »

4- 4.1.

0

-I- 4.1 »

» 1.2 >

— 6.6 »

* 10.4 »

- 47.2 »

30

— 6.9 •

» 6.3 »

o

o

o

» 1.2 »

0

» 3-5 '

— 34.1 »

TABLE XXV (continued).

Gr. M. T.

Axel0en

Matotchkin Schar

Kaafjord

Pk

Pd

P,

Pk

Pd

ft

Pk

Pd

Pt

b m

4 45

— 86.0 7

E 68.57

+ 19-7 /

- 8-9 y

o

- 12.57

- 8.47

E 5-5 /

o

5 o

- 65.7 •

» 53.1 «

4- 4.9 »

— IO.I »

E 2.6 7

— 6.6 »

- 8.4 »

» 4.7 »

- 4.27

15

— 68.0 »

» 39-a •

— 22.1 »

o

o

+ 8.8 t

- 4.8 »

o

— 2.1 *

3°

— IO. I >

• 19.7 .

- 49.2 »

+ 14.4 >

0

+ 19.8 » | 4- 3.0 »

» 8.4 >

+ 6.4 »

45

— 40.8 »

« 17.0 »

- 49.1 »

- 5-8 »

W 3.5.

o

- 1.8.

» 2.2 »

0

6 o

o

» 7.8 »

- 49-2 »

+ 7-4 •

0

+ 25.7 .

o

W 1.8 »

4- 4.2 >

15

+ 11.5 »

» 44.8 i

-51-5'

- 5-6 »

> 3.1 »

o

o

E 3.6.

+ 9.6 »

3°

- 8.3.

« 9.2 «

— 24.6 »

- 5-a »

E 1.3 •

+ 18.3 »

i

> 9-5 '

+ 5-7 »

PART I. ON MAGNETIC STORMS. CHAP. III. ryi

Current Arrows for the 28th December, 1902; Chart I at 4h 45m and 5h , and Chart II at 5h 15m, 5h 30m and 5h 45°

it1^/

c,

rv

-:

'

-

7

(.5.0-,

Fig. 80.

172

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

Table. XXV (continued).

Gr. M. T.

Stonyhurst

San Fernando

Pk

Pd

Pk

ft

h m

4 45

W6.3y

o

W 9.07

5 o

> 6.9 >

+ 1-37

. 7.4 »

'5
3°
45

No copy
recieved.

» 4.0 »
a i.i »
» 1.7 »

+ 5-i »
+ 3-8 »
+ 3-a »

» 4.1 »
o
» 0.8 »

6 o

> 8.5 »

+ 4-5 "

» 5-7 *

15

1 5-7 »

+ 7-7'

o

3°

» 2.3 >

+ 9.0 »

E 0.8 »

THE PERTURBATION OF THE 15th FEBRUARY, 1903.

(PI. XIX).

'*• — f,

57. This perturbation appears on an otherwise very quiet day. It is of fairly long duration,
commencing at about 2 p. m. Greenwich mean time, and lasting about 4^2 hours. It is nevertheless
very well defined, and in most cases the normal line can be easily determined, as the conditions before
and after are rather normal. In this respect, however, the conditions in North America present some
difficulty, as the normal line commences at the moment when the curve shows a marked curvature owing
to the diurnal variation; and it appears that, even assuming that conditions are quiet, the form of the
curve is not repeated exactly from day to day.

We have drawn up a table for this perturbation, giving the times of its commencement and ter-
mination and of the P1 maximum, as also the value of the last-named. It appears, as regards the
European stations in particular, that the perturbation does not begin and cease simultaneously in D and
H; and we have therefore determined these times separately.

We see that in Central and Southern Europe the perturbation begins almost two hours sooner
in H than in D, and ends about half an hour earlier in D than in H; but as a set-off, it is on the
whole very strong in D as long as it lasts. We further see from the table that on the whole the
maximum occurs almost simultaneously everywhere, somewhere about i6h 40™. It should be remarked,
however, that the time of the maximum cannot be exactly determined, as the maximal point is not
sharply defined.

Axeleen, Sitka and Tiflis form exceptions in this respect. Axeleen, as the curve shows, has no
well-defined maximum; but the force is maintained, with occasional violent oscillations, in great strenght
from i6h 15™ until I7h 30™. Before the great storm, however, there is a fairly well defined, but much
slighter perturbation. Its course is almost similar to that of the first perturbation appearing at Sitka; it
occurs at about I4h, and has its maximum at about I4h 40™.

At Sitka, the impression given by the curve is that of two almost separate perturbations, each
with its well-defined maximum. The first last from I4h iom to i6h iom, and the second from i6h iom
to about i8h, the peculiarity here being that, in contrast to the other parts of the world, the first part
is the more powerful of the two.

At Kaafjord the conditions on the whole are similar to those farther south in Europe, with the
exception that the conditions in D and H are interchanged, the perturbation in H at Kaafjord almost
corresponding with that in D farther south. During the first part, from 13^ 45m to I5h 35m, it is a

PART I. ON MAGNETIC STORMS. CHAP. III.

TABLE XXVI.

173

Observatory

Beg. in H

Beg. in D

Time of max.

P, (max.)

End in H

End in D

I4h 6m
'5 501
15 4°
ca. 14 40

J4 !5
14 15
14 16

14 '5
M 15
14 14
14 14
14 g1

14 15
ca. 13 15
ca. 13

!4 15

ca. 13 27
ca. 13
ca. 15
14 20
ca. 15 7-5
ca. 15 30

ively the begi

i6l> 14101
15 48'
J4 r5
16 15!

'3 45
r° 5
16 to

16 5
16 15

1° 7-5
i° 7-5
M 45 '
16 12
indeterm.
»

16 7-5
ca. 15
ca. 14
ca. 1 6
16 12
?

16 30

ining and end

jfih a7m

i° 45
16 28
16 33
16 30
16 39
16 42
16 38
i° 45
i° 37-5
i° 45
I5h&i7lii5m

16 38
17 o
16 36
16 45
ca. 16 40
15 45
16 37-5
i° 37-5
i° 37-5
16 33

of the actual

392 /
280 »
141 >
140 »
65 »
58.5 »
50 »

43-5 »

39 >
39 »
38 >
35 & 3i »
29 »
35.3 »
35.3 >

25 »
21.5 »
30.5 »
18 »
16.4 »
12.4 >
10.6 »

storm.

t8h 19"!

17 3o1
17 40
ca. 18 45
18 20
18 19
18 16
18 18
18 18
18 18
18 16

17 45
18 21
18 18
18 8
18 15
18 6
ca. 1 8 30
17 20
17 35
17 15
18 15

i-jh ggml
18 15
18 15
ca. 17 50
18 30

17 44
17 48

17 45
ca. 18

17 45

n 45

18 o

17 45
indeterm.
1
18 o

17 5°
ca. 1 8 30
ca. 17 30
ca. 17 30

7

17 54

Matotchkin Schar .
Kaafjord

Dyrafjord

Wilhelmshaven . .

Potsdam

Val Joyeux ....
Kew

Sitka

Pola

Cheltenham ....
San Fernando . . .

Tiflis

Dehra Dun ....

1 Respecl

well-defined perturbation, occurring almost exclusively in D and V, and having a course similar to that
of the already-mentioned perturbation which occurs at Sitka during this period.

Neither at Dyrafjord nor Matotchkin Schar is any perturbation with a course such as this to be
observed between 13** 45"* and I5h 35™.

At Tiflis a peculiarity appears, in that the maximum occurs much earlier than in Central Europe;
and when the maximum is reached there, there is nothing of that kind at Tiflis, or at any rate only a
small secondary. At the time that the powerful perturbation in D commences in Central Europe, the
declination conditions at Tiflis are undergoing no particular change. The //-curve, on the other hand,
forms a bend similar to that appearing in D farther north; but this deflection is in the opposite direction
to that before and after it, its only effect being to cause the perturbing force to become smaller and
make an oscillation.

At Dehra Dun, Bombay and Batavia also, the //-curve is about of the same form, the only differ-
ence being that this deflection in an opposite direction is so prominent that the total force PI, becomes
greater than that with the previously reverse direction, and the maximum comes at the given place after all.

The conditions are probably most likely to be understood as follows. While the perturbation in
Central Europe is great in D, we are concerned with the effect of at least two simultaneously acting,
principal systems. One of the perturbations is of long duration, and in low latitudes the form of its field
remains fairly constant. While it is going on, a comparatively poverful storm commences, with a some-
what different distribution of force.

174

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

There are fairly powerful perturbations all this time at the Norwegian stations. We also receive
a distinct impression that a perturbation commences during the time in which the great deviation takes
place in more southern latitudes. The conditions before and after the intermediate storms, however, are
somewhat different. Before it, both at Axeleen and Kaafjord, there is apparently a comparatively inde-
pendent system occuring simultaneously, with a course similar to that of the first powerful perturbation
at Sitka, which has its maximum at i5b.

It must thus be assumed that these are in the main polar perturbations; but the conditions are not
simple, indicating, as they do, both in the arctic regions and in lower latitudes, that there are a number
of systems acting to some extent simultaneously. This then is not an elementary storm, but must be
classed among the simplest compound storms.

According to the above, we may consider it beyond a doubt that during the time from i6h to
i7h 30™, we have the effect of an intermediate perturbation with a field of force of its own, the
latter differing considerably, especially in Europe and Asia, from the field before and after.

We have worked out a plate for this perturbation from I4h to i8h, showing the perturbing forces
at one place at various times (fig. 81).

On considering the conditions in Europe and Asia, we get a direct impression that in the above-
mentioned period the effect apparent is that of an independent system.

is* 16* IT* is* »* is* ie* n* is* / n* is* is* n* is

Fig. 81.

PART I. ON MAGNETIC STORMS. CHAP. III. 175

As regards Europe and Asia, the circumstances on the whole justify the decomposition of the per-
turbing force. In America the forces act the whole time almost in one direction, so that decomposition
there cannot be effected.

THE PERTURBING FORCES.

58. In giving a detailed description of the field of force, we will divide the subject into three
separate sections, viz.

(1) from the commencement of the perturbation up to i6h 15™,

(2) „ i6h I5m to i7h i5m, that is, during the powerful intermediate storm, and

(3) » T7h I5m to its termination.

The conditions during the first section are shown on the Charts I, II, III, and IV for the hours
I4h 30™, 15'' om, i6h om, and i6h 15™.

During this period the field of force in southern latitudes, and also at Dyrafjord and Kaafjord,
remains fairly constant. At Dyrafjord the current-arrow points along the auroral zone, but in an easterly
direction. At Kaafjord its direction is SE and E, and at Pawlowsk SSW. At the stations in Central
and Western Europe their direction is WSW, and in the United States WNW.

We thus see that the current-arrows in these districts during this period maintain the form of a
positive vortex, which means that there is here an area of divergence for the perturbing force.

It will be seen that the arrows at Dyrafjord and Stonyhurst are in opposite directions, indicating
that the point of divergence must lie between these stations, that is to say somewhat to the north-west
of Scotland. In the vicinity of the point of divergence, P\ = o. We find moreover that the arrows in
the district between Pola and Stonyhurst decrease throughout, and even at Wilhelmshaven are compara-
tively small. In accordance with our theory, the vertical arrows at Kaafjord have downward direc-
tion. The arrows at Ekaterinburg and Irkutsk indicate further that there is also an area of convergence
for the perturbing force with a storm-centre lying in the north-east of Siberia. During the first part,
hardly any perturbation is noticeable at the equatorial stations, the force on the charts at 14'' 30 m and
I5h being either zero or very small.

In the district about Dehra Dun, distinct perturbations do not begin until about I5h, and at
Honolulu half an hour later, indicating the existence of a perturbing force directed almost due south,
along the magnetic meridian.

It appears from the curves, as also from Charts III & IV, that the perturbations at Dehra Dun and
at Batavia are very similar both in magnitude and course.

The current-arrows moreover are very different in direction from what one would expect if the
direction were to harmonise with the field farther north, that is to say if it were a direct effect of polar
systems. For this reason it seems probable that it is not exclusively polar systems that we have to do
with here. On looking at the charts (III & IV), we receive a very decided impression that in addition
to the polar system, which undoubtly exists, there is an equatorial system, or more correctly speaking
a system of which the greatest effect is to be looked for in low latitudes. The fact that the system in
north has lasted for a appreciable time before anything is noticed at the equator also goes to prove that
the perturbation in the south is due to something relatively independent.

The conditions at the Norwegian stations, Dyrafjord and Kaafjord, have been already mentioned.
The perturbation there is rather slight, and the curve quiet in character. The conditions moreover are
closely connected with those farther south.

As regards Matotchkin Schar, the current-arrow is at first eastward in direction, along the auroral
zone, that is to say in direction similar to that at Dyrafjord. At i6h om the force has already changed.

176 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

The curve on the whole is much more disturbed; and at i6h I5m the instruments oscillate so violently
that we were unable to determine any perturbing force. These great disturbances shows that we are
now in the vicinity of the current-systems; indeed there are indications of precipitation close to
the station.

At Axeleen the arrow during this period is on the whole westward in direction. It oscillates back-
wards and forwards about this mean direction.

The form of the field, as we have seen, remains unchanged during this period in medium latitudes;
in other words, the course of the lines of force is retained. The conditions, however, are not such as
can be explained by the assumption of the existence of a simple, stationary system with constant form,
that has only altered in strength in the course of that time. Were this the case, the relative distribution
of strenght would remain constant all the time. This is not so, however. Sitka, for instance, shows a
very marked maximum in the perturbing force during this period, a maximum that we have already
found at Axeleen, Kaafjord, and Pawlowsk, and of which there is an indication " in North America, but
which is not found in the south of Europe.

The polar storm thus seems to be somewhat variable in character; but there appear on the whole
to be fields with the characteristic properties of the polar elementary storms. We find especially two
areas that are characteristic of the polar elementary storms, the area of divergence in Europe and
America, and the area of convergence in Asia.

If we imagine these two to belong to the same system, and the transverse axis to be drawn in
that system, this axis would pass from a point in the vicinity of Iceland, right across the Pole, to the
district of east Siberia. If we imagine a plane passing through the sun and the magnetic axis of the
earth, the above-mentioned line will almost coincide with the line of intersection of this plane with the
earth. The point of divergence lies nearest to the sun, the point of convergence far from it; and the
field of force shows that as the negatively charged particles sweep down to the earth, they turn off to
the left, as viewed from the sun.

It is difficult to imagine, however, that these are only the effects of a single field of precipitation.
It seems far more probable that the precipitation is concentrated about various areas, and that each of
these produces its characteristic field of precipitation in the north of Asia, which should produce the
area of convergence that we find. The direction of the current-arrows in this storm-centre must be
westerly. The current-arrow at Axeleen indicates, too, a continuation of this system, and thus seems to
confirm our assumption. But in addition to this system, we must assume a weaker one that should
produce the area of divergence in Europe and America, where the direction of the current-arrows in the
storm-centre is easterly, the centre being situated somewhat north of Dyrafjord. Whether we have further
to assume perturbing forces that act principally in lower latitudes, it is impossible to decide; and we
will therefore content ourselves with establishing the fact that these two fields of precipitation account,
in the main, for the fields before us. That we are justified in assuming two such systems is perhaps
not shown with sufficient clearness by the observations we here can bring forward ; but in the chapter on
the perturbations in 1882 — 83, we shall find that this is the view to be taken of the conditions. It
should be possible to account for the direction of the current-arrows in the centre of the weaker system
north of Dyrafjord by rays out of space that are drawn in the manner, shown in fig. 38 b. To make
the matter still more clear, we may refer the reader also to the second case in fig. 39, with values of y
about — 0.7 and further to fig. 50 b.

The second section, from i6h 15™ to I7h 15™.

At most of the stations from which we have observations, the storm is at its height during this
period, and its pronounced polar character is now very marked. We here at least have the effect of

PART I. ON MAGNETIC STORMS. CHAP. III.

177

two systems, as the field in low latitudes, as described under the first section, is supposed to continue
through this period also.

In the intermediate storm, the form of the field in America will be very much as before, the effect
of the force there being rather slight as compared with that in Europe. The perturbing forces also,
which appear during the intermediate storm, and are conditioned by it, form an area of divergence in
this district. An endeavour has been made to separate the field of force of the intermediate storm in
the district of Europe and Asia from the total field. The result of the decomposition is given in Charts
V, VI, & VII. This has not been done in Chart VIII, but the effect of the intermediate storm is still
distinct. This field has the following course. The current-arrow passes through Europe in a SSE
direction, and turns eastwards through India. We here have a distinctly-marked area of convergence,
lying much farther west than in the previous field. The neutral field should be in the region about
the river Obi or perhaps somewhat farther to the east.

This accords well with the conditions at the Norwegian stations. At the north-easterly stations,
Axeleen and Matotchkin Schar, the storm is very violent; and this fact, together with the rapid alter-
nation with time and place, in the curves, shows that the current system must have approached those
stations. Even at Kaafjord we find conditions quite different to those at the two stations named, the
force at the former being much smaller, and its direction very different.

The current-arrows at Axeleen and Matotchkin Schar on Chart V, for i6b 30™, are somewhat
different in direction, that at Axeleen being WNW, and that at Matotchkin Schar WSW. On the follow-
ing charts, they have become almost parallel, a fact which points decidedly to a westward movement of
the current-system along the auroral zone. This condition is rather unusual, for the ordinary polar
elementary storms that we have treated up to the present, and which have had their centre between
Dyrafjord and Axeleen, move eastwards (see I5th December, 1902). This storm, however, occurs ear-
lier than the above mentioned; and we shall find from the material from 1882 — 83 that this is to be
regarded as the normal condition at this time of day. In southern latitudes the corresponding movement
in perturbations such as that of the I5th December, is a turning of the force clockwise. This time we
should have expected a turning in the oposite direction, and on looking at three charts in succession,
we do find a slight counter-clockwise turning in Central and Southern Europe.

At Matotchkin Schar, during the intermediate storm, the balance makes a distinct deflection in one
direction, such as would imply a vertical component directed upwards. The centre of the current -system
should therefore lie almost to the north of this station. At Axeleen the balance oscillates up and down
about its mean position. The force is at first directed upwards, then downwards. If this effect is mainly
due to the system under consideration, it would mean that the greater part of the current-system at first
lay somewhat to the north, and afterwards somewhat to the south, of this station. In accordance with
this, Pt is generally more powerful at Axeleen than at Matotchkin Schar. The total force at the latter
station, however, ,is somewhat smaller than the force that is due to the intermediate storm, as the two
systems probably counteract one another.

At Kaafjord and Dyrafjord the perturbation is much weaker, Pt attaining at both places at the
most about 140 y. The direction of Pt is particularly worthy of notice. At Dyrafjord the direction of
the current-arrow all the time is ENE along the auroral zone, that is to say exactly the reverse of the
arrow at the two north-eastern stations. At Kaafjord it has an intermediate direction. At first it is south-
east in direction, and thus has a tendency to be regulated by the conditions at Dyrafjord. It changes
afterwards to SSW, more in accordance with the conditions at Matotchkin Schar. But on the whole
the conditions at Kaafjord form the transition to the conditions farther south.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 —

178 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

If we seek a simple explanation of the fields formed during this second section of the storm, we
find that it is only necessary to assume a further development of the systems that were supposed to
have produced the fields during the first section. We saw, that the system on the midnight-side had a
westward motion, and the conditions at Dyrafjord may be considered as produced by a system similar
to that assumed in the first section of the storm, that is to say by rays that descended upon the day-
side and were deflected, perhaps in a manner resembling that shown in fig. 50 b on p. 105.

Here, too, the same difficulties present themselves as on several previous occasions. At Tiflis, for
instance, we find positive values of Pv, at any rate at first in Charts V and VI; and we are therefore
compelled to assume that, as already mentioned, perturbing forces also appear in lower latitudes, possibly
produced by systems similar to those producing the cyclo-median storms. We cannot, however, go
into this subject, as the fields do not furnish us with any reliable information concerning these systems.
In any case, the perturbation clearly shows the great variableness of the storm in the region about the
auroral zone, a condition which plainly proves that during this storm the current must come compara-
tively near the earth.

The third section.

The field is given in two charts, IX and X, for the hours I71' 30™ and 17'' 45™ respectively.
The form of the field is the same, on the whole, as during the first period. The chief difference is that
hardly any disturbance is now noticeable at Dehra Dun and Batavia. The conditions at the Norwegian
stations also are the same. At Matotchkin Schar the current-arrow is in the act of swinging round to
the opposite quarter counter-clockwise; and at 17'' 30"° its direction is SSE. There is no current-arrow for
this station on Chart-X, the magnetogram-paper having been changed at that hour. The curves show,
however, that the force ends by being directed northwards along the magnetic meridian. It thus seems
reasonable to assume that all through the intermediate storm; the effect of this system, which we find
before and after, has been perceptible.

Upon the whole we recognise in the current the characteristic feature of these perturbations,
namely, greatly varying local conditions in the arctic regions, while in lower latitudes they vary less
rapidly with time and place. We conclude from this that the perturbation there must be due to a distant
system.

There is another circumstance connected with this perturbation, that may be worth noticing. If we
look at the //-curve in the district from Stonyhurst to Pola during the intermediate storm, we notice
three types of curves. The first of these is formed at the stations Stonyhurst, Kew, and Val Joyeux,
the second at Wilhelmshaven and Potsdam, and the third at Munich and Pola. The curves of the first
and second types both have a marked undulating form; while in the 3rd type there is a single, uni-
formly-directed deflection. This last condition is also found at Asiatic stations.

In accordance with the undulating form in the first two types, there is a more pronounced turning
of the current-arrow. In this there is possibly a resemblance to the previously-described polar elemen-
tary storms. There, too, the turning of the current-arrow was most pronounced at the stations whose
curves were classed under the first two types, and less pronounced in southern latitudes ; and the cause
would then be sought for in a movement of the current-system that produced the effect. I have already
drawn attention to this circumstance in my report "Expedition Norve'gienne 1899 — 1900," pp. 32 & 33.

PART I. ON MAGNETIC STORMS. CHAP. III.

I79

TABLE XXVII.
The Perturbing Forces on the I5th February, 1903.

Gr. M. T.

Honolulu

Sitka

Baldwin

Toronto Cheltenham

Ph

Pd

Pk

Pd

Ph

ft

Ph

r,t

P*

Prf

h ni
13 3°

o

o

- 4-r •/

E io.6v

- 5-° •/

E 4.4 y

- 3-i y

E 4.5/'

- 5-57

E 6.3 y

14 o

0

o ; o

o

- 5-o >

• 3-8 »

— 6.5 »

» 5-° »

— 6.4 »

» 4.9 »

30 o
15 o o

o

—ai.g »
-3i-5 •

» 4-5'
W 15.8 »

— 12.6 »

-15-5 •

W 1.2 »
» 2.5 »

-17.1 »
—24.7 i

W 30 »

» 4-5 »

-13.8 «
— 16.6 •

W 7.1 »
• 7-7 •

3°

o

W 3.3 y

— 17.0 «

» 14.4 »

— 12. 0 »

» 5.1 .

— 17.6 '

» 4.6 »

— 14.2 »

• 9-9 '

16 o

- 4.0 ;.

E 1.7 ,

- 7.8 .

« r.8 »

— 12.5 »

» 8.2 « —15.3 »

> 11.4 »

— 16.2 »

> IO.2 »

15

- 6.6 »

» 1.7 »

- 5-3 •

• 4-5 •

-15.81

« 5.1 » —16.7 «

» IO.2 »

— 16.1 »

» 9.9 »

3°

— i o. r »

o

-14.9 »

E 9.9 »

— 19.3 »

» i. 9 « I —17.6 »

" 14.4 »

— 24.8 »

> 4.9.

45

- 8.0 »

W 4.15 »

— 18.0 »

W 1.3.

— 22.4 »

» 1.9 > |; 2O-3 »

» 8.7 .

-23-3 •

» 3-3 *

17 o — 6.1 »

» 6.6 > —20.9 «

» 20.3 •

— 25.2 »

» 6.36 »

— 21.6 »

» 6.6 •

-23.7 »

» 3-8 »

15

- 4.5 > » 6.6 »

-27.3 »

• '4-9 •

— ig.O »

> 8.9 >

— 21.6 »

» '7-5 '

— 21. 0 »

• 8.2 »

30

- 4-5 »

• 6.2 «

-15-9 •

» 5.0 »

— '5-3 "

• 6.3 »

— 15-3*

» 11.4 »

-15-3 »

» 4.4 »

45

- 2-65 »

» 5-° "

- 1.8 >

» 5.0 »

— 10. 0 »

» 4.4 .

- 8.1 »

» 6.0 »

- 8.6 »

» i.i «

TABLE XXVII (continued).

Gr. M. T.

Dyrafjord

Axel0en

Matotchkin Schar

Kaafjord

ft

Pd

Pc

A

Pd

P,

Ph

Prf

ft

Pk

Pd

ft

1

li m

14 3°

+ 47-6 7

Wi9.8v

-1- 28.7 y

- 87.47

W 23.1^

0

+ 49-57

E 66.6 y

- 12. 0/

+ 4-37

E 8.0 j<

+ 56.57

'5 o

o

?

•p

- 73-7 »

a 56"

0

+ 79-5 »

. 38 2 «

4- 56.0 »

4 8.6 »

» 31.8 »

4-8i.o »

30 + 78.0 »

» 2 1 .0 »

4- 28.7 »

- 35-3 »

' 9-5 »

o 1 4- 70.0 »

> 2.2 >

4- 40 o •

4- 5-5 »

W 6.6 I

4-44.8 »

1 6 o ' 4 109.5 "

,1 3.1 »

+ 34-2 »

- 46.0 »

> 33.0 >

4- 17.2^

— 16.0 .

* 29.0 »

— 176.0 »

4-93.2 »

» 7.3 .,

4-57.2 »

'5 ' 4 93-5 "

O

4- 10.8 »

- 83.0 »

o

4- 17.2 >

Violent oscillations.

— 440.0 »

4-21.5 »

E 29.3 »

+ 33-7 »

30 i 4 126.0 »

E 74.0 >,

4- 8.0 »

— 202. o »

» 103.0 »

-135-0'

- 92.0 .

E 67.0 «

- 5°o,o »

4- S6.o »

» 80.7 »

4-44.8»

45

-1- 84.0 »

W 1.4 .

- 34-7 '

-294.0.

E 43-5 •

— 123.0 •

— 201.0 «

» 109.0 »

-517.0 •

- 3-6 »

» 50.3 »

-27.4 »

17 o

+ 45-5 "

E 2.7 »

o

— 205.0 »

» 129.0 »

-t- 172.0 »

— 96.0 »

« 107.0 •

— 296.0 »

-17.2 »

» 48.8 »

— 30.6 »

15

4- 70.5 .

o

4- 12.2 •

— 290.0 «

W 81.5 .

-135-0 "

- 23.0 . ! » 89.0 »

— 216.0 »

+ 23.3 "

» 25.0 >

IO.2 »

3°

+ 46.6 •

» 15.2 »

+ 32.0 »

-159.0.

E 27.2 »

4- 17.2 «

4- 28.0 »

' 53-o «

— 148.0 »

4-24.5 »

» 34-2 »

+ 19.6 »

45

+ 35-o "

» 9.0 »

4- 41.2 »

— 69.0 »

« ' 8.1 «

4- 22.2 «

?

?

?

4- 5-5 »

» 26.4 »

+ 25.8 .

TABLE XXVII (continued).

Gr. M. T.

Pawlowsk

Stonyhurst

Kew

Val Joyeux

Ph

Pd

P,

Ph

Pd

Ph

Pd

Ph

Pd

P,

h m

14 30 — 10 I •/

E 23.0 y

+ i-57

- 10.7 •/

0

— IO.2 /

o

- 15-27

E 5-87

15 0 — 12. 1 .

' 34-1 •

4- 4-5 '

- 15-8 •

o

- 17.8 »

o

- 18.8 .

» IO.O »

3° i — 7-° *

» 17.2 »

4- 6.6 »

- 8.7.

0

— 12-7 »

0

- M-4 »

• 6.3.

16 o - 6.0 » » 18.4 »

4- 6.0 »

— 1 1.2 »

o

- 14.8 •

o

— 16.4 »

0

No no-

'5 4 4-5 •

» 17-5*

4- 4-5 •

— 16.3 »

E 11.4^

— 18.9 «

E 10.3 •/

— 19.2 »

» 14.7 .

ticeable

30 4- 25.7 »

• 55-2 »

4 1.5 »

— 23.0 »

» 31.4 »

— 23.0 .

. 26.9 »

— 19.6 »

• 31-8 »

deflec-

45 + 21. 1 »

' 41-4 •

+ 1.5 »

- '3-3 »

» 44.2 »

- 15-3 »

• 36-5 "

— 10.4 •

» 24.3 .

tion.

17 o i 4- 5.0 .

• 37-7 »

- i-5 »

— 10.2 »

. 29.4 »

— 12.8 »

• 25.7 »

- 18.8 .

» 22.6 »

15

- 5-0"

» 31-3 '

0

- 18.9 »

. 2O.O «

— 20.4 .

. 15.2 •

— 20.8 »

» IO.O »

30

- 4-5 '

' 81.3 »

o

— 20.4 «

» 12.8 >

— 20.4 1

• IO. I «

- 18.4 »

. 12.6 »

45

— 6.0 . . 23.0 » o

— 12.8 »

» 7-4 "

- 15-3 »

» 3-7 »

- 14.4 .

1 4.2 »

i8o

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

TABLE XXVIII (continued).

Gr. M. T.

Uccle

Wilhelmshaven

Potsdam

ft

Pd P,

Pk

Pd

Pr

PA

Pd

h m

M 3°

— 10.07

W 0.9 7

o - 9-3 7

0

- 14-27

E 5-67

15
3°
16

— 16.0 »

— II.O »

— 20. o »

» 0.5 »
i 0.3 »
o

+ 4.57
+ 7.0.

+ 10. 0 »

- 8.4 »

— 12. 1 »

E 11.67
» 6.8 »
» 4.2 »

1

i!

- 19-9 »
- 14.2 .
- 18.3 »

» 12.7 »
» 5.1 »
o

15
3°

-17.7 »
-24.7 »

E 27.1 »
» 52.6 >

4- 4.0 « II - 8.4 »
+ i.i » - 3.3 »

» 16.5 »
» 45-o •

•S «

— 12.6 •

- 6.6 «

» 12.7 »
» 36.6 «

45

— 1 1 .6 »

» 56.2 »

4- 4.7 » '! 4- 11.7 >

• 5°-7 •

K-i

4- 4.7 »

» 38.6 »

17 —10.6 »

» 41.4 »

+ 14.6 » o

• 25.7 >

2!

s

- 9.2 )>

» 22.3 »

15 -23.9 »

» 24.7 »

4-15.0 »

— 16.3 »

» 14.7 »

<

— 19.0 »

» 11.7 »

3°

-23.9 »

t 14.4 »

4- 9.8 »

— 2I.O »

» 9.2 »

— 19.6 »

» 1 1. 2 »

45

-17.7 »

» 1.3 »

4- 9.2 T

— 14.0 J>

•a 2.4 >

— 14.2 «

J 3.6 »

TABLE XXVII (continued).

Gr. M. T.

San Fernando

Munich

Ph

ft

P*

Pd

ft

ll m

14 3°

- 9-37

0

— 10.07

o

15 0

- 17-7 »

o

— 16.5 »

E 9.97

cfi

3°
16 o

15

- i6-3 »
- 17.8 »
— 19.2 »

o
o
E 6.1 7

— 16.5 >

- 17-5 '
— 16.2 »

» 5-3 «
" 5-3 »
• 19.8 >

"c

0 „

§1

'€ a

3°

' - 18.5 »

» 18.0 »

- 15-5 >

» 36.5 »

c £

45

- i6-3 »

» 22. 1 »

• 7-5 »

» 27.4 »

•3 a

17 o

- 14.8 »

» 18.5 »

- 5-0 »

» 21.7 «

2

S

15

— 20.O *

» I I.I >

- 13-5 »

i 10.6 »

<

3°

- 17.8 »

» 10.7 »

— 17.0 »

• 9.1 >

45

— 12 6 »

» 6.6 »

- 13-5 »

» 2.3 >

TABLE XXVII (continued).

Gr. M. T.

Pola

Dehra Dun

Tirtis

n

ft

A

Ph

ft

Ph

Pd

ft

h m

M 3°

- '3-57

E 3-57

+ 3-2 ;•

O

o

- 12.47

E 10.4 7

0

15 0

- 14.8 «

> 10.4 i

+ 1.2 »

+ 1.57

0

- '3-3 "

» 14.8 »

— 2.87

3°

• 7.2 „ i> 6.9 »

0

- 9.9 »

o

— '5-9 "

» 8.5.

0

16 o

- 16.6 »

o

0

— 12.6 »

W 2.07

- '5-9 '

• 7-4 >

- 2.5 >•

15

- 15.2 »

» 6.9 »

+ 2.7 »

- 9.1 »

» 2.0 J

— 11.9 i>

» 8.3 »

- 1.8 »

3°

— I 1.2 «

» 25.7 »

4- 4.7 r

+ 17-3 '

» 6.9 • i 4- 6.2 »

» 18.5 »

•4- 3.1 i-

45

- 4-5 »

> 26.4 »

4- 2. i »

4 15-8 »

• 4-9 •

4- 9.4 »

» IS-6'1

4- 1.8 «

17 o

- 6.3 »

• 17.411

4- 1.2 >

4- 9.9 >•

0

+ 4-4 »

* 17.4 »

o

15

- 12-5 »

» ii. I »

0

4- i.i »

r 4-9"

- 4-9 »

» 16.0 »

- 23 »

3°

— II. 6 «

» 7.6 »

o

- i.i »

» 3.0 »

— 5-a »

» 13.4 »

- 1.3 »

45

— 9.0 »

» 4.2 »

0

0

» I.O »

- 4.0 '

» IO.O »

o

PART I. ON MAGNETIC STORMS. CHAP. 111.

181

TABLE XXVII (continued).

Gr. M. T.

Bombay

Batavia

Ekaterinburg

Irkutsk

Ph

Pd

P»

Pd

P*

Pi

p.

ft

ft

ft

h m

14 3°

o

+ 4-97

W2.47

o

E ' 7-57

4 11.37

E 9-5 y

15 °

o

+ 4-9 »

> 2.4 >

o

* 28.5 .

4- 15.0 >

» n.8 »

3°

- 7-2 7

- 4-3 »

» 3.0 »

0

> 2O.O »

4 16.0 »

> I I.O »

16 o

-10.75 •

- 9.8 >

» 3-° »

0

» 5.6 »

No

4 16.0 »

i 9.4 »

15

— ii. a »

Wanting.

— 10.3 t

» 3.6 »

+ i-57

» 8.0 »

noticeable

4 16.3 »

» 8.7 »

Indeter-

3°

4IO.2 >

+ 12.8 •

» 7.2 >

+ S-o »

• 14.0 »

deflection.

4 17.0 »

>' 5-5 •

minable.

45

+ I2.O *

4 14.6 »

• 6.0 >

4 10.0 >

> 20. 0 1

4 17.5 »

» 5-3 »

17 o

4 7.4 »

-1- 9-3 »

» 3-° »

4 13.0 »

> 22.5 »

-4- 18.0 »

» 3-5 »

ID

4 I.O »

4 3.9 »

» 2.4 »

4 12.5 >

' 31.4 >

4 16.3 »

» 3.0 »

30 — i.o »

o

» 3-o»

4 10.0 >

» I7.41

4 12.5 i

> 2.8 >

45

0

0

» 1.8 »

4 1.5 »

1 12.6 »

+ 7-5'

» 2.8 »

TABLE XXVIII.
Partial Perturbing Forces on the

February, 1903.

Gr. M. T.

Pawlowsk

Stonyhurst

Kew

Wilhelmshaven

Potsdam

Val Joyeux

PA

Pd

Ph

F'd

/**

Pd

Ph

Pd

P1*

^

P1*

Pd

h m

16 o o

o

o

0

0

o

0

E 427

o

0

o

0

15

4 12.1 x

W 2.3 7

0

E n-47

- '-57

E 10.3 7

+ 3-3 ;•'

a 16.5 »

4 6.0 y

E 12.7 /

0

E 14-77

3°

4 32.2 »

E 34-5 '

- 5-17

• 3i-4«

- 4.1 »

x 26.9

4 8.0 »

» 45-° •

+ 12.0 >

» 36.6 "•

0

» 31.8 »

45 + 27.3 »

» 15.6 »

4 2.5 »

» 44.2 •

- 3-<>"

» 36.5 »

+ 24.0 >

» 5°-7 •

4 21.8 «

> 38.6 »

+ 7-27

> 24.3 >

17 o | 4- n.6 »

» 12.9 »

+ 9-7 »

> 29.4 »

4 8.6 .

» 25.7 •

•f 13.0 >

" 25-7 •

4 7.9 »

» 22.3 •

- 2.4 »

> 22.6 »

15 0

» 6.0 »

4 1.51

» 20.0 >

4 2.0 »

i 15.2 i

- 1.8 »

» 14.7 •

— 2.2 !>

» 11.7 i

0

> 10.0 »

30 4 2.0 »

» 6.0 »

0

» 12.8 •

o

» IO. I »

- 7.0.

» 9.2 »

- 3-1 »

» n. a •

o

1 12.6 »

TABLE XXVIII (continued).

Gr. M. T.

Munich

Pola

San Fernando

Tifiis

Dehra Dun

Batavia

Ph

P-d

P'h

p-d

Ph

Pd

P'*

Pd

P1*

Pd

P'»

Pd

ti in

16 o o

E 5.2 y o

o

o

o

o

o

o

W 2.07 o

W 3.0 7

15 + 2.07

» 19.8 *

+ 3-r7

E 6.9 y

o

E 6., y

4 18.1 7

0

0

> 2.0 » O

i 3.6 »

3°

+ 4-5'

» 36-5 »

-f- 6.7 »

* 25.7 «

0

i 18.0 i

4 20. i »

E 9.2 7

+ 24.3 7

• 6.9 » -t- 22.07

i 7.2.

45 4 11.5 »

» 27.4 »

-h ia.6 »

i 26.4 »

+ 3-77

' 22.1 '

4 12.2 »

» 4.8 »

4 24.3 »

» 4-9 » n + 21.4 »

» 6.0 »

17 o | 4 13.0 »

» 21.7 • . 4 10.3 »

» 17.4 »

4 5-3"

» l8.g »

+ 2.6 »

• 3-3 »

4- 14.6 »

o

+ 12.8 »

» 3.0 «

15 •*• 4-5 »

» 10.6 » ! *f- 2.7 »

i n. i >

0

• II. I »

4 0.8 i

» i.i «

+ 4-3'

< 4.9.

4 5-3*

» 3.4 >

30 o

» 9.1 ^>

o » 7.6 »

0

!> IO.7 '» O

0

o

» 3.0 » o

> 3-° *

l82 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Current-Arrows for the 15th February, 1903, Chart I at 14h 30m; and Chart II at 15h.

Fig. 82.

PART I. ON MAGNETIC STORMS. CHAP. III. jgo

Current-Arrows for the 15th February, 19O3; Chart III at 16h, and Chart IV at 16h 15m.

:

;

»

•

T

1^1

Fig. 83.

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igo2 — 1903.

Current-Arrows for the 15th February, 1903; Chart V at 16h 30m , and Chart VI at 16h 45m .

Fig. 84.

PART I. ON MAGNETIC STORMS. CHAP. HI.
Current-Arrows for the 15th February, 1903; Chart VII at 17h, and Chart VIII at I7h 15m.

Fig. 85.

l86 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.

Current-Arrows for the 15th February, 1903; Chart IX at 17h 30m, and Chart X at 17h 45m.

8.1

1

¥1*. —) e

.

-

»t^

x^

7

7

s

.

,

, .

L

V?) ^

it i

PART I. ON MAGNETIC STORMS. CHAP. III. 187

THE PERTURBATIONS OF THE 7th & 8th FEBRUARY, 1903.

(PI. XVI & XVII).

59. The storms now to be described, some of them powerful ones, break in upon a very long period
of calm, which may be said to have lasted with single exceptions since the cessation of the storms at
the end of November, 1902.

This interruption of the quiet conditions occurs suddenly at the Norwegian stations with a fairly
powerful storm, commencing at 2ih 5™, on the 7th February, and lasting, at Kaafjord, until about i a. m.
on the 8th Februay.

The first perturbation on the 7th does not belong to the series of perturbations mentioned in the
circular, and our material is therefore not sufficiently complete to allow of our investigating it more fully
in southern latitudes. As it happens, however, registerings for this date have also been received from
a few stations in addition to the Norwegian stations, namely from Kew, Wilhelmshaven, Munich, Toronto
and Christchurch. Judging from the conditions at these places, we here have a typical polar elementary
storm, with its centre near the Norwegian stations.

This storm is not succeeded by calm, however. Towards morning on the following day, there are
varying precipitations about the auroral zone. Between 2h and 5'' for instance, there are powerful
storms round Axeleen; and they are also very powerful in Toronto. In southern latitudes too, there is
constant disturbance as time passes.

From 9h to nh on the 8th there is a perturbation that is especially powerful at Sitka and the
American station, and is accompanied by simultaneous perturbations all over the northern hemisphere and
over the southern right down to Christchurch.

Commencing with this perturbation, we will study the conditions more carefully, although in the
first place it is the powerful polar storm, with a maximum at about igh 25™ on the same day, to which
we have especially turned our attention, and which is given in the circular.

As we must confine ourselves to a study of the chief features of the perturbations, we shall here
mainly give our attention to three periods of time, in which the perturbations are particulary powerful.
It will easily be seen from the conditions at Sitka that a division such as this is the natural one, the
three sections being:

(1) the above-mentioned perturbation from gh to n'1,

(2) a perturbation between 14^ and i8h, and

(3) the period from i8b to 23h.

The curves for the second and third periods are shown on the same plate, those for the first
being separate.

THE PERTURBING FORCES.

60. The first section (PI. XVI).

The perturbation is particularly powerful at Sitka, and is especially violent from gh to gh 35m.
Simultaneously at the other stations in the New World, there are fairly powerful perturbations; and we
see directly from the curves that the conditions vary greatly from place to place. We shall find, for
instance, a considerable difference if we compare the //-curves for the three stations, Toronto, Chelten-
ham and Baldwin. At Toronto there is a long, rather powerful perturbation, as also at Cheltenham,
both showing a diminution in H. At Baldwin, on the other hand, H remains almost normal, if anything
a little too great during the perturbation. At Honolulu there is a faint but distinct perturbation in
declination, coinciding with the perturbation farther north. In H too, there is some resemblance in the
form of the curve to that of the declination-curves for the three eastern stations in North America, as
a comparison with the declination-curve for Cheltenham will at once show. A peculiarity is now apparent,

1 88

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

however, inasmuch as the normal line lies in such a position that while the perturbation is at its height,
H is almost normal. At one of the Norwegian stations, Kaafjord, the perturbation is only just percep-
tible, the reason of this probably being that only at Kaafjord are the conditions so quiet that the com-
paratively slight effect is observable. At Axeleen and Dyrafjord. the conditions are very disturbed
before and after. This disturbed condition is also observable in southern latitudes, and is instrumental
in making this perturbation less clearly defined.

It is the conditions in southern latitudes in Europe and Asia that contribute to make those of this
period especially worthy of remark. A very well-defined perturbation makes its appearance there in H,
with a simple course. The force gradually increases to a maximum, after which it once more diminishes
to zero. Throughout this district, the deflection represents a diminution in H,

The table below shows the hour at which the perturbation commences and terminates, and that at
which the maximum is reached, as also the value of Pt at the last named hour.

TABLE XXIX.

Observatory

Commen-
ces

Reaches max.

Pj max.

Terminates

Sitka

h in
8 45
9 o(l)
9 o(')
9 o(l)
8 33
8 34
8 36

8 35
8 38

8 35
8 33
8 38
8 38

he commer

h m

9 i6,5
9hi5m-iohom
9 15 —10 o
9 15 —10 o
10 8
10 o

IO 0
IO 2

10 7

IO O

10 6

IO IO

1° 5
cement is here ta

123 y
4i 7-39 7
37 »—30-5 »
27 > — 39 »

35 >
30.7 »
30.0 >
29.0 »
27.0 »
24.4 »

22.8 »

22.5 »
22.5 >

ken from the

h m

II O

i indeter-
minable

10 49

10 48

10 50
10 51
10 47

10 48

10 52
10 52

Z>-curve.

Cheltenham ....
Wilhelmshaven . .
Kew

Val Joyeux ....
San Fernando . . .

Pola

Dehra Dun. . . .

t1) The time of t

It will be seen, that the conditions at Sitka are rather peculiar as regards the course of the per-
turbation. The three stations in the east of North America come nearest to Sitka. The simple conditions
found between San Fernando in the west and Zi-ka-wei in the east, and between Kew in the north and
Batavia in the south, form a strong contrast to these variable conditions. In the latter district, the
perturbation is throughout chiefly in H. It is well defined, and as far as we can determine, commences
everywhere simultaneously at about 8h 35m. The maximum is not very distinct, but the time of its
occurence nevertheless does not vary greatly. It terminates simultaneously at about ioh 50™. As the
force is practically constant for several minutes about the maximum, Pt max. will represent simultaneous
perturbing forces. The strength, it is true, is throughout somewhat greater in Europe than in the Asiatic
district; but nevertheless, between Kew and Zi-ka-wei and Batavia it does not vary more than from about
30.7 y to 22.5 y. This time the force is comparatively great at Wilhelmshaven too, a circumstance that
may be due to local conditions.

The conditions are represented in three charts for the hours 9'' 15™, gh 36™ and ioh.

From 9h to gh 30™ at Sitka, there is a great current-arrow directed almost due south, as shown
on Chart I. Subsequently the current-arrow becomes smaller and is directed westwards along the auroral
zone. This condition continues from gh 30™ to the conclusion of the perturbation.

PART I. ON MAGNETIC STORMS. CHAP. III.

In the United States, the conditions are fairly uniform all the time. The current-arrows show a
great convergence of the perturbing force.

Owing to the above-mentioned similarity between the form of the curve at Honolulu and that at
the three eastern American stations, we may conclude that this polar storm must have an effect in Hono-
lulu. It is impossible to take out any decided values; but a glance at the curve will show that the effect
consists in a perturbing force directed towards the north-east. The current-arrow, inasmuch as it is
dependent upon the polar system, thus comes to be directed towards the south-east. In this way the
force at Honolulu completes the area of convergence.

In the above-mentioned equatorial district on the eastern hemisphere, the forces are directed along
the magnetic parallels.

With regard to the wiew to be taken of this perturbation, it may in the first place be considered
probable that the conditions in the north of America are mainly determined by a polar elementary storm
at first not very far north-east of Sitka. The centre afterwards travels westwards. It may be remarked
that during the perturbation this district passes midnight. The current-arrow about the centre is pro-
bably directed westwards along the auroral zone. The storm is in the main of a character similar to
those that usually occur a little before midnight, with their centre near our Norwegian stations, and almost
always travelling eastwards.

As regards the simultaneous perturbation over the district between Kew and Batavia, it seems
impossible, both on account of the form of the field and of the magnitude of the force, that this storm
can be a direct effect of the polar system. On the other hand, the field must immediately suggest the
thought of the current round the earth as the cause of the perturbation. Some doubt may be felt on
this hand owing to the disturbing influence occasioned by the polar storm in the western hemisphere.
We have previously mentioned conditions, however, especially as regards Honolulu, which indicate that
there two systems appear simultaneous in H, counteracting at one another. The polar system, from the
form of the curve, must be assumed to act in a northerly direction, when the other must act i a southerly
direction in order to compensate the former, in which case the conditions in Honolulu should be in
accordance with those in the eastern hemisphere.

According to this, it is not improbable that simultaneously with the polar storm there is a pertur-
bation answering to a current round the earth from east to west, a perturbation of the type we have
called negative equatorial storms. Owing to the slight variation of the force from place to place, and
to the uniform course of the perturbation, this current may be assumed to lie at a distance from the
earth of at least a magnitude equal to the radius of the earth; and symmeiry would point to the
regions round the plane of the magnetic equator as its situation.

The main features in the form of the field may thus be explained, as we have seen, fairly simply
in the above manner. If we look at the charts, however, we see, that the field bears an unmistakable
resemblance to those that we should expect to find during the cyclo-median storms. Under such an
assumption, the perturbing forces that appear at Sitka at about gh 15™ also receive quite a simple ex-
planation. It is only necessary to refer to the photographs of the terrella, when, if we compare the
light-area in fig. 68, i with our field, we find the resemblance is striking, if we imagine Sitka as being
near the uppermost angle. If we then imagine the field moved westwards with the sun, we have more
or less the conditions of Charts II and III. The arrow at Christchurch on Chart II is worthy of notice.
It answers to that part of the light-area that falls upon the southern hemisphere; and the direction of the
arrow is also in accordance with what we should expect to find if the system on Chart I were moved
westwards. There may well be some doubt as to the view to be taken of the conditions. Perhaps the
most probable is that at first the perturbation partakes most of the nature of a cyclo-median storm, and
subsequently changes into a more purely polar one.

I go IllRKKI.ANI). TI1K NOKWKr.I AN ATROKA POLARIS KXPKDI T1ON, J 902 1903.

The woiut scftimi, from 14'' om to i8h (I'l. XYIIl.

(al 1 'lie conditions in northern latitudes.

At Dvrafjord, beginning at 13'' 40™, there is a rather long, not violent, but still considerable per-
turbation, which arts principally upon //, tending' to increase it. This condition lasts until the com-
mencement of the violent storm about i8h 35"', and is continued for some time after the conclusion of
the latter at 22'' 15'".

At Kaafjord the conditions are more variable, giving almost the impression of two separate storms,
the lirst with maximum at 14'' 45™, the second lasting from i5h 30"' until the commencement of the
great storm. All three elements are here about equally disturbed, // however most.

At Axeloen the conditions assume the nature of a fairly long perturbation, which maintains more
or less the same character from 74'' o'" until the commencement of the great storm. The perturbation
is strongest between 14'' and 15'', and at about 18'' o"1.

At Matotchkin Schar the conditions between 14'' and the commencement of the great storm, arc
very variable. They very much resemble those at Kaafiord. There is first a very well defined storm
between 13'' 45'" and 15'' 15'", with maximum at 14'' 35™, after which, in the course of a few minutes,
comparative calmness, and then once more the storm leaps up with oscillations principally in the same
direction as during the first part of the perturbation.

In connection with these conditions at the Norwegian stations, we will examine those at Sitka.
Here the perturbation is particularly powerful from 14'' 24'" to 15'' 45™, the maximum being at 74h 45™.
Thus this storm commences during the same period of time, and has its maximum at the same hour as
the first powerful impulse, which was especially well defined at Kaafjord and Matotchkin Schar. We
find, however, that on the whole it apears somewhat later at Sitka. After this first powerful storm there
is comparative quiet, and then once more a slight perturbation appears, principally affecting //, and
lasting from j6h 30™ to i8h.

(b) 1 he conditions in loiter Intitudcs.

In Europe the conditions assume the character of a lengthy perturbation, which begins to be par-
ticularly perceptible at about 13'' 45™. In declination the conditions vary a good deal, the curve being
now above, now below, the normal line. In tin: horizontal intensity the conditions remain more constant.
All the time, until the powerful storm commences, there is an oscillation in II, answering to a diminution
there, this condition being also continued after the cessation of the powerful storm, and lasting until past
midnight. Here too we notice a particularly powerful perturbation with maximum at 14'' 42™. This
augmentation occurs at the same time as the previously-mentioned, particularly powerful storm at the
northern stations. This characterisation of the conditions is also applicable to Tiflis, and indeed, especi-
ally as regards //, also to the district from Dehra Dun to Hatavia.

At Dehra Dun there is quite a powerful perturbation in //. Here too 11 remains on the whole
below the normal, right up to the commencement of the great storm; and this condition continues after
the latter has ceased. In declination, especially as regards Dehra Dun, there are small oscillations
towards the east.

At ( hristchurch also, perturbations occur throughout the period under consideration. In // the
conditions here are nearly the reverse of those at Dehra Dun, as // throughout has too large a value.
The already-mentioned perturbation with maximum at 14'' 45"' is very marked here too, and is quite
powerful both in // and in 1), and quite distinct even in / '. Here too its maximum is at 14'' 45™;
but it is of shorter duration than in the northern hemisphere.

There is some disturbance in the United States, but strange to say no particularly well defined
oscillations such as at Sitka anil the European stations.

PART I. ON MAGNETIC STORMS. CHAP. III. jg!

At Honolulu the conditions are very quiet, with the exception of the period about I4h 45™. If we
look at the //-curve about the time mentioned, we shall find some similarity between its course here and
at Christchurch, a similarity which may lead to the bringing of the perturbations here and at Christchurch
into connection with one another.

The field during this second section is given on three charts (IV, V and VI).
Chart IV represents the conditions at I4h 45™,

„ V at three hours, viz. i6h iom, i7h, and 17^ 30"*, and

„ VI at i8h om.

As we see from the curves, the perturbations within this period cannot be regarded as consisting
mainly of a single perturbation, but as a series of short, principally polar impulses with somewhat chang-
ing centre.

Axeleen occupies a peculiar position, the perturbing force there remaining throughout fairly constant
both in magnitude and direction. The conditions here do not in any way resemble those at the other
Norwegian stations, the force at Axeleen being almost equally strong, but opposite in direction, and the
current-arrow principally directed towards the west. The conditions at Axeleen, moreover, show an
entirely independent course, in which there is nothing answering to the successive maxima and minima
that we notice, for instance, at Kaafjord.

On Chart IV, for 14'* 45™, we find at the three southernmost Norwegian stations, current-arrows
of considerable strength directed eastwards along the auroral zone. In Europe and the west of Asia,
there is now a corresponding area of divergence. At Sitka there is a fairly strong current-arrow directed
towards the north-west; and at the same time, the other American stations indicate that there is an
area of convergence. It would appear from the form of this area that we had before us the effect
of polar precipitation with the storm-centre a little to the west of Sitka, that is to say in a district situ-
ated on the night-side. The direction of the current-arrows round this district must then be westerly.
The field as it appears on this chart thus seems to be somewhat complicated, but the form is not
an unknown one. If we compare these conditions with those, for instance, shown on Charts IV and V
for i6h 45m and 17'' on the gth December, 1902 (p. 75), we find that the resemblance is striking.
The time, moreover, should be noted at which these two storms commence. The conditions remain
more or less constant throughout this period, the changes consisting principally only in a certain amount
of variation in the strength of the forces, but little in their direction, so that the form of the field is not
essentially changed, at any rate in higher latitudes. The changes that do occur can all be accounted
for by the translocation of the systems. The period extends, as we have said, from I4h to i8h and we
thus here too find a resemblance to the gth December.

In the preceding perturbation on the I5th February, we also found exactly analogous conditions at
these stations during the first two sections. There does not seem to be any essential difference between
the fields on these two days, the only ones being that on the present occasion the stormcentre, with its
eastward-pointing arrows at the more southerly Norwegian stations, stands out more distinctly, and that
the system extends farther east than in the preceding storm. The current-arrows are also stronger, and
the area of divergence is more distinct.

The resemblance between the fields is so great that it is impossible to regard it as chance; and
we involuntarily receive the impression that the field before us is possibly typical of the polar storms
that appear at this time of day, just as we have previously found the typical form of the field that forms
about midnight, Greenwich time. In what way, in my opinion, the field is to be understood has been
already indicated in the description of the preceding storm, and I will therefore only refer the reader to it.

192 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

In the perturbations that follow, we shall moreover have an opportunity of studying the fields that
form at this time of day; and we shall see that conditions similar to those that we have here pointed
out will be continually repeated.

At the three hours shown on Chart V — i6h iom, T7h, and I7h 30™ — we also find on the whole
the same conditions as at I4h 45™, the only difference, besides a diminution in the strength of the
forces, being a change in the direction of the arrows in the eastern hemisphere, as if the precipitation on
the day-side were moving westwards with the sun. The change, however, also may be due only to the
diminution in the strength of this system upon the night-side.

We have previously mentioned that the curve for the field now under discussion gives the im-
pression of several relatively independent systems succeeding one another. In this case therefore, it
would perhaps be natural to consider the one system as vanishing, and new systems being formed, in
such a manner that they advance towards the west. The curves for Dyrafjord seem perhaps to make
such an assumption of new systems doubtful, as the conditions there remain fairly constant. The move-
ment may also be explained by the assumption that the night-system moves westwards, and little by
little destroys the effect of the eastern part of the day-system.

The conditions at Sitka and Honolulu indicate, though only faintly, an area of convergence answer-
ing to a precipitation on the night-side. At Baldwin, Cheltenham and Toronto, there is a very small
force. It appears, from investigations of the material from 1882 — 83, that systems on the night-side have
a west-ward motion. The reason why the forces in eastern America are so small in the present instance,
may therefore possibly be that the storm-centre has now moved too far away. This, moreover, is in
accordance with the fact that its effect in Europe becomes more noticeable.

On Chart IV, for i8h om, the same conditions continue at Axeleen. Matotchkin Schar also seems
now to be mainly influenced by this precipitation.

At Dyrafjord the force is now particulary strong, and the current-arrow is still directed towards
the east. It seems to be this precipitation on the day-side, which now lies farther west that especially
gives to the field in lower latitudes its character, as there is here an area of divergence. At Kaafjord
the force is smaller, but seems mainly to be determined by the precipitation at Dyrafjord.

The third section, from i8h to 23**.

We have already, in the preceding section, had an opportunity of observing that the powerful
storm breaks in upon one of long duration. This we found to be the case both at the Norwegian sta-
tions and, on the whole, at stations in the eastern hemisphere. This is a well-known circumstance, and
we will only refer to the perturbation of the I5th February. With the same reason as on that day,
we can, by drawing a normal line that forms a harmonious connection between the conditions before
and after, obtain a more exact determination of the perturbation, in so far as it is dependent upon the
powerful polar storm. It will be in the main for the horizontal component as the perturbations in D at
most places seem to be chiefly connected with the polar system.

(a) The conditions at the Norwegian stations.

The violent storm is powerful at all the four Norwegian stations simultaneously, most powerful at
Axeleen and Matotchkin Schar. It is very varied in its details, but the oscillations retain in the main
an uniformity of direction.

At Dyrafjord the powerful storm commences at i8h 33™, and is over at 22h 17™. After this time,
perturbations still appear for a time; but they are principally in accordance with the conditions before-
hand. The perturbation is at its height between I9h 8m and 2oh 14™. At about 2oh 37m the oscillations

PART I. ON MAGNETIC STORMS. CHAP. III.

193

are relatively very small, both in declination and in horizontal intensity, while they remain very powerful
in V. The oscillations in H and D, however, immediately become stronger again.

At Kaafjord the storm becomes powerful at igh 5™, with a deflection that is particularly marked in
declination. It does not become really great in H until 19'' 22™. At about 21'' 41™ the conditions are
quiet for a time, after which there is only a very slight perturbation; and at 22h 40™ comparative calm
has supervened. In all the three curves the deflections are uniform in direction all the time, and towards
the side that is typical for these powerful polar storms. The deflection in the F-curve is particularly marked.

At Axeleen we also get an impression that the storm makes its appearance while other disturbances
are taking place. The actuel storm begins here very decidedly at 19'' jm. It suddenly increases, and
ten minutes later it is at its height. Right on to 21 u om, it continues very violent; but from that time
until its close at 22'' 33"" there is only a small perturbation.

At Matotchkin Schar the powerful storm is of longer duration than at the other stations. In H it
sets in with considerable strength as early as i8h 37™, and in the D-curve at i8h 58™. The perturba-
tion principally affects the //-curve, where it lasts until 22'' 2im. Considering the violence of the storm,
the oscillations in the Z>-curve are very small and variable. What is especially remarkable is that the
perturbation throughout has so little effect upon V. It does, it is true, generally decrease V; but the
oscillations are not great and sometimes to the opposite side of the mean line.

The oscillations at the Norwegian stations, with the exception of those in declination at Dyrafjord,
which are deflected towards the west, have the directions characteristic of those storms, which occur
before midnight at the Norwegian stations, and are powerful and of short duration.

(b) The conditions in southern latitudes.

Simultaneously with the storm in the north, a powerful perturbation is noticed on the continent of
Europe. It is especially powerful after 19'* 5™, and increases in the course of a few minutes to a
maximum, which occurs at igh 18™. At 2oh 34™ it is once more comparatively slight, and at 22'' 48™
it ceases in declination, although it still continues for a long time in H.

At Potsdam, and still more at Pawlowsk, there is a well-defined perturbation in V. The deflection
is always in one direction, and answers to a diminution of V.

At Munich a small deviation from the normal is just perceptible. Here, too, V becomes less.

At Pola there is a greater effect in V, and principally on the opposite side.

The conditions at Tiflis form the transition to those at Dehra Dun and the Asiatic district. On
the one side they very much resemble those farther north in Europe; but on the other hand, the varia-
tion in the //-curve at Tiflis exhibits a close correspondance to the variations in the district between
Dehra Dun, Zi-ka-wei, and Batavia, which exactly correspond with these in the storm in the auroral
zone. We notice, for instance, the sudden great change that took place in H about 19'' 5™, indicating that
the polar storm at the Norwegian stations makes its appearance at this hour. We here find conditions
that justify a decomposition of the perturbing force. We will in the first place remark that there are
variations in //, which in the main closely correspond with simultaneous variations in the perturbation-
conditions at the Norwegian stations. We find, for instance, at 19'* 6™, a sudden change in the //-curve,
H having risen, in the course of twenty minutes, from a value that is 14 y below the normal, to its
highest value, which is 28 y above the normal. The oscillation then decreases a little in strength, and
then once more increases, attaining a new maximum at 2oh iom. The perturbation then gradually de-
creases, and about 2oh 40"', the //-curve coincides with the normal line. In the course of an hour, the
horizontal intensity has become almost normal, and continues to decrease, remaining below the normal
until far into the night. There is, as we see, an oscillation which actually accompanies more or less
simultaneously the storm in the north; and in order to bring out the conditions that belong to these

Birkeland. The Norwegian Aurora Polaris Expedition. 1902—1903. 25

194 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

storms, we must, if possible, consider as an effect of the polar storm the deviations from the conditions
before and after the period in which the polar storm occurs. In this way the conditions are certainly
elucidated, as will best be seen when we come to consider the field of force. If we look at the total
force as belonging to the polar storms, we here find a change in the direction of the force that has no
parallel farther north, where, as we shall see, it remains almost constant in direction throughout the
perturbation.

At Christchurch too, there is a very considerable and well-defined perturbation, which is particularly
well developed in H, and exhibits a course that in the main resembles that at Dehra Dun, but has
perhaps a still greater resemblance to those in North America.

In the western hemisphere we also find simultaneous considerable perturbations, which are especi-
ally powerful at Sitka, but also of no little strength in the United States; while even at Honolulu there
is a very considerable effect on that day.

We will first consider the four northernmost stations.

In the //-curve, in particular, the course of the perturbation exactly corresponds with that at our
Norwegian stations. It commences with some strength at about I9h om, increases rather rapidly to a
maximum, and remains fairly powerful for about an hour, after which it diminishes, but then once more
increases somewhat, and forms a new, secondary maximum at 21 h 3om. We have then first a powerful
maximum and then a weaker one — a condition we observed at all the Norwegian stations. In declination,
on the other hand, the conditions here are somewhat peculiar. A perturbation appears at the three
stations in the east of North America, at 17'' 56™, answering to a deflection westwards, and remains,
excepting for a short interval when the polar storm is at its height, almost constant for several hours,
only ceasing at about 23'' om. Whatever this deflection may be due to, we must assume that it cannot
be the effect of the system we are now considering, as this does not begin to act until more than an
hour later.

At Honolulu a distinct variation is noticed especially in the //-curve, coinciding with the polar
storm; but on drawing the mean line, it appears that there are perturbations both before and after.
Before, H is greater than the normal, while after, it has a value that, is considerably below the normal.

The field during the powerful storm is shown on ten charts. The first represents the conditions at
19'', the last at 22h 30™. In southern latitudes a decomposition of forces has been effected on the charts
from I9h 15™ to 21'' 30™, but at the Norwegian stations and Sitka this has not been done. At the latter
places the powerful storm is so dominant that the total forces are principally conditioned by the powerful
polar storm. The field at these northermost stations remains, as we see, fairly constant in its -form
throughout. At the Norwegian stations the current-arrows on the whole are directed westwards along
the auroral zone.

At Dyrafjord the current-arrows at first have the very usual direction, WSW (see the chart for
jgh i^m^ byj afterwards turn northwards, and remain almost the whole time pointing towards the west,
or even farther towards the north. The vertical component of the perturbing force is directed upwards
all the time.

At Axeleen and Kaafjord we have the field that is typical of these storms. The current-arrows
are almost parallel — except at about 19'* I5m — , and WSW in direction. The horizontal component of
the perturbing force is greatest at Axeleen; but on the other hand, the vertical component at Kaafjord
is greater throughout, and is directed upwards at this station, and downwards at the former. At
about i9h 15™ a peculiarity makes its appearance at Kaafjord, namely, that the horizontal component
becomes about 0, while at the same time the vertical is very powerful. To explain this, it is natural to
conclude that there is a local perturbation at Kaafjord of contrary effect. Sharp local deflections such

PART I. ON MAGNETIC STORMS. CHAP. III.

195

as these are very frequent in these regions. This impression is also confirmed by a study of the copies
of the curves.

At Matotchkin Schar the current-arrow maintains the characteristic direction, making oscillations
about the main direction.

Up to the chart for 2oh, the force is almost as strong at Dyrafjord as at Matotchkin Schar; but
on the next chart, that for aoh i5m, the field in the north shows that the storm-centre has moved east-
wards. The force at Matotchkin Schar has increased, while that at Dyrafjord has diminished. At the
same time the current-arrows for Axeleen and Kaafjord have acquired a distinct divergence.

In southern latitudes the field is decomposed. The dotted arrows represent the field as it is before
and after the polar storm. As regards this field, we will only state that it has on the whole the same
character as that in the previously-mentioned perturbation from 9'' to nh. The current-arrow in the
eastern hemisphere is directed westwards, and that in the United states towards NNW.

That which here especially interests us, however, is the field in so far as it is connected with the
storm in the north. The current-arrows to represent this force are drawn with broken lines. The field,
as we see, may be characterised in a few words by referring to the previously-described polar elemen-
tary storms e. g. of the i5th December, 1902, and the loth February and the 22nd March, 1903. This
holds good, at any rate during the time when the storm is at its height, and the perturbing forces can
be most accurately determined. There is a distinctly-marked area of convergence in the eastern hemi-
sphere, and a distinct area of divergence in the western. In Europe the direction of the current-
arrows is at first south-west; but between igh i5m and ig11 46™, they turn a little counter-clockwise. They
then, however, turn back, a turning that is in accordance with the eastward movement of the field, which
we deduced from the conditions at the Norwegian stations. Simultaneously with this, there is also a
clockwise motion of the arrow at Sitka.

Although the conditions in the main are similar to those found during the usual polar elementary
storms that appear at this time of day, there are also certain deviations from the typical conditions.
The force in Europe, for instance, at about 2oh and 20'' 30™, seems to be comparatively small, while at
Sitka at the same time it is comparatively great, and turns, as we have said, in a positive direction.
The distribution of force cannot here be explained by the assumption of a single elementary system.
The comparatively great force at Sitka indicates that there is a simultaneous precipitation on the day-side ;
and it seems as if in Europe at this time — 2oh om — there are possibly two systems counteracting one another.

We will look more closely into this peculiar variableness of the conditions in Central Europe.

While the direction varies greatly from place to place, the force is small. There is no doubt
that the direction of the force, especially during lengthy perturbations, becomes uncertain, when the
absolute value of the force is small, as the unavoidable error in the placing of the mean line with small
forces will have a great influence; but nevertheless when we look at the curves, there is a very notice-
able change from place to place. This difference is especially evident in the //-curve. Here there are
three types of curves; the first is found at the stations Stonyhurst, Kew and Val Joyeux, the second at
Wilhelmshaven and Potsdam, and the third at Munich and Pola. Within each type the form of the
curve is very similar.

It has been already said that this storm exhibits many points of resemblance to the storm of the
1 5th February, 1903, and in this respect also, there is now a complete accordance between the two days.
On that day also the //-curve showed exactly similar differences in the European field; and the stations
were separated into exactly the same three groups, a circumstance which strongly confirms our opinion
that this is not a chance resemblance.

196

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902— 1903.

TABLE XXX.
The Perturbing Forces on the 8th February, 1903.

Gr. M. T.

Honolulu

Sitka

Baldwin

Toronto

Cheltenham

Ph

Pd

Pk

Pd

Pk

Pd

Pk

Pd

PI,

Pd

h m

9 15

+ 3-5 7

E 7-5 y] +74-3 7

E 97.8 y

-r 5-1 7

W36.9 y

-a8-4 7

W29.5 •/

- 6-3 7

W26.I V

36

+ i-5 »

., 4-1 »

-48.4 ,

„ 18.0 ,

+ 1-4 .

n 22.9 „

-28.4 „

n 22.9 .

- 3-7 .

, 25.5 .

10 O

+ 2-3 .

. 5-° .

-39-5 »

n 22.6 „

- I.I .

. 3°-5 »

-24-7 .

. 3°-2 .

- 7-3 .

. 28.5 .

14 45

+ 7-1 .

W 7.4 .

-54-8 „

W34-7 ,

- 7-9 »

. 12.7 „

-14-4 ,

, 16.3 „

- 6.3 ,

„ 8.9 „

16 10

o

0

- 1 .0 „

E 14.0 „

+ 9-7 ,

E 3-7 ,

+ 1.8 „

0

+ 4-° ,

. 2.3 „

17 o

+ 2.O „

„ 8.3 ,

-I3-I »

W 5.4 .

4- 1.8 „

. 5-7 »

- 0.9 „

E 4.8 „

- 2.3 „

E 2.3 „

3°

*- 4-1 .

» 12-4 »

-H-7 .

„ 10.4 ,

- 1-8 „

0

- 3-6 „

0

- 7-9 .

,, 3-° „

18 o

+ 7-9 .

„ 12.4 ,|+ 1.8 „

. 6.3 „

+ 1-4 .

W 4.4 „

— 4.0 w

W IO.2 „

- 5-2 .

w 5.3 .

19 o

+ 1.8 .

, 10.0 , -I4.2 „

,, i3-5 .

-10.7 „

. 12.7 „

- 9-0 .

, 16.3 „

- 9-2 ,

, 1 1 -3 »

15

- 5-4 »

„ 10.0 „ —23.5 „

. 6.3 „

-21.5 ,

. n-4 »

-15-3 ,

. '5-6 .

-22.4 „

. '3-i .

3°

-13-0 .

,, 10.8 ,

— 40.0 „

. 19-° »

-38-4 „

. 14-° .

-38-6 „

. n-5 ,

— 42.6 „

, 14-3 „

45

-15-8 „

. ".6 „

-4'-5 »

. i3-5 .

-37-o «

» '3-3 .

-29.7 „

, "-4 n

— 40-4 »

. 7-i .

20 o

— 16.9 „

„ IO.O ,

-45-i .

» 22.5 ,

-42-0 .

. 1-9 »

-34-2 ,

EIS-I .

-43-o »

E 14.8 „

15

-i5-i ,

» 10.8 ,

-42.5 .

. 47-4 .

-37-o .

. 5-7 .

— 35-2 »

. 4-8 „

-37-5 n

. 1.8 .

3°

-IO.I ,

, 8.3 ,

— 26.2 „

„ 6O.O „

— 27.2 „

. II-4 .

— I7-I ,

W 6.0 „

-28.3 „

W 7.1 „

21 O

- 8.2 ,

. 1-6 .

-15-1 .

, 32-5 .

-iS-i .

» r4-6 »

- 4-0 .

. 9-6 ,

-16.0 „

„ 1 1-9 .

3°

— 1 0.0 „

E 2.5 .

-18.1 .

» 34-3 .

— 21.2 „

» 18.4 „

-10.3 ,

, 1 8.6 „

— 21. 0 „

, 17.8 „

22 o

- 9-2 .

. 5-8 .

-"•7 »

» 23.4 „

— 19-4 »

. 16.5 „

- 8.1 „

» '3-2 ,,

— 16.0 „

i, u-9 »

3°

— 1 1-5 .

. 5-8 „

- 3-9 »

» 2-7 .

-I2.5 „

. H-O ,

- i-3 »

„ 10.8 „

- 8.7 .

„ I°.t »

TABLE XXX (continued).

Gr. M. T.

Dyrafjord

Axeloen

Matotchkin-Schai

Kaafjord

Pk

Pd

ft

Pk

Pd

P,

ft

Pd

P»

ft

Pd

P,

b m

9 15

- 13-7 y

W 20.5 y

- 58.67

+ 55.1 y

E 15.87

+ 44.27

?

?

7

- 13-5 y

E 8.4 7

- 3-9 7

36

o

„ 1 1-4 «

— 2 1-6 „

+ 42.3 »

. 38.8 „

-f- 22.O ,

7

7

7

7-3 »

» 9-5 „

0

10 o

+ 23.1 „

„ 28.5 .

— 21.6 „

o

» 29.4 ,

- 30.8,

?

?

?

- 9-a»

, 13-2 „

+ 13-8 ,

M 45

+ 77-° »

E 1 2. 1 „

+ 15-5 r,

- 88.0 „

W 50.8 ,

- '9-6,,

+ 134.07

W 58.07

- 47-77

+ M5-0 „

W 43-8 ,

-i- 60.3,

16 10

+ 118.0.

» 2.7 „

- 8.0 „

- 57-o ,

» 31-8,

+ 14-7 »

+ 87. o „

, 69-3,1

+ 183.0 „

+ 78-0 ,

„ i5-o „

+ 50.4 „

17 o

+ 107.0,

» 2.7 „

1-9 .

- 61.1 „

, 21.2 ,

o

+ '33-o.

E 7-1 „

+ 165.0,

+ 70-5 „

o

+ 62.0 ,

3°

+ 47-8,

„ 6.3 „

4- 6.6 „

- 108.0 „

. 24.7 „

+ 37-o „

+ 75-5 »

5-3 ,

- 5-9,

+ 30-0,

E 18.7 „

+ 64.0 ,

18 o

I- 97-° .

. 5-2 „

+ 13-6 .

-129.0 ,

. 12.8,

4 118.0,

5-4 .

„ 26.6 „

- 89.3,

+ 30.0,

» II-° n

+ 28.2 „

19 o

- 35-7 ,

W a6.i ,

-134-0,

- 47-5 .

, 54-8 ,

4- 22.1 ,

-223.0,

„ 144-0 „

- 57-o r

+ 33.9,

W 44-7 „

— 7-° »

15

— 262.0 „

E 21.5 ,

-213.0,

-509-0 „

E 59-o .

+ 2II.O,

-294.0 „

* 136.0 „

— 282.0 „

+ 48.5.

E 52.5 *

— 190.0 „

3°

— 226.0 „

W 96.1 ,

-188.0,

— 428.0 ,

,, I2I.O,

+ 211. 0 „

—383.0 „

„ 3°-° »

- 106.0 „

— 226.0 ,

0

— 242.0 „

45

- 175-0 »

. 163-0 ,

-258.0,

1—480.0 ,

„ 116.0,

1-492.0,

— 292.0 „

. 8z.on

- 7i-5»

— 282 o „

„ 37-o »

- 196-0 „

20 o

- 199.° .

. 195-0 „

- 96'0 „ , — 297.0 „

, 38.9 .

+ 334-o»

—33°.o „

» 307.0 „

- 85-2,

-346.o,

» 86.5 „

— 282.0 „

15

- 59-3 .

„ 10-!. 0 „

— 108.0 .

—299.0 „

o

+ 354.0,

— 292 o „

„ 172.0 „

— 134-0,

-288.0,

, 141.0 „

-355-0,

3°

7-7 .

K 64.9 ,

— 148.0 ,

-330.0 ,

„ 104.0 ,

+ 302.0 „

— 221.0 „

» 44-3 »

— 136.0 ,

— 182.0,

„ 87.5 ,

-253-0 .

21 0

- 66.5 ,

. 50.7 .

-199.0,

— I IO.O ,

0

+ 343-0,

-353.0 „

, 190-0,

- 87.0,

- 77-2 ,

, 29-o „

— 232.0,

3°

- 94-o „

. 5°-7 .

- 7i-o „

- 46.5 „

W 38.9 ,

+ 208.0 ,

— 142.0.

» 160.0,

+ 22.3,

-128.0,

„ I04-o ,

- 48.5,

22 O

+ 36-3.

. 42-3 .

— I59-0 »

- 71-5 .

E 9-8,

+ 187.0,

- 18.7,

» 67.0 „

— SI-I „

- 54-o,

, 30.5 ,

- 69.5,

30

+ 72.0 .

E 12.8 „

- 92-0 ,

— 21.2 „

0

+ 145-0,

+ 22.0 „

» 20.3 „

- II.9,,

2-4 „

» 19-4 ,

- 54-° „

PART I. ON MAGNETIC STORMS. CHAP. III.

I97

TABLE XXX (continued).

Gr. M. T.

Pawlowsk

Stonyhurst

Kew

Val Joyeux

PA

Pd

P,

P*

Pd

PA

Pd

PA

Pd.

P,

h m

1

9 15

?

9

?

7

?

- 20.9 7

E 1.9 y

- 16.07

O

C

it

36

7

?

?

?

?

- 26.4 ,

o 1 — 27.2 „

o

f

10 O

7

•p

7

?

?

- 32-5 .

W 4-7 .

- 3°-4 .

0

c
•

M 45

-34-7 /

W 6.4 7

4- 6.7 7

-n-3 y

Ws4.o 7

- 15-8 .

„ 10.7 „ - 26.4 „

W 8.4 7

u
Ml

c

16 10

- 7-° n

„ 1 8.0 „

4- i.o » o

o

- 3-o ,,

« 4-2 « || — 10-4 a

n 7-5 .

'•£

o

17 o

-"•5 »

o

4- i.o „

-iQ-7 »

0

- 11.7 »

O

— 15-2 .

o

c

3°

- 1.5 -

E 9.6 „

0

-13-3 „

E 8.6 .

— 10.2 „

E 13.1 „

— 1 1.2 B

En.7 ,

I

18 o

- 7-5 »

O

0

- 4-1 »

,.j

- 8.7 „

„ 8.4 .

- 4-8 „

. 6.7 „

jf
o

n

19 o

-26.6 „

W 2.3 „

+ 3.0 „

- 9-7 „

Wio.g „

- 12.8 „

W 6.1 „

— M-4 »

W 4.2 „

c

15

4/ 20. 2 „

E 39-i ,,

4- 1.5 .

-H-7 .

£45.1

— 24.0 „

E 30-9 »

— 10.4 „

E 20.8 ,

a

e

0

3°

4- 30.6 „

a I °.6 „

- 9-o „

4- 25.4 „

. 49-7 „

4- 19.4 „

. 52.9 „

4- 12.8 „

, 62.0 „

*

45

4 25.1 „

O

-16.4 .

4-19-4 »

-, 39-4 „

4- 16.8 „

. 4LI .

4- 23.2 „

. 43-5 .

a

M

20 0

- 7-0 „

„ 1 6.6 „

— 20.2 ,1+5.1 „

, 8.6 ,

+ 4-1 .

« !5-9 n

4- 20.0 „

, 20.8 „

1

15

4-10.6 „

n 32.6 „

— 26.2 H

- 8.1 „

» 47-5 . j - "•? »

,, 44-9 .

- 2.4 ,

. 50.2 „

1

i

3°

- 8.0 „

„ 30.8 „

— 23.9 „

-15-3 »

» 3r-4 u

- 18.8 ,

, 33-6 ,

— 12.O „

n 35-2 .

co

'rt

21 O

— 21.6 „

n 15-2 „

-15-7 „

— n.7 »

» 9-1 »

- '6.8 „

, '4-5 .

- 13.6 „

. 19-2 ,

'E

3°

— 21.6 „

„ 34-5 „

— 1 1. 2 „

-20.5 „

, 11.4 ,

- 25.5 „

. '4-5 .

- 25-6 „

, 20.9 ,

=

32 0

-18.6 „

„ '9-8 „

- 3-7 „

-'3-7 »

. 8.6 ,

- 18.3 „

. 9-3 »

- 18-4 ,

. I5-I .

1

3°

— 12.6 „

„ 10.5 „

— 1-5 „ I1 —12.2 „

„ 2.8 , — 14.3 „

, 5-i »

- 18.4 „

. I0.9 „

o

H

TABLE XXX (continued).

Gr. M. T.

Wilhelmshaven

Potsdam

San Fernando

Ph

Pd

P,

Ph

Pd

ft

Ph

Pd

h m

9 15

— 33-7 y

o

o

?

?

?

— 17.0 7

W 1.6 7

3°

— ig-6 »

E 1.2 y

0

?

7

?

-17-0 „

„ 8.2 „

10 o

— 3°-° .

0

0

?

?

?

— 26.4 „

.. 12.3 „

14 45

- 41.1 ,,

W3o.6 „

0

— 36.0 y

Wi6.3 y

4-3.67

— 26.4 „

» 21.3 „

16 10

- 13-' .

» I4'1 H

4- i.o j

-10.7 „

, II-2 „

o

- 89 „

. 9-8 „

17 o

— 18.2 ,

„ '-2 „

4- i.o ,

-'5-8 ,

E 2.5 ,

o

-14.8 .

0

3°

— 1 2. 1 „

E 16.5 „

+ 3-°»

- 7-6 „

. 14-2 .

-0.6,

-14-8 „

E 1.6 „

18 o

- 8.9 „

, 3-6 .

-t- 2.O „

-12.3 .

B 4.O „

-"- 0-6 „

-17-° «

W 3.3 „

19 o

- 25.2 .

W 9.2 „

+ 2.0 „

-23-3 »

W 4.0 „

+ 2.7 „

—35.2 „

„ 8.2 „

15

- 3-7 »

E 62.3 .

4- 6.0 „

- a-5 .

E45-7 ,

4- 0.6 „

—a6.6 „

E 13.1 „

3°

4- 57.0 „

, 66.0 „

4 12.0 „

+ 35-I »

> 39-6 „

- 4-5.

0

„ 27.8 „

45

4- 24.7 „

. 39-1 »

-f 4-0.

+ 24.3 »

» 29.5 „

-3.6,

4- 1 1.8 „

„ 2.1.6 „

20 o

- 13-5 .

, 8.6 „

— a.o „

- 8.5 „

. 13-2 »

0

- i-5 .

„ '3-9 .

15

+ 3-7,

. 57-5 .

4- 3-° »

+ 3-5 .

. 46.6 „

- 5-4 „

-13-3 .

„ 18.8 „

3°

- 17-2 „

» 37-3 »

o

-14.8 ,

. 3°-5 .

- 2.7 „

— 22.2 „

H 4*1 l»

21 0

— 24.7 .

, IO-4 .,

o

— 20.5 „

„ 11.7 „

— 2.1 „

— 25.2 „

o

3<>

— 32.2 „

. 19-6 „

o

-3a.a „

, 20.3 ,

0

-32-5 »

0

22 0

— 22.9 „

» 13.3 „

o

— 34.6 „

„ 12.2 „

O

-25.8 „

0

3°

— 19.6 „

„ 8.6 „

0

— 22.7 „

„ 8.1 „

o

— 22.3 „

o

198

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

TABLE XXX (continued).

Gr. M. T.

Munich

Pola

Tiflis

Dehra Dun

Pk

Pd

P,

Pk

Pd

P,

Pk

Pd

P,

Ph

Pd

b m

9 15

-11.57

o

0

-'i-5 7

0

o

1

7

-15-7 y

Wn.8 v

36

- ii-5 „

0

0

-18.8 „

W 0.7 7

0

?

?

-17-3 .

,, 5-9 ..

10 o

— 22.5 „

o

o

— 24.2 „

o

o

7

7

— 31.2 „

„ 3-o „

M 45

— 23-5 „

. 12.9 y

o

—32.2 „

ii 1 6-° ii

- 5-1 y

-33-2 7

E 5-9 7

-14-5 ..

E 15-8 „

16 10

- 10.5 „

. 7-6 „

o

— 12.6 „

„ 9-9 .

- 1.9 I,

-17-4 i,

W 7.8 „

— 12.2 „

n 3-9 .

17 o

- 13-0 „

o

o

-'5-3 .

0

+ 1-7 .

— 14.8 „

E 4-8 .

+ 1-9 -

n 7-9 »

3°

- 9-5 ,,

E 9.1 „

0

- 9-4 ,,

E 6.9 „

+ i-9 ,,

- 7-7 ii

,, 7-8 „

•a
G

+ 6.3 „

,, 3-o „

18 o

- 5-0 „

ii 4-6 „

o

- 9-8 „

„ 3-5 ,i

0

- 7-7 „

„ 3-3 ,,

t

O

. 4-9 ,,

19 o

- 19-0 „

W 8.4 „

0

— 21. 1 „

W 2.8 „

+ 2.9 „

— 25.0 „

„ 10.8 „

e

-13-4 ,,

, '3-8 „

15
30

45

- 9-5 f.

4- 22.0 „

4- 23.0 „

E 1 6.8 „
,, 41-2 „
„ 28.2 „

0

o

4- 0.7 7

— '3-9 n
+ 16-6 „

4-19-7 ,,

E 29.2 „
» 29.9 „
,, 22.9 „

4-n.g ,,
4- 3-8 „
- 0.8 „

-14-6 „
4-24.3 „

4-21.7 „

ii 10.8 „
„ 10.8 „

TT 5.2 „

o.

o

CJ

o

4- 9.0 „
+ 26.7 „
+ 18.5 „

„ 6.9 „

» 3-0 „

20 o

+ 1 1 .0 „

„ 7-6 „

+ 1.5 „

4- 6.7 „

„ 22.9 „

4- 2.7 ,

+ n -3 ii

. 6.3 .

+ 16.9 „

„ i-o „

15

4- 4-0 „

,, 37-4 ,,

+ i-5 .,

4- 2.2 „

,. 35-4 »

4-10.6 „

+ 13-9 ,,

„ 17.8 „

+ 17-7 »

„ 4.9

30

- 6.0 „

„ 29.7 „

4- t-5 »

- 9-4 ..

,, 27.1 „

- 1-9 i,

o

„ 1 8.6 „

+ 6.7 .

i, 10.8 „

21 O

— 12.0 „

f, 12.2 „

4- i.i „

-14-8 „

,. 13-9 n

- 1.2 „

-10.6 „

, 14-9 ,,

o

. 1 1.8 „

3°

- 23.5 ,,

,, n-5 ,,

o

— 24.6 „

„ 18.1 „

o

— 14.6 „

„ 22.3 „

o

„ 12.8 ,

22 O

— 19.0 „

„ 9.9 „

o

-19-7 »

„ 13-2 „

o

-18.1 „

„ 13-4 ,,

- 7-i »

, 8.8 „

30

— 18.0 „

,, 5-3 n

o

— 19.2 „

n 6.9 „

°

„ 6-7 ,,

- 8.6 „

,, 4-9 ,

TABLE XXX (continued).

Gr. M. T.

Zi-ka-wei

Batavia

Christchurch

Ekaterinburg

Pk

Pd

P,

Ph

Pd

Ph

Pd

P,

A

Pd

ft

h m

9 15

- 19-27

W 5.0 7

— 22.1 7

O

o

W32.0 /

- 1-5 y

?

7

?

36

~ 19-2 „

o

-18.1 „

o

+ 5-9 y

I, 3-7 n

o

?

7

7

IO 0

— 26.4 „

0

— 13-2 „

o

4- 7.6 „

„ I7-I „

0

?

7

7

'4. 45

4- 1.2 „

E 8.0 „

- 3-2 „

W 7.27

4- 19-2 „

E 20.8 „

-2.8 „

?

?

7

16 10

- 15-6 „

0

-13-5 i,

E 4.8 „

4- 8.7 „

Wii.g „

o

?

7

7

17 o

4- 8.4 „

o

8

4- 4.6 „

o

+ 3-3 »

E 8.9 „

o

7

1

7

30

+ 3-6,,

0

H

4- 4.2 „

o

+ 3-' ,,

„ 8.1 „

4-0.6 „

+ 5-7 y

E 33-i 7

+ 3-7 y

18 o
19 o
15
30
45

o
- 10.8 ,

0

+ 6.0 „
4- 6.0 „

„ r -o „
„ 4-o „

W 3.0 „

» 5-o „

remarkable destu

o
- 9-6 „
- 3-9 „
+ 9-9 ,i
4 9-2 „

n 2.4 „

„ 8.4,,
„ 13-2 „
„ 6.0 „

+ 6-7 ,,
+ I3-4 n
- 8.5 „
-17.8 „
-24.1 „

W 1.5 „
« 3-7 ,,

0

E 8.9 „

.. 7-4 „

4- 1.2 „

+ 1-5 n

+ 0.9 „

0

o

+ 4.5 „

— 2 I.O „

-18.7 „

o

4 20.O „

„ 32.2 „
» 44-5 „
» 44-5 „
» 38.2 „
» 28.5 „

o

- 3-2 „
- 9-5 „
— IS-0 »

ao o

+ 7-2 „

» 5-o „

o

f 8.9 „

» 1.2 w

-25-4 „

i, 8.9 „

o

4-26.0 „

» 24.9 „

-17-4 »

15

+ 8.4 „

n 2.O „

+ IO-7 ,,

» 1-2 „

-'4-3 -i

* 9-6 „

o

4-22.0 „

, 26.8,

-'5-7 „

30

+ 2.4,,

E 2.0 „

4- 4-6 „

11 3-6 „

- 4-9 „

,, 9-6 „

+ 0.9 „

4-14.0 „

n 35-0 »

-'3-9 »

21 O

o

,, 5-o „

- I.O „

» 3-6 „

- 4-9 „

., 3-7 ,i

4-2.8 „

+ 4-2 „

» 44.8,

— II. 2 „

30

o

,, 5-o „

o

„ 3-6,,

- 5-3 .

„ n . I „

+ 3-7 „

- 1-3 »

» 42.0 „

— IO.O „

22 O

- 6.2 „

,i 3-° ,,

- 5-3 »

» 2.4 „

0

I, I4-I I,

+ 4-3 »

- 5-2 „

i> 37-7 n

- 8.7 „

30

— 7-2 „

,, 3-o „

- 7-8 „

,, 2.4 „

?

O

?

- 7-7 „

r, 25.2 „

- 5-o „

PART I. ON MAGNETIC STORMS. CHAP. III.

199

TABLE XXXI.
Partial Perturbing Forces on the 8th February, 1903.

Gr. M. T.

Honolulu

Baldwin

Toronto

Cheltenham

Pk

ft

Pk

Pi

/"*

Pa

fk

ft

h in

19 15

- 5-97

0

— ia.a 7

0

- 7.27

W 3.07

— la. i y

o

3°

- "-Si,

o

- 3°-° n

o

- 30-2 „

n 5-4 «

— 3»-5«

0

45

- "-a,,

0

- 27.2 „

o

- 23-° r,

0

- 28.0 „

E 7.17

20 o

- "-8n

o

- 33-0 n

E ia.1 7

~ 27-8 „

E 27.1 „

- 29.7 „

n 28.5 „

15

- 8.9 „

W 5.07

- 28.2 „

n 5-7 n

- 19-4 n

„ i6.8B

- 23-8 „

H 14-3 *

3°

- 4-1 »

n 2-5 »

-18.6,

0

- 9-9 „

o

- '3-9 n

n 4-8,

21 0

0

E 2-5 »

— 7-5n

W 1.9 ,,

o

o

— 3-1 n

O

3°

- i-°»

n 5-° n

— xa.a „

n 6-3n

- 8.1 „

W 12. 0 „

- 8.3 „

W 5-9,

23 O

+ i.on

* 5-8 „

— "-I »

» 6-3 „

- 8.1 „

n 7-2 „

- 5-° „

n 2.9 „

3°

0

„ 6.6 „

- 5-4 n

n 5-1 »

- 2.2 ,,

n 7-a»

o

i, 2-9,,

TABLE XXXI (continued).

Gr. M. T.

Pawlowsk

Stonyhurst

Wilhelmshaven

Kew

ft

ft

Ph

Pd

Pk

ft

PH

Pd

h in

19 IS

+ 39.2 7

E 39.1 /

- 9-7 >'

E 45-i •/

+ 17.77

E 62.3 y

- 9-1 y

£30.9 7

30

+ 48.2 „

n I°-6 „

4- 4i.aB

n 49-7 n

+ 80.3 „

„ 66.0 „

+ 34-2 n

11 52-9 n

45

4- 44.2 „

o

+ 28-5 »

n 39-4 r

+ 47-5 n

n 39-1 n

+ 32.6 B

n 4I-I n

20 o

+ T3.6,,

n I6.6B

+ "-7ii

» 8.6 „

+ 3-7 „

„ 8.5 „

+ 14.3 „

n *5-9 „

15

4- 28.2 „

n 32-6 „

o

» 47-5 n

+ 24.7 „

n 57-5 n

+ 3-° n

n 44-9 n

3°

4-I&6,

„ 3°-8 „

- 7-1 n

» 31-4 n

+ 2-3n

n 37-3 n

- 3-0 „

n 33-6 n

21 O

- I0-6 n

» 'S-2 n

- 6.6 „

» 9-1 B

- 6.5 „

» IO-4 n

- 3-5 n

» M-5 n

3°

- 6-5,,

n 34-5 n

- l6-3 n

n 1 1-4 n

- 14.0 „

n 19-6 n

- M-8B

» M-5 n

23 O

- 7-° n

» 19-8 „

- 8.1 „

« 8.6 B

- 7-0 „

n I2-2 n

- 9-a „

n 9-3 ..

3°

- 3-5 n

n I0-6 r

- 6.6 „

n 2.8 „

- 2-8B

1, 8.6 „

- 6-1 n

n 5-i n

TABLE XXXI (continued).

Gr. M. T.

Potsdam

Val Joyeux

Munich

Pola

Ph

ft

Ph

ft

Pk

ft

P1*

Pi

h m

19 '5

+ 23.07

E 45-7 /

O

E 20.8 /

+ 6.57

E 16.8 7

4- 6.77

E 29.2 7

3°

+ 61.2,,

n 39-6 n

^ 28.7 7

„ 6a.o „

+ 39-5 n

» 41-2 »

+ 39-3 „

» 29-9 »

45

+ 48.8 „

n 29-5 »

+ 36-8 „

n 43-5 i,

-t- 4°-5 »

. 28.2 „

+ 4°-7 n

» 22.9 „

20 0

+ r4-5»

n '3-2 »

+ 29-5 n

» 20-8 n

+ 3°-5 >

» 7-6 ,

+ 27.3 „

» 22.9 „

15

+ 27.4 „

n 46-6 n

+ 10.4 „

n 5°-3 n

+ 20.5 „

» 37-4 »

+ 23-7 .

» 35-4 »

3°

+ 7-6 „

n 3°-5 »

o

» 35-2 „

+ 10.0 „

» 29.7 „

4- u. a „

» a7-r »

21 O

o

n "-7 ,,

o

n '9-2 n

-f 2-5»

, I2-2 .

+ 4-o,

» '3-9 .

3°

- "-7,1

» 20.3 „

- 12.8 „

n 20.9 „

- 8.5,

» x7-5 »

- 6-7,

. 18.1 „

22 O

— 5-3 r

T, 12.2 „

- 8.0 „

n IS-I n

- 6.5 „

» 9-9 .

- 4-4 n

» '3-a »

3°

- 5-3 n

n 8.1 „

- 8.0 „

n IO-9 n

- 6-5 „

> 5-3 »

- 4-4 „

. 6.9 „

200

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

TABLE XXXI (continued).

Gr. M. T.

San Fernando

TiHis

Dehra Dun

Zi-ka-wei

Batavia

Ph

P

Ph

Pi

P1*

I'd

/"*

Pd

Ph

Pt

li la

19 IS

0

E 13.1 7

-»- 7-27

E 10.8 7

4- 13.8 v

W 7.9 y

+ 14.4 y

W 5.07

+ 8.57

E 8.47

3°

+ 25.8 7

„ 27.8 „

+ 44-1 »

. i°-8 „

4- 41.0 „

, 14-8,

+ i9-a»

„ I2.O „

4- 22.8 „

» '3-2 „

45

4- 35-5 ,

» 24-6 „

+ 42-8 „

» 5-2,

+ 32.7 »

. 9-8,

4- ai.6 „

, *5-° »

4- 22.8 „

» 6-°,

20 0

4- 22.2 „

» 13-9.

+ 32.1 „

» 6-3»

+ 3*-S»

» 9-8,

4- 22.8 „

„ IS-",

4- 22.8 „

„ 1.2 „

15

4- 10.4 „

. 18.8 „

+ 34-1 „

. '7-8 „

-*- 31-5-

. 4-9 »

4 22.8 „

. 10-° »

4- 24.2 „

1-2 „

3°

0

4-i »

4- 20.7 „

» 18.6 .

+ i9-3 „

o

4- 15-6 „

» 3-0,

4- 18.8 „

„ 3-6,

21 O

— 2.2 „

0

+ 7-5,

. 14-9 »

4- ii.8.

0

+ 15-6.

0

4- 14.6,

. 3-6 „

3°

— 12.6 „

o

+ 3-i»

» 32-3 »

+ 7-9 »

o

4- 10.8,

o

+ " -4 D

. 3-6,

22 O

- i°-4 *

0

- 0.8 „

. 13-4 .

+ 3-i,

o

+ 10.8 „

o

+ 5-7,

»-4 >

3°

- 8.1 „

0

- 2.2 „

» 6-7 „

O

o

+ 3-6.

0

+ 4-6 „

„ 2-4 „

Current-Arrows for the 8th February, 1903; Chart I at 9h 15m.

Fig. 87.

PART I. ON MAGNETIC STORMS. CHAP. III. 2OI

Current- Arrows for the 8th February, 1903; Chart II at 9h 36m , and Chart III at 10h.

\

••

II

"

.

;

.

f

7

'

Fxnpriil

Fig. 88.

1002—100^1.

26

2O2 BIRKELANb. THE NORWEGIAN AURORA POLARIS EXPEDITION, I9O2 — 1903.

Current-Arrows for the 8th February, 1903; Chart IV at 14h45m, and Chart V at 16h 10m, 17h and 171' 30m.

£V

-s^-

^

-

"T

a;

s

$-

tr~

}k

Chlh
Oi Qi
Dh D £iAm DM*

fa

5 F So* FfnaM-

.,

Zkw Ii •*•-•

ro

Scd.

_i_j '

PART I. ON MAGNETIC STORMS. CHAP. III.

203

Current- Arrows for the 8th February. 1903; Chart VI at 18h Om , and Chart VII at 191' Om .

Fig. go.

204 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Current Arrows for the 8th February, 1903; Chart VIII at 19h 15m, and Chart IX at 19h 30m .

PART I. ON MAGNETIC STORMS. CHAP. III.

Current-Arrows for 8th February, 1903; Chart X at 19h 45m . and Chart XI at 2Oli Om .

205

Fig. 92.

206 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 1903.

Current- Arrows for the 8th February, 1903; Chart XII at 20h 15m, and Chart XIII at 2O1' 30m .

PART I. ON MAGNETIC STORMS. CHAP. III. 207

Current-Arrows for the 8th February, 1903; Chart XIV at 21h Om, and Chart XV at 21h 30m,

B 3 k Oatltka/l

.,

Zll vj Ii -fci.n

i,

%x

...

.; ,

Br

T1'

c?

17

I

Fig- 94-

208 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Current-Arrows for the 8th February, 1903; Chart XVI at 22h Om, and Chart XVII at 22h 30m.

**'/

* V

%

'• .

Ekitcrmt* p.

«!

,

"CL

V

\_rn_

Fig. 95-

PART I. ON MAGNETIC STORMS. CHAP. III. 209

THE PERTURBATIONS OF THE 27th & 28th OCTOBER, 1902.

(PI. IV).

61. Throughout the first half of October, there was calm as far as our arctic stations were con-
cerned. About the 24th, however, a violent storm takes place, lasting from about 5 hours before mid-
night Gr. M. T. until 4 hours after. During the succeeding days, perturbations of more or less strength
occur, beginning late in the evening and attaining their highest development at about midnight. As day
advances, there is once more calm, but the storm returns again before midnight. This condition of
things contjnues, and culminates m the violent storms about the 3ist. From some of the stations there
is included a characteristic equatorial perturbation, occurring on the 2gth and soth. This perturbation
is already described Art. 54.

The time occupied by the perturbations of the 2yth and 28th October is from 14'' on the 27th
until about iu on the 28th, the curve for this period being shown on Plate IV.

At the arctic stations, the character of the conditions is that of two separate storms, one of which
occurs early in the afternoon, with its maximum about 16''. This is fairly powerful at Axeleen, while
at the other Norwegian stations it is comparatively less so. The other storm is at its height at about
22 h to 23'', and is a well-defined, fairly powerful perturbation, lasting about three hours.

In southern latitudes, the direct impression of the conditions of this perturbation is to some extent
quite different. We will take, for instance, the condition at Tifiis, a station that occupies an intermediate
position between the polar and the equatorial regions, and where we are therefore likely to find con-
ditions that are characteristic of both. Here the perturbations last much longer. Even earlier than noon,
there are perturbations indicating the presence of a perturbing force directed northwards. At about 13''
the force turns round, the perturbation appearing also distinctly in declination, where it is directed east-
wards. With the exception of one intermediate storm, this state of affairs lasts until 20'' 24™. The
interruption lasts from 15'' 24™ to i6h 54™, and thus coincides in time with the already-mentioned
perturbation in the north. The same thing is found at Dehra Dun and Batavia, but there the perturba-
tion is chiefly in H.

Finally, from 21'' 40™ until about midnight there is a perturbation that occurs simultaneously, and
is in connection with the perturbation round the Norwegian stations. It is most powerful at our Nor-
wegian stations, but in southern latitudes it is much less than the perturbation that occurred earlier.
In this way, the treatment of the perturbation falls naturally into two sections, the first from I4h to
2oh 30"", and the second from 2ih 40™ until about midnight.

THE DISTRIBUTION OF FORCE.
62. The first section. I4h — 2oh 30™.

The perturbation during this period is especially worthy of remark from its being particularly
powerful at the equator, in the regions about Dehra Dun and Batavia.

While these comparatively powerful perturbations are taking place at the equator, there are also
storms round the auroral zone. We see, on the other hand, that the effect in America increases
towards Sitka, where there are two distinct maxima during this period. One of them coincides with the
already-mentioned intermediate storm and occurs between ish 30™ and iyb i5m. This is preceded by
a powerful perturbation lasting from I3h to I4h 45"".

From this it would appear that this part of the perturbation shows, to some extent at any rate,
the effect of polar systems, which this time seem to keep, in some measure, fairly near the regions to
the north of Sitka.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903. 27

210 HIUKll-AM). Till: .XORWFC.IAN AfROKA POLARIS EXPEDITION, 1902—7903.

There is much resemblance between this lirst section of the perturbation and that of the whole on
the 1 5th February, which is -worthy of notice, and is immediately apparent on looking at the curves.
They also both occur at about the same time ol day.

At Sitka the two perturbations resemble one another also in detail. On both days the rendi-
tions are those of two separate perturbations, each of about the same duration and following the same
course, and each with a wcll-dclined maximum. The chief difference is that the perturbation of the 151!)
February occurs on the whole about 40 minutes later in the day. The resemblance extends still farther,
lor about three hours before this perturbation, there are on both days two fairlv powerful and well-
defined, but brief perturbations; but the perturbation occurring at about midnight on the 2yth October
has no parallel on the 151!) 1-ebruarv.

The resemblance is not, however confined to Sitka. Both in Furope and India, the conditions
exhibit surprising points of similarity. If we look, for instance, at the curves for Tiflis, we find on both
days a long perturbation answering to a perturbing force towards the south and south-east. This is inter-
rupted by another perturbation of short duration, which represents a perturbing force directed towards
the north-east; and in both cases this occurs simultaneously with the latter of the two almost separate
storms at Sitka.

The curves for the Norwegian stations also exhibit some similarity. At A.xeloen there is the distinct
effect of the system that forms the first perturbation at Sitka from 13'' to 14'' 45™; this however pos-
sibly does not appear so distinctly from the copied curves, as these lirst begin at that time when the
perturbation has re-ached its maximum. After this perturbation the intermediate storm commences with
a strength, which relative to the preceding storm and to the storms on the other Norwegian stations,
forms a good analogy to that taking place on the 151)1 February, 1903.

The perturbation of the 1 5th February has already been described at length, and most of the
remarks there made with regard to the theory of the perturbation may be applied to the present case:
On the whole also we find a good correspondence with the conditions for the 8th February but the
details that day are here not quite so striking resemblant as on the i5th.

As on the '5th February, the distribution of force be-fore and after the intermediate storm is about
the same. This section ot the perturbation therefore divides into two parts,

(1) the long storm, and

(2) the brief, intermediate storm.

The field during the long storm is shown on Churls I, II and ///at 14'', 15'' and 15'' 30™ and
alter the intermediate storm on L'lnni III at 17''. Here too, it shows as a whole the very same con-
ditions as the field on the 151)1 February.

The current-arrow at Kaafjord and at Matotchkin Schar is directed eastwards on the whole, while
that at Axeloeii is directed westwards. Also the same conditions which we have found (see p. 191!
with the previously described storms which appear at this time of day. Farther south in Furope, the
current-arrows also point in a westward direction. There is also the remarkable circumstance that the
force increases southwards from Stonvhurst and Kew. At 1'awlowsk, the force before the intermediate
storm is almost insensible, whereas in the district between Tillis and Batavia it is very strong, and
strongest of all at 1 >ehra Ihm. In the United States the direction of the current-arrow is NNW. At
Sitka the current-arrow has a typical direction, north-west. At Honolulu the conditions are very quiet
during the whole twenty-four hours.

It thus appears that the strong effect found in the south of Asia is not limited to those regions only,
but does not extend round the equator. We see that as on the 151)1 February, North America and
Europe constitute an area of divergence ol the perturbing force. The neutral point should be situated

PARTI. ON MAGNETIC STORMS. CHAP. III. 211

in a region not far from Stonyhurst. Whether there is an area of convergence on the other side of
the world, we cannot say, as there is no material from those regions.

The intermediate storm, like the corresponding one on the i5th February, is particulary powerful
at Axeleen and Matotchkin Schar, and probable less so at Kaafjord as far as we can see from the curve,
which at this time has disappeared from the magnetogram-paper. The current that conditions the per-
turbation seems therefore now be near our north-eastern stations. The duration of this storm is also
about the same. In Central Europe and southwards to Batavia, its commencement and termination are
well characterised. It occurs between I5h 30'" and i6h 45™. The corresponding storm on the I5th
February lasted from i6h I5m to 17'' 45m.

In the eastern hemisphere a decomposition has been undertaken, the result being shown on
Charts IV, V, and VI, at i6h, i6'1 20™, and i6h 30"' respectively.

Throughout the western hemisphere, with the exception of Sitka, the perturbation is somewhat less
powerful than in the eastern. The effect in the United States is principally noticeable in H, showing that
the current-arrow for the intermediate storm would be directed westwards. As these however are very
small, we have not marked them on the charts, but only drawn the current-arrows corresponding to the
total force. The eastern field in this storm is of about the same form and proportional strength as that
of the 1 5th February. The current-arrow in Europe points south-east, and turns off towards the east
through southern Asia. As Zi-ka-wei it even goes a little north, so that there is a good indication that
the current-lines here form an en entire circle, as they return in the regions round the Norwegian sta-
tions, where the arrows are directed westwards along the auroral zone. On the western hemisphere, on
the other hand, there is certainly an area of divergence, with, it appears a weaker perturbing force.
The field in the intermediate storm is thus of the same character as that found in the polar elementary
storms. This also applies to the northern stations.

At Matotchkin Schar and Axeleen there is a powerful perturbation with current-arrows directed
westwards. The vertical intensity at Matotchkin Schar is very great, and is directed upwards; at Axel-
een the balance moves up and down about its mean position. At first P, is directed downwards, but
in less than a quarter of an hour it has changed, and is directed upwards, after which it changes once
more. There is the same variableness in P, on the I5th February, but on that occasion it begins by
being directed upwards. At Kaafjord, both now and on the isth February, the conditions are more in
accordance with those in southern latitudes, the arrow being directed towards the south-east. The circum-
stance of the current-arrow at Kaafjord having almost the opposite direction to those at the two north-
eastern stations, is also found on the 15th February, and its probable explanation we assumed, in the
description of that perturbation, that there was a precipitation on the day side.

For this storm there are unfortunately no registerings from Dyrafjord; they would have been of
very great significance.

The second section. 2ih 40"° -- about midnight.

The polar storm from 2ib 40™ to about midnight is very powerful round the Norwegian stations.
Its beginning and end are fairly distinct; it is well defined and simple in its course. This time, too, the
changes in the perturbation are most rapid at Axeleen, where the conditions on the whole are more
disturbed. This storm manifests itself by simultaneously-occurring perturbations, that are observable all
over the northern hemisphere. The table below gives the time at which the storm begins, reaches its
maximum, and ends, as also the maximum value of P,.

212

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

TABLE XXXII.

Observatory

Begins in H.

Begins
in D.

Reaches
Max.

pi Max.

Ends in //.

Ends in D.

li m
22 45<')

21 40(')

21 4o(')
21 38

21 32
21 40
21 40
21 ^8

ca. 2 1 36

21 42
21 ^0
21 42
21 25

21 45

21 40

ca. 21 30
ca. 21
ca. 21

ning of this s

h m
21 45(')

21 40(')

21 40)')
21 36
21 44
21 44

21 40
21 48

21 44
21 45

22 IO

21 40

indeterm.

»

21 40

indeterm.

0

o
>ecial storn

h m
ca. 23 o
ca. 22 20

22 18
23 40
22 46
23 50

22 47
22 54

23 50
22 50

22 58

23 o
ca. 23
ca. 23
23 o
ca. 23
ca. 22 30
23 o

i.

265.0 ;'
240.0 »
225.0 »
30.0 »
29.0 >'
29.0 »
24 o >
23.0 »
22.5 »

21.0 »

16.0 »
14.5 »
14.0 ><
13.0 >;
II.O »
10.5 I>

43 »
4.0 I

h m
ca. o to
23 48
23 5°
23 28
23 20

33 20
23 20
23 26

ca. 23 30

ca. 23 25
ca. 23 40

23 20

oa. o

23 55
ca. o
ca. 23
23 20
ca. o

h m
ca. o 20
ca. 33 50

23 55
o 8
ca. o 20

O 12

ca. o 15
ca. o
ca. o 10
ca. o 15
ca. 23 20
ca. o
indeterm.
»
ca. 23 20
ca. o
o
o

Matotchkin Schar .

Kew

Wilhclmshaven . .

Val Joyeux ....
San Fernando . .

Sitka

Tjflis

Dehra Dun ....
(!) The begir

This storm, as the table and the curves show, appears to be a system tha.t occurs simultaneously
at all the places at which it is in any degree observable, and has more or less the same course. The
effect of the force diminishes on the whole, with increasing distance from the district surrounding the
Norwegian stations. This storm must therefore be classed with the polar elementary storms, and as one
of the very simplest.

The properties of the field may be briefly characterised by saying that its form is typical of the
polar elementary storms that have their storm-centre about the Norwegian stations. It commences also
at the usual time of day. In this way we find again the following typical properties:

(1) An area of convergence situated in the regions about Europe and western Asia.

(2) The point of convergence moves eastwards.

(3) An area of divergence in North America.

On the charts VIII and IX the hours 22h and 22'' 20™, the point of convergence is in the regions
north of Pawlowsk. Pt is comparatively small, and P, is directed upwards. In the later charts, the
forces show that the point of convergence has moved towards the east, the arrow having turned with
the hands of a clock. The current-arrows at the Norwegian stations are directed westwards along the
auroral zone. At Kaafjord and Matotchkin Schar, P, is directed upwards, and at Axeleen downwards,
showing that the horizontal portion of the current passes to the north of the two former stations, but to
the south of the latter.

PART I. ON MAGNETIC STORMS. CHAP. III.

213

TABLE XXXIII.
The Perturbing Forces on the 27th October, 1902.

Gr. M. T.

Honolulu

Sitka

Baldwin

Toronto

Pi,

Pd

Pk

Pd

Ph

Pd

Ph

Pd

h m

14 o

+ 5-6 7

W2.5 y

- 29.0V

W 42.0 y

- 7-8 y

W 5.7 7

- 6.7 y

W 3.0 y

J5 °

0

„ 2-5 »

- 9-7 .

0

- 4-° „

. 14-0 .

0

,, 10.8 „

3°

o

M 7-5 »

- 10.1 „

W 5-4 ,

- 4-0 „

H II-4 M

o

it 9-0 -,

16 o

+ i-3 .

. 5-8 .

— 20.9 „

„ 10.8 „

- 6.1 „

. '7-8 .

- 5-4 n

11 '5-° n

20

+ 3-5 .

. 9-i .

— 22.1 „

,, 44-6 »

- 7-8 .

* 24.2 ,

- 5-8 „

„ 16.8 „

3°

-1- 7-5 ,

i, 2.3 „

— 24.6 „

» 42-0 „

— 5-i „

» 27.3 ,

- 5-8 n

n 21.0 „

17 o

+ 10.8 „

0

— II.O „

,, 26.2 „

o

„ 21.6 „

O

n '9-8 n

22 0

- 7-0 »

0

- 7-8 ,

°

- 5-8 .

. 1-9 .

- 8.1 „

O

20

- 8.9 .

« 2.5 „

— 10.6 „

E 0.9 „

- 8.5 „

0

-I3-5 n

E 8.4 „

40

— 10-3 »

tt 4*2 a

- 8.3 „

W 0.9 „

•>

o

- 9-9 n

,, 7-8 „

23 o

— 10.8 „

„ 4-2 „

- 13-8 .

. 2.7 ,

— 10.8 „

E 2.5 „

-13-5 ,,

n 8.4 „

SO

- 9-8 „

« 4-2 „

— 10.6 „

„ 3-6 „

- 6.1 „

0

- 6-8 n

it 3-6 „

TABLE XXXIII (continued).

Gr. M. T.

Axeloen

Matotchkin Schar

Ph

Pd

P,

Ph

Pd

P,

h m

14 o

— 60.8 ;/

WaS.3 y

— 1 10.0 7

4 43-47

W 6.2 7

+ J7-57

15 o

- Sa-5 it

n 15-0 it

- 61.5 n

+ ca. 78.0 „

n 42.3 n

— 35-i n

3°

- 108.0 „

,, 43-8 „

— 93-5 it

+ ca. 22.0 „

,, °'-° n

— ca. 1 68.0 „

16 o

-ca. 345.0 „

n 04-7 n

4 6i-5 it

- ca. 92.0 „

E 75-8 ,,

-> 168.0 „

20

- 290.0 „

it 6a-5 „

- 46-7 »

- 79-Q n

n 61-5 „

- 152-0 „

3°

19.8 „

it 49-5 n

4 56.5 „

- 97-2 n

» 67-8 „

- "9-0,;

17 o

- 99-0 n

n 52-8 „

- Ia-3n

+ ia.i „

11 20.0 „

47-o „

22 0

— 51-5 n

E 30.2 „

+ 19-1.0,,

- 195-0 11

n I8-0 tt

— I 12.0 „

2O

28.0 „

,, 58.0 „

-f aaa.o „

- ca.2i4.on

„! 12.0 „

- 89.1 „

40

69-0 n

n 63.6 „

4 266.0 „

194.0 „

n 03-3 n

- 70.2 „

23 o

253-0 „

n 81.6 „

+ IIO.OB

- 108.0 „

it 9-8 „

- 56.2 „

2O

- 177-0 n

» 81.4 „

4 295.0 „

- "9-0,1

n 48.2 n

70.2 „

TABLE XXXIII (continued).

Gr. M. T.

Kaafjord

Pawlowsk

Stonyhurst

A

Pd

P,

P*

Pd

P,

Ph

P,

h m

14 o

+ 16.5 7

Wi5.i 7

+ 29.6 y

o

E 6.0 v

o

- 3-5 7

O

15 o

+ 35-2 „

n 25-9 it

+ 26.3 „ - 0.5 7

W 5-5 ,,

0

- 4.6 „

W r. i y

3°

+ >35-2 „

it 37-8 ,,

•+ 35-7 it - r-° it

E 4-6 n

4 0.7 ;

o

n 5-7 n

16 o

+ >35-2 „

E 46-2 „

+ 36.3 „! +12.5 „

it 42-3 n

4 3-0 „

-20.4 „

E ao.o „

20

+ 23.6 „

n 33-3 »

+ 5-2 ,,

+25.1 „

,, 36-8 „

o

- 3-1 it

n 29-7 »

3°

+ 26.5 „

W 2.6 „

+ 17-4 n

0

n 20.7 „

0

0

n I2-6 „

17 o

+ >35-2 „

it 33-3 it

+ 45-1 n

-IS-' n

n 10.6 „

4 i-5 «

- 8.3 „

W 6.6 „

22 0

135-0 „

E 39-2 „

- 75-a n

+ 12.6 „

W 2.3 „

- 3-o „

+ 14-8 „

E 11.4 „

2O

- 1980 „

it 74-0 „

-IOI.On

+ 6.0 „

n 1-3 >

- 6.0 „

4io.7 „

n 10.3 „

40

144.0 „

n 27-7 n

- 137.0 „

+ 10.6 „

it 5-5 ,,

- 8.2 „

+ 12.2 „

n 26.8 „

23 o

- I0°.° n

« 53-3 it

- 127.0 „

4I4-I it

0

-12.0 „

4 8.3 „

n 24-0 „

20

74-9 it

n 72-2 „

-117.° n

- 4-5 n

E 13.8 „

-12.0 „

- i-° it

n >o.8 „

2I4

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

TABLE XXXIII (continued).

Gr. M. T.

Kew

Val Joyeux

Wilhelmshaven

ft

Pd

Ph

Pd

Pv

Pk

Pd

P,

h m

14 o

- 4-o 7

o

- 4-o 7

o

- 4-6 7

W 2.4 7

o

15 °

- 7-7 n

E 3-7 7

- 5-6 „

0

- 7-o „

O

o

3°
16 o
20
3°

- 3-1 »
-23-0 „

-11.2 „

- 7-7 n

o
n "7-3 „
n 35-° n
n 22.5 „

- 9.6 „
-16.0 „
-18.4 „

w 3.3 y

E 15-9 n

29.3 H

n '5-9 n

No
noticeable
deflection

- 7-0 „
-'3-0 „

+ 7-9 i,
- 2.3 „

E 33-6 „
« 42.8 „
« l6-5 n

- 2.0 V
f 9-° n
+ 6.0 „
+ 4.0 „

17 o

*5-3 «

o

-'3-6 n

W 5-0 „

-20.5 „

Wio.4 „

- 3-° n

22 0
20
4°

+ 15-3 n
+ I7-8 „
+ '5-3 n

E 9-7 n
n 4-7 *
n 18.3 „

+ II.2 „

+ 13-6 „

+ 12.0 „

E 8.4 „

n 3-3 n
» J3-4 „

+ 17-7 n
+ 10.7 „

+ 20.0 „

E 9-2 „
» 3-i »
» !5-9 „

A small
pos. deflec-
tion at

23 o

+ 10.2 „

„ 18.7 „

+ 16.0 „

„ i6-7 „

+ 17-7 n

» I7-I n

221*

20

o

n 9-7 n -1 + 3-2 „

» IT-7 n

0

» I2-2 n

TABLE XXXIII (continued).

Gr. M. T.

Potsdam

San Fernando

Munich

ft

Pd

Ph

Pd

ft

Prf

h m

14 o

- 6.3 7

o

- 4-5 7

o

- 4-5 7

E 1.5 V

15 0

- 9-8 „

W 1.5 7

- 8.3 „

o

-10.0 „

n 3-8 „

3°

- 9-8 „

n 4-4 n

- 3-8 „

W 4.2 y

- 8-5 „

o

16 o

-12.0 „

E 28.0 „

-13-4 »

0

-IS-0 n

„ 22.8 „

20

+ 4-4 „

, 3°-5 n

- 6.4 „

E 16.4 „

- i-° n

n 32.7 n

3°

- 6.3 „

n IO-7 »

- 6.4 „

n 9-8 „

- 3-° n

n 21.3 „

17 o

-18.7 „

W 6.2 „

- 4-5 n

O

-I2.S „

o

22 0

+ 15-4 »

E 3-1 n

+ 14.1 „

n 9-8 „

+ I2.5 n

n 4-6 n

20

+ 12.6 „

o

+ 16.9 „

n 8.2 „

+ 12.5 „

o

40

+20.9 „

» 7-6 „

4-I3-I n

n J4-4 »

+ '5-0 „

n 8.4 „

23 o

+ 17.8 „

n IO-7 n

+ 14.1 „

n J7-2 „

+ I5-° n

n ri-3 n

20

o

n 1 0.3 „ 4- 4.5 „

n u-5 n

+ 4-5 n

n >2-2 „

TABLE XXXIII (continued).

Gr. M. T.

Pola

Tiflis

Dehra Dun

Ph

Pd

ft

ft

ft

ft

ft

Pd

h m

14 o

— 6.2 y

E 2.8 7

O

— i i-3 7

E 4-1 7

0

— I i.o y

E 8.8 7

'5 o

-II. 2 „

o

- 0.4 7

-l6-9 „

o

+ 1-3 7

-21.7 „

n 3-9 n

3°

-II.6 „

0

o

-14-3 n

n 2.2 „

o

-'7-3 n

n 3-9 „

16 o

-'3.9 „

E 18.7 „

+ 5-5 n

- 3-2 „

» 20-4 „

- 1-8 „

+ 4-3 „

n 5-9 n

20

+ °-9 n

T. 25-0 n

+ 3-2 „

o

n 14-8 „

+ 2.6 „

+ 2.6 „

* 6-8 ,,

3°

- 3-i *

„ 14.6 „

0

- 7'9 v

» M.8 „

+ 1-8 „

- 7-1 „

„ 8.8 „

17 o

- 9-9 n

O

0

-21-4 n

n 9-2 „

+ 2.8 „

-18.9 „

„ 8.8 „

22 O

?

7

9

-f- 5-8 „

W 1.9 „

- I.O „

+ 1.6 „

20

?

•>

?

+ 6-4 n

1. 2-2 „

- 0-5 n

+ 1-6 „

Very

40

23 o

7

V

9
?

7
7

+ 8.6 „
+ i°-5 n

n 1-9 n
n J-1 »

- 1-3 n
- i-3 n

+ 2.4 „
+ 3-9 n

small
westerly
deflections

2O

?

?

7

+ 4-7 n

E 5-2 „

- °-3 n

+ 3-1 *

PART I. ON MAGNETIC STORMS. CHAP. III.

215

TABLE XXXIII (continued).

GM T

Zi-ka-wei

Batavia

Christchurch

r. ivi. i .

Ph

Pd

A

Ph

Pd

Ph

Pd

h m

14 0

- 4-9 V

E 7.2 v

o

o

+ 14.7 7

E 3.0 y

15 °

-12-3 n

. 4-i *

-13-1 /"

o

o

o

3°

- 6.2 „

H 5-2 „

-12.8 „

W 1.2 7

+ 2.3 „

0

16 o

+ 16.0 „

* 3-1 r,

+ 11.3 „

„ 4-8 „

- 8.3 „

n 17-6 „

No

20

4- 8.6 „

* 4-1 „

- 4-3 „

n 2.4 „

•*- 6.4 „

» M-9 n

3°

+ 6.2 „

» 7-2 „

deflection.

o

n 2-4 *

4-n.o „

„ 8-9 „

17 o

o

n IO-3 n

- 7-7 „

o

+ 9-2 „

n 3-7 r

22 0

- 4-3 n

0

- ca. 2.3 „

0

20

No measurable

- 4-3 „

o

-ca. 4.1 „

o

40

deflection.

- 2.1 „

n i-a »

- ca. 3.7 „

ca- n 3-7 n

23 o

- I.I „

,1 3-° „

- ca. 4.1 „

n n 4-4 M

20

°

» '-8 „

- ca. 1.8 „

n n 2-9 n

TABLE XXXIV.
Partiel Perturbing Forces on the 27th October, 1902.

jgh om

l6'> 20m

i6»> 3om

n

P"d

P1*

Pd

f»

P-d

Honolulu
Sitka

The inte

to

— 276.0 y
-1 79.0 „
->

+ 20-1 »
- 17-8 „
- 12.2 „

- 9-6,,
— i-9 »
+ 1-3 „
- 6.4 „

i- £:

— 1-3 »
+ 16.0 B
4- 26.0 „
+ 25-8 „
+ 25.0,
- 18.4 „

rmediate si
be a pert

o

E 94.0 y
* 85.0,
„ 4i-3*

» 22.8,
„ 17-8,

a *9-*»
„ 4°-3 j,
. „ 35-5 ,
» 4-1 „
» 3I-3»
» 20.8 „

» l6-3»
o
W 6.2,,
, 4-8 „
E 17.1 „

onn not w
urbing fore

— 216.07
- 162.0 „
?

+ 29.6,,

+ 3-1 „
+ 2.6,

- 12.0,,
+ 23.3,,
-1- 20.6,,

- 3-2 „

+ IO.O „

+ 9.0 •
+ 21.4 „

4- 21.2,

4- 20.9,

4- 21.4 „
- 6.0,,

ell defined
E directed

E 95-o •/
n 35-6 ,
„ 74.o,
„ 25-3 »
» 34-3 »
» 35-o«
„ 36.8 .,
,, S3-' ,,
» 37-o „
» l6-4 „
,, 32.7 „
» 27.8,,

» "-1 >
o

W 5.1,
» 2.4 „
E 14.9,,

; the effect
southwards

-117.07
-172.0,,

7

4- 12.6,,

+ 7-7 „
+ 8.2,,
+ 3-2 „

+ 15-0,,

4- 9-8,,
o
+ 9-5 *
+ 9-° »
4- 12.6,
+ 12.6,,
+ 17.3 „

+ M-6»
o

seems

E 12.87
. 83.0 „
» 37-o»
» "-S.
„ 18.3,,
» 23-4 »
» 20.9 „
- 26.9 „
„ 16.7 „

n I2-3»
„ 22.8 „

» n-3»
„ 7-8,

o

W 2.6 „

i> a-4 ••
E 9-7,

Matotchkin-Schar .

Kew

Val Joyeux ....
Wilhelmshaven . .

San Fernando . , .

Pola

Tiflls

Dehra Dun ....

Christchurch ....

2l6

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.
Current-Arrows for the 27th October, 1902; Chart I at 14h, and Chart JI at 15h.

;j

K° AV

w'."Ah M^AJmSttar

f d>

Fw»k

Sib a»yW*

TiHis 7I««

TO

X

o

L

S

Z

Ib-

l

:,

,s

PART I. ON MAGNETIC STORMS. CHAP. III.
Current-Arrows for the 27th October, 1902; Chart III at 15h 30m, and Chart IV at 16h.

217

7C

•

'

,\

Jl

. •

AJ • Jbrrtafl,

t! w Haldanr,

*• galafut

Qilh

Ch i'h Oirutftuir.ti

Oh D /'/Ar.i />ut

5.1 «r

c : Xaa/ftnt

K™ *<TB

MjLSch Mai..lfhJUn-.^it,u

II.,; . /'. '•:,-

,

,

Fig. 97.

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

Current-Arrows for the 27th October, 1902; Chart V at 16h 20m , and Chart VI at 16h 30m.

PART I. ON MAGNETIC STORMS. CHAP. III.

Current-Arrows for the 27th October. 1902; Chart VII at 17h , and Chart VIII at 221' .

219

Fig. 99.

22O BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.

Current-Arrows for the 27th October, 1902; Chart IX at 22h 20m, and Chart X at 22h 40m.

PART I. ON MAGNETIC STORMS. CHAP. III.

Current-Arrows for the 27th October, 1902; Chart XI at 231', and Chart XII at 23 '' 20m.

221

Fig. 101.

222

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

THE PERTURBATION OF THE 28th & 29th OCTOBER, 1902

63. After the last polar elementary storm that occurred before midnight on the ayth October, the
conditions once more become comparatively calm, and continue so until about i8h the following day,
when another perturbation of considerable power occurs. Sitka is the only place that forms an exception
to this, as there a perturbation of a rather considerable strength occurs about midnight, local time; but
its sphere of action is rather limited, as it is not noticed either at the Norwegian stations or at the other
stations in North America.

The perturbation-conditions during this twenty-four hours closely resemble those of the preceding
day and night. On both days, the conditions at the Norwegian stations are characterised by two separate
storms; but on the 28th, these two storms are closer together, the first storm on that day being about
two hours and a half later than the first on the ayth, and the second on the 28th perhaps half an hour
earlier than that on the 27th.

When we come to lower latitudes, we find the conditions during the time from I4h to aoh rather
different on the two days. There is no trace on the 28th of the long storm that occurred on the 27th,
and was especially powerful at the equator; it is the intermediate storm that answers to the first storm
on the 28th. On the other hand, there is an astonishing resemblance between the conditions of the two
days in the last storms both at our Norwegian stations and in lower latitudes. We thus notice that the
deflection in H at Kaafjord are in the same direction on both days, and the Z>-curve has an undulating
form while the deflection in V is uniform in direction and very great. Farther south we find that the
//-curve on both days is of an undulating character; there are two intermediate more or less marked
maxima separated by a minimum.

It appears from the curves that the distribution of strength in the northern hemisphere is about
the same on the two days. It is thus evident that on this occasion also there are two separate polar

TABLE XXXV.

Observatory

Perturb. I

Perturb. II

Begins
in H

Begins
in D

Reach,
max.

Pt

max.

Ends
in H.

Ends
in D.

Begins
in H

Begins
in D

Reach,
max.

P,

max.

Ends
in H

Ends
in D

h m
18 9
18 3(1)
18 8
'8 5
18 12
18 15
18 8
18 8
18 12
18 7

18 15
18 10
18 5
18 15
18 15

17 57
18 15

lencement

h m
18 9
ca. 18 15
• 18
18 15
18 10
18 15
18 8
18 6
18 10
18 7

indeterm.
18 12
ca. 18 15
no pert,
indeterm.
indeterm.
no pert.

of these s

h m
18 33
18 50

18 45
18 45
18 45
18 45
18 45
18 45
18 45
18 45

18 45
18 45
18 45
18 45
19
18 45
19
Decial s

248.0 y
138.0 „
78.o „
M-Sn
a5-5n
i7-°n
16.5 „
23-5 „
i5-or
i6.on

3-° „

21.0 „

I4.on

3-5 „
n.on
10.6 „
7-° n
torms.

h m
19 io(l)
ca. 19 30
n 19 45

19 20
19 26
19 30

19 24
I9 24

19 45
19 24

19 45
19 45
20 1 6
ca. 19
20 15
indeterm.
20 15

h m

19 is*1)

19 8

19 I5(')
indeterm.
19 10
19 20
19 16
19 3
'9 5
19 20

indeterm.
ca. 19 30
indeterm.
no pert,
indeterm.
indeterm.
no pert.

h m
21 45
ca. 20 35

20 40

ai 30
21 34

21 40
21 27
21 30

21 35

21 30
21 30
21 30
31 32

21 35

indeterm.

21 2O

ca. 21 40

22

h m
21 30

21 33
21 33(])

21 30

21 56

ca. 22
ai 40

21 18

31 40

20 50

ca. ai 30

21 40
21 40

21 35

21 40

21 40

indeterm.
no pert.

h m
22 15

21 57

22 2O
21 50
22 IO
22 IO
22
22 IO
22 IO
22 8
22 IO
21 50
22
22 IO
22 IO
22 2O
22 2O
22 20

266.0 ;/
209.0 „
1 75-0 »
27.5 „
25-5 „
24-0 „

21.0 „

19.0 „

n-o*
16-5 B

i6.on
r5.on
rS-Sn
!3-5r
tS-O*
8.2 „
7-5 „
2-5 »

h m
ca. 24
n 23 40
„ 22 50
23 25
23 30
22 45

22 32

23 3°

ca. 23 30
22 40
23 3°

22 40
23 5

ca. 34
indeterm.
23 30

22 45

23 15

h m

ca. 23 aol1)
„ 23
„ 23
23
23 30

23 35
23 20
23 27
ca. 23 45
23 24
23 45
23

23 20
22 30

ca. 23 20
n 23
indeterm.
no pert.

Matotchkin Schar .

Wil he 1m shaven . .
Val Joyeux ....

Pola

San Fernando . . .
Tiffls

Dehra Dun ....
Sitka

(1) The comn

PART I. ON MAGNETIC STORMS. CHAP. HI.

elementary storms, both with fairly simple course. The table above gives the time at which the two
perturbations begin, attain a maximum, and end, and the value of Pt at its maximum. We find here a
distinct confirmation of the statement that the effect of the force diminishes from the poles to the equator.

The table shows that the two perturbations differ essentially as regards distribution of strength.
Although the first storm is less powerful at the Norwegian stations, and rather less powerful in Central
Europe, it is nevertheless somewhat more powerful than the second when we come nearer to equator.
There is a still greater difference with regard to the conditions in America, the first storm being
almost imperceptible there. '

We thus receive a decided impression that the current-system that conditions the field — however
this may be constituted in the second storm — is situated, on the whole, farther west, a circumstance that
may to some extent explain the different distribution of strength in the two storms.

THE FIELD OF FORCE.

64. The field during the first storm is in the main of the same form and relative strength as in
the intermediate storm on the 27th, but less powerful. The current-arrows in the north are directed
westwards along the auroral zone, and the effect is strongest at Axeleen and Matotchkin Schar.
P, at Kaafjord and Matotchkin Schar is directed downwards, at Axeleen upwards. There is an area
of convergence with a fairly strong force in the eastern hemisphere, but an area of divergence with
comparatively little force in the western. The point of convergence is situated in the regions round
the north-east of Russia. The field, at those places from which we have observations, is almost
stationary. At Pawlowsk, P, is directed upwards.

The field during the second storm is almost exactly the same as that during the second storm on the
previous day. All that has been said of the field on the 2yth may be directly applied to this perturbation.

As on the previous day, there is a movement of the system towards the east. This is evident,
both from the clockwise turning of the arrows in the south of Europe, and from the conditions at the
Norwegian stations. If we look at the current-arrows for Axeleen and Kaafjord, we see that they are
at first convergent, showing that the storm-centre is to the west of those stations. When the storm is
almost at its height, they become parallel, and end by being Divergent, thus indicating the eastward
position of the storm-centre.

These two storms, as we see, are the very ones to afford favorable conditions for a determination
of the strength of the horizontal portion of the current, and such a calculation will therefore be made.

The very interesting systems of current-arrows are shown on the Charts I to VII.

TABLE XXXVI.
The Perturbing Forces on the 28th October, 1902.

Gr. M. T.

Sitka

Baldwin

Toronto

Axeleen

Ph

Pd

Ph

PA

Ph

Pd

Ph

Pd

Pk

h m

18 15

- 4-2 7

0

- 0.7 v

o

o

o

- 44-6 7

o

+ 103.0 7

30

- 6-7 „

o

- 3-0 »

o

- o-9 7

o

- 12.8 „

W 7.67

+ 96.0 „

45

-'0-3 »

E 2.3 y

- 3-7 »

0

- 2.7 n

o

- 89.7 „

* 38.i „

+ 258.0 „

19 o

- 7-8 „

n 4-1 n

— 1-7 n

o

o

0

-153-0 n

rca.32.3B

+ 88.5 „

21 40

- i -a „

» '-4 n

-12.2 „

E 6.4 y

- 6-3 „

E 3.0 7

- '3-8 „

E 40.8,,

+ 183.0 „

22 O

- 6.6 „

» M n

-13-5 n

* 3-2 „

- 9-0 »

„ 12.6 „

- 89.7 „

n 95-2 „

4349-0 n

20

- 7-i »

0

- 8.5 „

n a-5 „

- 6.8 „

n 7-2 n

-!66.o „

n 1 12.0 „

+ 352-0 „

40

- 1-8 „

o

-ca.7-4 „

n r-9 n

- 1-4 n

» 3-6 n

-116.0 „

» 25-8 „

+ 246.0 „

23 o

- °-4 „

o

- 6.8 „

o

o

o

— 172.0 „

i) 69.5 „

-1-231.0 „

224

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE XXXVI (continued).

Gr. M. T.

Matotchkin Schar

Kaafjord

Pawlowsk

ft

Pd

P,

ft

Pd

P.

Ph

Pd

P,

h m

18 15

- 67.7 7

O

- 37-9 /

- 26.6 7

E 12.6 v

- 16.4 7

+ 13.1 7

W 1.8 x

0

3°

-161.0 „

E 46.8 7

- 49-1 B

- 49-6 „

n I2-9 n

- 60.! „

4- 8.1 „

B 4-6 „

- 3-0 '/

45

-147.0 n

,1 29.0 „

- 54-8 „

- 7°.i B

„ 18.5 „

- 68.1 „

4- 14.6 „

B 2-8 „

- 4-5 n

19 o

-127.0 „

» 36-7 B

- 39-3 n

- 39 5 „

» 20-7 n

- 48.4 „

+ 7-0 „

0

- 5-2 B

21 40

-143.0 n

B 50.8 „

- 46.3 B

- 91-5 n

W 5-5 „

- 84.6 „

+ 3-o „

B I5-6 n

0

22 O

-I9I.O „

n 39-7 ,

- 52.6 „

-IjI.O „

E 29.2 „

-147.0 „

4- ii. 6 „

B 18.4 „

— 4-5 B

20

— 175-0 n

„ 26.8 „

- 39-3 B

-147.0 „

B 94-7 B

-I32.o n

+ 12.6 „

n '-4 B

-1 1.2 „

40

-1 08.0 „

n 22.3 n

- 35-1 n

- 57-8 „

n 54-0 „

-119.0 „

+ 3.0 1,

E 4.1 „

-II.2 „

23 o

- °3-4 n

W 4-5 *

- 35-1 B

- 17-7 „

B 15-9 ii

-103.0 „

+ JO-1 n

,, 1-8 „

- 8.2 „

TABLE XXXVI (continued).

Gr. M. T.

Stonyhurst

Kew

Val Joyeux

Wilhelmshaven

Ph

Pd

P*

Pd

P*

Pd

P.

P*

Pd

ft

h m

18 15

+ 3-5 7

E 14.8 7

+ 5-1 v

E 8.0 7

f 2.4 7

E 3-3 r

4-14.0 7

E 12. a /

30

4 7-7 n

B 9-7 B

+ 8.2 „

n 5-1 „

f 8.8 „

, I0-0 r,

No

+ 15-9 „

n 3-7 »

45

4- 8.2 „

n T4-3 B

4-IO2 .,

„ 1 2.3 „

4-H.2 B

« I2-5 „

measur-

4-21.0 „

n M,6 „

Slight

19 o

+- 3-5 „

n 5-7 n

•+• 5-6 „

it 7-o „

4-120 „

« I09 „

able

+ 10.3 „

n 3-1 n

deflec-

21 40

+ Il-3 B

n 4-0 „

-I-II 0 „

o

+ 3-2 „

0

deflec-

4- 9.8 „

W 1.2 „

tions.

22 O

+ '3-3 n

„ 1 6.0 „

4-13-3 n

E 9.4 n

-I-I9.2 „

w 3-3 «

tion.

4-18.7 „

E 6.1 „

20

+ 5-i *

„ T6.6 „

-1- 5-6 „

n 14-5 n

+ 12.0 „

r iS-9 n

4-12.6 „

n I?-' n

40

- 2.5 „

n 9-7 n

o

„ 6.1 B

+ 3-2 „

n 8.4 „

- 2-3 „

n 6.7 „

23 °

o

n M.8 „

o

n I2-6 n

+ 2.4 „

n "-7 n

+ 4-2 „

* l6-5 n

TABLE XXXVI (continued).

Gr. M. T.

Potsdam

San Fernando

Munich

Pola

PA

P

P

Pd

P*

Pd

PA

Pd

Pf

h m

18 15

4-16.8 7

E 7.6 7

4-13.1 7

E 8.2 7

4- 7.0 v

E 5-3 y

?

7

7

30

+ !3-5 n

n 2-5 n

4 16.9 „

n 9-0 n

+ 8.5 „

B 4-6 B

7

7

7

45

4-21.5 „

n 9-2 n

4-16.9 „

» I2-3 n

4-12.0 „

B 8.4 „

?

7

7

19 o

+ H-4 »

B 2.5 „

4-16.6 „

n 9-0 „

+ 9-o B

B 4-6 B

7

?

?

21 40

+ I3-6 „

W 4.0 „

+ 9.0 „

n 4-1 n

+ 7-5 B

0

4 12.1 7

W 2.8 7

22 0

+ 21.2 „

o

+16.9 „

„ 8.2 „

+ I6.0 „

0

-t'13-4 B

E 6.9 „

Slight

20

+ 13-5 n

E 10.2 „

-J- o.o „

n 90 „

4-12.5 „

B 9-9 n

+ 9-o „

B 8.3 „

deflec-

40

+ 1-9 »

n 4-6 „

+ 6.4 fl

B 1-6 B

+ 3-5 n

B 7-6 B

4- 4.0 „

» 7-6 B

tion.

23 o

+ 7-9 B

n 9-2 n

+ 3-2 „

» 5-7 B

+ 4-5 B

B I0-6 B

+ 4-9 B

B 9-0 „

PART I. ON MAGNETIC STORMS. CHAP. III.

TABLE XXXVI (continued).

Gr. M. T.

Tiflis

Dehra Dun

Batavia

ft

Pd

p.

A

Pi.

a

Pd

h m

18 15

H- 7.1 y

W 0.4 y

- 1.3 /

4- 5.9 /

W 1.9 y

+ i.i x

3°

+ 9-2 „

n i-5 *

- 0-8 n

+ 5-9 n

» 3-0 n

+ 1.8 „

45

+ r3-7 n

» i-5 n

- 1-8 „

H- 9-8 „

n 4-9 n

+ 1-8 „

No

19 o

+ 11.6 „

n °-7 »

- i-o „

+ 9-0 „

n 3-0 n

+ 7-1 n

deflec-

21 40

+ 2.6 „

n 5-6 „

- I.O „

- 1.6 „

n 3-0 „

o

tion.

22 O

+ 9-2 „

n 9-7 „

- 1.8 „

+ 3-1 „

n 6-9 n

o

2O

+ "•3 n

n 2-2 n

- 2-0 n

+ 6.3 „

n 4-9 n

4- 2.8 „

40

-r 54 n

o

- 0.8 „

+ 3-5 „

„ I-° n

+ 1.8 „

23 o

+ 6.4 „

o

- 2-0 n

+ 5-5 n

o

-f 1-8 „

Current- Arrows for the 28th October, 1902; Chart I at 18h15m.

Fig. loa.
Birkeland. The Norwegian Aurora Polaris Expedition. 1902—1903.

29

226 I3IRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

Current.Arrows for the 28th October, 1902; Chart II at 18h 30m, and Chart III at 18!l45m.

Fig. 103.

PART I. ON MAGNETIC STORMS. CHAP. III.

Current-Arrows for the 28th October, 1902; Chart IV at 19h, and Chart V at 21h 40m.

227

Fig. 104

228 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

Current-Arrows for the 28th October, 1902; Chart VI at 22h Om , and Chart VII at 22h 20m.

T~

•-
7

PART I. ON MAGNETIC STORMS. CHAP. III. 22Q

Current-Arrows for the 28th October, 1902; Chart VIII at 22h 40m , and Chart IX at 23h Om .

•

-

OV

, '.;

tr

:.

i* f main*

ttia

rS"

.

„

Fig. 1 06.

230 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

THE PERTURBATIONS OF THE 31st OCTOBER & 1st NOVEMBER, 1902.

(PL VII).

65. After the last storm on the 28th October, quiet conditions once more prevail; but at about i8h
on the following day, the storm bursts out again, and continues until midnight, and it seems, that the
two polar perturbations, that occured rather destinctly on the 28th now come so near one another, that
they form a single one (cf. PI. VI).

On the next day again, this is repeated. At Axeleen in particular, there are powerful perturba-
tions, but they commence at about i6h. In southern latitudes, this twenty-four hours is fairly quiet; but
during the morning of the 3ist, a storm begins, which lasts uninterruptedly for nearly twenty-four hours.
It appears at the poles with tremendous violence, although perhaps its strength is even more unusual at
the equatorial stations. Considering its long duration and its universal distribution, we may say that it
is the greatest storm that has been observed by us.

A circumstance which adds still more to the interest of this storm is that it occurs at the new
moon, and what is more, there was even an eclipse of the sun during the perturbation. This eclipse
began at 5h 58.5m on the 3ist October, and ended at ioh 2.3™. It was only partial, and the greatest
phase (0.699) occurred at 8h o.4m, in longitude 100° 56' East, and latitude 70° 53' North. The eclipse
cannot in itself be considered as affecting this perturbation in any essential degree. Whatever direct
effect there may possibly be of the eclipse itself this must at any rate be very small as compared with
the total amount of the perturbation, as no special change is observable in the curves, coinciding with
the time of the eclipse. We know that powerful storms often occur at the same time as an eclipse,
without being directly due to it; but it has been stated "that an observable magnetic variation makes
itself felt during the time of a solar eclipse, and that this variation is analogous in its nature to the
solar diurnal variation, differing from it only in degree." (a) In this case it is difficult for us to study
this direct influence, as we have no material from the places at which the eclipse was greatest.

If the moon can be supposed to exert any influence on the perturbation, it must be owing to
the fact that it is a new moon. We will not here, however, enter more particularly into these questions
but only describe the perturbation, and find out its actual distribution and course.

It exhibits great variableness round the Norwegian stations. The curves have a very serrated
appearance, resulting from great vibration in the field of perturbation. Notwithstanding this, however,
the conditions of the perturbation as a whole, run a fairly simple course, which may be characterised
as follows.

During the time that the perturbation lasts, namely from about gh on the 3ist October to 3h
on the ist November, most of the curves for the magnetic elements form a single undulation with
crest and sinus. This wave differs, however, in phase at the three stations. At Kaafjord the deflec-
tions changes sign in all three elements between i8h and i8h 30™. At Matotchkin Schar it changes
in H at about i6h, in D at i6h 45"™, and in V at I9h 15"", thus taking place on the whole earlier than
at the former station. At Axeleen, the undulating form is very marked in the declination, the change
not taking place until about 22b. The smaller variations must be regarded as ripples upon this princi-
pal undulation. Two of these shorter variations in particular are considerable and worthy of notice.
One of them appears at about I4h, the other at about midnight, with maximum about 23h 45™. At
Axeleen, where the main undulation was somewhat less marked in H, these two intermediate storms are
very prominent.

(') L. A. Bauer: Terrestial Magnetism Vol. 7, p. 192.

W. van Bemmelen: Contribution to the Knowledge of the Influence of Solar Eclipses on Terrestrial Magnetism.
C. Nordmann, Bulletin Astronomique, Mars 1907.

PART I. ON MAGNETIC STORMS. CHAP. III. 231

At Sitka too, this storm occurs with a violence that approaches what we find at the Norwegian sta-
tions, this being greatest between i3h i5m and I4h, at which time the H variometer-needle is deflected
out of the field. This storm occurs at the same time as the first great intermediate storm at Axeleen.
Great storms also occur at the other stations in the western hemisphere; and even at Honolulu the
perturbation on that day is fairly powerful. In the United States the character of the perturbations
varies more or less with time and place. Unfortunately we here only have registerings for the first
part of the perturbation.

In Central and Southern Europe the perturbation is rather considerable though relative to that in
the equatorial stations comparatively slight, especially the first part. Up to ijh 45"" the conditions remain
fairly uniform — a deflection in H, indicating a decrease in the horizontal intensity, and a westward
deflection in D. At about ijh 45™, the .D-curve goes over to the opposite side of the mean line, while
the deflection in H is increased. The D-curve of San Fernando forms an exception to this; as the
change in direction here does not take place till about 2 hours later. The course somewhat resembles
that at Kaafjord, as the change in D takes place at about the same time as the above-mentioned change
in the amplitude. Between 23h and oh 35™ there is a rather strong impulse in D, this being simultaneous
with the second powerful storm at Axelaen.

In the region of Dehra Dun, Batavia and Christchurch, the storm is very powerful, the first part
of it being even more powerful than in England, France and Germany. At I2h 30™, the perturbing
force at Dehra Dun attains a value of 80 y.

The conditions on the whole are fairly simple. At Dehra Dun for instance until 13'' I5m the
perturbation is noticed principally in H and then there also is a deflection in the declination towards the
east. Similar conditions we also find at the other stations. The deflection in H is uniform in direction
throughout, as H is decreasing all the time. The character of the curve is quiet on the whole, without
any great, sudden changes; and only at about I3h 30™ is there such a change in the deflection.

It appears from the coincidence of the previously-mentioned powerful storm at Sitka with that on
Axeloen, that these deflections are connected with one another. The perturbation on this date resembles
in many respects the preceding perturbations of the I5th and 8th February and that of the 27th Octo-
ber. We may thus make a comparison with the perturbation of the 27th October for instance. On this
day we also found a storm of long duration, that was especially powerful and of similar effect in the
south Asiatic districts. During that perturbation there was an intermediate storm that was also powerful
in the districts of Dehra Dun and Batavia, and was almost the reverse of the long storm.

A little before midnight there was another short storm, the effect of which was very slight at
Dehra Dun, but powerful in Europe. The chief difference is that the long storm of the 3ist October
is much more powerful and of much longer duration, so that both the short storms come within its
limits. The first intermediate storm, moreover, occurs a little earlier in the day, and the second a little
later, than those on the 271)1 October.

Analogous with what we have done in the case of the last described storms this perturbation is
divided into three principal phenomena, the long storm and two intermediate storms. There are indeed
more interruptions than these two during the long storm, that might well be studied, for there are in-
numerable small interruptions; but as far as we can tell from our material, it is only these two that
have a universal and powerful effect, and between them and the other irregularities there is a wide
gulf that cannot be crossed without leading to so great a multiplicity, that the main lines would be lost,
and the study of the phenomena rendered nearly impossible.

232 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

THE FIELD OF FORCE.

66. (i) Charts I to VIII represent the conditions during the time between gh and I2h 30™.

During this comparatively long time, the form of the field in the eastern hemisphere remains almost
constant. It may be briefly charaterised in the following manner:

At the equator there are powerful perturbing forces directed southwards. In Central and Southern
Europe, the force is only about half as great as at Dehra Dun and Batavia, and throughout is south-
west in direction. At Kaafjord and Matotchkin Schar, the current-arrow is directed all the time east-
wards along the auroral zone, a circumstance that seems to have some connection with the fact that
during this time these stations are situated on the day-side. At Axeleen the force is almost in the
opposite direction. The current-arrow is at first directed southwards, but in the course of the above-
mentioned period turns clockwise until at I2h 30™ its direction is WSW.

In medium and northern latitudes in the western hemisphere the conditions are more variable,
whereas at Honolulu there is a powerful perturbation that remains almost constant all the time. The
conditions there are very similar to those at Dehra Dun; the current-arrow at both places is directed
westwards, but is a little smaller at Honolulu.

The conditions in North America are very interesting, and require a fuller description.

At Sitka, as already mentioned, the perturbation is extremely violent; and the curve presents the
same very serrated appearance that is so characteristic of the powerful storms about the auroral zone.
On looking at the charts, we see that the perturbing force remains more or less constant in direction.
The current-arrow is directed principally westwards, sometimes a little WSW. The strength too, varies
but not much on the whole.

During the polar elementary storms that occur about midnight, and have their centre in the regions
round the Norwegian stations, we have always found that there is only little difference between the condi-
tions at Sitka and those at Toronto and Baldwin; but on this occasion there is a very great difference
between them, and even considerable difference between Toronto and Baldwin. In the case of the last-
named two stations, moreover, there is great variableness from time to time, which makes these perturba-
tions very distinct from those in the eastern hemisphere with their more constant conditions. This cir-
cumstance is to be explained by the fact that the perturbation in the north of North America is due
in a great measure to the occurrence of more or less independent storms that are confined to those
regions.

In order to obtain a clear idea of the field that is produced by these storms in the north of
North America, we should examine it at those times when the force is greatest, as we may then most
safely disregard the other forces that are acting through other systems. Let us look then at Charts IV
to VIII. We see that the arrow at Sitka remains almost constant. The arrows at Toronto and Baldwin
show that there is an area of convergence there, with very great convergence, of the perturbing force.
We cannot help noticing that this field exhibits the same properties that characterised the field in the
previously-discussed polar elementary storms with their centre at the Norwegian stations. At Sitka there
is a comparatively powerful perturbation with constant direction of the perturbing force, corresponding
to the conditions at the Norwegian stations; and in both cases the current-arrow is directed towards the
west. The area of convergence in North America on this day corresponds with the area of conver-
gence in the European district under the above mentioned elementary storms.

The correspondence appears still greater when we notice that the centre of these storms has about
the same position in relation to the sun as the previously-mentioned polar elementary storms at the
Norwegian stations, the storm-centre in these cases being in the district that has midnight at the time of
the storm, or often on the morning side. In the case of the perturbation here described we also find
the same. The chart for 9h 3om forms an exception to this. In the first place it must be remarked

PART I. ON MAGNETIC STORMS. CHAP. III. 233

that the arrows are small; and as we have only taken out total forces, we cannot know how much is
due to local storms. The circumstances are explained quite naturally, however, by assuming that the
storm-centre now lies farther east. As the perturbing forces at Toronto and Baldwin are very small,
we must then make the assumption that the point of convergence of the system is now situated in the
vicinity of these stations, a little to the east of them; but as the conditions here, if minutely entered
into, are rather complicated, we must not investigate the matter more closely.

In this connection we may refer to the previously-described perturbation of the 28th December,
where we also met with an area of convergence in North America. On that day, however, the storm-
centre seems to lie at a greater distance from Sitka, the curves having a far less disturbed character
than now. There we also found that the field of precipitation was at first situated farther to the east,
and then moved westwards.

(2) Charts IX, X and XI represent the conditions as they appear during the first powerful inter-
mediate storm. The perturbing force at Sitka has about the same direction as before, but is much
greater. This perturbation, moreover, is particularly powerful at Axeleen, with a perturbing force that
is directed SSE all the time.

We have endeavoured to separate the effect of the intermediate storm from the rest, the total
force being decomposed. Owing to the manner in which the decomposition has been carried out, one
of the systems of arrows gives a field with almost the same form as the one already described.

With regard to the field in the intermediate storm, we first notice how rapidly the force dimi-
nishes, both in the neighbourhood of Sitka and in that of Axel0en, at any rate in the districts from
which we have observations.

In the district of Zi-ka-wei, Dehra Dun, and Batavia, the direction of the intermediate perturbing
force on the whole is almost the reverse of what it had been earlier, and the magnitude is very consi-
derable. This circumstance also occurred during the intermediate storms of the 27th October, 1902, and
the 8th and i5th February, 1903.

In Europe there is a peculiarity in the conditions, namely, that the effect of the intermediate storm
is very small. The perturbing forces throughout are smaller than in the Asiatic district, and exhibit
considerable variableness, although the current-arrows all through are directed south-west.

At Baldwin and Toronto the effect is great, but the conditions are somewhat different, as the per-
turbing force has rather a different direction.

(3) The remaining charts, XII to XIX, embrace the period from 17'' 45™ to i1' on the ist
November.

We have no observations of this period from America and Honolulu. In the eastern hemisphere
the perturbation-conditions change very slowly. During the day-period the current-arrows at the Norwe-
gian stations Kaafjord and Matotchkin Schar are directed eastwards; at the beginning of the night-period
they begin to turn. In the case of Matotchkin Schar, this has already taken place at i7u 45™ (Chart XII).
At i8h 3om, the current-arrow for Kaafjord has its usual direction westwards along the auroral zone.
Throughout this last period, Axeleen has a comparatively small horizontal component, which sometimes
varies greatly in direction. The vertical component, on the other hand, is very considerable, and is
directed downwards, thus indicating that it is perhaps an effect of the current that causes the powerful
perturbations in H at Kaafjord and Matotchkin Schar. The vertical components at these stations indi-
cate that the main bulk of the current is passing right over, or a little to the south of, Matotchkin Schar,
and south of Kaafjord. Simultaneously with this reversal of the force, we notice a great change with
regard to the force in the rest of Europe, this, on the chart for i8h 30™, being about as powerful
as at Dehra Dun; but on the other hand the force has now diminished considerably at Zi-ka-wei. The
current-arrows in Central Europe on the whole at this point of time are south-west in direction.

Birkeland. The Norwegian Aurora Polaris Expedition, 1903—1903. 30

234 B1KKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

As we come southwards towards San Fernando, we find the arrow turning more to the west. We
receive the impression that the perturbation-conditions have moved westwards with the sun. This move-
ment seems to be continued, as the magnitude of the force in Central Europe, as compared with that
at Dehra Dun, is increasing, while the direction of the arrows becomes more southerly, that is to say,
the turning is counter-clockwise.

On Chart XVIII, for 23'' 45™, the force is decomposed, as we have endeavoured to take out the
force for the other powerful storm at Axeleen. This storm, which commences at about midnight, and
is powerful at the Norwegian stations, has also, as far as may be judged from our material, the out-
ward field that is characteristic of these storms. There is an area of convergence in the north-east of
Europe and the north-west of Asia.

The last chart — at ib — shows the perturbations in Europe, including the Norwegian stations, to be
greatly diminished, while at Dehra Dun the perturbation still continues fairly powerful for a long time.
Throughout the next twenty-four hours, H has a value that is about 10 y below that of the preceding
calm days, notwithstanding that the curve on the following day is of a quiet character. As the mean
line has been drawn in relation to the calm days, this low value of H will affect the perturbing force,
and serve to increase its total amount.

HOW THESE PERTURBATIONS MAY BE EXPLAINED

67. In the above description we have pointed out the most important properties of this pertur-
bation. These we will now briefly recapitulate.

(1) The perturbation is very violent at the Norwegian stations. The character of their curves is
very disturbed. The curve for Sitka for that day is of the same character.

(2) The perturbation, in the eastern hemisphere especially, may be divided into one long, principal
storm, whose field, in its main forms, varies only very slowly, and two intermediate, powerful, but
briefer storms, that differ considerably from the first-named in the fields of force that they produce.

We will first take the conditions during the long and more constant storm, beginning with that part
of it for which we also have material from the American stations and Honolulu.

On account of the violent nature of the storms round the Norwegian stations, we must assume that
the systems come close to these places. There are thus great precipitations on the day-side, and the
current-arrow during the period is directed eastwards along the auroral zone.

The effect in lower latitudes undoubtedly seems to some extent to be due to the direct influence
of these polar precipitations. The fact that the perturbations in this period are all more powerful in the
district of Dehra Dun and Batavia than in Europe, might make it natural to suppose that in addition to
the polar systems there are also systems that have their greatest effect in the equatorial regions. This
kind of storm we have already mentioned, and have referred them to the so-called negative equatorial
storms (p. 83). In this perturbation we have a typical example of such a storm.

In North America the perturbation-conditions varied in a manner that was without parallel in the
eastern hemisphere. This, together with the great changes in the perturbation-conditions from place to
place, points to the conclusion that the perturbations here are due to systems that are relatively inde-
pendent as compared with that which occurs farther east; and on a closer investigation, it also appears
that the field is of the same form as that during the polar elementary storms that occur on the night-
side of the earth. From the great strength of the perturbation at Sitka as compared with Toronto and
Baldwin, we may conclude that the first-named station must be situated in the neighbourhood of the field
of precipitation. The current-arrow also remains constant, pointing westwards along the auroral zone.
It would appear that on this occasion these polar storms occur rather far south. If we were thus to

PART I. ON MAGNETIC STORMS. CHAP. III.

235

assume, as we might with reason do, that these polar storms in North America, and perhaps also farther
west, surround themselves with a field whose properties resemble those during the series of polar
elementary storms already described, with centres near the Norwegian stations, it will be impossible to
explain the strength and direction of the force at Honolulu as a direct effect of correspondent polar
systems with centres in North America. The perturbation at Honolulu must mainly be conditioned by
the equatorial system.

During the second part of the long storm, the Norwegian stations begin to enter the evening and
night side, and we see that the current-arrows turn round. This takes place earlier at Matotchkin Schar
than at Kaafjord, showing that the cause producing this change in direction moves westwards with the sun.
At the Norwegian stations the perturbations have a very local character, but the conditions on the whole
are almost alike at Kaafjord and Matotchkin Schar, that is to say the direction of the current-arrows;
but at Axeleen they are very different. There there is a great vertical component, but a small hori-
zontal component (e. g. Chart XVI). A possible explanation of this is, perhaps, that as the current on
this occasion lies rather far south, Axeleen comes near to the neutral area.

In lower latitudes also, we see that the district of the most powerful field has moved westwards
or in other words, this perturbation is of such a kind that the greater part of it follows the sun.

We have already mentioned that at the stations Dehra Dun, Bombay and Batavia, a long diminution
in the horizontal intensity ensues, continuing throughout the day and night following.

At the Norwegian stations the polar storms cease, and comparatively quiet conditions supervene as
early as 3h on the ist November.

In this manner we see that the perturbations that have appeared at the equator make themselves
independent of the polar storms, and outlast them. It might indeed be argued that the perturbation is
due to an after-effect of the long storm, in other words, that after the polar storms have ceased, it is
not real current-systems with which we have to do, but only an induced and slowly-vanishing temporary
magnetism in the magnetisable masses of the earth. This would be in accordance with the quite character
of the curve on the following day.

In reality we here have before us a question of a fundamental nature, the answering of which
would be of the greatest importance to our comprehension of terrestrial magnetism itself, but would
require an acquaintance with these magnetisable masses such as we do not possess.

It is certainly not impossible that a storm such as this, which has been powerful and lasted long,
may have after-effects. But the after-effect cannot explain it entirely; for at 5'' on the ist November, at
a time when the storm in the north has ceased, H at Bombay still amounts to 33 y. It is true the force
at Bombay has passed a value of 89 y, and during several hours maintains a value of about 70 y; but
nevertheless an after-effect of half this amount seems improbable.

If such an after-effect at the equator were due to a temporary remnant-magnetism in the earth, and
if we suppose the magnetisable masses to be arranged symmetrically with reference to the magnetic
equator, we should also expect to find the direction of this effect the reverse of that of the exterior
magnetising force.

In treating of the first part of the perturbation, by considering the conditions at Honolulu, we arrived
at the conclusion that we must here assume the existence of a negative equatorial system (see Art.
32), as the perturbations at Honolulu did not harmonise either in direction or strength with the condi-
tions farther north, and took no part in the great variations undergone by the perturbations in North
America. According to this, we may conclude that this time there is the effect of a current-system
which acts most powerfully in the regions round the equator. We are naturally led to connect this
perturbation with a circular stream of electric corpuscles flowing round the earth, resembling the
luminous ring round the terrella in the experiment represented in fig. 37. On account of the universal

236 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

distribution of the effect, the current cannot lie near the earth, but should be at a distance of at least
the same magnitude as the earth's radius. If this were the case, we should expect to find similar distur-
bances in the vertical intensity near the poles, and, still more, an increase in this force in the north.
It is at once apparent that the form of the vertical curve for Axeleen has some resemblance to that of
the //-curves at Dehra Dun and Batavia; and the quiet character of the curve may perhaps indicate that
here we have not principally direct effects of the polar storms. The deflection really answers to an
increase in V, and remains powerful and so constant that the probability of its being caused only by
the powerful storms about the auroral zone is not very great.

A calculation of the magnetic effect produced at various places by a circular current round the
earth at a considerable distance from it, may here be of some interest.

Let us first assume that such a corpuscular circular current has the same magnetic effect as a
galvanic linear current. This circular current we will suppose to be situated almost in the plane of the
magnetic equator, its centre coinciding with that of the earth, and its radius equal to 2 R, R being the
radius of the earth.

The effect of such a current upon a magnetic mass i cm.3/2 gr.V3 sec.-i, situated in the plane of
the current, we find to be

f
„ _ I (a — / cos <p) d(p

I 10 (a2 -(- P — 2a/cos(p) I*
J

o

where a is the radius of the current-circle, / the distance of the magnetic pole from the centre of this
circle, / the current in amperes, and F the force expressed in C. G. S. units.

This integral may easily be transformed into elliptical integrals of the normal types.

We have here calculated it numerically for the values a = 2 R, I = R, and we find that

„ in

F1 = 1.23

ioR
In the centre of the current-circle we have

„ _ in
'2=ioR

It will be seen that the force is somewhat less at the centre of the earth than in the equatorial
districts; but the difference is not very great.

We will now consider the earth as a homogeneous magnetisable sphere, situated in a uniformly
magnetic field of a strength

P in

~7oR

The magnetisation produced in the sphere will give rise to the forces

respectively at the pole and at the equator, where

fi being the permeability of the sphere. (See Mascart: L'Electricite et le Magnetisme. Paris, 1896; p. 417.)
The value of /.i, that may be used for the earth, is very difficult to determine. F. Pock els
(Wiedemanns Analen 63, p. 199, 1897) gives values of about i.i for basalt for the smallest field-intensities.
For other minerals, however, we find values of even a hundred times greater, e. g. magnetite, pyrrhotite,
haematite, limonite, etc.

PART I. ON MAGNETIC STORMS. CHAP. III. 237

If we take 2 as an average value of /.i, we obtain

In this way we should expect to find values of Pv at the magnetic poles about double the value
of PI, observed near the equator. For greater values of ,« the proportion P, : Ph will increase, and
vice versa.

From about i6h to i8h we really find conditions that seem to favour our assumptions, when
we compare the values of P, at Axeleen with the value of Ph at Dehra Dun and Batavia. Later on,
however, we find that P0 increases greatly, while PI,, at the equatorial stations, is slowly diminishing
and that before this period P, is much less and even sometimes directed to the opposite side.

We cannot, of course, draw any further conclusions from this, as it is impossible to determine how
great a part of P, at Axeleen is due to polar precipitations. There is all the greater need of caution
in drawing conclusions, from the fact that the conditions at Christchurch — which is in a comparatively
high southern latitude — show that at that place there is only a very slight perturbation in the vertical
intensity, and from about I3h 30™ onwards, the corresponding P, is directed downwards, not upwards
as we should expect when only the equatorial perturbation is acting. We there find, moreover, com-
paratively poverful perturbing forces in the horizontal components, and it would thus appear that there
were precipitations of a more polar character in the southern hemisphere also.

If, with the assumed value of /<, we make the force PI, at the equator equal to 75 y, we find that

~ . ~ 3 TCI

/r+F' = 4^ = 75'I° '

and / must then be equal to about 2 . io6 amperes, a value of the same order as that which we shall
find in the calculation of the current-strength in the polar perturbations (see Chap. IV).

The first intermediate storm, with maximum about 13'' 42™ occurs during the same time and with
great violence, at Sitka and at Axeleen. Its local character at these places shows that the current-systems
are comparatively near to both stations.

It is plain from the simultaneous appearance of the intermediate storms at Sitka and at Axeleen,
that these two storms must be closely connected with one another; but whether they are the effect of a
single system, or of separate and more limited systems of precipitation in the vicinity of the two stations,
it is impossible to decide with any certainty.

We have seen in Art. 52 (cf. fig. 68) how well the assumption of separate fields of simultaneous
precipitation agrees with our theory; and circumstances are actually found here that seem to favour such
a view. The maximum occurs, indeed, at about the same time, namely at I3h 42™, but the storm begins
at Sitka about a quarter of an hour before that at Axeleen, and perhaps does not end until a quarter
of an hour after the latter has ceased. If we look at the declination at Baldwin, where the intermediate
storm is well defined, it appears that the storm there begins at 13'' 8m, and concludes at 14!' 34™.

If we look at the //-curve for Kew or Wilhelmshaven, we notice that during this perturbation the
course of the curves is as follows: first at i3h 12™, there is a deflection answering to a diminution of H;
at I3h 24™, H has an intermediate minimum, then increases until I3h 42™, then decreases until I4h 5m,
when it again increases, and at I4h 30™ the effect of the impulse has ceased. The Z)-curve has a similar
course. It may perhaps therefore be natural to interpret the conditions in Europe in the following manner.

Between I3h I2m and 14'' 30™ there is a perturbation of uniform direction, occurring simultaneously
with the perturbation in America. Ph and Pd are directed respectively south and west, answering to a
current-arrow pointing north-west or west-north-west. This is interrupted by another perturbation, which
lasts from i3h 24"" to I4b 5™, and acts in almost exactly the opposite direction; and at the moment
when this latter storm reaches its maximum at Kew, it causes the effect of the former perturbation to

238

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

cease as far as Kew is concerned. Here, on account of the intermediate storms, the perturbing force
thus becomes 0 at the moment when the storm is at its height. During the brief storm, the current-
arrows are directed ESE, and these should be connected with the brief, powerful storm at Axeleen, just
as the latter is naturally connected with the powerful impulse in the southern Asiatic district.

The assumption that a distant system such as that in the vicinity of Sitka would have so great an
effect in Europe as we find here, may, however, present some difficulty; and yet more doubtful does
such an explanation become when we look at the conditions at Kaafjord, where, all through, a system
is acting which produces current-arrows with an easterly direction. Simultaneously with the intermediate
storm at Axeleen, there appears to be an intermediate storm here, which, as far as H is concerned,
begins, reaches its maximum, and ends, almost at the same times as the storm at Axeleen. The deflec-
tions, however, are the reverse of those at Axeleen, as in this case we find positive values of PI, , and
the strength is considerably less. In the declination, on the other hand, there is a rather brief impulse in
an easterly direction, with maximum at about 13'' 30"', being therefore almost exactly simultaneous with
the maximum of the first deflection at Wilhelmshaven. The curves at Matotchkin Schar show in some
respects a resemblance to the conditions at Axeleen, and in others to those at Kaafjord. In H the maximal
negative deflection occurs earlier than at Axeleen, and about simultaneously with that in the declination at
Kaafjord, i. e. at about I3h 30™, while at the same time there is also a fairly powerful easterly deflection
in the declination. As regards the intermediate storm, the conditions at Matotchkin Schar might seem
to form a connection between the conditions at Axeleen and those at Sitka, thus indicating that we had
before us a connected intermediate system with current-arrows on the night-side of the earth directed
westwards. If we accept the first explanation of the conditions, we should thus have to ignore completely
the effects of the system in the neighbourhood of Kaafjord, a system which seems, indeed, to be compara-
tively weaker, and in that respect will have a more limited sphere of action, but on the other hand is
so close to the Central European stations, that its effect there will in all probability be very apparent.

It should be remarked that the effect in Central Europe of this system in the neighbourhood of
Kaafjord is similar to that of the assumed system at Sitka, as they will both produce current-arrows
directed westwards.

Finnally, as the conditions at Matotchkin Schar appear to indicate that the system at Sitka is con-
tinued westwards to Axeleen — a circumstance that we have previously continually met with — there is
every probability that the westward-directed intermediate current-arrows are the effect of the system
observed at Kaafjord. Farther west we should without doubt have found this system more fully deve-
loped; and observations from Dyrafjord would therefore have been of great importance here.

We must suppose then that the effect of the southern system near Kaafjord might first predominate,
then the stronger but more distant system near Axeleen at the time when the latter is at its height, and
finally the southern system once more. The fact that the conditions in the Asiatic districts are more
analogous to those at Axeleen also finds a natural explanation here, the southern system at Kaafjord
being of far less strength than that at Axeleen, and therefore having a correspondingly smaller area
of action. We are confirmed in these assumptions by the course of the broken-lined arrows in
Charts IX and X. Thus on Chart IX we find an indication of a small area of divergence on the day-
side, and a larger area of convergence on the night-side; while on Chart X this area of convergence
extends farther west to the western stations of Central Europe.

The storm at Axeleen is an afternoon storm, and ought therefore to be compared throughout with
such storms, e. g. those of the I5th and 8th February, 1903, and the 2yth October, 1902, where we
also found two rather different systems acting at Axeleen and at Kaafjord.

The last great intermediate storm, from n1' i2m to o1' 42m, has on the whole been already charac-
terised, as we have previously proved that it has the same field of force as the ordinary polar elementary
storms that occur about midnight, and have their centre about the Norwegian stations.

PART I. ON MAGNETIC STORMS CHAP. III.

239

TABLE XXXVII.
The Perturbing Forces on the 3131 October, and ist November, 1902.

Gr. M. T.

Honolulu

Sitka

Baldwin

Toronto

Ph

Pi

P*

Pd

Ph

Pd

A

Pd

h m

9 o

-34-77

E 5.8 x

- 75-3 7

E 1 1 7.0 y

+ 14-97

0

+ 17-1 7

W 25.8 y

3°

-34-7 »

» 5-8 »

— 66.6 »

» 7a-5 »

+ 3-4 »

E i-;.iy

+ 5-8 »

E 6.0 .

10 o

-33-2 »

» 10.8 »

— 91.0 »

" 57-a »

— 2.O »

W 10.2 »

- 2.7 »

W 23.5 ,

15

-35-6 »

» 1 1.6 »

- 135-0 »

» 78.8 »

+ 19-7 •

• 34-2 "

0

> 75.8 »

3°

-35-6 »

» 9.9 •

— IOI.O »

» 142.0 »

+ 42.3 »

o

4- 52.2 «

» 52-3 •

II O

-32.3 "

» 7.4 »

— III.O »

» 105.0 »

+ 26.1 »

E 8.9 »

4 30.2 »

» 36.6 »

30

-32-3 '

» 12.4 »

— 98.9 »

» 86.4 »

+ 5-4 •

W 14.6 »

4 5-8 •

• 47-5 '

12 30

-31-9 *

* 7-4 »

- 97-3 »

» IOO.O »

+ 58-3 »

» 27.3 .

+ 12. 1 »

» 65.0 »

13 3°

-25-3 »

» 1 1.6 »

— > 2I2.O »

• 8.1 »

— 31.2 »

» 59.0 »

— 48.1 >

» 56.5 »

42

-27.7 .

» 16.6 »

— > 212.0 »

» 84.8 >

— IO. I »

» 76.2 »

— 36.0 »

» 71.0 »

14 o

-25-3 »

• 7-4 »

— 203.0 »

> 40.5 •

4 2.3 »

» 64.8 >

— 21.2 »

» 87.8 »

'7 45

Q

?

7

7

7

?

?

7

18 30

?

?

7

?

7

?

7

9

'9 15

7

7

?

?

7

?

?

?

20 30

?

?

7

?

?

7

7

7

21 45

?

7

?

7

7

?

7

7

22 O

?

?

?

?

?

?

?

?

23 45

9

?

?

?

7

?

?

7

r o

9

7

7

?

?

7

?

?

TABLE XXXVII (continued).

Gr. M. T.

Axeleen

Matotchkin Schar

Kaafjord

/';,

Pd

ft

Ph

Pd

P,

Ph

Pd

ft

h m

9 o

— 1 1 . i y

E 39-47

4-97

+ 94-07

W 22.2 J'

7.6 y

+ '5-3 •/

W 13.97

4 18.87

3°

- 19.3 »

* 5i-4 »

9-7 »

4 ni.o »

" 53-5 »

- 15-3 •

4 38.0 »

» 12. 1 »

4 81.5 »

IO O

- 15-2 »

* 43-° "

— 29.2 »

+ 128.0 »

» 31.0 »

- 18.6 «

4 68.2 »

O

4 92.5 J>

15

- 46-5 '

* 43-° "

— 31-6 '

-1- 152.0 «

• 36-3 »

— 27.2 »

4 91.0 »

" 9-9 »

4 89.3 »

3°

- 43-2 »

» 40.5 •

- 31-6 '

4 194.0 >

' 31-8 »

- 30.7 "

4138.0 »

• 15-7 "

4 71-3 >

I I 0

- 40.4 »

» 44.6 »

- 17-3 »

42OI.O »

» 52.0 »

- 66.4 >

4 125.0 »

» 30.7 »

4 39.2 »

3°

- 59-° •

» 26.3 »

- 17-3"

4 169.0 »

» 18.6 »

- 86.0 »

4 100.0 »

« 24.8 »

4 39.2 >

12 30

— 86.0 »

» 9.2 »

- 17-3 »

4142.0 «

• 56.3 »

— > 102. 0 «

4219.0 »

» 50.2 »

- 40.8 »

13 3°

-394-0 '

» 24.2 >

4 131.0 »

— 142.0 »

E 46.5 »

— > IO2.O »

4 189.0 B

E 117.0 »

-317.0 >

42

— 547-0 "

» 51.6 »

4383.0 »

4 21.5 »

W 1 30.0 »

— > IO2.O »

4257.0 >

W 133.0 »

— > 512.0 »

14 o

-234.0 »

» 11.9 '

4 85.0 »

-t-2I4.O »

» 181.0 »

— > 102. 0 »

+ 316.0 »

» 53-8 .

— 269.0 »

17 45

— 42.2 »

W 80.0 >

4 119.0 i

-177.0.

0

— > IO2.O »

4 22.1 »

E IO.2 »

- 35-a '

18 30

— 64.0 »

> IOO.O »

4 195.0 »

— ^> 240.0 »

E 52.2 «

— > IO2.O »

— 165.0 »

» 17.6 »

4 125.0 »

19 15

- 36-7 •

" 92.3 •

4317.0 »

— > 240.0 J

» 237.0 »

0

— 212. 0 »

» 65.2 «

4 172.0 »

20 30

— 124.0 >

• 32.8 »

4 397.0 »

— > 240.0 »

» 257.0 '

4 29.0 »

— 282.0 »

» 159-0 »

4247.0 »

21 45

- 35-8 •

o

•+ 421.0 »

— > 24O.O !>

• 337-0 .

4 147.0 »

— 294.0 »

» 193.0 »

4 188.0 »

22 0

- 29.4 »

I 30.2 >

4 367.0 »

— > 240.0 »

» 203.0 »

4154.0 »

— 263.0 »

• 95-3 •

4l6l.o »

*3 45

— 108.0 »

E 82.9 •

4343-0 •

— > 240.0 «

» 163.0 »

4 0.8 »

-351-0 »

• 88.3 »

- 20.3 »

I 0

4 18.4 »

» 39-6 *

4214.0 »

- 65.0 «

» 68.2 »

— 1 08.0 »

— 113.0 >

' 75-o »

— 7.0 »

240

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2— 1903.

TABLE XXXVII (continued).

Gr. M. T.

Stonyhurst

Wilhelmshaven

Kew

Potsdam

Ph Pd

Pi

Pd

Pi

A

ft

F*

ft

h m

9 o

— n.ay

W 14.37

- 16.87

W 18.97

0

- 12.77

W 12.2 7

- 8.9 y

W 15.77

3°

— 12. a »

» 2O.O »

- 16.8 »

> 21.4 >

0

— II. 2 »

» 20. 2 >

— 6.0 »

» 20.3 «

10 o

- '4-3 »

» I3-1 *

— 19.1 »

» 8.5 »

o

— 16.8 »

» 10.3 »

- 7.0 »

» 14.2 »

15

- 15-3 »

» I3.I »

— 21.5 »

» 7.9 »

o

- 19-4 •

• io-3 *

- 13-9'

« 17.2 »

3°

- 12.7 »

» 18.8 «

— 20.5 »

» 14-7 '

o

- 15-8 •

» 17-3 »

- 13-9 »

* 22.8 »

II 0

- t9-4 "

» 18.8 »

— 20.5 »

» 14.7 >

o

- 15.8 »

» 24.8 »

- 17-4 »

» 17.8 »

3°

- 16.3 »

» 12. 0 »

— 12. 1 »

» - 9.7 »

o

- 11.7 »

» 14.5 »

- M-S '

» 8.6 »

12 30

— II. 2 »

» 24-5 »

— 18.2 *

• 34-2 »

0

- 4.0 >

» 23.8 »

?

7

13 3°

— 18.3 »

• 5-7 »

- 38.6 .

o

o

— 26.4 »

> 6.5 «

7

7

42

7.1 »

» 22.2 »

- 6.1 »

> 7.9 »

+ 14.0 v

— 9.2 »

» 11.7 »

7

7

14 o

- 22.4 .

» 16.6 >»

— 41.0 »

» 12.2 »

4- 13.0 «

— 22.8 »

» 14.9 »

?

7

17 45

- 41.8 I-

» 25.7 .

— 61.5 »

» 20.2 »

4- I I.O »

— 27.0 >

» 26.2 »

?

7

18 30

- 47-4 »

E 32.3 »

— 48.0 »

E 29.3 »

-t- 22. 0 »

- 46.9 »

E 12.2 »

7

7

19 15

- 57-5 *

• 3i-4 »

- 54-5 »

» 45.8.

+ 16.0 »

— 52.0 >

» 22.9 »

?

?

20 30

- 49-4 »

» 3i-4 »

- 44-3 *

» 41.0 »

4- 16.0 »

- 41-3 »

» 28.6 »

7

7

21 45

- 38.2 »

» 28.0 »

- 34-5 •

» 31.8 »

4- 7.0 >

- 28.5 »

» 25.2 »

7

7

22 O

- 37-* »

» 42.8 »

- 3i-7 »

> Si-4*

4- 7.0 »

— 31-6 »

» 40.0 »

7

7

23 45

— I3-2 »

» 57-7 «

— 14.0 »

» 57-5 '

4- 9.0 t

— 4.6 »

» 51-5 »

7

7

I O

- 15-8 »

» 48.0 »

- 16.8 »

» 31.2 »

0

— 14.8 >

a 1 6.8 »

7

7

TABLE XXXVII (continued).

Gr. M. T.

Pola

San Fernando

Dehra Dun

Ph

ft

P.

A

Pd

Ph

ft

It m

9 o

- 7-i y

W 15.3 /

- 7-4 y

- 7-6 /

W 9.0 ;•

- 45-6 7

E 6.9 y

30

- 7.6 .

» 1 8. i »

- 7.6 »

- 5-i »

» 9.8 »

- 5°-4 "

» 1.9 »

10 o

— 13-° »

» 17-3 »

— 6.7 »

- 13-4 »

» 4.9 »

- 56-3 »

» 3.0 »

15

— n-s »

» 18.7 »

- 4.8 »

- '7-9 »

» 8.2 »

— 60.2 »

» 3-9 »

3°

- 16.6 »

i) 23.6 »

- 4-4 »

- 12.8 »

» 15.6 »

-66.5 »

o

II 0

— 2O.6 »

» 26.4 »

4- 0.4 »

- 14-7 »

> 1 8.8 »

— 71.0 »

o

3°

- 1 8.8 »

» 18.7 »

4- 8.2 »

- 14-7 »

» 1 8.8 »

- 64.5 >

» 1-9 '

12 30

— 2O.2 J>

» 27.8 »

+ 9-5 »

— 19.8 »

» 18.8 »

— 81.0 »

» 3.0 »

'3 3°

— 46.2 »

0

^ ]> 2O.2 »

— 49.9 »

» 14.8 »

— 36.2 »

» 21.6 »

42

— 29.6 »

» 4.2 >

4- > 2O.2 »

— 40.8 »

» 13-9 »

- 48.5 »

» 12.3 »

14 o

- 42.5 »

» 4.1 »

+ > 20.2 T>

— 44.8 »

» 8.2 11

- 59-° »

J> 19.7 »

n 45

— 32.6 t

» ii. i »

+ > 21.2 1>

-- 38-3 »

» 13.1 »

- 59-o »

• 15.8 >

18 30

— 44.8 »

E 1 1 . i »

4- > 21.2 »

— 56.2 t

» 6-5 »

- 54-° »

» 19.7 t

19 15

— 42.6 »

» 21.6 »

4- > 21.3 »

— 60.8 »

E 4.1 »

- 47-5 »

« 17.8 »

20 30

— 30.8 »

» 26.4 »

-i- > 21.2 »

— 46.6 »

» 9.0 »

— 40.2 »

» 15.8 )•

21 45

- 12.5 »

» 22.8 »

4- 1 8.6 »

- 26.8 »

» 9.8 >

— 33-5 »

» 7.8 »

22 0

- '4-3 »

» 29.2 »

+ 18.6 »

- 33-2 >'

> 13.1 »

- 33-5 »

» 8.8 »

23 45

4- 13.0 »

» 26.4 »

+ 9-9 »

- 13.4 »

» 27.0 »

- 31 8 >

o

I O

- 17.9 »

» 7.O »

4- 2.9 »

- 14-7 »

» 10.6 »

- 43-3 »

o

PART 1. ON MAGNETIC STORMS. CHAP. 111.

TABLE XXXVII (continued).

241

Gr. M. T.

Zi-l<a-wei

Batavia

Christchurch

/'/,

Pd

P*

Pd

/>*

Pd

P.

h m

9 °

- 45-5 y

E 2.0 y

- 57-° 7

0

- 33-a y

E 8.2 /

- 4-6 /

3°

- 52-8 »

W 4.0 »

— 60.5 »

o

— 41.4 »

W n. i •

-4.6 »

IO O

- 54.0 »

o

— 60.5 »

0

- 35-4 »

» 17.1 »

- 3-7 "

15

- 63.5 »

» I.O »

— 6o-5 »

0

- 39-i »

» 22.3 »

— 2.2 >

3°

- 73.1 »

» 4.0 »

- 67.5 >

o

- 51-5 •

• 27.5 »

— 2.3 »

I I O

— 68.4 »

» 3.0 »

- 74-5 »

o

- 58.3 »

• 27.5 »

-4-3 •

3°

- 58.8 >

» I.O »

- 64.5 >

o

- 45-5 •

• 31.6 »

- 3-7 »

12 30

- 73-i »

» 3.0 »

— 81.5 »

0

- 58.3 •

" 53.5 »

0

13 3°

- 6.0 »

E 6.0 »

- 18.5 »

W 15.6 y

- 4.1 »

• 35.3 »

o

42

— 28.8 »

» 5.0 »

- 33-° •

» 15.6 »

- 13-8 •

» 44.6 »

-1- 4.9 »

14 o

— 30.0 »

> 6.0 »

- 45-5 »

» 6.0 »

- 13-3 »

• 54-2 »

+ 4-9 »

17 45

— 34.0 »

» 3.0 »

— 54-3 »

» 13.3 >

— 13.4 »

E 8.9 »

+ 3.7 »

18 30

— 13-2 »

i 7.0 »

- 46.8 »

» 15.6 »

- 8.7 .

» 37-8 •

4- 2.5 »

19 '5

- 13.2 »

» 4.0 »

— 41.3 »

> 15.6 »

- 18.4 >

• 43-9 '

+ 4-3 >

20 30

- 14.4 i-

o

- 34-a »

* 9.6 »

- 36-3 »

• 53-5 «

+ 4-3 »

21 45

- 7.2 >•

W 8.0 »

- 38.3 »

0

- 52-5 •

» 38.6 »

4- 3.7 »

22 O

- 4.8 »

» 8.0 »

- 35-8 »

o

- 54-8 •

» 33-5 »

+ 3-7 »

23 45 — 16.8 «

» 5-° »

- 49.0 >

?

— 60.2 >

?

?

I O — 9.6 »

» IO.O «

7

?

?

7

?

TABLE XXXVIII.
Partial Perturbing Forces during the Perturbation of the 3ist October, 1902.

I3h 3<

>m

I3h 4

2m

I4h c

m

/";,

P'd

/"»

/"d

Ph

Pd

Honolulu

E 14. SV

— 16.4 v

E 15.8 /

Sitka

— ^> n8 o »

» 22.^ »

W 4 S »

- IO.2 »

W 44.0 »

-H 2.^ »

» 8.4 »

» 21. 1 »

— 17.6 »

Axeloen
Matotchkin Schar .
Kaafjord

—307.0 »
-367.0 »

E 35-8.
» 166.0 »

—457-° '
— 232.0 j>

4- 81.5 »

E 87.5 »
W 73.5 »
» 86.1 »

— IOO.O »
0

-4- 14.8 >

E 25.8.
W 13.3 »

— IQ.Q »

» 9.1 »

o

» 4.5 >

- 14.8 »

o

Wilhelmshaven . .
Kew

— 24.3 >

» 18.3 »

» ^.T »

+ 8.4 >

— 5.6 »

E n.6»

0

- 23.8 a
— 23.9 »

E 5-5'
W 3 7 >

Pola

— 24.3 »

» 15.3 »

— 8.S *

» I I.O »

— 20.7 >

E 10.3 »

San Fernando . . .
Dehra Dun ....

- 26.8 »

+ 37-o »
+ 58.8 »

W 6.5»
E 16.7 »
» 8.0 '

— 17.2 »

+ 19-3 »
+ 34.8 »

W 5-7'
E 4.9.
• 3-o •

— 2I.O »
+ 8.3 »

4- 22.8 »

W 6.5.
E 6.9.
» 8.0 »

4- ^o.e; »

W I2.O »

+ 34-8 »

W 9.6.

4- 18.8 »

W 4.8 »

Christchurch ....

«- 38.6 »

E it. a »

+ 26.7 >

> II. a >

+ 31.6 »

• 19-3 *

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903.

31

242 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

Current-Arrows for the 31st October, 1902; Chart I at 9h Ora , and Chart II at 91' 30m .

PART I. ON MAGNETIC STORMS. CHAP. III. 243

Current Arrows for the 31st October. 1902; Chart III at 10h Om , and Chart IV at 10h 15m.

Fig. 108.

244 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

Current-Arrows for the 31st October, 1902; Chart V at 101' 30m, and Chart VI at Ilh Om.

--

i *

4?

B*k

CWh

Ch Ch

i ' r . 0

S.l

.,

H Ch Munffirif

\
/

\

\

\

fiWfJ

sfoofrj

pf

itewste

^

r "^sf

TO

2fc.

uH

^

V

^d

y

HOA^-

(f«C*

32

\

/^

AS

Z5~

r»

/-A^

,J

>'

P

^S

>

fc

J^g

fit

/•

(1)1

V

^N

s

X)
•^^

i*^=

kJ

^

^

H

5

iw

z

"^o^

^3

Aifl AftUen

BJ w Smtdmtn

CHh £Miart«i

OiCh OrtttfJuuTh

Dh D £Mra AM

Sol saa?

KO
Mr

M&lSch
U ch

Pwsk

FV,1»

PU-d

XacjWtf

A>u>

JW»frMw -,V*w

14^,?^"^-

U-An-m^

-v/K

Z

7

1

(7

/

V^
u

r\"

^

QTP

IT1'

PART I. ON MAGNETIC STORMS. CHAP. III. 245

Current-Arrows for the 31st October, 1902; Chart VII at llh 30m , and Chart VIII at 12h30m.

-

ft. talaeia

S F S»fi™».fo

PitJi* Attfl

5th StvyhMTJt

Tulis JWUf

:

II

v

•

•'

••>...

Fig. no.

246 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION T.gO2 — 1903.

Current-Arrows for the 31st October, 1902; Chart IX at 13h 30m, and Chart X at 13h 42m.

Fig. in.

PART I. ON MAGNETIC STORMS. CHAP. III. 247

Current-Arrows for the 31st October, 1902; Chart XI at 14h Om, and Chart XII at 17h 45m.

;

Cs

9

v7ffT.ii

"

-

2

Ax 0 Axrlain

Bl w KahttMn

ILi

Mai Sch

Fwak ._.

PoU /Wo

Pud

7

Z k w Ii -Ad -«•<

Fig. na.

248 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

Current- Arrows for the 31st October, 1902; Chart XIII at 18h 30m, and Chart XIV at 19h 15m.

PART I. ON MAGNETIC STORMS. CHAP. III. 249

Current-Arrows for the 31st October, 1902; Chart XV at 20h 30m , and Chart XVI at 21h 45m .(')

1 1!-.'

si

•,

•: '

m

7

'

Oilh Outlaid

CfcCh Otmtflu
D)i D Drtra I'

£,-** AMd

Si li Slfuhunl

Tuiis nv>

0

[^ — /

s*

;-

Bih 5w»b>/i

Qilh Cntliaika*

Oi Ch Qvui.j-uir,

DhD D An Dun

'

;-*v^

T

Zkw b-Ad-jH

Fig. 114.

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.
Current-Arrows for the 31st October, 1902; Chart XVII at 22h Om(i), and Chart XVIII at 23h 45m.

•:,

I'll

5

-nr

"OFT

\

DhD
Dfl
Kolu

teg

7

5F satKr.

Sllka AM*

*> %ff~

?lu

PART I. ON MAGNETIC STORMS. CHAP. III.

Current-Arrows for the 1st November, 1902; Chart XIX at

251

lh Om.

Fig. 1 1 6.

THE PERTURBATIONS OF THE llth & 12th OCTOBER, 1902.

(PI. II).

68. From iih on the nth October, to about oh 30™ on the I2th, perturbations that are some-
times violent are noted at all the stations from which we have observations. They are unusually violent
in the equatorial regions, where the conditions become rather complicated, as there are undoubtedly often
several current-systems, sometimes even occurring simultaneously.

The perturbations seem to fall naturally into three principal sections,
The first from nh to I7h.2om on the nth October,
The second from iyh 2om to i8h 3om on the nth October, and
The third from i8h 30"" on the nth October, to oh 30™ on the izth.

In the first section, it is especially in the horizontal intensity that the perturbation occurs. We see
that the perturbing force allmost everywhere is directed northwards along the magnetic meridian. The
way in which the force is generally distributed during this period is shown on Chart II, for I7h om.

It appears from the copies of the curves, that this part of the perturbation is especially well deve-
loped in the equatorial regions. This, together with the serrated character of the horizontal intensity
curve, and the direction of the force, would make it appear that this is mainly a positive equatorial
perturbation of the well-known type (cf. e. g. Art. 27).

252 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

During this first section, polar storms also occur at our Norwegian stations ; but they are not very
considerable, although of sufficient strength to explain the partial loss of the typical character of the
equatorial perturbation, especially as regards the northern stations.

Between I2h 25™ and I3h I5m, however, a considerable polar perturbation sets in.

It should be especially noticed that, as the curves show, during this interval of time there is a
perturbation at Sitka that, for that place, is rather violent. The direction of the perturbing force is very
nearly west all the time, and its greatest value is reached at about I2h 50™. It is also noticed at the
Norwegian stations, most distinctly at Matotchkin Schar; at Axeleen it is less, but still noticeable, and at
Kaafjord it is almost imperceptible. If we look at the curve for Matotchkin Schar, we see that the force
there is uniform in direction along the magnetic meridian; and we notice particularly that the maximum
does not occur until I3h i8m almost half an hour later than at Sitka. This must either be explained
by a movement of the current-system, or we must assume that the perturbation at Matotchkin Schar is
due to a relatively different system.

The farther we go from the polar regions, the less perceptible does this brief polar perturbation
become. It is distinctly noticeable at Baldwin and Cheltenham, but not at Honolulu. At the European
stations, it is only just perceptible. At Zi-ka-wei and Dehra Dun it is distinctly noticed, at Batavia it is
almost imperceptible. At Christchurch on the other hand, there is a rather violent perturbation in
relation to the place, only noticeable in the //-curve. The perturbing force is here directed northwards
along the magnetic meredian, corresponding to a current-arrow from west to east. The effect at Christ-
church cannot have been produced by the same system as that which acts in the northern hemisphere;
for the effect of the latter is imperceptible even at Honolulu and Batavia.

The explanation of this seems to be that simultaneously with the descent in the north, a similar
phenomenon appears near the south pole, and it is the effects of the latter that we observe at Christchurch.

On Chart I, for I2h 50™, only the current-arrows corresponding to the polar storms are shown,
as we have endeavoured to separate their effect from that of the equatorial system by a decomposition
of the total perturbing force.

The second section includes the interval from i7u 20™ to about i8h 30™, and it commences with
the appearance of violent storms in the arctic districts. The effect is especially strong at Matotchkin
Schar, but less so at Axeleen. At Sitka, on the other hand, it is very marked.

Chart HI at i8h om. The distribution of force seems on the whole to be conditioned by this
polar storm. Judging from the serrated character of the curves, however, it seems that the effect of
the equatorial storm is still perceptible.

Of arctic stations, Matotchkin Schar is the one at which the force is strongest; and its direction
is there south-east. At Axeleen it is less, and is directed south-west.

If we look at the European stations from Pawlowsk to San Fernando, we find that at all of them,
with the exception of Pawlowsk, the forces are rather small. Even at Stonyhurst it is less than at
Tiflis and Dehra Dun. The direction of the current-arrow at Pawlowsk is about south, in the district
Potsdam to Wilhelmshaven and Munich, south-west, and at Stonyhurst and Kew, almost west. If we go
right across to North America, we find the direction at Cheltenham NNW, at Toronto still more
northerly, and at Baldwin almost north. They form, as we see, a harmonious continuation of the direc-
tions in Europe, becoming more and more northerly as we pass from the European stations across the
Atlantic to North America. Thus the current-arrows should indicate the existence of current-vortices
with a clockwise motion in the North Atlantic. In reality there is something like a divergence of the
horizontal component of the perturbing force out from a point in these districts. Somewhere or other,

PART I. ON MAGNETIC STORMS. CHAP. III. 253

possibly near Iceland, there should be a point of divergence for Pk. At Val Joyeux and Pawlowsk,
there is a distinct vertical component directed downwards.

It may further be stated that the current-arrows at Sitka, Baldwin, Toronto, and Cheltenham con-
verge towards a point in the vicinity of Prince Albert Land.

Eastwards from Europe, the arrows turn off, but now towards the east. The directions of the
arrows, in connection with that at Sitka, indicate that somewhere in the north-east of Siberia, there is
a point of convergence for the perturbing force.

The third section, from about i8h 30™ to oh 30™, is characterised by a long polar storm. The
field of force of this storm is shown on the Charts V, VI, XI, XII, XIII and XIV, respectively for

Igh 30mj 20h gotn^ 2Ih I5m( 2Ih ^o™, 22h, and 23**.

We see that the distribution of force is about the same in all of them, the strength of the field
alone showing any variation.

At the arctic stations, the direction of the force is generally SSE and SE.

There is a departure from this condition at igh 30™, when the force at Axeleen and Kaafjord is
almost westerly in direction. At 2oh 30™ the force at Kaafjord is SSE in direction, but it is still west
at Axeleen.

In the rest of Europe and in Asia, the direction of the force is ESE. At San Fernando it turns
a little more south, and in America the direction is south-west. This shows that in the North Atlantic
there must be a point of divergence of Ph similar to that described at i8h. At Sitka, the direction of
the perturbing force is WNW.

During this period, however, there are several departures from these conditions, and it is evident
from the copies of the curves, that of these there are three principal ones, the first occurring at about
r8h 34m (see Chart IV), the second between 2oh 45™ and 2ih 20™ (see Charts VII to X), and the third
between about 23h iom and oh 25™ (see Chart XV).

The fact that after these short interruptions the field once more assumes its original form, makes
it probable that the interruption is due to comparatively independent, brief current-systems, that occur
simultaneously with the long polar storm. The correctness of this view of the matter is also confirmed
by the fact that the differences do not occasion the same relative increase in strength at the various
stations. If we look at the curves, we shall see that these differences occur simultaneously all over the
world, even as far off as Christchurch. At the Norwegian stations also, sudden powerful perturbations
are observed, some of which have a different direction from that of the long storm. The three short
perturbations are thus polar storms, which intrude themselves upon the long storm. The latter we will
designate as the principal storm, and the three others as intermediate storms.

The circumstances, as we see, are such as justify a decomposition of the perturbing forces into two
components, each of which is the effect of a separate current-system. This decomposition has been
effected in the case of the last two intermediate storms, but not of the first, as that storm commences
at the time of transition from the second to the third section.

This is apparent in the curves, e. g. for Tiflis and the south-east Asiatic stations, where the
//-curve, at about i8h 30™, drops suddenly, showing that P,n from being positive, has become negative.
This circumstance makes it impossible to draw any exact normal line for the taking out of the partial
forces.

We will now describe in detail the three intermediate storms.

The first intermediate storm, at about i8h 34™.

This perturbation appears in the curves as a great, but brief, deflection at about 18'' 34™. At the
southern stations, such as Tiflis, Dehra Dun, etc., it appears to be the long perturbation only that is at

254 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

all powerful during this period. It is evident, however, from the conditions at the arctic stations,
especially Kaafjord and Matotchkin Schar, that it cannot be regarded only as an increase of the principal
storm, for the horizontal component of the perturbing force during this period turns round in the opposite
direction.

Chart IV shows the current-arrows answering to the total perturbing force at i8h 34m.

The current-system on the whole bears a fairly close resemblance to that of the principal storm,
which has already been described.

The chief difference between them is that at Kaafjord and Matotchkin Schar the direction of the
force is the reverse of that which we find during the succeeding part of this section, as the current-arrow
is now directed along the auroral zone from west to east. The magnitude of the total perturbing force at
Matotchkin Schar now gives a false impression of the forces that are in operation, as the total force
there seems to be about equal to the difference of the forces actually present. At Kaafjord, however,
the long principal storm, with current-arrows directed westwards, does not seem to have any noticeable
influence until about igh 3Om.

As regards Matotchkin Schar, we find that the current-arrows again point in the direction they had
in the first section.

Unlike the distribution of force during the principal perturbation, the current-arrows in Europe are
now directed westwards, and at the most northerly stations even a little north. These last, during the
principal perturbation of the third section, had a more southerly direction.

In America the conditions are essentially the same as those during the long perturbation, the only
exception being that the arrow at Sitka is comparatively longer and more eastward in direction:

We thus see that this time also, the perturbing forces approximately diverge from a point in the North
Atlantic. The strength with which the perturbation appears in the regions round Batavia, Dehra Dun
and Zi-ka-wei is especially worthy of notice.

The arrows at Irkutsk, Honolulu and Sitka indicate the formation of negative vortices corresponding
to a convergence of the perturbing forces. In this case, the area of convergence would be situated in
the regions surrounding the Behring Sea.

The second intermediate storm, from aoh 45™ to 2ih 2om.

In the decomposition of the total perturbing force in this storm, we have attempted to distinguish
between its effect and that of the principal storm, "at all the southern stations where the conditions before
and after are constant.

At the arctic stations the curve shows distinctly that a particularly strong impulse occurs during
this period, especially noticeable at Axeleen, where the surrounding conditions are fairly normal.

We have therefore not thought it advisable to undertake any decomposition there. The normal
line for the taking out of the partial part, should be the curve as it would be drawn on paper if the
principal storm only had been acting; but owing to the rapid change in the principal perturbation,
this line cannot be determined with sufficient certainty.

The result of the decompositions is shown on Charts VII — X. The resulting arrows are here
drawn entire. The arrows representing the principal storm are drawn with a dotted line, those repre-
senting the intermediate storm with a broken line.

The field in the principal storm is of course the same as that previously described.

In the field of force and its variations, this intermediate storm shows a great resemblance to the
ordinary polar elementary storms, such as those of the I5th December, 1902, the ioth February, 1903, etc.

On Chart VIII - - for 2oh 52.5m - - the partial current-arrows in the district Pawlowsk to San
Fernando are directed south-east, and at Tiflis east, while farther east they turn more north. This
indicates a convergence of the perturbing force in the north-west of Asia or the north-east of Europe.

PART I. ON MAGNETIC STORMS. CHAP. III. 255

The conditions in North America at this point of time are peculiar. At the three stations in the
east of that continent, the direction of the current-arrow is east, and at Sitka south-west, or on the
whole rather different from that which might be expected from its resemblance to the above-mentioned
polar elementary storms. This lasts, however, only for about 10 minutes during the first part of the
perturbation, whereupon Ph decreases, and for a moment is about zero ; and in the two succeeding charts
the directions of the arrows are the same as, for instance, on the i5th December, 1902, and the 22nd
February, 1903.

The resemblance to these storms is still further increased by the circumstance that in Europe there
is a corresponding positive turning of the perturbing force.

The third intermediate storm, from about 23** iom to oh 25™.

As regards the arctic regions, this polar storm is powerful at Axeleen, rather less so at Matotchkin
Schar, and at Kaafjord, strange to say, it is almost imperceptible in H and D, while in the vertical intensity
it is quite distinct.

At the same time there is a distinct difference in the perturbation-conditions in southern latitudes,
these being particularly powerful and distinct in Europe, and noticeable also in the East and in the
United States, while at Sitka the perturbation is almost imperceptible. The oscillations are on the whole
uniform in direction, indicating that the forces remain in one direction all the time. We have therefore
considered it sufficient to show the distribution of force at one moment during the time when the
perturbation is at its height. This is represented on

Chart XV; time 23* 45™.

This storm, on the whole, has a great resemblance to the previously-described elementary night-
storms, e. g. to that of the 23rd March, 1903. They commence at about the same time of day, i. e.
a little before midnight. In both of them, the distribution of force remains constant throughout the
perturbation, and is in the main similar.

The perturbing forces of southern latitudes, as the chart shows, seem to indicate that we have a
point of convergence situated, in this case, very near Kaafjord, the effect of this system being there
almost exclusively in a vertical direction. The horizontal arrow drawn for Kaafjord would appear, to
judge from the curve, to be due mainly to the effect of the principal storm, which is still in activity.
At one place in the north of Canada, perhaps near Hudson's Bay, there is a point of divergence of the
horizontal component of the perturbing force.

Notwithstanding the long duration of the perturbation, and its somewhat varied character, we believe
that we have succeeded, by means of the foregoing analysis, in elucidating the main features of the
perturbation-conditions, and taking out the elementary phenomena that together form the present storm
in all its diversity. In the course of the period of time considered, the following principal phenomena
have been shown :

A positive equatorial perturbation from about nh — i8h, and the six following polar storms:

(1) The polar storm from I2h 25™ to 13'' 15™,

(2) The polar storm from about i7h 20™ to i8h 30™,

(3) The main polar storm from about i8h 30™ to oh 30™,

(4) The first intermediate polar storm, maximum at i8h 34™,

(5) The second intermediate polar storm from 2oh 45"" to 21 h 2om,

(6) The third intermediate polar storm from 23h iom to oh 25™.

256

B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE XXXIX.
The Perturbing Forces on the iith October, 1902.

Gr. M. T.

Honolulu

Sitka

Baldwin

Toronto

Cheltenham

Pk

Pd

Pi,

Pd

Ph

Pd

Pk

Pt

Ph

P,

h m

12 50

+ 5.0 y

o

-22.47

W5i.77

- °-7 •/

0

7

w 5.6 y

0

O

17 o

+ 7.6 „

o

+ 8.6,

E 18.4.

+ 8.1 „

W 6.4 7

+ 15-77

B 6-°B

4-20.6 y

W 8.9 y

18 o

+ 6-5 .

W 5.8 •/

-20.8 „

W 9.0,

- 3-7 B

n 13.7 B

- 4-° n

B i8.6B

- S-OB

B u-3 B

3°

o

n 22.5 „

- 4-6 „

„ 86.4 „

-25-0 „

B '3-4 B

-29-7 n

B 28.6 „

-43-9 B

B 12.5 B

34

0(?)

. 12.5 ,

0

. 81.0,

-25-4 B

„ 8.9 „

-41.0 „

B 25.0 „

-4o.on

B 9-5 »

19 o

- 3.8 .

ff 12.4 „

- 8.6 „

. 20-7 ,

— 7-8 „

B 6-4 B

- 4-5 »

B IS-OB

-14-7 B

B 6.5 „

3°

- 4.2 „

. 13-3 .

- 6.9,

n 18.5 .

- 5-1 B

. 2.5 „

+ 2-3 »

B IO-3B

- 9-4 B

» 7-7 B

20 o

- 8.1 „

. >6.6 .

-U-3 .

ff 20.7 „

,-l6-9 »

°

-'5-7 n

B 9-6 *

-25.0 „

n 7-3 n

3°

- 9-1 ,

. 19-1 »

-i6.5»

„ 29.3 „

— '5-2 „

B 4-8 „

- 9-4 „

ff 16.9 ,

-22.1 „

B 'O-1 B

45

- 6-5 ,

. i9-i .

-17-9 .

ft 39-3 »

- 8.8 „

l) 6-4 n

- 7-2 „

n 17-3 B

— '7-7 B

B 13-7 B

52-5

-+- q.p m

o

— 20. o „

» 45-0 .

- 4-9 B

B 7-6 „

0

, 18.1 „

-io.5n

B 14-0 »

21 O

- 8.4 .

„ 20.8 „

-27-5 .

. 67.6 .

-31.1 .

» 9-5 B

-28.4B

B 23.5 „

-42.1 „

B l8.4 „

7-5

- 2-4 »

, 4-2 „

— 21.0 „

n 23-0 B

— 23.6 „

B 3-8 „

-37-o B

B 21.0 „

-29-4 B

B 20.0 „

IS

- 7-8 „

„ 20. o a

-i i-5 .

» 33-4 n

-15-2 ,

„ 9-2 .

-i6.6n

B 26.6 „

- 23-5 »

B 21-4 .

3°

- 6.5 „

„ 1 6.6 „

- 7-i if

B 27-0 „

-"•5 ,

n I2-i n

-15-3 B

B 27.7 „

-20.6 „

„ 20.8 „

22 0

- 3-9 .

. 15-8 „

- 4-3 .

11 23.4 „

-ii.8 „

B I2-I »

-*3-S»

B 22.3 „

-H-4B

„ 16.1 „

3°

- 3-9 .

„ IO.O „

o

B 13-0,,

— 11.2 „

,, 3-2 „

-13-5 B

B 6.6 „

— 14.1 „

B 3-6 „

23 o

- 3-9 .

„ 6.6 „

+ 1-2,,

B 7-2 „

-11.8 „

E 2.9 „

-12.3,,

E 1.8 „

-"•SB

0

45

0

o

o

B "-3B

-12.8 „

B 2.5 „

-IS-OB

o

-I5-OB

o

24 o

- 2.6 .

0

— 2.2 „

„ 10.4 „

— 9. 1 „

W 2.6 „

-10.8 B

W 1.8 „

-II.2M

0

TABLE XXXIX (continued).

Gr. M. T.

Axeleen

Matotchkin Schar

Kaafjord

Pi,

Pd

P.

Ph

Pd

Pv

Pk

Pd

ft

li in

12 50

+ 22.9 y

W 26.0 y

- 24.67

+ 43-57

W it. i y

o

W 8.07

+ I2.Oy

17 o

+ 3-2 „

B 34-o „

- 8i.on

+ 66.0 „

B 22.0 „

?

?

?

18 o

- 92.0 „

B 73-5 B

- 56-5 B

- 93-0 „

E 254.0 „

?

?

?

3°

- 57-3 B

B 6l-2 „

+ n-2B

+ 3°-o „

B '3-4 B

No values

+ 113-07

B 29.4 „

-107.0 „

34

- 46.0,,

B l6-2 B

+ 42.0 „

4- 88.0 „

W 7.4 B

can be

4-126.0 „

B 80.0 „

- 120.0 „

19 o

- 20.5 „

B 42.2 „

O

48.8 „

B 53-5 B

taken out.

+ 35-6 „

B 34-8 B

O

as the po-

30

o

B 35-9 B

O

96.0 „

B 69-° B

sition of

- 59-3 B

B 73-4 »

- 13-3 B

20 o

- 20.5 „

B 39-4 B

+ 228.0 „

- > 180.0 „

„ 89.0 „

the normal

-'SS-OB

E 86.2 „

- 42.6 „

30

- 2.3 „

B 42.2 „

I" I30-0 „

- > 180.0 „

B 187.0,,

line seems

- 296.0 „

B 174-0 „

+ 5-6,,

45

-1 79-o „

E 139-0 „

+ 442.0 „

- > 180.0 „

B 4I4-0 „

to have

- 225.0 „

B 1 76.0 „

+ 58.6 „

52.5

-'37.on

B I'I-0 B

+ 290.0 „

- > 180.0 „

B 340.0 „

become a

—346.0 „

B 259-0 „

4- 242.0 „

21 O

-238.0,,

B 76-2 „

+ I2-3B

- > 180.0 „

B 348.0 „

permanent
change

- 296.0 „

B 238.0 „

+ 237-0 „

7-5

— I IO.O „

B 94-5 B

+ 492.0 „

-> 180.0,,

B !90.on

during the

-i6i.on

» H6.0,,

- 32.0 „

15

- 130.0 „

B 53-o B

+ 327-0 „

-> 180.0,,

B 178.0,,

perturba- n— 182.0 „

B 58.8 „

-US-OB

30

- 41 3»

B 10-4 „

+ 287.0 „

- > 180.0 „

B 85.0 „

tion.

- 152-0 „

w 53-3 n

- 94-0 B

22 O

— 10. 1 „

B H-0 B

+ 216.0 „

- 168.0 „

B I29-o „

(See PI. II).

-ISO-OB

B 84.4 „

- 98.0 „

30

+ S-OB

W 10.7 „

+ IIO.O,,

- IS6-0 B

B 125-0 B

-IIS-OB

B 67.8 „

- 96.0 „

23 o

+ '3-7 B

E 9.4 „

-1- 86.0 „

- 91-3 B

B 94-° B

-118.0 „

B 82.5 „

- 70.3 B

45

- 69.0 „

B 65-9 B

+ 393-0 „

91.0 „

B 53-5 B

- 44-4 B

» 18.4 B

- 122.0 „

24 o

- 43-5 „

B 43-5 „

+ 182.0 „

- 51-0 B

B 38-0 „

- 49-8 B

B 9-2 B

-I ig.O „

PART I. ON MAGNETIC STORMS. CHAP. III.

257

TABLE XXXIX (continued).

Gr. M. T.

Pawlowsk

Stonyhurst

Kew

Val Joyeux

n

Pd

Pr

Ph

Pd

Ph

Pd

P*

Pd

P,

b m

12 50

— 10.2 y

W 5.0 v

0

0

W 4.0 y

0

W 7.0 y

+ 4-4 >'

W 4.2 y

0

17 o

+ 15-1 ,,

» 12.4 „

4- 0.7 ;-

+ -5-3 7

» 11.4 f,

+ 18.3 ;/

„ n-7 .

+ 22.4 „

, 7-5 .

0

18 o

- 5-° „

E 44.2 „

+ 4-9 „

— 12.2 „

o

- i 1-7 „

0

- 4.8.

E 6.7 „

+ 6.0 v

3°

-35-2 „

„ 1 8.8 „

4- 1 1. 2 „

-35-6 „

, '4-3 „

- »9-5 „

» 1 1-7 .

- 39-6 ,

Wio.5 „

+ I0-o „

34

— 44.0 „

„ I O.O „

4*i2.o w

-28.5 „

„ 17.0 „

- 35.5 »

n I5-° »

- 33-6 »

» I2-° o

+ 10.0 „

19 o

— 12.6 „

,, 7-4 ,,

4-II.2 „

- 6.6 „

H 4.0 „

-- 8.3 „

„ 4-7 »

— 4.0 „

o

+ 6.0 „

3°

- 8.1 „

» ii-5 .

+ 7.5 ,

— I 1. 2 „

0

— IO.2 „

0

- 6.4(,

E 0.8 „

+ 7-5.

20 o

+ 7-6 „

„ 42.2 „

0

-21.4 „

E 21.7 „

- 20.8 „

E 19.6 „

— 16.0 „

» 26.7 ,

+ 9.6 .

30

- 15.6 „

„ 5°-6 „

- 5.6 ,

-22.4 ,

„ 26.3 „

— 27.0 „

» 24.4 „

— 2O.O „

„ 26.7 „

4- I2.O „

45

- 1.6 „

» 55' 5 »

- 5.6 „

-21-9 »

» 54-5 »

— 22.8 „

. 42-1 »

— 16.0 „

» 47-7 .

+ 10.0 „

52-5

+ 4-5 „

» 62.0 „

— I O.O „

— 12.2 „

,, 54-o „

- 12-7 „

„ 53-o „

- 8.0 „

» 53-5 „

4- 8.0 „

21 O

+ 5-o „

„ 72.6 „

-15-0 „

— 29.6 „

. 58.2 „

- 3°-5 „

» 52-4 »

- '5-2 „

» 54-2 .,

4- 13.2 „

7-5

— 10.6 „

„ 78.0 „

-15-0 „

-5--o „

ft 49-o »

- 5°-° „

» 59-0 „

- 40-8 „

„ 54-o „

+• 13-° »

T5

- 7-i „

„ 52.7 „

-12.4 „

— 30.0 „

„ 5°-9 .

— 32-1 „

» 46-° „

- 24-4 »

» »4-3 .

4- 10.0 „

3°

— 10. 1 „

, 3°-3 „

- 7-5 ,

-15.3 »

. 32.8 .

- 15.8 „

-, 32-3 „

- 1 1.6,

» 29.2 „

4- 8.0 „

22 0

- 7-6 „

,, 27.6 „

- 7-5 ,,

-15.3 .

„ 28.6 „

- 13.8 „

„ 25.8 „

— i o.o „

if 25-5 *

4- 6.4 „

3°

- 9-6 „

„ 19-8 „

- 6.0 „

— 16.3 „

„ 2O.O „

- 15-3,,

„ 18.7 „

— 1 1 -a „

» 14-2 „

+ 5-0,

23 o

- 6.5 „

,, 13-3 ,,

- 5-2 „

-"•7 »

. -4-3 .

- 9-7 .

„ 12.6 „

- 8.0 „

., "-7 .

+ 4-0,

45

+ 12.8 „

0

— 2.5 „

4/64.0 „

* 28.0 „

+ 7-6.

, 23.0 „

+ 8.0 „

ft 21.0 „

4- i.o.

24 o

+ 7.6 „

o

- 5-6 .

+ 3.8 „

„ 20. o „

+ 3-6,

„ 2O.O „

+ 5.6,,

, 17.6 -,

0

TABLE XXXIX (continued).

Gr. M. T.

Wilhelmshaven

Potsdam

San Fernando

Munich

Ph

Pd

P,

Ph

Pd

Pi,

Pd

Pk

Pd

h m

12 50

— 2.3 y

Wir.6 y

O

- s-7 y

W 2.5 y

?

?

+ 5-0/

0

i7 o

+ 23.3 „

„ 18.3 „

4- 2.0 y

+ 20.6 „

„ 11.7 „

4-20.8 y

o

4- 14.0 „

W 9. i y

18 o

- 7-o „

E 7-9 »

+ 4-0 „

- 9-5 »

E IO.2 „

- 46 „

0

— 1 0.0 „

E 11.4,

30

- 37-3 .

WiS.g „

+ 5-0,,

-39-5 „

W 9.1 „

— 26.2 „

Wi5.6 7

- 35-o „

W 3.0 „

34

- 46.7 ,

„ 26.8 „

o

— 39-° »

„ -5-3 ,

— 25.0 „

„ 16.4 „

- 38.5 »

r> 7-5 n

19 o

- 4-7 «

4-3 »

4- 6.0 „

- 7.6 ,

•, i -5 »

- 8.0 „

0

- -4-0 „

E 1.3.

30

- 7-5 „

E 3.0 „

4- 7-0,,

- 7-9 „

E 3.0 „

- 9-0 „

o

- M-O „

, 3-8.

2O 0

- 7-9 „

„ 33-o „

4- 8.0 „

- 7-6 „

. 3°-° -,

-18.6 „

E 9.8 „

- 15-0 „

r, 25.1 „

30

— 19.6 „

„ 33-° .

+ 9-0 „

— 19.0 „

, 33-5 ,

— 24.6 „

„ I O.6 „

- 22.5 „

n 34-3,

45

- 7-9 ,,

, 5i-3 .

4- 8.0 „

- 4-- .

„ 48.8 „

-'9-2 „

,, 27.8 „

- '4-5 »

» 40.3 -,

52.5

+ 4-7,,

» 57-3 „

4- 8.0,,

+ 3-2 »

,, 5O.O „

— 'oo „

» 37-o „

- 3-o,,

n 48.0 „

21 O

- 7-9 ,,

„ 64.2 „

-(- 6.0 „

— ao.6 „

, 55-8 „

-38.4 „

,, 20.5 „

- 9-o „

, 59-3 .

7-5

- 38.7 .

„ 7O.O „

4- 3-0,,

-3--7 ,.

„ 58.8 „

—41.0 „

,. 22. 0 ,.

- 32-5 »

-, 57-o „

15

— 20.5 „

„ Si.8 „

•+• 3-° »

-18.1 „

, 49-2 „

-28.8 „

„ 26.2 „

- 25.0 .

» 48.7.

30

— 13-0 „

„ 27.4 „

4- 1 .0 „

- 10.8 „

. 27.5 ,r

- -9-2 „

„ 20.8 „

--3S-,

,, 30.5 .

22 0

— 12. 1 „

. 21.3 „

0

-10.5 „

. 21.3 „

-12.8 „

,, -7-2 „

- 12.5 „

» 24.3 „

3°

- '4-4 »

„ 12.8 „

0

— 1 1 .4 „

. 14-2 ,

-12.8 „

, 9-8 ,

— I 2.O H

. n-s »

23 o

- 14-' ,.

,, 7-3 .,

o

- 9-5 .

. 9-7 ,

- 9-6 „

» -0.3 .

- 10-5 „

» 12.2 „

45

+ 13-5 .

,, -7-7 »

0

+ 13-0 ,

. 15-3 »

o

« n-o »

-^ 7-5 ,

„ 16.8,

24 o

+ 9-3,,

a 13-4 -,

0

4- 8.5 „

„ 8.9 .

o

„ ia-7 »

- 7-5 ,

n 12.2 „

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903.

258

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

TABLE XXXIX (continued).

Gr. M. T.

Tiflis

Dehra Dun

Bombay

Pk

Pi.

ft

ft

Pd

Pk

Pd

P,

h m

12 50

0

W 4-8 /

0

O

E 4-5 V

o

O

o

17 o

+ iS-o 7

» 3-7 ,,

— 2.6 }'

+ 15-8 /

„ 3-° ,i

+ 11. 2 y

o

0

18 o

~*~ 8.4 „

E 24.1 „

o

+ 20.0 „

„ 13-8 „

+15-8 „

E 8.4 y

o

3°

- 25.7 „

„ 18.5 „

+ 9.4 ,

— 25.6 „

,, 24.6 „

-14-3 I,

ii 9-6 „

+ 8.0 }•

34

— 36.0 ,

I, 20-5 ,

-4-12.2 „

- 39-° ..

ii 22.5 „

-25-7 I,

„ 8.5 „

+ 8.0 „

19 o

— 14-6 »

,, "-I ii

+ 2.6 „

- 13-8 „

„ 1 1.8 „

-13.8 „

„ 7-8 „

o

3°

- 14-8 „

„ 12.6 „

-4- 2.6 „

- 16.5 „

,, 9-9 „

-14-3 I,

„ 6.1 „

0

20 o

- 5-6,

,, 17-4 n

0

— 7-8 „

„ 6.9 „

- 9-2 „

„ 4-8 „

0

3°

- 10.7 ,,

„ 28.5 ,.

+ 1-3 ,i

- 9-1 ,i

,, 12.8 „

— 9-2 i,

„ 8.4 ,

0

45

o

„ 26.0 „

- i-3 »

+ 2.4 „

» 4-9 ,,

- 4-1 ii

ii 1-2 „

- 4-8 „

52-5

4- I I.O „

» 25-0 „

- 5-i .

+ 12.6 „

ii r -° »

+ 3-6 „

0

- 8.0 „

21 0

+ 7-7,,

„ 37-8 „

- 2-3 .

+ 2.4 „

» 9-9 ,,

+ 8.7 „

ii 9-6 „

+ 6.4 „

7-5

- '3-5 ,,

,, 43-5 ,,

+ 2.8 „

+ 9-5 ,i

» 13-° ,,

- 9-4 ,,

,, 7-4 ,,

+ 2.4 „

15

- i°-9 »

,, 3'-5 ,,

+ 2.8 „

- 8.3 „

„ 1 1.8 „

- 8.2 „

„ 8.4 „

o

3°

- 7-3 ,,

., 13-6 „

0

- 8.7 „

i, 8.9 „

- 6.4 „

„ 6.6 „

o

22 O

- 7-5 „

. I7-I »

o

- 9-5 ,,

.. 9-9 i,

- 5-6 „

„ 6.1 „

0

3°

- 8.8 „

„ I 3.O „

0

- 9-1 »

„ 6-9 i,

- 7-7 ,,

„ 3-6 „

o

23 o

- 8.6,,

„ 8.5 „

0

- 8.3 „

. 5-9 .

- 7-9 „

„ 3.0 „

0

45

+ 4-9 »

ii i-8 „

- 2.3 „

0

o

+ 2.5 „

0

o

24 o

+ 2-4,,

ii i- 1 ii

- 1-6 „

+ 2.8 „

o

+ 2.6 „

0

0

TABLE XXXIX (continued).

Gr. M. T.

Zi-ka-wei

Batavia

Christehurch

Ph

Pd

Ph

Pd

Ph

Pd

Pv

h m

12 50

+ 6.4 y

E 8.9 y

+ ^.Iy

W 6.0 y

4-23.0 y

O

+ 1-5 y

17 o

+ 15-5 ,,

ii IO-9 ii

+ 12. 1 „

E 2.4 .

+ 9.2 „

W 10.4 /

+ i-5 „

18 o

+ 33-1 ,,

» 10.9 „

+ 3°-3 ,,

W 4.8 „

4- 4.6 „

E 7-4,,

0

3°

- '4-° ii

,i '3-4 ,,

~ 13-5 ,,

E 6.0 „

+ 6.9 „

„ 16-3,,

o

34

— 19.1 „

i, 7-4 »

- 21.4 „

ii 6.0 „

+ 3-7 „

„ 13-4 i,

0

19 o

— 14-1 »

n 5-9 »

— IO.7 „

» 2.4 „

- 6.4 „

W 7-4.

+ 2.5 „

3«

-16-5 „

„ 3-5 ,,

— 12.8 „

o

-12.0 „

„ I I . I „

+ 1-9 „

2O 0

-12.8 „

o

— 1 2. 1 „

W 2.4 „

— 18.4 „

ii 3-5 „

+ i-3 I,

3°

" 7-6 „

„ I.O „

- 9-6,,

a 6.0 „

-19-3 ,i

H 2-2 rt

+ i-5 „

45

0

,, 2.Q „

- 1-8 „

„ 9-6 „

— 24.2 „

,, 6.7,,

+ 3-6 „

52.5

+ 7-6 „

W 7.4 „

+ 7-8,,

„ 14-4 ,,

-23.0 „

H 5-4 ii

+ 4-o „

21 O

o

* 3-° ,,

O

„ 8.4 „

-i 8.8 „

E 4.4 „

— I.O „

7-5

— 2.5 „

E 3-5 „

- 8.5,,

n 7-2 „

-17-5 ,,

„ 10.4 „

+ 2.5 „

'5

- 5-1 „

,, i-o ,,

- 7.5 II

„ 6.0 „

-18.8 „

„ 7-4 ,,

+ 3-6 „

3°

- 6.4 „

„ 0.6 „

- 8.9,,

i, 4-8 „

-23-3 ,,

,, °-7 ,,

4 3-3 ,,

22 O

- 7-° „

o

- 9-3 „

,, 3-6 „

-18.4 „

,, o-7 ii

+ 2.O „

3°

- 7-6 „

o

— I2.I „

E 1.2 „

?

?

+ 0.7 „

23 o

— 7.0 „

0

- 13-2 „

ii 3-6 „

?

?

7

45

o

0

- 5-0 „

W 2.4 „

7

?

7

94 o

o

0

- 3-2 „

ii !-2 ,,

?

?

7

PART I. ON MAGNETIC STORMS. CHAP. HI.

259

TABLE XXXIX (continued).

Gr. M. T.

Ekaterinburg

Irkutsk

n

Pd

P,

Pk

I'd

-Pt

b m

17 o

+ 5-° y

o

+ I.O y

+ 17.0 y

E 5.0 y

4- 2.0 y

18 o

+ I.O „

E 6.0 /

+ I.O „

+ i5-o „

» 20.0 „

- 4-° »

3°

- 7-5 .

„ 12.0 „

+ 2.0 „

34

- 9'5 „

» 13-5 „

+ 2.0 „

+ '3-5 „

» 19-0 „

- 5-o „

19 o

-15-0 »

. 20.0 „

+ 3-o »

-4- 12.0 „

» M-5 »

- 4-0 -

3°

— 16.0 „

. 25-0 ,

+ 3-0 „

20 o

— I2.O „

» 28.5 .

+ 2-° »

+ 7-0 .

W 4.5,

- i-o „

3°

- 2.5 „

» 36-0 »

+ 7-5 *

45

+ i-5 .

. 41-0 »

— 14-5 »

52-5

+ 2.7 „

. 43-5 ,.

-16.0 „

SI 0

4- 3.0 „

» 43-5 »

-16.0 „

+ 3-0 »

» 8.0 „

- 4-° .

7-5

+ 2-7 ,

» 43-° ,

-15-5 ,

15

+ i-o „

» 41.0 „

-14-5 „

3°

- 1.5 .

» 32.0 ,

-I2-5 „

22 0

- 5-o .

» M-o .

- 9-0 „

+ 2.O „

E 5-o „

- 4-o ,

3°

- 6.5 „

» 9-o .

- 6.0 „

23 o

— 6-0 „

» 4-° „

- 5-o „

- 9-° ,

W 4-5,

— I.O „

45

- °-5 n

. 5-6 „

- 5-o „

24 o

o

n 7-3 M

- 5-o „

- 8.0 „

3-° „

+ 2.O „

TABLE XXXX.
Partial Perturbing Forces on the nth October, 1902.

Gr. M. T.

Honolulu

Sitka

Baldwin

Toronto

Axeleen

Fh

ft

P'k

Pi

P'h

Pi

/"*

ft

/"*

p-d

h m

12 50

•>

o

- 25-5 '/

W 63.0 y

- 4-2 y

0

?

o

+ 22.9 y

W 26.07

20 45

+ 1.6 y

o

o

E 4-5,

+ 4-4 „

o

+ 4-57

E 3-6y

- 1 79-0 n

E 173.0 „

52.5

+ 3-9 n

0

o

n 13-5 »

+ 9-2 „

E 3.2 y

+ M-4 n

n 3-6 n

- 137-0 n

n M5-0 „

21 O

o

W 4.1 y

- 10.6 „

0

- i7-on

n 2.5 „

- 13-9 *

o

- 238.0 „

n 109.0 „

7-5

- 2.3 „

« 4-1 n

- 6.2 „

W 27.0 „

- 8.8 „

W 5.1,

- 20.2 „

n 4-2 n

- 1 10.0 „

n 97-5 „

15

o

E 2.5 „

O

,, 6.8 „

- i-7 B

o

- o-5 »

n 1-3 n

0

0

23 45

o

0

o

,, 6-8 n

- 6.0 „

E 2.5 „

- 5-4 «

W 1.0 „

- 78.0 „

.. 53-o .

TABLE XXXX (continued).

Gr. M. T.

Cheltenham

Pawlowsk

Stonyhurst

Kew

Val Joyeux

P'k

P"d

P'k

Pi.

P'k

P'd

P'k

/*,*

rt

P'd

h m

12 50

- 5-3 r

o

— i o.i y

O

- 9-2 y

O

- 8.7 7

o

— la.oy

o

20 45

+ 4.4.

0

+ 8.5 „

E 8.3 y

o

E 20.5 7

+ 6.1 „

E 11.77

+ 4-4 n

E 15.1 y

52.5

+ ii.Sn

o

+ 14.1 „

, i6-5.

+ 10.2 „

n 20.0 „

-1- 13-8 „

» '5-o n

+ 12.4 „

n 18.4 „

21 0

o

W 3.07

+ I5.I n

„ 32-2 „

- l°-2 „

n 22.8 „

- 5-i »

„ i6.8B

+ 4-° n

n 2O'1 B

7-5

- '3-5 „

* 1-8,

o

, 36.8 „

- 30.6 „

n 23-4 n

- 21-3 n

n '7-3 »

- "a-0 II

n 20.9 „

15

o

o

o

„ 17.4 „

— 10.2 „

n '3-1 n

- 9-7 »

. I'-Ti,

- 8.0 „

. IS-' .

23 45

- 5-9 „

0

+ I3-S n

o

+ 10.7 „

1, 20.0 „

+ '3-2 n

n iS-o „

+ ia.o „

„ '3-8 „

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

TABLE XXXX (continued).

Gr. M. T.

Potsdam

Wilhelmshaven

San Fernando

Munich

Pk

f'i

/"*

Pi

Pk

1*

Pk

ft

h m

13 50

- 9-57

o

— n. ay

0

?

9

- 8.5 y

o

20 45

+ ia-3»

E 15.2 ;/

+ i3-o n

E 12.8 j-

-1- 5-7 J'

E 15.6 y

-4- 7.0 „

E 9.1 ;/

52-5

+ 19-0 n

n !9-3 n

+ 20.0 „

n 21.3 B

-4- n.2n

B 17-6 „

+ r3-o n

B 16.4 „

21 O

0

l, 25.8 „

+ i°-3 n

n 29.3 n

- 17.2 „

n 3-3 B

+ I0-5i.

n '9-0 „

7-5

- 19.0 „

B 31-4 n

- 22.3 n

n 35-3 B

- 19.2 „

o

- 18.8 „

B 25-i n

IS

- 4-1 B

„ 22.8 „

- 6.5 „

B 21-6 „

- 10-8 „

0

- 9-5 n

n 19-0 „

^3 45

-1- 19.6 „

n "-4 n

+ 21.8 „

„ 17-7 n

4- 6.7 „

B I0-6 n

+ iS-o „

<i 7-5 n

TABLE XXXX (continued).

Gr. M. T.

Tiflis

Dehra Dun

Bombay

Pk

PA

f*v

Pk

Pd

^A

Pi

p»

li m

12 50

- 4.6 r

E 4.8 ,-

o

- 5-9;'

E 4-5 y

- 5-i;'

o

o

20 45

-t- 10.0 „

» 2.6 „

- 0-5 r

+ 7-i „

W 7.8 „

+ 6.6 „

W 8.6 y

- 4-8;-

52-5

-f- 21.4 „

n 4'5 n

- 2.6 „

+ 15-7 n

n 12.8 „

+ J5-3B

n 7-3 n

- 8.0 „

21 O

+ I7-I n

n "-1 n

4- 2.6,,

+ J5-7 n

n 4-9 „

+ 10.2 „

o

f 64 B

7-5

- 2.1 „

n M-8 „

•*• 4-1 n

- 2.4 „

o

- 1.0.

E 1.2 „

+ 2..,,

15

- 2.1 „

n 5-6 n

+ i-3 »

- 0.8 „

o

0

0

+ 1-6 „

23 45

-1- to.8 „

W 2.0 „

- 3.0 »

+ 7-5,

« 3-o B

+ 8.4 „

o

O

TABLE XXXX (continued).

Gr. M. T.

Zi-ka-wei

Batavia

Christchurch

Ph

Pd

Ph

Pi

Ph

Pi

F1.

h m

12 50

+ 3-8 ;<

E 8.9 y

+ 3-6 y

W 6.0 y

+ 23.0 y

o

— o-9;'

20 45

+ 4-5 B

W 2.5 „

4- 6.0 „

B 5-4 B

- 4-4 „

W 7.1 ,-

o

52.5

+ *7-5 „

B 7-4 B

+ 16.0 „

B i°-8 B

- 1-8.

3-7 .

0

21 O

+ 12.8 „

B 4-0 „

4- 8.0 „

0

+ 3-2 „

E 3-7 „

- 5-8 „

7-5

+ 3-8 „

E 3-5 B

- °-7 „

o

+ 6.0.

B 10.8 „

- °-5 .

15

+ i-°»

B 1-0 „

— 0.7 „

o

4- 3-a»

» 5-6,

4- 1.6.

23 45

+ 8-7 B

o

•j

. 3-6 „

?

9

0

For ian 50"! we have nt

Kaafjoi-d: Very slight and indistinct partial deflections.
Matotchkin Schar: Ph = + 43.5 y, Pd = o, Pv = + 17.5 y.
Axel0en: Pt = — 35,0 j>.

PART I. ON MAGNETIC STORMS. CHAP. III. 361

Current-Arrows for the llth October, 1902; Chart I — Partial values - at 12h 50m , and Chart II at 17U Om.

f

r

-

..

•••••

••

W

&><>"
£££

o

:

-

I k w ti km

,

7

IV.

"

1

Fig. 117.

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903.

Current-Arrows for the llth October, 1902; Chart III at 18h Om , and Chart IV at 18h 34m .

PART I. ON MAGNETIC STORMS. CHAP. III. 26o

Current-Arrows for the llth October, 1902; Chart V at 19ii 30m, and Chart VI at 20h 30m.

rool>-

^

?

' /<

V,,

ft-

/

Iv

U

Zkw li 4.-»

©

^

;•

u

'

Fig. 119.

264 HIRKF.LAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

Current-Arrows for the llth October, 1902; Chart VII at 201' 45m, and Chart VIII at 201' 52.5m.

tfooO

v

\

*'• •'

;

•

Kfi Kaa/i»nt

U Ch Mun.-h.-n

•

T*-

^ "*=*

7

!

PART I. ON MAGNETIC STORMS. CHAP. Ill,

265

Current-Arrows for the llth October, 1902; Chart IX at 21h Om, and Chart X at 21h 7.5m.

Fig. 121.

266 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.

Current-Arrows for the llth October, 1902; Chart XI at 21h 15m, and Chart XII at 2lh 30m.

PART I. ON MAGNETIC STORMS. CHAP. III. 267

Current-Arrows for the llth October, 1902; Chart XIII at 22h O1", and Chart XIV at 23h Om.

Fig. 123.

268

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION igO2 — 1903.

Current.Arrows for the llth October, 1902; Chart XV at 23h 45m.

Fig. 124.

CONCERNING THE CAUSE OF THE PERTURBATIONS.
POSITIVE AND NEGATIVE POLAR STORMS.

69. In describing the preceding perturbations, we have discussed more or less fully the various
systems that might be supposed to be the cause of the various fields of perturbation. The results of
these reflections, as regards the polar storms, may be summarised as follows: that on the night-side,
and to some extent also, in very high latitudes, on the day-side (Axeleen), powerful perturbations will
as a rule be formed, with current-arrows directed westwards in the area of precipitation ; and that on the
day-side, only a few degrees farther south, fields of precipitation will often be formed, with eastward-
pointing current-arrows. There is a continual recurrence of conditions such as these, but they are often
indistinct, a fact which may probably be accounted for by the small number of polar stations from which
we have received registerings.

We have already touched upon the question as to how these systems may be supposed to be
formed; and we will therefore here only refer the reader to Article 36, especially pp. 105 and 106, and
fig. 50 a & b. From the experiment represented in fig. 38 b, there is every reason to suppose that
not only the rays that descend on one side of the screen in low latitudes, but also some, at any rate,
of those that descend in the polar zone of the terrella, are rays that curve round somewhat in the
manner shown in fig. 39, in the equatorial plane, for rays answering to values of y between — 0.5 and
— 0.9, and in fig. 50 b. In the experiment shown in fig. 47 b, there is a precipitatation at the top and

PART I. ON MAGNETIC STORMS. CHAP. III. 269

at the bottom of the screen, which undoubtedly turns off in a manner resembling that shown in
fig. 50 a.

The two systems will now produce, in southern latitudes, their respective areas of convergence
and divergence ; it is these areas that are represented on our charts, and which justify us in also drawing
conclusions respecting those parts of the auroral zone in which we have no stations.

These two types of perturbations thus seem to be those which characterise the polar storms; and as
we are constantly meeting with them, we will give them different names. It will perhaps be practical to employ
the same terms as in the equatorial storms. The characteristic difference in the polar regions between the
two types, which instantly strikes the eye, is the direction there shown by /\. We will then designate
those storms which produce in their field of precipitation negative values of PI,, negative polar storms,
and those that produce positive values of PI,, positive polar storms. These names are not chosen with
any regard to the actual rays which we imagine will produce these fields, but only on account of the
effect we find on the earth. On the other hand, however, we also see the agreement between, for in-
stance, the positive polar and equatorial storms by comparing the figures and experiments just mentioned
(figs. 39 for O>JO ~ °-9> anc^ 5° b) 38 b and 68 [i, 4, 7]). In these cases the rays pass the
earth in a westerly direction. A similar agreement exists between the negative polar and equatorial
storms, as will be easily seen from the corresponding figures and terrella-photographs (figs. 39 for
y <C — i and 503, 37 & 47 b). In these last, according to our assumption, the corpuscular current
passes the earth in an easterly direction, in a manner already frequently indicated.

With this circumstance before us, we shall also find that during the present perturbations all the
fields formed can be explained comparatively easily They will, of course, not be polar systems alone
that act. At the outset it is more or less probable that rays will also descend in lower latitudes, and
thus have an effect, that will possibly sometimes obliterate the effects of the polar systems.

As the probable cause of the first-occurring positive equatorial perturbation has been already
sufficiently discussed, we need here only refer the reader to our previous remarks in Article 31.

We will first look then at the first polar storm, represented on Chart I. The time is I2h 50™, not
long, that is to say, after noon Greenwich; and we do actually find on the day-side what appears to be
an area of divergence. We have here endeavoured to distinguish the effects of the polar storm from
those of the equatorial, and the arrow-directions shown on the chart answer only to the former. The
certainty with which the perturbing forces are determined is therefore somewhat diminished. In the
next place there are no observations from Dyrafjord; and they would hav»e been of the greatest impor-
tance here, as that station would probably have been situated not far from the storm-centre, the effects
of which seem traceable in the district to the south of it. The current-arrows at Matotchkin Schar and
Axeleen seem to indicate that this is the effect of a positive polar storm. The very small perturbing
force at Kaafjord may possibly indicate that that station was situated in the vicinity of the point of
divergence; and the positive P, that we find is in accordance with this. It is impossible to say with
any certainty what precipitation there might be on the night-side of the earth. The only northern sta-
tion in this district from which we have observations, is Sitka; and there the conditions of the horizon-
tal intensity also indicate that we are near the field of precipitation of a negative polar storm, as we
find negative values of Pk. There is moreover a comparatively wide deflection in the declination, so
that the current-arrow is not directed north-west along the auroral zone, but almost due north. This
circumstance perhaps indicates that the storm-centre was situated a little to the west of the place. There
is no distinctly-marked area of convergence in southern latitudes, and as the system can only be com-
paratively weak this is natural enough, as we are very badly off for stations in that part of the world.

The second polar storm -- Chart III — exhibits fields, the form and nature of which are of the
greatest interest. A glance at the chart shows us two distinct characteristic areas, an area of conver-

270

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

gence in the east of Europe, Asia and the west of North America, and an area of divergence in the
district from Western Europe to the east of North America. The storm-centre of the negative polar
storm seems to be situated in the north-east of Asia. The arrows at Matotchkin Schar and Axeleen
indicate a continuation of this system. Unfortunately we have no observations for this point of time from
either Dyrafjord or Kaafjord, as the curves in this periode of time, in the case of the latter station, have
disappeared, the points of light from the magnetometers having been too faint to act on the photographic
paper. It is however probable that there have been positive deflections here in the horizontal
intensity curve, judging partly from the course of the curve immediately after, when it is drawn once
more, and partly from the conditions we have previously met with, where the fields have shown them-
selves on the whole almost exactly similar. In any case, circumstances such as these would agree
exactly with the area of divergence found in the district Europe to America, as has already been
pointed out in the preceding description. If we imagine a positive polar system in the district extending
from the regions west of Greenland, across Dyrafjord, towards Kaafjord, we here recognise the form of
field with which we are continnally meeting during the storms that occur at that time of day, namely in
the afternoon, Gr. M. T., only that the positive system sometimes extends a little farther to the east.
In this connection we need only refer the reader to the storms on the gth December, 1902, the i5th
and 8th February, 1903 (see especially p. 191), and the 27th and 315! October, 1902.

In this manner a close agreement with the first polar storm is arrived at. As may be seen, we
have only to assume that the old systems have moved a little westwards and have altered, the positive
storm having become less, and the negative greater, so that the latter is now the more powerful and
greater in extent.

The third or main polar storm is shown on Charts V, VI, XI, XII, XIII and XIV. The form
of the various fields is here the same in all essentials, and bears no small resemblance to the field
during the preceding storm. We still seem to have a similar area of divergence in the same district as
before. On looking at the northern stations, we find that the arrow at Kaafjord has taken a westerly
direction, which would indicate that the positive polar system that is supposed to produce this area of
divergence does not now extend so far east as before, a circumstance which recalls conditions found
during the preceding perturbation of the 3151 October and ist November, 1902. We then found that
the reversal of the direction of Ph occurred earlier at the eastern stations than at the western, as if
the cause of this reversal were in some way or other moving westwards with the sun.

It now seems as though the negative polar system extends as far as Kaafjord; but if we investigate
matters in lower latitudes, we find no distinctly-defined area of convergence. We do indeed find cur-
rent-aiiows in Europe directed southwards as we should expect, and they are of considerable strength,
a fact which may possibly indicate that the two systems are here acting more or less in the same di-
rection. At Honolulu and Sitka, we also find current-arrows such as we should expect to find on the
east side of the area of convergence; but in the intermediate district we find no eastward-directed
current-arrows forming a transition between these two areas. The current-arrows in the south of Asia,
on the other hand, have a westward direction.

It should here be remarked, however, that if the system in the north is not very powerful, the
effect in the extreme south of Asia will be comparatively slight; and if, at the same time, there occur
systems whose greatest effect is at the equator, they will there easily gain the ascendancy and obli-
terate the effects of the polar storm. We should therefore, in order to explain the conditions during this
period in such a manner, have to assume that simultaneously with the negative polar storm there occurred a
storm of a kind similar to the negative equatorial storms that caused the current-arrows in the south of
Asia to point westwards instead of eastwards; and there are actually circumstances that indicate that
this would be the case. In the first place, the character of the horizontal intensity curve at these Asi-

PART I. ON MAGNETIC STORMS. CHAP. III. 27!

atic stations is fairly quiet, with the exception of the districts surrounding the intermediate storms, a
peculiarity which we found to be characteristic of this kind of equatorial storm. In the second place,
the conditions in P, also give a similar indication. A negative equatorial storm in the northern hemi-
sphere will produce vertical arrows directed downwards, while the system that should form the area of
convergence would produce vertical arrows directed upwards.

At first, it is true, positive values of P, are found at Pawlowsk, Ekaterinburg and Tiflis, when
the polar storm is still comparatively slight (see Chart V); but when the latter has developed consider-
able power, we must imagine that the greatest effect of the polar system is in the north. We now
find all the time, moreover, negative values at Pawlowsk and Ekaterinburg (see Charts VI and XI —
XIV); while on Chart VI P, is still positive at Tiflis. This subsequently diminishes at Tiflis too, be-
coming for the most part zero (Charts XII — XIV), and sometimes turning a little round to the opposite
side (Chart XI). At those stations of Western Europe from which we have observations of the vertical
intensity, we find throughout positive values of Pv, though sometimes zero. We may imagine this
circumstance to be partly caused by the positive polar system of precipitation, which produces positive
values of Pe in the area of divergence, but also partly by the assumed negative equatorial storm, which
will here operate in the same direction. One might perhaps be tempted to believe that this last polar
system might possibly produce the positive values of P, at the more eastern stations; but this is not
possible if the systems are at all of the constitution we have supposed. If, for instance, on Chart V,
the vertical arrow at Tiflis were solely due to this positive polar system, the horizontal arrow produced
by this ought at least to be as large as the one really found there. It seems impossible to explain this
circumstance by comparison with the size of the current-arrows in Europe and America ; and as regards
Chart VI it is still more difficult to imagine that this system, which, in all probability, should be considered
as comparatively weaker than the more easterly one, should have a greater effect at Tiflis than the last-
named storm, which is moreover nearer to that station.

There thus seems to be sufficient reason for supposing that this is really a storm that acts most
powerfully at the equator, and is of the nature of the so-called negative equatorial storms.

We hereby also get a comparatively simple explanation of these fields as only the result of a simple
cooperation between the already-described elementary phenomena.

We will in conclusion refer to the remarks that have been made concerning the positive value of
P, at Tiflis, which, in several of the storms described, has occurred in similar areas of convergence,
e. g. in the perturbation of the 26th December, 1902 (Charts I and II, and especially the description
on pp. 137 and 138), and that of the 15th February, 1903 (Charles V and VI, with description on
p. 178). In these earlier cases, we could not come to any definite decision regarding the systems which
produced this apparent abnormal value ; and we only suggested the possibility that these storms resembled
the cyclo-median perturbations. Here, however, it seems more probable that the type resembles the
negative equatorial storms.

The fourth polar storm, or first intermediate storm, is shown on Chart IV. The field here does
not differ essentially from that described under the third polar storm. We can only imagine the altera-
tion to be produced by the fact that the positive polar system, which we supposed existed there, now
undergoes a sudden increase in power and extent, so that it reaches beyond Matotchkin Schar. The
arrow at Irkutsk, moreover, in connection with those at Honolulu and Sitka, indicates, though faintly,
an area of convergence in that district; and the arrow at Axeleen ought probably to be interpreted as
a continuation of this more easterly system. We must here, however, be careful not to draw too
certain conclusions from the conditions at Irkutsk, for we have only hourly observations to go upon.

The fact that these two systems of precipitation work into one another, is one that we have often
observed before, especially in the case of Matotchkin Schar, e.g. in the intermediate storms of the

272 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

February, and the 27th and 3ist October (see the corresponding Plates), where the change, however,
was of an opposite kind, a more easterly negative storm seeming to encroach upon the westerly posi-
tive storm for a time. On the gth December, 1902 (PI. IX), there is an example of still more typical
conditions. At Dyrafjord and Kaafjord the arrows have strongly-marked easterly directions. The pro-
nounced westerly directions at Axeleen are, we are inclined from the above to think, a continuation of
a more easterly-situated negative polar storm. At Matotchkin Schar, on the other hand, we find that
now one storm, now the other, seems to be the stronger, so that the directions of the arrows are
always swinging round from west to east, or from east to west. These conditions, however, can be
better studied in the material from 1882—83, where we have at our disposal observations from a
larger number of polar stations.

This sudden change may be illustrated by imagining the two systems like those in fig. 50 a & b,
moving together until they are lying close to each other, and imagining the rays to the east deflected
as in fig. 50 a, and those to the west as in fig. 50 b. If we imagine a system such as this displaced,
we shall obtain conditions at those places through which the boundary between the two kinds of
polar storms passes, similar to those found at Matotchkin Schar.

The fifth polar storm, or second intermediate storm, shown in Charts VII — X, also exhibits in its
main features the same peculiarities as the long storm. The explanation of the change we here see
should apparently be sought in a suddenly strengthened impulse in the polar system, whereby the
latter, in southern latitudes, acquires a greater effect. This causes the area of convergence here too,
to appear more distinct, the effect of the polar system being for a time greater than that of the equatorial
storm ; and we obtain current-arrows pointing eastwards (see Chart VIII). The area of divergence also
becomes stronger, and it thus appears that in this system too, there should be an impulse at the
same time.

Finally, with regard to the sixth polar, or third intermediate storm (Chart XV), the conditions are
quite analogous. There is -an increased impulse in the polar systems, especially in the negative, an
increase which is only slight, although relatively strong, the perturbing forces now being very small.
The equatorial storm still seems to have an effect which acts in the very opposite direction in the
south of Asia, but in America in the same direction as the polar systems.

In this way we have succeeded in explaining all the above phenomena in a manner that is exactly
analogous to that employed in the preceding perturbations, and based only upon our previously-discovered
simple elementary phenomena.

THE PERTURBATIONS OF THE 23rd & 24th NOVEMBER, 1902.

(PI. VIII).

70. After the powerful storms at the end of October and the beginning of November have ceased,
conditions are fairly quiet, at any rate at the Norwegian stations; and the few perturbations that do
occur are of comparatively small strength. On the igth November, however, quite a powerful pertur-
bation appears rather suddenly. This forms the introduction to a series of powerful perturbations which
develope daily for rather more than a week, the last powerful storm being on the 26th. These storms
reach their maximum of strength between the 23rd and the 25th. The conditions recall those in October,
when there was a similar period of powerful storms.

We remarked then that the position of the moon must have exercised an influence upon the
behaviour of the perturbations, as the maximum occurred just about the time of the new moon. On this
occasion too, we are in a period not far from the new moon; but the maximum does not coincide with
it in time. The most powerful storms occurred, as we have said, between the 23rd and the 25th November ;

PART I. ON MAGNETIC STORMS. CHAP. 111. 273

whereas the new moon was on the 3oth, or at a time when the powerful storms had just ceased.
Although it seems probable that the proximity of the new moon has something to do with the strength
of the storms, other circumstances here seem to be of greater importance. We will not enter more fully
into this question, however, but merely suggest that the time between the two maxima of about twenty-
five days corresponds very nearly to the sun's period of rotation in low heliographic latitudes, a
circumstance that may possibly help to explain this condition. In the case of this series of perturbations
we find, moreover, a very striking harmony with the observations of the occurrence of sun-spots during
the same period.

To represent this series of perturbations, we have selected those occurring during the period from
the afternoon of the 23rd to the morning of the 24th, having copied the magnetograms from J5h on the
23rd to 7h on the 24th (see PI. VIII).

We have observations for this day from all the stations. Unfortunately, however, the horizontal
intensity curve for Matotchkin Schar has not been drawn, so that we have registerings only of the other
two elements. At Dyrafjord, moreover, the registerings are somewhat defective, as they were some of
the first that were made there, and can therefore only be regarded as trial registerings. The deter-
mination of the mean line is therefore a little uncertain; but as the conditions at about i7h, or a little
earlier, judging by the other stations, are more or less normal, the uncertainty is not so great after all ;
and as the deflections, at any rate during the greater part of the period in question, are considerable,
the uncertainty will not seriously affect the current-arrows.

THE DISTRIBUTION OF FORCE.

71. The storms that occur here, as a close examination will show, may be referred to those types
of perturbations with which we have become acquainted in the preceding perturbations. In order to
distinguish them in some measure from one another, we will here, too, divide the perturbations into
three sections,

the ist section from I5h 20™ to about i6h,

the 2nd section from i6h to about 22h, and

the 3rd section from 22h to 7h on the day following.

The first section comprises a slight, brief perturbation that is perceived simultaneously at almost
all the stations from which we have received observations. The effect is strongest at the equatorial
stations in the south of Asia. In low latitudes there are deflections only in H, and Pk is positive every-
where. At the Central European and arctic stations, on the other hand, there are also deflections of
varied extent in the declination curve. This then is a typical positive equatorial storm, as Chart I
for the hour i5h 48m distinctly shows.

There are a few peculiarities in this equatorial perturbation that are worth noticing. The first of
these is the shortness of its duration. Judging from the conditions at the stations in the south of Asia,
it ends at about i6h, and thus lasts only a little more than half an hour. If, on the other hand, we
look at the district Tiflis to Stonyhurst, the storm appears to be going on for another hour and a half,
the perturbing forces there having the peculiarities that characterise these storms; but the conditions, at
any rate, are not so unmixed as to allow of its being on the whole characterised as such.

In the second place, the conditions in America are somewhat peculiar. There is no sudden rise
of the horizontal intensity curve at about I5h 30™ as at the other stations. It is not until somewhat
later that the curve ascends, and its rise is comparatively slow. We may therefore reasonably assume
that here too, other perturbing forces come into play, perhaps polar precipitation of some kind or other,
acting with comparative strength. We have also previously found similar abnormal conditions during

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903. 35

274 RIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

the positive equatorial perturbations in these districts, and we then suggested, that it would probably be
due to polar precipitation in the north of North America (cf. pp. 67 & 128). Here, however, the abnormal
condition is far more marked than in these two earlier storms.

Upon the conclusion of this equatorial perturbation, we enter upon

the second section, from i6h to about 22h.

The perturbing forces appearing here are generally small; but from about i7h 30"" to about 18'' 20™
they are comparatively large, especially in southern latitudes.

The conditions at I7h 40™ are shown on Chart II. If we look at the curves for the Norwegian
stations during this period, we find, as regards the horizontal intensity, that there is a perturbing force
at Axeleen directed southwards, and at Dyrafjord and Kaafjord there are perturbing forces directed
northwards all the time. The declination-curve oscillates at all the stations above and below the mean
line. We have unfortunately no registerings of H from Matotchkin Schar for this perturbation; but from
the other three stations there is sufficient material to enable us to conclude that the field during this
period is the typical one for a post-meridian storm. There are distinct effects of a positive polar storm
at Dyrafjord and Kaafjord, and at Axeleen the effect of a negative storm, which, after what has been
said, we are inclined to suppose extends eastwards on the night-side of the globe. This comes out
clearly on Chart II. In Europe and Asia there is a distinct area of convergence; and in America and
the districts east of it, there seems undoubtedly to be an area of divergence. These conditions agree
well with the results we have already arrived at, regarding the appearance and formation of the systems
at various times of day. As the forces, however, for the later part of this period are small, we have
contented ourselves with this one chart as representative of the period.

The third section from about 22h on the 23rd November, to 7h on the 24th.

At about 22h, the conditions begin to alter considerably. The Norwegian stations have now entered
the night-side of the earth, and accordingly the deflections in H for Kaafjord and Dyrafjord swing round
so that we now get the westward-directed current-arrows that are characteristic of the night-storms. The
change in direction does not take place, however, until about 2ih 30™ at Dyrafjord, and an hour later
— at about 22h 30™ — at Kaafjord. This may seem to be at variance with what we have previously
found to be the case, as for instance in the perturbations of the 3ist October and ist November, 1902,
when we found that the cause of the change appeared to move westwards with the sun. Here, however,
we find the opposite, as the change takes place earlier at the more westerly-situated Dyrafjord than at
Kaafjord.

There are, however, several things to notice in this connection that may aid in a comprehension
of these conditions.

In the first place, on the 315! October, we were considering the stations Matotchkin Schar and
Kaafjord, both of which are situated to the south of the auroral zone; whereas here we have one sta-
tion — Dyrafjord — to the north, and one — Kaafjord — to the south of the zone. It is by no means
improbable that this circumstance is of some importance. It would be natural, indeed, to imagine that
owing to the more northerly situation of Dyrafjord in relation to the magnetic axis, it would be easier
for the system acting at Axeleen to have an influence here than at Kaafjord, which in this respect has
a more southerly situation; and that on this account the positive storm of the preceding section would
be able to act longer at Kaafjord than at Dyrafjord.

In the next place it should be observed that the times considered in the two cases differ very
considerably from one another, a fact which is undoubtedly very important; for if we assume that the
position of the sun in relation to the magnetic axis of the earth is of great importance in deciding the
position of the systems of precipitation, we must also assume that the relative motion of the earth and
the sun will govern the displacement of the systems from time to time.

PART I. ON MAGNETIC STORMS. CHAP. III. 275

There are two circumstances in connection with this relative motion, that must here be considered.
This is easily seen by looking at the conditions at the point of intersection of the magnetic axis with,
for instance, the northern hemisphere. In the first place, the sun's azimuth will increase, in the course
of the day, more or less evenly by 360° in a westerly direction; and in the second place, the height
of the sun above the astronomical horizon of this place during the same period, will vary periodically
with an amplitude of about 23° 20'.

If we now look at these two components of the motion separately, we must in the first place
assume, as regards the change of azimuth, that this by itself will cause the systems to move right round
the earth in a westerly direction in the course of the twenty-four hours.

The alteration of altitude will cause a displacement of the systems in a manner characteristic of
this condition; and it is quite conceivable, that this displacement may sometimes be the reverse of that
due to the variation in azimuth. It is therefore probable at the outset that the displacement of the
systems would be somewhat different at different times of day. When the sun is near the meridian of
the magnetic axis, and the variation in altitude is therefore very slight, it might be supposed that the west-
ward movement of the systems, caused by the variation in azimuth, will most frequently predominate.

At times when the alteration in altitude is comparatively great however, we might possibly expect
to find comparatively greater effects from this second component of the motion; and it would then be
natural that the conditions became rather more complicated. Nor does it appear to be impossible for
the displacement due to the alteration in altitude to be sometimes greater than that due to the variation
in azimuth.

We now find, when we look at these two perturbations, that the time at which we considered
the conditions in this respect on the 313! October, was just about that at which the sun passed the
above-mentioned meridian. There, too, we found a displacement of the systems westwards with the
sun; whereas in this perturbation we are just at a time when the alteration in altitude is very great; and
we find that the conditions are actually now developing somewhat differently.

It might not be out of place here, as an analogy to these conditions, to compare them with those
found by Stormer's calculations. This cannot, of course, be regarded as anything more than an analogy,
at any rate here; for a number of circumstances have been set aside in the calculations, which would
certainly exert no small influence. In this connection we need only look at fig. 76, p. 160, to obtain
a general idea of the conditions.

To every altitude, tp, of the sun above the magnetic equator, there are one or more corresponding
fields of precipitation, whose positions are determined by the corresponding value of <£. If we imagine
the sun to sink, for instance, from </> = io°toi/; = — 10°, we should find a field of precipitation for
the negative rays that would move during this period from about <P = — 37° to — 53°, or eastwards on
the post-meridian side. The next system, which appears on the evening and night-side, will have a
westward motion from about <P = — 157° to -- 121° and thus changes place with almost double
the rapidity. The third system again, will undergo an eastward displacement, from about <P = — 218°
to — 259°, that is to say with a rapidity even greater than that of the preceding one. We thus see that
the displacement, on account of the alteration in the sun's altitude, of the systems of precipitation, con-
sidered from the place mentioned above, is sometimes in one direction, sometimes in the other.

In this case, that is when the sun is sinking as indicated, in the first and third systems of preci-
pitation the two components of the motion will move the systems to opposite sides, and they will thus
counteract one another. The alteration of altitude will moreover have the greatest significance for the
system on the night-side. In the case of the second system, the two components will move the system
in the same direction.

276 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

We see further from the figure, that near those places at which -~ = 0, even a very small
change of altitude will produce comparatively great displacement of the systems. It would perhaps be
interesting to examine a little more closely the velocities of the displacement corresponding to the two
components of the motion; but this would carry us too far. We are only considering these conditions for
the purpose of finding analogies, and not in the hope of finding perfect correspondence in the details.
In conclusion we must also remark that the system with the eastward-directed arrows on the 3ist
October, was of far greater strength than the corresponding system in the present perturbation.

When all these circumstances are taken into consideration — and there might be many others that
also exerted an influence — there is no necessity whatever for supposing that they contradict the results
previously found. Nor is this in reality anything new or unknown; it is only a negative night-system,
which, at the Norwegian stations, appears to move eastwards along the auroral zone, a condition that
we have continually found in earlier perturbations. The storms that occur in this section prove also to
be of the form that is typical of these night-storms with centre at the Norwegian stations.

As in the earlier perturbations, we might also here separate several intermediate storms from one
long main storm; but as in this case in southern latitudes they do not stand out so distinctly from one
another as in the previous perturbations, we have thought it better not to attempt any such decomposi-
tion, as its uncertainty would be too great. At our Norwegian stations we find, almost all the time,
deflections in the horizontal intensity curve, indicating a diminution in H. Two or three times there is
a slight, brief deflection to the opposite side, e. g. at Kaafjord at about 23h 3om, and at Axeleen from
2h to about 2h 2om. Both the declination and the vertical intensity curve for Dyrafjord oscillate above
and below the normal line all the time, while at the other three stations the deflections are nearly uni-
form in direction, with only a few short interruptions where the curve goes over to the other side.
The direction of this long deflection is easterly at all three stations. In V the perturbing force is
directed upwards at Matotchkin Schar and at Kaafjord, and downwards at Axeleen, indicating that the
horizontal part of the current is situated to the north of the first two places, and to the south of
Axeleen, or in a manner exactly similar to that of the preceding storms. Between 23*" and 24'', we
find a brief deflection to the west in the declination-curve for Kaafjord, corresponding to the above-
mentioned brief reversal in the //-curve, but a little earlier. We also find a similar reversal of direc-
tion in the vertical intensity curve for Axeleen, the perturbing force at that time being directed upwards
for a short time.

With regard to the other European stations, we find that the greatest deflections, at any rate
during the greater part of the perturbation, are in the declination-curve. These deflections are in the
same direction at all the stations, namely east, indicating that the current-arrows have a southerly direc-
tion. Between 2h and 4'' however, P/, sometimes prevails over P&. At the same time we notice at
our northern stations a powerful intermediate storm, which, however, has the same direction as the
main storm.

The horizontal intensity curve is very sinnous in form at all the stations, and the deflections are
now positive, now negative. At Pawlowsk, however, they are positive throughout, with the exception
of two or three short, slight deflections to the opposite side. In southern Asia also, comparatively
powerful disturbances are distinctly observable, occurring both in H and in D. The deflections here are
not in one direction all the time, but in different directions at different times. On comparing the curves
with the registerings at the Norwegian stations, we find that the stronger impulses at the latter are also
accompanied by similar impulses at the stations of southern Asia, a circumstance which clearly indicates
that the two are closely connected.

PART I. ON MAGNETIC STORMS. CHAP. III. 377

At Christchurch there are also powerful storms at this time, both in H and in D, lasting far
longer than the period we are now considering.

Finally, in America there are also powerful storms, during which the deflections in H are negative
all the time, whereas in D, while sometimes very powerful, they are more variable as regards the
direction of the perturbing force.

On Charts III — VIII are shown the various fields that appear during the various phases of the
perturbations in this section.

We have already remarked that the perturbation-conditions as a whole are to be understood as a
long, more or less constant, perturbation, going on all the time, accompanied by several intermediate,
short, but powerful storms. The latter will now form fields, which, as a rule will differ to some extent
from those produced by the long storm. The form of the field answering to the long storm will thus
be more or less obliterated during these intermediate storms. In the earlier perturbations, similar long
storms, interrupted by short, intermediate storms, have continnally been found, and their conditions have,
as a rule, been comparatively so simple, that it has been possible to separate the two phenomena.
Here, however, the conditions during the long storm are so disturbed, that it has not been possible to
take out the intermediate perturbing forces, although conclusions as to their behaviour may be drawn
from the form of the curves.

The conditions which we have been led to consider as the typical ones, are, as we have
already said, a combination of negative and positive polar storms, the former occurring prin-
cipally on the night-side, while the latter are characteristic of the day-side, and in latitudes that as a
rule are a little more south than those in which the negative storms attain their greatest strength (see
Art. 69). The position of these systems may of course vary somewhat, according as the conditions
under which the perturbations are formed alter. In addition to these polar precipitations, there have
also been, as we have often seen before, simultaneously-acting storms of types that should be due to
stiffer rays, which acted most powerfully in low latitudes. Rays of this kind do not appear to have had
any specially noticeable influence during this perturbation. We shall find, however, that the conditions
as a whole may be referred to two polar systems of the two types mentioned above; and we shall thus
receive fresh confirmation of the correctness of our former assumptions.

The resemblance between the fields is quite striking, even on a casual glance at the various charts.
The typical form of the field is most clearly seen in the charts in which Ekaterinburg and Irkutsk are
also shown. These charts are only marked for the full hours 23b, 24'' and 21', as has generally
been done when the conditions varied considerably from time to time. They distinctly show an area
of convergence of most characteristic form in the district Europe and Asia, but displaced a little on the
various charts in a direction east and west. We find the same conditions at the other hours in the
case of most of the stations. At the stations of Southern Asia, on the other hand, the conditions are
often rather peculiar, and the perturbing forces sometimes directed the opposite way to that one would
expect to find as the effect of the long polar night-system. The current-arrows, however, are as a
rule very small, and therefore the accuracy with which the directions are determined is considerably
less. Uncertainty in the position of the normal line will exert a considerable influence. Sometimes,
however, the deflections are so great that it cannot be put down to inaccuracy alone; and we are then
obliged to assume that there are other forces asserting themselves. This, for instance, is the case on Chart
VI for oh 50™ on the 24th. In order to explain these, it might be well to see whether here, too, there
were not an equatorial storm such as we have often found before. Although it is not impossible that
a storm such as this may be acting here, there is nothing that decidedly points in that direction. On
the contrary it seems more probable that these deflections are produced by a more or less intermediate
positive polar storm, such that would act in these districts. In the first place, the stations in the

278 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

south of Asia have begun to move into the day-side; and we have repeatedly seen that these systems
are more readily formed there. In the second place, the current-arrows in the east of North America
differ a good deal in direction from the general one. Their main direction is south-east, and they thus
appear to be instrumental in forming the most easterly part of the area of divergence, which we should
therefore expect to find on the day-side of the globe.

Finally, in the third place, the course of the horizontal intensity curve during this period, indicates
quite distinctly at Kaafjord the effects of an intermediate positive polar storm, which, however, are a
little weaker than those of the long negative storm acting simultaneously in that district. A similar
effect seems to be traceable at Sitka, as also at Dyrafjord. It is therefore not improbable that this is
also a similar effect.

In this case, as so often before, Honolulu occupies rather a peculiar position as regards the per-
turbing forces. If, however, we assume that the centre of the positive storm lies comparatively far
south, the conditions at Honolulu might be explained, if it were imagined to be in proximity to the
point of divergence. The more northerly negative storm might then also produce current-arrows directed
eastwards. It may also, and perhaps with more probalility, be imagined that purely local conditions might
exert no little influence.

In addition to the great area of convergence that we have found throughout this section, the
current-arrows in Western Europe and the east of North America indicate an area of divergence in
that district until 2h on the 24th. In accordance with this, we here also find positive values of Pv.

Thus the conditions do not seem to differ essentially from those we find in the second section of
these storms. The systems acting appear to be on the whole the same as before, only altered as regards
their strength and displaced a little. The area of divergence, which at first appeared on the day-side
of the earth, has thus, during this storm, remained for a considerable time, continuing indeed on to the
evening and night side. Charts VI and VII, for the hours ih 20™ and 2h 40™, clearly show, however,
how this area of divergence now rapidly moves westwards, until at 2h 40™ it is in the district of
North America and the east of Asia. In accordance with this, the positive vertical arrows in Europe
disappear, some becoming zero, as at Val Joyeux, some turning round to the opposite side, as at Pola.

The last chart for this period, Chart VIII, shows the conditions as they appear at 6'1 30"* shortly
before the termination of the storm. At Axeleen and Dyrafjord we find about this time increased strength
in the deflections, and simultaneously in southern latitudes corresponding deflections in the magnetic
elements. The forces on the whole are small, and from several stations we have received no observa-
tions; nevertheless there seems to be an area of convergence in the district extending from Europe to
the east of North America, with a point of convergence a little south of Iceland and Greenland. The
arrows, moreover, in the east of North America, together with Honolulu and Zi-ka-wei, possibly indicate
an area of divergence in those districts; but as we have so few stations there, we can draw no certain
conclusions in the matter.

According to this, we again appear to have the effects of the two polar storms as before, only that
the storms have moved considerably westwards.

We have thus, by going through this perturbation in its various phases, succeeded in explaining
all the fields that occur, from the previously-mentioned simple points of view. The conditions here have
been simpler, in so far as there appear to be no particularly marked effects of equatorial systems, but
on the whole only of polar systems. Although we have not, as before, thought it expedient to attempt
a decomposition of the forces that appear, into the separate elementary phenomena, we have been able,
by observation of the fields, to make such a separation. We thus obtain, through the study of this
perturbation, a further support to our theory of the simple elementary laws that govern the apparently
complicated conditions found in the great compound storms.

PART I. ON MAGNETIC STORMS. CHAP. III.

279

TABLE XLI.
The Perturbing Forces on the 23rd & 24th November, 1902.

Gr. M. T.

Honolulu

Sitka

Baldwin

Toronto

Cheltenham

a

Pd

Ph

Pd

Ph

Pd

ft

Pd

Ph

Pd

h m

IS 32

+ 4.0 7

+ 2.1 7

W 8.67

0

E 2.57

o

E 9.1 7

+ 3-7 7

E 3.0 7

48

+ 3-° B

+ 1-7 B

E 1.4 „

+ 6.9 •/

0

+ 6.7/

B 1-8 „

+ 10.3 „

o

16 30

o

- 2.8 „

o

+ 2.8 „

W 6.4 „

?

?

+ 4-7 B

o

17 40

- 3-° n

-15-7 »

W 9-0 „

- 6-0 n

B 3-5 n

7-8 „

W 2.4 „

- 4-8 „

0

18 20

o

-10.6 „

B i8.oB

0

B 3-2 „

o

B 4-8 „

o

o

22 O

+ 18.2 „

-14-9 B

o

+ 4-1 B

n 6-4 n

+ 7-6 B

B '^B

+ 6.5 „

B 2.4 „

3°

+ 12.0 „

No

-48.5 B

E 5-° n

-i 8.0 „

B 17-8 „

- i8.oB

B 25. 3 B

- I9-I B

W 14.8 „

23 o

+ 9-9 „

noticeable

-56-4 n

W 6.8,,

-18.1 „

n 9-5 n

o

B 12-4 B

- 9-4 B

B 17-2 B

deflec-

20

+ 7-9 „

-43-8 „

n 6-3 n

-!5-5 »

n 21.5 „

5-8 „

B 39-8 „

- 18.2 „

- 23-8 „

tions.

24 o

+ 5-2 „

-21. 1 „

r, 7-7 B

-18.6 n

,, I2-7 n

- 17-5 B

B 21.0 „

- 25-0 B

B "-6B

o 50

+ 2.0 „

-14.2 „

E 9.0 „

-'4-5 B

E 3-2 „

3-4 «

E 18.1,

4-4 B

E 8.6 „

1 2O

0

-45-0 B

W 18.2 „

-32.8 „

W38on

— 3°-° n

W3i-4B

- 48.5 B

W 20 8 „

2 0

o

- 1-3 n

B I8.0B

-21.0 „

B 9-5 B

- 20-5 B

B 2.4 „

- 28.0 „

o

40

-1 1.8 „

-46.0 „

B 23-5 n

— 41-5 B

E 63.6 „

- 26.0 „

E 76.0 „

- 28.8 „

E 60.0 „

4 3°

-"•4 »

-n.6 „

n 35-5 n

-23.0 „

n 12-7 B

- 20.0 „

B '9-9 B

-- 28.5 „

B 14.8 „

5 3°

-10.4 „

+ 4-8 „

n 25-0 „

-I8.3 „

n IO-8B

- 13 5n

B a4-0 B

- 22.0 „

n 14-8 „

6 30

— 10.4 „

-28.1 „

E 28.0 „

- 2.1 n

B I2-7 »

- ".2B

B !3-oB

- ".O „

B 8.9 „

TABLE XLI (continued).

Gr. M. T.

Dyrafjord

Axeloen

Matotchkin-Schar

Ph

Pd

iv rt

Ph

Pd

PC

Ph

Pd

Pa

h m

[5 S2

•>

•)

?

— i o.i 7

E 15-37

+ 13-57

W 15.07

+ 13-07

48

•)

?

?

8.3 .

, 8.8 „

+ 28.3.

. 8.0 „

I7-0»

16 30

7

•>

7

— I2.O „

W 51.0,

- 54-o „

» 3-0,

- 20.0 „

17 40

4- 23.0 7

O

79.07

- 72.0 „

E 26.0 „

+ 57-0 »

E 8.0,,

— 6O.O „

18 20

+ 90.0 „

o

I02.O , — IIO.O ,

. 77-o »

+ 71.0 „

o

O

22 O
3°

— ca. 310.0 „
— 170.0 „

W 14.07
M 76.0 „

288.0 „

- 88.0 „

— 225.0 „
— 288.0 „

„ 146.0 „
»>i63.o „

o
+ 309.0,

The
//-curve

W 39.0 „
E 87.0,

168.0,
— 252.0 „

23 o

253-0 .

E 145.0,

— 16.0 „ ';— 149.0 „

„ 36.0 „

+ 420.0 „

is not

„ 480.0 „

->343-o „

20

— 272.0 „

W 23.0 „

+ 8.0 „

-450.0 „

?

- 37-° r,

drawn on

„ 172. o,,

— 1 86.0 „

24 o
o 50

— I 12. 0 „
- 288.0 „

, 36-0 „
„ 46.0 .

+ > 85.0 „

+ 60.0 „

-H7.0 „
— 67.0 „

„ 126.0 „
„ 62.0 „

+540.0 „
+466.0 „

the mag-
netogram.

» 8l-°»
. 59-0 „

— 222. 0 „

— 227.0 „

I 20

— 225.0 „

f, 3O.O „

+ 55-o ,

— 240.0 „

„ 156-0 „

+ 415.0,

„ 92.0 „

278.0 „

2 O

— iSl.O,,

E 53-0,,

+ >«5.o „

- 43-° »

93-0 .

+ 360.0 „

, 63-o „

247.0 „

40

- > 800.0 „

„ 148.0 „

+ > 85.0 „

-608.0 „

„ 150-0 „

+540.0,,

0

336.0 „

4 3°

— 240.0 „

„ 84.0 „

-*- 50.0 „

— 212.0 „

„ 46.0 „

+ 154.0,

„ 4-0 „

- 173-0,

5 3°

80.0 „

, 55-0 .

— 92-0 „

- 61.0 „

49-0 „

+ 154.0,

W 22. 0 „

IOI.O „

6 30

244-0 ,

(> 3'° »
"\<43-o „

+ 18.0 „

- 97-0 »

„ 61.0 „

+ 98.0 „

. 27.0 „

lor.o „

(') The value of ft here somewhat uncertain.

a8o

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

TABLE XLI (continued).

Gr. M. T.

Kaafjord

Pawlowsk

Stonyhurst

Kew

Pft

Pd

P,

Pk

Pd

Pi

Ph

Pd

PA

Pd

h m

15 32

+ 47.0 y

E 11.07

O

+ 15-1 y

E 3-7 7

0

+ 10.2 y

0

-t- 10.2 y

o

48

+ 21.0 „

W 2.0,

0

+ ia.6 „

0

0

+ 7-6 „

0

+ 8.9 „

W 3.37

16 30

+ 5-o »

8.0 „

o

+ 7-5 .

W 2.3 „

0

+ 8.2 „

o

4- 10.2 „

B 1-9 B

17 40

-1- 23.0 „

E 66.0 ,

o

4- 12.1 „

E 34-o „

— 2.2 7

2.0 „

E 11.27

0

E 7-o „

18 20

+ 18.0 „

29.0 „

o

- 6-0 „

» 9-2 n

O

0

W 1.7 „

0

W 1.9 „

22 0

+ 33-o »

„ 48.0 „

— 6.0 Y

4- i.o „

* 15-6 ,

O

+ 1-5 „

E 11.4 „

o

E 9-4 .

3°

- 25.0 „

138.0 „

— 50.0 „

+ 49-3 »

„ 59-0 „

- 14-0 „

- n-r »

„ 70.8 „

- 17-4 »

» 54-° »

23 o

— 455-0 „

ir 442.0 „

+ 6.0 „

+ 5-0,

„ 96.0 „

- 22-4 „

- 28.0 „

* 59-5 „

- 30.5 „

» 59-o „

20

— 172.0 „

W ca. 63.0 „

- 76-0 „

+ 5-8,

„ 55.5 *

- I8.7 „

- 13.8,

. 58.o,

- 17-8,

n 47-2n

24 o

— 272.0 „

E 172.0,

— IOI.O „

+ 24.4 „

, 14-2 „

- 28.4 „

+ 8.2 „

» 71-° »

+ 5-1 B

B 62.8 „

o 50

— 168.0 „

165-0 „

— 104.0,

+ 25.1 „

» 22.0 „

- 37-o „

— '5-3 »

n 32.1 „

- "-4»

B 29-0 „

I 20

— 224.0 „

132-0 „

— IOO.O „

+ 30.9 *

„ 39-0 „

- 40-7 „

- 12.2 „

„ 68.6 „

- ii-7 »

n 65-o „

2 O

-197-0.

» 163.0 „

- 88.0 „

+ 5-o „

20.7 „

- 30-0,

- 13.8,

» 25.7 „

- 17-8,

B 3'-8n

40

- 329-0 „

J54-0 „

— IO2.O „

+ 46-8 „

W 17.9 „

- 43-3 „

+ 23-2 „

» 70.8 „

+ 23-1 „

. 57-o B

4 3°

- 33-o ,

„ 6.0 „

- 8i.oB

4- 9.1 „

„ 6-9 .

- 33-5 »

O

B 25.1 n

- 2.5 „

B 25.7 „

5 30

+ 18.0 „

W 11.0,

- 62.0r

— 2-5 »

„ 13-8 ,

— 23.1 „

4-6 „

» 17-a »

- 8.7 „

B "-7 11

6 30

— 30.0 „

E 22. 0 „

- 50.0 „

?

?

?

+ 4-6 „

W 10.3 „

+ 1-5 B

W 8.9 „

TABLE XLI (continued).

Gr. M. T.

Val Joyeux

Wilhclmshaven

Potsdam

PA

Pd

Pt,

PA

Pd

ft

PA

Pd

Pr

li m

15 32

-1- 8.8 7

E 3-4 7

o

+ 13-6 7

E 8.5 7

0

+ 13-6 7

E 8.6 7

o

48

+ 9.6 „

o

o

4-H.6 „

B 3-o „

o

+ 12.0 „

B J-5 B

o

16 30

+ 8.0 „

o

o

+ H.6 „

B 3-7 B

0

4-II.4 „

B 2.5 „

o

17 40

o

B I2-I „

o

+ 4-7 B

B 2T-5 „

o

+ 5-7 B

B 17-8 „

0

1 8 20

o

O

o

- 3-3 B

O

— 6.0 7

0

O

o

22 0

4- 2.4 „

n 4-2 „

o

- 3-7 B

B 6.1 „

- 5-o „

0

B 7-6 n

-t- 2.1 7

30

- 3-6 „

„ 46.0 „

+ 6.3 7

+ 15-4 B

B 85-8 „

-t 4-o „

420.6 „

B 66.0 „

+ 2.7 „

23 o

-24.8 „

B 53-4 „

+ 10.8 „

-24.2 „

» 73-5 B

0

-15-8 „

B 66.0 „

+ 6.3 „

20

-12.8 „

» 41-4 B

+ 5-4 B

-II.6 „

B 51-3 B

- 4-o „

o

B 47-2 „

+ 2.1 „

24 o

4-12.0 „

B 50.0 „

+ 4-5 B

4-21.0 „

B 51-3 B

- 6-0 „

+23.7 „

B 42.6 „

- 7-2 „

o 50

-H.6 „

B 25-0 „

f 4-0 „

-13-0 „

« 18.4 B

-15-0 „

- 6.3 B

B 24.0 „

- 7-2 „

I 2O

- 6.4 B

B 58.5 „

+ 5-o „

4-18.6 „

B 73-5 B

- 5-5 B

+ I7-I B

B 56.0 „

-12.6 „

2 O

- 8.4 „

B 30-0 „

+ 8.5 „

-II.6 „

B 21-5 B

-10.0 „

-13-6 n

B 21-5 B

- 8.7 „

40

+ 3'-2 „

B 50.0 „

o

+ 63.0 „

B 52-3 „

-10.0 „

-1-55.8 „

B 34-2 „

-23.8 „

4 30

+ 3-6 „

B 23.0 „

o

4-14.4 „

B 22-° n

-M-o „

+ 9-2 „

B 12.2 „

-.8.. „

5 30

- 4-o „

B 14-2 „

o

- 2.1 „

B 9-5 B

-10.0 „

- 6.3 B

0

-13-0 „

6 30

4- ..6 „

W 7-5 B

0

- i-9 B

W20.8 „

- 7-o „

1

'*•"

Wi7.8 „

- 9-7 B

PART i. ON MAGNETIC STORMS. CHAP. in.

281

TABLE XLI (continued).

Gr. M. T.

San Fernando

Munich

Pola

Tiflis

Pi,

Pd

PA

Pd

PH

Pd

P.

P*

Fd

P,

h m

15 33

+ 9-6 7

0

+ 9.8 7

E 3.8 y

+ 10.3 v

E 2.1 7

o

+ H.8 7

E 1.8 7

- 3-8 7

48

+ 13-4 „

o

+ 12.0 „

0

+ II.2 B

0

- i.i 7

+ 13-2 B

o

- 3-8 B

16 30

+ 9-6 „

0

+ 10.0 „

B 2.3 „

+ 7-2 n

o

0

+ 6.3 „

B 5-3 B

- '-4 B

n 40

+ 4.2 „

E 7.5 y

+ 6.0 „

14 I

IS 2

+ 21

+ I5O

18 2

— i I

* i tw
1 8 20

o

a 8

1 •** y
O ^

+ 2. 1

B •**•• B
F2 6

4*1 B

22 O

+ 2-9 B

B 4-9 B

o

B 3-0 „

- 4-7 -

B ^-° n
B 3-8 B

°-5 n
+ 2.8 „

+ 2.1 „

B i^'0 B

B '6.5 „

O

30

- 7.6 „

B '9-7 B

0

B 48.7 B

+ 2.2 „

B 41-0 „

-II.O „

+ 21.4 „

B 32-0 „

- 4-1 B

23 o

— 26.2 „

B 25-4 B

-18.0 „

„ 55-1 B

-15.6 „

B 53-0 „

+ 9-4 B

+ 10.0 „

B 45-6 „

- 1-3 B

20

-16.0 „

B 25.4 B

-1 1.0 „

B 37-3 B

-'3-4 B

B 38.0 „

+ 6.4 B

+ 3-0 „

B 33-4 B

- i-5 B

24 o

4- 1.6 „

B 39-3 B

+ "•5 B

B 34-2 B

+ 9.0 „

B 34'6 „

+ 4-1 „

+ 13-4 B

B 9-3 B

- 3-1 „

o 50

- 7-6 B

B !3-I „

- 7-5 B

B 16.0 „

- 9-4 B

» 23.5 „

- 1.0 „

O

B "-5 B

- 3-6 B

I 2O

-H.8 „

B 32.8 „

+ 2.5 „

1, 46-4 B

"" *** n

B 46.5 B

+ 4-2 B

+ 12.8 „

B 20.2 „

- 6.9 B

2 0

!O.3 M

B T3-I B

-16.0 „

B 16.8 B

-'9-5 B

B 25.0 „

0

-"•5 B

B "-° B

- i-5 B

40

+ 28.1 „

B 36.9 B

+ 37-5 „

B 30.5 „

+ 28.6 „

B 26.4 „

+ 0.8 „

+ 31-0 „

W.3.o „

- 8.9 „

4 3°

o

. '5-6 „

o

B 9-5 B

o

« ! I- 1 n

- 3.2 „

+ 2.3 „

B 9-3 B

- 53 B

5 30

- 5.1 „

B 7-4 B

-!2-5 B

B 3-8 „

- 8.7 „

B 6.6 „

- i-3 B

~ 5'* «

B IO-6 „

- 3-1 B

6 30

+ 6.1 „

o

— 9.0 „

Wi4.4 B

- 3.6 „

W 3-5 „

- 1-3 B

'

B 18.6 „

- 1-5 B

TABLE XLI (continued).

Gr. M. T.

Dehra Dun

Bombay

Zi-ka-wei

Batavia

Christchurch

PA

Pd

PA

Pd

PA

Pd

P.

PA

Pd

PA

Pd

P,

h m

15 32

+ '5-4 7

0

+ 13-0 y

+ 13.1 7

o

+ 11.0 7

0

+ 5-9 7

o

O

48

+ '3-4 B

0

+ 10.8 „

+ IO.I „

E 2.0 7

+ 9-3 B

E 5-4 7

+ 4-6 „

W 1.5 7

+ 0.8 7

16 30

o

E 3-4 Y

+ '-3 B

o

B 5-9 B

0

B 6.6 „

+ 1.8 „

0

o

17 40

+ 17-4 B

B 10.8 „

+ H.8 „

+ "•3 B

B 5-4 B

+ 11.6 B

B 9-0 „

- 4-6 „

En.a „

0

18 20

+ 3-1 B

B I0-8 B

+ i-5 B

7-^ B

B H-9 B

c
o

+ 5-0 „

B 6.6 „

+ 2.3 B

B 12.0 „

o

22 O

+ 1.2 „

B H-8 B

+ 1'5 B

6

0

B 3-0 B

V

- 1.8 „

» !5-6 B

- 8.7 „

B J!-2 „

f 3-4 B

3°

+ '4-2 „

B 13-8 B

+ 11.2 „

1

o

W 1.0 „

u

•o

+ 1-4 B

B I2.O „

- 9-2 B

B I3-0 B

+ 1-5 B

23 o

+ 10.8 „

B "-3 B

+ 7-2 B

ft

+ 6.5 B

B 7-9 B

«

-r 6.2 „

B 12° B

-I8.3 B

B '9-5 B

+ 1-5 B

20

- 1-8 „

B "-3 It

3

1.2 „

B 9-9 „

1

- 0-7 B

B 10.8 „

-"•9 B

B 21.7 „

+ 1.8 „

24 o

- i-o B

0

+ 3-6 „

<J
O

- 3-o „

B I2'9 B

1

0

0

- 2.7 B

B 28.5 „

' r-2 n

o 50

-12.6 „

0

5-1 n

K

-"•9 B

B 6.9 „

o

?

?

+ 14.0 „

B l8-° B

+ 1-4 B

I 2O

+ 5-7 B

o

j + 4-1 71

o

B I'° B

z

?

?

+ "•4 B

B '9-5 n

+ Z'5 B

2 0

-,,.8 „

W 7-4 B

-10.8 „

- 5-9 B

B 3-0 „

?

?

+17.8 „

B I2.O „

+ 0.9 B

4°

+ 9-8 „

B 29-5 B

~*~ 4-1 «

- 7-1 B

B '7-8 „

?

?

-16.0 „

B 8.2 „

+ 0.6 „

4 3°

- 2.8 „

B 4-9 B

+ 3-8 B

- 2.4 „

E 6.4 „

?

1

- 8.2 „

B 3-8 „

o

5 30

? 0

1

o

B 9-4 B

?

1

-i 7-8 B

O

o

6 30

? 0 ?

- 9-5 B

B '"5 B

7

?

-18.3 „

W 9.0 B

o

TABLE XLI (continued).

Ekaterinburg

Irkutsk

Gr. M. T.

PA

Pd

P"

P*

Pd

P,

h m

22 O

+ 29.0 y

W 5.0 y

- 8.0 y

+ 4-0 7

E 5-8 7

— 2.0 y

23 o

+ 32.0 „

B '5-0 B

-'3-0 B

-t-33-o „

W 3-5 B

- 6.0 „

24 o

+ 36.0 „

B 25-5 B

-19.0 „

+ 21.0 „

B 20.3 „

- 6.0 „

2 0

+ II.O „

B 8-9 B

-'5-0 B

- S-o „

B 9-9 B

- 7.0 „

Birkeland. The Norwegian Aurora Polaris Expedition, 1903—1903.

282 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Current-Arrows for the 23rd November, 1902; Chart I at 15h 48m , and Chart II at 17h 4Om .

\

<(i

$J

'

,

' S

/l"'

T:-. .
^^s_^.

"

CWh

Ql Ch Olnilftiureh

Dh D Artra Dun

SA.

Ktw A>»

v eh

Pwik

POU 'Un

Ptsd Ate

PART I. ON MAGNETIC STORMS. CHAP. 111. 283

Current-Arrows for the 23rd November, 1902; Chart III at 22h 30"', and Chart IV at 23h .

Fig. 126.

284 B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Current-Arrows for the 23rd and 24th November, 1902; Chart V at 23h 20m and 24h on the 23rd,
and Chart VI at Oh 50m and lh 20m on the 24th.

PART I. ON MAGNETIC STORMS. CHAP. III.

Current-Arrows for the 24th November, 1902; Chart VII at 2h and 2U 40'", and Chart VIII at 6h 30"

Fig. 128.

286 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

THE PERTURBATIONS OF THE 26th & 27th JANUARY, 1903.

(PL XV).

72. After the conclusion of the characteristic equatorial perturbation at 14'' 20™ on the 26th
January (Art. 27), the conditions are comparatively quiet until about i8h. At that hour they begin to be
disturbed, especially in the north; and at about I9h they assume the character of a powerful storm.
From now on, powerful storms alternate with calmer periods, the most powerful being at about 23h;
and it is not until late in the morning of the 2yth that comparative calm once more ensues.

While this is going on, there are powerful storms in low latitudes, both in the eastern and in the
western hemisphere. We may at once mention, as a characteristic circumstance, that the deflections in
the curves both in the western hemisphere and in Europe remain fairly uniform in direction throughout,
notwithstanding the length of the storm. The strength of the perturbation diminishes greatly on the
whole towards the equator. When we come as far south as Christchurch, it is very slight during the
period up to 22** on the 26th January. It subsequently becomes somewhat more powerful, though not
more so than, for instance, at Dehra Dun.

(a) Concerning the Occurrence of the Storm at the Norwegian Stations.

The curves for Dyrafjord are indistinct, to some extent, indeed, altogether invisible. There is,
however, sufficient to show that the storms have been violent. The declinometer especially has oscillated
violently. From the vertical intensity curve, which is reproduced the best, we obtain an impression of
two storms. The first of these commences at i8h 35m, and lasts until about 21 h om. P, is powerful
here, and directed upwards. The second storm, which is of much longer duration and greater strength,
reaches its maximum at about midnight. During this storm Pv is directed downwards.

From Kaafjord we have registerings only for the first part, up to 23^ om. Here too, a relatively
independent perturbation is observable, which is particularly powerful in V, where a maximum is reached
at I9h 45m. Subsequently the storm increases, and is very powerful at about 22h 30™, after which time
it once more diminishes.

At Axeleen, very disturbed conditions commence at about i6h 35™, and from that time storms
continue until far on in the morning of the day following. The two storms already mentioned are very
distinct here, and very powerful. The first is particularly powerful in H, where it begins and ends very
suddenly at ig*1 iom and 2oh 32™ respectively. This is followed by an interval of comparatively quiet
conditions. The second powerful storm, which is so powerful in H that the curve runs off the paper
— a thing which at this station very rarely happens— commences very suddenly at 22h 24m. In D it
begins earlier and more gradually. It is very violent between 22h 30™ and 23'' 30™. The storm
decreases until midnight, when another powerful storm commences, reaching a maximum at about oh 35™
on the 27th.

The first storm, as we see from the curves, occurs almost simultaneously at the above three stations.
As regards the second storm there is a remarkable circumstance, in that it appears earlier at Kaafjord
than at Axeleen. At 22h its strength at Kaafjord is considerable, while at Axeleen, at the same hour,
it is comparatively slight. There is a movement of the storm from Kaafjord to Axeleen; and from this
too we may conclude that the cause of the storm must come comparatively near to the earth in that
region.

The first part of the perturbation at Matotchkin Schar— up to i9h 45°°— is wanting. Even by that
time it is exceedingly violent. It then diminishes for some time, and reaches a distinct minimum at
2ih 6m, whereupon it once more suddenly increases, and maintains a considerable strength until 2h. It is
particularly violent in the horizontal intensity. The light from the principal reflector passes, as is usual in

PART I. ON MAGNETIC STORMS. CHAP. III. 287

the greater storms, out of the field, and at the same time that from the other reflector enters; but the
latter also passes out of the field at 2ih 39™, and does not return until 23h 25™. The storm is then
losing strength, and at 23h 54™ reaches a distinct minimum, after which it once more increases, and the
light from the second reflector again passes repeatedly out of the field of observation. At o1' 46™ it returns
finally, and from that time the storm abates rapidly.

This perturbation, as we see, developes into one long storm, though with indications of the three
maxima that were so conspicuous at Axeleen.

(b) A General Characterisation oj the Conditions in Southern Latitudes.

As in most of the preceding compound storms there here appears to be a long perturbation in
Europe, lasting from about i8h om on the 26th January to 7h om on the 27th. During this long storm,
there occur some powerful intermediate storms, with a distribution of force differing from that produced
by the long storm. We have here three of these sharply-defined intermediate storms; and they coincide
on the whole in time with the three previously-described powerful storms at Axeleen.

The conditions at Pawlowsk are to some extent different. The //-curve there on the whole shows
very little disturbance, there being powerful, well-defined perturbations only during the three intermediate
storms. In D, on the 'other hand, there are powerful perturbations from i8h I5m until the morning
of the day following. The conditions in the vertical intensity are especially interesting. The curve shows
a deflection of long duration and uniform direction, answering to a perturbing force directed upwards.

Tiflis forms the transition from the conditions in Europe to those in the south and east of Asia,
and these in their turn to the conditions at Batavia.

There is on the one hand a great resemblance between Tiflis and the district Kew to Pola; there
is the same maximum, and the course of the perturbation is on the whole the same, the only difference
being that the field is turned so that the conditions in the declination most resemble the //-curve at Tiflis.
But on the other hand, the //-curve at Tiflis shows so great a resemblance to that at Dehra Dun, for
instance, that it might almost be supposed that they were taken at the same place with apparatuses that
differed a little in sensibility.

At Dehra Dun, Bombay and to some extent Tiflis, the horizontal intensity has on the whole a value
that is below the normal. On the morning of the 27th, the normal line runs for a long distance almost
parallel with the curve, and does not join it until about noon on that day.

The two last maxima are fairly distinct as far south as Christchurch, one at about 23** om, the
other at oh 38"°. These maxima, however, are not nearly so pronounced as they are farther north ; the
perturbation-conditions remain more constant.

The perturbations in the western hemisphere are on the whole weaker than in the eastern, especi-
ally during the first part. The first maximum, which at Axeleen assumed the character of a brief,
powerful, well-defined storm, is distinctly noticeable though not very powerful, at Sitka; while at the
other stations it is almost imperceptible.

From 22h I5m on the 26th, right on to 8h on the 27th, there is unrest. We here have the same
two maxima as in the eastern hemisphere, namely, at about 22h 55™ and at oh 30™.

There thus occurs in southern latitudes a long perturbation in H, with a perturbing force directed
southwards; and to some extent the deviations in the curves are occurring simultaneously with those at
the polar stations.

On glancing at the curves, we notice a no slight resemblance between those for Sitka and those
for Christchurch. It is true that the perturbations at Sitka are much more powerful, but the course
has nevertheless a great resemblance, especially noticeable in the last maximum, at about o'1 35™. This
is a resemblance not infrequently observed.

288 BIRKELAND. THF NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

At Honolulu the conditions resemble those at Dehra Dun, the horizontal intensity remaining below
the normal until far into the morning of the 2yth. We cannot say when it became normal, as we have-
no magnetogram for the 24-hours following. It appears that the position of the curve at the conclusion
of the magnetogram received is a little too low, and the normal line is therefore here put a trifle low.

THE FIELD OF FORCE.

73. The perturbation-conditions, as already mentioned, appear to some extent to be those of a
long storm interrupted by powerful intermediate storms.

The decomposition of these phenomena, however, is somewhat difficult of accomplishment; and \\v
have therefore, as in the case of the preceding perturbation, calculated only the total perturbing force.
We then obtain at each place only the aggregate effect of all the simultaneously-acting forces; and it is
therefore probable that the characteristic peculiarities of the polar fields will be most apparent at the
times when the polar storms are most powerful, unless the other systems, equatorial or otherwise, that
might be supposed to be acting, were at the same time correspondingly increased.

If we look at the various fields that occur, we find an exact resemblance to the fields in those
perturbations that occurred about midnight Gr. M. T. All the systems exhibit the peculiar fields that
characterise the polar storms, namely an area of convergence and an area of divergence. The first of
these comes out clearly on all the charts. Its position varies indeed, but only slightly ; and it remains,
throughout the series of charts, in the district Europe and Asia. This indicates that the negative system
of precipitation extends very far in a direction east and west along the auroral zone on the night-side
of the globe, a circumstance that we have frequently met with in previous storms.

The area of divergence is often very faint and indistinct, for instance in the first three charts, in
which the current-arrows in America are very small. In Europe, however, at these hours, there is a
more or less distinct indication of its existence. In Chart II, for instance, the current-arrows in the
west of Europe seem to be turning westwards, while those at the eastern stations turn in the opposite
direction. In the subsequent charts, the perturbing forces in America attain to considerable dimensions,
and the area of divergence also comes out distinctly there.

The arrow at Sitka, which throughout is directed westwards along the auroral zone, seems to
indicate that the influence of the polar precipitation which produces the negative polar storm in Europe
and Asia, also has some effect at that place. It might indeed be imagined that the positive storm also
would predominate at Sitka, so that the current-arrow there would belong to the area of divergence ; but
this does not seem very probable, as in that case the positive field of precipitation would need to have
a disproportionately high northerly position.

With regard to the vertical intensity we find that there are exceedingly distinct negative values of
P, in the area of convergence, especially at Pawlowsk and Ekaterinburg, near which the point of
convergence, or rather the neutral district, appears to lie. This district, according to the charts,
seems to be situated in the north-east of Europe or the north-west of Asia. Here the vertical arrows
are comparatively powerful all the time, while the horizontal component of the perturbing force is often
exceedingly small, a condition of affairs that we should expect to find in the vicinity of the point of
convergence. As, therefore, this is very clearly shown by the vertical intensity curve for Ekaterinburg,
we have placed on the charts current-arrows for the hours 22h and 23h, as well as for intermediate
times, although the values interpolated between the entire hours will often be very uncertain, especially
when the perturbing force is small. A similar course has been followed with respect to Irkutsk; for the
field, as already mentioned, does not appear to vary much as time passes, and the uncertainty of the
interpolated values is therefore smaller.

PART I. ON MAGNETIC STORMS. CHAP. III.

289

In the area of divergence, at the time when it is rather well developed in Europe, there are also
positive values of I\ at the western stations. This appears on Chart II both at Potsdam, Pola and
Tiflis. It may however be a little doubtful whether it is the positive polar storm that produces these
values at the last-named station; it is perhaps more probable that they are brought about by a storm
that was caused by perturbations of a more equatorial nature. That this was the case seems probable,
moreover, from the conditions at the other stations of Southern Asia, which also appear to run a slightly
abnormal course. There, however, the perturbing forces are so small that nothing certain can be said.
At Pola, the positive deflections in the vertical intensity curve continue until nearly 23**, when they go
over to the opposite side.

On Chart IX, the conditions at Dehra Dun and Bombay seem once more to be a little abnormal ;
and a study of the curves for the succeeding period will show that the perturbing forces there continue
to act far on into the 27th. These forces, as we have said, occur principally in H, which they serve
to diminish. We have also already remarked that before the end of the period we find at Honolulu
an abnormally low horizontal intensity curve, which thus seems to agree with the conditions at the
stations in Southern Asia. The character of the curve is comparatively quiet, and it is therefore pos-
sible that this is the effect of a storm of a more equatorial nature, perhaps a negative equatorial storm.

If we now in conclusion compare the perturbation-fields that have appeared during this perturbation
with those that we have found in the preceding storms, we at once notice the great resemblance. The
storms here described occurred, as we have seen, about Greenwich midnight; and we found the characteristic
large area of convergence on the night-side in Europe and Asia. There also appeared more or less certain
indications of an area of divergence upon the day-side. And these are the very conditions that we have
continually met with before.

We therefore feel justified, after having gone through this long series of perturbations, in concluding
that the phenomena that we have previously described as elementary, viz. the positive and negative polar,
the positive and negative equatorial, and the cyclo-median perturbations, generally are sufficient to explain
the fields that will be formed during the most varied magnetic storms. All the fields that we have met
with thereby receive a very simple explanation, and no serious disagreement has presented itself, although,
of course, the material has very often been insufficient to allow of certain conclusions being drawn.

TABLE XLII.
The Perturbing Forces on the 26th & 2?th January, 1903.

Gr. M. T.

Honolulu

Sitka

Baldwin

Toronto

Pk

Pd

ft

Pd

Pk

Pd

Pk

Pd

It in

19 30

o

o

-14-7 y

W 7.2 y

- a-5 y

W 6.4 •/

- 4-5 7

E 2.4 y

20 o

+ 2. i y

o

-17-7 n

n '7-6 »

- 7-' n

n '1-4 n

- 6.7 „

W ..8 „

30

+ 5-2 *

o

- 8.9 „

. 24-3 r,

- 2-1 n

n 14-0 „

- 5-4 ,,

r 6.0 .

22 0

- 3-6 „

o

-H-5 „

0

0

n 8-3 ,,

-10.4 .

E 5-4 »

3°

- 9-i „

W 5.0 y

-33-8 „

„ 1-8 „

-24.1 „

. 6-4 *

-3°-6 „

W 6.0 „

23 o

-'7-9 „

„ 5-8 *

— 64.1 „

>, "-3 n

?

?

-58.4 „

E 18.1 „

3°

-'3-8 „

* 5-o „

-46.0 „

„ '8.0 „

-21.2 „

* 3-8 „

-35-0 „

n 6.0 „

24 o

-12.0 „

0

-26.6 „

n 4-5 n

-12.0 „

E 3-2 „

— 28.0 „

* 3-° n

o 22.5

-II. 2 „

o

-28.8 „

n 4-5 *

— '5-9 n

o

-36-9 „

W 3.0 „

30

-19-2 n

n 1-7 *

-35-4 „

„ 18.0 „

-35-4 n

Wi5.9 „

-52.5 ,

r, '6.9 n

45

-34-7 n

o

-26.6 „

» 9-9 n

-36-1 n

n '4-0 i,

-46.4 n

•• '6.9 „

i 30

-25-2 „

o

1

?

-24-8 „

0

-28.0 „

E 20.4 „

Hirkclancl. The Norwegian Aurora Polaris Expedition, 1903 — 1903.

290

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

TABLE XLII (continued).

Gr. M. T.

Dyrafjord

Axeleen

Matotchkin Schar

Pk

Pd

p,

Ph

Pd

P,

Pk

Pd

P,

b m

19 30

+ 25-47

E 41.67

— 178.0 y

-253-oy

E 46.3 y

4- 324.07

9

?

•)

20 0

*3

W i8.in

-no.o,,

- 198.0 „

B 46.2 „

•+• 344-°,,

323.0 7

E 220.0 •/

-173.07

3°

+ 58.8B

O

- 7'-°«

- 22.5 „

W 6.8 „

+ 334.0,,

264.0 „

» M5-0 „

— 162.0 .,

aa o

-141.0,,

„ i8.on

0

+ »5-3 B

E 22.3 „

+ 300.0,,

->4o8.o „

„ JOO.O „

+ 47-6,

3°

Curve almost

Curve diffi-

ca. — 281.0 „

n 102.0 n

+ 643.0 .

->4o8.o „

„ 205.0 „

A violent

23 o

invisible.

cult to dis-
tinguish from

Rather

ca. -519.0 „

„ > 166.0 „

+ 648.0,,

->4o8.o „

„ 199-0 »

positive

3°
24 o

The points
that can be

the K-curve.
There are
however

large posi-
tive de-

-347-0 B
- 9i-5 »

„ ca. iaa.0 „

1 38-0 „

+ 700.0 „
-*- 635.0,,

— 402.0 „
->4o8.o „

„ 357-°,,
„ 279-0 .

deflection
of about

o 22.5
3°

seen indicate
a negative
deflection of

principally
easterly de-
flections

flections.

— 232-° B
-366-0,,

„ ca. ni.on
„ > 166.0 „

+ 755-0 „
+ 702.0 »

->4o8.on
355-0 „

„ 3I5-0-
„ I 82.0 „

440 /',
after which
the curve

-15

considerable

somewhat

-3I5-0 r,

B 129-0 „

+ 598.0,,

->4o8.or

„ 208.0 „

dis-

I 30

extent.

greater than

-1870,,

n '63.0 „

+ 547-0 „

105.0 „

„ 93-0 „

appears.

ding ones.

TABLE XLII (continued).

Gr. M. T.

Kaafjord

Pawlowsk

Stonyhurst

Kew

Pk

Pd

P,

Ph

Pd

P,

Pk

Pd

Pk

Pd

h m

19 30

- 72.37

E 14.77

— 2O2.O 7

+ 23.1 7

E 16.87

3-77

+ 5-17

E 41.77

+ 4.1 7

E 37-47

20 o

- 95-o „

n 72-0 „

- '3-7 B

?

?

?

9-2,,

„ 34-9 »

- ii-2,,

» 33-7 .

30

- 69.9 „

B 63.8 „

-i 29-0 „

— 10.6 ,,

a 35-0 „

7-5 ,

- 15-8,,

.. '4-3 »

- 17.8,

* l6-4 r,

22 0

- 368.0 „

B 41-5 B

4-7 „

o

„ 27.6 „

- 16.5,

— 12.2 „

» 46-3 „

- r5-3B

„ 38.3 „

30

-577-0,,

B 66.0 „

-253-0 „

+ 52.8,,

» 22.1 „

- 36.7 B

- '7-8 B

,1 I07-o,

+ 10.2 „

, 82.7 „

23 o

-276.0 „

„ 104.0 „

?

+ 28.7,,

„ 27.6 „

- 46.4 *

+ M-8,,

„ I OO.O „

•*- J5-3 B

B 98.2 „

3°

+ 7-5,

* 57-5 „

- 486,,

- 27-5 B

„ 81.1 „

- !9-4 B

B 72.5 B

24 o
o 22.5

Curves disappeared.

o

+ 3O. I „

„ 36.8 „
» I0-6 »

- 44-8 „
- 42-6 „

- i8.8B
+ 20.4 „

„ 57-r ,
,, 79-9 »

— IS-2 B
+ '5-3 B

B 56.2 „
B 60.9 „

30

+ 24.1 „

» 27.6 „

- 48.6 „

+ 1 1.2,,

„ 97-i ,,

+ 10.2 „

„ 84.8,,

45

7-5,,

» 33-1 „

- 50-1 „

- 24.0 „

„ 70.8 „

- 20.4 B

B 73-o „

i 30

+ 7.8,,

- 22.5 „

- 40-3 B

„ 29.7 „

- 17-8,,

B 56.2 „

TABLE XLII (continued).

Gr. M. T.

Val Joyeux

Wilhelmshaven

Potsdam

Pk

Pd

P,

Ph

Pd

p.

Pk

Pd

P,

li m

19 30

0

E 37.67

From i ou to

+ 23-3 7

E 47.07

+ 7-0 7

+ 20.5 7

E 30.57

- 1.27

20 o

- 6.47

B 34-3 B

i h there ap-
pears to be a

- 5-1 n

B 38.5 B

0

- 9-2 „

B 30.5 B

-15-8,,

3°

- 18.0 „

B 2°-9 B

negative de-

- 22.8 „

B 18.3 »

0

- 20-5 B

B 17-2 „

-1- 2.7 „

flection with

22 O

- i6°B

B 41-0 „

maximum at

- 4-2 „

B 42-2 B

o

- 7-3 B

B 31-0 „

- '-5 B

30

-1- 13-6 „

B 87.8 „

about I2^h

+ 42.0 „

B 90-5 B

o

+ 46.1 „

B 65.0 „

- 10.8 „

23 o

+ 20.0 „

B 86.2 „

of —ii 7; but
it is not easy

+ 39-7 B

B 80.2 „

- 7-° B

+ 34-1 „

B 59-4 B

-i*8«

30

- 12-8 „

B 71-0 B

to determine

- I3-I B

B 7I-°»

- 19-0 „

- 9-5 B

B 56.4 B

- 12.0 „

from the

24 o

— 12-0 „

B 58.4B

magnetogram

- !5-4 B

B 43-4 B

- !5-on

- H-7B

B 34-5 B

- 13-2 „

o 22.5

+ 16.8 „

B 51-0 „

whether the

+ 28.0 „

B 43-4 B

- 20.0 „

+ 29.0 „

B 25.4 „

- 21.0 „

30

+ 18.4 »

B 72-8 „

curve has too
great a value

+ 33-8 B

B 69.I „

- i8.on

+ 28.4 „

B 49-7 n

~ 22.5 „

45

- 16.8 „

B 62.7 „

before, or too

- I2.I „

B 52-0 „

- SO-0 B

~ 17-4 B

B 35-5,

- IS-" B

small a value

i 30

- 4-8 „

B 49-3 B

after.

- 3-3 B

B 45-2 „

- '9 °B

- 5-4 n

B 33-5 B

- 15-0 „

PART I. ON MAGNETIC STORMS. CHAP. III.

291

TABLE XLII (continued).

Gr. M. T.

San Fernando

Munich

Pola

Ph

Pd

Ph

Pd

P.

Ph

Pd

P,

h MI

19 3°

4- 3.0 •/

E 24.67

+ 8.07

E 29.77

o

-4- 7.17

E 34.37

+ 4.2 7

20 o

- 8.9 „

» '4-8 „

- 5-o „

n 3°-5 n

- o-97

- 2.7 „

„ 29.8,

+ 3-o »

3°

- 18.5 „

. n 4-' n

- H-On

„ 19-8 „

o

- H-3 n

n '3-9 n

+ a.iB

22 0

- 16.3 „

n tS-6n

- 8.5 „

n 29.7 „

o

- 9-4 n

n 27-7 n

-t- 4.0 „

3°

O

* 6l-5»

+ 22.5 „

n 51-7 n

- I.I 1.

+ 17-5*

n 49-9 n

-4- 7.0 „

23 o

+ 7-4 „

n 59-5 «

+ 3'-° n

n 67.0,,

- 4-2 „

+ 29-1 „

n 52.7 „

- 2.1 „

3°

- 18.5 „

n 34-4 *

+ i-5 „

n 5°-i „

- 4.5,1

+ 1.8 „

» 47-2 „

- 2.1 „

24 o

- 16.3 „

n 29-1 n

- 6.0 „

n 43-7 »

- 4-5 n

O

n 34-° n

5-5 n

o 22.5

+ 6.7 „

« 49-2 „

+ 25-5 n

n 29-7 *

- 4-7 „

+ 23.8 „

n 23.6 „

- 4-2 „

3°

- 3-7 n

n 54-0 „

+ 24-5 n

n 45-7 n

- 4-9 n

+ 23.0 „

n 4°-2 .

- 1-7 »

45

- 29-6 „

* 3°-3 „

- 3-5 „

n 49-5 n

- 6-4 n

- 7-i „

n 4°-9 n

- 6.1,

i 30

- 17-8 „

n 31-5 n

- 3-° n

n 35-8 „

- 4-5 n

- 2.0,,

n 31-2 „

- 5-3 n

TABLE XLII (continued).

Gr. M. T.

Tiflis

Dehra Dun

Bombay

Ph

Pd

Pv

Ph

Pd

Ph

Pd

P,

h m

19 30

•+• 9-3 r

E 5-6 y

- 2.8 7

+ 5-9 y

W 8.97

+ 3.6 7

W 1.87

o

20 o

+ 4.2,,

„ 20.4 „

— 1.3 „

+ 7-i .

o

+ 5-6 .

0

o

80

- 8.8 „

„ 18.6 „

+ 1-3 ,.

— 1-6 ,,

E 4-9,

- 4-6 »

E 4-9,

o

22 O

• 4-2 „

n H-I ii

O

— 5-9 ,,

W 4-9,

— IO.2 „

W 6.2 „

o

30

+ 33.1 „

O

- 7-7 »

+ 5-9 ,,

. '9-7 ,

+ 2.6 „

„ 14.8 „

- 1.6,-

23 o

+ 33-2 „

„ 5.6 „

- 6.4 „

+ 37-5 .

,, 19-7 .,

+ 20.5 „

„ 18.4 .

- 1.6.

3°

+ ii.S »

» 1 8.6 „

- 1.8 „

+ 13-° i,

,, 4-9 .

+ 10.8 „

,, '2.3 „

o

24 o

+ 7-7,,

„ 8.2 „

- 2-6 „

+ 5-9 »

7-9 »

+ 5-6 .

I, 14.8 „

— 2.O „

o 22.5

+ 19-9 ,

W 9.3 „

- 5-i .,

+ 12. a „

, 18.7 .

4- IO.2 „

II 18.4 „

- 8.0 „

3°

+ 19-4 ,

o

- 3-3 ,

+ IS-2 „

,, 14-9 .

+ IO.2 „

„ 18.4 „

- 6.4,

45

- 5-5 ,,

E 13.0 „

+ i-3 .

- 8.7 „

4-9 »

- 8.2 ,

,, 12.3 „

o

i 30

- 2.2 „

„ 8.9 „

- 2-6 ,,

- 5-9 ,,

4-9 i.

— IO.2 „

„ 20.8 „

o

TABLE XLII (continued).

Gr. M. T.

Zi-ka-wei I1)

Batavia

Christchurch

Ph

Pd

ft

Ph

Pd

Ph

Prf

ft

h m

The

19 30

o

W 6.07

+ 3-3 r

o

+ 1.8 y

W 3.7 7

F"-curve

20 o

+ 12.6 7

„ 9-° .,

+ 12.4 .

W 3.6 7

+ 4-6 ,

o

seems to

3°

4- 6.0 „

E 4.0 „

+ 5-3 »

o

+ 6.9 „

E 5-9 ,

be a trifle

22 O

- 6.0 „

W 10.0,,

- 3-5 »

0

— n.o „

Wi3.4 .

too high,

3°

— I2.O „

„ 2I.O „

No

- 1.6 „

„ 3.6 „

-22.1 ,

. 1 1-9 »

answering

23 o

+ IS-2 „

„ 35-o .

noticeable
deflection.

4- 17.1 „

„ 1.8 „

— 23.0 .

,, 3-0 .,

to a posi-
tive P,

3°

+ 14-4 ,,

. I9-° »

+ 8.9 „

o

-16.1 „

n 3-7 .,

until 3h ,

24 o

+ 12.6 „

„ 16.8 „

-t- 3-3 M

„ 6.0 „

— i o.i „

„ 9-7 -

afterwhich

o 22.5

+ 7.2 .

ii '4-0 ii

+ 6.7,,

,, 8.4 „

- 7-8 .

., 5-9 .

it is a little

3°

+ 12. 0 .

„ 16.0 „

+ 4-6 „

?

-23-9 ,,

i, 3-7 ,,

too low,

45

- 2.4 „

,, 15-° »

?

?

-20.7 „

E 3.2 „

answering
to nega-

i 30

- 7-2 „

» 14-4 n

?

?

-ii-S »

0

tive P,

(!) The determination of time is here somewhat uncertain, as only midnight is marked upon
the copy received, which, moreover, is reduced to half the linear size of the original magnetogram.

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION', 1902—1903.

TABLE XL1I (continued).

Gr. M. T.

Ekaterinburg

Irkutsk

Ph

Pd

ft

Ph

/>d

P,

h ni

19 30

+ 1.9 y

E 31.0 Y

- 6.5 Y

+ '4-5 7

0

- 1.5 y

20 O

+ 9-5 »

, 34-0 ,

— IO.O „

4- 19.0 „

W 2.9 ;<

— 2.O „

3°

4- 17.2 ,

„ 28.0 „

— II.O „

+ i i-5 ,

» 1-8 „

- 3-6 „

22 O

+ 27.5 ,

3-4 »

— 18.0 „

— i .0 „

„ 15-0 »

- 5-° ,,

3°

4- 30.8 „

W 5-6 „

- 22.0 „

•+• 14-5 ,,

. 46.3 »

- 5-5 »

23 o

+ 32-5 »

„ IO-3 »

— 24.0 „

+ 33-° »

n 56.2 „

- 6.0 „

3°

+ 27.0 „

,, 9-° »

- 22.5 „

-f 24.0 „

» 46.3 »

- 8.8 „

24 o

-1- 18.5 „

„ 7-8 „

— 20.0 „

4- 9.0 „

» 31-3 »

— IO.O „

o 22.5

+ n-7 »

» 7-3 »

- 18.4 „

o

„ 27-5 »

- 9-5 „

3°

+ 9-5 ,,

i> 6.7 „

- 1 8.0 „

- 3-° »

n 26.4 „

- 9.0 „

45

+ 6.5 „

. 6.2 „

- 17-0 „

7*5 »

n 24.0 „

- 8.0 „

i 30

+ 6.0 „

o

- 13-5 »

- 8.8 „

„ 12.8 „

- 6.5 „

Current-Arrows for the 26th January, 1903; Chart I at 191' 30m(i).,

Fig. 129.

(') By an unfortunate mistake, the arrow for Pf at Axelaen in this and the eight following charts, has been given a direction the reverse of
should be.

what

PART I. ON MAGNETIC STORMS CHAP. III. 293

Current-Arrows for the 26th January, 1903; Chart II at 20b 30m. and Chart HI at 22h Om (').

Fig. 130.

294 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

Current-Arrows for the 26th January, 1903; Chart IV at 22h 30m , and Chart V at 23h Om (').

BIS

ff/oo;

'

\

^

£

v

\

I ~,\.J

Qtlh
Qi '.'.
Dh D Actot

./

SI

k clj
Pw.k

'

:

PART I. ON MAGNETIC STORMS. CHAP. III. 295

Current-Arrows for the 26th & 27th January, 1903; Chart VI at 23h 30m, and Chart VII at Oh 22.5m (i).

-

It

/

"*"J

•

All AmrL*,n

. .'iirui

Oil h Ckttlraitm

Ch Ch (Ju-uLi-Au/-,-A

DhD lldtrallun

H

.

; -

l

(7

,

n_

Fig. 132.

t'l Arro\v inr Pr nt Axrtnen reversed. See note. D. 202.

296 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 1903.

Current-Arrows for the 2?th January, 1903; Chart VIII at Oh 30m , and Chart IX at Oh 45m («).

Fig- '33-

PART I. ON MAGNETIC STORMS. CHAP. III.

297

FURTHER COMPARISON WITH THE TERRELLA-EXPERIMENTS.

74. In order to obtain a clear idea of the way in which the various light-phenomena around our
terrella appear under conditions answering to the earth's positions at the various seasons, I have made
three series of experiments representing an equinox, and the summer and winter solstices.

For each of these seasons, 12 photographs have been taken in four groups of three. The position
of the magnetic north pole in the four groups answers respectively to noon, 6 p. m., midnight and 6 a. m.

In order to obtain a position answering to the summer or winter solstice, the discharge-tube was
inclined so that its axis was at an angle of 23^2 ° below or above the horizontal position answering to
the equinox. The terrella was suspended by a universal joint in such a manner that it always main-
tained the desired position in relation to the cathode rays during a rotation of the terrella answering
to the diurnal revolution of the earth.

Thirty-six photographs have thus been taken, with the highest possible magnetisation of the ter-
rella with a magnetising current of 33 amperes, corresponding to a magnetic moment of about 10 ooo
cm.5/a gr.Va sec.— i (see fig. 70, p. 155).

I have also taken 36 photographs of the terrella in exactly the same positions as the above, but
with a magnetising current of only 15 amperes, corresponding to a magnetic moment of about 6200.
These 72 photographs, with descriptions, will be found farther on in this work.

It will be interesting, however, to describe here some few examples of these with their photo-
graphs, because of the great significance of the light-phenomena observed, in the explanations of magnetic
storms given in the preceding pages.

In the eight photographs following, the terrella has a position answering to the winter solstice and
6 a. m. at the earth's magnetic north pole.

The experiment represented is almost the same, but the photographs are taken from eight different
points of view.

r>g- 134-
Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903.

38

298 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

The pressure employed in the discharge-tube was about 0.02 mm., except in the case shown in
photograph 7, where it was 0.013 mm. The current-strength was 8 milliamperes with a voltage of 3300 ;
and lastly a magnetising current of 33 amperes was employed upon the terrella.

In taking photographs i, 2, 3 and 4, the axes of the cameras were directed towards the centre
of the terrella, and were lying in a plane that passed through the axis of the discharge-tube. This
plane formed an angle of 66l/-2° with the vertical line, and thus formed the same angle with the hori-
zontal plane as the axis of the discharge-tube.

When the angular distances to the axes of the cameras were measured from the axis of the tube
in the direction of the cathode, and in the above-mentioned inclined plane with the centre of the terrella
as the vertex, measuring contrary to the hands of a clock seen from above, the angles in the four posi-
tions were respectively 90°, 180°, 270° and 315°. Photograph 6 was taken with the axis of the camera
horizontal in the vertical plane through the axis of the tube, and directed towards the centre of the
terrella, and towards its night-side.

Photographs 5, 7 and 8 were taken in positions that may be described as follows : in three vertical
planes through the centre of the terrella at angular distances of 45°, 270° and 315° respectively from the
vertical plane through the axis of the tube, the axes of the cameras pointing towards the centre of tin;
terrella, and forming an angle of 20° with a horizontal plane.

There are two different phenomena that come out very clearly in these photographs, or rather in
the experiments which the photographs reproduce.

In the first of these, we have the luminous spirals, almost closed rings, that are formed round, and
at a certain distance from, the magnetic poles of the terrella. These spirals vary in position with the
rotation of the terrella; and I consider them as answering to the auroral zones on the earth. These
principal spirals of light form in my opinion the most remarkable phenomenon that I have discovered in
my terrella-experiments. The more highly the terrella is magnetised, the narrower does the band of
light become, keeping, however, its intensity. The bands of light are here almost coherent; but different
degrees of luminosity in the precipitation are easily seen, answering to the various districts of precipita-
tion shown by the experiments given in fig. 47 a & b.

It will be seen from photographs Nos. i and 5, fig. 134, that the spirals begin above as a broad
luminous band, indicating a great descent of rays upon the terrella. At the top, to the left of the band
in No. i, there is a slight illumination in space outside the terrella, as also in No. 7. These two illu-
minations are the beginning and end of the greatest precipitation of rays in the band of light. The
principal bands of light can be easily followed in photographs 2 and 6, then in 3 and 7, and 4 and 8,
right round the terrella, until they disappear. In No. 8 especially, we see both beginning and end of
this long spiral of light round the south pole of the terrella-magnet, which answers to the terrestrial-
magnetic north pole.

These continuous bands of light recall a most remarkable and ingenious hypothesis made by A. E.
Nordenskiold (i). He assumes that the usual arc of polar aurora seen in Bering Strait was part of a
ring of light situated in a plane perpendicular to the radius of the earth, which terminates in a point
near the magnetic pole (lat. 81° N., long. 80° W. Gr.). He concludes that the plane which contains the
auroral arc, and which is perpendicular to this radius, cuts it at a distance of 125 kilometres below the
surface of the earth. In this plane the lower edge of the ring of auroral light would be about 200
kilometres above the surface of the earth.

The second phenomenon, which is clearly visible in the experiments shown in fig. 134, is the
presence of portions of luminous rings, also almost circular, which lie considerably nearer to both poles

(') A. E. Nordenskiold: Vega-Expeditionens Vetenskaplige lakttagelser. Forsta Bandet, p. 417, Stockholm, 1882.

PART I. ON MAGNETIC STORMS. CHAP. III.

299

of the tcrrella's axis of rotation, than the previously described luminous spiral. These portions of luminous
rings, with a very much smaller radius than the first rings had, have already been shown, e. g. in photo-
graphs 3, 6 and 9 in fig. 68. It will be easily seen that these small luminous half-rings are comparatively
independent of the large luminous spirals round the poles, when the magne-
tising current for the terrella is reduced to, for instance, 15 amperes. There
then appear the peculiar, triangular patches also covering the equatorial
regions, that are seen in fig. 68, in place of the large polar rings; while the
small rings continue almost unchanged up at the poles. On looking more
closely into the phenomenon, we see that these small ring-portions are formed
round a luminous point upon the terrella, this point being the apex of a cone
of light that may often be seen in space outside the terrella. I have selected
three photographs in which this cone of light comes out well, and reproduced
them, with the contrasts brought out as clearly as possible (see fig. 135). The
apex of these cones falls upon the terrella near either pole, and strange to
say does not greatly change its position during the rotation of the terrella.
It remains on the post-meridian side near the noon meridian through the
centre of the cathode, and moves a little backwards and forwards, principally
east or west, during the rotation.

It should be remarked that the cones of light seen in the figure appear
to withdraw from the terrella when the magnetisation is increased, whereas
the little ring of light still strikes the terrella. To the east of the apex of the
cone of light, the ring of light is seen in the air (see photograph 2, fig. 135),
while to the west it is thrown upon the phosphorescent terrella in the form
of a semicircle (see photographs 3, 4, 7, and 8, fig. 134).

These cones of light are extremely interesting. They are similar to
those that I first described in connection with the drawing-in of cathode rays
towards a magnetic pole, in the same paper (') in which I expressed for the
first time my belief that the northern lights are formed by corpuscular rays
drawn in from space, and coming from the sun.

On looking closely at fig. 135., we see that the drawn-in cone really
consists of several envelopes; in the original photographs, as many as three
cones, with very different apical angles, are distinguishable.

This is a very interesting phenomenon, which is also demonstrated in
another way in the paper just mentioned. I found by studying a series of
successive inversions of a shadow-cross at the bottom of a Crookes' tube
standing before a strong magnet, that the cathode rays must intersect one
another several times before they reached the bottom of the tube.

Poincarc'(2) has made this drawing-in phenomenon the subject of mathematical investigation, and has
demonstrated that the cathode rays move like geodetic lines upon certain cones with a common gene-
ratrix, so that each ray has its conjugate cone.

Wiedemann and Wehnelt (8) thought they could prove that this repeated crossing of rays in the
discharge-tube was produced by the frequent intersection of the same cathode rays in the tube, and that
the phenomenon recalled the circumstances connected with a vibrating cord.

Fig- '35-

11) Archives des Sciences Physiques et Naturelles, Geneva, 4th period, vol. I, 1896.

12) Comptes Rendus, 123, p. 930, 1896.

(•'') Wiedemanns Annalen, Vol. I.XIV, No. 3, 1898.

300 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQOZ 1903.

In investigations made at the same time, but not published until some months later (') I had shown,
however, that the phenomena were not so simple; it is certain, indeed, that no theoretically clear under-
standing has yet been arrived at with regard to the formation of the cones of light shown in fig. 135.
In the above-named paper, I have shown how the theory can explain a number of discontinuously occurring
luminous rings in the discharge-tube, even if we suppose the cathode to emit a whole sheaf of rays, and
not only separate bundles with definite angles of emanation for the rays. It may possibly also be shown
that the above-mentioned cones of light in space are formed by a maximal agglomeration of rays about
certain surfaces, thus making the density of the rays there so great that the rarefied air in the tube
becomes more luminous near these surfaces.

I have here touched upon this matter because these cones of light and their attendant phenomena
will be found to play an important part in our theory of terrestrial-magnetic and auroral phenomena.

My special reason for here reproducing the above photographs in fig. 134 and mentioning the experi-
ments, is my desire to indicate phenomena that may possibly afford a full explanation of a peculiar circum-
stance that has frequently been pointed out in the preceding pages. We have seen that during the
so-called positive polar storms on the post-meridian side of the earth, the current-arrows at Dyrafjord,
Kaafjord and Matotchkin Schar have often been directed eastwards, more or less along the auroral
zone, while at the same time the arrow at Axeleen pointed in the opposite direction, westwards along
the auroral zone (cf. the perturbations of the nth, 2jth and 3131 October, 23rd November, gth December,
and 8th and I5th February).

The great spiral of light round the magnetic south pole of the terrella represents, in my opinion,
the precipitation of rays on the night-side of the globe during long magnetic storms. It represents the
"horizontal part" of the current generally passing between Kaafjord and Axeleen at about midnight, the
breadth of which I have estimated to be not more than 500 km. While discussing the long magnetic
storms, we have frequently pointed out that in the afternoon the negative storm at Axeleen seems to
be closely connected with storms farther east on the night-side of the earth; while at the same time a
positive storm is observed at Dyrafjord and Kaafjord.

Our photographs in fig. 134 answering to 6 a. m. at the magnetic south pole, clearly show that
the spiral of light begins in a very high latitude on the post-meridian side, whence it passes round
the terrella in its descent to lower latitudes. When, for instance, the terrella is turned so that it
is noon at the pole the beginning of the spiral also moves down towards lower latitudes, its longitude,
however, changing only slightly, measured from the cathode.

In this connection I will mention that during the observations of aurora at the Haldde observatory
in mid-winter, 1899 — 1900, the following phenomena were observed day after day. Early in the after-
noon, generally at about 5 or 6 p. m., local time, an arc would appear far to the north and close down
on the horizon, and would remain through the evening, moving farther and farther south, and higher
and higher in the sky. As it came nearer, it would sometimes divide into several separate arcs. At
about 9h or ioh it would disappear, generally rather suddenly. During these auroral displays, our magneto-
meters were generally disturbed; but the most powerful magnetic storms almost always occurred after
midnight, when there was generally no aurora to be seen. This seems to agree well with the conditions
on the terrella, where the first great precipitation begins on the post-meridian side far up near the pole,
and descends to lower latitudes before it ceases or becomes a faint band of light, which continues
round the terrella. This greatest precipitation consists of rays that descend almost perpendicularly upon
the terrella; while the slighter precipitation on the night-side must be produced by rays that rather
glance past the terrella. Corresponding rays that glanced past the earth on the night-side would generally
produce magnetic storms.

(!) Archives des Sciences Physiques et Naturelles, Geneva, 4th period, vol. IV, 1898.

TART I. ON MAGNETIC STOKMS. CHAP. III. 30!

It is with a view to a careful study of the conditions connected with the positive polar storms that
I have endeavoured to bring out in my terrella-experiments the directions in which the rays descend
tangentially to the terrella's surface at various times of day in the polar regions, by the aid of narrow
phosphorescent screens.

Owing to an accident to my discharge-tube, the final results of these investigations will not appear
until the next section of this work; but I nevertheless have so many photographs of experiments that I
have made, that I seem already to have a tolerably clear idea of the phenomena. We will first look
again at some of the experiments already described, namely those shown in figures 38, 46 and 47

These experiments show indeed perfectly clearly that there are bundles of rays that graze the
terrella from east to west along the auroral zone, corresponding, in my opinion, to the conditions on the
earth during positive polar storms, and also bundles of rays that graze the terrella from west to east,
corresponding to negative polar storms.

Fig. 38 b shows a tongue of light on the screen, down towards the "auroral zone" of the terrella,
which is not found on the other side of the screen in the position observed. We will call the first
side of the screen the a-side, and the other the 6-side. The tongue of light does not appear upon the
screen in the position shown in fig. 38 a, but it is found on the a-side of the screen in fig. 38 c, where,
however, it does not extend so far in towards the terrella; and on the other hand we also see already
on the 6-side, on the opposite part of the screen, a considerable amount of precipitation. In the position
shown in fig. 46 a, which forms a direct continuation of the experiment in 38 c, the precipitation does
not even extend so far on the a-side, while on the 6-side it has become very marked, and goes right
down to the terrella, indicating rays that glance past the terrella from west to east, though without
doubt single rays curve in towards the terrella, and form narrow loops before they go out again, very
much as shown in the diagram, fig. 50 a.

In fig. 47 b, we see a powerful precipitation on the 6-side of the screen, produced by the same
kind of rays.

The precipitation on the a-side of the screen in fig. 38 distinctly shows that a wedge-shaped tongue
of rays is thrust in towards the terrella, reaching farthest on the afternoon and evening side; the rays
turn back as shown in fig. 50 b, and in my opinion correspond to the rays that occasion positive polar
storms on the earth.

These conditions are confirmed and rendered still clearer by the experiments represented in the 8
photographs in fig. 136.

The first five of these refer to an experiment in which the position answers to that of the earth
in the winter solstice, and to about noon at the earth's magnetic north pole, and the last three to another
experiment in which the position represents an equinox, and midnight at the same magnetic pole. From
the north pole of the terrella issue three narrow, phosphorescent screens, 3 millimetres in height and
about 3 centimetres long, by the aid of which it was intended to determine the direction of the rays in
the various instances of precipitation in the polar regions.

The five positions of the camera, from which photographs i to 5 of the first experiment were
taken, may be determined as follows:

The axes of the cameras pointed towards the centre of the terrella, and were situated in vertical
planes, at angular distances of 45°, 90°, 180°, 270° and 315° from the vertical plane through the axis
of the discharge-tube. In each case the axes of the cameras were at an angle of 20° with the horizon.
In the three positions from which photographs 6, 7 and 8 were taken, the axes of the cameras were
situated in three vertical planes, at angular distances of 45°, 90° and 135° from the above-mentioned
vertical plane, the axes being pointed towards the centre of the terrella, and forming the same angles with
the horizon as before. It will easily be understood from these last three photographs, that the object

302

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.

Fig. 136.

in taking them thus was to investigate the conditions on both sides of one of the above-mentioned three
screens, the one whose position answered to about 6 p. m.

Photographs i, 2, 3 and 5 show very distinct precipitation on the Z>-side of the screen, and shadows
on the a-side, indicating that the precipitation on the terrella has a tangential motion from west to east
in the "auroral zone". Photographs 3, 4 and 5 also show, however, a slighter precipitation at the very
bottom of the a-side of the screen.

We obtain a clearer understanding of this twofold phenomenon from photographs 6, 7 and 8. We
here see quite distinctly, although not nearly so distinctly as in the experiment itself, that the broad
band of light consists of two bands, one more northerly that moves from west to east, and one more
southerly that moves from east to west. The northern band of light breaks off just to the east of the
screen, while the southern band breaks off just to the west of the screen, in both cases because of the
shadow cast by the screen.

These circumstances seem to give us the key to the apparent enigma of the simultaneous occurrence
of a negative polar storm in Spitsbergen, and a positive polar storm at Kaafjord and Matotchkin Schar.

CHAPTER IV.

CONCERNING THE INTENSITY OF THE CORPUSCULAR PRECIPITATON
IN THE POLAR REGIONS OF THE EARTH.

75. While discussing the magnetic storms, we have pointed out a number of such storms,
affecting the whole earth, which are evidently brought about by electric currents of some kind or other,
acting in the region of the auroral zone. The current-system that might explain these storms is often
of a very complicated nature, as the magnetic effect round the auroral zone frequently inclines us to
believe that there are precipitations of electrically-charged corpuscles over several districts simultaneously
all round the auroral zone.

When the conditions are so complicated, it will be inadvisable to try to obtain a practical result
by comparing the magnetic effect of the corpuscles upon the earth with the effect of galvanic currents ;
for generally speaking at present a direct calculation of the magnetic effect of the electric corpuscles in
different parts of the earth is too difficult of accomplishment. Up to the present, the possible paths 01
the electric particles have been found by numerical quadrature; but the actual distribution and density
of the rays round the earth have not been found by calculation. The solution of this problem would 01
course be of the very greatest importance, if by its means a calculation might be made, from the magne-
tic effect upon the earth, of the number of corpuscles emitted by the sun per second. It will be easily
understood that the greatest interest will attach to the establishment of the relation between the energy
emitted by the sun in the form of corpuscular currents, and the energy sent out in the form of heat and
light, more especially for the purpose of deciding whether the amount of the latter energy might possibly
have been produced by a disintegration of the sun corresponding to the calculated quantity of corpuscles.
At the present standpoint of the theory, however, we must be content with rough calculations and estimates
such as those we shall make in the next few articles.

In certain simple cases, especially during the perturbations that we have called elementary storms,
it may, however, be useful to compare the magnetic effect of the corpuscular currents with galvanic
currents of so simple a nature that a calculation of the magnetic forces is easy. It may now be regarded
as an undoubted fact that in the regions round the auroral zone we sometimes have currents which, at
any rate for short distances, have the magnetic effect that a more or less horizontal current above the
earth's surface would have, and which is comparatively small in section.

This is especially shown in the elementary storms that we have considered, where we very often
have currents that pass over the earth between Axeleen and Kaafjord. The main intensity of these
currents is probably compressed into a comparatively small section, judging from the fact that the
vertical components of the perturbing force at the two stations generally have contrary direction, and
are of about the same magnitude as the horizontal components. In this case we could compare the

304 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

magnetic effect of the corpuscular current with the effect of a galvanic current, and endeavour to deter-
mine the strength of the current, or rather, obtain some idea of its magnitude by assuming, as a first,
most simple approximation, that the magnetic effect outwards might be satisfied by a linear galvanic
current of a certain strength, situated at a certain height.

In describing the separate elementary storms, we were able to show that the main features of the
distribution of force in those perturbations were explained by the assumption of two vertical electric
currents with opposite directions, connected by a horizontal portion of current. In Art. 36 we investi-
gated the effect of a current-system such as this, and found a very close agreement with the actual
circumstances during the polar elementary storms. The results there arrived at might now be employed
for the purpose of estimating the operating strength of the currents. If, however, we look at the sta-
tions that are situated at all near the auroral zone, we can there simplify the problem considerably. It
is immediately manifest that observations from points on the transverse axis of the system and near the
storm-centre, must be favorable for a determination of the strength of the current. The field in the
immediate vicinity of a linear conductor is somewhat similar to the field about an infinitely long,
rectilinear current along the tangent at the nearest point on the conductor. When both stations have
the same point on the conductor as their nearest, the field for both of them, at the place under con-
sideration, will be determined by one infinitely long, rectilinear current; and as this is horizontal, it
will simplify the reckoning considerably, and at the same time furnish a calculation of the degree of
proximity of the current to the earth.

Fortunately for the solution of our problem, Axeleen and Kaafjord, in a number of perturbations,
occupy this very position; and we shall only take those cases in which the current passes between the
two stations, as we shall thus obtain a more certain determination of the altitude.

The question now is whether it is possible to decide when the current-system is thus situated in
relation to the two stations. This must be decided separately in each case. We will only mention, as
a necessary condition, that the current-arrows for Axeleen and Kaafjord must point in the same direc-
tion, and their vertical components be in opposite directions.

A calculation, similar to that given below, of the currents that cause polar storms, was made by me
some years ago, for the stations Bossekop and Jan Mayen, with the aid of material from the expeditions
of 1882 and iSSst1).

We shall now proceed to calculate the current-strength and altitude of an infinitely long, rectilinear,
horizontal current above the surface of the earth, when we know its effect in magnitude and direction
at two points on the earth's surface.

Since we cannot on the whole lay claim to accuracy, we will here assume that the surface of the
earth in the district in question is a plane surface.

A B is the horizontal projection of the current; (/) and (2) represent re-
spectively Kaafjord and Axeleen.

. According to the above, the connecting line between the points (/) and (2}

should be perpendicular to A B. This would be an ideal case, which will only
approximately be attained. We will therefore assume that the lines form an
angle, ip, with one another. In cases in which the calculation will be employed,
this angle will be nearly 90°.

We will further imagine the system projected upon a plane perpendicular

Fi j to the line of the current. This line and the two points (/) and (2) on the earth's

surface are then projected as three points, C, S\ and Sa.

(') Expedition Norvcgienne de 1899—1900, p. 27.

PART I. ON MAGNETIC STORMS. CHAP. IV.

305

p;p-

Fig. 138.

We will use the following signs:

The distance from point 5^ to the current is designated rt,
the distance from point S2 to the current, r2. The angles these lines
make with the ground-line we will call cpt and (jp», and the height of
the current above the earth's surface, /». The portions into which
the height-line divides the ground-line of this triangle, we will call al
and «a. The distance between Kaafjord (/) and Axeleen (2) is

designated D ; hence the projection of this distance on the above plane is d = D sin i//. For the
perturbing forces we will use the signs P', /Y and P,' respectively for the total, the horizontal and
the vertical forces at Kaafjord, and correspondingly P", P\" and P," for those at Axeleen.

If the magnitude and direction of the perturbing forces are given, the problem will be not only
determined, but over-determined, so that it affords a test of the correctness of our assumption.

The direction of the forces, for instance, is sufficient to determine the situation of the current. The
strength of the current can then be determined by that of the perturbing force at the one station. The
strength of the perturbing force at the other station may then serve as a check.

The calculation can be made according to the following formulae:

_/Y'

*Y

tan o>j = ^7 ,

sin cp j

sn

+ r/>2)
sin

sin (99 j

Two values will be obtained for the strength of the current, according as the force at Axeleen
or that at Kaafjord is employed:

5 Pf

sn

n^j -f 9?a)

. ^ 5 P" sin (pi d
2 sin (9?, +gt>2)

In these and the succeeding formulae, P, and P, are always to be regarded only as the numerical
values of the respective perturbing forces.

As it occasionally happens that one of the vertical components is wanting, we shall also solve the
droblem under that assumption. If the other vertical component is there, it may be used as a check.

If we introduce:

and

P/ =

_/y_ 3

we obtain the following equations:

«t -|-a2 = «, (i + d) = D sin (/; = </,

h

- = tan gr>, = p ,
"i

PI = = '-p cos2 0>, ,

5 rf 5«i

Birkeland. The Norwegian Aurora Polaris Expedition, 1003—1003.

(I)
(2)

(3)

3°6

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

p " _ '
1 " s

5

(4)

If we divide (3) by (4), we find that

<? = + . (5)

In the cases we shall come to examine here, however, the current is always between Kaafjord
and Axeleen, so that <J will always be positive. In equation (5) p and q are known quantities; hence
d can be calculated, and from (i) and (2) we obtain

Dp

h = — -£--; sin ip
From (5) and (3) / can then be calculated, and we obtain

sn

(6)

(7)

With regard to the determination of the angle (//, we should remark that if the current-arrows

for Kaafjord and Axeleen make the same angle with the great circle between these two stations, t// will

simply equal that angle. The angles will generally be somewhat different. Calling them respectively
t^j and tjj.2> we put

NUMERICAL VALUES FOR HEIGHT AND STRENGTH OF CURRENT.

(i) The Perturbation of the ijth December, 1902.

76. During this perturbation the balance at Kaafjord stuck fast, so the direction can only just be
distinguished. As the sensibility of the balance at Axeleen was not determined until after the return
of the expedition, and may thus be not altogether free from error, we will see what can be concluded
regarding height and strength of current, when we suppose that we know only the horizontal compo-
nents, and the direction, but not the strength, of the vertical components.

Between ih 45™ and 2h om, the horizontal components at Axeleen and Kaafjord are almost alike
in direction; and the outer field shows that the storm-centre during this time must be somewhere near
Spitsbergen. We will therefore take ih 52-5m as the most favorable moment for determining the
strength and altitude of the current. At this point of time, the values are as follows:

P," = i86y
P,' = 30 »
D = 896 km.

(// = 70°.

We further introduce here a quantity x which is thus defined,

_P,"

6.2 .

If we divide the equation (4) by (3), we find

and by employing equation (6) we obtain

ft ^

D sin i// 1/ i — x(52

i -f- (J ' x — i

(8)

PART I. ON MAGNETIC STORMS. CHAP. IV.

By inserting this value for h in (7) we obtain

— J)

and

tan

h i i/ i — «d*
q>, = — = ~ I/- - ,
a, <J " x— i

3°7

(9)

By the above equations, // and / are determined as functions of d. On account of the direction
of the vertical components, we have

d>o.

If our assumptions are correct, we must have real quantities, and the strength of the current
must be finite. We then obtain

<5<Cy -j where ]/ -- = 0.402 .
' x ' •/.

It is easily ascertained that the function for // in this interval has neither maximum nor minimum.
As the function in the interval considered is continuous and finite, we may conclude that it has its
extreme values at the limits of the interval, and especially in such a way that we get the greatest
height when d = o.

In the case of / we find that the function has a minimum for the value d = - that is to say

x

for a value within the interval considered.

Still narrower limits may be set to the interval, however, if we now make use of our knowledge
of the vertical intensity at Axeleen.

The sensibility of the balance was determined, after the return of the expedition, as 24.6. If,
therefore, we employ a value of 35, there is no doubt that it is too high. We then obtain

tan

P "
== -^77 > 0.885 <

or 6 <d 0.312 .

o and 0.312 can thus be employed as the limits for <J.

In the following table, the height and strength of the current are calculated for 4 values of <5,
namely d = o, - , 0.263 and 0.312. The value d = 0.263 anwers to a sensibility of the balance of

X

24.6, and therefore the values we obtain there should be the nearest to the true values.

TABLE XLIII.

S = 0

£ I

X

$ = 0.263

S = 0.312

/,

•568

286

22O

177

km.

374,000

amperes

We see that even if we pay no attention at all to the vertical intensity for Axeleen, we may still
conclude that the current cannot lie higher than 368 km., answering to a current-strength of 342,000
amperes, and also that the current-strength cannot be less than 314,000 amperes, provided our assump-
tions in other respects hold good.

Considering that P, for Axeleen is known with very fair accuracy, the true values should lie near
those that answer to d = 0.263.

The values found for h and i are, as we shall presently see, comparatively small in this pertur-
bation, indicating that the perturbation is comparatively slight, and of rather a local character in the north.

3o8

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

(2) The Perturbation of the loth February, 1903.

77. The current-arrows for Axeleen and Kaafjord remain in one direction for a considerable time,
and are almost perpendicular to the arc of the great circle between the two stations. It also appears
from the outer field that the storm-centre of the current-system is in the neighbourhood of Axeleen and
Kaafjord. We have therefore calculated the strength and altitude of the current at several hours at
which the conditions are approximately those mentioned in the introduction.

In this case we employ P, for Kaafjord. The vertical component for Axeleen we shall use as a
check. This quantity, if our assumption is correct, will be determined by the formula

P " _ P "
~P '

In the following table, the calculation has been made for four different hours.
It may here be remarked that both in this and the succeeding Tables, the units of length and
current-strength are respectively a kilometre and an ampere.

TABLE XLIV.

Time

Pi1

P,'

P,"

d

P

1

1

h

i

?„" cal.

P," obs.

ash 22.510

235

229

200

890

1.026

1-553

1.166

422

966,000

227

15°

37-5

200

253

308

890

0.790

1.026

o-653

426

1,109,000

254

164

45

187

258

353

890

0735

0.889

0-532

421

1,143,000

259

158

24!" o

1 20

1 68

146

860

0.714

1.114

0-855

328

582,000
<

175

172

V.
The table shows that at the first three of the hours mentioned the current would be at the same

height — about 420 km. — ; and this is the more strange as the separate quantities in the formulae
differ considerably.

The values for d seem to indicate that up to 23'* 45m the current is moving towards Axeleen.
While moving thus, the current, on an average, would keep at about the same height above the surface
of the earth.

A comparison between the calculated and the observed values for P,", will show that the cal-
culated vertical components on the whole are too large; the observed values are only about two thirds
of the calculated. A result such as this is just what might be expected. Our calculations presuppose
that the transverse section of the current is very small in proportion to the distance between Kaafjord
and Axeleen; but considering the cosmic constitution of the current, this is not very probable.

We could make the calculation here also, assuming both the total forces to be given. The result
will be found in the following table.

TABLE XLV.

Time

P'

P"

h

''i

"I

Mean of
«'i & «t

2311 22. 5m

328

250

5i6

1,182,000

806,000

994,000

37-5

323

349

495

1,289,000

974,000

1.131,5°°

45

3'9

387

-187

1,324,000

1.033,000

1,178,500

24 o

206

225

345

612,000

600,000

606,000

From this it appears that the two calculated current-strengths are not quite alike, but the difference
is not greater than would be expected. The mean gives values that agree very closely with those
previously found. The height found is somewhat greater in the last case. It will easily be perceived
that if the current is spread over a larger section, we shall find the height somewhat too great.

PART I. ON MAGNETIC STORMS. CHAP. IV.

3°9

Fig. 139-

Our calculated current will lie, for instance, at C (fig. 139), whereas in
reality the current may be gathered at a lower level A B.

In this way the height of the current will be rather an indefinite con-
ception; but we believe the values found will at any rate give an approximate
determination of the heights at which the greatest density of the current in
each separate case must be looked for.

We will now, in conclusion, see how far the conditions at Dyrafjord
and Matotchkin Schar agree with the values found. Assuming the strength
of the current to be the same, we will calculate the height at which a

horizontal current must pass in order to produce the magnetic disturbances that occur at the two
stations. If we call the distance from the station to the nearest point in the current r, we obtain

r=5P'
where P is the total perturbing force.

If we assume the current to be horizontal, we obtain

h — r sin <p ,

where

p

tan = -W-

TABLE XLVI.

Dyrafjord

Matotchkin Schar

T"

t

P

r

h

P

r

h

23h 22.5»»

966,000

388

498

482

419

461

410

37-5

1,109,000

132

723

1176

333

668

614

45

1,143,000

193

1504

754

216

1058

973

24 o 609,000

124

731

947

74

i645

'574

These calculations show that if the current were horizontal, it would lie especially high above the
two stations, Dyrafjord and Matotchkin Schar, particularly during the latter part of the perturbation.
Our assumptions for these calculations can only, as we have already said, be regarded as a first approxi-
mation; but it is most probable that the erroi will be in the same direction in all the calculations, so
that the relative proportions will be fairly correct. If the current were to continue with the same average
strength, it could not do so at the same height as between Kaafjord and Axeleen, but would curve
upwards.

This harmonises well with our view of the current-system, which maintains that the system would
curve upwards. The actual circumstances at Dyrafjord and Matotchkin Schar could also be explained,
however, if we assume that the current there is spread over a large section. Moreover the assumption
that the average strength in the advancing current would preserve its value unchanged, owing to the
undoubtedly cosmic nature of the current, can by no means be regarded as safe, as the paths of the
separate electric corpuscles will be very numerous. The constancy of the average current-strength can
therefore only be regarded as a very rough assumption.

A comparison of the current-strengths found for this perturbation, with those for the perturbation
of the I5th December shows that the former are about three times as great as the latter. At the same
time the effect of the force at corresponding places in the field outside the arctic regions is much smaller
on the 1 5th December -- only about one third.

3io

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

This shows that the strength of the universal disturbances that accompany the storms in the north,
stand in about the same relation to one another as the strength of the currents which we assume to be
the direct cause of those storms. This accords well with our assumption; for if it be assumed that
during these polar storms the form of the current-system is more or less the same, the force at
corresponding places in the outer field would be proportional to the strength of the current.

In connection with these calculations of current-strengths, I will here refer to the current-strengths
that I found for the stations Bossekop and Jan Mayen, given in my former report, "Expedition Nor-
vegienne de 1899 — 1900" etc., pp. 27 & 28. They agree well with those now found, as they vary
between 317,000 and 983,000 amperes.

(3) The Perturbation oj the 22nd March, 1903.

78. In this perturbation, as already mentioned, the storm-centre is in the neighbourhood of Axeleen
and Bossekop, whither the station at Kaafjord had now been moved (see p. 10). The current-arrows
for these stations are similar in direction, and are almost at right angles to the great circle between
them. The vertical components are very large and in contrary directions. It would thus appear that the
conditions are such as to justify a more elaborate calculation of the strength of the current, according
to the methods previously given.

In the calculation on this occasion, we shall consider the total force for Axeleen as known, as
also Pj for Bossekop. At the latter station the patch of light for the balance has moved off the paper,
so that there, during the time at which the storm is most powerful, we only know the lower limit of
this quantity.

In the table below are given the most important values that enter into the formulae, as also the
values found for Pt' , h and ;'.

TABLE XL VII.

Time

V

d

Pi'

P,' obs.

P,"

P,"

s

h

1

P,' cal.

aah oni

7i°

847

207

205

315

408

0.738

278

1,170,000

363

15

73

856

211

> 205

372

492

0.674

259

1,324,000

414

3°

73

856

2 2O

> 205

157

484

1.209

156

1,282,000

56i

45

81

885

134

> 305

I48

396

0.946

156

945,000

379

The height on this occasion is not great. The strength of the current, on the other hand, is
fairly great, amounting to il/3 million amperes. If we compare the calculated values of P,' with those
observed, we also on this occasion, at 22h om, find that the calculated value is too high. As regards
the subsequent hours we can say nothing decided; probably they also are too high. For the explanation
of these conditions, the reader is referred to the perturbation of the roth February.

(4) The Perturbations of the 2jth & 28th October, 1902.

79. In the storms that occur just before midnight on these two days, there are, as we said when
discussing them, circumstances which justify a calculation of the strength and altitude of the horizontal
portion of the current. The results of this calculation are given in the table below.

TABLE XLVIII.

Time

V

Pi

*v

Pi"

P," obs.

P," cal.

S

k

1

Oct. 27, 23*! om

78°

"3

127

266

no

imaginary

20

67°

104

117

195

295

91-5

0-4'3

522

614,000

„ 28, 22 2O

68°

175

132

2OO

352

lao

0.767

608

835,000

PART I. ON MAGNETIC STORMS CHAP. IV. 31 1

On the 27th, at 23*, 6, as we see, is imaginary. This shows that the perturbation-conditions at
the two stations at that moment do not satisfy the assumptions made. The reason of this is possibly
to be sought in the cross-section that the actual current must have, or perhaps in the fact that the
perturbation-conditions could in no way be ascribed to the effect of a more or less aggregate system.
We might have several simultaneously-acting systems of to some extent more local character. We
very frequently see at these stations in the north, that disturbances occur at one station that are not
noticed at another. We shall never be without these local disturbances; but the thing is that they shall
be slight in comparison with the total effect.

A great local disturbance seems really to occur just about 23b. There is a sharp deflection of
rather long duration, which tends to increase /V'- From the fact that there is no corresponding change
at Kaafjord, we may conclude that this deflection cannot be ascribed entirely to a movement of the
main system.

We also, by looking at the curve for Pv, obtain the impression of a new system, which would lie
to the north of Axeleen, as the deflection is in the opposite direction.

At the second hour, 23h 2om, the great local disturbance at Axeleen is over, or at any rate fainter,
and we now obtain a real solution. The calculated vertical component for the time, however, is some-
what smaller than the observed. This is also the case on the day following.

THE ENERGY OF THE CORPUSCULAR PRECIPITATION.
THE SOURCE OF THE SUN'S HEAT.

80. We consider it to be beyond doubt that the powerful storms in the northern regions, both
those of long duration, and the short, well-defined storms that we have called elementary, are due to the
action of electric currents above the surface of the earth near the auroral zone.

These currents, as far as the elementary storms are concerned at any rate, act, in the districts in
which the perturbation is most powerful, as almost linear currents, that for a considerable distance are
approximately horizontal. In the preceding articles, we have attempted, in some of the magnetic storms
described, to calculate the strength of horizontal currents such as might be the cause of the storms,
supposing that they acted magnetically as galvanic currents. The values found, which cannot certainly
lay claim to any great accuracy, will yet give an approximate idea of the strength of these currents.

In the case of the greater storms, we found current-strengths that varied between 500,000 and
1,000,000 amperes, or even considerably more.

It might be interesting to know the amount of energy per second of this current. According to
my hypothesis, the currents would not, in reality, be galvanic, but be formed of cathode rays, or more
generally of rays of electric corpuscles. We will make this hypothesis, then, the basis of our estimates.

By energy we in the mean time understand the kinetic energy of the corpuscular current that passes
per second through a cross-section of the horizontal part of the current, and where the corpuscles are
assumed to flow in the path of the before-mentioned galvanic current. In Article 36, fig. 50 a & b, we
gave a diagram of the manner in which we in reality approximately imagine the corpuscles to move.
With the method of calculation here employed, we obtain only a small lower limit of the energy of the
corpuscular current.

If we call the number of corpuscles that pass the cross section in the time-unit n, the apparent mass
of a particle //, and the velocity v, we obtain as the energy W.

W = \ nf.iv'1.

312 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902— 1903.

If each particle carries a charge of e electrostatic units, we have

f . «

-fl- amperes

and thus

3 X 10

W = 3 • io» •' ''

2 £

If the C.G.S. system be employed, we obtain IV expressed in ergs per second.

The energy of the current will chiefly depend upon the kind of rays that form the current. It is
evident, however, from the magnetic storms previously described, that the corpuscular rays here referred
to must be very "stiff" magnetically.

Leaving the question of the particular nature of these rays for the present undecided, we will make
the calculation for two types.

(i) For cathode rays, whose velocity is small in proportion to the velocity of light, we have, when
e is calculated in electrostatic units,

15

sec.

"1

- = 510 x IC> cm- gr-
P*

For rays where v = 0.7 X IC)10> we thus find that

W = -Xloi) '• — —35 — z-44 X iQ11 ' ergs Per second,

or

W = 19.6 /' h.-p.
(2) For § rays with velocities of

v = 2.59 x r°10 cm- sec."1,
we have, by Kaufmanns determinations,

Corresponding to this,

— = 255 x Iolr' cm- * gr- 2 sec-

W = 3.94 X Io12 ' ergs Per second,

or

W = 535 ' h.-p.

The energy in each separate case can then be calculated according to these expressions.
For i = 1,000,000 amperes, we obtain in the first case

W = 19.6 x I0<' h.-p.,
in the second case

^ = 535 X io6 h.-p.,

or 100 times more than the maximal amount of force that all the waterfalls of Norway together could
deliver by a perfect regulation of all water-courses.

There is much that seems to favour the idea that the rays that come to the earth are very "stiff",
and may possibly have considerably more energy than the here assumed /? rays. We recollect that the
apparent mass increases comparatively quickly when the velocity of the corpuscles approaches that of
light. We know of /? rays whose velocity is only 5 per cent, less than that of light, and whose apparent
mass is 50 per cent, greater than that of the /? rays assumed above.

We have moreover, in the preceding pages, during powerful magnetic storms, calculated current-
strengths greater than a million amperes, which is the amount here taken as the basis.

(') The values are calculated from those given in Sir J. J. Thomson's "Corpuscular Theory of Matter"; London, 1907.

PART I. ON MAGNETIC STORMS. CHAP. IV. 313

We may thus take it for granted that a kinetic energy answering to io9 horse-power during power-
ful storms, will not be too high for the corpuscular current.

This is calculated, however, on the supposition that the corpuscular current moved parallel with
the surface of the earth in the auroral zone.

The matter, however, as we have shown at the conclusion of Article 36, is not so simple. In
order to know what kinetic energy should be ascribed to a corpuscular current that had the observed
magnetic effect upon the earth, we should need to have a complete mathematical solution of the manner
in which the rays from the sun would distribute themselves round the earth. Up to the present, indeed,
St0rmer has found the possible paths of the rays by numerical quadrature, and he may perhaps in time
succeed in finding a more complete solution, from which the above-mentioned magnetic effect might be
calculated. We will even now, however, make an attempt, by an estimate, to find out whether it is
possible that the corpuscular current which the sun emits from a sun-spot is so large as to indicate a
disintegration on the sun, which might account for the solar radiation of heat and light.

Let me say at the outset that in making certain, for the time being, purely computational assump-
tions, which yet may subsequently, at any rate in their aggregate effect on the result, prove to be more
or less correct, we come directly upon a value of the development of heat by disintegration per square
centimetre of the sun's surface, that is very near that which is deduced from the solar constant.

These assumptions, or estimates, are as follows.

In the first place it is assumed that the corpuscles issue at right angles to the sun's surface, and
that their density decreases inversely as the square of their distance from the sun.

In the second place it is assumed that as the corpuscles do not move parallel with the earth's sur-
face, but come in towards the earth more or less as shown in fig. 50 a & b, their kinetic energy is much
greater than calculated for the district between Kaafjord and Axeleen during the storms under considera-
tion; we assume 100 times greater.

In the third place we take it for granted that the quantity of rays that are drawn in towards the
polar regions of the earth, is not nearly so great as the quantity of rays that would have come into
contact with the earth if the latter had been non-magnetic. This we conclude from our terrella-experi-
ments. We there see distinctly that the more strongly the terrella is magnetised, the narrower does the
zone become, where the rays come in towards the terrella. And we see by the illumination that fewer
and fewer come in.

If our terrella were to be magnetised so powerfully that the conditions corresponded with those on
the earth, it would have to be immeasurably more magnetic than it is possible to make it (see "Expedi-
tion Norvegienne de 1899—1900", etc. p. 40).

We now assume that 100 times as many rays would fall upon the earth if it were non-magnetic,
as actually do so in the auroral zone.

By these assumptions we thus arrive at the fact that a corpuscular current, of which the energy
amounts to io13 horse-power, would have come into contact with the earth, if the latter had been non-
magnetic.

The last factor is perhaps rather large. On the other hand we have disregarded the fact that
only a portion of the rays that are eventually formed by the disintegration in the sun, succeed in
forcing their way into space; most of them will be absorbed into the solar atmosphere. Only the most
penetrating, most inflexible rays escape into space and reach the earth. If this were also taken into
consideration, it would perhaps compensate in the result for the possibly too high estimate of the above-
mentioned factor 100.

We found, then, that we could put the energy of the rays that would come into contact with the
earth, if the latter were non-magnetic, at io13 horse-power.

Birkeland. The Norwegian Aurora Polaris Expedition, 1903 — 1903.

314

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.

We will now imagine this amount of energy radiating from a sun-spot, and that the bundle of rays
is so large that the conditions, so far as the earth is concerned, are the same as if corpuscles were being
steadily emitted from the entire surface of the sun. We may mention that farther on, when explaining
other terrestrial-magnetic phenomena, we shall assume that corpuscles do continually radiate from the
whole of the sun's surface ; but they must be assumed to possess properties somewhat different to those
of the corpuscles that radiate from the sun-spots.

In our calculation we shall employ the same value for the earth's radius as in Article 36, namely
6366 kilometres, the radius of the earth's orbit is taken as 23,440 times that of the earth, and the radius
of the sun as 109 times that of the earth. The amount of energy that is emitted per square centimetre
from the sun's surface in the form of rays will then be

10

It

• • 7.36 X io9 = 2.7 X io9 ergs per second.

it • 63652 • io10 iog:
If we keep the same designations as before, we thus obtain

£ Nf.iv* = 2.j X io9,
in which, employing the same ft rays as before, we have the following values:

,U = 1.2 X IO-*7 (!)

v = 2-. 59 X io10.

Hence we find that

N = 6.7 X io1",

which is the number of ft particles that each square centimetre of the surface of the sun-spot would
per second.

Now i gramme of radium emits 7.3 X io10 ft particles per second, and at the same time gives ofl

100
3600

gramme-calories (2

We then obtain

6.7 X iolr' 100

7.3 X io10 3600

gr. calories, answering to about 14 h.-p.,

which is thus the amount of energy that is set free by a disintegration of the sun's matter, which would
answer to the quantity of rays emitted from it in the form of these corpuscular rays.

This amount corresponds, as already stated, to the amount of energy which the sun sends out ir
the form of light and heat. If the solar constant equals 3, we find a radiation from every square centi-
metre of the sun's surface of about 13 horse-power.

A disintegration such as this in the sun does not necessarily presuppose the presence there of
great quantities of radium, uranium, or thorium.

Rutherford, in his work entitled "Radio-Activity" (3), says :

"There seems to be every reason to suppose that the atomic energy of all the elements is of a
similar high order of magnitude. With the exception of their high atomic weights the radio-elements
do not possess any special chemical characteristics which differentiate them from the inactive elements.
The existence of a latent store of energy in the atoms is a necessary consequence of the modern view

I1) See Sir J. J. Thomson's "Corpuscular Theory of Matter", pp. 16 & 33 London, 1907.
f2) See E. Rutherford's "Radio-Activity", 2nd edition, pp. 436 & 474 Cambridge, 1905.
(8) I. c., p. 475.

PART I. ON MAGNETIC STORMS. CHAP. IV. 315

developed by J. J. Thomson (1), Larmor and Lorentz, of regarding the atom as a complicated structure
consisting of charged parts in rapid oscillatory or orbital motion in regard to one another".

Under the temperature-conditions prevailing in the sun, it is possible that ordinary matter may be
so radio-active, that it is not necessary to assume the presence in great quantities of the radio-elements
known in ordinary temperatures.

It was pointed out by Rutherford and Soddy (-), that the maintenance of the sun's heat for long
intervals of time did not present any fundamental difficulty, if a process of disintegration such as occurs
in the radio-elements were supposed to be taking place in the sun.

We may perhaps succeed, in the way here indicated, in obtaining a distinct idea of the amount of
heat that can be developed in the sun by disintegration ; and thus an important contribution will be made
to the solution of the old, and to natural philosophy so important, question of the origin of the sun's heat.

(') I see with great satisfaction that Sir J. J. Thomson, in his classic research on the nature of the cathode rays (Phil. Mag.
Number CCLXIX, October 1897), in which we find the first definite experimental evidence towards proving that the chemical
atom is not the smallest unit of matter, has taken as his starting-point my discovery that the magnetic deviation of cathode rays
depends only upon the tension between cathode and anode, if the magnetic force is constant. (See Birkeland, Compt. Rend.,
Sept. 28, 1896.) This theorem has been verified by Sir J. J. Thomson, 1. c., and W. Kaufmann, Wied. Ann. Vol. LXI.
No. 7, 1897.

(a) Phil. Mag., May, 1903.

PI. I

The Perturbation of the 6th October, 1902

Registerings from 13h 30m to 15h 3Qm, Gr. M. T.

R| &5 bx

tq KI ^

3

I
I

I

I

£
•2

I

itt q

•s

1

3

-5
^

^
^

4

C

I

I

|

pq

*

c

CM

O

I

^

53

PI. II

The Perturbations of the 11th October, 1902

Registerings from 12h on the llth to 2h on the 12»h, Gr. M. T.

of
w
n
o

H
O
O

u

d.
O

oo

iz;
O

U
OU

u

\

C4

O
05

PI. Ill

The Perturbation of the 23rd October, 1902

Registerings from l?h on the 23rd to 5h on the 24th, Gr. M. T.

CM

o
a*

m
o

r-

o
o

CO
CM

u

DC

fc
O

u

Ou

u
DC

PI. IV

The Perturbations of the 27th & 28th October, 1902

Registerings from 14h on the 27»h (O lh on the 28th, Gr. M. T.

PL V

The Perturbations of the 28th & 29th October, 1902

Registerings from 14h on the 28*h to lh on the 29»h, Gr. M. T.

PL VI

The Perturbations of the 29th and 30th October, 1902

Registerings from 161' on the 29th to 41' on the 30th , Gr. M. T.

THE PERTURBATIONS 0]

,ND 30th OCTOBER, 1902

PI. VII

The Perturbations of the 31st October and 1st November, 1902

Registerings from 6h on the 31st to 2h on the 1st, Gr. M. T.

The Perturbations of the

md 1st November, 1902.

20h 22h 24fl 2h

PI. VIII

The Perturbations of the 23rd and 24th November, 1902

Registerings from 15h on the 23rd to 7h on the 24th, Gr. M. T.

•

f

•

\

L

*

1

-I

PL IX

The Perturbations of the 9th December, 1902

Registerings from 51' to 18h , Gr. M. T.

K
U

pa
s
u
o
u

Q

u,
O

00

2

O

PQ

(K
D

U
OU

u

E

PI. X

The Perturbation of the 15th December, 1902

Registerings from 23h on the 14th to 5h on the 15th, Gr. M. T.

-I

$2

*
^

^
^

<

*s

t

4

^5

K?

^

4

I

8

I

C\J

o
OT

CM

,oX

X

•

Q_

PL XI

The Perturbation of the 25th December, 1902

Registerings from 23h on the 24*h to 5h on the 25th, Gr. M. T.

\

.-_-

-

->_

^

-«v

I

I

-

j

^v

1

j

^

•

^

i |

I
'

. - , -

•

-

_

:

.

^

9

1

*

•

,

\

j

1

•
1

'

I

i

\

1

\

'

'

•

'

CM

* 5

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THE PERTURBATION OF THE 28th DECEMBER, 1902.

PI. XIV

The Perturbation of the 26th January, 1903

Registerings from 7h to 15h, Gr. M. T.

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The Perturbation of the 15th February, 1903

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PI. XX

The Perturbations of the 22nd March, 1903

Registerings from 12h on the 22nd to lh on the 23rd, Gr. M. T.

PI. XXI

The Perturbations of the 31st March, 1903

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OU

THE NORWEGIAN

AURORA POLARIS EXPEDITION

1902-1903

VOLUME I

ON THE CAUSE OF MAGNETIC STORMS AND
THE ORIGIN OF TERRESTRIAL MAGNETISM

BY
KR. BIRKELAND

SECOND SECTION

THE NORWES1AH STATIONS
1902-1903

LEIPZIG

JOHANN AMBROSIUS BARTH

CHRISTIANIA

H. ASCHEHOUG & CO.

LONDON, NEW YORK

LONGMANS, GREEN & CO.

PARIS
C. KLINCKSIECK

CHRISTIANIA. A. W. BR0GGERS PRINTING OFFICE. 1913.

PREFACE.

Five years have gone by since the first Section of the present work, Volume I, was
published. In spite of uninterrupted and persevering labour, we have only now succeeded in
making Section II ready for publication.

The observations that formed our material were however exceedingly numerous, and the
questions that in the course of our work presented themselves for solution were of a somewhat
multifarious nature. The limits that were originally designed for Vol. I have therefore been over-
stepped, and the volume has been expanded to about double the compass at first intended.

The present section begins with the discussion of magnetic observations from 15 stations
of the well-known polar investigations of 1882—1883, by which my earlier results from obser-
vations from 25 stations in medium latitudes in 1902—1903, have received a most valuable com
plement.

As regards the conditions during the positive and negative polar storms, and particularly the
diurnal motion of the respective magnetic storm-centres, we have arrived at results that seem to
us so valuable, that they have fully rewarded us for the exertions and personal sacrifices that
the work has cost.

In order further to make it clear whether our results from the working-up of the above-
mentioned observations from the most varied parts of the world could be brought into theoretic
harmony with my previous assumptions, I have carried out a long series of experimental invest!
gations with a magnetic globe in a large vacuum-box intended for electric discharges. I have
hereby been enabled to obtain a representation of the way in which cathode-rays move singly,
and group themselves in crowds about a magnetic globe such as this. Special study has been
made of those crowds of rays that produce magnetic effects analogous to those observed upon
the earth during positive and negative polar storms.

Those who will go through the whole labyrinth that this concatenation of experiments
forms, cannot but be attracted by their scientific beauty; and in the end they will see that great
difficulties have resolved themselves into a surprising clearness.

I hold that I have demonstrated that the magnetic storms on the earth - the positive and
negative polar storms, and the positive and negative equatorial storms -- may be assumed to
have as their primary cause the precipitation towards the earth of helio-cathode rays, of which
the magnetic stiffness is so great that the product H.Q for them is most usually about 3 X 10°
C. O. S. units.

On account of the magnetic condition of the earth, these new solar beams which I have
discovered, will especially make their way towards the earth in the polar regions in the two
auroral zones, where they also certainly produce other effects which play an important part in
various meteorological phenomena.

SCHUSTER, in a later work, considers that from energy and from electrostatic considerations
alike, he can prove that even originally well-defined pencils of cathode rays from the sun cannot

IV

reach the earth. The existence of such pencils of rays was clearly presupposed to be necessary
to the theory as already formulated by me in 1899; and this assumption is now said to be
untenable.

From the results which are here produced, however, it will undoubtedly appear that there
must be a flaw somewhere or other in the reasoning of the distinguished natural philosopher;
for one is inclined to regard the descent of the above-mentioned pencils of rays to the earth as
an experimental fact.

I have also endeavoured, in Chapter VI, directly to demonstrate the points in which Schuster's
assumptions in no way admit of being applied to our case. I will here, moreover, with regard
to the electrostatic repulsion between our helio-cathode rays, refer to formulae by OLIVER HEAVISIDE.
In his Electrical Papers, Vol. II, Part III, p. 495, mathematical investigations are to be found of
electrically charged corpuscles in translatory motion, and from these it appears, on a discussion
of the formulae, that when the velocity of the corpuscles equals that of light, the electrostatic
repulsion between the rays maintains the balance with the electro-dynamic attraction. And as
regards our helio-cathode rays, their velocity, according to the theory, differs no more than a
hundred metres from that of light.

We find, with regard to these rays that the acceleration with which an electron is repelled
from the pencil of rays will not be what Schuster gives, but from the very first moment 3.3 million
times less. Subsequently this acceleration decreases with very great rapidity, in so far as the
longitudinal mass of the repulsed electron comes into play.

In a paper he has just published, HALE communicates some preliminary results on the
general magnetism of the sun, at which he has arrived by the aid of instruments and experi-
mental methods that are altogether admirable. He considers that the entire sun must be mag-
netic, with polarity like that of the earth, and with a vertical intensity at the poles of about
50 gausses.

These results seem at first sight to be quite irreconcilable with those in this work. If the
sun were perceptibly magnetic in the same manner as the earth, but with an intensity 70 times
as great, it is perfectly certain that no helio-cathode ray of the kind in question could ever reach
the earth.

Hale, however, is of opinion that the magnetism of the sun differs radically from that of
the earth.

It seems to me that the phenomena observed by Hale might be explained as the effects
produced by invisible spots, or by the pores, considered as electric vortices, notwithstanding
all the reasons that Hale adduces against such an assumption.

In a note to the Comptes Rendus de 1'Academie des Sciences, Paris, Aug. 25, 1913, I have
given the reasons that favour my view.

The experimental investigations which at first were designed to procure analogies capable
of explaining phenomena on the earth, such as aurora and magnetic disturbances, were subse-
quently extended, as was only natural, with the object of procuring information as to the con-
ditions under which the emission of the assumed helio-cathode rays from the sun might be
supposed to take place.

The magnetic globe was then made the cathode in the vacuum-box, and experiments were
carried on under these conditions for many years.

It was in this way that there gradually appeared experimental analogies to various cosmic
phenomena, such as zodiacal light, Saturn's rings, sun-spots and spiral nebulae.

V

The consequence was that attempts were made to knit together all these new discoveries
and hypotheses into one cosmogonic theory, in which solar systems and the formation of galactic
systems are discussed perhaps rather more from electromagnetic points of view than from the
theory of gravitation.

One of the most peculiar features of this cosmogony is that space beyond the heavenly
bodies is assumed to be filled with flying atoms and corpuscles of all kinds in such density
that the aggregate mass of the heavenly bodies within a limited, very large space would be only
a very small fraction of the aggregate mass of the flying atoms there.

And we imagine that an average equilibrium exists in infinite space, between disintegration
of the heavenly bodies on the one hand, and gathering and condensation of flying corpusles on
the other.

I cannot conclude this great work without expressing my warmest thanks to my numerous
assistants for their most able collaboration. If I mention them according to the number of years
in which they have faithfully helped me, I must begin with my good old friend, now dead,
schoolmaster DIETRICHSON, who for ten years continued to work every day at my side. In the
next place there are some young, energetic men, a few of whom have already begun independent
work - Mr. KROONESS, now manager of the Haldde Observatory, Mr. VEGARD, now a tutor at
our university, Mr. SKOLEM, a very skilful mathematician, and Mr. DEVIK, a capital experimenter.
Further Captain BULL, of the Norwegian Navy, and Mr. NORBY, have done a large amount of
calculation, and Mr. NATRUD and Mr. B. TOLSTAD, assistants at the Norwegian Geographical
Survey, have made many drawings. The translation of also the whole of this volume has been
done very satisfactorily by Miss JESSIE MUIR.

Christiania; September, 1913.

Kr. Birkeland.

CONTENTS.

PART II.

POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS.

CHAPTER I.
POLAR MAGNETIC STORMS 1882—1883.

Page

Art. 81. The Treatment of the Observations from the Polar Expedition of 1882 & 1883 . . . 319

„ 82, 83. The Perturbation of the 15th January, 1883 323

„ 84. The Perturbations of the 2nd January, 1883 339

„ 85. The Perturbations of the ist November, 1882 350

„ 86. The Perturbations of the I4th and I5th February, 1883 361

„ 87. The Perturbations of the I5th July, 1883 371

„ 88. The Perturbations of the ist February, 1883 386

„ 89. The Perturbations of the isth December, 1882 397

„ 90. The Perturbations of the I5th October, 1882 412

CHAPTER II.

MATHEMATICAL INVESTIGATIONS. PRELIMINARY RESUME.

„ 91. The Calculation of the Field of Force for the assumed Polar Current-System .... 423

,, 92. Resume 439

„ 93. A Possible Connection between Magnetic and Meteorologic Phenomena 449

CHAPTER III.

STATISTICAL TREATMENT OF MAGNETIC DISTURBANCES OBSERVED AT THE
NORWEGIAN STATIONS 1902—1903.

„ 94. Introductory 451

„ 95. The Total Storminess as a Function of Time and its Relation to Solar Activity . . . 517

„ 96. On the Possible Influence of the Moon upon Magnetic Storms 519

,, 97. The Seat of the Radiant Source 521

„ 98. Sun-Spots and Storminess 524

„ 99. Annual Variation of Storminess 526

„ 100. On the Diurnal Distribution of Storminess .' 536

„ 101. Positive and Negative Storminess 536

„ 102. P and N Storminess 537

„ 103. Properties of the «Average Polar Storm» 53^

„ 104. Comparison of Storminess at the four Stations 541

,, 105. Separation of Great and Small Disturbances 546

„ 106. The Distribution of Storminess and the Solar Origin of Polar Storms 547

,, 107. Application to Theory 55*

VIII

CHAPTER IV.

EXPERIMENTS MADE WITH THE TERRELLA WITH THE SPECIAL PURPOSE
OF FINDING AN EXPLANATION OF THE ORIGIN OF THE

POSITIVE AND NEGATIVE POLAR STORMS. Page

Art. 108. Introductory 553

STUDY OF RAYS OF GROUP A.

,, 109. Experiment in which the Terrella had only a Vertical Screen 560

„ no. Experiments in which the Terrella is surrounded by a Horizontal Screen 566

„ in. Equatorial Rings of Light 569

STUDY OF RAYS OF GROUP B.

„ 112. The Course of the Rays in the Polar Regions over the Terrella 572

„ 113. Experiments for determining the Tangential Component of the Polar Precipitation in Relation

to the Surface of the Terrella 580

„ 114. On an Intimate Connection between Rays of the two Groups A and B 583

,, 115. On the Size of the Polar Ring of Precipitation 591

„ 116. The Value of H . Q for the Helio-Cathode Rays 598

„ 117. Experiments for the Determination of the Situation of the Polar Zone of Precipitation in

Various Positions of the Magnetic Axis 600

„ 1 1 8. Investigations Regarding the Angle formed by the Precipitated Rays with the Magnetic

Lines of Force. Application to the Polar Aurora 603

CHAPTER V.

IS IT POSSIBLE TO EXPLAIN ZODIACAL LIGHT, COMETS' TAILS, AND
SATURN'S RING BY MEANS OF CORPUSCULAR RAYS?

,, 119, 120, 121. Zodiacal Light 611

„ 122. Appendix. Expedition to Assouan and Omdurman 624

„ 123. Magnetic Registerings, the 9th April, 1911 629

„ 124. Comets' Tails . . 631

„ 125. Halley's Comet, May, 1910 639

„ 126. Meteorological Observations about the Time of the Transit of Halley's Comet, 1910 . . 647

,, 127. The Saturnian Ring 654

CHAPTER VI.
ON POSSIBLE ELECTRIC PHENOMENA IN SOLAR SYSTEMS AND NEBULAE.

„ 128. The Sun 661

„ 129. Experiments showing Analogies to Solar Phenomena 662

„ 130. Application of the Analogies to further Study of Celestial Phenomena 670

„ 131. The Worlds in the Universe 677

„ 132. Investigations of the Motion of Electric Corpuscles in the Field of an Elementary Magnet

especially to find the Conditions for the Approach to Boundary-Circles 678

„ 133. Study of the Approach to Boundary Circles, when there is a Resistance in the Medium 686

,, 134. Study of the Approach to Boundary-Circles, when the Charge of the Particles is variable 693

n I35- Study of the Approach to Boundary-Circles outside the Magnetic Equatorial Plane . . . 697

„ 136. Comparison of Boundary-Circles approached by Different Sorts of Corpuscles .... 706

,, 137. Experiments made with the largest Vacuum-box with a Capacity of 1000 Litres . . . 709

„ 138. On the Charge of Metallic Particles ejected from a Cathode 716

,, 139. On the Possible Density of flying Corpuscles in Space 720

IX

PART III.
EARTH CURRENTS AND EARTH MAGNETISM.

CHAPTER I.
EARTH CURRENTS AND THEIR RELATION TO CERTAIN TERRESTRIAL

MAGNETIC PHENOMENA. Page

Art. 140. Introduction . 725

„ 141. Strength and Distribution of Earth-Currents 728

„ 142. Diurnal Variation of Earth-Currents 729

,, 143. Earth-Currents and Magnetic Disturbances 730

„ 144. Earth-Current Registerings at Kaafjord and Bossekop, 1902 — 1903 731

,, 145. Constants for the Experimental Arrangements 734

„ 146. The Magnetic Effect of Earth-Currents 736

,, 147. On the Connection between Polar Storms and Earth-Currents 741

„ 148. Earth-Currents and Positive Equatorial Perturbations 746

,, 149. On the Simultaneity of Earth-Currents and Magnetic Disturbances 746

„ 150. Earth-Currents at Bossekop 748

„ 151. The Influence of the Earth- Current upon the Vertical Intensity 749

,, 152. Observations of Earth-Currents at Kaafjord, May, 1910 751

» J53- Theoretical Investigation of the Currents that are Induced in a Sphere by Variation of

External Current-Systems 757

„ 154. Numerical Calculation of the Currents 768

,, 155. Currents that are Induced by Rotation or Removal of the Systems 779

„ 156. Earth-currents in Lower Latitudes 784

,, 157. Earth-currents in Germany 784

,, 158. Earth-currents in France . 788

„ 159. Earth-currents in England 791

,, 1 60. Earth-currents at Pawlowsk 792

,, 161. Comparison of Simultaneous Earth-Current Observations 793

„ 162. Consideration of the Conditions during Positive Equatorial Storms 794

„ 163. The Diurnal Variation of the Earth-Currents 796

X

11 XXII.

Tl

11 XXI 11.

Tl

11 XXIV.

Tl

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11 XXVI.

Tl

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Tl

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T

11 XXX.

K;

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F,

PL XXXII.

K;

PI. XXXIII.

K;

PI. XXXIV.

!•:

11 XXXV.

F;

11 XXXVI.

K;

11 XXXV11.

F.;

11 XXXVIII.

K;

11 XXXIX.

K;

11 XL.

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F,

11 XI. 11.

K

PLATES.

i 5th ( Ictober, 1882.

ist Xoveinber, 1882.

i 5th I)eci mber, 1882.

2nd January, [883.

i 5th lanuarv, 1 883.

ist Februarv, 1883.

i |.th and 1 5th February, 1883.

i 5th July, 1883.

tie elements. Seric
Serie

Seric
Seriu

Serie

I. Kaafjurd.

II. Kaatjord.

II continued. Kaaljord and Bossekop.

II continued. Bossekop.

III. Kaaljord

III continued. Bossekop.

6 also France and Fntrland

element

element-
element

element
elements. Sel'i,

element- from (iennanv tor Nov. 5

, •lenient- from ( ireemvieh.

elem-uts from Pare St. Maur and (ireemvich.

element- troni Pare St. Maur.

elements from P.u'c St. Maur.

elements Iron) I 'arc St. Maur and ( ireemvich.

element- from ( ireemvich and Pare St. Maur.

ERRATA.

I'.IL;I- 616, line 9 1'roltl l)i'ln\\-; l'"n]-

- 670, line 17 troin bi-lo\v: I'oi- th' Ai'ticlmuinbcr 129, read 130.

H — " , read () > fl > -

PART II.

POLAR MAGNETIC PHENOMENA AND TERRELLA

EXPERIMENTS.

CHAPTER I.
POLAR MAGNETIC STORMS 1882—1883.

81. The Treatment of the Observations from the Polar Expeditions of 1882 & 1883.

In the discussion of the magnetic storms in Part I, it was frequently pointed out that we obtained
only an imperfect knowledge of the conditions round the auroral zone, owing to the fact that,
with the exception of our four arctic stations, all the stations from which we had observations were in
southern latitudes. We have frequently drawn conclusions as to how the phenomena up there might
naturally be assumed to have developed, if the perturbation-areas that appeared in southern latitudes
could be explained by the previously-mentioned simple points of view.

We will therefore, in this part of our work, subject these conditions to a closer study, and will
then be able to see whether the actual conditions round the auroral zone prove to be in accordance
with our previous conclusions.

It is the polar storms in particular that will make an interesting subject of study; and it will then
be especially necessary to investigate the movement and formation of the various systems of precipitation
in the course of the twenty-four hours.

It will be remembered that in the compound storms of 1902 — 03, we arrived at a very simple
interpretation of the occurrence of the polar storms, and of the changes in their main features. This
interpretation we now have the opportunity of verifying, and even supplementing on various points. We
will here recall to the reader's mind the more important of the main features.

In the first place, we divided the polar storms into two kinds, namely, the negative polar storms,
during which we found negative values of PI,, in the district of precipitation round the auroral zone, and
the positive polar storms, during which we found positive values of PI, in the district of precipitation
(see Art. 69. Part I).

The negative storms had, as a rule, an extensive area of precipitation on the night-side of the earth,
and also on the day-side in high latitudes (Axeleen). The positive storms had a more limited district of
precipitation, and as a rule appeared on the afternoon-side of the earth.

It further appeared that during the great magnetic storms, these areas of precipitation seemed to
move, the movement to some extent following the sun in its apparent daily course round the earth, and
being dependent upon the sun's change of altitude above the magnetic equator (see Art. 71, Part I).

In the material we are now going to study, these conditions can be investigated far more thoroughly.
In the reports of the international polar expeditions of 1882 and 1883, we have a material carefully
worked up, that will prove to be of the greatest interest to us in this study. It is the term-days observa-
tions that are of special importance for our purpose. We have at our disposal observations from ten
stations scattered round the auroral zone, namely, Godthaab, Kingua Fjord, Fort Rae, Uglaamie (Point
Barrow), Ssagastyr, Little Karmakul, Sodankyla, Bossekop, Cape Thordsen and Jan Mayen, and also
from Fort Conger, a station situated in the vicinity of the magnetic axis of the earth, and from some
more southerly stations, four of which have been employed, namely, Christiania, Pawlowsk, Gottingen
and Kasan.

320 BIRKELAND. THK NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

The method employed in the working-up, is exactly analogous to that used with the observations
from 1902 and 1903, except that here, instead of registerings we have readings of the magnetic elements
for every fifth minute.

The variation in these elements, in the case of a number of stations, is represented graphically in
the respective publications, and for stations where this is not already done, we have ourselves drawn
the magnetic variation curves. The same hour-length is employed throughout, namely, 15 mm. per hour,
whereas the scale for the deviations varies somewhat from place to place, according to the amplitude of
the oscillations.

These curves are placed under one another in plates, thereby affording a clear view of the course
of the perturbations from station to station. These plates in reduced size will be found at the end of
this section. Further, the perturbing forces are calculated for a series of points of time, these beinj.
represented on a polar chart by current-arrows in precisely the same manner as before. In this con-
nection, however, it should be remarked that in calculating Pd, it is the value of H existing at the
moment, that has to be employed but during the powerful storms this value may vary so considerably
that the same value of H cannot be used for the whole perturbation, and a correction must be intrc
duced. This correction is always evident during the powerful storms that take place in the regions here
studied. Z./,°° is given in the plates for the value of H, which answers to the normal line. During
powerful storms in H, therefore, direct use cannot be made of this, if fairly great accuracy is desired;
but as a rule the error will not be very great. For this reason, the values of Pd that we find at Fort
Conger during powerful storms will be somewhat uncertain, as we there have only absolute observations
of H to go upon. This is of little significance, however, in our studies.

The scale of the arrows on the charts is given, and, as will be seen, is generally about five times
that employed in the previous observations. By this means the current-arrows at the polar stations are
of a suitable size, while at the southern stations another scale must be used. This is indicated by thtre
adding |, f , and so on, which means that the scale employed is f , f , etc. of the general given one.
This is a reversal of our former plan of introducing the factors £, f , etc. at the polar stations in order
to indicate the local scale there in each case.

On most of the charts here, moreover, there are several sets of current-arrows for one series of
generally as many as three different points of time. Instead of vertical arrows, which are found upon
the charts on which only one point of time is marked, a little table is here placed beside the station,
giving the corresponding values of P,. A similar table is given for P^ at Fort Conger, where only
term-days observations of the declination were carried out. Further, the magnetic meridian of that place
is indicated, and an idea is thus obtained of the direction, and to some extent of the magnitude of the
perturbing force at the various times. A powerful westerly-directed perturbing force in D thus corres-
ponds to a current-arrow directed westwards, more or less NW or SW, according as the perturbing
force in H might be more or less powerful, positive or negative. It will be seen that the magnetic
meridian and the geographical meridian at this place are nearly at right angles to one another, so that
a westerly-directed perturbing force as regards the magnetic meridian, answers to a perturbing force
directed southwards. If, on the other hand, Pj is only small, there is either, if PI, is also small, only a
small current-arrow, or, if PI, is fairly large, a current-arrow directed northwards or southwards. In this
way it is possible to make use of these observations.

For the calculation of the perturbing forces, it is necessary to have a more or less accurate know-
ledge of the diurnal variation. By the diurnal variation must be understood the variation that there
would have been in the magnetic elements, if there had been no perturbations, in other words, if the
day had been a 'quiet day'. The diurnal variation, however, in the case of certain stations, has been
calculated as the mean of all the observations in a certain space of time. The results found therefrom,

PART II. POLAR MAGNETIC PHENOMENA AND TERREU.A EXPERIMENTS. CHAP. (. 321

however, arc useless in this connection, just because the perturbing forces themselves then come into
the diurnal variation, and it was these we wanted to eliminate. By taking a sufficient number of obser-
vations, it might be thought that the perturbing forces would be eliminated, as the oscillations would
possibly be as frequent to one side as to the other; but this is not the case. The oscillations, when
they occur, generally have a definite direction for every distinct time of day. Perturbations, for instance,
that occur about midnight, local time, at most of the polar stations, in horizontal intensity, will almost
exclusively show negative values of Ph. By the addition of all the values, too low a mean value of H
will therefore be found here. If we would use such a determination, perturbing forces would often be
found, for instance, at times when the conditions were quite normal.

At several stations, however, the diurnal variation has been calculated exclusively from observations
on quiet days. If the days used in these calculations really were 'quiet' we might apply these determi-
nations. A quiet day in the Polar regions is, however, a very rare occurrence, and in most cases, on
the majority of the 'quiet' days made use of, deviations having the character of minor perturbations occur.
When these perturbations are not eliminated, the result would not always be applicable to our purpose.

For us, in the calculation of the perturbing forces, the best means of obtaining an approx-
imately accurate determination of the diurnal variation on the day in question is, by means of the
hourly observations made daily at the various stations, to draw the magnetic curves for the nearest
quiet days before and after the fixed day; by comparing these we can draw a normal line, that is in
correspondence with only the quiet parts of the curves, from which consequently the perturbations are
eliminated. This is the method that has mainly been followed.

In Kingua Fjord not a single really quiet day is to be had, especially in the afternoon, Greenwich
time ; the conditions are always more or less disturbed. In the forenoon, however, the conditions are
very often fairly undisturbed. From the most quiet days found in the material, it seems, however, to
become clear, that the diurnal variation in the afternoon is but small, and that consequently the disturbed
conditions here must be regarded as perturbations. As normal line, we have therefore here drawn a
fairly straight line, and as the variations as a rule are somewhat considerable, the error in the position
of the normal line will be of less importance.

This circumstance, that magnetic perturbations occur much more frequently at this station than at
the other polar stations, is a fact of very great importance for our theory, and we will return to this
later on.

At the stations where the hourly observations have not been taken, namely, Christiania, Gottingen,
and Kasan, the determination of the diurnal variation becomes considerably more difficult and to some
extent rather uncertain. We here have only the more or less quiet term-days to go upon, in addition
to the comparisons we can draw with observations of recent years and adjacent stations. The determi-
nation of the normal line at these two stations may therefore sometimes be somewhat arbitrary, espe-
cially in the case of the vertical intensity of Gottingen, where it has occasionally been impossible to
make any determination.

On the whole we may remark, that the diurnal variations that we have used must of course not
be regarded as entirely correct, when the oscillations attain a certain amplitude, however, the uncer-
tainty in the normal line is of smaller significance.

With regard to the vertical intensity, the observations are often a little unreliable, and it may
perhaps be doubtful on the whole whether any conclusions at all may be drawn from these observations,
especially in the case of those stations at which the method employed was that of induction in bars of
soft iron.

We have thus made no use of the vertical intensity observations from Ssagastyr, as the perturbing
forces constantly appearing there are of an altogether different order of magnitude to that which we find

322

BIKKELANI). THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903.

at the other polar stations, whereas the agreement in the horizontal elements is very close. In Sodan-
kyla too, the perturbing forces taken from the observations of vertical intensity, are often apparently
abnormal compared with the conditions at the stations situated in the vicinity of that station.

As stated in Art. 23 the map-projection employed for our polar chart is not orthomorphic. The
deformation is not great, however, but yet sufficiently so, especially at the southern stations, to be taken
into consideration in the placing of the current-arrows. These are thus not placed at the angle which
they form on the earth with for instance the geographical east and west, but at a rather smaller angle.
The amount by which this angle (v) is reduced has been calculated for two or three latitudes, the result
being given in the following table :

TABLE XLIX.

V

0°

i5°

3°°

45°

60°

75°

90°

Gottingen

0

i°3'

i°5i'

S° 13'

i°56'

i°8'

o

60 ° N. Lat.

o

39'

i°8'

I°I9'

1° 10'

40'

o

70 " N. Lat.

o

17'

3°'

35'

8*'

17'

o

In these charts also we have indicated the position of the sun and the moon. Their signs (Q and
©) are placed in the margin of the chart, that for the sun on the noon meridian, that for the moon on
the meridian that it is crossing at the moment under consideration. The point in which the magnetic
axis intersects the surface of the earth, has been calculated for the beginning of 1883 as situated in lati-
tude 78°2o'N., and longitude 68°49'W(').

In the preceding observations, Greenwich mean time has been employed throughout, and it will also
be used now in order to facilitate comparison.

In the observations of which we make use, everything relating to the fixed days is given ac-
cording to Gottingen mean time, and we have therefore effected the necessary reduction all through.
The difference in time between these two places amounts to oh 39m, 8, or in round numbers to oh 4Om,

•

the latter being the figure we have employed. Lastly, the hours, as before, are counted from o to 24,
12 answering to Greenwich mean noon.

With regard to the arrangement of the perturbations, we have used the same method as previ-
ously; first treating of the days on which the simplest and most perspicuous conditions of perturbation
prevail — those on which the typical phenomena are most prominent. The more complicated phenomena
are dealt with later.

Amongst the disturbances we find here, is also an equatorial one, but, as it is the polar distur-
bances that interest us most, this perturbation is noticed amongst the last.

The plates of the curves are, on the other hand, arranged in chronologic order.

In conclusion, we give a table of the perturbations in the order in which they are described.

(') V. Carlheim Gyllenskold, "Note sur le Potentiel Magnetique de la Terre exprime en Fonction du Temps". Arkiv for
matematik, astronomi och fysik. Vol. 3, No. 7. Upsala 1906.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I.

TABLE L.

323

No. of
Perturbation

Date

No. of Plate

ai

January 15, 1883

XXVI

22

January a, 1883

XXV

=3

November i, 1882

XXIII

24

February 14/15, 1883

XXVIII

25

July 15, 1883

XXIX

26

February i, 1883

XXVII

27

December 15, i88a

XXIV

28

October 15, i88a

XXII

THE PERTURBATION OF THE 15th JANUARY, 1883.
(PI. XXVI).

82. The part of this day, which we now intend to study, is, as the Plate shows, that between ioh
and 23h 2om Gr. M. T., the latter hour corresponding with 24h Gottingen mean time, at which point of
time the observations on this term day cease.

The first glance at the Plate shows us that during this period a number of characteristic, well-
defined and more or less powerful storms occur at the various stations.

A closer examination shows that these storms would naturally be divided into several groups.

In the first place we find in the period from iob to about I4h a fairly well defined group of toler-
ably powerful perturbations. Before and after it, the conditions are more or less quiet at all the stations.
The curves moreover indicate that for this period the perturbation-area can be divided into two parts,
(i) the regions of Kingua Fjord, Fort Rae and Uglaamie, (2) Little Karmakul and Ssagastyr.

In (i), Kingua Fjord, Fort Rae and Uglaamie, it is evident that there is a negative polar storm
with its centre in the neighbourhood of Fort Rae, where the deflections on the whole are greatest.

In (2), Little Karmakul and Ssagastyr, we distinctly see the effects of a positive polar storm.
The forces are considerably more powerful at Ssagastyr than at Little Karmakul (note the values of e\t
at the two stations), and the storm-centre of this positive storm must thus be assumed to lie nearer the
former station than the latter.

It is difficult to prove with certainty the existence of any distinct movement in these systems dur-
ing this period, at any rate by only a direct consideration of the curves. The perturbation begins a
little earlier at Fort Rae that in Kingua Fjord and at Uglaamie. If we look at the close of the pertur-
bation, we find that the deflection in H lasts a little longer at Fort Rae than at the other two stations;
whereas in D the deflections last longest in Kingua Fjord. It is difficult, however, to draw any con-
clusion from this.

Nor it is easy to find any distinct movement in the other system of precipitation. The deflections
begin more or less simultaneously at the two stations, and then increase fairly evenly. To a certain
extent we may speak of two maxima, the second of these being considerably greater at Little Karmakul
than the first, a circumstance which may possibly indicate that a removal of the storm-centre actually
takes place westwards towards this station. At Ssagastyr, however, the storm lasts a little longer than
at Little Karmakul; but no conclusion can be drawn from this fact, as the conditions at Cape Thordsen
are rather peculiar, and will probably exert an influence at Little Karmakul.

If we look at the conditions at Cape Thordsen during this period, we see that the curve for the
horizontal intensity is very peculiar, first of all showing positive values of /-*/,, then negative values,

324 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

and finally positive values once more. It seems evident that we here have before us the effects of a
negative storm, which during the interval from iah to I4h, encroaches upon a positive storm of longer
duration, and that from 12'' 50™ to 13^ 50™ the effect of this negative storm is the strongest, so that
negative values of PI, are found. This view seems to receive support from the conditions in declination,
where, from I2h to I4h, there occurs a clearly defined deflection.

If we continue to follow the series of polar stations, we find during this period practically no per-
turbation at Bossekop and Sodankyla, nor is there any deflection in Jan Mayen until the end of the
period under consideration, when a new positive storm begins there, with a very well-formed and
clearly-defined deflection, during the period from 13'' to 16'' 4om. The defining of the first section, which
we have previously undertaken, is thus not suitable for this station.

At Fort Conger also, there occurs a deflection which bears no small resemblance to the deflection
in the horizontal-intensity curve in Kingua Fjord; only in this case the perturbing forces are small. At
the southern stations there are no perturbing forces of any strength during this period.

It may be as well here, in connection with these conditions, which are read directly from the
copies of the curves, to consider at once the area of perturbation, as represented in Chart I and II
for the hours //'' 2om, u1' jom, I2k 20™, 12*' jo"' and ijh 2om, Gr. M. T.

The two characteristic areas of precipitation described above, the negative in the north of America,
and the positive in the north of Asia and to some extent also in Europe, are here very distinctly seen.
At first it is only the negative system that has a marked effect, and its storm-centre appears to be
situated in the vicinity of Fort Rae. At Uglaamie, during this first part of the time, the current-arrow
has an easterly direction, the reverse of that which we find subsequently. It is as though we had before
us the effects of a positive polar storm, and this may possibly be the case; but if so, it is very ill-
defined, and this makes it impossible to decide the question with any certainty. At the succeeding hours
moreover the current-arrow at this station swings round anti-clockwise, and remains directed westwards
during the remainder of this first section which we are now considering. We may perhaps be justified
in taking these conditions as a proof of a movement of the systems of precipitation in a westerly direction.

At the other stations situated in the vicinity of the areas of precipitation, the current-arrows
increase more or less evenly, so that at the last of the hours of observation they attain their greatest
strength, and the areas undergo no great changes. A quite distinct impression of a westerly movement
in the positive precipitation area will be obtained by comparing the Chart II for I2h 30™ with the two
last times on Chart I. On Chart I I2h 2om it is only at Ssagastyr that the positive storm occurs with
considerable violence, in Little Karmakul the perturbating force is still comparatively insignificant. At
I2h 5om, on Chart II, also in Little Karmakul, a somewhat powerful perturbating force occurs. The
strength is, however, as yet greatest in Ssagastyr, but at 13'* 2om, as we see from Chart I, the
strength of the perturbing forces is about equal at these two stations. The centre of the storm seems
thus constantly to move westwards.

At Cape Thordsen only do we see the current-arrow turning clockwise in accordance with the
peculiar conditions that we have just described.

According to what we have seen in Part I, the positive polar storm will now, in lower latitudes,
produce an area of divergence.

With regard to the conditions in lower latitudes, we find only small perturbing forces at the first
three hours of observation; but at 13'' 2om, the forces have increased to no small extent; and the shape
of the western portion of an area of divergence is now actually recognised.

We will finally also draw attention to the agreement that we find between this and our previous
results, namely, that the negative area of precipitation is formed upon the night and morning side, while
the positive system is formed upon the afternoon and evening side.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 325

In conclusion, we must also consider the values that we find of P,. These, as we have said, will
sometimes be rather uncertain, inter alia on account of the construction of the measuring apparatus;
and we must therefore be careful not to think we can draw definite conclusions, especially where there
are only slight deflections.

At Fort Rae, as we see, there are all this time positive values of Pv, which would thus imply that
the main body of the current-system was situated slightly to the south of this station. At Uglaamie, on
the other hand, negative forces first appear in the vertical intensity. When the horizontal current-arrow
has assumed the more constant westerly direction, the vertical curve goes over to the opposite side,
and the positive deflections then last for the remainder of the period under consideration.

Also on looking at P,, it seems thus, as though at first there were perturbing forces of a more
local character at Uglaamie.

At Little Karmakul, the positive values of P, indicate that the positive system of precipitation must
lie a little to the north of the place.

We will now pass on to consider the conditions that develop after the conclusion of this first period.

It would be quite possible, in the succeeding part of the term day also, to mark off several divisions;
but such a marking-off would scarcely be advisable, as the perturbation-conditions, as a whole, are all
the time undergoing a more or less continuous change.

Here, as in the preceding section, the perturbations admit of being arranged in two groups. On
the one side we have a negative polar storm, on the other side a positive.

We will first consider the negative storm. This occurs, as will be seen from the plates, in the
district about Kingua Fjord, Fort Rae, Uglaamie and Ssagastyr, and furthermore at Cape Thordsen and
Fort Conger. In the preceding section, however, the storm-centre was in the vicinity of Fort Rae; and
now the perturbing forces there are considerable weaker than at the other stations.

The storm-centre thus seems to have moved. In the first part of this last section, the most powerful
perturbing forces seem to be concentrated upon the districts about Uglaamie and Ssagastyr; but this
condition is not very apparent, as the forces round the auroral zone at these stations rarely vary much
in magnitude.

Later however - - at about 20h or aih — there is a distinctly defined storm-centre at Cape
Thordsen. At the other stations, where the negative storm occurred before, the perturbations at this
hour are practically over.

It thus seems as if we here had a distinct westward movement of the negative storm-areas.

There next occurs, as already mentioned, a positive polar storm, but in a much more limited area
than the negative, judging at any rate by the stations from which we have observations.

We stated in the ' preceding section, that at the conclusion in Jan Mayen, a positive polar storm
began. In the present section, this positive storm developes greatly, and forms a system of precipitation,
which at first extends from Godthaab eastwards to the regions near Little Karmakul, but is afterwards
concentrated more upon the regions about Bossekop.

These are conditions which are immediately apparent from the curves. Judging from the deflec-
tions in the horizontal-intensity curves for Jan Mayen and Bossekop, it would appear that the storm-
centre during this period, after lying in the vicinity of Jan Mayen while the storm is comparatively less
powerful, has subsequently moved eastwards to Bossekop, the storm, at the same time, attaining its
greatest strength. Whether the conditions do actually develope in this way, it is impossible to deter-
mine merely by the aid of the observations from these two stations, seeing that magnetically considered,
Jan Mayen lies considerably farther north than Bossekop. Observations from the southern border of the
auroral zone would here have been of great importance.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903.

226 B1RKKI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

The great difference in the effects of the force at Bossekop and Sodankyla is characteristic. At
the latter station the forces are on an average only about one quarter of those at Bossekop. As these
stations are situated very near to one another, it may be concluded that the acting systems come fairly
close to the last-named.

The conditions at Little Karmakul during this period are particularly interesting and peculiar. This
station is situated, as will be seen, upon the boundary between the two districts of precipitation ; to the
east and north we come upon the negative polar storm, to the west there is the positive. It would
therefore be natural to suppose that at this boundary-station, both these systems would act; and this
proves to be actually the case.

In both the areas of precipitation, the positive as well as the negative, the deflections in horizontal
intensity continue to be in one direction as long as the storm lasts. At Little Karmakul, on the other
hand, the conditions are different; at one time there are wide deflections in the positive direction, at
another wide deflections in the negative direction, and again smaller deflections up and down about the
normal line. It thus appears from a direct consideration of the curves, that we now have a direct effect
of the positive system, and then of the negative, and now again the two systems neutralise one an-
other's effect.

Altogether analogous, although less marked, conditions are found in Jan Mayen, where at first the
positive system acts almost exclusively, then mainly the negative, but only in a series of brief impulses,
after which the horizontal-intensity curve returns once more to its normal height. As regards declination
the conditions are somewhat similar; but there it is not possible to determine so directly which system
it is that is acting at the various times.

At about 23'', the perturbations are ended at almost all the stations, and after that time it is only
at two or three places that perturbing forces of any special magnitude appear, and these should pro-
bably be regarded as more local.

Six charts have been drawn up for this period, representing in all 17 epochs, by means of which
the course of the perturbations may be followed from hour to hour.

Similar fields in the main are found upon the various charts, only displaced to some extent from
time to time.

Chart III; time 14'' 20'", //'' 2om and i&> 20m.

At the first-named hour there are more or less powerful forces only in the district about Jan
Mayen, Cape Thordsen and Ssagastyr; and the current-arrows there are directed eastwards. It is impos-
sible to decide from the charts whether this is a connected system or not. The curves seem to indi- '
cate, however, that it can scarcely be an entirely connected system.

Nor has the perturbation developed any special power at 15'' 2om; and at Ssagastyr, and Cape
Thordsen, the earlier perturbing forces have almost entirely disappeared. In Jan Mayen only is there
still the effect of the positive system.

It may even now be worth while to notice the conditions at Godthaab and Kingua Fjord. At these
two stations we now have arrows that point in exactly the opposite direction; at one place a positive
storm is evidently acting, at the other a negative, and it would thus seem as if the boundary between
two such tracts just chanced to be between the two stations. This is a condition with which we shall
subsequently frequently meet, and which we therefore at once point out.

We thus again meet a peculiarity in the state of things in Kingua Fjord, and further on we will
have an opportunity of also coining in contact with other cases diverging somewhat from what we find
at the other stations. It might therefore be well to examine here at once what might be supposed to
be the natural reason.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP.

327

When we have hitherto considered the polar storms, the conditions of the horizontal intensity
have always been of the greatest importance, as the direction of the current-arrows was either pointing
eastwards or westwards.

This is, however, not always the case as regards Kingua Fjord; on the contrary, it is in the decli-
nations that the strongest forces frequently are shown, and the direction of the current-arrows is very
frequently pointed pretty nearly due south.

These somewhat peculiar conditions are surely connected with the northerly situation, as regards
magnetic conditions, of this station compared to the others with the exception of Fort Conger.

We will here refer to the terrella experiments, which will be more fully dealt with in a sub-
sequent chapter. In order to elucidate the subject, we will however here give a copy of a photograph,
Fig. 140.

Fig. 140.

In most of the illustrations hitherto given, the terrella has been suspended on an axis, the position
of which has corresponded with that of the earth, thus forming an angle with the terrellas magnetic
axis of about 20°.

As this however gave a less easily seen representation of the entire polar area of precipitation,
the terrella is here suspended on an axis in the magnetic equatorial plane. The position of the electrode
can be thus altered as desired by turning the terrella on the axis on which it hangs and thus produce
some positions which should -correspond to various positions of the earth in relation to the sun.

In the experiment corresponding with the three above given photographs, the cathode is placed in
the magnetic equator of the terrella and thus answers to the times when the direction from the earth to
the sun is perpendicular to the magnetic axis of the earth.

On the first figure, the camera is pointed directly on the south pole of the terrella magnet, the
position of which on the plate is marked with a cross. The figures of light we here see represented,
should therefore correspond to the areas of precipitation which we would expect to find round the earth
magnetic north pole, or, more accurately expressed, about the intersecting point of the magnetic axis
with the northern hemisphere. The other picture is taken with the axis of the camera parallel to the
cathode-rays' direction of issue, so that the conditions should represent the areas of precipitation we find
on the night side of the earth. The third picture is meant to show the conditions around the earth
magnetic south pole, the photograph being taken directly towards the terrella magnet's north pole. The
position of this is also marked on the plate.

BIRKKI.AM). Mil: NOUWKIilAN AURORA I'OI.ARIS KXI'K] >l TION, I QO2 1903.

As will l>c seen from the picture, the areas of precipitation form a distinctly spirally shaped belt,
winding np\\ arils towards the magnetic pole.

'1'he upper part of this spiral belt always appears sharply and clearly defined, sometimes as a
more isolated patch, sometimes, as in this instance, this patch appears in connection with an elongated
adherent polar belt. The patch comes out very plainly in the first and third plates, as an oval shaped
figure of light within the long spiral belt. This patch does not alter its place much for different posi-
tions i if the terrella in relation to the cathode, and it exists under all degrees of stiffnesses of the
cathode rays. The remainder of the polar belt is, on the other hand, more variable in its formation.
According as the magnetic and electric conditions are altered, this belt undergoes severe changes. At
times the whole is continuous, as on the plate here, at other times several well defined figures of light
can be found, and at times the whole can almost disappear. As regards further details, we must, how-
ever, here confine ourselves to referring to a subsequent chapter, in which the terrella experiments
are described and in which the tangential direction of the rays nearest the earth in various parts of the
area of precipitation are examined. As will be found there, we have also further succeeded in showing
that the cathode rays, close to the terrella, arc bent in a manner which in the main features exhibits
the most complete analog\r to the characteristic systems of precipitation on the earth which we constantly
meet, I!y fixing screens at suitable places, it has likewise been possible to show that the rays which pre-
cipitate themselves in the luminous polar belts on that side which corresponds with the afternoon side in the
vicinitv of the terrella will be bent off towards the west -and thus corresponding rays will have magnetic
actions on the earth as a current towards the east -while the other rays, especially on the night side,
will be bent in the opposite direction, i. e. towards the east; to the north and south we must then
imagine the direction respectively to the south and north poles of the terrella magnet. We thus find a
clearly evident analogy between the actual conditions and the experiments.

The analogous system of corpuscular rays, which we imagine around the earth, will thus, by the
rotation of the earth, in the course of a day be moved round, at the same time its shape will be some-
what changed owing to the sun's altered height above the magnetic equator. The only part which never
disappears is the marked patch near the axis.

If we now assume that Kingua Fjord is situated just at that part of the earth where the system
of precipitation corresponding to this patch is passing, we seem to get a natural explanation of the
peculiar phenomena we observe here.

(1) In the afternoon, Greenwich time, which would be noon and afternoon local time, strong varia-
tions in the magnetic elements constantly occur; this corresponds with the light patch always being
visible, and thus every day the corresponding system will pass the spot.

(2) That the direction of the current-arrows is frequently pointing southwards, agrees with the
luminous belt in the innermost portion nearest the pole swinging strongly northwards or southwards.

13) I Hiring a later perturbation, i^th December 1882, we find at Kingua Fjord for a prolonged
period polar precipitations, while none such made themselves distinctly noticeable at the other stations.
1 his accords with the system corresponding with the luminous patch also occurring simultaneously with
the equatorial ring - compare fig. 37 Part I.

At the third hour given on Chart III, J 6'1 20'", perturbations of no inconsiderable magnitude have
developed at all the stations.

At Ssagastvr and Cape Thordsen, a negative polar storm is now distinctly acting, a storm that is
also continued round the geographical pole to Fort Conger, Kingua Fjord, Fort Rae and L'glaamie.

On the afternoon side, moreover, south of this negative system, we have the effects of a positive
system in the district embracing (lo Ithaab, Jan Mayen and Bossekop. Little Karmakul is situated, as

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 329

we sec, upon the boundary between these two regions, and at the hour in question has a current-arrow
directed southwards, which may be interpreted as a resultant of the effects of these two systems.

The sun has now almost reached the meridian of the magnetic axis.

We will now consider the further course of the perturbation upon the succeeding charts.

Chart IV also represents three epochs, namely, 16'' jo'", 77* 20"' and 77* 40"'.

The fields on this chart have, in the main, exactly the same appearance, the only difference being
that the strength of the perturbing forces at the various stations has undergone certain alterations.

The positive storm now appears at first only at Bossekop, and then in the district about Bossekop
and Little Karmakul. The perturbing forces there are now very considerable, and at the same time
the forces arrange themselves at the southern stations in a manner that accords very well with what,
from our previous investigations in Part I, we should expect to find. This, at any rate, is the case at
the nearest stations, Sodankyla, Pawlowsk and Christiania.

Between Bossekop and Sodankyla the forces diminish greatly, in accordance with the fact that the
point of divergence is being approached. At Pawlowsk this point has been passed, and the direction of
the current-arrow is the reverse of that at the two stations just mentioned. The forces at Christiania are
also what they would be if there were an area of divergence in that region; and at Gottingen also, the

accordance is in a measure satisfactory.

i
We have seen that the perturbing forces during this period first appeared with considerable power

at Bossekop, and then at Little Karmakul. Whether this is a displacement of the positive system, or
only owing to an increase in the size of the area of precipitation, is a question about which there may
be some doubt. If we look, however, at the area at the stations situated a little farther south, the pro-
bability seems to be in favour of the first alternative. Unfortunately we have no observations from the
district in, or south of, the auroral zone west of Norway ; where there would undoubtedly have been
marked effects of the positive system of precipitation, which would have been of some assistance in
studying it. We must thus, in employing the more southerly stations, once more make use of the same
method of procedure as in Part I. In the present case, however, we have a station, of which the situ-
ation in this connection is of no small interest, and which was wanting in the former observations, na-
mely Christiania. This station, in connection with Pawlowsk, will be, as we shall see, of much service
in finding a kind of limit for the positive area of precipitation.

At i6h 5om the arrow at Pawlowsk shows that this station is now in the eastern part of the area
of divergence, while Christiania at that time is probably not far off the transverse axis of the system.

At I7h 40™ Pawlowsk is in the vicinity of the transverse axis, while Christiania is then evidently
in the western portion of the area.

These circumstances thus appear to indicate that this is rather a movement of the system, than
an increase in the size of the precipitation-area of a system which does not change its position much.

The conditions at Gottingen also to some extent agree fairly well with the above, although the
direction of the arrows there seems perhaps to be a little too southerly.

The conditions in Jan Mayen are rather interesting too. They show that the positive system there
must lie to the south of the station. The inconsiderable forces occurring in a horizontal direction may
be naturally explained by assuming that the negative system to the north, and the positive system to
the south, neutralise one another's effect in a horizontal direction, but on the other hand act together
in a vertical direction, so that the aggregate effects are all the greater.

As regards the vertical intensities at the other stations in the positive polar area, the conditions at
Bossekop show that the area of precipitation must be looked for somewhat to the north of that station.
This has also been the case in most of the previous instances of similar storms in Part I (see perturba-
tions of nth, 23rd and 313! October, and gth December, 1902, and 8th and 15th February, 1903). At

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Sodankyla, on the other hand, we find negative precipitation in the vertical intensity, that is to say a
direction the very reverse of that which one would have expected. The easiest explanation of the circ-
umstance — but hardly a permissible one — is, that an error has found its way in, either as a conse-
quence of a fault in the apparatus, an error in observation, or an error in calculation; for there seems
to be no local current-system at work here. Earth-currents might possibly be supposed to exert a con-
siderable influence, but scarcely as much as in the present instance.

Conditions, however, are found at this place which may be capable of accounting for these dis-
crepancies; we have just recently ascertained that in the regions round Sodankyla, there are enormous
ironfields, the ore of which possesses magnetic properties of extraordinary strength.

This could affect the perturbing forces in vertical intensity especially, if we imagine the magnetic
masses distributed in a horizontal layer. It would be easy to imagine a distribution of magnetic masses
which, by means of induction, might be supposed to occasion anomalies such as these which \ve
find here.

If we, for instance, imagine the station to be situated immediately above the one end of a horizontal
magnetic shaft, then the horizontal forces in the neighborhood could be expected to induce free magnetism
at the ends of this shaft, and that again would be able to produce strong effects in vertical intensity in
a station situated directly above.

At Godthaab we now have no particularly noticeable effect of the positive system. The perturbing
forces are of inconsiderable magnitude.

At the other stations, as will be clearly seen, negative storms are acting, which, during the three
epochs here represented, remain more or less unchanged both in form and strength. Fort Conger evi-
dently follows closely upon this series of stations, there being a westerly-directed current-arrow there
of a strength similar to that at the other stations.

From the values of P, to be found at the various stations, a few details may be concluded as
to the situation of the current-system. At Fort Rae and Uglaamie, we see that the negative preci-
pitation takes place north of the former place and south of the latter, and thus, probably more or less
in the auroral zone, which just comes between these two stations.

In connection with this, we should remember the meaning of the two curves drawn, which show
the position of the belt of Northern light. The more southerly, shows the places where aurora is most
frequently observed. The more northerly, connects points where aurora is seen as frequently in the south
as in the north.

At Cape Thordsen, we also have small negative values of Pv. We must not however, conclude directly
from this, that the negative precipitation takes place north of that place, as to the south of it there is the
positive polar system, which will here just produce negative values of Pt. It would therefore be a fairly
probable assumption that the negative precipitation occurred a little to the south of, or possibly more or
less directly over, the place. If the area of precipitation were to the north of the station, the perturbing
forces in the vertical intensity would probably be greater than we here find them to be, as the two sys-
tems would then cause vertical forces directed in the same direction. In all probability, this is the case
on Jan Mayen; and we also find powerful perturbations in the vertical intensity.

Chart V, /<$* 2/'", j<f /"', 79* 25'". The sun is now in the vicinity of the meridian of the magnetic
pole, which it crosses in this period.

Here, too, we find the same areas of perturbation as before. The negative storm has now concen-
trated itself more upon the night-side of the globe. In the district Cape Thordsen, Jan Mayen and Kingua
Fjord, however, there are quite distinct effects of a negative system which is acting there. The area of
perturbation here, however, is not so well defined as before. The positive system is distinctly noticed
at Bossekop, and at 19'' 5™ at Little Karmakul too. This chart also shows with extreme clearness at this

1 PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 331

station, how the two systems encroach upon one another. At i8h 25m they almost entirely neutralise one
another's effect, at I9h 5™ there is a strong effect of the positive system, and at I9h 25™ a strong effect
of the negative system.

The current-arrows at Pawlowsk and Christiania now seem to indicate, that this positive system
does not extend so far westwards.

It is interesting to follow the movement of the arrow at Pawlowsk from I9h 5™ to I9h 25™, that
is to say, at the time the negative system is extending its area of precipitation westwards to Little Kar-
makul. The arrow at Pawlowsk moves with it. Thus, at I9U 5m the current-arrow indicates that the
station is more or less in the middle of an area of divergence somewhat to the west of the transverse
axis, so that we then have principally the effects of the positive system. At I9h 25™, on the other hand,
the current-arrow shows that the station is either in the east part of an area of divergence, or in the
west part of an area of convergence. This, then, indicates, that we here have either the effects of the
westerly positive system that we find in the neighbourhood of Bossekop, or those of the negative system
extending eastwards from Little Karmakul. It is probable, however, that both of these will exert an
influence, and that the current-arrow must be regarded as the result of their united action.

The conditions here, are thus evidently governed by the polar systems, just as we supposed in
Part I.

The direction of the deflections in the vertical intensity, are now, on the whole, the same as in the
preceding chart. We still find the same disagreement between Bossekop and Sodankyla; and at Paw-
lowsk Pt = O, just as in the preceding chart. There is, howewer, a slight deviation in the curve, corre-
sponding to positive values of P,, which are too small to allow of being taken out.

On Chart I' I and I'll, the conditions develope farther in the same direction, inasmuch as the areas
of precipitation are now concentrated more on the night-side of the earth, if we may judge by the
observations at our disposal. At the other polar stations, however, there are still, on the whole, more or
less distinct, westerly-directed current-arrows.

It is very possible, however, that a little farther south there may be areas of precipitation that
cannot be observed here. The rather abnormal current-arrows at Fort Rae, which is situated south of
the auroral zone, might, perhaps, indicate something of the sort. On Chart VI too, Gottingen and Christiania
seem to be situated in the eastern part of an area of divergence, and thus indicate the ' existence of a
positive system of precipitation.

We notice such a system at Bossekop and Sodankyla, and we should therefore have to suppose
that this system extended westwards along the auroral zone, and probably south of it, or into its south-
ernmost part, so that its effect at the stations from which we have observations, and which are situated
to the north of it, are not affected in any great degree by it.

On Chart VII, the negative polar system in the north of Europe seems to have got the upper hand
and to be also governing the conditions in the stations in the south of Europe. As regards Christiania
and Gottingen, however, a positive polar system such as that we assumed to exist on Chart VI, will also
act in more or less the same direction. At Bossekop, up to 2ih 5™ on Chart VII, there are marked
effects of a system such as this, although at the last hour shown, 2ib 20™, this storm is over there.

There is little to be said regarding the vertical intensities. At Fort Rae only, it may be remarked,
that there is now and again a deflection in a positive direction. This is in a kind of accordance with
the fact that the conditions of the current arrows are also slightly different from those at the other neigh-
bouring polar stations, which thus also seems to indicate that other perturbing forces are at work here.

On Chart VIII, for the hours 2ih 40™ and 22h 4Om, the powerful storms at the stations here
under consideration, are over, although at several places there are sometimes quite powerful perturbing
forces; but there is now no distinct impression of a coherent current-system.

332

I3IRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

The Perturbation

TABLE LI.

on the I5th of January 1883.

Gr. M. T.

Uglaamie

Fort Rae

Kingua Fjord

Godthaab

Pi,

Pd

P.

Pi,

Pd

P,

ft

Pd

ft

Pd

h m

II 20

+ 56 r

W 13 / — 51 7

— I OO /

E 28.57

4- 35 7

- 7 7

W 9.57

- 6 7

W 3 7

5° - 24 »

„ 90 „

- 82 „

-146 „

» 5°-5 »

+ 75 .

- 60 „

E 3 -

- 25 „

, 24 „

12 20

-MS ,,

E 26 „

— 20 „

-2,8 ,

„ 81 „

+ 85 „

-62 „

W ,1.5,,

- 23 »

„ 22 „

13 20

-353 »

» 415 »

4- 4' ,

-368 „

. 155 »

+ 85 „

-78 „

» 3i-5 .

- 4° ,,

»I7 ,,

14 20

4 II „

» '3 «

4- 31 .

— 38 „

» 54 »

4 15 .

- 19 ,

E 22.5,

4-35 .

E 20 „

15 20

- ao „

. 37 »

+ 3i .

- 27 „

» 3a »

— 5 M

- 35 »

W 67 .

4-27 „

„ 20 „

1 6 20

- 4i-5 .

» IO1 »

+ 31 .

- 53 .

M 44 n

— 5 M

-87 „

» 84 „

4-3' »

. 18 „

50

- 80 „

„ i°9 «

•4- 92 „

— 100 „

„ 83 „

— 25 „

-60 „

„ 85 „

o

W 28 „

17 20

-154 i,

„ 13 .

4-ioa „

-108 „

„ 82 „

-55 .

- 57.5 „

» 95 „

4- 7 .

. 5-5 „

40

- '68 „

>, 89 „

+ 61 „

— 99 »

n 52 M

-65 „

- 45 *

. 91 »

4 28 .

» 3 ,,

18 35

-"4 »

„ H5 „

4 10 „

+ 3 ,

. is „

-65 „

- 25 „

» 109 „

4-55 .

n 1° .,

'9 5

-i°7 »

„ '49 ..

o

+ 33 „

. i »

-35 ,

— 'a „

. 65 .

- 4 i,

„ 34 „

25

- 7i-5»

» 79 »

- 3i .

o

W 18 „

- 25 „

o

. 44-5 .

4- 19 „

„ 22.5 „

40

- 61 „

. 7' „

— 5i »

— 7 .

» 22 „

— '5 »

4- 4 .

, 48.5,

4 20 „

o

20 o

- 3° „

» 3 »

- 61 ,

- 26 „

„ 25 „

- 25 »

0

» 57-5 .

4- 23 „

» 3

20

- 24.5 „

W 3 „

- 82 „

+ 6 „

„ 20 „

4- 15 .

4 9 „

» 4i-5.

4 8 .

,, 22.5 „

40

- 33-5 „

E 3 .

-112 ,

- 38 „

» 23.5 „

— 5 ,,

- 4 »

. 48.5.

- 8 „

» 39 „

21 5

- 55 »

. 8 .

-133 „

- 26 „

» 1° »

4- 15 ,,

+ 4 „

,, 59 „

- 13 »

„ 53-5 ,

20

- 19 » ! . 8 „

— 112 „

— 22 „

. 26 .

+ 5 .

0

» 44-5 ,

- 10 „

n 45 ,.

40

- 27.5 .

W 24 ,

— 112 „ — 36 „

» 32.5 »

— 5

— 'a »

n 37

— 21 „

.. 39-5 ,

32 20

4 2 „

» 4° n

- 71 „ I 4- 18 .

,, 24.5 „

4-25 „

o

. 5-5 »

+ 8 „

„ 5 .

23 '5

— 5 »

. 3 »

- 41 » j: 5 ,

E 2.5 „

+ 5 „

o

• I •

o

E 3 .

TABLE LI (continued).

Gr. M. T.

Jan Mayen

Bossekop

Sodankyla

Ph

Pd

P,

ft

Pd

Pv

PA

Pd

P»

h m

ii 20

- i 7

W 5-57

-57

0

o

- 67

o

0

- 4 7

5°

* n

n '4 n

o

o

E 3-57

- 3 n

4-37

o

- 20 „

12 2O

— 4 n

E 5-5 „

+ 7 „

427

n 3 n

4- a „

4- 6 „

0

0

13 20

4- 24 „

n a n

4- 4 n

4- 13 „

w .9.5 «

+ '5 »

4- 9 „

W 18.57

- 10 „

14 20

4- 95 n

W 7-5 „

- 4 n

4 16 „

o

4- 27 „

4 8 „

n 2 n

- *7 *

15 ao

+ 64 „

n 1-5 n

- 8 „

4- 10 „

E 3 „

4- 22 „

4- 3 „

o

- '4 n

16 20

4- 59 n

. '8 „

- 83 „

4- 65 „

W 3-5 «

+ 72 „

+ '0 „

E 8.5 „

-65 r

5° 4- 18 „

if 50 „

-no „

4- 90 «

E 7 *

+ Il8 „

4- 20 „

» 23-5 n

- 74 n

17 20 4 17 „

« 3-5 „

-126 „

4-17' n

n '°-5 „

4-l64 „

+ 27 „

0

-60 „

40 6 „

W 3 H

-127 „

4-185 „

W3» „

+ 192 n

+ 24 „

W 4-5 „

- 92 n

18 25 4 28 „

n 31-5 „

-153 „

4-126 „

n 42.5 n

4-H8 „

4- 23 „

« '5-Sn

- 72 n

19 5 -no „

n ! 7:5 n

-'33 n

4-157 „

n 96 „

+ 110 „

4- 33 »

n 33-5 n

- '0 „

25 - M »

r 89 „

-'5° n

4- 65 „

n 32 „

+ 88 „

4 28 „

o

-86 „

40 - ii „

E 7-5 n

-M3 n

4i28 „

n 35-5 „

4-125 „

4- 52 „

E 4-5 „

- 70 „

20 o

- 52 n

W74 „

-I67 „

+ 76 „

„ 46 n

+ 49 „

4- 25 „

W 16.5 „

-38 „

20

+ 5 „

« 68 „

-'56 „

+ 65 „

n '2.5 n

+ 54 n

4 30 „

E 6 „

— 45 „

-1° '. - "3 »

» *4 H

-160 „

+ '°5 „

11 9 n

4- 7° n

4- 26 „

W 13.5 „

4 ii „

21 5 - 78 „

E 75 „

-'54 n

4- 92 „

II 22 „

4 44 n

4 28 „

E a.5n

— '3 n

20 - 38 „

W3i ,

-164 „

- 5 »

E 24.5 „

- 82 „

+ 21 „

W 4 „

4 22 „

4° - 46 „

n 156 n

-'56 „

- 43 » W 33.5 „

-148 „

4- 3 „

n 7 n

4- 34 „

22 20 4 47 „ „ 54 „

-106 „

o « 3-5 n

- 66 „

4 12 „

n 6-5 n

4- 18 „

23 15 4- 2 „ „ 9 „ - 51 n

° n 7 » - 34 n

- a » n 8 „

' 7 »t

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I.

333

TABLE LI (continued).

Or. M. T.

Cape Thordsen Little Karmakul

Ssagastyr

A

p<i

ft

n PJ

A

Pk

Pd

It m

1 1 20

+ 19 /

W 1.5 7 + u 7 + 17 7 E 4 7

0

+ 3 y

E 15 /'

5° + 59 „

E l8 * 9 „ 4- 14 „

O

+ 17 7 ' + 58 „ „ 9 .

12 20

+ 3 „

» 28.5 „

7 « + 60 „

W 9 „

+ 35 n

+ 107 „ W 16 „

13 2O

- 52 „

u 35-5 n

- 38 „ +M3 „ n 63 „

+ 84 „

+ 138 „ „ 54 .,

14 20

+ 54 „

W 4 „

~ 57 n I 4 n

E 5-5 . + 4i „

+ 75 ,,

n I2 n

15 20

+ ,6 „

„ 6 *

- 3' • I + 16 » „ 2 „

+ 26 „

- >3 n 0

1 6 20

- 66 „

* '5-5 „

- 47 n ! 4- 17 n n 68 „

+ '2 „

-288 „

n !35 n

5°

- 7° „

» 20 „

- 25 „ o „ 6, „

- I0 n

-203 „

n 45 n

17 20

~I29 „

n 24.5 „

- 23 „

+ 361 n iW 41 „ + ii n

-"3 n

0

40

— I°7 n

K 28.5 „

- 20 „

+ 211 „ ' „ 50 „

+ 3" n -107 „

E 6 „

18 25

- 56 „

„ 36-5 „

- 35 „

+ '6 „

n '4-5 n

+ 3' „

-'82 „

n 29 „

'9 5

- 26 „

» 53-5 „

- 22 „

-202 „ E 34.5 „

- 6 „

-218 „

n 4' n

25

- 22 „

n 47-5 n

- "3 n

+ 135 „ JW 11.5 „

+ 20 „

- 40 „

„ 46 „

40

- 95 „

n 65 „

9 „

0 n 3 „

- 35 „

- 56 „

n 29 „

20 O

— 161 „

n 73 n

- 71 „ 8 „

E 12.3 „

- 27 „

- 29 „

it 32 „

2O

-108 „

n 23.5 „

- 39 „ L- 27 „

n 39-5 n

- 23 „

- 43 „ n 44 n

40

-254 »

E 91 „

+ 51 *

- 28 „ iw35.5 „

- 3° „

- 5' n

» 37 „

21 5

-357 „

Wio8 „

-217 „

-279 n

» 21 „

- 9° »

- 63 „

» 49 n

2O

-135 n

E 10 „

+ 22 „ -2I3 „

E 50 „

- 59 n

- 37 „

w 32 „

40

-100 „

W 64.5 „

- 25 n - 7 n

n "2.5 n - 45 n

+ 96 „

» 4* «

22 2O

0

» 38-5 „

— 5 n + 74 »

W II „ | - 40 „

+ 21 „ „ 39 n

23 '5

+ 14 »

E 6 B

+ 27 „

+ 38 „

« :'5 n

+ 7 n

- 10 „

0

TABBLE LI (continued).

Gr. M. T.

Christiania

hPawlowsk

Fort
Gottingen | -

Ph

Pd

Pd

Pk

Pd

A

Pd

h m

II

ii 20

- 2 7

W 3 7 o

o i 7

E 4 7

•f- 4 y

E 4-5 y

5°

- 3 x

x 3-5 n

o

° tt~ * "

° | 4- 3 x

W 7-5 x

12 2O

O

n 3 n

o

E 2.5 7

3 x

x 3 x

+ 4 ,

x 9 x

13 20

+ 3.5 „ ! „ 14.5 „

- 3 y

W 9-5 x

I x

W 8 „

+ 7 »| . 45-5 x

14 20

-1- 1-5 n

» 4-5 x

o

0

4 6 „

E 9 x

+ 11 x

X 2 „

15 so

- 2 „

o

- 3 x

o

o

x IO-5 x

+ 8 „

x I°-S x

16 20

- 7 n

x 3 x

8 x

E 10.5 „

- 6 „

x 8 x

+ 5 x

x 58 x

5°

- 11 . o

- '0 x

X '9 X

- ii-5x

x I2 „

+ 4-5 x

x 73 x

17 20

- 9 x n 3 »

7 x

„ 3-5 x

- 10 „

« 6.5 „

+ 7-5 xij » 98 „

40

- 8 „ „ 12 „ II - 10 „

o

- 8 „

W 2 „

+ 6 «

x 66.5 x

18 25

0 i x I0 »!| I x

W 7 „

o

« 2.5 „

+ 3 X

x 57 x

'9 5

+ 9-5 n n r'5 n

7 x

X 5 X

+ 3-5 x

E 8 „

0

x 57 x

25

— 4-5 x n 7-5 x

5 „

E 9 x

4-5 X

o

+ 7-5 X

X 38 X

40

- i n

E 5 x

+ 5 x

x 9-5 n

5-5 x

x 8.5 „

+ 5 x

x 5° *«

20 0

- 3 11 J n 4-5 n

+ 5 x

0

- 2 „

X M x

+ 3 x

x 54 x

2O

- 3 ti

» * a

+ 2 „

X Ia x

7 M

w 12 „

+ i-5 x

X 58 x

40

- 4-5 x

x 33.5 x

+ 5 x

x " »

- it-5x

x 28 „

+ I x

x 51-5 n

21 5

+ 19 n

X 38 „

4- 16 „

x 5-5 x

O

x 31-5 x

- i-5 x

x 56 „

20

+ 13 n

x 30-5 x

+ '4 x

x 13-5 x

o

- 30-5 x

- 3-5 x

x 30 „

40

+ 11 „ „ 14-5 x

+ 7 „

x 1-5 „

+ 5-5 x

x l8-5 x

0 x 31-5 x

22 2O

+ 4 x x 9-5 n

+ II „

o

+ 3 x x 8 „

- 3 x E 11.5 „

23 15

- 7 n W 3-5 n

— 6 „

W 3 „

4 x x 3.5 „

- 8 „ „ 42.5 „

Birkrland, The Norwegian Aurora Polaris Expedition 1002 — 1903.

43

334

B1RKF.LAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

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338 IHKKKI.ANU. THK NORWEGIAN AURORA POLARIS KXPKDITION, igO2 1903.

83. We may here draw a comparison with the areas of precipitation that may be calculated
according to fig. 76, Part I, p. 160.

If 6 is the angle that the sun's declination-circle makes with the meridian of the magnetic axis,
(J the sun's declination, and (90 — rp) the angle made by the magnetic axis with the earth's axis,
i. e. (f> — 78° 20', we have

A

sin i/> = cos (y> — 6) — 2 sin2 cos 6 cos rp ,

where (// has the same meaning as in Art. 53 in Part I.

We will reckon the angle 0 positive towards the west like 'P, 0 thus standing for the time that
has passed since the sun crossed the meridian of the magnetic axis.

The longitude of ®, as already stated, is 68° 49' W, so that the period during the perturbations
under consideration here, namely io'' — 23'' 2om G. M. T. corresponds to values of 6 lying between about

- 100° < 9 < + 100°
which answers to about

- 22.5" < y < - 9.5°.

Thus i// first increases from — 22.5° to — 9.5°, and then decreases from — 9.5° to — 22.5°.

We will now see from these calculations what areas of precipitation we should expect to find.

In making such comparison, we do not mean that the areas of precipitation we find by calculation
should exactly correspond with the various storm centres which occur during the perturbations. The
areas of precipitation found by calculation, are those in which the rays fall perpendiculary on the sur-
face of the Earth, what are actually calculated are rays which go to the origin, where the assumed
elementary magnet is situated. The regions that just correspond with these, must, in my opinion, best
be compared with the places where aurora occurs, but these do not always correspond with the storm-
centres of the magnetic disturbances. But we might, however, expect to find analogies and we will
therefore proceed here briefly to make such comparison.

We will first consider the negative rays. For tp = — 22.5° we find, as fig. 76 shows, no precipi-
tation, but as soon as ever ip has increased a couple of degrees, an area of precipitation appears on
the afternoon-side, at first spreading with considerable rapidity east and west, and subsequently dividing
more into two systems, one of which moves towards the morning-side and the other towards the evening-
side, as the sun approaches the meridian of the magnetic axis.

Shortly after the formation of the first area of precipitation, a new one is formed upon the morning-
side, which also, as the sun rises higher, divides into two parts, one of which moves towards the night-
side of the earth, the other towards the morning-side. There will moreover be areas of precipitation
answering to rays that have passed round the earth before their descent, and correspond to values of
\<P\ that are greater than 360°. These are not taken into consideration here.

For positive rays we find more or less the same values of <? for the first two areas of precipitation.

After the sun has crossed the meridian of the magnetic axis, it might be supposed that the pheno-
mena would be repeated in the reverse order, but with the whole area moved westwards. We will now
see whether analogies to these conditions are actually found.

At first, then, we should expect to find two areas of precipitation, one on the afternoon-side, and
one on the morning-side.

This agrees exceedingly well with what we found in the first section, where we pointed out the
two areas in which the storm was concentrated. One of these, the negative, appeared on the morning
and night side from Kingua Fjord to Fort Rae and Uglaamie, beginning slightly earlier at Fort Rac than
at the other two stations. The other, the positive, occurred on the afternoon and evening side, from
Little Karmakul to Ssagastyr. Here then there appear to be distinct analogies.

PART II. POLAR MAGNETIC PHENOMENA AND TERREI.I.A EXPERIMENTS. CHAP. I. 339

Afterwards, four areas of precipitation should be found, distributed over the polar regions. Owing
to the scarcity of stations, it is of course difficult, if not impossible, to prove any agreement in detail.
We will only point out that on Chart III, the perturbing forces are distributed more or less evenly
about the auroral zone.

At the conclusion the negative storms are concentrated upon the night and morning side, perhaps
moved a little more towards the night-side than one would expect. On the afternoon-side there are no
particularly powerful areas of precipitation, but we have no observations either, from the regions south
of the auroral zone.

While speaking of the repetition of the phenomena in reverse order after the sun has crossed the
meridian of the magnetic axis, we will draw attention to the two deflections in the horizontal-intensity
curve at Uglaamie, which seem distinctly to be almost a repetition of the same phenomenon. The second
phenomenon does not, it is true, occur when the sun is exactly as far west of the meridian of the mag-
netic axis as it was east in the first, but only approximately so.

If this phenomenon is to be explained in this manner, it must be assumed that as, at the first
deflection, the station lay to the west of the storm-centre, and as the strength of the deflections is more
or less the same, at the second deflection the station must be almost equally far to the east of the
storm-centre; and it is very probable that this is the case.

Similar remarks may also be made with reference to Fort Rae.

THE PERTURBATIONS OF THE 2nd JANUARY, J883. .

(PI. XXV.)

84. The perturbation-conditions on the above day exhibit in many respects a great resemblance
to the conditions during the preceding perturbation of the I5th January, 1883. This is at once evident
on comparing the plates for these two days.

The period of this day which we shall discuss is from u1' to the conclusion of the day, 23'' 20™,
Gr. M. T.

During this period there occur, as on the i5th January, a series of powerful, well-defined storms,
while for some time previously, it had been more or less calm.

On this occasion also, the perturbations occurring may be divided fairly distinctly into two sections,
namely, a first section from n1' to i6h, and a second section from i6h to 23h 2om.

The first section is mainly characterised by the powerful negative storms that appear in North
America.

At Fort Rae, there is a considerable and well-defined deflection in the horizontal-intensity curve,
with a corresponding deflection in the declination curve. The deflections increase at first fairly
evenly from uh 3om. We find the most powerful perturbing forces at about I4h; after which the forces
decrease, until about 15*' 3om, when the conditions are again more or less normal.

At Uglaamie, the conditions are somewhat more complicated. At a little before I2h, wide de-
flections suddenly' occur in the magnetic curves. In the horizontal intensity, they are in a negative
direction, and the curve has a very jagged appearance. At about i3h, however, they decrease, and
for a time the curve oscillates over and under the normal line. In the declination, on the other hand,
the deflections at this hour are very considerable, showing the presence of powerful perturbing forces,
which are evidently acting in the neighbourhood of this station.

Later on there are again considerable negative deflections in the horizontal-intensity curve, these
deflections now being very well-defined without any sharply projecting points. The}' continue to the
end of the first section, the conditions at about I5b 45™ being once more normal.

340 UIRKKI.AND. THF NORWEGIAN AURORA I'Ol.ARIS EXPEDITION, 1 gO2 — 1903.

A third station, whicli ought to be mentioned in connection witli these two, is Kingua Fjord; for
these three stations together form a more or less distinct group, as a negative polar storm is now acting
in this district. We have considered the effect of this storm at the two preceding stations, and we
found that at the conclusion of this first section, the storm there was over. This is not the case,
however, in Kingua Fjord, where the storm continues without cessation into the next section, although
for a short time about i6h iom, the perturbing forces are very small.

At the time when the curves at Fort Rae and Uglaamie have their maximal deflection, a distinct
maximum is also to be found in Kingua Fjord; but the perturbing forces there are considerably weaker.

It appears, upon the whole, as if the storm-centre must be situated in the district Fort Rae —
Uglaamie, at first probably nearest to the former; at the conclusion however we find the strongest effects
at Uglaamie.

It is not impossible, therefore, that we have before us a displacement, in a westerly direction, of
the area of precipiation ; but the conditions are probably more complicated.

In these districts then, a negative system of precipitation is acting.

If we now examine the other curves in this first period, we find at Little Karmakul and Ssagastyr
quite distinct, although comparatively slight, effects of a positive system of precipitation. At Cape
Thordsen there are also positive deflections in the horizontal-intensity curve at first; but at the time
when the negative storm at the American stations is at its height, the curves seem to show that here
too there is a negative polar storm which counteracts the effect of the positive, and makes the curve
oscillate to the opposite side. The conditions in the declination and vertical intensity also indicate some-
thing similar; for at the time when the negative storm here should begin, we find distinct deflections
in these two elements, lasting about as long as the negative storm seems to be acting.

In the district Godthaab to Jan Mayen, there is also a positive storm which continues into the next
section, and there attains considerably greater strength.

We thus find in this perturbation also, the characteristic systems of precipitation, a negative
and a positive, of which the first is fairly powerful and very pronounced, while the second is
comparatively slight.

We may now at once look at the first four charts, which represent the perturbation-conditions
during this first section.

Chart I shows the conditions at rj1' 20™, that is to say at a time when the negative storm at
Fort Rae has about reached its height. For the time before this, in which, as already mentioned, there
are fairly powerful forces at Uglaamie, while those at the other stations were comparatively small, no
charts have been drawn, as the condition is clearly apparent from the curves.

The current-arrow at Uglaamie is now directed NNE, and thus indicates that the conditions are
somewhat different from those that are usual in the auroral zone during the polar storms in which the
current-arrow is directed either westwards or eastwards. In order to explain this condition, it might be
assumed, as has previously been done, that there was here a co-operation between a positive and a
negative polar storm.

In the district Kingua Fjord and Fort Rae, there are distinct effects of a negative polar storm,
while at the other stations the perturbing forces are very small.

On the next charts, Charts II — IV, for the hours /./' /"', /./' 20'", ijk and //'' 20'", the conditions
are but little changed in the main. Now too we find a distinct negative polar system in the north of
America; and in the district Godthaab eastwards to Ssagastyr, there occur more or less distinct traces
of a positive system. This is most cleary apparent on Chart III, for i4h 20™ and on Chart IV at i5h.
At the latter hour we notice especially strong effects of this system at Ssagastyr. At Cape Thordsen,
on the other hand, we find at I4h 5m a distinct westward-pointing current-arrow, which should indicate

PART II. TOLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 34!

that we had before us the effect of a negative system of precipitation, which is, indeed, in accordance
with what we have already noticed when considering the condition of the curves.

After this first section, there supervenes, at most of the stations, a brief period of fairly quiet
conditions. The only exceptions to this are the stations Kingua Fjord, Godthaab and Jan Mayen, where
there are now quite distinct oscillations. At Cape Thordsen too, there are distinct oscillations in the
declination, but the perturbing forces are very small.

This intermediate period of time, commences at about 16'', that is to say at about the time when
the sun crosses the meridian of the magnetic axis.

Fairly powerful storms, however, soon develope at all the stations from which we have observa-
tions, some of them appearing as negative polar storms, and some as positive.

The perturbations in this last section also exhibit in the main exactly the same conditions as the
preceding perturbation of the I5th January.

Exclusively negative storms appear, as we see, at the stations Kingua Fjord, Fort Rae, Uglaamie
and Cape Thordsen. At Godthaab, Bossekop and Sodankyla there are almost exclusively positive storms;
but these have not so distinctly the character of a positive storm, as the course of the curve is fairly
quiet, and the perturbing forces are comparatively small. In the declination, moreover, there are perturbing
forces that exceed in magnitude the values of Ph.

Little Karmakul is now, as also in the preceding storm, situated just on the boundary between the
two areas of precipitation. On the east and north of the station are the negative storms, on the west
the positive. In consequence of this, the conditions here become rather peculiar, as sometimes the
negative system, sometimes the positive, exerts the strongest influence, and the horizontal-intensity
curve accordingly oscillates now to the one side, and now to the other.

This condition comes out very characteristically here in this period.

In Jan Mayen also, we find similar conditions. There we evidently have a negative storm, which,
during the period from 17'' to 19'', breaks in upon a positive storm. The latter is of much longer
duration than the former, but of comparatively smaller strength; and therefore, when the negative storm
breaks in, it will gain the ascendancy and cause the deflections in the horizontal-intensity curve to go to
the negative side. In the declination also, at about the same time, there is a corresponding change in
the direction of the deflections.

From about i8h 30™ to ao'1, there are once more positive deflections, but then the curve changes
again, and from the last-named hour until the close of the period, we find once more negative values of
/',. It is not easy to say, merely from a direct consideration of the curves, whether, at the close of the
period, positive storms are also exerting an influence here.

At Bossekop and Sodankyla the positive deflections are only slight, and the character of the cur-
ves is fairly quiet. It might therefore possibly be assumed that the deflections were the effect of the
negative system, whose area of convergence was situated to the north of these stations. Such an assump-
tion, however, cannot at any rate be applied to the conditions in Jan Mayen, at Little Karmakul or at
Godthaab, as the positive deflections there are far too considerable in amplitude.

If we endeavour to fix the position of the centres of these storms from the intensity of the deflec-
tions, we find as regards the negative storms that the greatest forces on the night-side are at Ssagastyr
and Cape Thordsen at about i8h, when the storms are at their height.

At Uglaamie, the deflections in this section are of exactly the same character as those in the pre-
ceding section, and of very nearly the same strength.

At Fort Rae, on the other hand, there is a deflection which is very distinct, but far slighter than
that in the preceding section, and also considerably slighter than the deflections at Uglaamie.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903.

ii

r,iKKKLAM>. i in: NOKWKI.IAX .M'KI>KA POLARIS F.xi'F.mno.\, igoa -1903.

In tin: first section we found the most powerful perturbing forces at Fort Rac, indicating the prox-
imitv to that station ol a storm-centre.

This storm-centre was then situated to the east of Uglaamie. Now, in this last section, it is situated
to the \ve.-~t of it; and the conditions at that station during' these two perturbations, are in the main ex-
actlv similar.

It' we look at the time of the appearance of the two perturbations, we find that the first takes
place just about as long before the passage of the sun through the meridian of the magnetic axis, at
about if)'1 .50"', as the second perturbation does after it. In the description of the preceding perturbations,
we also pointed out a similar circumstance; but it was not arranged quite so symmetrically with regard to
the time tor the1 sun's passage through the meridian in question, as on the present occasion. As regards
the. positive storm, the position of its centre cannot be so directly determined, as no district can be pointed
to, about which the forces evidently concentrate themselves.

As regards the southern stations ; we find there too, simultaneously with the powerful polar storms
at about i8h, a distinctly-defined perturbation, which, at Christiania and Gottingen, is particularly strong
in the declination; while at I'awlowsk the- deflections in horizontal intensity and declination are about equal.

In the vertical-intensity curve for Jan Mayen, we notice a particularly characteristic, well-marked
deflection in a negative direction. It increases at first fairly evenly, but comparatively quickly, reaches
a maximum at al>ouf 18'' 30"', and then once more decreases rather more slowly until about 22'', when
the conditions are almost normal.

Almost exactly the same thing is found at Little Karmakul.

At the intermediate stations, Bossekop, Sodankyla and C'ape Thordsen, on the other hand, the
conditions are somewhat different. At the first-named station, the forces are of comparatively smaller
strength, and the deflections there are first positive, then change and become negative, after which, for
the remainder of the period, the curve oscillates over and under the normal line. At Sodankyla the
order is reversed, negative deflections coming first, then positive, and then small deflections, now in a
positive, now in a negative direction.

At Cape Thordscn, the course of the vertical-intensity curve is peculiar. We there find, at the time
when the storm is at its height, very strong but brief impulses, now to one side, now to the other, but
more often in a positive direction. Later on, when the storm has diminished in strength, we find first
a negative deflection, then for a time fairly normal conditions, and then finally, at the end of the period,
positive deflections.

In what way these conditions in the vertical intensity are to be interpreted will best be learnt by
looking at the charts, which show the perturbation-conditions for this section.

The last four charts, /' t<> I' 1 1 1. for the hours //'' 211'", //'• ./</'", /<?'' 20'" and /(/ 20'", represent the
conditions as they developc during this period.

On Chart Y, the most powerful storms have not yet begun. \Ve see the negative system of preci-
pitation, which extends in a ring round the north pole.

\Ye now find the strongest perturbing forces at Ssagastvr and Kingna Fjord. The conditions at
Cape Thordsen, Fort Kae and Uglaamie, seem, however, to indicate that there can hardly be several
sharply-divided systems of precipitation in the negative storm, but that the whole must be regarded as a
more or less coherent phenomenon. The succeding charts show this even more distinctly.

A positive system of precipitation also appears quite distinctly at Godthaab. At Bossekop, Sodan-
kyla and Little Karmakul, at which, together with Jan Mayen, we have also seen effects of the positive
polar storm, the direction of the arrows is easterly, but the arrows are small.

At the three southern stations, the current-arrows have a south-easterly direction, at the two west-
ern of them a little more south, and at I'awlowsk a little more east. These1 conditions indicate that the

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 343

stations in question are in the western part of an area of convergence; and it therefore seems as if the
influence exerted by the negative system were also predominant in these southern latitudes.

The forces here are of smaller strength, but in Charts VI and VII we see this condition developed
to a very much greater degree. The form of the field has undergone no special change, but the per-
turbing forces have now increased considerably in strength at the great majority of the stations. This
is especially the case on the night-side of the globe. At Cape Thordsen the forces have greatly increa-
sed, the most powerful being now found there, although at Ssagastyr the perturbing forces are almost
of the same magnitude. We now evidently have a powerful negative system of precipitation on the night
side of the globe, which also has a distinct effect in Jan Mayen. At both Little Karmakul and Godthaab,
on the contrary, there is, as Chart VI shows, a positive storm at i7h4Om; while Chart VII, for i8h 2om,
shows a distinct negative polar storm at those stations. The effects of the positive storm, however, do
not come out distinctly on these two charts, as the negative storm, owing to its strength, seems to
dominate the whole area; but as we have no observations from the districts south of the auroral zone
on the afternoon-side of the earth, it is not possible to determine with any certainty the manner in which
the conditions actually develope. We have already seen from the curves that this is in all probability a
positive storm, and probably also the one that asserts itself to some extent at Bossekop and Sodankyla,
and is the cause of the current-arrow having so marked an easterly direction. Finally, if we look at the
conditions in the north of Europe and Asia on Chart VII, the discontinuity apparent on a comparison
of the conditions at Bossekop and Sodankyla with those at the other stations, would be difficult to ex-
plain, if we do not assume that a system of precipitation actually exists there, which counteracts the
strong negative system, of which the effects are so apparent everywhere else.

Lastly, there is another circumstance which should be taken into consideration, namely, the condi-
tions in the vertical intensity. If we look at Chart VI, we see that at Bossekop there is a perturbing
force, of which the vertical component is directed downwards. A circumstance such as this cannot be
explained if we only assume the negative system, of which the area of precipitation falls north of the
place; for this would here act in the opposite direction. On the other hand, a positive storm north of
the place will actually produce positive values of Pw and as already remarked in the account of the
preceding perturbation, the positive systems will as a rule have their area of precipitation somewhat to
the north of this place.

The vertical intensity at Sodankyla, however, exhibits just the opposite condition. We have already
pointed out once or twice the abnormal condition appearing in the direction of the deflections in the
vertical intensity at Sodankyla, and we will therefore merely refer here to what has been previously
mentioned respecting the probable cause of this.

At the three southern stations, the conditions appear to be mainly affected by the negative storm,
as the current-arrows indicate that this district is in the western part of an area of convergence; but it
is not, of course, on this account impossible that there may be positive precipitation in the district along
the southern part of the auroral zone from Norway westwards.

If we assume that such a system exists, then Christiania and Gottingen would be situated in the
eastern portion of its area of divergence; here, however, the current-arrows are directed southwards.
Whether there is a negative storm-centre in the district east of this, or a positive storm-centre to the
west, the direction of the current-arrows at these stations will be very much the same. It may therefore
be very reasonably supposed that these two systems actually existed simultaneously; the conditions at
the more southerly stations would also be very much satisfactorily explained on the basis of such an
assumption.

On Chart VIII, for I9h 20™, the powerful storms are over, at any rate at those stations from which
we have observations. Simultaneously with the decrease in the strength of the negative storm from the

344

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

dominant magnitude that it had in the two preceding charts, the positive area of precipitation once more
shows up distinctly, extending from Godthaab, across Jan Mayen, to Bossekop.

The shape of the negative system of precipitation is the same as before, but the forces throughout
are considerably weaker, the strength being more or less uniform at all the stations of the group in
which the storm is acting. The strongest perturbing force is at Uglaamie, but this is comparatively little
greater than those at Ssagastyr, Cape Thordsen and Kingua Fjord.

With regard to the conditions in the vertical intensity, we notice all the time in Jan Mayen the
strong negative forces. This may be explained as the effect of the negative system to the north of the
place, or of the positive system, which must be situated to the south of the place, or best of all, of
course, as a co-operation of these two factors.

The probability of the correctness of the last assumption is manifest. Whether the one or the
other of the two systems has the greater influence in a horizontal direction, and causes the current-
arrow to point to one side or the other, as these systems here counteract one another, the conditions
in the vertical intensity do not change the direction of their deflections, as the two systems act in the
same direction, the strength alone varying so that when the storms are at their height, the vertical arrow
is also greatest.

After I9h 20™ the magnetic elements are a little disturbed before the close of the period, but the
disturbances are of little strength, and therefore do not give rise to perturbation-areas of sufficient power
and coherence to make them worthy of being studied in detail. For one reason, our observations are
too few, and for another these storms will have a more local character, so that the connection will not
come out so clearly.

In conclusion we will point to a circumstance, which one cannot help noticing in going through this
perturbation, namely that the positive storms always occurred on the afternoon-side. The negative storms
formed as a rule a more or less circular or spiral area of precipitation round the geographical pole, or
the pole of the magnetic axis; but when there were strongly-marked storm-centres, these were formed,
as a rule, upon the night-side of the globe.

Thus far then, this perturbation also furnishes a support to the view of the behaviour and course
of the perturbations, which we have previously put forward.

Unfortunately we have no observations of this day from Fort Conger, as the ist January had been
taken there as the term-day, instead of the 2nd January.

TABLE LI1.
The Perturbation of the 2nd January 1883.

Gr. M. T.

Ph

Uglaamie

Fort Rae

Kingua Fjord

Godthaab

Pi

A

Ph

ft

P,

Ph

PA

A

Pi

h m

12 20

- 47 r

W 105 ;'

- 57 3'

- 65 ;'

E 36 y

+ 60 y

- 27 r

W 153'

+ 43'

w 7.5;-

13 20

- 27 „

n 160 „

- 18 „

-a'5 n

n 57 n

o

- 62 „

» 38 „

- 23 „

„ 3 „

14 5

-220 „

E 70 „

+ 8 „

-275 „

»HO n

- 73 n

-123 „

n 18.5 „

+ 23 „

E 48 „

20

-158 „

» II0 n

-*- 55 B

-175 „

45 «

- 60 „

- 65 *

» 6-5 „

-f la „

n 42 „

15 0

— 92 „

W 7 „

+ 52 „

-"3 »

» 34 n

- 5° »

- 54 n

. 46-5»

o

„ 22 „

20

-117 n

E 78 „

+ 57 n

- 55 n

n 27.5 „

- 3° n

— 6l n

n 57 r,

o

» " H

16 20

+ I' n n ° n

+ 20 „

- 5 n

Wl2.5n

- 10 „

- 28 „

» 18.5 „

+ 9 „

„ 8.5 B

17 20

- 68 „

n 72 „

+ 20 „

- 55 „

E 3° *

o

- 77 n

ni48 „

+ 74 n

n 3< •

4° - 94 n n 93 n + 4 ' „

- 74 n

n 45-5 n

- J5 n

- 87 „

n Ioa »

+ 32 »

n 5-5 n

18 20

~J6S n

» 72 „

+ 61 „

- 57 n

n 33 n

- 10 „

- 65 „

n I°9 n

o

W20 „

19 20

— 2O5 „

» 48 „

- 26 „

- 32 n

o

- 10 „

- 33 n

» 82 „

4a n

E45 „

2O 20

— "4 ii

n 9° „

- 43 n

- 4° „

Wio „

0

- 13 n

n 64 » I + 8 „

W4o „

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I.

345

TABLE LII (continued).

Gr M. T.

Jan Mayen

Bossekop Sodankyla

fk Pd

P,

Pk Pd

P,

Pk

Pd

P,

h m

\

12 2O

7 y E 3 y

+ la y

o

W 8 y

0

0

o

+ 7 y

13 20 —

5BW3B + 12 „

o

0

- 5 7

- 3 7

o

+ 7 B

14 5 +

22 „ 0 + 18 „

+ 13 y • B s „ 4- 10 „

+ 9 n W 5.5 y o

20 4-

24 B ° + '8 „

+ 5 B B 20 „ 0

+ 3 B B '5 n 1 °

15 o +

35 „ E 10 „ 4- 35 „

0

E 6.5*

4- 19 „

7 „ ; E 8 „ - 15 „

20 4-

12 „ „ 6 „ ' + 22 „

0

o

4- 10 „

4 B o

— 9 B

16 20 +-

'3B ° + 34 B

+ 5 B ! o j + 10 B

O 0

o

17 20 4-

SB W 31 B

- n B

•+• 23 „ „ 15 B ; + 20 „

•+• "» B » '3-5 B - '7 B

40 —

13° B B 58 „

- 30 „

4- 60 „

B 78 B + 57 „

+ 37 B

B 53 B

- 43 B

18 20 —

155 B E 116 „ -247 „

+ IS B B 28 „

- 28 „

-"-MB B 29.5 B

o

19 20 4-

50 „ „ 17 „ -160 „

+ 47 B

B 9 B

+ 28 „

4- 12 „

B '3 B

9 B

2O 20 —

9 B :W I7 „

65 B

— ' 5 «

B 21 „

- 1° B

- 5 B

B 22.5 B

- 8 „

TABLE LII (continued).

Gr. M. T.

Cape Thordsen

Little Karmakul

Ssagastyr

A

n

-Pf

fll

^d

P,

Pk

Pi.

h m

12 20

+ 42 /

En y

- 10 ;•

- 6 7

Way

0

4- 37 y E 19 y

13 20

+ 20 „

n " n + 41 »

+ 5 B

E 8 „

O

+ ia B ; B 37 n

'4 5

- 67 »

„ II.5 „ - 22 „

+ 43 „

W 16.5 „

+ ia •/

+ 24 „

B 9 ,1

20

- I2 n

n 8 „ o

+ 66 „

„ 3» »

+ 35 B

+ 64 „ W 4 „

15 0

— 47 »

w 26 „ — 25 „

+ 15 » E 19 „

+ 3° »

+ 225 „ „ 63.5 „

20

- 28 „

n 29 „

- J9 n

+ 17 n

» 8-5 n

+ 28 „

+ 69 „ E 3 „

1 6 20

+ 3 „

• »• -•

- 33 n

- 1 6 „

n ^Sn

+ 9 B

- '9 B

B 4 B

17 20

- 75 n

W 17.5,

- 13 n

+ 41 „

B 23-5 n

- 23 B

-235 B Wi6 „

40

-53° „

£385 „ +422 „

+ 93 * W3o „

- 79 B

-544 B °

18 20

-378 „

„ 68.5 n

-3°2 „

- 82 „

E 70.5 »

-J74 B

-339 B

E 26 „

19 20

-no „

n 17 „ , -169 n

o

n 24-5 B - T B

- 93 B B 28.5 „

2O 2O

- 57 n

n 5 n

+ '4 n

- 19 „

B 76 B

- 76 B

- 72 „

B 41 B

TABLE LII (continued).

Gr. M. T.

Christiania

Pk

Pawlowsk
Pd

Pk

GOttingen

Pk

Pd

Pk

Pd

P,

h m

\\ '

12 20

+ 2 y

O

o E 2.5 y

+ i /

E 6 y

— i y

13 20

- I-SB ° ° " 3-5 B

- I B

o

+ °5 B

'4 5

+ 7 B °

+ 8 y o

Perhaps

0

B 2 „

+ 14 B

20

+ 3-5 B W 7 y

+ 3 B

W 5 B

small devi-

— I B

0

+ '3-5 B

'5 °

- 7 „ ' °

3 n E 4.5 „

ations, but

- 8.5 „

B 8 „

+- 6.5,

20

- 4 „ o o

o

nothing

- 6 „

» 8 „

+ 4 B

16 20

o

can be

+ I B

B 8.5 „

- I B

17 20

+ 4-5 B

E 7 B

+ 8 „

„ 6.5 „

taken

+ 5 B

B I0 B

- 7-5B

40

- '-SB

B 21 B

+ 16 „

B 20 „

out.

+ I B

B aa n

- ' B

18 20

+ 15 B B 37-5 B

+ 26 „ „ 15.5 „

+ 12.5,,

B 36 B

- '-SB

19 20

4 B B 7 B

° B 5 B

- I B

B 2.5 „

- 0.5 „

2O 2O

— 11 n

B 9-5 B

o

B 'S-Sn

+ I «

» 6 „

+ 3 B

346

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, lgO2 — 1903.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I.

~

347

Bo

M

n

>

u

a
c

v

o

e

a
U

N

rf

bo

348

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

isiltt

r

S
u

fO

00

CO

X

«

a
c

•a

a

V

in
I

u

;

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I.

349

BIKKKI.AND. TIIK XURWKC.IAX AURukA I'OI.AKIS KXI'KIMTIOX, !9O2

THE PERTURBATIONS OF THE 1st NOVEMBER, 1882.

ll'l. XXIlIi.

}{o. 1 he striking resemblance that these perturbations bear to the two preceding storms, is appa-
rent on a first glance at the copies of the curves. All the storms occur at the same time of <lav; they
are on the whole very characteristic and well-defined; the direction of their deflections is the same ; they
are <>f mure or less the same strength; anil they are preceded by a Comparatively <|uiet period.

In this case, too, it will be best to divide the period into two sections, the first being from io''to
about 16'' 30'", the secund from about 1 61' 30'" to 23'' ao"1.

This division, however, dues not, as in the case of the preceding perturbations, suit all stations
equallv well. The conditions at Jan Mayen and Godthaab in particular, do not admit of a natural divi-
simi such as this.

The principal phenomenon in the first section is the powerful negative storm that we find in North
America.

This storm is exceedingly characteristic and well-delined, anil the perturbing forces, during the
time when the storm is at its height, are ol very considerable strength. Thus at I'glaamie, the oscilla-
tions are so great that the needle for the horizontal intensity between 14'' and 15'' is deflected beyond
the field of observation, and onlv re-enters it now and then, namely, at 14'' 5'", 14'' ionl and J4h2om,
so that there are once more definite readings for these hours. The strongest perturbing forces, it will
be seen, appear at Uglaamie, and we must therefore look tor the storm-centre of this negative system
of precipitation in the neighbourhood of that station.

The/ storm-centre on this occasion is a little more easterly in position than in the storms in the
first section of' the two preceding perturbations. At the same, the conditions at Ssagastyr are also some-
what different. \Ve there have now distinct effects of the negative system of precipitation. The forces
are not so strong as at Uglaamie, but the curve has a very jagged character. At first the perturbing forces
in the declination are directed eastwards, and in magnitude considerably exceed those in the horizontal
intensity. Subsequently, at 14'' 15"', the deflections are reversed, and after 14'' 20'" there are only small
values of l'r/, which is now east, now west; and from that hour the perturbing forces in the horizontal
intensity are the predominating. This station is thus evidently situated to the west of the centre of the
negative storm, although probably actually in the field of precipitation. In the first section of the two
preceding storms, we did not find at Ssagastyr any special effect of the negative system of precipitation,
which was also found during these two storms in North America.

\\V found, on the contrary, more or less distinct effects of a positive system of precipitation. At
Uglaamie, on the other hand, the conditions during these two preceding storms were exactly analogous
to the conditions we now find at Ssagastyr. In these regions, during the first section of the perturba-
tions, there appears a negative system, which, in its behaviour and character, exactly corresponds with
those- we found during the two preceding storms; but the position of the system on this occasion has
moved a little westwards, so that the conditions at Uglaamie during the preceding storms, answer to
those at Ssagastvr during the present storm.

It will be well to carry the comparison still further, and see how far the conditions at the other
stations are analogous to those we have formerly found. Before doing so, however, we will remind the
reader of what we said in the two [in-ceding perturbations regarding the conditions at C'ape Thordsen
during the first section. It appeared from the curves that simultaneously with the powerful negative
storm in North America, a negative storm also occurred at Cape Thordsen, counteracting the positive
storm which prevailed during the period before; and after, and causing the deflections to some extent to
alter, so that we found negative values of />, at the hours at which the storm in America had its maxi-
mum. During the present perturbation, in the interval before the powerful negative storms, there is no

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 35!

pronounced positive storm at Cape Thordsen; and we now find simultaneously with the storms in Ame-
rica, very strongly marked effects of a negative polar storm of very considerable strength (compare
Plates XXVI, XXV and XXIII). If we go on farther, to Fort Conger, we find there, too, quite distinct
effects of a negative storm as the declination-curve there, just at the period under consideration, in
which the negative storm occurs, exhibits a very distinct, well defined, westerly deflection of the decli-
nation curve of very considerable amplitude. As previously remarked, current-arrows directed westwards
answer to a westerly deflection such as this.

It would appear, therefore, that this is an effect of more or less the same system as that acting at
Cape Thordsen. At Kingua Fjord also, there seems to be a negative storm, judging from the deflection
of the horizontal-intensity curve; but it is difficult to decide so directly here, as the absolute value of
the declination in this case is fairly great, thus giving the deflections in the declination curve greater
importance than at those stations at which the declination-value is only small. It seems, however as if
this too were principally the effects of a negative storm, and if so, one of longer duration than at the
other stations; but these conditions will be better studied by the aid of the charts.

In addition to this, or these, negative area or areas of precipitation, we find in the region about
Godthaab, Jan Mayen and Bossekop, a distinctly positive system of precipitation. The effects of this system
are most clearly apparent in Jan Mayen, where the positive deflections in the horizontal-intensity curve are
of considerable amplitude and very well defined. The deflections, however, as already remarked, do not
terminate at the conclusion of the first section, but continue, without great alteration in strength, directly
into the next section. This is at any rate the case as regards Jan Mayen and Godthaab, where the
storm is most powerful. At Bossekop the perturbing forces are only small, and here we find a distinct
strengthening of the positive deflections, just at the time when the negative storms are at their height.
Here too, however, the absolute value of the forces is not particularly great.

A positive area of precipitation such as this, was also one of the peculiarities of the first section
of the two preceding storms. The position here, however, is a little different from what it was earlier;
but the only way in which it differs from that of the other storms is that the area of precipitation does
not extend so far eastwards as before.

At Little Karmakul, there are no perturbing forces, in this first section, of sufficient magnitude to
warrant the supposition that they are due to the effect of systems of precipitation in the vicinity of the
place. In declination, however, we find at about I5h, that is to say, just at the time when the negative
polar storm has its maximum, a very well defined deflection, though of comparatively little strength.
In the horizontal intensity, on the other hand, the conditions during this deflection are more or less
normal, and it is not until a little later that we find perturbing forces here too, and these in a negative
direction.

In the vertical intensity the conditions here are interesting. Simultaneously with the deflection in
declination, there is a corresponding negative deflection here. Immediately before this, there is a deflec-
tion in the opposite direction. As these deflections are very well defined, it is possible to attribute some
importance to them, notwithstanding their comparatively small strength. It seems reasonable to suppose,
both on account of the quiet character of the curves, and the small strength, that the conditions are due
to the effect of a system that is not in the immediate vicinity of the place. The direction of the current-
arrows that we find here is northerly, and will thus answer to conditions in the eastern part of an area
of convergence. The vertical arrow, in accordance with this, is directed upwards. It must thus be either
the negative system with district of precipitation in the neighbourhood of Cape Thordsen, which pro-
duces these characteristic perturbation-conditions at Little Karmakul or the southern positive system,
which has its area of convergence to the north of the main axis, or perhaps both these two in co-
operation.

352

BIKKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

If we look at the conditions at Bossekop, we find, as already mentioned, a peculiar strengthening
in the positive deflections in the horizontal-intensity curve, just at the time when the negative storms
are at their height. This, as we have said, may be explained directly as an effect of the positive storm;
but we will here draw attention to the fact that it is also possible to explain the conditions as effects
of the negative system lying to the north, if we assume the point of convergence of the system to be
situated to the north of Bossekop. Lastly, it is possible that these two factors act simultaneously, and
this might perhaps be the most probable explanation.

At the southern stations, the conditions seem mainly to be ruled by the positive polar storm. We
here find a distinct, well-defined deflection in the horizontal-intensity curve in a negative direction; where-
as in declination we find only deflections of small amplitude. These are first directed eastwards, and
then, at about 15'' 20™, turn round. The current-arrow in these regions turns distinctly clockwise for a
certain angular distance. This, it must be assumed, would indicate that as the point of divergence of
the positive system is situated to the north of these stations, as PI, is negative, the system of precipi-
tation now would be moving, although only slightly, eastwards. As we have learnt in Part I, it is just
such a deviation of the current arrow that marks a movement of the system of precipitation. As, how-
ever, we have so few stations in the positive area of precipitation, it is scarcely possible to prove with
any great degree of certainty the existence of such movement by the aid of our observations from the
arctic regions.

If we look, lastly, at the perturbing forces in the vertical intensity, we find that at Pawlowsk they
are in accordance with the fact that that place is situated in an area of divergence, as Pv there is positive.
At Gottingen also, we find evidently positive deflections in the vertical-intensity curve at the time the
perturbation is in progress. This is apparent on a direct consideration of the curve. We have not taken
out any perturbing forces, however, as the position of the mean line is rather difficult to determine from
the data at our disposal. Its determination would therefore be too uncertain, and the values obtained
might possibly give misleading ideas of the actual conditions. In this first section, however, there seems
to be no doubt as to the direction of the deflections, although they cannot easily be given decided values.

At Bossekop we find a well-defined positive deflection in the vertical curve. This should indicate
that the positive system of precipitation exerted a distinct influence here, and was situated to the north
of the place, for the negative system that is found still farther north, would here occasion deflections to
the opposite side. If the actual perturbation-conditions at Bossekop are in accordance with the observa-
tion taken, it must necessarily be supposed that the effect of the positive system extends thither. This
is moreover natural, to judge from the conditions at Pawlowsk, where there are strikingly clear proofs
of the effect of the positive system. While there are thus positive deflections in the vertical-intensity
curve at Bossekop and Pawlowsk, at Sodankyla the deflections are as usual in exactly the opposite
direction. The probable explanation of this has already been mentioned.

On Charts I and II, for the hours // 20'", // /"', // 20™, 14'' jo">, //'' //'" and i6h 20'", all
these conditions come out very distinctly. On the night side, from Fort Rae, through Uglaamie, to Ssa-
gastyr, extends the great negative system of precipitation.

A kind of continuation of this is found at Cape Thordsen and Fort Conger, or it might be sup-
posed that a more or less independent system is at work there.

At Kingua Fjord the direction of the arrow is distinctly southerly, but swings round from east at
I3b 2om — at which hour the storm thus really seems to belong to the positive system of precipitation — to
a fairly decided west at the close of the period, which would indicate that a negative polar storm was
then acting. The transition from the more positive to the more negative character of the storm does
not, however, take place so discontinuously as we are accustomed to find at Little Karmakul, for instance
where we very frequently find such reversals. On account of the fairly constant direction of the current-

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 353

arrow, one might be tempted to believe that these were really systems of precipitation in which the
direction of the principal axis is not so decidedly east and west, but more north and south. It is easy
to imagine a connection established between such a system in Kingua Fjord, and the negative system of
precipitation at Cape Thordsen and Fort Conger. Such a condition is not only conceivable, but, as
previously observed, we find by the experiments, phenomena which clearly demonstrate that we should
expect to find, just in these tracts, areas of precipitation the main axis of which were directed tolerably
nearly due N— S; compare p. 327, fig. 140, art. 82.

The conditions at Godthaab and Jan Mayen in connection with the southern stations, show us
distinctly a positive system of precipitation with accompanying area of divergence. At Pawlowsk, as we
see, there are also positive vertical arrows; and we have already seen that at Gottingen, during this
period, a positive deflection appeared in the vertical-intensity curve. We thus have every indication of
the existence of this positive system of precipitation.

These are in the main the most characteristic conditions during the first section of the perturbation.
It is difficult to prove with certainty any movement of the systems.

At several stations there now ensues a longer or shorter period of more normal conditions, after
which the new perturbations belonging to the second section commence. At other stations there is no
such distinct division, but the deflections continue without ceasing on into the next period.

The perturbation-conditions here prove to be rather more complicated than in the preceding section.

We will here make Ssagastyr our starting-point. The perturbing forces appear here chiefly in the
horizontal intensity. The amplitude of the deflection is now about the same as during the preceding
section ; but its duration is here a little longer. No exact statement of the time of the appearance and
termination of the perturbation can be given, but roughly speaking, the perturbation occupies the period
from i6h 30™ to 20''. Simultaneously with this, the conditions at Uglaamie and Fort Rae are very inter-
esting, as we there find simultaneous deflections in the curves, especially in the horizontal-intensity curve,
in a negative direction; but the forces are now comparatively very weak.

At the stations west of Ssagastyr, however, there are fairly powerful perturbing forces. As before,
we can follow the negative storm over Cape Thordsen and Fort Conger; and at the first of these
stations, the perturbing forces are of considerable strength.

The conditions at Little Karmakul and Bossekop are now of special interest. At the first-named
station we again meet with a condition of which we have so often before had instances, namely, the
simultaneous action of positive and negative perturbing forces. We there find now positive, now nega-
tive deflections in the horizontal intensity, until about i8h 30™, from which time the deflections are
negative and remain so for the rest of the period. From this hour then, the effects of the negative
storm predominate, and the perturbing forces are exceedingly powerful, thus indicating the proximity of
a storm-centre.

At Ssagastyr, we found, it will be remembered, exclusively negative deflections in the horizontal-
intensity curve, beginning at the very beginning of the period.

At Little Karmakul, it is not until considerably later that the negative storm gains the ascendancy;
and this would therefore seem to indicate that the negative storm-centre, or district of precipitation, is
moving westwards.

This last view of the conditions is also confirmed by a comparison with those at Bossekop. At
first there is evidently a positive polar storm acting, and we cannot perceive any special trace of a
negative storm. At about igh 30™, however, the curve for the horizontal intensity goes to the opposite
side, and for the rest of the time we find fairly powerful effects of a negative polar storm, although the
perturbing forces here are not so great as those we find at Little Karmakul. If we look at the time

^4 HIKKKI AND. II IK NOKWKC ,l.\.\ Al'KOKA 1'OI.AKI.-, KXI'I-.IH I 1OX , I QO2 1903.

after which the negative storm acts exclusively, at the last two stations, we find here too a considerable
difference in time between them, namelv, of almost e.xactlv one hour.

Thus the negative storm appears considerably later at the more westerlv stations than to the east,
in thi> district; and wo feel justified in taking these circumstances as a proof that the negative storm-
centre in this section of the perturbations, is moving westwards, and thus in some wav or other is fol-
lowing the sun in its apparent diurnal motion.

It would not be right, however, to draw conclusions respecting the details of this movement from
these facts, tor it cannot, of course, be taken for granted that the district of precipitation moves exactly
along the auroral /.one as the perturbations run their course. This is all the more inadmissible from
the fact that at Cape Thordscn and Fort Conger, there arc distinct proofs that also polar arc-as qf
precipitation exist farther north, and that therefore- in detail the conditions may be a little more com-
plicated. It would at anv rate be natural to expect that the conditions would not be so simple if, instead
of comparing stations that were all situated south of the auroral /.one — as was the case with the three
stations just considered we were to compare the conditions at stations lying some to the north and some
to the south of that /one. This proves to be the case, when we go farther west to Jan Maven, and
compare the conditions there with those, for instance, at Bossekop. There too, it is true, there is first
a positive storm, which is very powerful and pronounced, and later on the direction of the deflections
in the horizontal-intensity curve change, indicating that now, instead of a positive polar storm, the
effects are those of a negative storm ; but the change takes place earlier than at the more easterly situ-
ated Bossekop. The cause of this may therefore naturally be looked for in the circumstance that Jan
Maven is situated to the north, and Bossekop to the south, of the auroral /one, and that therefore the
northern, or north-western, branch of the negative district of precipitation -if it may so be called— might
be supposed to reach |an Maven earlier than its eastern, or more southern part reaches Bossekop. The
explanation of the conditions in Ian Maven might thus be that it was the effect of the negative system
of precipitation at Cape Thordsen, extending, as the perturbation proceeded, westwards to Jan Mayen,
or possibly moving in that direction. This view is further supported by the fact that the change in Jan
Mayen occurs just at the time when there is a sudden, very considerable increase in the negative deflec-
tion in the horizontal-intensity curve lor Cape Thordsen. When we finally come to consider the con-
ditions of the vertical intensity, we shall return to this subject with other circumstances that favour
our view.

1 he negative deflections in the horizontal-intensity curve for Jan Mayen are comparatively small.
In the declination, on the other hand, there is n uniformly-directed, westerly deflection, which, as a
rule, exceeds those in the horizontal intensity in strength. About the time when the change in the
horizontal intensity takes place, there is no special change to be observed in the deflections in the
vertical intensity or the declination.

It is possible, perhaps probable, that here too, after the change has taken place, there are still
effects of the positive system. The comparatively small forces in the horizontal intensity, and the
comparatively powerful forces in the declination, seem to indicate something of the kind; but it is
difficult, indeed impossible, to settle the point with certainty.

The other station where there were distinct effects of the positive system of precipitation was Godt-
haab. Here the system acts a trifle longer than in Jan Mayen; but there is no negative storm after-
wards, the conditions being fairly normal.

With regard to the southern stations, we see that the conditions in the horizontal intensity, during
the first part of the section, are rather variable. At those lying more to the west, such as Christiania
and Gtittingen, however, there- are throughout perturbing forces that act in a negative direction, and are
of sufficient magnitude- to indicate, more or less certainly, an area of divergence which should answer to

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 355

the positive system of precipitation that we find in the district Godthaab, Jan Mayen and Bossekop. At the
more easterly station Pawlowsk, on the other hand, the curve for the horizontal intensity oscillates more
about the normal line, without exhibiting any marked direction. It appears therefore as if the effect of
the positive system of precipitation were weaker here, which is quite natural, seeing that we are
approaching the negative storm-centre.

Later on, it is the deflections in the declination -- which are easterly all the time -- that pre-
dominate. This, as we have often seen before, is a circumstance that has to do with the moving into
these southern districts of the negative system's area of convergence. We should also find the same
direction of current in the eastern part of the area of divergence, which is connected with the positive
system of precipitation. Of these two systems, which of course may be imagined to co-operate, the first
will here have the greatest effect.

The course of the vertical-intensity curve at Pawlowsk also seems to indicate — although one
cannot here venture to draw very certain conclusions -- that at first it is in an area of divergence,
where P, is positive, and afterwards in an area of convergence, at the time when we find negative
values of P, there. The course of the vertical-intensity curve at Gottingen exhibits similar conditions,
but there they are still more uncertain, as the normal line is very difficult to determine. It would not
therefore be advisable to draw any conclusions from this.

With regard to the vertical intensity in other respects, it may be noticed that in Jan Mayen there
are negative deflections all through the section, with the exception of the last few hours of the period.
This is what we have found previously, and indicates that there is a negative precipitation to the north
of the place, or a positive precipitation to the south, or both simultaneously. At Bossekop we first have
positive deflections, as long as the positive storm is acting; and this should indicate that the positive
system is situated to the north of the place. Simultaneously with the alteration in the horizontal intensity
curve, there is also an alteration in the curve for the vertical intensity; and from the moment when the
negative storm gains the ascendancy, we find negative values of P, for the rest of the period. It would
seem, from the above, natural enough that the conditions should actually be in accordance with this.
At Sodankyla, on the other hand, we find the exact opposite; and we thus again meet with that
peculiar phenomenon, to which we have several times drawn attention.

If the vertical-intensity observations at Cape Thordsen are to be relied upon, the negative system
acting there should at first lie to the north of the place, but in the last part of the period to the south.
This agrees very well with the conditions at Bossekop, as the supposed passage of the system over the
station at Cape Thordsen, at the time when P, there goes over from a negative value to a positive,
takes place just when the negative storm gains the ascendancy at Bossekop. Thus at the time when the
vertical intensity at Cape Thordsen indicates that the negative system of precipitation is approaching
Bossekop, we really find there marked effects of a negative polar system.

This gives us a clear hint of the way in which the movement of the systems of precipitation up
there are to be understood, and seems to confirm our previous assumptions in the matter. We found,
it will be remembered, a removal of the system of precipitation towards the west, when we looked at
the three stations Ssagastyr, Little Karmakul and Bossekop, which were all situated south of the auroral
zone. No similar movement, however, could be traced to Jan Mayen, and we adduced, as a possible
cause of this, the circumstance that magnetically considered, that island had a comparatively much more
northerly situation. We further indicated that the conditions in Jan Mayen might possibly be explained
by assuming that the system at Cape Thordsen was moving westwards. We see now, however, that at
these hours there are also indications that the system at Cape Thordsen has a southerly movement, or
at any rate that its movement will have a component in a southerly direction; and it therefore seems
fairly probable that the change will take place a little earlier in Jan Mayen than at the more southerly
situated Bossekop.

356 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

The simplest conception of the matter might be, that this was a to some extent connected negative
system of precipitation, whose eastern part extended more or less along the auroral zone, but whose
western part curved more northwards; and that the whole of this district of precipitation moved west-
wards with the sun.

Such an assumption also agrees with what we find by experiment. We may here, for instance,
refer to fig. 140, pag. 327, where we clearly see such a deviation of the area of precipitation towards the
N., and particularly to the subsequent chapter in which the terrella experiments are specially treated of.

Having discussed the conditions of perturbation so thoroughly, we need now only briefly touch upon
the perturbation-areas that we find represented on the charts for this section.

On Charts III, IV and V, we find the direction of the current-arrows for the period in question
shown for nine epochs.

In its main features, the movement of the negative system of precipitation that we found and have
described above, can be distinctly followed.

If we considered the three polar stations mentioned above, which are situated to the south of the
auroral zone, we see, on Chart III, distinct effects of the system only at the most easterly of these,
namely, Ssagastyr. At Little Karmakul, the negative storm does not gain the ascendancy until Chart IV;
on Chart III the current-arrow swings backwards and forwards.

Lastly, at Bossekop it appears that it is not until the last epoch represented on Chart IV that the
negative storm is predominant. Before that, there are only more or less distinct effects of the positive
system. We further see on Chart IV that the negative storm appears earlier in Jan Mayen than at
Bossekop. As regards the negative storm in other respects, we see all the time at Cape Thordsen
strong westerly-directed current-arrows. East of Ssagastyr, the strength of the current-arrows diminishes
considerably, so that the boundary of the area of precipitation is probably between Ssagastyr and Uglaamie.

At the close of the section, we find the negative storm-centre in the north of Europe or the north-
west of Asia.

The positive system asserts itself distinctly only on Chart III, at Godthaab, Jan Mayen, Bossekop
and Little Karmakul.

With regard to the conditions in southern latitudes, we see only slight, though sometimes fairly
distinct, indications that the stations are in an area of divergence. Nor is this unlikely; for, judging from
the observations from the northern regions, we should expect to find the area of divergence farther west.

On the other hand, we find on Charts IV and V, quite certain indications of an area of con-
vergence.

There is one circumstance, however, which to some extent seems to point in the opposite direction,
namely, the conditions in the vertical intensity at Pawlowsk. We have already noticed that first positive,
and then negative values of Pv are found here; but now we see that the positive forces also appear
to last longer than the period in which the positive storm predominates, being even apparent at times
when there are fairly distinct indications in a horizontal direction that we are in the area of convergence
of the negative system of precipitation. It is not impossible that the conditions are actually like this;
but on the other hand it should be remarked that the position of the normal line during this period,
might very possibly be a little different from what it is here; and one must therefore not conclude too
much from this circumstance. There is, moreover, a great possibility that in southern latitudes perturbing
forces might be operating that are imperceptible here, but which may yet exert a disturbing influence
upon the perturbation-conditions that we are now considering.

At Gottingen, as we have said, the vertical intensity also exhibited conditions similar to those at
Pawlowsk. Here, however, they were more easy of explanation, as the station lies so much farther
west, that one might well imagine the positive system to be acting as long as the positive deflections
appear to continue.

PART 11. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I.

357

The last phase of the perturbation, as will immediately be seen, is just what we have previously
designated as a negative polar elementary storm, with the storm-centre in the north of Europe, a storm
such as we have again and again met with in Part I. In these storms, we have learnt to understand how
they are a link in a long chain of perturbations, which, it appears, steadily develope in the course of
the day, in more or less the same manner. In the succeeding pages, we shall see how confirmation of
this will actually be obtained.

TABLE LIU.
The Perturbations of the ist November, 1882.

Gr. M. T.

Uglaamie

Fort Rae Kingua Fjord

Pk

Pd

Pv

Pi,

Prf

P,

Ph

/;/

h in

12 2O

0

E 18.5;'

0

- 5= /

E 22.5;-

4- 25 r

0

E 17 ;•

13 20

o

,t 32 »

-r M ;•

- 44 n

i, 22 „

+ 65 ,,

0

„ 68 „

'•1 5 - 257 ;•

o

4-112 „

-236 „

n I03 n

+ 255 n

- 53 r

n 43 n

20

152 „

i, 23 „

4-118 „

-231 n

11 I02 n

+ 255 n j - 45 n

„ 26.5 „

40

->258 „

,,217 n

+ 89 „

-337 n

n '6° „

+ 55 „

- 76 „

0

'5 '5

"99 n

it l62 it

4- 80 „

-285 „

. I02 I,

— 10 „

- 55 *

W 57 „

I 6 20

5 i,

W 37 „

+ 28 „ 0

„ 38.5 ,,

— 35 n

- 5° „

n 95,,

1 7 20

'5-5 n

n 5 »

- 5 . |1 - 20 „

W I „

- 5° n

- 12 „

n 95 n

5°

- 15.5 n

,, '6 .

- 33 it

o

E 4 „ ro „

+ 7 *

n 47 n

1 8 20

- 69.5 „

E 26 „

- 56 „ 1 - 20 „

0 - 20 „

7 n

„ 5 -

19 o

- 5! „

W 2, „

- 56 „ - 22 „

W 2.5 „ 4- 20 „

+ 25 „

n 32-5 „

20

51 „

E 16 „

- 56 „ - 27 „

„ 23 „ i 4- 5 „

+ 9 „

n 29 n

20 0 -t- 11.5 „

W 40 „

- 37-5 n

— 20 „

,, 28 „ 5 „

4 n

« '7 „

20

+ 4 „

„ 66 „

- 33 i,

- H It

n '5-5 „

o

0

« 26 „

21 IO

o

n 64 „

- 23.5 „

O

n 9 n

^ 25 „

+ 3 n

n 31 n

22 2O

0 In 72 n

+ 9-5 n

- 19 ,,

E 1.5,,

+ 20 „

- " n

n 3° "

TABLE LIII (continued).

Gr. M. T.

Godthaab

Jan Mayen

Bossekop

Ph

Pi

ft

Pd

P,

ft

Pd

P.

h m

12 2O

+ 53'

o \ + 5 ;•

w 3 ;-

O O

0

0

13 20

o

E 25 J' 4- 37 „

n 8-5 n

+ 6 r il + 53'

0

- 27 ;•

14 5 \+ 6 „

n 5° « , + '33 l!

E 11.5 ,t

— 12 „ 4- 16 „

W 12.5 ;<

-+• 39 n

20 4-19 „ „ 56 „

4- 128 „

W 8 „

- 34 * + 37 „

o

+ 78 „

40 + 20 „

n 65 „

+ "27 n

o

- 40 „ 4- 15 „

E 6.5,,

4> 29 „

IS '5

+ 32 „

n 42 n

4- 122 „

E 17 ,,

- 44 „ 4- 62 „

n 14 n

"T 9O „

16 20

+ 3° „

n 36-5 n

4- 7t tt

W 6.5 „

o

+ '4 -i

W ,8 „

4- 10 „

I7 20 ; 4- 15 „

n 34 n

+ 97 „

» 5-5 n - 22 „ : 4- 7 „

„ 6 „

+ '3 *

50

+ 32 „

„ 28 „

-•- 78 „

n I" n

- 3° „ : + '5 „

»1 7 n

+ ie ..

18 20

+ 5° „

n 53-5 n j| + 6 «

n 45-5 n

- 44 n

+ 50 „

n 7 w

+ 63 „

19 o

+ 15 »

W n „

- 53 n

E 11.5,, - 36 „

+ 66 „ „ 33 „ + 18 „

20

"~ 5 n

n '7 n

- n n

W 63 „ - 80 „

— 21 „

« 45 w

- 21 .,

20 O - II „

0

- 64 „

„ 89 „

- 85 „

-168 „

0

- a? n

20 | — 5 „

n IJ »

5r n

„ 64 „ - 60 „ '! - 83 „ E 18 „

- 82 „

21 10

— 7 >i

n r7 It

- 28 „

n 48.5 „

+ 23 „ -123 „

« 67 „

-'77 n

22 2O - 20 „

it 25 „

- 77 »

., 24 „

o - 86 „

n 25 »

-'77 n

Kirkelnnd. The Norwi-gian Aurora Polaris Kxpeclition, 1902-1903.

i'.lKKKI AMi. 1111 MiK\Vi:i,!AN AI'UnKA 1'ul.AKI^ 1 :.\ I 'Klll'l li )\, IQO2- 1903.

TAIJLK L1II (continued).

I O O
L'O

'JO O

20

13 1 It)

5 -. \V 6.5;-

;;o .. \\' 8 .. oo

io I .. „ 12 „ 52

MO., 1'- uo 5 .. - 10

162 .. \\' 50.5 ., - 18

o ; .. .. 10 .. • .>/)

13 ., „ 10.5 .. -r 1 5

-O ,. .. '-; „ -i to

PART ii. POLAR MAGNETIC HIKNOMENA AND TKRRELLA EXPERIMENTS. CHAP. i.

359

•a
c

o

"^f

•—

V

o
Z

N

E

in

x.

£o

"m

I \,

36o

U1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, I <)O2 1903.

n

g "
b

N

a
ffi

s

f>

V

'

_: 'L

I

a
I

'

00

1

a"
o
in

t~-

«-H
«

tt
«

d

PART II. POLAR MAGNETIC PHENOMENA AND TEUUELLA EXPERIMENTS. CHAP.

Current-Arrows for the 1st November 1882.
Chart V at 20h 20m, 211' 10m, and 22h 20m.

361

Fig. 15'-

THE PERTURBATION OF THE 14th and 15th FEBRUARY, 1883.

(PI. XXVIII).

86. The three preceding perturbations have exhibited a very great resemblance to one another
in their manner of occurrence and course.

It will be remembered that in the last-described of these three perturbations, we found at the close
a strong negative area of precipitation in the north of Europe, while at the other stations there were only
small perturbing forces.

This last perturbation, with its rather limited area of precipitation, was of the same type as those
we so often met with in Part I. It was this type of perturbation that exhibited the simplest conditions, and
that we found was the usual one about Greenwich midnight. At the beginning of the present term day, we find,
as the curves show, an exactly similar negative polar storm, whose district of precipitation is also restricted
to the very same region. The perturbation is here exceedingly characteristic and well-defined, and the
subsequent conditions are very normal, so that the day, on this account, at several places where there
are no daily hourly-observations has been of great importance in the determination of the diurnal variation.
At the beginning of the period, the storm, in several places, has almost reached its maximum.

I ()();->.

It i- at the four stations, Little Kannakiil, ('ape Tnordsen, Bossekop, and Jan Maven, tliat the storm
de\ •(•]( ipi-s to its greatest strength.

If we look at the curves, \vc see that there are several peculiarities in this perturbation that are
\vorthv ol notii'e.

In the lirst plaee, the maximum does not occur exactly simultaneously at these stations.

At Little Karmakul and Jan Mayen it occurs almost simultaneously at 123 '' 25'" -30'", at anv rate if
\ve consider the conditions in the horizontal intcnsitv, where' the dellections are most characteristic. At
the two intermediate stations, on the other hand, the maximum does not occur until a little later, at
~;V' -Jl>!" 4r>'"- I'his circumstance is evidently to In- ascribed to a movement in, or of, the svstem of
precipitation. In the next place, the negative deflections in the horizontal intensity do not cease sinuil-
taneouslv either. At Little Karmakul the dellections decrease rather rapidlv, and even go over to the
other side at o1' is"', so that after that time we find almost cxclnsivelv positive values of/', until about
21' ,-jo'", after which, for the rest of tin; period considered, the curve oscillates about the normal line,
but with very small deflections.

Here then, the negative storm appeal's to be superseded by a positive storm at about o1' 15'".

At the three other stations, howi vcr, there is no indication of any positive storm.

At Cape '1 hordscn, the conditions in the horizontal-intensity curve have once- more become normal
at about o1' 50"'; at ISossckop anil Ian Mayen, on the other hand, this does not take place until about
r'1 20"' -30'".

It will be difficult to demonstrate anv single movement of the svstem of precipitation, by the differ-
ence in time between the various maxima of the negative dellections; but at the conclusion of the storm,
the conditions seem to be simpler. \Vc see that the storm lasts longer at the more westerly stations
than at those farther east.

I»y east and west, here, must not be understood geographical east and west, but rather the direc-
tion, parallel with the auroral /one, and by north and south the directions perpendicular to it. If we
use the geographical east and west, C'ape '1 hordsen is ol course situated to the west of Bossekop;
whereas magnetically, it must be considered as lying to the east of that station. We saw too, that the
storm terminated earlier at Cape Thordscn than at ISossekop.

This last tact also seems to indicate that the system of precipitation is moving westwards, more or
less parallel with, or along, the auroral zone.

In the declination too, there are quite considerable perturbing forces; but the curves here have
sometimes rather a disturbed character, in contrast to those of the horixontal intensity.

It is, as we have said, principally at the- four stations mentioned above, that the perturbation especi-
ally asserts itself; although distinct effects of the system of precipitation are found also at Kingua Fjord
and (iodthaab. The conditions at the last-named station are moreover of peculiar interest, as at about
i h there is a strong, well-dctincd deflection there in the horixontal intensity curve. At that hour we do
not find deflections at an}' of the- other stations, which might indicate anv special connection with this
deflection, and thus this storm appears to be very local.

As regards the American stations, we find at Fort Kae distinct signs of a positive polar storm. 1 he
greatest deflections are at about 3'', at which hour there is also a distinct deflection in the other elements.

At Kingua fjord and I'glaamie, there are also deflections at the same hour, which might be the
effects ol a positive system of precipitation, but they are quite small.

We have then, on this day, once more two systems of precipitation, a negative and a positive-.
Of these the lirst is the stronger, and it appears on the night-side of the- globe. The positive system
appears to be considerablv weaker, judging from the observations we have at our disposal, and it appears
upon the afternoon-side of the earth.

' PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPKRIMKNTS. CHAP. I. 363

At Little Karmakul there seems moreover to be a positive system of precipitation. But it is
especially interesting here to find the positive system of precipitation in the vicinity of Fort Rae, as this
is the only station in this district situated to the south of the auroral zone, and where therefore one
would expect to find effects of a positive system, if such a system actually existed in those regions.
This is the first instance we have of a storm, which appears at Fort Rae at this time of day, and it
thus proves to have the character of a positive polar storm. This instance is of peculiar interest, as it
shows that the occurrence of positive afternoon storms, which we have so often demonstrated at the
European stations, as also at Ssagastyr during the storms just described, is also found in these regions.
The reason why opportunities of observing this phenomenon here are comparatively rare is probably
principally that this is the only American station in a suitable position a little south of the auroral zone.

The perturbation-conditions at Sodankyla are also interesting. The horizontal forces are compara-
tively very small, indicating that this station is not far oft the point of convergence of the negative
system, a circumstance which is immediately evident on looking at the charts.

If we consider the vertical perturbing forces, we see in the negative area of precipitation, that at
the two polar stations, Cape Thordsen and Jan Mayen, which are to the north of the auroral zone, there
are perturbing forces directed downwards; while at the two polar stations, Little Karmakul and Bossekop,
which are to the south of the auroral zone, the forces are directed upwards. This seems clearly to
prove that the precipitation takes place more or less exactly in the auroral zone.

With regard to the vertical forces at Sodankyla, the conditions are just as abnormal as in the
previous perturbations. The forces are positive and fairly powerful. Concerning them, we will only
refer the reader to the remarks previously made about this condition. At the southern stations there are
well defined perturbations in the various elements, simultaneously with the negative storm in the north.

Seven charts have been drawn for this perturbation. On the first three, we instantly recognise the
principal phenomenon that was the characteristic one in this storm, namely, the strong negative area of
precipitation on the night-side of the globe in the regions around Northern Europe. South of the area
of precipitation, a very distinct area of convergence is formed, with all its characteristic peculiarities.
The vertical intensity at Sodankyla is the only exception. In order to obtain a better impression of this
area of convergence, we have also drawn a current-arrow on Charts II and III for Kasan. From
this station, we have five-minutely observations in declination, but in horizontal intensity only readings
at an average interval of two hours. At about 23'" 5om, Gr. M. T., we find a reading, which, when
compared with the other readings, shows with tolerable certainty that at that time there is a perturbing
force PI, of about -f- I5J/- -As we had drawn no chart for this hour, we have employed this value
together with the two values of P^, which can be determined directly for the two points of time. The
two current-arrows are thus only to be regarded as an approximately correct expression for the respec-
tive perturbing forces; and they have only been included here in order to bring out more distinctly the
form of the area of convergence.

On the other side of the principal axis in the system of precipitation, one would expect to find an
area of divergence; but during the preceding storms, the conditions in these high latitudes have been so
perturbed that it has been impossible to prove the existence of anything of the kind. This time, however,
the area of precipitation is so local that we might perhaps expect to find it.

We do moreover actually find perturbing forces at Kingua Fjord and Godthaab, which, in strength
and direction, are very much what we should expect to find in that part of the area of divergence,
which comes into these districts.

At Fort Conger, there are only small perturbing forces in the declination. If the point of diver-
gence of the system were between this station and Cape Thordsen, the direction of the current here

364 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

should be northerly. As we have no observations of horizontal intensity here, we are unable to verify
this; but it may perhaps be worth while to point out an interesting harmony with the conditions
in the area of convergence. We see from the chart that Fort Conger and Pawlowsk are situated more
or less symmetrically one on each side of the principal axis of the system. The tangents to the mag-
netic meridian at the two places are moreover more or less parallel. (The declination at Pawlowsk is
very near 0, and we see that the line magnetic N — S, which is drawn on the chart through Fort
Conger, is very nearly parallel with the meridian of 30° east longitude.)

As the forces on the two sides of the principal axis would probably be more or less symmetrical
in arrangement, we might perhaps expect to find a certain amount of symmetry in the declination-
deflections at the two places. When the declination-curve at Pawlowsk swings out to the west, the curve
at Fort Conger should swing out to the east, and vice versa. This will be immediately apparent if we
imagine the polar elementary field (fig. 40, p. 86, Part I) placed with its principal axis along the auroral
zone in the north of Europe. If we here imagine the storm-centre to move from time to time, and as
a consequence the current-arrow at Pawlowsk to turn clockwise, the current-arrow at Fort Conger will
turn through a corresponding angle counter-clockwise, and vice versa.

It will be seen from Charts I — IV, that we now have before us considerable oscillations of the
current-arrow at Pawlowsk, and it would therefore be another reason for now being able to find a corre-
sponding movement at Fort Conger. If we compare the declination-curves at about o1', we do actually
find a similarity in form, which at first glance may seem unimportant, but which nevertheless is quite
characteristic. It is at this time, too, that the negative storm is most strong and the area of precipitation
so far concentrated, that one might expect to find- similar conditions as mentioned.

The reason why the normal line is situated differently at the two stations, may only be that the
situation of the stations in respectively the areas of convergence and divergence, is a little different. It
is the form of the curve that gives the change in the force's strength and direction from time to time,
and the normal line that gives the absolute values of the force. In comparing the curves, it must of
course be remembered that the scale at Fort Conger is considerably larger than that at Pawlowsk, so that
the variations in the perturbing forces at work are somewhat similar in magnitude.

In the interval between Chart II and Chart IV, the current-arrow at Pawlowsk, as we sec, makes
a considerable turn clockwise. During the same period, Pd at Fort Conger changes from east to west,
which means that the current-arrow, if assumed to have a component in a northerly direction, turns a
certain angle counter-clockwise. In the interval from Chart I to Chart II, in which the movement at
Pawlowsk is certainly distinct, but slight, nothing can be decided, as we do not know P/, at the other
station, and there is little variation in Pj.

We must, of course, be careful not to attach too much importance to this circumstance, and the
apparent harmony between the actual perturbation-conditions and theory; but on the other hand, this has
a special interest, as it is one of the very few cases in which we seem able to trace the areas of both
convergence and divergence of the same polar elementary storm.

This movement of the current-arrows, which we see, at any rate, distinctly in the area of conver-
gence, should therefore indicate that the storm-centre was moving eastwards during the perturbation.
The conditions at Little Karmakul, however, do not seem to indicate any such movement; on the con-
trary, the perturbing force diminishes here rather rapidly, and then, from Chart IV, changes. The field
in the first three charts does not, however, present any difficulties, as we only need to assume that the
district of precipitation to the east of the European stations is rather more northerly in situation than it
is in these regions. This is not at all at variance with what we have seen before, for even in Part I we
have drawn attention to the fact that the negative areas of precipitation on the day-side would be situated
a little farther north than those on the night-side.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELI.A EXPERIMENTS. CHAP. I.

365

The direction of the current-arrow at Little Karmakul on Chart IV might be explained by the cir-
cumstance that the station was situated in the area of convergence of the negative system of precipita-
tion, and south of the point of convergence; but a consideration of the course of the curve seems to
make such an assumption at any rate very improbable, as the forces are much too strong, and the char-
acter of the curve too disturbed. These conditions seem to indicate more or less certainly that we have
before us the effects of a positive precipitation.

The fact that it is difficult to follow the movement of the system in the polar regions, may to some
extent be due to our lack of observations for the time about the beginning of the perturbations.

If we assume that the negative district of precipitation continues also in the districts to the east-
ward of Europe as indicated above, we have a good explanation of the perturbation-area that appears on
Chart IV. If, on the other hand, we assume that it terminates somewhat to the west of Little Karmakul, it
will be much more difficult to find a simple explanation of that, supposing the storm to be more or less
purely polar. Altogether it is difficult to say anything more definite about the conditions here, as the
observations supply only very imperfect information regarding the perturbation-conditions.

On Chart V we see however that the positive system in Little Karmakul, which hitherto have not
been very prominent and which on the whole would appear to have been of mainly local character,
begins to assert itself more strongly. Simultaneously with this, the traces of converging area, which
we up to Chart IV find at the southerly stations, disappear.

On Chart VI the negative system in the north of Europe has disappeared, but on the other hand
we now find the previously mentioned system at Godthaab very well developed. At Fort Rae the posi-
tive polar storm also begins to develope, although the forces there are still very weak.

Lastly, on Chart VII, for 2'' I5m, the positive system at Fort Rae has attained a more or less con-
siderable magnitude. We find moreover a negative storm that is only slight, though very distinct; and
on each side of the principal axis; the two characteristic areas of convergence and divergence seem to
be formed here too.

Subsequently the positive storm at Fort Rae deyelopes further, and attains its greatest strength at
about 3''. As, however, at this hour, there are no perturbations of any great strength at the other
stations, we have drawn no chart.

TABLE LIV.
The Perturbation of the i4th & I5th February, 1883.

Gr. M. T.

Uglaamic

Fort Rae

Kingua Fjord

ft (I)

Pd

P,

n

Pd

P,

ft

/•/

Ii m

23 25 - 32.5 y

W42.5^-

+ ii r

w,55,

+ ii2'

W 45 2'

40 _ 2. „

i) 4° n

No deflec-

~T~ ! r n

fl 20 „

+ 10 „

+ 7 „

n 48.5 n

45 — 27 „

n 34-5 „

tion suffici-

-r 6 „

n 22 „

o

4 12 „

n 5° n

55 - 35 „

n 45 r

ently well

+ 17 „

n 20 „

- 3° „

+ 17 r

n 52-5 n

0 0

— 45-5 »

x 32 fl

defined to o

n T r n

0

"*- 13 *

n 51-5 n

allow of

10

- 27.5 „

n 53 n

4 9 „
anything

n 9 «

4- 10 „

4- 3 »i

n 42 „

20 - Ig „ „ 8 „

being

'5 n

n 6-5«

0

•*• 4 «

n 27 „

50 i - 18 „ I 0

deduced.

•*• 3' n

n 4-5 „

0 7 *

n 39-5 n

I o - 6 „ F, 105 „

The tem-

4- 21 „

E 4-5).

+ 1° n 5 n

n 43 i,

10

+ 13 n 2.5 „

perature,

+ 29 „

W 2 „

+ 1° n 5 n

„ '8 „

20 4 so „ | W 5.5 „

has also -I _j_

n 2 „

° + 3 n

« 3' n

varied

40 ; 4 12.5 „

n 8 „

greatly.

-*- 4° n ! n 13 n

4 10 „

^ 1° „ n 7 n

2 15

~*~ T4 »

» 24 n

+ 7° „

» 17-5 n

0 -f 21 „ , „ 12 „

55

+ 27 „

„ 8 „

4 70

» 22 M

-100 „

+ 21 n ' E 3.5,,

(') Great variation in temperature, which has a great influence on the form of the normal line.
Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903. 47

366

B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

TABLE LIV (continued).

Gr. M. T.

Godthaab

Jan Mayen

Bossekop

Ph

Pd

Ph

Pd

P.

Ph

Pd

Ft

h m

23 25

+ 15 r

W54 5'

-376 3'

E 35-5;'

-i- 103 3'

- 95 r

W24.5;'

-213 7

40

- 1° n

w 54 «

-279 n

n 32 x

+ 25 x

-166 „

E 2.5 „

-280 „

45

8 „

« 54 n

-274 »

W43-5x

+ 62 „

-'53 n

« 23 n

-246 „

55

- 8 „

n 60.5 „

-204 n

„ 42.5 x

+ 57 »

-135 n

B 54 n

-220 „

o o

o

„ 60 „

-196 „

E 32.5 n

+ 47 n

-"7 n

„ 62 „

-212 „

10

4 n

n 47 „

-'77 n

0

+ 51 x

- 83 B

n 46.5 n

-176 „

20

+ 3 „

n 33 „

-I°5 n

W 4 „

•+• '5 «

- 61 *

n 43 »

-'45 n

5°

- 92 „

n 34 n

- 25 x

n 63 x ! + 35 n

- 38 „

n J3'5n

- 88 „

I O

- 54 „

n 84.5 „

- 59 n

„ s „ ' + 56 „

- 4.

» r« «

- 51 n

10

-'3° n

n 42 „

- 37 n

.
n •* n

4- 46 „

- 6 „

n 124 „

- 33 „

20

- 49 „

x 56 „

- 3<> *

EiB- „

+ 55 x

+ 5 „

H 9 n

6 „

40

- 47 B

r 8.5 „

+ 2 n

x 7-5 M

+ 36 „

8 „

n J5 n

- 22 „

2 15 + la „

n '4-5 n

- 38 „

„ 22.5 „ 4- 38 „

7 „

» 23 „

- 19 n

55 + M ,, » 8.5 „

- 23 „

„ 10 « + 58 „

- '5 n

x 31-5 n

- 36 r

TABLE LIV (continued).

Gr. M. T.

Sodankyla

Cape Thordsen

Little Karmakul

n

Pd

ft

ft

Pd

ft

Fit

Pi

A

h m

23 25 ' + 3 ;•

W 4 /

+ 70 j'

- 763'

ES9-S;'

+ 185 y

-174 r

E44 3-

-139 r

40

- 18 „

n 4-5 n

+ 88 „

-'83 „

M 3 n

+ 96 „

-i46 „

n 35-5 n

-129 „

45

- 16 „

E 6.5 „

+ 76 „

-214 „

» 37 j?

-Hi6 „

- 56 „

W42.5n

-"3 n

55

- 21 „

» 25-5 n

+ 77 n

-203 „

n 73 n

4-142 „

-108 „

£42 „

-124 „

0 0

- 17 „

« 32 n

* 58 „

-168 „

n 57 r.

+ I33 x

- 59 n

x 44-5 n

-III „

10

- «i n

n 25 „

+ 39 n

-136 „

» 77 „

+ 140 „

- H n

n 42.5 r

- 97 «

20

- 12 „

n 24 5 „

+ 62 „

- 77 x

n 43 «

+ 88%

+ 32 „

0

- 74 „

5°

- '3 n

n 7-5 n

+ 3° n

+ 15 „

Wir.s»

-+- 34 '»

-1- 9' „

W 4 „

- 23 „

I O

- 10 „

„ 8.5 „

+ 24 „

- 32 „

E64 „

4- 18 „

+ 97 »

» » li

- 1° n

10

- 6,,

* 6 „

+ '5 „

6 „

r 4° n

- 27 „

+ 60 „

« 8 „

- 13 *

20

- I2 „

x 7-5 „

+ 5 n

- I n

,, 31 »

- 38 „

+ 47 n

O

8 *

40

- '3 »

n 9 n

- 6 »

+ 2 „ 0

+ 23 „

4- 24 „

E 3-5 „

- 17 „

a 15

+ 3 „

n J3 n

7 n

- 6, „

„ 80 „ + 89 „

+ 39 „

W 2.5 „

- m

I3 M

55

1 n

» 16 „ 4- 8 „

7 n

n 48.5,, +105 „ |! + 26 „

n 3 «

- 32 „

For this hour there was no observation, and the value given is interpolated between o'1 15™ and o" 25"'.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP.

367

TABLE LIV (continued).

Gr. M. T.

Ssagastyr j Christiania

Pawlowsk

GOttingen

Fort Conger

ft

P*

ft

Pd

p.

PA

Pd

p.

P*

h m

23 25

~3 c "S
c -^ u

+ 32 7

K 41-5;'

4- 18 y

E 8.5;-

5 /'

+ '3-5 /

£37 y

-16.5;'

E ai ;<

40

w .2 3

*• -3

+ 29.5 „

B 25 „

+ ID B

W a „

- 8 „

+ 24 „

B 27.5 B

- 3-5 B

B 16-5 B

45

c

+ 34 B

» 25.5 „

+ 15 B E 3 „ 8 r

+ 22.5 „

B 27-5 B

- 2 „

B 4-5 B

u iJ 5}

55

£ rt

0 D C

+ '3-5 B

B 3I-5B

+ '3 B B 13-5 B

- I2 B

+ '9 SB

B 29.5 B

~ * n

W 18.5 „

0 0

B u <4

tfl u o

+ 8 „

B S2 B

+ 8 B , B '7 B - I2 B

"*" ^^-5 n

. 28.5 „

- o.5 „

B 19 B

10

* 1 -2

+ 2 „

B 230 B

o „ 14 „ - 10 „

+ 7-5 B

B 17 B

0

B I2 B

20

>> u

"c «r ja

+ I B

B J7'5 B

-SB

B 13 B

?

+ 5-5 B

B "-5B

o

B '4-5 B

5°

0^-5

§r*

— 6 B

**3B

- 10 „

B 3 B

?

"*" I n

W 6.5 „

+ 1-5 B

B i<5-5 B

I 0

3 W
O O C

_ 3.5 ^

O

7 B

B 5 B

?

~ 2 n

O

+ °-5 B

E 13 B

c w IS

10

.2 5 c
1 .3 e

0

0

- . 4 B

B 1-5 B

?

0

E 2.5 „

0

B I0 B

20

1 i 3

+ I B

n °-5 B

— 3 I.e -i- 2 -

-t- 2 n

B 2 n

— J B

B 4-5 B

40

t! o o
o "~ -.£

-1- I „

B '"5 B

o ; „ 1.5 „ 4- 3 „

+ 3-5 »

O

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B 6'5 B

O, _« o

2 15

v r, c

+ 4 „

E 4 B ii -"- 5 B

n 5 w

+ 4 B | + 3-5 B

B 7-5 B

0 B 23 „

, tfl <U

H

55

HOT:

n

B 2 -

+ 2 „

B 5 B 1 ° + ' B ; °

- 3 B j B 41-5 B

Current-Arrows for the 14th February 1883.
Chart I at 23h 25m.

fig- 152.

368

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PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I.

369

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BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1QO2 — 1903.

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PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP.

371

THE PERTURBATIONS OF THE 15th JULY, 1883.

(PI. XXIX).

87. As the curves show, the storms occurring on the above date, especially those in the polar
regions, are exceedingly characteristic and well defined, and of considerable power.

We have previously described principally magnetic storms that occurred in the winter, and two
or three perturbations about the spring equinox. Special interest will therefore attach to a case of a
magnetic storm occurring near the summer solstice, and the storm now to be described is a good example
of just such a storm.

It may at the outset seem very unlikely that the main features in the occurrence and course of
the perturbations should change character; indeed one would rather expect to find the same principal
features, while the details might possibly exhibit more peculiar conditions.

We will now go through the various phases, and see how well these assumptions are confirmed.

We may consider the interval from 6'1 to io'' as a first section, for during that time there occur
at several places, as the curves show, perturbations that are all comparatively slight, but sometimes
very well defined. The most powerful forces occur at Fort Rae, where the perturbation is a series of
brief impulses taking place at about 7h 30"", 8h 20™, and from gh to gh 2om.

The deflections in the district Fort Conger to Cape Thordsen are particularly characteristic, and
the time of their commencement there is a little earlier than in the perturbation at Fort Rae.

At Bossekop and the southern European stations, disturbances are only sometimes noticeable, and
the deflections are as a rule too small to be taken out.

It may here be worth while pointing out one circumstance connected with this first perturbation,
namely, that there is at the same time a deflection in one of the earth-current components at Pawlowsk,
which exhibits a remarkable resemblance to the deflections in the magnetic curves to the north. Whether
this is accidental, or whether a close connection between these phenomena exists, we will not attempt to
decide here. In this connection we will refer to a later chapter where the earth-currents are described.

As the systems acting here are rather weak, the drawing of the corresponding current-arrows on
the charts will not give a much clearer idea of the perturbation-conditions than we obtain by the direct
consideration of the curves. We have not therefore drawn any chart for this period of the storm: Its
field of operations appears to be rather limited, and its occurrence more or less local in the north.

At Fort Rae, where it is about midnight at this time, the storm is of the nature of a negative
polar storm; but nothing decided can be said as to what it may be at the other stations.

After this slight, comparatively brief perturbation, a long period supervenes during which the
conditions are normal.

At about 14'', however, powerful perturbations begin to develope all round the polar stations. In
the district Fort Rae, Uglaamie and Ssagastyr, an exceedingly characteristic, powerful negative polar storm
developes, which also seems to act with considerable strength at Kingua Fjord, judging from the deflec-
tions in the horizontal intensity. At the last-named place, the system appears to be a little earlier in its
occurrence than at Fort Rae. We must not, however conclude too much from the conditions in the
horizontal intensity alone, as the deflections in declination have a greater significance at Kingua Fjord
than at the other stations.

A perturbing force in the horizontal intensity will thus here produce current-arrows directed more
or less north and south, while at the other stations the variations in the horizontal intensity will answer
to current-arrows pointing east and west. It is therefore best here to keep principally to the charts for
a general idea of the conditions.

In the district Jan Mayen, Bossekop and Little Karmakul, on the other hand, a fairly powerful

370 laUKKl.AM). 1111 NoUWKOIAN AI'kORA I'OLAkls KXI'KI MTIUN, 1 9O2-- - I QO'}.

positive polar storm developes, its effects also being at first apparent as far north as Cape Thordsen,
and at (iodtliaal).

On Cape Thordscn and Jan Maven, that is to sav at the two stations situated to the north of the
auroral /.one, the conditions are a little more complicated, from the fact that later on, at about 16'', a
negative polar storm appears to break in upon the positive, which, in Cape Thordscn, it considerably
exceeds in strength, causing in consequence strong negative deflections in the horizontal-intensity curve.

The negative storm that asserts itself here, also acts, and verv powerfully too, at Fort Conger,
where the deflections are strong! v marked.

With regard to Jan Maven, the eflects o| the negative storm are not so apparent, parti v because
the effects of the positive sturm are verv strongly marked, and partlv because perhaps the area of pre-
cipitation of the negative storm is not so much in the immediate vicinitv of this station as of Fort
Conger and Cape Thordsen. The negative storm, when at its height that is to sav at about ry'1 or
18'' - oiilv succeeds in almost neutralising the effect of the positive storm as far as the horizontal
intensitv is concerned. In declination and vertical intensitv, on the other hand, especiallv in the latter
component, then.- are verv marked deflections at the above-mentioned time. /', is in one direction all
tlu- time, and negative. This is what might be expected, as both the negative svstcm to the north, and
the positive svstem to the south, will cause deflections in a negative direction. The character of the
declination curve is more disturbed, and several powerful, bnel impulses occur, now in one direction
and now in another.

The perturbations are evolving, when thus looked at as a whole, c.xaetlv in the same manner as
in the most tvpical of the cases we have alrcadv considered.

It is moreover easy here to study the movements of the svstems, which stand out with peculiar
distinctness in the case of the negative svstem of precipitation.

At Kingua Fjord, the wide deflections in the horizontal-intensity curve begin rather suddenly at
14'' 10'". At Fort Rae, on the other hand, the deflections at first increase more slowly, so that no
definite time for their commencement can be given. On looking at the horizontal-intensity curve, however,
we find a considerable difference in time, by comparing the beginning and the time of the maximum
deflection. It is a little doubtful how great this difference is, but we mav put it roughly at one hour.

We cannot, however, take it for granted that the effects observable at these two stations are
those of one and the same system; but we obtain a better general idea from the charts.

At I glaamic we also have a very characteristic deflection in //, which both begins and ends rather
abruptly. It is therefore easy here to determine a difference in corresponding hours. Compared with Kingua
1' jonl, there is a difference of about i' .> hours in the time of its commencement, while it ends only
about three quarters of an hour later than at Kingua Fjord. Between L'glaamie and Fort Rae there is
a distinct difference of about half an hour, observable both at the beginning and the end; and there
seems to be no doubt that this is the effect of one and the same svstem. The deflections in // are
here so powerful that the needle is outside the field of observation from 16'' 55" to [Q1' 35'", except
at j8'' 25'" and i8!l 30"', when readings have been taken.

The next station at which the negative storm acts is Ssagastyr, where the deflections in // begin
about half an hour later than at L glaamie, ami are very sharp and distinct. A comparison, as regards
the time of the maximum, with Fort Rae, shows a similar condition, tin- difference being about one hour.

The deflections in // do not decrease regularly until the conditions have once more become normal ;
but for two hours after about 19'' there1 is a more or less constant perturbing force of about — 150;'.
The character of the curve seems to indicate that there has been some defect in the instruments, and
that the needle in some way or other has become fixed; but as there are at the same time perturbing
forces in the declination, it is impossible to be sure of this.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 373

We can thus, in this district from Kingua Fjord, or at any rate from Fort Rae, through North
America to Ssagastyr, trace a distinct westward movement of the system of precipitation. A powerful
but not extensive system first developes in the vicinity of Kingua Fjord, and apparently spreads towards
the west and forms the great, connected system of precipitation in the north of America, presumably
simultaneously with the westward movement of the entire system with the sun.

No specially pronounced movement is descernible, on the other hand, in the positive system. It
might appear, indeed on a cursory glance at the deflections in Jan Mayen as compared with those at
Bossekop and Sodankyla, as if there were a distinct eastward movement of the system ; for at about I4h
20™ the positive deflections at the first-named station attain a considerable strength, and remain more or
less constant until 16'', when they once more diminish rapidly. At Bossekop and Sodankyla, the positive
deflections begin at about the same time as those in Jan Mayen ; but they increase slowly, and the most
powerful forces are not found until between i6h 30™ and 17'' 30™, the time at which the conditions in
H in Jan Mayen are fairly normal. It might thus appear as if the positive system had here moved
eastwards; but we have already explained the way in which this phenomenon is to be understood, and
how the negative system to the north breaks in upon the positive system first acting in Jan Mayen.
This, however, does not preclude a possibly eastward movement of the system of precipitation. It is
also probable that the positive storm-centre will be moved; but the observations we possess do not afford
sufficient evidence of this.

Little Karmakul is now also upon the border between the two systems of precipitation ; and its
curves have consequently the disturbed, jagged character so often observed before. At one time the
positive system is the stronger, at another the negative, although at first the positive system predomi-
nates, while from about I7U 30™ onwards, the effect of the negative system is the more apparent.

The negative storm at Cape Thordsen and Fort Conger must on the whole be regarded as a con-
tinuation of the negative storm in North America and the north-east of Asia, although it is very possible
that it forms a more independent system.

At the southern stations it is sometimes rather difficult to determine the normal line, as the diurnal
variation at this season of the year is considerable, and the data from which the determination is made
are as a rule few. It is therefore possible that some error will attach to the values found; but at the
times when the perturbing forces are powerful, this will have no great signifiance.

At about 2oh, this perturbation is practically over. This is clearly apparent from the curves of the
horizontal intensity. It is not yet quiet everywhere, however, as, in the declination especially, there are
sometimes fairly powerful perturbing forces.

In the district Fort Conger to Kingua Fjord, the effects of a fairly powerful system of precipitation
are still distinctly apparent, and are noticeable at Godthaab and to some extent in Jan Mayen. The
perturbation is especially powerful at Kingua Fjord. At about 23*", however, new storms begin to
develope, evolving in the usual manner of the polar storms at about midnight, Greenwich time. A
powerful negative storm on the night-side, from Little Karmakul, across Bossekop to Jan Mayen, forms
the main system, its effect also extending westwards across Ssagastyr to Uglaamie. We find moreover
distinct traces of a positive system on the afternoon-side, especially at Fort Rae; but the horizontal-
intensity curve for Godthaab and possibly Kingua Fjord indicates that these stations are also affected
by this positive system. Here, however, the conditions seem to be rather more complicated, perhaps
because the effects of the above-mentioned system occurring in these regions are still apparent.

Special attention should be paid to the positive system of precipitation on the afternoon-side in
North America. It occurs principally at Fort Rae, that is to say it is most marked at the station situated
to the south of the auroral zone.

Birkeland. The Norwegian Aurora Polaris Expedition 1902—1903. 48

374 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

It is, as stated in the description of the preceding perturbation, comparatively seldom that th<
effects of positive systems of precipitation can be observed in these polar regions. This, however,
the most characteristic example of such effects, and therefore goes far towards confirming our previous
assumptions. Unfortunate!}', only the first half of the perturbation can be studied, as the period of
observation ends while the deflections are greatest.

We have now briefly reviewed the development of the perturbation by considering the curv
and have found that in the main the same conditions are repeated, and the development takes place i
exactly the same manner, as in the earlier storms.

We will now pass on to consider the charts in which we have represented the various fields of
perturbation. These fields are here slightly more complete, as we have also made use of observations
from Kasan, from which place we have entire series of observations of the two horizontal components
for the last term days from the t5th May onwards.

For this day we have drawn 14 charts representing 15 epochs in all.

As Chart I shows, it is the positive storm that first developes. It is especially noticeable that the
positive system of precipitation appears to be situated comparatively far south, judging from the condi-
tions at the southern stations ; for if it is principally only this positive system that is acting, the stations
that we have included here must lie to the north of the point of divergence of this system. There is
of course also a possibility that in addition there is precipitation of stiffer rays in rather lower latitudes,
these being here those with the greatest effect.

The positive system has developed most fully in the district Godthaab to Jan Mayen, while its
effects farther east are comparatively slight.

There is perhaps rather more uncertainty as to the manner in which the conditions at Kingua Fjord
are to be understood. The direction of the current-arrows there is almost due south. Judging from the
chart, it would seem likely that the conditions might be considered as a continuation of the positive
system of precipitation. When we considered the curves and compared them with those at Godthaab,
we found, it will be remembered, that the character of the deflections at the two stations was sufficiently
different to justify the assumption that they were not very closely connected with one another, but that
on the contrary a system was acting at Kingua Fjord that was scarcely noticeable at Godthaab. This
assumption also seems to be the most probable on looking more carefully at the charts. At first, however,
this system at Kingua Fjord is comparatively inconspicuous and rather limited in its effects; and the positive
system that has formed to the east of it sometimes seems to encroach upon it and get the upper hand.
This is the case at the time of Chart II, when there clearly seems to be a positive system of precipitation
right from Kingua Fjord eastward past Little Karmakul, possibly as far as Ssagastyr. No effects of a negative
system of precipitation are noticeable. The strong current-arrows at the southern stations also seem to
indicate now that in addition to the great precipitation in or about the auroral zone, there may be smaller
amounts of precipitation farther south. Without such an assumption it would be difficult to find a simple
explanation of these current-arrows. The jagged, disturbed character of the curves, especially the hori-
zontal-intensity curves, is moreover a circumstance that supports this view, this fact indicating that the
systems in operation cannot be very far from the station itself. At the same time, the oscillations at the
polar stations to the north — Jan Mayen, Bossekop and Sodankyla — as also at Cape Thordsen, are com-
paratively gentle, without any sudden, violent changes backwards and forwards. At Little Karmakul,
however, the curve is rather jagged.

The negative system of precipitation does not appear distinctly until I5h 30™, (Chart III), either
at Kingua Fjord, where it is strongest, or at Fort Rae. The positive system is also well developed
here; but at Cape Thordsen the perturbing forces in the horizontal components are rather small, this

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 375

being due to the fact that the negative system, which there developes subsequently to such considerable
straight, is already encroaching upon the positive. In other respects there is little alteration in the
appearance of the field, and the forces at work are only sometimes weaker than before.

The current-systems continue to develope upon the succeeding charts. On Chart IV, for the period
I5h 40™ to i5h 50™, the conditions are not very different from those on Chart III, except that the forces
at Fort Rae are a little more powerful.

On Chart V the development of the negative system can be followed. At the first hour shown,
i6h i5m, Uglaamie is in its district of precipitation, but the latter does not extend as far west as
Ssagastyr. At i6h 40™, however, the great negative system has developed all round at the various
stations. This now forms a more or less continuous circuit, which can be traced from Godthaab to
Kingua Fjord, across Fort Rae, Uglaamie and Ssagastyr to Cape Thordsen and Fort Conger.

The northerly position of this system on the afternoon-side is worthy of notice, as also its com-
paratively southerly position on the morning-side, as, judging from the vertical intensity, it should lie in
the first case to the north of Cape Thordsen, and in the second to the south of Fort Rae.

We must, however, once more urge the necessity of caution in drawing conclusions from the con-
ditions in the vertical intensity, and need only point to the vertical arrows at Sodankyla during these
storms, which here too exhibit rather abnormal conditions as regards direction.

The positive area of precipitation seems now to be considerably reduced, and distinct effects are
found only at Bossekop, Sodankyla and Little Karmakul. In reality, however, it may possibly extend
farther west, but then farther south than the regions from which we have observations.

On Jan Mayen the current-arrow is comparatively very small, while the vertical arrow is of con-
siderable length and is directed upwards. This is in accordance with a circumstance that we have also
drawn attention to previously, namely, that the station is situated between a northern negative and a
southern positive system of precipitation.

We find no special change in the form of the field in Charts VI and VII, but the forces increase
considerably everywhere. The high value of Pj. at Fort Conger should be especially noticed, it being
about 864 y at I7h 2om (Chart VII), or considerably more than any of the other perturbing forces observed.

PI, cannot be measured at Uglaamie, as the needle has swung out of the field of observation; so it
may possibly have been as great or even greater here. It is interesting, however, to find that there is
also powerful precipitation close to the magnetic axis.

As Charts VIII and IX show, the negative system encroaches farther upon the positive, and causes
a reversal of the current-arrow at Little Karmakul; while at the same time the current-arrows at Pawlowsk
and Kasan become more southerly in direction. On Chart IX, the effects of the positive system are
slight at the stations under consideration.

At i8h 20™, on Chart X, we once more find a fairly powerful polar positive system of precipita-
tion from Kingua Fjord eastwards to Little Karmakul. This time, however, the system appears to be a
little farther north, at any rate in Europe; as Pawlowsk, Kasan and Gottingen are now distinctly in the
southern part of the area of divergence of the system. As this only lasts for a short time, it should
rather be regarded as a brief impulse. The effects of the negative system still continue, however,
although the forces are to some extent less powerful than before.

Chart XI, for i8h 55™, represents the perturbation-conditions as they appear shortly before the
great systems disappear. We still find distinct traces of the great negative current-circle, while on the
other hand, the effects of the positive system are less distinct, although it seems to exist, judging from
the conditions in Jan Mayen and the southern stations; but this cannot be decided with certainty.

When these storms have ended, there is an interval of more or less normal conditions at most
places, although it is by no means quiet everywhere; but what perturbations there are, are of a more

376

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

local character, and the existence of large connected systems can hardly be proved with certainty. This
is clearly evident from Chart XII, for the hour I9h 5om.

Two Charts, XIII and XIV, have been drawn for the last section of the perturbations of the day
under consideration, from about 22h to the end of the period. The conditions are comparatively simple
and clear. On the night-side there is a powerful negative system of precipitation, which extends from
Ssagastyr westwards through the north of Europe to Godthaab and Kingua Fjord. At the two last-
named stations the direction of the current-arrows is a little peculiar. The principal axis of the system
seems to turn off towards the north rather abruptly. This seems to be analogous to the circumstance
we have so often observed before, namely, that the negative system turns up, on the afternoon-side, into
higher latitudes to the north of a positive system in the vicinity of the auroral zone (fig. 140 p. 327).

At Fort Rae too, there is certainly a positive system, while the storm-centre of the negative system
is in the north of Europe.

The current-arrow at Fort Rae, which should give the direction of the positive system of precipi-
tation, has, it is true, a rather marked southerly direction; but this is so nearly the opposite of what
we find during the ordinary negative storms here, that there seems no doubt that this is a positive
area of precipitation.

TABLE LV.
The Perturbations of the I5th July, 1883.

Gr. M. T.

Uglaamie

Fort Rae

Kingua Fjord

Ph

Pd

ft

Ph

Pd

P,

Ph

Pd

P,

h 111

6 50

+ 47 ;'

W 26.5 ;'

+ 30 y

+ 7 Y

W ii y

- 10 ;<

+ 28 y

0

O

7 3°

+ 46 „

o

+ 10 „

-202 „

E 102 „

o

+ 8 „

E 22.5;'

0

8 20

+ 27 „

E 2, „

o

-"9 „

n 15 n

— 100 „

+ 5 „

n 22-5n

+ 22 )'

9 5

+ 4 „

« 5-5 T)

o

- 68 „

W 82 „

+ 20 „

- 23 n

n 9-5 n

0

10 20

+ 9-5*

o

0

o

0

O

- 15 «

o

0

n 50

-•- 3-5 n

n 2.5 „

o

o

0

o

- 52 „

0

0

13 20

- 2 „

n 8 „

o

+ 17 „

o

o

- 55 n

W 15 „

o

M 35

-1- 3-5 n

W .8.5 „

+ 05 „

- 24 „

E i3-5«

+ I0 n

-222 „

E 55-5,,

- 27 „

55

+ 8 „

n 9° n

+ 35 n

- 47 n

n IJ n

+ 20 „

- 83 „

ni84 „

- 22 „

15 3°

'7-5 n

E 9.5 „

+ 23 n

-MS n

» 7° n

+ 45 „

— 323 »

WiiS „

- 52 „

40

53 n

.1 2.5 „

+ 80 „

-181 „

„ 83 „

+ 65 „

-300 „

0

— 72 „

5°

- 9i „

n 53 n

+ 80 „

-202 „

n '53 n

+ =8 „

-205 „

K MO »

-I65 »

16 15

I87-5 B

n 26.5 „

+ I37 „

-325 „

n 209 „

+ 220 „

-285 „

n 233-5 n

- 85 „

40

- 290 „ „ 172 „

+ 180 „

-522 „

» 280 „

+ 100 „

-343 n

it I2o „

- 71 n

17 o

->3°° n ' n 20 „

+ 205 „

-6l3 n

« 298 „

+ I40 „

-240 „

n 62.5 „

-'25 n

20

->3oo „ ;Wio8 „

+ 23° „

-606 „

n 4" n

+ 120 „

-364 »

„ 86 „

-126 „

35 ' ->3°° „ £246 „ + 180 „

— 545 n

n 325 n

+ 4° n

-255 „

n 62.5 n

-'36 „

1

55

->3°° „ ,,609 „ +135 „

-338 „

„ '28 „

-200 „

-216 „

n '44 »

-MO „

18 20

->3°° „ ; n2i8 „ + 80 „

-134 n

Wn5 „

- 55 „

- =6 „

E 174 n

- 91 n

55 ' 239 „

n 205 „ + 57 „

+ 3° n

E 47 „

- 20 „

+ 24 „

W27o „

— 101 „

19 50 i-f 30 „

W 55 „ + 10 „

+ II „

W 20 „

- 20 „

- 7 n

n I24 n

- 63 „

22 55 48 „

n 8 n - '5 n

+ 221 „

E 46 „

- 4° „

+ 182 „

n 191 n

- 21 „

23 15

0 n 77 n ' + 33 n

+ 3H „ n II6 n

- 60 „

+ 197 n

* 210 „

+ 84 „

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I.

377

TABLE LV (continued).

Gr. M. T.

Godthaab

Jan Mayen Bossekop

«

Pd

Pk

Pi

P,

Pk

Pd

ft

b m

6 50

4 14 ;'

W 7.5y

- '5 P'

E n.5y

0

0

E 7 /

o

7 3°

0

E 4 „

0

o

- 10 y

0

0

0

8 20

o

n 14 n

0

W 5-5 *

o

0

o

o

9 5

0

O

- 9 n

n 3 n

o

0

0

o

10 2O

0

0

o

o

0

0

o

0

II 50

5 „

W 8.5.

o

,, 8.5 „

0

0

0

0

13 20

+ i° „

0

+ 19 „

0

— 7 ,,

o

o

0

M 35

+ 9 „

E 83.5 „

•+M3 n

n 4 it

- 24 n

+ 73 7 °

+ 47 7

55

- 3° „

» '53 n

+ 249 „

E 15-5,

- 37 »

+ 142 „ W27 „

+ J'3 »

15 3°

+ 109 „

n I27 n

+ 220 „

* 33 ,,

— 20 „

+ "3 ,,

E 7 „

4-130 „

4°

4 24 „ „ 188.5 „

+ 235 „

n i5-3,i

— 35 •

+ '4° „

Wl2 „

+ 118 „

50 4 103 „ „ 137 „

+ 260 „

W 19 „

- 61 „

4 120 „

0

4- 170 „

16 15 o W II „

•*-i3*5«

» 5-5 n

-160 „

-1-200 „

» 21.5,

+ 250 „

40 ; -161 „

» 59-5 »

+ 35 »

» 5a.5 n

-183 „

+ 260 „

E 5° „

+ 208 „

17 o

-107 „„ 61.5 „

+ '3 „

* Io8 n

-204 „

+ 255 „

W8i „

+ 272 „

20

~!32 „

„ 89.5 „

- 59 n

» 54 „

-157 ,,

+ 288 „

» i° »

4 200 „

35

-105 „ E 67 „

- 37 n

„ 52.5 I,

-200 „

+ 247 „

0

4 no „

55

- 80 „

0

5 „

, 'o6 i

— 22O „

4 76 „

. 8-5 „

- 38 .

l8 20

+ 29 „

» '57 n

+ 277 „

I, 52 „

-283 „

+ 95 „

E 25.5 „

4 100 „

55

+ 15 „ W 37 „

+ 81 „

„ 53 ,,

-'32 n

o

W 7 „

- »3 i

19 50

+ 27 „ „ 38 n

0

„ 34 ,,

- 97 „

+ 55 „

0

4 78 „

33 55

-33° n » 235 n

-5°° „

E 138 „

+ 225 „

-577 „

„ 10° »

-207 ,

23 15

+ 54 n ,,286 „

-S32 „

W 19 „

+ 393 „ i —606 „

- 23-5 »

-213 »

TABLE LV (continued).

Gr. M. T.

Sodankyla

Cape Thordsen

Little Karmakul

Pk

Pd

A

Ph

Pd

ft

A

Pd

ft

h m

6 50

0

E 4 y

0

4 14 y

E 44 y

+ 26}'

4 42 y

o

+ 35 7

7 30

0

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+ 27 „

» 5 »

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+ " „

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W 4 „

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0

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+ 5 ,

0

— 10 „

+ 25 „

0

- 13 It

ii 50

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0

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0

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4- 5 -

0

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13 20

0

o

0

o

0

0

+ 10 „

o

— 1° II

14 35

4- 64 y W 4 „ I o

4 68 „

w 53 w

— 42 „

+ 83 ,

W 417

5 „

55

+ 112 „

.17 » i 4 90 ;'

-^S2 „

„ no „

- 74 *

+ 237 „

„ 100 „

-5«

15 30

4 88 „

E 6 n 1 - 27 „

+ 3° »

» 57-5 »

-150 „

+ 76 „

» 44 „

4 2 „

40

+ 9° „

o

+ 78 „

— 20 „

« 6o »

-200 „

+ M3 »

» 66 „

+ 2 „

50

4 80 „

» 6 „

- 60 „

— 22 „

, 57 »

-180 „

+ 133 „

» 57 -

+ 27 „

16 15

+ 105 „

W 4 „

- 90 „

-I°5 »

» 48.5 „

-225 „

+ 180 r

, '53 „

- 26 „

40

+ 177 .,

» 25-5 „

- 60 „

-I65 „

» 33-5 »

— 248 „

+ 55 -

> '34 »

— 133 „

17 o

4-149 „

» 4i-5 »

+ 10 „

-156 „

» i°3-5 .

— 296 „

4 82 „

» 61 „

— 3° 11

20

+ 253 „

o

0

-45° „

„ 28 „

-430 „

+ 150 „

» i °8 .

- 60 „

35

+ 234 „

E 6.5 „

4 81 .

-287 „

„ 178 „

-476 „

-212 „

» J5 „

-273 „

55

+ it>5 »

. 4 .

4 82 „

-178 »

r 133 »

-237 »

-307 „

£128 „

-178 „

18 20

4 60 „

„ 19 »

- 8r „

- 35 »

,108 „

-125 „

4133 „

W 90 „

-120 „

55

+ I2 „

o

4 32 „

- 86 „

. "5 «

-'50 „

-373 ,

E 9 .

- 30 „

19 50

4 10 „

„ 6 „

4 10 „

- 33 .

» 39 -

- 62 „

4 1 60 „

W 96 „

4 67 „

22 55

-460 „ „ 75 „ ; 4150 „

4 60 „

£129 „

4192 „

-775 „

E 167 „

- 33 „

23 15

— 520 „ o — loo „

- 37 -

« 55-5 »

433° n

-658 „

. i73 »

- 70 „

I: M>K\Y|-.(.I A.N AI'KOKA I'OLAKIS I-.M'I-.I ) I I l< >\, I gO2 - T

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III-. M. 1 .

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o 50 4 20 ;• o 4- 2 ;'

o o o 4 i . ' ; '

7 3° 4 10.. \Y 0.5 ;• o

o o o -+ i

8 20 o „ 1 2.5 ., - i „

o o o -t- 8 „

"5 o „ 0.5 „ 4 i „

o o u o

1 O 2O O O O

o o o o

I I So o o o

o o o o

13 20 - 10 .. o 4 15.5 ., I-.

9.57 4 20 ;• o o

1 1 35 „ 10.5 „ 4 48.5 „

o 4 52 .. W i | ;• o

55 4 50 „ „ 23 .. • 4 80 „ \V

9-5 i' ''!'., n 20 „ O

'5 3° + 1" •- „ 27 „ 4 |8 .. ..

2-5 !• + 52 „ ., I3V5 „ 45,.

|o 20 .. .. 73.5 ,. -i-O* ,, „

1-5 - 4 36 .. „ 12 .. 4- 5 ..

5o 4 30 „ .. 37 „ -,.38 .,

0 + 35 - » '3-5 11 40,,

IOS 4 5 „ ., 189 .. 4 |2 .. ,,

9-5 ., + 33 •• 11 7 11 4 8 „

i° - -n v - 50.5 ., 1-83 „ ., i

1 ,. + 02 „ „ 10.5.. + ,5 ..

17" - 137 - •• 60 .- 4-8] „ „ 2

3-5 i, 4 52 .. ,, 14.5 „ +18 „

20 22 | „ ,. 296 .. 4 O8.5 ..

" + 5H „ K 19 „ 4 19 „

35 a/8 „ I'. 91 .. 4 83 „ K. I

9 ,. + 75 ., i, 20 „ 4- 20 „

55 — 285 „ \V 150 „ - 4 17 ., „

1-5 .. 4 20 ., ,, 28.5 .. 4 19 „

18 20 - 381) ., K i |o .. — 13.5 „

1-5 ,1 • 37 .. 11 '6 „ 4- 10 „

•-Ml.. W 14.5 „ -T 2 1.5 „ \V i

7 5 11 4 1 8 „ W 1 2 „ 48 „

1 9 5o — 1 52 ., M 39 „ -f 3 „ .,1

9 „ o „ 9.5 „ 42,,

22 55 — 242 „ .. 30.5.. - 9 11 „ 19 ,i i, 24 ., - 3| .,

23 '5 -235 - .. 05 ., - o „ ., ,

2 ,. - I | „ „ 20 .. (7..

uncertain vuln< s.

TAHLIC LV IcontiniK (1).

(Mitlinuvn

Ka--aii I-iirt Conger

Gr. M. 1.

/';, I'd r.

/'/, /',/ /:/

h in

6 50 o W 2 ;- - 5 ;•

o o Ii 51 ;'

7 3^ i r ,, 7 .. - 3 11

o o ., |O-5 „

0 20 2 „ 0 4 1 „

o o W 15 ..

95+2.. o o

o o ., 0 „

1O 2U O O 4 .j

o o K 18 ..

1 1 50 0 „ 1.5 .. 2 .,

o o o

'3 20 + 3 „ I-! 2.5 „ 4 9.5 .,

4 1 1 ;• w 3.5;- o

i 1 35 4 22 .. \V 8.5 „ 4 7.5 ,i

-: 3 ' .. „ 10 „ W 25.5 „

55 4 50 „ .. 8 „ o

4 -19 „ .. 19 n 11 1° 11

1 5 30 -r i | „ „ 8 ,, 4 1 3 ..

4 20 ., „ 1 6 I'. 5 ,.

|o -4 21 .. ..7 ., 4 21.5 ..

4 32 „ .. ,0 „ W 0 ..

5° 4 3 „ .. 5.5 „ 4 26 ,,

+ M n ° " 1 ° 11

'6 '5 + 3 - „ 8 „ +21 .,

-1- I ' 11 ., 8.5 .. „ 99 n

1° 4 2| „ .. 1 I..S .. 4 2| „

4 28 ., ,, 7 ., ,. 225 „

'7° + 10 ,. .. 13 .. 435 „

417,- i, 8 „ .. 5 19 .-

20 4 10 ,, o +44 ,,

4 4 ' - K 24 „ .. 86 1 ..

35 -1- I ., I1- 29 .. 451.5 ,.

4 31 11 i, 25 .. ., 684 ..

0 11 ' ° 11 4 4 7 „

4 19 .. „ 28 „ .. 087 ,.

18 20 53 „ „ 7.5 ,. +|9 ,.

- 38 .. ,, 21.5 „ .. 198

55 4 i , .. W 22 „ 4 25.5 „

o \V 8.5 .. .. 280.5 ..

1 1) 50 o ,,17,, 4 38.5 ,.

« - „ 3 i, o

• ,1" •• -ilv - 7-5 ••

<' .. 11 31 11 1'- 37-5 -•

23 '5 •* 33 ,1 1'- 4-5 .. -21.5 ..

» „ - 27,5 „ .. "2.5 ..

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I.

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PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I.

383

384

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, I QO2 — 1903.

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PART II. POLAR MAGNETIC PHENOMENA AXD TERRELLA EXPERIMENTS. CHAP. I.

385

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386 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

THE PERTURBATIONS OF THE 1st FEBRUARY, 1883.

(PL XXVII).

88. Here, as on the preceding term day, we can separate a first comparatively slight pertur
bation, appearing, more or less isolated, at about nh, from the subsequent powerful storms. Only at
two stations, Fort Rae and Godthaab, do we find, during the first period, rather powerful perturbing
forces. We find, moreover, distinct deflections at several other stations, but these in the first place are
considerably weaker, and in the next, of longer duration, than at the two stations just mentioned; and
the character of the deflections does not seem to indicate that they have any very close connection
with one another.

This first perturbation is particulary distinct at Fort Rae. At ioh 55m the deflections suddenly
increase to a maximum, and then again decrease rather rapidly. The perturbing forces are negative in
the horizontal intensity, and directed eastwards in the declination; and the current-arrow, as will be seen
from Chart I, is directed westwards along the auroral zone at the time when the deflections are strong.
There is thus, certainly, negative polar precipitation in the neighbourhood of this station; and at Godthaab
too, a negative polar storm seems to be acting.

If we look more carefully at the chart, there appear to be signs of positive forces at Ssagastyr,
and possibly a positive system has formed on the afternoon-side, but if so, it is not very clearly developed.
In this respect, however, we have not sufficient data to go upon.

After this precursor of the subsequent powerful storms, there follows an interval in which no very
great forces appear. Soon, however, new storms begin, which rapidly develope until they attain con-
siderable strength, and form the principal systems of that day.

The storms in this period will naturally be divided into two sections,

(1) those that occur between i4h 3om and igh 45™, and

(2) the storms from I9h 45m until the end of the period.

Such a division of the phenomena will of course be imperfect, and may appear somewhat artificial,
since we have constantly found, that one system developes from another; but it is done for practical
reasons, in order, if possible to obtain a clearer general view of the conditions.

At about 14'' 3Om, some more or less powerful deflections begin at Kingua Fjord in the horizontal
intensity and declination simultaneously, their direction indicating the presence of a negative polar storm.
This can apparently be traced farther, over Fort Conger, where there is at the same time a distinct
deflection in the declination-curve; and judging from the conditions of this curve at Cape Thordsen, this
system is also at work there. There appears to be a weaker positive storm in the vicinity of Jan Mayen.

This perturbation, however, is of brief duration, and its field of operations is comparatively restricted.
In the course of about an hour, it is practically over. At about i6h, on the other hand, powerful storms
begin to develope at all the stations round.

The deflections at Kingua Fjord increase most rapidly to a considerable amplitude, and attain their
highest value as early as 17'', after which they remain more or less powerful in declination, while PI,
decreases fairly evenly, reaching its normal condition again at about 2oh. This negative system of pre-
cipitation apparent at Kingua Fjord, now extends as a great system westwards. It is felt at all the arctic
stations, more strongly, indeed, than anything else at the time when the deflections are greatest; for
here too, there occurs simultaneously a positive system of precipitation, which to some extent counter-
acts the negative.

The distribution of force round the auroral zone is here, too, exactly similar to that found during
the earlier storms. At Kingua Fjord, Fort Rae, Uglaamie, Ssagastyr, Cape Thordsen, and possibly Fort
Conger, it is almost exclusively the negative system of precipitation that acts; at the other polar stations,
the positive system also asserts itself more or less strongly.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 387

As regards Ssagasiyr, however, there is one thing to be noticed. From I7h 40™ until i8h 30™,
the deflections in the horizontal intensity are too great to allow of being observed. The direction in
which the needle moved is not given, nor is the character of the curve such as to enable the direction
of the deflection to be determined with certainty. Judging from previous experience, however, there
would seem to be no doubt that the deflection has been in a negative direction.

In the first place, we have never met with positive perturbations here that have been powerful
enough to make the needle move out of the field of observation. Further, this station lies just between
Uglaamie and Little Karmakul, at both of which, it may be seen, the negative storm is very powerful.
This is also the case at Cape Thordsen.

As the negative storm is powerful at all the stations surrounding Ssagastyr, it would be very
improbable, judging by all that we have seen previously, that a strong positive system could act at that
one station; and moreover, the part of the curve for the time immediately after this interval, indicates,
although faintly, that there has been a negative, not a positive, deflection. The current-arrows we have
marked, indicate, therefore, that the needle has moved out in a negative direction ; but, in order to indicate
the slight uncertainty, we have placed an asterisk by the arrows in question.

The perturbing forces everywhere are exceedingly powerful; and the storm-centre of the negative
storm is in the district from Uglaamie to Little Karmakul, probably about Ssagastyr.

We think, however, that we can prove a distinct movement of the system. This is developed
earliest round Kingua Fjord, where the forces even at i6u iom, have attained considerable power. The
deflections here increase rather rapidly to a maximum. At Fort Rae and Uglaamie, on the other hand,
the deflections at first increase more slowly; but, at both these stations the perturbing forces are of con-
siderable magnitude as early as 17''.

At Ssagastyr, the negative deflections do not begin until 17'' 40™; but they are then suddenly so
strong, that the needle passes out of the field of observation.

The negative system thus seems to begin in the neighbourhood of Kingua Fjord, developes there
with considerable rapidity, and, simultaneously with the extension of the area of precipitation and the
increase of the perturbing forces, the storm-centre moves westwards. If we endeavour to trace a similar
movement onwards to Little Karmakul and Cape Thordsen, it appears that the same observation may be
made with regard to the first of these two stations ; but consideration must be paid to the fact, that this
is within the positive system's sphere of operations, and, before the negative storm gains the ascendancy,
there are distinct positive forces. This is also the case afterwards. When the powerful, but brief, nega-
tive precipitation is over, positive forces appear once more, this time more powerful than before. The
powerful negative forces appear a little later than at Ssagastyr, but we must beware of drawing con-
clusions from this condition respecting the movement of the system, the more so as there was powerful
negative precipitation north of the auroral zone even earlier, as the conditions at Cape Thordsen show.
The deflections in the horizontal intensity at the last-named station, resemble, in many respects, the corre-
sponding deflections at Uglaamie. At both places we find, at about 17'' or 17'' 30™, a secondary maxi-
mum, and at about i8b 30"° the true maximum. There is a slight time-displacement, however, especially
in the first secondary maximum, so that the deflections at Cape Thordsen come a little later than those
at Uglaamie. The similarity of these curves is strikingly evident at the very first glance; but if we look
at the declination-curve, we find no particular resemblance, and the deflections in this component will
have a greater significance at Cape Thordsen than at Uglaamie. What we will here draw special attention
to, however, is that the negative deflections at Cape Thordsen begin rather early, and thus develope more
or less simultaneously with those at Uglaamie, possibly a trifle later; and there are thus considerable forces
at Cape Thordsen before they appear at Ssagastyr. The explanation of this must be, either, that simultane-
ously with the extention of the negative system of precipitation westwards through North America from

388 B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

Kingua Fjord, it also spreads eastwards towards Cape Thordsen and perhaps farther, and then unites
with the western branch ; or the system in America will most rapidly spread on the north of the auroral
zone, and will not extend farther south to Ssagastyr until later, or there may be two rather distinct
areas of precipitation.

It is possible, too, that the circle which the negative system of precipiatation appears to form round
the pole of the earth, is formed more or less at once, and that the displacement that we find in the
deflections is occasioned by the movement and deformation of the entire circle.

The most probable cause of these phenomena, however, seems to be, that several of them separately
exert influence.

A more or less circular, negative system of precipitation will be formed somewhat rapidly, in
which there may be one or several districts in which the strength of the precipitation is greatest. By
imagining these maximal zones to be moved from time to time, the differences in corresponding hours
that appear can be simply explained.

In addition to the negative system, there is also, as already mentioned, a positive system in the
district from Godthaab eastwards along the auroral zone to Little Karmakul. At these two stations,
especially the former, this system is comparatively weaker to begin with; but, on the other hand, at
Godthaab, at the end of the section under consideration, we find practically no effects of it, while at
Little Karmakul, at the end, it is quite distinct and powerful.

The effects are strongest at the intermediate stations, Jan Mayen, Bossekop and Sodankyla; and
there we find the characteristic condition that we have so frequently met with.

At first the positive system is at work, being then broken in upon by the stronger negative
system, which causes a partial reversal of the direction of the deflection at the time when the storms
are at their height. Finally, simultaneously with the decrease in the negative precipitation, the positive
forces once more gain the ascendency, and the conditions are again such as would be found in the
neighbourhood of a positive district of precipitation. It is interesting to observe the conditions at these
stations, and see how they alter the farther magnetically north we go. At the three polar stations, Jan
Mayen, Bossekop and Sodankyla, the perturbation-conditions are, on the whole, exactly analogous; but
we can trace a continuous variation in them from Jan Mayen, through Bossekop to Sodankyla.

At the first of these three stations, the negative storm is the strongest, although the positive deflec-
tions are at first quite strong. At Bossekop, the precipitation is, on the whole, less, but the positive
deflections are more numerous than the negative. Lastly, at Sodankyla, the effect of the negative storm
is comparatively slight, and the positive deflections predominate. We can thus trace a continuous change;
farther north the negative storm acts the more strongly, farther south the positive. If we look still
farther south, at Christiania, the positive storm seems to be acting alone. At the time when the negative
storm is at its height, there is a strong deflection there in a positive direction; and the curves are
sufficiently jagged to make it probable that this station is not far from the district of precipitation of the
positive system. The positive system therefore seems to be somewhat far south in its position.

If, on the other hand, we go still farther south to Pawlowsk and Gottingen, we seem to have passed
the point of divergence, for the forces there, in the horizontal intensity, are in a negative direction, and
we thus have a change. It must be principally the positive storm which also acts here, if there are not,
at the same time, systems of which the greatest effect is exerted in lower latitudes.

If we look for some movement of the positive system, we find, at first, that the forces are strongest
in the west, but at the close the storm is most fully developed farther east. The positive forces in the
horizontal intensity also appear very much earlier at the western stations Jan Mayen and Christiania
than farther east. At Godthaab, the effect is of short duration, and the storm is not very clearly
developed. This might indicate a movement eastwards, such as we have frequently met with at this

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 389

hour of day ; but it should also be remembered that there possibly exists another movement of the systems.
We might, for instance, imagine the positive system to be moved southwards, which would cause the
occurrence of phenomena such as those we now have before us; for the western stations, Godthaab and
Jan Mayen, are in the north of the auroral zone, while the eastern stations are in its southern part.

The order of the systems is thus exactly such as we are accustomed to find at this time of day
during the most typical of the storms already described.

With regard to the movement of the systems from time to time, we find apparent traces of a
westerly movement of the negative system in America, and possibly a less pronounced easterly move-
ment of the positive storm-centre.

On the three charts following, //, ///, and IV, the development of the perturbations in this section
can be distinctly followed. That of the negative storm is the more marked. Between I5h 2Om and i6'1
20™, it is distinctly developed only at Kingua Fjord; but at i6h 50™ there are also distinct, strong current-
arrows at Fort Rae and Uglaamie on the one side, and Cape Thordsen on the other. The most powerful
forces, however, are still at Kingua Fjord.

At 17'' aom the great current-circle has already formed, and we find the most abundant precipi-
tation in the district Kingua Fjord to Fort Rae, showing that the storm-centre has moved a little west-
wards. At both Godthaab and Jan Mayen, where previously the positive storm was the strongest, there
are now powerful negative forces.

The storm is at its height from i8h I5m to i8h 3om, and we find very strong perturbing forces,
especially on the night-side. The most powerful are apparently at Ssagastyr; but as the deflections at
both Uglaamie and Little Karmakul are too wide to be measured, it is possible that they may be just
as powerful there as at Ssagastyr. The negative storm then decreases once more on Chart IV, while at the
same time the storm-centre moves back to the regions about Fort Rae and Uglaamie. It may be noticed
that this contrary movement of the system of precipitation, takes place after the sun has crossed the
meridian of the magnetic axis.

The positive system can be followed in a similar manner. At first it extends from Godthaab
eastwards as far as Little Karmakul, as shown on Chart II. On Chart III the negative system breaks in
upon it, causing, in some cases, distinct reversals of the direction of the current, as, for instance, at
Little Karmakul and Jan Mayen ; while in others the current-arrow only swings backwards and forwards
as at Bossekop and Sodankyla. At Christiania, however, the effects are still chiefly those of the
positive system.

At the end, we find again stronger effects of the positive system, the force at Little Karmakul, at
i8'1 50'", for instance, being of remarkable magnitude. Its effect are also distinct at the more westerly
stations. At Jan Mayen, where, not long before, the effects of the negative system had been so distinct,
the current-arrow has once more begun to oscillate, and at 19'' 2om is more indicative of the positive
system, although there are evident signs of the action of both systems simultaneously.

The negative values of P, constantly found at Jan Mayen should also be noted. They show that
although at one time the positive system is the stronger, and at another the negative, this variableness
has no special significance as regards the vertical forces. As we have so often pointed out, the expla-
nation of the phenomenon is, that the negative system, whose area of precipitation must be assumed to
be chiefly to the north of Jan Mayen, and the positive system, whose storm-centre is certainly situated
to the south of that station, will both act in the same direction, namely a negative direction.

The conditions at Little Karmakul are also somewhat variable, and on Chart IV we find both
distinct negative and distinct positive forces.

The last current-arrow for 19'' 50™ comes more properly in the next section of the perturbations,
which we shall now proceed to examine.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903. 50

3QO 13IRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

The second main section of the powerful perturbations on this date, is, as we have said, from
igh 45™ to the end of the period.

At about i9h 45m, it appears that comparatively quiet conditions have once more supervened at
almost all the stations. At a few of them the conditions are almost normal for a short time; at others
we find a more or less marked minimum in the deflections; while at others again there appears to be
a transition, as the storm, which was previously positive, now changes to negative.

That which characterises this second section of the perturbations, is the powerful negative polar
storms which we find at all the stations. These are certainly only to be considered as a further
development of the earlier negative systems of precipitation observed. In the deflections at Kingua Fjord
at this time, there is a minimum of no great distinctness. The declination-deflections, which have
previously continued to be quite strong, have shown a slight indication of a minimum at about i9h 45™;
while the horizontal-intensity curve, which, since about jy11 has been more or less evenly approaching
the normal line, has now reached it. The horizontal intensity then remains almost normal for a couple
of hours, only oscillating slightly about the normal line.

The conditions at Uglaamie form a suitable starting-point for our reflections upon the perturbations
in this section. There are, as will be seen, two strong deflections separated by an interval in which the
deflections have a brief, but very marked, minimum just before 2ih. These two deflections are so strong
that in both cases the needle passes out of the field of observation.

To the first of them, there are corresponding deflections at Ssagastyr and Fort Rae, as also at a

number of other stations, although, the resemblance at some of them, is less marked. At Fort Conger

the resemblance is quite striking. At Little Karmakul, there are also two maxima, which show some

resemblance to those at Uglaamie; but the resemblance between the first pair of them is not so great.

It has more the appearance of a brief but powerful impulse, a precursor of the subsequent strong deflection.

The storm thus appears as a negative polar storm; with its centre in the vicinity of Uglaamie.

On Charts IV and V there are two hours which represent the conditions during this first phase

of the second section. There are fairly powerful perturbing forces at several stations.

The different systems that we here see are, of course, connected in some way or other with each
other; but it seems as if the system in the neighbourhood of Uglaamie was more or less independent.
It is therefore very likely that there is a large, more or less connected, negative system of precipitation,
in which there are two storm-centres, one in the vicinity of Uglaamie, and the other in the region east-
wards from Kingua Fjord.

The hour 20'' 30™ on Chart V, also belongs to this first phase of the perturbations. We here
see the conditions at the time of the strong deflection at Little Karmakul.

The negative system of precipitation now also forms a circle round the geographical north pole,
and the forces seem to be concentrated about several storm-centres. There still seems to be one at
Uglaamie, one at Little Karmakul, and one less powerful one at Kingua Fjord; but whether they are in
reality so clearly separated as they appear to be, it is difficult to say.

We find here no distinct traces of positive systems, although it is possible that such do actually
exist, and from what we have seen, are to be looked for to the south, or in the southern part, of the
auroral zone, from Europe westwards; but we have no stations there.

A distinct, though rather faint indication of such a system is to be found indeed in Jan Mayen at
about 20'', and the rapid transition from Little Karmakul to Bossekop, found on Chart V, for the hour
2Oii 30™, is possibly due to the existence of positive polar precipitation to the west. The direction of the
current-arrow at Gettingen, which is a little more westerly than might be expected if the negative
systems only were acting, may also possibly indicate the existence of a positive system of precipitation
such as this.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 39 1

The most powerful storm does not develope, however, until this first phase is past.

The second phase of the storms in this second section may be considered as coming in the interval
between 2Oh 40™ and the close of the period. The deflections, which at first, at any rate, correspond
to the effects of a negative polar storm, are very powerful everywhere; and at Uglaamie and Ssagastyr
the needle passes out of the field of observation. The various deflections, however, are not so well-
defined as to make it easy to find any distinct movement of the systems.

What we will, however, draw particular attention to, is the perturbation-conditions at Fort Rae.
At the close of the period, a distinct change takes place there in the direction of the perturbing force.
We previously found only negative deflections in the horizontal intensity, indicating that negative
systems of precipitation were at work; but now a positive system appears here. That this station is on
the afternoon-side of the globe, and further that it is to the south of the auroral zone, are circum-
stances that agree closely with what we should have expected to find; and the positive system, the
existence of which, during the last storms, we were unable to prove, and could only suggest the possibility
of, appears once more just at a time when we might expect to find its effects at the stations we are
considering.

At the southern stations the forces are unusually powerful.

The fields of force for this last phase of the storms, will be found represented on the last three
charts, from 2oh 5om to 23h i5m.

We now find, as so often before during the powerful storms, a negative current-circle round the
geographical pole.

The greatest forces are found upon the night-side, and they are of unusual magnitude. The
storms are negative everywhere, except at 22b 2om and 23** i5m in America, where we meet with the
effects of the already-mentioned positive storm. In Europe, the negative area of precipitation has moved
farther south, if we may judge by the conditions in the vertical intensity; for both in Jan Mayen and
at Cape Thordsen there are now positive values of P,, whereas previously they were negative only.
The precipitation seems therefore, now to take place to the south of these stations, whereas, previously it
was chiefly to the north. This is in agreement with the fact that the negative area of precipitation comes
farther south on the night-side than on the day-side

In Europe, the direction of the current-arrows is rather south, even as far north as Bossekop. In
Central Europe this is the normal condition during similar storms; but the forces there are now so
powerful, that to a certain extent we have used the same scale as at the polar stations.

On Chart VII, the powerful negative storm is almost over, and only at a few places we now find
perturbing forces, indicating that it is still in existence. At Fort Rae, on the other hand, we find
powerful effects of the positive storm that has been mentioned as occurring there.

392

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.

TABLE LVI.
The Perturbations of the ist February, 1883.

Gr. M. T.

Uglaamie

Fort Rae

Kingua Fjord

Godthaab

Pk

Pi

Pt

Pk

Pd

p.

Ph

Pd

P P

h m

II 20

0

w 4 y

+ 20.57

— no Y

E 4° y

+ 120.57

- 20.57

E 7-5 y

- 97-57

W i, .57

12 2O •

61 ;'

n 4 n

o

- 3° „

B 41-5,,

+ 25 „

- '4-5,,

W ,2 „

- 37-5,,

» 1° r

13 20

o „

O

o

+ 10 „

„ 7 „

0

- 5-5 n

E 20.5 „

- I0 „

E 3 „

14 20

+ 20 „

» 2 „

- I0 »

+ 20 „

0

o

+ a° „

„ '9-5 „

- .0 „

W 5-5,

15 20

33-5 „

E i „

+ 20.5 „

- 32.5 „

„ a6.5 „

- 3'-5,

-'72 „

W 79.5 „

+ '5 „

E 31-5,

16 20

- 23.5 „

0

o

- 25 „

,, 3°-5,,

o

-i°5 „

;, 75 „

+ 34 „

» 36.5 .

5°

101 5 „

n 7 n

+ 20.5 „

- 90 „

B 84 „

- 57-5,,

-'47 „

B 92 „

+ 29 „

» 55-5 .

17 20

"7 „

„ '0-5,,

+ 81.5 „

-'55 n

» Iaa B

- 82.5,,

-162.5,,

B 87.5,

-'32 „

Wii5 „

18 I5

->3°4-5«

„ 66.5 „

+ 214 „

-255 „

„ '80 „

+ 335 „

- 92.5,,

„ I29 „

- '26.5 n

„ 1 18.5.

3°

->3°4-5 ,,

n 32 „

+ 254 „

-45° „

„ 123.5,,

i 268.5 „

- 91 „

„ 94 „

-W-Sn

r, 88.5n

5°

276.5 „

„ 13 „

+ J97 „

-355 „

» 73-5 „

- 90 „

-121.5,,

„ 94 „

~*3l „

» 58.5,

i g 20

44 B

W 8 „

+ 122.5 „

— 17° „

» 23.5,,

- 37-5 „

- 55 „

„ 94 „

— 6l a

n 34 „

50

237-5 n

E 27 „

+ 41 „

- 28.5,,

„ 26.5 „

— 80 „ . o

„ '32 „

+ 37-5,,

» 135 „

20 30

294-5 „

, 6 „

4 I03 „

- 64 „

„ 56-5 ,,

- 4° „

0

„ IOO-5 „

- '5-5 „

,1 I03 r

5°

'34 „

» 9-5 „

+ 184 „

- 85 „

„ 86.5,,

0

+ 34-5,,

Bir5 „

- 6.5,,

» 106 „

21 15

->308 „

„ 22.5,,

-1-376 „

-24<> „

« '42.5 „

-MO „

- °-5 „

Bl82 „

- 48.5,,

n 179 „

30

->3°8 „

W 6.5,,

+ 299 n

-268.5,,

„ 72 „

-I3L5 n

+ ii „

., '94 „

- 54 »

» 198.5 »

40

->3o8 „

» 47-5,,

+ 206 „

-280 „

n"3 n

-258.5,,

+ 7 „

B '9° a

- 5° „

,1 207 „

22 20

->308 „

E 56 „

- 71-5,,

- 24 „

W25 „

- 3° „

+ 46 „

„ i£9 „

— 4 n

,,214 „

23 '5

+ 50.5 „

Wi4 „

- 74-5 n

+ '7° »

. 82 „

- 20 „

+ 60 „

„ 67.5 „

+ 50 „

.. 9'5 n

TABLE LVI (continued).

Gr. M. T.

Jan Mayen

Bossekop

Sodankyla

Ph

Pd

F»

Pk

•

Pd

P,

Ph

Pd

Pi

h m

II 20

4 7

0

+ I4-5/

o

W 7 7

- 0.57

0

W 17.57

o

12 2O

* 1-5 »

o

- 5-5.

- I ,,

o

- i »

o

» 9-5 ,

0

13 20

+ 22.5 „

W 3 7

+ 6 „

f i „

„ i-5 »

0

+ 3-5 y

» 12 „

o

14 20

+ 3 „

o

o

o

E 1.5,,

- i-5 »

0

» 7 »

+ 2.57

15 20

+ 70 „

„ 26.5 „

- I0 n

+ 4 *

W 16.5 „

+ 6 ,,

+ 3 „

„ '9-5 »

+ 9 „

l6 2O

+ 4O „

„ 36 „

— 10 „

+ 4 »

* 22.5 „

+ i »

+ 7-5 H

B '8 „

+ 9 „

5°

+ 135 *

n 55 »

- 5° »

+ II „

» 4i.5«

+ 10 „

+ 7-5,

ft 36.5»

+ 5-5 »

17 20

— 9 »

,, 82 „

- 80 „

+ 26 „

„ 80 „

+ 15 »

+ 35 „

ft 58 .

- '4-5 „

18 15

-223.5 »

» 150 „

- 20 „

- 49 „

» 63-5»

- 45-5 n

- 60 „

ft 17 »

+ '03 »

3°

—240 „

„ no „

- 20 ,1

- 24 „

» 7i »

-60 „

+ 35-5 „

„ 88.5,,

+ 160 „

5°

— 123 „

„ 84-5,

- 54 „

+ 40.5,,

« "°9 ,,

- 8 „

+ 122 „

„ '32.5 ,

+ 112.5,,

19 20

+ 21 „

» 60.5 „

-145 „

+ 25 „

„ 25 „

+ ii „

+ 6l.S „

ft 4-5 „

o

5°

^ 66 „

» 77-5,

-13° .,

+ 6 „

» 35-5 »

+ 6.5,

+ 10 „

E 8.5,

- 40 „

2O 30

+ 6 „

n I04-5 »

- 43 „

— 5-5 ,,

n' 65 „

- x ,,

- 55 «

» 59 „

- 39 -.

5°

- 51 „

,,i'5 »

- 17-5,,

- 77-5 „

Ei55 ,

-16 „

- 75 »

ft 58 „

+ 15 »

21 15

-145 „

» '66 „

+ 40 „

- 84 „

„ 222 „

- 25 n

-I04 „

ft 274 „

+ 42 „

3°

-565 „

„ 81 „

+ 3I7.5,,

-"5-5»

„ 94 »

- 47 „ — 167-5 »

» 228 „

+ 31 ft

4°

-35° „

» 80 „

+ 205 „

-103 „

» 173 „

- 59-5 »

-'So „

» 192 »

+ 106 „

22 20

- 55 „

,, 89 „

+ "5 „

- 56 „

„ 'SO „

5 »

-152.5,,

,,!4i »

- 55 «

23 15

+ 65 „

. 47-5 .

+ 68 „

- 22 „

» 85.5,,

+ 11 „

-100 „

„ 86 ,

- 46 „

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP.

393

TABLE LVI (continued).

Gr. M. T.

Cape Thordsen

Little Karmakul

Ssagastyr

n

ft

P,

Pk

Pd

/',

A

Pd

h m

1 1 20

+ 8 y

W 3 y

- 4° y

+ 13 r

W 7.5/

- '3 /

+ 57 Y

E 2.5;-

12 2O

+ 7 »

» 6 „

o

o

E 10 „

— 2 n

+ 28 „

o

13 20

+ 10 „

» IO-5,,

+ I ,,

+ 8,

0

- '4 „

+ 34 „

0

14 2O

5 »

» 7 »

4 n

- 12 „

n J5 „

4 „

"*" 2 n

0

15 20

+ 15-5 „

» 45 »

- 25 n

o

W 10 „

+ 3 „

5 „

0

1 6 20

1-5 n

„ 3° »

- 22 „

+ 6n

n I0 11

+ 2 „

+ 28 „

0

50

— 39-5 „

i, 64.5 „

- 56 „

+ 64,

11 45 n

+ 4 „

!4 „

W 21.5,,

17 20

- 70 „

» 7° »

- 61 „

- 26 „

a 40 „

- 67 „

- 95 „

„ 47 „

18 15

-177-5 „

,, '35 »

-137 n

->76oB

ESIO „

- 5 „

->655 ,,(l)

„ 236.5 „

3°

-295-5 »

,i "6.5 „

-120 „

- 59 11

„ 65 „

- 4° n

->655 „(')

o

5°

-156 „

„ I02 ,1

- 5° „

-*- 273 „

Wi48 „

— 125 „

72 „

E I25 „

19 20

- 50 „

n 54-5 „

- 21 „

4- 82 „

„ 76 „

- 36 „

42 „

n °8 „

50

7-5 „

» 65 „

— 25 n

5° n

E '9 11

+ 1° n

72 „

» '5° „

2O 30

- 34 ,

» 7<> „

- 10 „ 647 „

„ 325 „

+ 138 „

60 „

W 2.5 „

5°

~ I2 n

n I25 n

- 27 n — 632 „

,,660 „

+ '37 „

->655 „ (')

» I2-5 „

21 15 ; —170 „

» 95 „

+ 172 „ - 636 „

n34° n

-140 „

->655 „ f1)

.•i '5 a

30 -174 „

„ 84 „

+ 219 „

— °33 ,1

„ 640 „

- 26 ,

->655 „ (')

£296 „

4o

-205 „

* 49-5 „

4-270 „

63° *

n 375 j>

+ 33 n

->655 „ O

„ 52° ..

22 2O

-112 „

E 66.5 ,. + 188 „

'45 n

» 2'4 ,,

+ 24 „ 35° 11

„ 277 „

23 15 °

W 104 „ 4- 96 „

153 n

„ 193 .,

4- 68 „ 4- 44 „

» 73-5,,

(') See description p. 387.

TABLE LVI (continued).

Gr. M. T.

Christiania

Pawlowsk

Gottingen Fort Conger

Ph

Pd

Ph

Pd

P,

Pk

Pd

n

Pd

h m

II 20

o

O

+ 5 y

W 15.5;'

o

- 3-s y

W 15 y

o

E 8.5 y

12 2O

0

E 3-5 y

+ 3-5 >,

.» 7-5 .,

+ s-5 y

- i-5 »

» 4 n

+ 0-5;'

W 6.5 „

13 20

+ s y

o

+ 6 „

;> 6-5 "

+ 7 ,,

+ i „

„ 6 „

+ I ,,

E 6 „

14 2O

+ 9 ,,

.. 3 »

+ 5 ,,

o

+ i-5,,

4- 6 „

„ 0.5 „

+ 7 ,,

W 1.5 „

15 20

+ 17 „

W 9.5 „

+ 95 *

,, 1 6 „

+ 0.5 „

+ 18.5,,

,, II a

+ 6 „

,, 55-5 „

]6 2O

+ 24 „

„ 8 „

+ 15

;. M-5 »

0

+ 22 „

n 7-5 ,'

+ 0.5 „

,, 76.5 „

50

+ 23.5 „

,. 25.5 „

+ 6 „

„ 24 „

0

+ 23.5,,

,, 19-5 ,,

— 2 „

,, 120 „

17 20

+ 27 „

,, 48 „

+ i-5.

„ 36 „

+ 5-5,,

+ 23.5,,

,, 37 »

- 6 „

,, 124-5 ,,

18 15

+ 45-5 »

E 2.5 „

- 45 ,,

E 52.5,,

+ 42.5 ,,

- 65 „

E 14 „

+ 24 „

» 337*5 n

30

+ i55-5»»

o

- 29-5 »

,, 16 »

-f 80 „

- 66 „

„ 5-5 ,,

+ 31-5,,

„ 289.5 „

50

+ 27 „

W 58 „

- 64 „

» 15 »

+ 95 ,,

- 54-5 »

W 73 „

+ 30.5,,

„ 121.5 ,,

19 20

- 26.5 „

E 8 „

- 27.5,,

„ 34-5 »,

+ 57 .

- 42 „

o

+ 28.5,,

E 26.5 „

50

— 6 „

,, 65 ..

- 14 „

„ 28.5 „

+ 32-5 »

- 10.5,,

E i „

+ 20 „

W 133.5 „

20 30

+ 8.5,,

» 37 »

— 2o „

» 67 .»

+ 21.5,,

- 3° ,,

,, 39 >,

+ 24.5 „

,, i'4 „

50

+ 3-5 „

W 9-5 „

- 25 „

» 7'-5»

4- 16 „

- 23 „

,, 25 „

+ 22 „

,, 93 ,,

21 15

- 3i-5..

E 142.5,,

- 14 »

» 181.5,,

+ 4-5 n

- 84.5,,

>> 139-5 »

4- 45 ,,

» 219 „

30

- '3-5 «

» 109 „

- 37-5 »

,, 138-5,,

o 1 - 55-5 ,,

,, 99 ,,

+ 39 ,,

, 214.5 ,,

40

4-5.,

„ 98 „

- 4° ..

,, 125 „

- 0.5 „

- 58.5,,

,, 83 „

+ 36 „

„ 206.5 »

22 2O

- 43-5..

,, 72.5 »

— 50 ,,

„ 80 „

- 16.5 „

- 37-5,.

„ 64 „

+ 18 „

» 75 »

23 15

- 19 „

». 30.5 .»

- 32 »»

,, 43 „

- ii »

- ii „

,, 31-5 ,,

+- 4 „

E 0.5 „

394

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

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PART a. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. i.

Current- Arrows for the 1st February, 1883.
Chart VII at 23 '' 15m.

397

Fig. 1 66.

THE PERTURBATIONS OF THE 15th December, 1882.

(PI. XXIV.)

89. The interest that attaches to the perturbations occurring on the above date, consists in the
fact that we at first have a clearly developed positive equatorial storm. In the storms previously de-
scribed, it was principally, at any rate, polar precipitation that showed itself, and the effects of which we
studied. On this occassion, therefore, a special opportunity is afforded of studying perturbation-conditions
in the polar regions about the auroral zone during an equatorial perturbation.

It may seem difficult to prove that it is really an equatorial perturbation with which wo are con-
cerned, seeing that our observations are chiefly from polar stations. It appears, however, that the more
southern European stations are quite sufficient to determine this; for the perturbation-conditions that we
have learnt to consider as characteristic of positive equatorial storms always come out very distinctly
there.

If we compare Christiania, Pawlowsk and Gottingen, we find the conditions during the period
previous to ioh 15™ fairly normal; but then, at all three stations, there suddenly appears a perturbing

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903. 51

398 nlRKELAND. THE NORWEGIAN AUKOfcA POLARIS EXPEDITION, IgO2 — 1903.

force, which, at ioh 2om in the horizontal intensity, has a negative direction, but is then once more
rapidly reversed; and from ioh 25m there are continuous positive perturbing forces, until the equatorial
storm is interrupted by the polar storm that occurs during the last part of the period of observation.
The course of the horizontal-intensity curve is the same at all three stations mentioned above, the simi-
larity being most marked between Christiania and Gottingen. The curves for these places are drawn
on the same scale, but in that for Pawlowsk the same serrations are found, notwithstanding that the scale
employed is only one fifth that of the other two stations. The positive forces continue moreover all the
time, as the storm remains more or less constant in strength. Further, on the most southern station, Gottin-
gen, we find, it is true, at first from ioh I5mto about ioh 25™ some small but very characteristic deflections
in D; from that time, however, the declination-curve coincides fairly well with the normal line, until the polar
storm sets in at the end of the period. We thus find here the well-known characteristic features always
to be found in positive equatorial storms, and there is therefore no doubt that this is one of that class.

The determination of the normal line for this date is somewhat difficult, on account of the small-
ness of the perturbing forces and the length of the perturbation. The uncertainty thus arising is most
apparent at the close of the equatorial perturbation. At its commencement, on the other hand, the
uncertainty is not great, so that the forces taken out then differ very little, at any rate, from the actual
values; and in the subsequent polar storm, the perturbing forces are of sufficient magnitude to make any
uncertainty in the position of the normal line less important.

From Part I it will be remembered that the direction of the current-arrows in the north of Europe
was not so nearly due east as at the more southern stations, but was as a rule a little more northerly,
as there were also perturbing forces in declination. This is also the case now. At Pawlowsk there is
a considerable deflection in the declination curve, whereas at Christiania and Gottingen this deflection
in the declination is not so marked. It is possible, however, that there too there are some more power-
ful forces than those indicated on the plate, as the normal line is very difficult to determine, on account
of the absence of daily hourly-observations.

At nearly all the polar stations, we find, at ioh 20™, a rather sudden deflection in the curves,
which indicates that the effect of the equatorial storm begins suddenly and simultaneously everywhere.

At three polar stations in the eastern hemisphere, which are situated to the south of the auroral
zone, namely, Bossekop, Sodankyla, and Ssagastyr, there are positive deflections of fairly constant
strength in the horizontal intensity, from the beginning of the positive storm until about i6h 30"". Simi-
larly we find in the declination at the first two of the above stations continual westerly deflections of
fairly constant amplitude, while at Ssagastyr the deflections in this component amount to almost nothing.

At Cape Thordsen, the course of the declination-curve shows conditions very similar to those in
the south, and is thus evidently due to an equatorial current-system; but polar precipitation makes its
influence more felt here than at the stations just considered. This seems to be especially the case at
first, when the horizontal-intensity curve has a rather more disturbed character.

The equatorial character of the perturbation disappears, however, as we go westwards. We also
find the first impulse again at the other stations, and it is therefore evident that the perturbations \ve
find here are connected with the equatorial storm, while it is equally certain that other effects seem to
be present. If we look, for instance, at the conditions in Jan Mayen, we find at first only very small oscil-
lations to either side of the normal line. In the horizontal-intensity curve these are principally above the
line, thus answering to positive values of PI,, but farther on, at Godthaab, we find deflections which,
though inconsiderable as regards strength, are mainly in the opposite direction, representing negative
values of PI,.

Continuing westwards, we come to the station that is the most important in this instance, namely,
Kingua Fjord. The disturbances there are evidently of a distinctly polar character; and the uneven

I

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 399

nature of the curves seems to indicate that the polar system of precipitation is at no great distance from
the station. This is especially evident in the declination. At first the deflections are mainly directed
eastwards, but subsequently change, and from about I3h 30'" until the close of the period, are directed
westwards. The strength of the deflections is considerable, and as early as 15'' they have attained
a magnitude of the same order that we are accustomed to find during the polar storms in these regions.

At the other polar stations there are no specially marked effects of polar storms until about i6h 30™,
so that up to that time the storm is concentrated about the districts surrounding Kingua Fjord. Even at
Godthaab there are no distinct effects of the storm.

Continuing still westwards from Kingua Fjord through North America, we come to Fort Rae and
Uglaamie. Here the effect of the equatorial storm seems once more to be more evident. In the hori-
zontal intensity we find, at about ioh 2om, an impulse exactly similar to that at the other stations at which
the equatorial storm occurs; and after this we find, during the time that the equatorial storm is going
on, mainly positive deflections of more or less constant amplitude, and as regards strength very much
what one would expect to find them. There are, however, quite distinct effects of other systems. In
two or three places, for instance, we find in the horizontal-intensity curve, deflections to the opposite
side; and there are also sometimes impulses that are in all probability too powerful to be the direct
effect of the equatorial current-system. This circumstance is most clearly apparent in the declination-
curve. It is most natural here to assume that there is polar precipitation in addition to the equatorial
system.

The most interesting feature here is, as we have said, the pronounced polar storm at Kingua
Fjord. It is fairly powerful, but of very limited area, and recalls in a striking manner circumstances
that we have previously found in our experiments.

We see, for instance, in this connection, in looking at fig. 37 on page 80, Part I, that in addition
to the equatorial ring that is formed, there is a very distinct patch of light in the polar region, and
some fainter, less distinct polar precipitation more on the noon or morning side of the terrella. This
clear, sharply-defined patch answers to rays that descend towards the earth and leave it again in paths
that lie comparatively close together. A system of precipitation of this form, in the immediate vicinity
of the patch, will probably exert a considerable magnetic influence; but this will rapidly decrease with
increasing distance from the patch. It is just an effect such as this that we appear to have at Kingua
Fjord. There are, as we have said, powerful perturbing forces, which indicate comparatively abundant
polar precipitation, while the effect of this precipitation at a station no farther off than Godthaab, is
scarcely traceable. Lastly, if we look at the position of the patch in the figure, in relation to the mag-
netic pole of the terrella and the direction to the cathode, and imagine where this patch would fall if the
earth and its magnetic axis were to take the place of the terrella and its magnetic axis, and the direction
to the sun that to the cathode, it will easily be seen that the patch would fall more or less in the region
round Kingua Fjord. It thus seems very probable that this is an in-drawing of rays such as we find
by experiment. As we have said, there arc also certain effects of polar precipitation at Fort Rae and
Uglaamie, which may be connected with the slighter polar precipitation seen in the figure to the left of
the distinct polar patch. The latter, however, may possibly be a more or less accidental resemblance;
but the subsequent experiments may perhaps give fuller information regarding this circumstance.

With regard to the occurrence of the comparatively powerful polar storm at Kingua Fjord simul-
taneously with the equatorial storm, we may remind the reader of the various more or less abnormal
conditions that we have come across at the American stations during the equatorial storms described in
Part I. Of these we will mention the storms of the 23rd and 24th November, 1902, described on pages
273 and 274 in which these abnormal conditions were very greatly developed, and also the storms of
the 26th January, 1903— page 67 — and the 22nd March, 1903— page 128.

400 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

At the time we believed that these more or less abnormal conditions must be due to polar precipi-
tation of some kind, concerning which we were then unable to express an opinion. Here, however, we
have distinct proofs of the existence of such polar systems during equatorial storms also. It was especi-
ally in America that this precipitation occurred then, and now we find the same thing occurring here.
The fact that it is in America that it occurs, is without doubt connected with the appearance of these
storms at more or less the same time of day; and the situation of the magnetic pole in those regions
is a circumstance of no little significance.

The equatorial storm is represented on the first four charts.

Chart I is drawn for a number of hours, to show the characteristic oscillation of the perturbing
forces, which we have previously always observed simultaneously with the commencement of the effect
of the equatorial storm. As the curves we have to go by are not continuous, but only readings for
every fifth minute, the variation cannot be followed as it might have been if we had had photograms.
It will be seen that the current-arrows at the stations in the south of Europe turn right round through
an angle of about 180°, but it is not possible to determine whether the movement is clockwise or anti-
clockwise. Later on, when the movement is less pronounced, it can be followed.

At the three southern stations the current-arrow moves in a direction contrary to that taken by the
hands of a clock from ioh 25"° until io)l 30™, from which time until ioh 35m or ioh 40™ it reverses
its direction.

At Gottingen, where the first two current-arrows are not in quite such opposite directions as at
the two other stations, it appears from the chart that the movement from ioh 2om to ioh 25™ has been
in the same direction as from iou 25™ to ioh 30™, namely anti-clockwise, and that the principal pheno-
menon at the beginning of the equatorial perturbation would therefore be first a turn through 180° in a
direction contrary to that of the hands of a clock, and then a smaller, slower turn back, after which the
direction of the current-arrow remains constant as long as the effects of the equatorial system pre-
dominate.

At Ssagastyr, on the other hand, the current-arrow moves through a smaller angle, clockwise, and
apparently more or less regularly, from ioh 2om to ioh 30™, and then remains more constant for tin-
remainder of the period represented on Chart I.

At Uglaamie too, the movement of the current-arrow is similiar to that at Ssagastyr; but its direc-
tion, unlike that at most of the other stations, is northerly.

At Fort Rae, the equatorial character of the perturbation is once more clearly apparent. The
direction of the current-arrow also undergoes a great change as the perturbation begins, exactly similar
to that which takes place at the southern European stations.

At the other stations too, there are great deflections, at Godthaab, for instance, as much as 180°.
At Cape Thordsen the movement is less, and anti-clockwise;, while south of that station it is generally
clockwise, at any rate after ioh 25™.

While there are considerable perturbing forces from ioh 30™ to ioh 40™ at the stations round
Jan Mayen, those at Jan Mayen itself have now almost disappeared. There is evidently some connec-
tion between this circumstance and the fact that the current-arrows at Cape Thordsen and Godthaab
are now almost in opposite directions. At the first of these stations, the equatorial system appears to
exert a considerable influence, while in the region round Godthaab and Kingua Fjord, there seem to be
other influences at work, probably polar precipitation, which, as we have seen, subsequently developes
to a considerable strength in this very region.

On the other charts which represent the conditions during the equatorial storm, the current-arrow
at the stations to the south of the auroral zone undergo, as a rule, little change in direction or size;
and the form of the field remains fairly constant.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 40!

At the stations in and to the north of the auroral zone, on the other hand, the conditions are
somewhat more variable. This is especially the case at Kingua Fjord. This is quite evident on looking
at Chart II — IV. At nh 2om the current-arrow seems in a great measure to be due to the equatorial
system, although even now polar precipitation is also certainly asserting itself. At I4h 2om, however,
the polar system predominates, and at 15'' 20'" is still more evident.

With the exception of the polar storm at Kingua Fjord, there are none of any magnitude before
i6h 30"; but from that hour polar storms begin to be more and more apparent at other stations. At
the same time the equatorial storm still continues to act for some time.

Between 16'' 2om and I7h, we find in the horizontal-intensity curve at Gottingen and Christiania
a very characteristic wave; and at Pawlowsk exactly the same thing is found, although, as the scale is
smaller, it is less distinct. Similar deflections are also found at the same time in the horizontal-intensity
curve at Kingua Fjord, in declination and horizontal intensity at Godthaab and in declination and vertical
intensity at Cape Thordsen, in Jan Mayen, and at Fort Conger, all of which exhibit so great a resem-
blance to one another, that there must undoubtedly be some connection between them.

In cases such as this, in which there are effects of both polar and equatorial systems simultaneously,
the fact of finding conditions which seem to indicate that the two systems at the same time undergo similar
changes, is in perfect accordance with what theory would lead us to expect. According to this, all the
perturbing systems that appear simultaneously are due to one system of corpuscular rays, which become
deformed by terrestrial magnetism, and, in their effects upon the earth, are apparently more or less
separate phenomena. This however, it should be remarked, is only apparent. Theoretically there must
always exist a genetic connection between simultaneous perturbations of the most varied kinds, both
polar and equatorial, south polar and north polar, etc., etc. A connection such as this is often shown
during equatorial storms in which, simultaneously with the serrations in the horizontal-intensity curve,
there are found in the polar regions of the earth similar serrations or deflections that are too great to
be ascribed to changes in the equatorial system, and which are certainly effects of polar precipitation.
Another very typical example of this is to be found on this date, at about i4h, on comparing, for
instance, Christiania and Gottingen on the one hand, with Kingua Fjord or Fort Conger on the other.

We have often before pointed out simultaneous changes in positive and negative polar storms,
which of course are also only indicative of the above-mentioned connection between the phenomena.

The polar storms that occur at the close of the period are both positive and negative.

The order of these polar storms on this date is the same as that so often found to be charac-
teristic of afternoon storms, referred to Greenwich time.

At the more southern of the arctic stations in Europe, Jan Mayen and Bossekop, we find the
effects of the positive storm. The storm occurs a little earlier at Jan Mayen than at Bossekop, as the
horizontal-intensity curve at the former station begins, at about I5h, to increase more or less regularly
to its greatest height, which it attains at about i6h 40™. At Bossekop the greater positive deflections
do not occur until a little after i6h; but the curve there rises somewhat more rapidly, and attains its
greatest value at about 17'' 30™. After this first maximum has been reached, the positive deflection
remains more or less constant in amplitude for some time, until the negative storm breaks in upon it.

At about igh the positive deflections in the horizontal-intensity curve for Jan Mayen begin to
decrease, but at the same time the deflection in declination increases, thus forming the transition to the
last portion of the observation-period, in which, as we see, the negative polar storms predominate. At
Bossekop the transition from the positive to the negative storm is considerably sharper, and occurs at
about 2oh.

At the other stations, wherever perturbations of any magnitude occur, we find only negative
storms.

402 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

At Ssagastyr there is a short, comparatively small, but well-defined negative storm at about 17'';
and at Uglaamie there is also a negative storm. A maximum is found here a little before 19''.

At Cape Thordsen we find negative deflections that very much resemble the positive deflections
at Bossekop and Jan Mayen, for at all three stations we find deflections of fairly constant strength for a
period of some length. The similarity is immediately seen on looking at the curves.

Lastly we also find considerable perturbing forces at Kingua Fjord; but, as already remarked,
they will be more easily studied by looking at the charts. The most powerful storms, however, are
between 2oh and 22h. At almost all the polar stations here mentioned, there are negative deflections,
as a rule very well defined. Only at Sodankyla do we find a considerable positive deflection, this being
at about 2oh 3om.

There is a certain amount of time-displacement here. The great negative deflections, for instance,
begin a little earlier at Ssagastyr than at the European polar stations; but as we unfortunately have no
observations from Little Karmakul, this circumstance cannot be closely studied. Moreover there are
other phenomena which encroach upon it: for in all probability there will be positive storms occurring
simultaneously in districts from which we have no observations. Now and then too, we find positive
deflections, which may be interpreted as effects of such a system, e. g. the one just mentioned at
Sodankyla, a small positive deflection in Jan Mayen at about 22h 30"", and two or three distinct positive
deflections at Fort Rae, in the interval between 22h and the close of the period of observation.

On looking at the declination-curve for Kingua Fjord, we are at once aware of a peculiar circum-
stance. This is the jagged, disturbed character of the curve before 2oh, and the wide, but regular
deflection after that hour. We have seen that as a rule the curves in the polar regions during equatorial
storms are of an exceedingly jagged, disturbed character, whereas the curve during well-defined polar
stoms may frequently exhibit a fairly quiet course, even if the deflections are large. It may well be,
therefore, that this transition to a more quiet course is an indication that the equatorial system is dis-
appearing.

At the southern stations we find the most powerful forces in declination, and the deflection here
begins at the time that the more powerful negative forces appear in the northern regions.

We now pass on to consider the last eight charts, on which the perturbation-conditions for the
last part of the period are shown.

On Chart V, for 77'' 20"' we see evident traces of the positive polar storm, its district of pre-
cipitation extending from Godthaab across Jan Mayen to Bossekop. At all the other polar stations there
are distinct effects of negative storms; while at the southern stations the equatorial system is still
evidently at work.

On Chart VI, for 2oh 20™, the effects of the equatorial storm have disappeared, and those of the
positive polar storm are found only at Bossekop and Sodankyla. Everywhere else in the polar regions,
we find more or less pronounced effects of negative precipitation, these being especially marked in the
district Uglaamie to Ssagastyr. At Fort Conger there is also a more or less westerly-directed current-
arrow, which in strength considerably surpasses those at Kingua Fjord, Godthaab and Cape Thordsen,
This should probably be regarded as a continuation of the system of which traces were found in Jan Mayen.

The divergence of the current-arrows for Christiania, Gottingen and Pawlowsk, especially the
westerly direction that they have at the first two stations, seems clearly to indicate the existence of a
system of positive precipitation in the regions westward from Bossekop along the auroral zone; for
these two arrows appear to be enclosed in an area of divergence corresponding to such a system. The
positive vertical arrow for Gottingen is also in accordance with this.

The arrow for Pawlowsk, on the other hand, seems to be in the eastern area of convergence,
answering to the negative storm in the north of Asia, but may also be considered as belonging to the

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 403

area of divergence of the positive system of precipitation. The effects of the two systems will pre-
sumably be combined here, as they will each produce an arrow with a southerly direction.

On the next four charts, VII to X—from 20'' 50'" to 21'' 2jm,— we find the perturbation-conditions
represented as they appear at the time when there are powerful negative storms round the auroral zone.
The form of the field of perturbation undergoes no particular change, but from time to time there is some
variation in the strength.

The current-arrows at the European stations are directed southwards, as they usually are in the polar
night-storms. This circumstance is certainly in some measure due to the more western positive system;
for in the district in which it appears, this storm will diminish the effect of the adjacent negative pre-
cipitation, so that that system will in a manner be interrupted at the place where the positive precipi-
tation appears. In this way, however, the constitution of the current system will be such that the
characteristic areas of convergence and divergence would be prominent, and this is just what these
current-arrows indicate. The positive perturbing force in the vertical intensity at Gottingen also indicates
the existence of such a system. Without the assumption of a system such as this, it would perhaps be
rather difficult to find a simple explanation of these southern-pointing arrows, as the negative storms
seem to be fairly evenly distributed about the auroral zone. We should then have to assume a more
complicated constitution of the perturbing current-system, for instance, that rays came comparatively near
to the earth as far south as this, and that their direct effect was of the greatest importance, or some-
thing similar. According to what we have said above, however, assumptions such as these are not
necessary, our simple assumptions being apparently sufficient to explain the principal phenomena.

On the last two charts, XI and XII, for the hours 22* //'", and 2jh /"', the strength of the
negative storm has considerably decreased, and we once more find traces of the positive storm, at
22h 15™ in Jan Mayen, and at 23'' 5™ at Fort Rae. The negative storm now appears to be con-
centrated about the region from Ssagastyr to Cape Thordsen, i. e. on the night-side. At the south-
ern stations there are no great changes to be discovered. We found that the vertical arrows at
Gottingen must be due to the positive system; but the deflection in the curve is in striking harmony
with the negative storm in the north, as the deflections begin to increase simultaneously. This may
therefore only be indicative of the connection existing between the positive and the negative precipitation.

4°4

TAI'.LK LVII.
Tin- Perturbations of t h r i 51 h 1 ><•(• cm h <• r, 1882.

1 ,1.

\I. I'.

l-Bloamir Kurt Ra,

I\ i n i.' 1 1

ll

in

,

I 0

20

13 ;' \V 16 ;• o - 10 ;• K 0.5 ;•

t - 1 O J '

- 30 ;•

\Y 4

.""* /

-5

3' „ " 22 ,, -( 10 ;• 4 15 „ \V 6.5 ,.

H HJ .,

-t 8 ,,

K 32

..

3°

- '3 „ 11 -'8 ,, , 10 ., -i- 20 „ .. 9.5 ,,

-4 10 ..

+ 0 „

i- 31

n

35

- 35.. - 33 ,. o | 2!! .. K , ,.5 ..

t 10 ,,

5 "i

1 1

4°

O .. .. 40 .. 0 - 20 .. \V 2 ,,

4- 10 ..

- -'7 ,,

\Y 2

1 1

20

4- 25 „ ., 45 „ - 20.5,, + 22 .. !•: 25..

4 i o ..

- 17 -

]•: 2,

,.

1 2

I 0

-II „ ., 26.5,. - 30,5 .. 4 2 ., \V 4.5..

-t- 20 ..

o

.. 56

,.

'3

C)

— 8.5,, K 1 6 .. 20.5.. 4 18 „ „ o ,,

o

o

,i 3«

11

'-1

20

0 11 4 2 5 11 l o .. 4 1 6 ,, o

0

- 33 „

;\V 23

.,

1.5

20

4- 20 .. ..21 „ -- 20.5 ., 4- I7 .. I''. 25 ..

1 O ..

- 32 ,.

„ "2

••

16

20

o „ '->2 ., ' - ) i ,. -4- o, .. .. T. ^ ..

0

~ 55 .-

1. 05

*.

'7

20

-- --1 M .1 5° - — 3°-5 ,. ' 11 -- 'H ,1

o

- 7& „

„ 148

18

20

~ 61 ,. ., ,;o „ 01.5,, 6 „ „ i ,,

20 ,.

- -io „

„ ' 2 1

..

1 O

20

- 11 » - 66 « — '32 „ 7 « „ 15-5 «

- 35 51

- 52 ,1

11 '57

• •

20

20

109 „ ,, »7 - - ^3 v I" ia n « ->8-5 H

o

o

11 50

5 *i

5°

— 2QO ., ,, -|6 ., •-- l.|5 ,. — IO ., ,. lM

10 „

3.5 :•

11 '20

11

2 1

-

o

3 ^ *i

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15

--257 .. ,, 64 .. -315 „ - 80 ., \\' 2 ,,

- -13 i.

11 4 ^'
n MO

-'5

— i - 1 < » - o - - - r» i -

1 /I «i r? IJ / 11 -/n 51 /u •• >i ' i •"

- 20 ,,

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v "32

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..

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- 16.^ „ „ i '^ ,, -'o^ ., -*- I'M „ .. sf'-S ..

i 30 „

4- -6 .,

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35
-1°

1 1 20

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13 o

I.) 20

1.5 20

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17 20

I {{ 2O

1 Q 20

2O 2O

-I 70 ;•

+ 18 ..

>~> 11

o

2 Q „

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-- 1 I Q ..

'Mi.

4-
4-

+ 4 -

4-
4-

+ 8 ;•

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16 ..

2 I

8

+ 50
+ 57
+ 50

39

PART n. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. crtAP. i.

405

TABLE LVII (continued).

Gr. M. T.

Sodankyla

Cape Thordsen

Ssagaslyr

A

Pd

n

Pk

I'd

P,

Pk

'fit

h m

10 20 — 5 J'

0 , + 84 ;•

+ 65 ;' E 26 y j 9 ;'

+ 59 )' W 18.2;'

25 + 6 „ W 9.5;- + 26 „

+ 4° * !W:8 „

- 40 „

+ 18 „

E 2.9 B

30 + 12 n

B "-SB

+ 24 „

-f 16 „ „ T2 „

- 28 „

+ '3 B

B 7-5 B

35 + '2 B

n 'I n

+ =8 „

+ 4 „

» 5 n

- 34 »

+ 12 „

B 9 B

40 + 12 „ „ 10 „

+ 25 „

-*- 7 n

n 9-5 n

- 9 B

+ 10 „

B I0 B

1 I 20

+ 6 n » 7-5 B

+ 4° „

+ i? B

B 8 „

o

+ " B

W 7-5 B

12 IO

+ 10 „

„ 8 „

+ 25 B

+ 37 n

B I" B

0

+ 26 „

B 7-5 B

13 o + 12 „ „ 7 „

+ 30 „

•+• «5 »

B 7 B

o

- 22 „

B 6'5 B

14 20 + 8 „

» " n

+ 31 B

-f- 10 „

n 10-5 B

0

+ 36 B

o

'5 20 + 7 «

n "-SB

+ 24 „

4- 10 B

B *S •

o

+ 45 . B 2 „

16 20 + 6 „ „ 9 „ 4- 6 „

+ 15 B

n "-SB

o

+ 26 „

0

17 20 + 13 „

n '5-5,

+ 16 „

- 26 „

n a3-5B

o

- 95 B

E 10.5 „

18 20

+ * r

B 8 „

+ '» „

- 5° B

1. 20 „

o

+ 2 „

B 33 B

19 20 + 4 „ „ 4.5 „

+ M B

- 35 n » 30.5 n ' o

- 48 B

B 17 B

20 20

+ 85 B E 36 „

- 19 n

- 5 „

n 49-5 n

+ 43 «

-237 B

B 19 B

t

5° - 35 B ; n 4° „

- 23 „

-249 n

„ Si-Si.

+ 110 „

ca.-370B

B 20.5 „

21 5

- » * » 58 „

- 38 „

-275 »

„ 85 „ -loo „

-339 B

W 10 „

15

- 32 » n 53-5*

- 35 n

-3°8 „

E 4i „

+ I33 B

-3°i B

B 16 B

25

- n „

n 59-5 n

+ 43 B

-208 „

n 69 n

+ 196 B

-236 B

B 3-5 B

22 15 - 4 n n 35 n

+ 38 „

-123 „

n 37 * + 83 „ -102 „

E 84 „

23 5

- 17 n B 29 „

+ 54 n

-153 n

B 18 „

+ 140 B 1 — 44 n

n 26.5 „

TABLE LVII (continued).

Or. M. T.

Christiania

Pawlowsk

Gottingen

Fort

ft

Pd

Pk

Pd

ft

Pd

P,

Pd

h m

10 2O

— 12 J'

E 9-53'

- 7-5 y

E 4-52'

- 8.77

E 12.5;'

- 12.52'

E 16 r

25

+ 8.5.

W 3-5,

+ 12 „

W 6 ,

+ ii-S .

W 3-5,

+ i .

W 33-5 .

3° +12 ,

. 6.5,

+ 14 .

. M ,

+ 18.5 ,

. 13 ,

- 3 .

„ 33 »

35

+ 12.5 „

» 4-5 »

+ 18 ,

„ 8.5 „

+ 17 .

, 7 .

- 7-5 .

. 25 „

40

+ 10.5 ,

M 4 W

+ 17 ,

. 7-5 .

+ 15 .

. 4-5.

- 7-5 .

, M .

1 1 20 + 9.5 ,

0

+ ia ,

, 8 „

+ II , 0

- 5 ,

E 8 .

12 10 + II , | O

+ ii ,

,, 9 .

+ 'a ,

, 5 .

- 7 »

W 6 ,

13 o : + 13-5 , o

+ ii .

„ 5-5 .

+ 13-5 .

o (')

. 8.5,

14 20

+ 12 „

o

+ 8 .

8 „

•+ it ,

o <<)

E 2 „

15 20

+ H.5,1

o

+ 8 „

,i 5 ,

+ ii .

0

(')

W 8 ,

1 6 20

+ 9 i. °

+ 4 .

, 5-5 ii

-"- 9-5,,

o

(h

. 7 ,,

17 20

+ 13 , °

+ 10 „

. 8 „

+ 14-5 i,

o

0)

. 28.5 „

18 20

+ 4 , °

o

n 5 ii

+ 7 .,

0

0

» 26.5 „

19 20 ! + 2.5 „

0

o

o

+ 5-5 ., ' o

0

n 40.5 ,i

2O 2O

- 13 ,,

E 21 „

+ 5 .

E 32 .

- 13 . E 13.5 „

+ 9 .

, 107 .

50

+ ? »

, 63.5 „

+ 7 ,

. 39-5 »

— 1° ,

, 54 ii

+ 16.5 .

. 136 ,

21 5

— i „

n 59 .,

+ 3 .

» 44 »

- 9-5,

, 53 .

+ 16 „

. M8 .

15

- 5 , . 59 ii

+ 3 . 1 , 43.5 „

- s „ ; . 52 ,

+ 18 .

.155 »

25

— 6 ii

, 56.5 »

0

n 45 -

- 8 ,

. 50 .

+ 16.5 .

„ 180 ,

22 15

- 17 ,.

, 30-5 »

— 13 .

. 30.5 .

- 13 .

„ 21.5,

+ 13 .

. 128 „

23 5 - 8 .

, 26 .

- 7 ,

, 20.5 ,

- 4 .

. 18 .

+ 12 ,

.71 ,.

(') Small oscillations; probably negative deflections.
Birkeland. The Norwegian Aurora Polaris Expedition 1902—1903.

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412 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

THE PERTURBATIONS OF THE 15th OCTOBER, 1882.

(PI. XXII).

90. This observation-period differs from those already described, in the occurrence of fairly powerful
perturbations almost throughout the day, only the last part of the period being a little quieter. The posi-
tion of the normal line is therefore to some extent difficult to determine, especially at Christiania and Got-
tingen, where there is less to go by. In the case of the last-named station, therefore, no such line has been
drawn for the vertical intensity. It will nevertheless be possible, from the course of the curve, to deter-
mine the direction of the deflections when these are greatest. We have employed this quieter district
as the starting-point for the placing of the normal line, assuming the conditions there to be more or
less normal.

At the beginning of the period, a well-developed negative polar storm of considerable strength is
found in the district from Jan Mayen to Bossekop. The most powerful forces appear in Jan Mayen. At
the same time, we find at the stations to the south of this district, deflections which evidently appear to
be governed by the same forces that produce the storm in the north. At Christiania and Guttingen we
find serrations similar to those that are especially distinct in Jan Mayen. On the other hand we also
find positive polar precipitation developed in America, especially at Fort Rae.

At Kingua Fjord too, there seems to be the effect of a similar system, but, as we have said, the
conditions there will be better studied by the aid of the charts; for a mere consideration of the curves
may possibly be misleading.

The first part of the observation -period is at a time when it is night in Europe and afternoon in
North America. These storms are thus of exactly the same kind as those which we are accustomed to
find at this time of day.

Chart I represents the perturbation-conditions at the above-mentioned time. The district of pre-
cipitation of the negative storm is distinctly visible in Jan Mayen and Bossekop, and the effects of the
positive system at Fort Rae.

It will further be seen that round the district of negative precipitation, the current-arrows are
grouped in the manner generally, if not always, found in the polar storms. The current-arrows to the
south fit very well into the system of convergence, which corresponds to a negative system of precipitation.
At ih 2om Christiania appears to be in the immediate vicinity of the point of convergence of the system,
which, at the last hour given, 2h 20™, seems to have moved towards Pawlowsk. At the same time the
powerful forces in Jan Mayen are considerably reduced, and thus the storm-centre seems to have moved
a little eastwards.

Another circumstance that may possess some interest is the direction of the current-arrows at
Godthaab, Kingua Fjord and Cape Thordsen, where the forces at certain times are rather small, and
there thus appears to be no particular local precipitation. It would therefore seem probable that we
should here find effects of the powerful negative system acting in the neighbourhood of Jan Mayen. As
effects of this there should be an area of divergence in these regions, and the arrows do indeed admit
of being arranged in such a system; for if we follow a current-line in this district from Bossekop west-
wards across Jan Mayen, to Godthaab and Kingua Fjord, we see that it turns off" here to the right and
runs northwards. Fort Conger, unfortunately, cannot give satisfactory information concerning the further
course of the current-line, the conditions indicating only that the direction is somewhat easterly. This too
is in accordance with what we should expect.

The direction at Cape Thordsen indicates that the current-line turns southwards, back to the
regions about Bossekop. Thus the course of the current-lines seems to be similar to that which we
should expect to find in the system's area of divergence.

PART II. POLAR MAGNETIC PHENOMENA AND tERRELLA EXPERIMENTS. CHAP. I.

It is probable, however, that there will also be other forces in operation, and that the conditions
are not so simple as here described. One circumstance, for instance, that has not been touched upon
is the connection that seems to exist between the deflections at the southern stations and the system
in North America.

At the hours here observed there do not, it is true, appear to be any conditions that point distinctly in
this direction; but at about 3h the deflections, especially in H, at Fort Rae on the one hand and Christiania
and Gottingen on the other, exhibit so great a resemblance to one another that it would seem probable
that a more or less close connection existed. Simultaneously with these deflections at about 3'', we
also find similar changes at several other stations, e. g. at Kingua Fjord, where there is a characteristic
and well-defined deflection in declination towards the east, the forces here having previously had a west-
ward direction. This, as will appear from Chart II, seems to indicate the intrution of a positive storm.
At Fort Rae, on the other hand, it is evidently a negative storm; and at Jan Mayen we find at the
same time a corresponding change in the deflections, perhaps here, too, the effects of a positive storm
asserting itself, as the negative deflections diminish considerably, although none go over to the other side.

In the field of perturbation at 2h 5om, represented on Chart II, the negative system of precipitation
comes out very distinctly in Jan Mayen, Bossekop and Fort Rae, while at Kingua Fjord there are signs
of a positive polar storm.

The current-arrows at the southern stations, on the other hand, exhibit conditions that appear
more peculiar. If they are due entirely to the negative system of precipitation to the north, even
Gottingen must be situated to the north of the point of convergence of this system, or perhaps more
strictly speaking to the north of the neutral area of the system.

There will, however, be some difficulties in the way of an assumption such as this, and moreover
the course of the curves appears to indicate that the cause should be sought in a system that is closely
connected with that which appears most distinctly at Fort Rae and Kingua Fjord, and which in all
probability also causes the great diminution in the negative deflections in the horizontal intensity in Jan
Mayen just at this time. We have frequently observed a similar resemblance between the conditions in
Central Europe and those in North America; and in discussing our experiments in a later chapter, we
shall find conditions that are apparently similar to these.

The next phenomenon that strikes one on looking at the plate is a perturbation that is especially
characteristic and well defined at Cape Thordsen, more particularly in the horizontal intensity, where it
appears as a negative storm. Its effects are also distinctly apparent in Jan Mayen, where the perturbing
forces even exceed those at Cape Thordsen in strength. Of the arctic stations, it is only at these two
that this storm is distinct; even at Bossekop there is no distinct effect of the system.

On looking at Little Karmakul, however, and comparing its horizontal-intensity curve with that of
Cape Thordsen, we find, on closer examination, quite a remarkable resemblance. The deflections in H
at Little Karmakul, from about 3'' until about I5U, are positive nearly all the time. On the other hand
there are no perturbing forces of any magnitude at the same time as the negative storm at Cape Thord-
sen; but the commencement of the decrease in the positive deflections is exactly simultaneous with that
of the increase in the negative deflections at Cape Thordsen, and the maximum of the negative storm
at Cape Thordsen with the lowest position of the horizontal-intensity curve at Little Karmakul, and we
then have distinctly negative perturbing forces there. Lastly, the curves again increase at both stations
simultaneously, while the deflection at Cape Thordsen decreases, and the positive deflections at Little
Karmakul increase. It would thus seem reasonable to suppose that at the latter station we have before
us the effects of two simultaneous storms, the positive storm continuing all the time, and the negative
intruding upon it, and partly compensating the positive deflections, partly effecting their reversal. The
similarity between the curves is in fact so striking that this assumption seems very probable.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903. 53

414 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

At the southern stations the conditions are evidently regulated by the negative polar storm. This
storm appears particularly clear, if we compare the horizontal-intensity curves.

Except at Little Karmakul, no very distinct traces of positive polar storms are to be found during
this period, Uglaamie being the only station at which there appear to be any more or less evident
effects of such a storm. It will be seen that this station, at the time, is on the afternoon side of the globe.

The fields of perturbation at 3'' aom and at 4'' 2om are represented on Chart II.

At 3h 20ra we find the negative storm in the polar regions developed, to any extent, only in Jan
Mayen. The three southern stations indicate simultaneously by their current-arrows that they are in the
eastern part of the area of convergence.

At 4U aom, however, the storm-centre has move<l or perhaps rather expanded eastwards, thus
bringing Cape Thordsen into the district of negative precipitation. At the same time the current-arrows
for the three southern stations turn clockwise through a considerable angle, just as our previous assump-
tions would lead us to expect.

At Pawlowsk, at this time, we find negative values of Pt, indicating the existence there of an area
of convergence. At Gottingen too, the direction of the perturbing force in the vertical intensity seems
to be the same; there is a distinct wave in the curve just at the time of the negative deflections at the
two arctic stations.

At 5h the positive storms in America are over, and negative storms begin everywhere, developing
subsequently to a considerable strength.

At Godthaab the negative storm began to develope earlier. The negative perturbing forces here
must be regarded as continuations of the powerful eastern system.

At Fort Rae too, the negative deflections become stronger, and at 6'1 a fairly powerful negative
storm begins to develope, and continues until about 17''. There are two maxima here, separated by a
period during which the negative forces are considerably weaker, although the direction of the deflections
remains unchanged.

At Uglaamie the stronger negative forces appear somewhat later than at Fort Rae; but a little before
8h they begin to increase rapidly until they attain considerable strength. The negative deflections then
continue more or less constant in strength until about I7h, after which they are small.

At Kingua Fjord too, negative storms appear to be at work ; but we will reserve our description
of the conditions there until we come to the charts.

We note that this transition from positive to negative storms in America takes place at the time
when these districts enter the night-side of the earth. At the same time the districts in Asia and Europe
move on to the day-side of the globe, and at the polar stations here, Cape Thordsen excepted, we also
find a transition, but from negative to positive systems, and thus the reverse of that in America.

The change takes place earliest in the most easterly districts. At Little Karmakul, for instance,
there seem to be positive storms as early as 3h. At a little before 6h, however, they begin to be more
distinct, the positive deflections becoming larger and larger, until about I4h there is a maximum for the
positive deflections.

At Bossekop and Sodankyla the positive storm developes very characteristically; but the positive
deflections begin a little later. At about 5h 2om the negative storm at Bossekop is over, and from that
time until about iol1, there are small deflections now to one side and now to the other. At ioh the
positive deflections begin to increase with comparative rapidity, and reach their maximum at about 15'' 20m,
when they decrease rapidly. The development of the storm at Sodankyla is very similar.

If we go on to Jan Mayen, we still find, at the beginning of the period, effects of negative deflec-
tions. After ioh, the positive storm there developes powerfully. Thus while the effects of the positive
storm appear more or less simultaneously at Bossekop and in Jan Mayen, the previous negative storm

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 415

lasts considerably longer at the Jan Mayen station than at Bossekop. It seems evident from this that
the district of positive precipitation is moving westwards.

This movement, which has so often been mentioned, and which has undoubtedly some connection
with the earth's rotation, is here very distinct, as the perturbations concerned are of longer duration
than usual, and perhaps also because they are at a time not very distant from the equinox.

In Jan Mayen, however, forces soon appear which seem to counteract the effects of the positive
storm ; a negative system seems to encroach upon the positive for a short time, and once or twice cause
a reversal of the values of P/,.

This negative storm is evidently the same that appears at Cape Thordsen, but here it is far more
powerful. The effects of the positive storm are slight. Before nh 20™ the horizontal-intensity curve
at the latter station oscillates about the normal line, perhaps the result of the action of alternate slight
positive and negative precipitation. After n'1 2om, however, a very well defined negative polar storm
appears, which developes and reaches its maximum simultaneously with the positive storm in the south.
Simultaneous serrations are also frequently to be found, a circumstance which indicates the connection
which evidently exists between these cases of precipitation.

A comparison of the horizontal-intensity curves for Cape Thordsen and Jan Mayen will give a
distinct impression that it is the negative storm that breaks in upon the positive, and produces the
peculiar phenomena found in Jan Mayen. That the positive storm is going on all the time seems to be
clearly evident, however, from the fact that simultaneously with the disappearance of the negative storm
at Cape Thordsen, the positive forces once more assert themselves, and the positive deflections then
diminish just as at Bossekop. It is also characteristic that at Bossekop too, the negative storm intrudes
and produces the peculiar curve that we find at about i6u.

The horizontal-intensity curve at Little Karmakul also shows clearly a condition exactly similar to
that in Jan Mayen, namely a long positive storm, upon which the somewhat shorter negative storm
intrudes. For a time too, the latter is the stronger, just before it reaches its greatest height. At i6h,
however, positive forces once more appear, evidently the same strengthening of the positive system as
at Sodankyla. After that hour the curve oscillates about the normal line, thus indicating the supremacy
of the positive and negative forces alternately. In declination, however, the direction of the deflections
is nearly always the same, namely westward; but here too, the curve is exceedingly jagged and dis-
turbed in character.

At Fort Conger, the last of the polar stations, it will be seen that the declination-curve very much
resembles that at Cape Thordsen, and we may therefore assume that the system continues westwards
through that station.

At the southern stations, the deflections are evidently governed by the precipitation in the arctic
regions; and we sometimes find a very distinct resemblance between the various serrations. The deflec-
tions in the horizontal-intensity curves for Christiania and Pawlowsk are not constant in any part of the
period, but are sometimes in one direction and sometimes in another, although the negative deflections
predominate. Farther south, on the other hand, e. g. at Gottingen, we find negative deflections all the time.

In declination we find the deflections for the most part directed westwards at Christiania and
Gottingen, whereas at Pawlowsk there are no very considerable forces in that component. In the vertical-
intensity curve at Pawlowsk a very distinct positive deflection appears.

The conditions at Gottingen are exactly similar. The rise in the vertical-intensity curve at about
7h, and the fall at about nh, are undoubtedly connected with the diurnal variation, while the last rise
with a maximum at about i6h seems to be connected with the perturbations.

These conditions, the distribution of the districts of positive and negative precipitation over the
various regions of the earth, and their intermingling, are thus in perfect accordance with our previous

41 6 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

experience. The polar areas of perturbation are always manifested in the main in the same manner, and
every part of the day has, so to speak, its characteristic area of perturbation, which will always approxi-
mately form when there are any perturbations.

At the close of the period, the conditions are, as we have said, almost normal everywhere, with
the exception of Kingua Fjord, where there are still some powerful forces.

We will now look at the charts for this last section of the perturbation.

Chart III represents the conditions from 5h 2om to 7'' 2om. The storms are chiefly negative.
There is the powerful system in America, especially noticeable at Fort Rae, and one less powerful in
Jan Mayen, a westward continuation of which is indicated by the conditions at Godthaab and Kingua Fjord.

Of the positive storms there is little observable here. At 6'1 2om there is an indication of one at
Little Karmakul, but the force is not great.

The current-arrows at the southern stations at 7'' 20™ are rather more difficult to include in a polar
field of perturbation answering to the systems of precipitation appearing here. The observations we
have are too few for us to determine the nature of the perturbing forces at work; we will only draw
attention to the simultaneous deflections appearing in the horizontal-intensity curves for Fort Rae and
Kingua Fjord on the one hand, and Christiania and Gottingen on the other: The maxima occur simul-
taneously, and there are also several coherent serrations. This is apparent chiefly until nh, after whii-h
hour the polar systems in the north of Europe also appear much more powerful, so that the phenomena
in Central Europe are mainly governed by this precipitation.

This is certainly to some extent a phenomenon similar to that with which we meet at about 3h on
this day.

On Chart IV the positive storm appears more distinct, but has not yet extended farther than to
Little Karmakul. At Godthaab and Kingua Fjord, the same negative system is at work as in Chart III;
but it has now moved westwards, so that Jan Mayen is no longer in the district of precipitation.

1 he current arrows in Central Europe may either belong to the area of divergence of the eastern
positive system, or to the area of convergence of the western negative system. It is rather doubtful
whether the system at Godthaab, and still more that at Kingua Fjord, can be regarded as a negative system
of precipitation. Pln it is true, is negative everywhere, so it therefore might be called so; but the direction
of the principal axis is more north and south than usual, a circumstance that is more conspicuous later on.

On Chart IV, the arrows seem to be principally connected with the American system, while on
Chart V they form a transition between the negative system on the west and the positive system on
the east, or, as we might say, between the system at Cape Thordsen and the more southern system at
Jan Mayen and Bossekop.

It is an unfortunate circumstance that on Chart IV there are no observations of horizontal intensity
for Fort Conger. If there had been a strong current-arrow there, directed southwards, it would seem
likely that a current-circuit had been formed from Fort Rae, through Uglaamie, Fort Conger, and Godt-
haab, and probably back to Fort Rae. When the system has moved a little, we find a circuit similar to
this, as there is negative precipitation at Cape Thordsen ; but this circuit does not appear at all distinctly
until Chart VI. If this could have been demonstrated as early as Chart IV, a very much better survey
of the perturbation-conditions would have been obtained, and a fact to hold to when seeking, by experi-
ments, for points of similarity. A fact such as this would have brought about some modifications in our
reasoning, but no essential simplification.

As the observations, that we have at our disposal, seem to show, the negative system of pre-
cipitation developes by a more or less continual extension of its area westwards.

In the second case we should have to imagine that a more or less momentary current-circuit was
formed, which increased somewhat during the course of the perturbation, while at the same time, owing
to the rotation of the earth, its position was changed.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I.

Both these assumptions are possible, but it is not easy to say which is the more correct one.
It will thus be a matter for future research to procure a clear understanding of this point; the present
observations are too few.

The positive system, with its area of divergence, comes out very distinctly on Chart V, with all
the characteristics of such a storm. The point of divergence of the system is evidently in the vicinity
of Pavvlowsk. P, is here positive in direction, and the horizontal forces are sometimes very small.

In addition to this, the field is characterised by the negative storm, which now, as already men-
tioned, seems to have moved towards the west, while at Cape Thordsen we also now find negative
perturbing forces.

There is nothing very new to be seen on Chart VI. Judging from the current-arrows in Central
Europe, we should be inclined to suppose that the positive system of precipitation has extended farther
westwards; but at the same time the more northerly negative storm has also increased in strength, so
that the two counteract each other's effect in a horizontal direction in Jan Mayen. In vertical intensity,
however, both systems at that station act in the same direction, and we therefore find powerful negative
perturbing forces there.

As we have said, the negative circuit is now more distinct.

At Little Karmakul, sometimes the positive, sometimes the negative system is the more powerful.

On the last chart, Chart VII, the powerful systems have disappeared, and we find only faint
indications of the former powerful storms.

At the first, and to some extent the second hour, there are still forces of some considerable
magnitude; but at the last hour it is for' the most part only at Kingua Fjord that storms are still going on.

TABLE LVI1I.
The Perturbations of the i5th October, 1882.

Gr. M. T.

Uglaamie

Fort Rae

Kingua Fjord

Pi,

Pa

"•

/'/,

Pd

ft

Pk

Pd

li in

o 20

+ 3 /,W 2.5}' + 43.5;' -1- 83 ;'

W 185;' o

+ 59 y

W 56 }'

I 20 | + 30 „ 1 0

+ 44-5 »

+ 7° *

n J3-5 n - 4° /

+ 51 n

„ 28.5 „

2 20 + 34 „ „ 12 „

+ 25-5 n

+ 26 „

E 4-5 „

- 80 „

+ 30 „

n '3-5 n

5°

+ 45 „ n 26.5 „

+ 17 „

- 90 ,,

n 135 n

- 90 „

+ 20 „

E 60.5 „

3 20 +35 n I n 26-5 n

o

- 24 „ „ 19 „

-no „

+ 46 „

n '7 11

4 20

+ 35 „

E 5-5 *

4 n

- 3 it

n 3 n

- 80 „

+ 35 ,,

W 0.5 „

5 20

0-5 n

n 46 „

0

— '9 n

n 33 *

- 90 n

- 25 „

E 19-5 n

6 20 ; - 22.5 „

w 38.5 „

- 19 n

-146 „

W 2 „

+ 90 n

— i-Sn

It 21 „

7 20

+ 87.5 „

Ei88 „

- 66 „

-3°0 n

E 109.5 „

-100 „

- 66.5 „

n 24 „

8 20

-104 „

,, 56 „

— 32-5 n

-400 „

nll6-5n

+ 170 „

- 50 „

n 59 n

9 20

— 132 „ Wio6 „

- 40-5 n

- 93 n

» *• «

+ 17° n

- 59 n

n 54-5 ti

10 20

- 96.5 „ „ 26 „

+ 47 n

-182 „

n 62.5 „

+ 10 „

- 67 „ „ 44.5 „

1 1 20

-M3-S it

E 19-5 „

+ 47 „

-260 „

it 55 n

+ 180 „

- 56 „

n 31-5 n

12 20

— IS' n

„ i°3-5 *

+ 4-5 „

-823 „

» '20.5,,

+ 280 „

-120 „

n 55 n

13 20

-85 „ ! „ 49.5 „

+ 94 it

-258.5 „

« 5 n

+ 39° n

-125 n

it 27.5 „

M 20 - 57 „

n 222.5 „

+ 98.5 „

-S3' it

n 343-5 n

+ 230 „

-'3° n

W 2,.5n

15 20 ; - 81 „

n 35 n

+ 118 „

375 n

» J59 »

+ 20 „

-"3-5 »

E 5-5 n

16 20 -148 „ „ 62 „ + 98.5 „

—237-5 n

„ 121.5 „ 60 „

-100 „

W 77 n

5° : - 51-5 „ n '6 it + 75 n

- 89 „ „ 40 „ - 20 „

- M n

n I0 -i

17 20 - 45 „ W 26 „ 4- 56.5 „

- 3° n n '4 »

+ 10 „

- 24 „

n 7° n

18 20 - 20 „ : E 31.5 „ ' + 0.5 „

o „ 12.5 n | - 20 „

- 25 „ i n 78.5 n

418

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

TABLE LVIII (continued).

Gr. M. T.

Godthaab

Jan Mayen

Bossckop

Ph

PA

Ph

Pd

A

flk

Pd

A

1; m

o 20

+ 32 ;'

W 53.5 y

-395 r

E 37-57

+ i55 Y

-165 y

£39 r

-225 ;•

I 20

8 „

„ 36 „

-357-5 n

« 4° „

+ 227.5 »

-'77-5,,

» 54 »

-3°2 5 „

2 2O

+ 12 „

W 7 M

-Ia7-5n

w 53-5 n

+ i7i-5»

- 72-5 n

n 53 »

- 163.5 „

5°

- 75 „

E S°-5 n

-1 12-5 n

* 62 „

+ >44 „

— 121 „

n 63 „

--180 „

3 20

- 20 „

W 8.5,

- I96-5 n

n 87. 5 „

+ 128 „

- 45 •

o

- 36 „

4 20

- 60 „

>, 13 n

-290 „

» 65 „

+ 60 „

35 »

Wi7.5»

— 60 „

5 20

- 37 n

E 14 „

- 42-5 n

M 4-5 »

— 4 •

0

E 11.5.

0

6 20

- 50 „

n *3 n

- 77 n

n J7 „

— 8 „

4-5 n

W.5 „

0

7 20

- 73 n

» 43-5 n

-JIS n

„ 28 „

— 9

- 23.5 „

n 3 „

4- n „

8 20 • -235 „

W II „

- 35 n

o

- 55 „

+ 6 „

n 20 „

4 83.5,

9 20

-197 n

n 4° n

- 10 „

0

- '6 „

+ n-5»

» '7-5,

+ 50 ..

10 2O

-"5 n

E 0.5 „

+ 49 n

W 9 „

+ 5-5 »

+ 21.5 „

» M »

+ 57-5 »

II 20

- 68 „

n 33-5 »

4- 78.5 „

E 3 „

+ i-5 „

4- 61 „

n al o

4- 90 „

12 2O

- 34 n

n 79-5,1

+ '44 n

» 26.5 „

— 4 »

-f IOI „

» 37 »

4 147-5 „

13 ao

- 86 „

n 45-5 n

+ i°5 n

n 23 „

-107-5 »

+ 14° „

» 38.5 r

4-180 „

14 20

-106 „

W 18 „

4- 10 „

W 17 „

-'9° »

+ 130 „

n 3 »

4 161 „

15 20

- 33 *

E 55 n

4-5 *

n 58.5,

-100 „

+ 185 „

n 30-5 n

+ 155 »

16 20

- 85 „

W 32 „

- 21 „

„ 3° „

-"5 „

+ 160 „

„ 28 „

+ "5 »

5°

- 22 „

E 22.5 „

+ 84 „

.. "3 n

-no •„

+ 61.5 „

n 48.5 n

+ 7i-5 „

17 20

„ 6 „

+ 67.5 „

» 34-5,,

— • 1» •

+ 44 „

„ IO „

+ 75 n

18 20 - 18 „ „ 14.5 „

- I3-5 »

o

- 42-5 ,,

+ I „

n 5-5 n

4- 26 „

TABLE LVIII (continued).

Gr. M. T.

Sodankyla

Cape Thordsen

Little Karmakul

Ph

Pd

Pf

Ph

Pd

P.

Ph

Pd

P,

h m

o 20

- 22 ;< E 9 y

4- 72 ;'

- 13 Y

E 18 /

+ 170 ;'

- 42 ;'

£26 /

- 85 ;'

i ao

- 55 » „ 4 .,

+ 9° ,

— 5 n » 26.5 „

+ 130 »

- 46 „

. a-5«

- 95 „

2 2O

- 25 „ : „ 11.5,

+ 69 „

+ 1° , : » 60.5 „

4-176 „

+ 70 „

W 20 „

- 7° »

50

- 4° „ „ 23 „

+ 4° »

+ 10 „ „ 61.5 „

4-i6o „

0

E 7 „

- 45 •

3 20

- 25 „

W 8 „

+ 48.5»

— 6-5 „

» 75-5,

4- 120 „

+ 138 „

W44 „

+ 25 „

4 20

4 „

» 12.5 „

+ 2.5,

— '55 n

„ 85.5 „

4 ioo „

- 32 »

» M f,

- 42 „

5 20

4- 10 „

E 15-5 „

+ 19-5 .

- 8 „

» 4-5 ,

- 27 „

+ 38 „

E 9-5,

- 42 „

6 20

+ 4-5-

W 7-5 „

+ 16 ,

- 6-5 „

» 33 »

- 18 „

+ 55 .

Wai.5,

4- 16 „

7 20

9 »

0

+ ir-5.

+ 27 „

» 43-5 -

9 *

+ 23 „

E i „

4- .8 .,

8 20

- 6 „ „ 10 „

o

+ 5 J . *8 „ - 98 „

+ 88 „ W 37 „

+ 56 *

9 20

o „ 7-5 ,

+ 21-5 „

- '5 i,

» 22 „

-IOO „

+ "0 „

, 21-5,

+ 38 „

10 20

f '7-S»

» 1 1-5 »

9 M

+ 21 „

W 5 »

-tio „

4-102 „

., 38.5 „

+ 43 r

II 20

+ 46 „ „ 13-5 „

- 10 »

- 24.5 „ E 7.5 „

-'35 »

+ 154 „

» 59 »

+ 59 „

12 2O

+ 46 „ „ 23.5 „

- 3° »

- 67 „

W 47 „

-170 „

+ 46 „

» 54 -,

+ 55 „

13 20

+ 68.5 „

i. 23-5 „

- 92 „

- 51-5 n

» 20.5 „

-'SO „

+323 *

» 58 „

+ 79 -

14 20

4- 62.5 „ ' E 2 n

- 90 „

- 40 „

» i'-5»

-294 »

+360 „

„ 81.5 „

- 63 „

15 20

4- 132.5 „ W23.5n

-125 „

- 77 »

» 49-5 ,

— 148 „

-106 „

- 47 n

-273 „

1 6 20

+ 6l » n '5-5 n

55 »

""5 n

, 6. „

?

o

n 78.5 n

-135 »

5°

+ 26 , „ 14.5 „

- 27 „

— 70 „

» 60 „

- 62 „

- 72 „

n 38 „

4- 41 .,

17 20

+ 3 * o

- 24.5 „

- 33 n

» 27 »

- 60 „

- 81 „

E 3 „

+ 9 »

18 20

6 „ : o

+ 5 .

- 18 „

» J3 n

- 25 „

+ 8 „

W 8 „

+ 8 „

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I.

419

TABLE LVIII (continued).

Gr. M. T.

Pawlowsk

Christiania

Gottingen

Fort
Finger

A

Pd

P,

n

Pd

Pk

/',/

,

h m

O 20

+ 14 ;'

w 5.5;-

-10 ;•

+ 12 ;-

E 12 ;•

+ 21 y

F- 23.5;'

E 9 r

I 20

o

„ 14-5,

— io n

+ i „

W 4 „

•1-16-5.

„ 5-5,

» 13.5,1

2 2O

+ i *

0

— 13 »

- 8.5.

E 7 „

+ 4 »

» I0-5n

n 9.5 „

5°

-"on

n 5 M

-15 »

-25 »

W 3-5 „

— 8 „

W 6 „

r 49 „

3 2°

- 4 „

» 19 „

- ° n

— 9 w

n '7-5,,

+ 5 „

« " " i n 43 n

4 20

+ 9 „

„ 18 „

— I0 11

+ '5 .

„ 8.5,,

+ 14 »

E 4 ,,

n 3° n

5 20

o

E 2 „

- 8.5l,

- 5-5,

0

- 9 »

n 5-5 n

Wll.Sn

6 20

- 1-5,,

W 9-5 „

0

+ 5 »

,, 4-5 „

- i ,,

„ 3-5 »

E 3i »

7 20

-16 „

„ 9-5 „

o

-18 „

„ 5-5 n

-19 »

» 4-5 n

n 3°-5 „

8 20

-I0 *

« 19 „

+ 2.5 „

-23 ,

„ '9 „ - 20 „

W 9 „

33 M

9 20

"*• 4 n

„ 10-5 ,

+ 2-5 „

-15 ,

„ M ,,

-"•5,,

n "-5 ,,

» 9-5 n

10 20

+ I2.5 „

« 5 w

"*" 5 i>

— ii „

n '9 „

— Q w

n 20 «

W2,.5n

I I 2O

+ 10 „

E 3 .

+ 7-5.

o

» 14 rt

- 10-5 »

n 23.5 „

n 41-5 »

12 20

- 2.5 r

O

+ 15 „

+ 3 „

n 21 „

; 12 „

» 18 „

» 44-5 n

13 20

- 8.5 „

O

+ 21 „

+ 0.5,

n 23-5 „

— " »

n '5 n

„ 38 „

14 2O

-"•5n

O

+ 22.5 „

- 8 „

. 95,,

-W.S.

. 8 „

•• 56.5 „

15 20

-ii. 5*

W 5 „

+ 25 „

o

,, 4-5 51

-26 „

n 6 »

n 66-5 n

1 6 2O

-15 „

» 3-5 »

?

- 8.5.

n 4 »

— 19-5 «

„ 6.5 „

» 57 n

5°

- 6 ,,

w 5 n

?

— 6 „

0

—13 ,

n 4 n

n 27.5 „

17 2O

- 2 „

E 3 -

+ 10 „

— 5 »

o

i — 8 „

, 22.5 „

18 20

0

O

+ 7 .

- I „

o

- 2 „

" I>5" 1 °

Current-Arrows for the 15th October, 1882.
Chart I at Oh 20m, lh 20m, and 2h 20m.

420

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

o

N

a

N

"»

I

m

+^
a

n
j=

CO

v

2

o
O

in

v

a>

I

-

a

s

o

M

•a
c

o

a

-c

PART II. POLAR MAGNETIC PHKNOMENA AND TERRELLA EXPERIMENTS. CHAP. I.

42I

6
O

a
O

ft
"N

o

CM

£

,0
O
*->
U

O

.n
+4

l£

V

J=

IT

O

C

s

g

s

o

M

00

4-t

ra

422

UIRKKLAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1 QO2 — -1903.

O

B

a

a"
o

b

vi

SB

_
v

u

o

u

o

<n

O

£

a g'

U o

•a
a

a'

o

N

a

IBM

bo

£

CHAPTER II. .
MATHEMATICAL INVESTIGATIONS. PRELIMINARY RESUME.

91. The calculation of the Field of Force for the assumed polar current-system. While
studying polar perturbations of the most varied character, we have constantly met with what we called
the typical field for an elementary polar storm. We have also indicated the kinds of current-systems
that might be naturally supposed to give rise to such fields. In Art. 36 we moreover worked out
a little calculation in order to obtain some idea of the distribution of intensity in this field of force.
We there selected the simplest possible form of current-system, namely a linear current consisting of
two vertical portions, which were connected with a third portion that was parallel with the tangent to
the principal axis in the storm-centre of the current-system.

Our only aim in the earlier calculation was to prove the reversal in the direction of the force
which took place in the point of convergence, or that of divergence, when one moved from the storm-
centre out along the transverse axis of the system, and to obtain some idea of the proportion between
the magnitudes of the forces in the storm-centre and at great distances.

A more complete calculation of the field of force for such a system might, however, be of some
importance, and we will therefore make one here.

During great perturbations, the area of precipitation, as we have frequently pointed out, will extend
over large parts of the auroral zone, thus causing the principal axis, or those districts in which the most
powerful forces occur, to assume approximately the form of parts of a small circle. Very often, indeed, we
find conditions which indicate the existence of an entire current-circle. Instead, therefore, of the current-
system previously employed, it would be better to use one in which the rectilinear horizontal portion of the
current is replaced by a curved portion. The actual calculation will thereby be made a little more
complicated; but, as we shall see, a considerable advantage will be gained in another way.

We will consider, then, the effect upon the earth of a current-system consisting of two vertical
rectilinear pieces of current, in one of which the current, from infinity, will approach the earth as far
as a height //, and in the other continue, from the height //, out into infinity, the two pieces being
connected by a curved piece of current lying at a constant height /; above one particular small circle,
whose spherical radius is C.

We do not, of course, mean that the separate active corpuscular rays, which we assume to be the
cause of the storms, move in accordance with a diagrammatic arrangement such as this; the whole thing
is only an endeavour to find out how near we can get to the true perturbation-conditions, if we assume
that the integral effect of all the rays in a system of precipitation is replaced by a linear current-
system of this form.

We will first look at the effects of the vertical currents.

As our system of coordinates, we will employ a rectangular Cartesian system, with its origo in the
centre of the earth. We will further take the axis Z perpendicular to the plane of the current-arc.

As polar coordinates we will employ the signs Q, 6 and w, 0 being the distance from the origo,
6 the angle formed by the radius vector and the positive axis Z, and w the angle between the plane
A'Z and the plane through the axis Z and the radius vector.

424

HIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

We will further, in the case of the positive directions, employ the system of coordinates used by
HERTZ in his Inaugural Dissertation, "Ueber die Induktion in rotierenden Kugeln'^1), as in a subsequent

chapter we shall go into the subject of induction currents, and shall then
have occasion to use the developments we here work out, and it is therefore
best to introduce these signs at once. The positive directions of ^Y, Y, Z, 0,
and 10, are shown by arrows in the figure.

^ x We will, then, determine the force-components along the radius vector,

the meridian and the parallel circle in a fixed point upon a sphere with an
arbitrary radius Q, (Q supposed < /.). One of the vertical pieces of current
produced will intersect the surface of this sphere in a point p, 1", 11.

The total effect due to a piece of current such as this (see p. roi,
Part 1) is

Fig. 177.

sn

I

sin2 /J

sin [i

L — Q cos j

— 2 L cos

Lz

(i)

Fig. 178.

/- — c cos ft

where we have put R -\- h = L, and /i? is the arc of the great
circle between the place under consideration and the point of
intersection of the produced path of the current with the surface
of the sphere. We shall, moreover, when not otherwise stated,
always make use of the C. G. S. system, and the electro-magnetic
system of measurement.

The three components are thus

P? =O, P9 = Psm v, P,,, = — .Pcos v, (2)

where v is the angle between the direction of the magnetic force
and the parallel circle, reckoned positive, as shown in the figure.
In the case in which the positive current is flowing away from the
sphere, i. e. in the direction of increasing g, we will call the direc-
tion of the current positive.

What we have to do is to find an expression for fi and <r.

This is given directly by the spheric triangle drawn in the figure-
cos /? = cos (o» — |«) sin £ sin 0 -\- cos C cos 6,

sin £ sin (w — /u)
"sin/? '

cos £ — cos 9 cos (i

sin v = —

(3)
(4)

and

cos v = - -

sin |? sin 6
By simple combination, the effect of the vertical portions of the current may be found by these formulae.

We shall then consider the magnetic effect of the curved portion of the current.

We will call the direction of the current positive when it coincides with the direction of in-
creasing io.

The coordinates of the current-elements we will call L, t and ft, ft thus answering to w. What
we have to do, then, is to determine the effect of this element in a point g, 6, «>, on the sphere.

According to Biot & Savart's law, we then have

,0 . Lsin'Cdfi .
aP = / ,.," — sin a, b)

(') H. HERTZ, "Gesammelte Werke", Hand I.

PART II. POLAR MAGNETIC PHENOMENA AND TERKELLA EXPERIMENTS. CHAP. II. 435

when: ill' is the magnetic force produced by the current-element at the place, d the distance from the
place to the element, and a the angle between this distance and the direction of the current-element.

We now have to determine the force-components. The decomposition will be effected along the
radius vector, the meridian, and the parallel circle.
On looking at the figure we obtain

x = Q sin 8 cos w

v = Q sin 6 sin to (6)

Z = Q COS 6

Thus the direction-cosines for the radius vector are

sin 6 cos ID, sin 6 sin 01, and cos 9.

The direction-cosines of the tangent to the parallel circle are

— sin M, cos (a, and 0,
whence again we obtain the direction-cosines of the meridian,

cos 0 cos 10, cos 6 sin w, and — sin 0,
which is immediately apparent on looking at the figure.
For the distance if, we find

if- = L- -f- p2 — 2Z.p [cos L cos 9 -|~ sin £ sin 6 cos (w — <<)].
The direction-cosines for this distance d are

L sin £ cos fi — Q sin 6 cos 10 L sin f sin « — p sin 0 sin w , /. cos £ — q cos 6

— j — ~" ' j ~" ' <uid "" j

it d d

The direction of the force is now perpendicular to the current-element, of which the direction-

cosines are

— sin /i, cos fi, 0,

and to the direction towards the current-element. From this we find the cosines for the direction of
the magnetic force,

L cos £ — o cos 6 L cos 'C — o cos 9 L sin £ — a sin 9 cos («j — /<)

*-£* - cos//, 2_lf Sln/,, and- —g-

where

A = V(Z. cos C^p cos 0)2 + [Z. sin C — 0 sin 0 cos^w — //)]-

For a we find the following expression:

, _ _^^_ A

sin a = -^ V(£ cos £ — 0 cos 0)2 + [£ sin £ — p sin 0 cos (w — p)J» ^
Hence we find

and for the components

= ,'£ sin ? sin 0 cos £ -C°S ~ L sin ^ cos fl

,/P9 = iL sin 'C. (L cos L" cos 0 — 0) "'fl + L sin - sin # 'Js* ' and

dP,, = - iL sin ;- (Z cos £ e cos 0) -^i" ~ ^ ^ .

If we put

f"

cos («j — ft) an T "f

M = ^s ' - ~ J* '

J/'O

in which the lower limit may be chosen at pleasure, we obtain

426 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

Po = iL sin £ \L sin 0 cos £ . Ii — Z. sin £ cos 6 . L (g)

L J /' = ,"i

P0 = /Z. sin £ (Z, cos £ cos 0 — (>) . It + Z, sin £ sin 9 . L (10)

L J /' = ,"i

. .. L cos £ — o cos 9
Pw = — iL sin C . - — -5-—

o cos 9 I"

5-.—

sin 0 [

— s--.— , i i

eZ. sin £ sin 0 [ y/,2 _|_ pa __ 2? Z, (cos £ cos 0 + sin £ sin 0 cos (w — /«) J ,, = ,,,

where <<i and ^ represent the values of ft at the ends of the arc.

We may, then, say

Po = Po * (to — //.) — ZJP ° (w — //j) j

da)

If, therefore, we calculate the quantities /-"' (w — ,11) [i. e. P(,n (to — ft), Pg° (to — /(), and P,,,n (w — u)\
for all values of 6 and ft, we can afterwards determine the length of the piece of current.

These formulae cannot, however, be employed for 6=0 and 6 = 180, as in these cases Pu be-
comes, as will easily be seen, infinitely great. Here, therefore, special formulas must be developed for
the forces. The following formulae are found for these special cases.

- • i • T Z. sin £ A

Po = + iL sin C - • — si— A,«

• (L- + p2 + iLq cos ;f/* '

-T • r 2(±i,cos£ — $) . A/'

o = iL sin L - — 5^— sin =5

' (Z.2 + ea + 2Z,? cos £)3/a

— cos to

/'a + /'A
-

2 /

• , • Y 2 (Z. COS £ '+ P) . A/' • / /'2 + j" A

,,, = — //, sin L - — 57— sin - sin w — -

' Z.8 >"- 2L cos 3/2 2 /

• + Q"' + 2LQ cos £) /a

where A," = ,"2 — /'i> ar>d where the upper signs will be employed for 0 = 0, and the lower for 0 = 180°.

While P,,i is expressed in algebraic form, the other two components, as we may easily convince
ourselves, are expressed as elliptic integrals.

We have, then, to get these put into a practical form for the numerical calculation. This may be
accomplished by using Legendre's normal forms, by means of which we can make a direct use of his
tables of elliptic integrals.

We put

10 — ft = ic — 2r, i. e., cos (w — ft) = — cos 2r = — I -(- 2 sin-r (13)

7,2 _|_ g-2 _ 27,? (cos £ cos 0 — sin £ sin 0) = L- + Q- — 2Z.0 cos (£ -)- 0) = £; (14!

4Z.p sin £ sin 0

~^T" ~= ' l'5

Hence the expression for d becomes

d — k-> y 1 — AJ sin2r (16)

If we introduce this, we have

_ a [" l-2sin% , 4 | 1 -*» sin'r - 1 + -^L.

or, if we assume //0 so that T<> = 0,

rr

ch

1'AKT II. POLAR MAGNETIC PHKNOMKNA AND TEKKELLA EXI'ERIMENTS. CHAP. II. 427

If we employ Legendre's signs,

lt T) = I y lT^£f"sJn%
Jo

E (klt T) = I y lT^£f"sJn% di (17)

0

for instance we have, as can easily be proved (see Legendre's 'Fonctions Elliptiques', Vol. I, p. 70),

sin 2r

— ** sin2*

1 k'\ sin 2r 1 sin 2f

- ,--,- E(ffi,r) - -4— - = - 5- E (*1( r) — tan-V — j= - (19)

< 1 - *i 2i — ** sin2* cos^v 2i — * sin^r

as we can at once put

sinj/ = ^1. (20)

An angle such as this must in any case be determined, if Legendre's tables are to be used.
We have, then

' 8(2 — £*) (2 — k\) sin2r

., . ' • E (kit T) — VTI T- -7= 2I

KI R\ k\ sin2 2v *J cos2? y] _ £* sjn%

and further,

--n~Tf~ " z l*tf*J "1 Ta — • .. r. — • ^ l«

ki k\ k\ sin2 2y

k\ cos2j» yi — ^* sin'2r

ft

2 rfr 2 f

tan'2v sin 2r

• t*l»TJ ^ VI- >&2 sin2r

J 0

ft />" >E»2

T.i = : • E \k\ . T] ^^ ^ —

sin 2r

or, if preferred,

0 t2 A2 „;„ o».

(22)

whereby the coefficients of corresponding terms in Ii and L have a common denominator.

In this way we have determined all the quantities that we shall require to use.

In the tables below we have given the force-components of the rectilinear portion of the current, and
the values of the quantities P° , calculated for various values of 0 and o — ft. The special calculation
is only required for values of itt — /« between 0° and 180°, answering to values of-r between 0° and 90°.

For

T = m;c + t\j

7f

where ;;/ is a whole number, and t\ an arc <^ - , we have, for E and F,

(see Legendre, 1. c., Vol. I, p. 14). For the third term we also have exactly the same relation,

sin 2r _ sin

yi — k\ sin% yl — ^?sir

the only difference being that the value of the expression, for r = -^- is equal to zero. We therefore
have the relation,

Finally we will also give the formula for the magnetic potential of the current. This can very simply
be deduced from the formula for the components of the magnetic force.

428

HIKKKLAND. THK NOUWKGIAN AURORA POLAKIS KXPKD1TION, IQO2 — 1903.

As it is well known the expression for this quantity involve an additive constant, that may be
chosen at pleasure.

We may therefore, for instance choose such a constant, that the value of the potential at the centn-
of the sphere will be zero. Under this supposition we may write the potential, V, as

ft

Po.
jo

as the term on the right is an expression for the work done against the field when a positive magnetic
pole of unit strength passes from the centre of the sphere to a certain point on its surface.

Po is only due to the curved portion of the current. We find by equations (3), (8) and (9)

t'-2

cos (a* — it) sin 6 cos £ — sin L" cos 6
= //.- sin i. | — s-, — - (tii.

f'\

(U-

cos

We further have, as will be easily seen

._ . ,. cos £ cos tf — cos 6

cos (u — /() sin 6 cos t - - sin L cos 6 = - —5—

sin L

By introducing this expression and by integration with respect to Q, we find, pag. 101, Part I

","-2

,7 . (cos 9 — cos £ cos ft) (o — L cos ft) . (cos 0 — cos £ cos d) cos ft ,

I ' = i I — j=- —da -f- / I ~~2~j — "!'•

sin2 ft yp- -)- L- — 2(> L cos [i sm P

J ,"i ./ ,"i

or if preferred

r/'a

(r*r\c fl . r*r»c rric ti\ f/i (J /J\ r-rvc !^\

du.

. , I (cos ft — cos £ cos /?) [Q — (L — d) cos

r = — I \ . o ,, 7

sm* ft . d
."i

(28!

where d stands for the square root.

As will be seen, V may also be expressed as elliptic integrals.

For numerical calculations I think however that the above form is the most practical one.

By derivation of this expression we find the force-components of the whole current-system. This
we have done to control the correctnes of our calculations.

In our calculations we have imagined the current to lie at a height of about 400 kilometres
(L = 1,063 Rl> tne average height of currents, as we found by our calculations in Chapter IV of Part I.

In the tables, we have employed y as the unit for forces; and / = io5 [i. e. iofl amperes].

TABLE LIX.
Values of Po° for the horizontal portion of the current.

f)

1') — II = o° I

5° 3°° 45°

i

60° 75°

9°°

105°

120° 135°

I5o°

I63°

,80

0

- 135.72 - i

24.41 — 113*'° — 'oi.TP

- 90,48

- 79,17

— 67,86

- 56,55

- 45,24

- 33,93

— 22,62

- ii,3' °

IO

— 161,11 — i

22,92 -- 92,80 — 71,45

— 56,21

- 44,97 ' - 35-98

- 28,42

— 21,91

- 15,93 - 10.35

- 5,i6

20

- 62,04 -

54.26 - 43,07 -- 34,91

— 28.67

— 23,62 — 19,31

- 15,51

— I 2,O6

- 8,86

- 5.82

— 2,89 o

40

+ 13.01 -4-

3.13 - 3.73 - 6,96

- 7.94

- 7,79 • 7,07

- 6,07

- 4,93

- 3.72

- 2,48

- 1,25

0

60 + 4,22 . +

1,44 — 0,82

— 2,32

- 3°9

- 3,4°

- 3,3'

- 2,99 - 2,51

• i,94

- 1,32

- 0,67

0

go -(" T-69 +

0,8 1 -1- 0,03

0,58

— 1,00

• 1,23

- 1,29

1,24

— 1,09

- 0,87

- 0,60

- 0,31

0

140 4- 0,88 4-

0.65 4- 0,42

4- 0,22

4- 0,06

- 0,06

- 0,14

- 0,18

- 0,18

- 0,16

— 0, 12

— 0,06

0

180 + 0,78 -t-

0,71 4- 0,65

4- 0.58

4- 0,52 4- 0,45 ' + o 39

4- 0,32 -1- O,26

4- 0,19

+ 0,13 4- 0,06

0

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. II.

429

TABLE LIX (continued).
Values of PQ for the horizontal portion of the current.

V

«J_H = 0° I5 =

30°

45°

60°

75°

90°

•05°

1 2O°

•35°

.50°

165°

1 80°

5

4- 12.77

4- 10.90

+ 9-15

4- 7.60 4- 6.27

4- 5.13

4- 4-'5

4- 3-30

4- 2.55

4- 1.86

+ I.2I

4- 0.60

O

0

4 34-59 f 24.97

4- 17.65

4- 12.77 j 4- 9-55

4- 7.36

+ 5-72

+ 4-43

+ 3-37

4- 2.42

+ 1-55

4- 0.78

o

5

4- 100.55 4- 46.43

4 23.96

4- 14.94

4- 10.56

4- 7-95

4- 6.04

4- 4.64

4- 3.52 4- 2.49 ' 4- 1.64

4- 0.84

0

0

+ 270.45 | 4- 56.68

4- 23.35

+ I4-07 + 9-92

+ 7-47

+ 5-78

4- 4-51

+ 3-4°

+ 2.45

4- 1.6 1

4- 0.78

o

0

+ 26.99

4- J7-97

4- 12.59 + 9-53 4- 7-54

4- 6.06

4 4-89

+ 3-89

4- 3.00

4- 2. 2O

4- 1-42

+ 0.70

o

0

4- 7.42

+ 7-38

+ 7.01 + 6.37

4- 5.61

+ 4-82

4- 4-06

+ 3-32

4- 2.62 4- 1.94

4- 1.28

4- 0.64

o

0

4- 2.00

4 2.74

4- 3.28 4- 3.53 4- 3.49

+ 3-29

4- 2.94

4- 2.52

4- 2.05 4- 1.55

4- 1.04

4- 0.52

0

0

4- 0.67

4- 1.22

4- 1.70

+ 2.03

4- 2. 2O

4- a.ai

4- 2-09

4- 1.87

4- 1.57 + 1.22

4- 0.83

4- 0.42

0

o 4- 0.17 4- 0.56

4- 0.92

4 I-2I

4- 1.41

+ 1-52

f 1-52

4- 1.43

4-1.24 4- 0.99 4- 0.69 ! 4- 0.35

o

Values of Pm° for the horizontal portion of the current.

ty »-,, = o°

15°

3°°

45°

60°

75° 9°°

1

105°

o
120

135°

150°

165°

1 80°

o

5

- 6.69

— 18.21

- 6.32

- 14-71

- 5-52
- 10.36

- 4-71
- 7-72

- 4-°4
- 6.14

- 3-53
- 5.14

- 3.16

— 4-47

- 2.88
- 4-01

- 2.68

- 3.69

- 2.54
- 3-47

- 2.44
- 3-32

- 2.39
- 3-24

- 2.37
- 3-21

0

- 43-17 - 24-36

- 14.08

- 9-8i ' - 7-59 - 6.27

- 5-41

- 4-83

- 4.43

- 4-15

- 397

- 3-87

- 3-84

ci
o

— 21.91

- 15-65

— 18.92

- 14-79

— M-32
- 12.89

— ".05
- 10-97

- 8.94 - 7.55
- 9.41 - 8.23

— 6.60
- 7-35

- 5-94
— 6.70

'- 5-47
- 6.23

- 5-15
- 5-90

- 4-94
- 5-68

- 4-82
- 5-55

- 4.78
- 5-Si

0

- 12.78

— 12.52

— 11.82

- 10-93

— IO.O2 — 9.20

- 8.51

- 7-95

- 7-53

- 7.21

— 6.99 — 6.86

- 6.82

0

- 13.25

- I3-I3

- 12.81

- 12.34

— II.8l

— 11.26

- 10.75

— 10.31

- 9.94

- 9-65

- 9-45 - 9-32

— 9.28

o - 24.14

— 24.08

- 23.90

- 23.74

- 23.30 - 22.93

— 22.51

— 22.18

— 21.86 ' — 21.59

— 21.39 — 21.27

— 21.23

TABLE LX.

Values of PQ for one of the vertical portion of the current.

J

fij — (// = O°

15°

30° 45°

[_

60°

75°

90° 105°

1

120°

135°

150°

165°

1 80°

o

0

4- 7.86

4- !5.i8

4- 21.46

-f 26.29

4- 29.32

+ 30.35

4- 29.32

4- 26.29

4- 21.46

4- 15-18

4- 7.86

0

5

0

4- 13.11 4- 23.49

4- 29.78

4- 32.11

4- 3I-4I

4- 28.69

4- 24.78 4- 20.21

4 I5-31

+ 10.25

+ 5-13

0

0

0

+ 24.55

4- 36.78

4- 38.32

+ 34-87

+ 29.85

4- 24-65

+ 19-75

4- 15-25

•4- 1 1. 1 1

4- 7.25

+ 3.58

o

5

o

+ 49-70 4- 51.20

4- 41-63

->- 32.69

4- 25.55

4- 1991

4- 15-36

4- 11.56

4- 8.27 4- 5.34

-1- 2.62

o

0

0

4- 69.83 4-51-20

4- 36.61

4- 27.08

4- 20.49

4- 15.66

4- 11.90 4- 8.89

4- 6.33

+ 4.07

4- 2.06

o

o

o

4- 20.69 4- 23.47

4- 19.87

4- 15.80

4- 12.38

+ 9-64

4- 7-4i 4- 5.56

4- 3-97

4- 2.56

4- 1.25

0

0

o

4- 7.01

4- 10.24

4- 10.37

4- 9.18

4- 7.67

4- 6.21

4- 4.90 4- 3.73

+ 2.69 4 1.75

4- 0.86

o

0

0

4- 1.87

4- 3.'9

4- 3-79

4- 3.82

4- 3-51

4- 3-05

4- 2.52 4- 1.99

4- 1-47

4- 0.97

4- 0.48

o

o

o

4- 0.60

4- 1. 10

+ 1-43

4- 1-57

4- 1-57

4- 1.46

4- 1.27 4- 1.05

4- 0.80

4- 0.54

4- 0.27

o

1

o

4- 0.23

4- 0.44

4- 0.60

4- 0.71

4- 0.76

4- 0.76 4 0.71 4- 0.61

4- 0.48

4- 0.33

4- 0.17

o

o o ' + o. 17

4- 0.33

4- 0.46

4- 0.57

4- 0.63

4- 0.66

4- 0.63 4- 0.57

4- 0.46

4- 0.33

4- 0.17

o

Birkelaml. The Norwegian Aurora Polaris Expedition 1902—1903.

55

43°

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

TABLE LX (continued).
Values of Pm for one of the vertical portion of the current.

e

ca-f,= o°

is"

30°

45°

60°

75°

90°

.05°

120°

-35°

I5o°

165°

i8or

o

+ 30-35

4- 29.32

+ 26.29

4- 21.46

4- 15.18

4- 7.86

o

- 7.86

- I5.I8

— 21.46

— 26.29

- 29-32

- 30.35

IO

+ 53-33

+ 44.91

+ 27.65

+ 11.89

4 0.62

- 6.86

— 11.76

- 14.96

- 17.07

- 18.44

- 19.29

- 19-75

- 19.90

15

4 70-59

4- 42.62

4- 12.85

- 1.65

- 8.61

— 12. 2O

— 14.16

- 15-28

- 15-93

- 16.31

- i6-53

- 16.64

- 16.67

20

0

- 8.65

- 12.88

- 14-25

- I4-69

- '4-77

— 14.71 — 14.60

- '4-47

- 14-35

— 14.26

— 14.21

- 14.19

3°

- 53-32

- 42-95

— 29.28

— 21.39

— 17.16

- 14-74

— 13.24 — 12.26

— 1 1. 60

- 11.15

— 10.86

— 10.70

— 10.64

40

- 30-35

— 27.78

- 22.59

- 17-95

- 14.65

- 12.45

— 10.96

- 9-95

— 9.26

- 8.79

- 8.48

- 8.30

- 8.24

60

- i4->9

- 13-68

— 12.40

- 10.65

- 9-39

— 8.19

- 7.26

- 6.56

•— 6.04

- 5-68

- 5-43

- 5-3°

- 5-26

90

- 6.54

- 6.41

- 6.05

- 5-55

- 5-00

- 4-47

- 4.01 — 3.63

- 3-32

- 3.1°

- 2.94

- 2.85

- 282

140

- 2.27

— 2.24

- 2.13

- 1-97

- '-77

- 1-56

• i-34

• 1.14

- o-97

- 0.84

- °-74

- 0.68

— 0.66

1 80

— 0.66

— 0.63

- 0.57

- 0.46

- 0.33

- 0.17

o

+ 0.17

+ 0.33

•f 0.64

+ 0.57

4- 0.63

+ 0.66

From these quantities we can determine, by a simple combination, the distribution of force in
systems with a horizontal piece of current of arbitrary length.

In the following tables we have put together the force-components of three such systems, the length
of the arc in the first being 75°, in the second 180°, and in the third 270°.

w is here always reckoned from the transversal axis.

TABLE LXI.
Values of Po for a current-system corresponding to

= 75

e

«• = 7.5°

22,5°

37,5°

53,5°

67,5°

82,5°

97,5°

1 13,5°

127,5°

142,5°

157,5°

172,5°

0

- 56.55

- 56.55

— 56.55

- 56.55

- 56.55

- 56.55

— 56.55

- 56.55

- 56.55

- 56.55

- 56.55

- 56.55

10

- 157-97 - '43-10

— 116.14

- 86.94

— 64.39

- 49-55

— 40.28

- 34.62

— 30.82

— 28.42

- 27.07

- 26.28

20

- 46.11 - - 41.15

- 38.43

- 34-95

- 27.56

- 2285

— 19.82

- 17.80

— 16.42

- I5-5I

- 14-95

- 14.68

40

+ 37-91

4- 32.04

4- 21.40

4- 10.20

+ 2.33

- 2.03

— 4.22

- 5-30

- 5-82

- 6.07

— 6.17

— 6.22

60

4- 11-58

+ 10.09

4- 7.62

+ 4-75

4- 2.17

+ 0.18

- 1-15

— a.o8

— 2.64

— 2.89

— 3-n

- 3'27

90

+ 3-93

+ 3-57

+ 2.91

+ 2.IO

4 1.27

+ 0.50

- 0.13

— 0.63

- 0.99

— 1.24

- i-39

- 1.47

I40

4- 1. 12

4- i. 06

4- 0.94

4- 0.78

4- 0.60

4- 0.41

4- o 23

4- 0.06

— 0.07

— 0.18 — 0.25

- 0.28

180 jj 4- 0.32

4- 0.32

4- 0.32

+ 0.32

+ 0.32

4- 0.32

4- 0.32

+ 0.32

4- 0.32

4- 0.32 + 0.32

4- 0.32

Values of PQ for a current-system corresponding to f\n = 75 .

6

°> = 7,5°

22,5°

37-5°

52,5°

67,5°

82,5°

97,5°

"2,5°

"7,5°

142,5°

157,5°

172,5°

0

- 36.80

- 34-29

- 29.45

- 22.59

— 14.20

- 4-84

+ 4-84

4- 14.20

4- 22.59

+ 29.45

4- 34-29

+ 36.80

5

- 44-47 •- 36-83 -- 23.76

8.84

4 4-56

4- 14.61

4- 21.21

4- 2507

4- 27.11

4 28.08

4- 28.49

4- 28.63

10

- 36.35 — 24.71 | 2.62

4- 19.10

+ 30.25

4- 32-48

4- 30.88

4- 28.40

4- 26.01

4- 24.18

4- 22.98

+ 22.34

IS

4- 69.36 4- 61.71 4- 67.05

+ 70.18

+ 55- 1 7

+ 4 1 -50

4 32.48

4- 26.51

4- 22.50

t 20.00

+ 18.53

+ n-75

20

+ 415-77 , + 377-38

4 242.48

4- 105.07

+ 58.03

4- 43.10

4- 28.23

4- 22.20

4- 1 8.60

4- 16.42

+ 15.13

+ 14.45

3°

• 11.48

8.01

+ 8.54

4 24.14

4- 24.76

+ 20.84

4- 17.17

4- 14-45

4- 12.57

4- 11.30

4- 10.52

4- 10.16

40

19.16

• 14-33

5-07

4- 4-12

+ 9.04

4- 10.38

4- 10.16

4- 9.47

4- 8.77

4- 8.22

4 7-84

+ 7.66

60

9.78

7.92

4.81

1-38

4- 1.42

4- 3.27

4- 4-29

+ 4.80

4- 4-99

4 5-°4

+ 5-04

+ 5-°3

90

4.92

4.72

3-1 1

1.72

- 0.34

+ 0.84

4- 1.76

4- 0.42

4- 2.86

+ 3-14

+ 3-3'

+ 3-38

140

2.84

.2.59

— 2. 1 1

r.48

— 0.76

— 0.03

+ 0.65

4- 1.26

+ '-75

4- 2.12

4- 2.37

4- 2.50

1 80

2.43

— 2.27

— 1-95

1.49

- °-94

— 0.32

4- 0.32

4 0.94

+ '-49

4 1.95

•+• 2.27

+ 2.43

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. II.

43 *

TABLE LXI (continued).
Values of P,,, for a current-system corresponding to £±{i = 75°.

H '" = 7o°

22,5°

37,5°

52,5°

67,5°

82,5°

97-5°

"2,5°

127,5°

142,5°

'57-5°

172,5°

0

+ 4-84

+ 14.20 + 22.59

+ 29.45

+ 34.29

4- 36.80

4- 36.80

+ 34-29

+ 29.45

+ 22.59

4- 14.20

4- 4-84

10

+ 14-95

4- 42.01 4 57.04

+ 53-51

+ 39-98

+ 26.93

+ 17.56

+ "-33

4- 7.22

+ 442

4- 2.39

+ 0.75

15

-r 11.86

+ 42.66

4- 69.63

+ 46.54

4 21.78

+ 10.25

+ 5-°3

+ 2.51

4- 1.24

+ 0-59

4 0.25

4- 0.07

20

- 2.91

" 10-73

— 22.12

— 12.89

- 7-54

- 5-'7

- 3-78

— 2.80

- 2.04

- 1.40

- 0.81

— 0.27

3°

— 1 1.16

- 35-77 - 52.95

— 42.03

- 25-4°

— 15-37 - 9-8o

- 6.49

- 4-33

- 2.78

- 1.56

— 6.50

4°

- 6.56

- 18.50

- 25-33

— 24-25

- 18.82

- 13.43 - 9-38

- 6.51

- 4-46

— 2.91

- 1.64

- 0.53

60

- 2.45

- 6-79

- 9.58

— 10.43

- 9.71

— 8.20

- 6.53

- 4-96

- 3.60

- 2.43

— 1.40

- 0.46

00

- 0.97

- 2.74

- 4-05

- 4.78

- 4-93

— 4.63 ] - 4.06

- 3-35

- 2-59

- 1-83

— 1.09

- 0.36

140

- o-43

1.24 - 1.93

— 243

- 2.71

- 2.77 - 2.64

- 2.35 ' • 1.94

- 1-44

- 0.88

— 0.30

180 - 0.32 - 0.94 1.49

• 1.95 2.27

- 2.43 - 2.43

- 2.27 • 1.95

- 1.49

— 0.94

- 0.32

TABLE LXII.
Values for Po for a current-system corresponding to /\(.i = 180°.

1 ' ia = o°

15°

30°

45°

60°

75°

90°

105°

120°

•35°

•5°°

'65°

1 80°

.1

- 135-72

- 135.72

- I35-72

- I35-72

- I35.72

- 135-72

- I35.72

- '35-72

- 135.72

-'35-72

-135-72

-135-72

-135-72

)

— 250.27

— 248.84 — 244.11 — 234.84 — 219.07

- 194-15

— i6i.n

— 128.08

- 103.15

- 87.38

-78.12 —73-39

- 71-95

)

- 85.47

- 84.96, -- 83.35

- 80.32

— 75.20

66-94

— 62.04

- 57-14

- 48.89

- 43-77

- 40-74 - 39-13

- 38.62

o

+ 41-35

+ 41.08 j + 40.09

4- 37.90

+ 33-44

+ 25.34

4- 13-61

4- 1.88

6.23

— 10.68

- 12.88

- 13-86

— '4-14

o

4 15.06

4- 14.82

+ 14-03

+ 12.70

+ 10.57

+ 7.66

-t- 4.22

+ 0.77

— 2.14

4.27

- 5.6o

- 6.39

— 6.62

o

+ 5-97

4- 5.84

+ 5-4°

4- 4.83

+ 3-95

4 2.88

4- 1.69

4- 0.50

0.57

• 1-45

- 2.08

- 2.46

- 2.59

0

4- 2.04

4- 2.OO

4 1.89

4- 1.71

+ i-47

4- 1.19 4- 0.88

4- 0.58

4 0.30

+ 0.06

— 0.12

— 0.23

— 0.27

o

4- 0.78

4- 0.78

4- 0.78

+ 0.78

4- 0.78

4 0.78

4- 0.78

4- 0.78

+ 0.78

+ 0.78

4- 0.78

4- 0.78

4- 0.78

Values of Pn for a current-system corresponding to /\/.i = 180°.

« = 0°

'5° 3°° 45°

1

60°

75°

9°° 105°

o o
120 135

150° 165°

1 80°

3

- 60.97

- 58.89

- 52.80

- 43-II

- 30.48

- 15-78

o

4- 15.78

+ 30.48

4- 43-11

4- 52.80

4- 58.89

4 60.97

3

4 8.44

4- 7.79

4- 6.15 ; 4- 4.55

+ 5-95

+ 15-85

+ 3459

+ 5383

+ 63.23

4- 64.63

4 63.03

4- 61.39

4- 60.74

0

4- 498.02

+ 496.51

4- 491.61

4- 481.44

+ 460.77

+ 411.54

4-270.45 4- 129.35! 4 80.13

4 59.45 + 49.29

+ 44-39

+ 43.88

0

5-69

5.87 i - 6.30

6.53

5-44

1.04

4- 742 ! + 15.88

4 20.28

4- 21.37 4- 21.13

4- 20.71

+ 20.53

0

7-99

7-85 - 7-35 - 6.34

448

— 1.61 i 4- 200 4- 5.61

+ 8.47

4- 10.33

4- 11.34

4- 11.84

4- 11.98

0

- 5.76

- 5-59

— 5.06

4.14 ' — 2.83 - 1.18 4- 067

4- 2.52

4- 4.16

+ 5-47

4- 6.39

4 6.92

4- 7.10

3

4.21

4.07

3.64

— 2.95 — 2.05 - 0.98 4- 017

+ 1.32 4 2.38

4- 3.29 4- 3.98

4- 4.41

+ 4-55

0

4-°3

- 3-90

3-49

- 2.85

— 2. 02

1.04 o

4 1-04 4 2.02

+ 2.85 ; 4 3.49

+ 3-90

+ 4-°3

Values of Pu> for a current-system corresponding to

= 180°

,„ = 0°

15° 30° 45° 60°

75° 90°

105°

120"

135°

150° 165°

!

1 80"

3

0

+ 15.78

4- 30.48

4- 43.11

4- 52.80

4- 58-89

i
+ 60.97 + 58-89

4- 52.80

+ 43-II

+ 30.48

4- 15.78

0

a

o

+ 7.45 4- 16.33 + 28.16

4- 43.86

4 60.73

4- 68.91 4 60.73

+ 43-86

4- 28.16

4- 16.33

+ 7-45

0

0

>

o

0

- 1.62 - 3.39 j - 5-55
- 4.01 — 8.57 i - 14.23

- 8.73
— 21.32

- 14-93
— 28.71

— 25-14
— 32-25

- 14-93
— 28.71

- 8.37
— 21.32

- 5-55
- 14-23

- 3.39 - 1.62 : o

- 8.57 ' - 4.01 o

>

o

- 2.87 - 5.84

— 8.88

- 11.79 : - 14-03

- 14.89

- 14-03

- 11-79

- 8.88

5.84 - 2.87 o

0

>

0
0

— 1. 80
- 1.16

- 3-55
- 2.24

- 5-15
- 3.18

- 6.47 - 7.37
- 39i - 4-37

- 7-68 - 7.37
- 4-53 - 4-37

- 6-47
- 3-91

- 5-15
- 3.'8

- 3-55
— 2.24

- 1. 80
1.16

0

o

1

o

- 1.04

— 2. 02

— 2.85 - 3.49 - 3-90

4-03 , - 3-9°

- 3-49

- 2.85

— 2. 02

• 1.04 o

432

HIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1QO2 — 1903.

TABLE LXIII.
Values of Po for a current-system corresponding to A," = 270°.

0 ' ™ = 0°

i5c

30° 45°

60°

75°

90°

i°5°

o
1 20

135° 'So0

•65°

180°

0

— 203,58

— 203.58

- 203-58

— 203.58

— 203.58

— 203.58

- 203.58

— 203.58

- 203.58

— 203.58

- 203.58

- 203.58

-203.58

10 ! — 290.36

- 289.97

— 288 64 — 286.25

— 282.42

— 276.36

— 266.70 — 251.32

— 227.72

- '97 09

- 167.89 — 149.01 -142.91

20 — 106.37

— 106.21

- 105.69

- 104.78

- 103.36

— 101.23

- 98.03 -- 93.08 -- 85.34

- 81.35

- 77.88 •- 71.74 - 69.83

40

+ 34.67

+ 34-64

-1- 34 53 + 34.29

+ 33-76

4- 32.67 i 4- 30.45 4- 26.03 4- 18.02

+ 6.54

4.67

11.68 — 13.91

60 '! -f- 12.32

4- 12.26

+ 12.09 4- 11.75

4- 11.17

4- 10.21

4 8.82

4- 6.75

4- 4.01

+ 0.91 | • 1-96

- 3-9i - 4-65

9°

+ 5-II

+ 5.06

+ 4.92

4- 4.67

+ 4-3°

+ 3-77

4 3-°9

4- 2.26

4 1-33

4- 0.39 j - 0.42

- 0-97'- i-n

140 ! + 2.09

4- 2.07

4- 2.01

+ 1.91

+ 1.76

+ 1.58

4- 1.38

4- 1.16

4 0.95

+ 0.75

-t- 0.59

4 0.49

+ 0-45

180 4- 1.17

4- 1.17

4- 1.17 4- 1.17

4- 1.17

4- 1.17

4- 1.17 f 1.17

4- 1.17

4- I.I7 4 I.I7 4- 1.17 4 1.17

Values of Py for a current-system corresponding to /\u — 270.

:l
i]

150 ! 3°°

-45"

60°

75°

90°

105° 120°

135°

'50°

165° 180°

[I

0 : -43.11

- 41.64

- 37-33

' 30.48

— 21.56

11.16

o

4- 11.16

4 21.56

1

4 30.48 4 37.33

4 41.64 4 43-11

10 ' 4- 42.12

4- 41.76

+ 40.65

4- 38.81

+ 36-33

+ 33-57

4 31.61

4 33-37

4 43-88

4 64.96

4- 86.69

4 98.84 4102.21

20 4 523-35

4 522.94

+ 521-63

4 519-46

-•- 515.77

+ 509-57

4- 498.99

+ 478.73

4 430.81

-i- 291.89 4 154.48 4 111.46 4101.35

40 4 5.58 4 5.47

+ 5-13 4 4-57

4- 3.84 1 4- 3.08

+ 2.73 ! 4 3-93

4- 8.67

I- 17.68

4- 26.88 4 3^-°5 * 33-48

60 2.05 - 2.05

2.O5 - 2.0O

1.81 | 1.31 0.30. 4 1.57 4 4.43

4 7.99 4 11.41 4 13-77

t- 14.62

90 2.70 - 2.65

2.50 — 2.21

1.76 - 1.07

O.I I

4- 1.15

4- 2.65

4 4.21

4- 5-61

+ 6-57

-t- 6.91

140 , 2.61 - 2.54

2.31 - 1.94

1.42

0-77

o.or

4 0.82

4- 1.67

4 2.44

4- 3.08

+ 3-49

+ 3-63

180 j 3.85 — 2.76

2.47 - 2. 02

i-43 - 0.74

o

4- 0.74 i 4 1.43

+ 2. 02

4- 2.47

4- 2.76

4- 2.85

Values of Pia for a current-system corresponding to /\/ii = 270°.

9

,„ = o°

•5'

30°

45°

00°

75°

90°

-5°

120°

135°

o

150

165° 1 80°

0 O

— 1 1.16

— 21.56

- 30.48

- 37-33

- 41.64

- 43-n

- 4'-64

— 37-33

- 30-48

- 21.56

— II. 16

O

10 0

- i.98

- 4-29

- 7-35

- n-74

- 18.31

— 28.16

- 41.88

- 56.44

- 61.56

- 48.99

- 25-55

o

2O 0

4- 0.66

+ 1-34

4 2.09

4 2.96 4- 4.04

4 5-55

4- 8.07

+ 13-59

+ 23.04

+ 11.97

4 4.68

0

40

o

+ '-34

4- 2.80

+ 456

+ 6.81 + 9.91

+ 14.23

4- 19.98

4- 25.91

4- 27.69

4- 21.89

4 11.42 o

60 o

4- 1.14

+ 2.34

4- 3.69

+ 5.22 4- 6.98

+ 8.88

4 10.65

4- 11.68

4- ii. 20

+ 8.81

4 4.82

o

90

o

4- 0.87

4- 1.76 4- 2.66

+ 3-56

4- 4.42

+ 5-15

4- 5.60

4- 5.61

+ 5-03

4 3.81

4- 2.05

0

140 o

4- 0.70

4- 1.38 4 2.OO

+ 2.54

4 2.94

4- 3.18

+ 3.20

4- 2.99

4- 2.52

+ 1.83

4 0.96

0

180 : o

4- 0.74 4- 1.43 4- 2. 02

+ 2.47

4- 2-76

4 2.85

-4- 2.76

+ 2.47

4- 2. 02

-1- i-43

4 0.74

0

We have moreover shown these three fields of force on charts, one for each field separately, and
one giving the field for two simultaneous systems of the first kind, one in the north and the other in
the south.

The fields of force in these charts are not represented by current-arrows as in the perturbations,
but by current-lines (equipotential lines, see p. 85) and by lines of force for the horizontal components.
Lines have moreover been drawn on another chart for constant values of Po.

In order to construct the former of these easily, when the force components at various places on
the earth have been calculated, the following mode of procedure has been adopted.

P9
The relation f.— was determined for the various points at which the force-components were cal-

Pin

culated, this relation being a measure for the angle that the horizontal force-component forms with the
circles 6 = const, or 10 — const. These we may call, for the sake of brevity, parallel circles and meri-
dians. We next drew curves for the various meridians and parallels, showing how this condition varied

PART II. POLAR MAGNETIC PHENOMENA AND TERRELI.A EXPERIMENTS. CHAP. II.

433

along them. A number of points could then be determined by interpolation, upon the various sets of
curves where this relation had a constant value. It thereby became possible to draw upon a chart
curves in which this relation was constant. Along these "isogonic" lines ('), the lines offeree or the current-
lines, form equal angles with, for instance, the meridian. The tangent directions were now drawn in a
series of short, parallel strokes, which intersected the various isogonic lines; and by employing a suffi-
cient number of these, the chart could be as thickly covered with these small tangent directions as
might be desired. Lines of force and equipotential lines could then at once be drawn.

With regard to the equipotential lines, care must be taken that those drawn are equidistant.

We may here use the formula (23), or as we know that the potential along the parallel circles and
meridians varies respectively as

f» .

o SI

o sin OPi,i i

and

f#
J 9

\\\: may either by calculation or by graphic or by numerical integration easily find out the different data,
necessary for this purpose.

As regards the lines of force, it will be seen that they all point in towards the two characteristic
points, the points of convergence and divergence, so that here, in drawing, we have two fixed points
and also a distribution of tangent directions to hold to.

We must finally not omit to remark that while we have drawn equipotential lines in such a way
that the magnetic intensity in a horizontal direction is in inverse ratio to the distance of the equipotential
lines, the distance between the lines of force gives no indication of the intensity. The reason of this is
that the lines of force give only the lines for the horizontal components, and not the total magnetic force.

Field of force for a polar current-system of the assumed form.

$ = 20°, A« = 75°- A V = 0,2 1 8 i.

Fig. 179.
(') Cf. J. W. SANDSTROM: Ober die Bewegung der Fliissigkeiten, Annalen der Hydrographie und maritimen Meteorologic, 1909, p. 242.

434

13IRKELANU. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Fields of force for polar current-systems of the assumed form.

g = ao« A" = i8o«. A V= 0,349 '•

Fig. 1 80.

20°, A," = 270°. A y= 0,436 i.

Fig. 181.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. II.

Fields of force for polar current-systems of the assumed form.

?l = 20", ?2 = 1 6o« A" = 75°- A V = o,a 1 8 /.

435

Fig. 182.

Curves for constant value of P0.

I = 20", A." = 75°.

Fig. 183.

436

HIRKKI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

Curves for constant values of P0.

'C = 20, /\H = 180".

Fig. 184.

5 = 20", A" = 270".

Fig. 185.

PART II. Pnl.AU MAGNETIC PHKNOMKNA AND TERRKI.LA KXPKRIMKMS. (HAP. II.

Comparison between calculated and observed fields of force.

Chart I: A," = 75°, * = 4°° km, i = 625 ooo amp. Chart II: February 15, 1903, i'> p.m. Or. M. T.

437

Fig. 1 86.

438 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

If we look at these charts, the great accordance with the observed areas of perturbation is at once
apparent.

We have finally made a direct comparison with one of the observed elementary storms (see pag. 437).
We have here placed our current-system with its storm-centre in the neighbourhood of Dyrafjord, 6 = 0 jn
the point of intersection of the earth's magnetic axis with the surface of the earth, and we have employed
the system with the shortest horizontal piece of current, /\« = 75°. With this arrangement this will come
very nearly along the auroral zone. The projection of the assumed current-system is indicated on the
chart by a dotted line.

For this system the magnetic force-components are then calculated for the stations from which we
have observations. The agreement, as will be seen, is striking as regards the horizontal current-arrows,
except that the current-system employed seems to be a trifle too large. If we had taken £^tt a little
smaller, or if the storm-centre had been chosen somewhat more westerly, the agreement would unquestion-
ably have been still closer. In the vertical forces the arrow observed at Val Joyeux is considerably
smaller than might be expected from the calculations. The direction is the same, however, in both
cases. The cause of this is to be looked for partly in the fact that the constitution of the actual current-
system must only with a very rough approximation be assumed to be capable of being replaced by such
a system, and that the actual current-system might not possess such a strongly-marked horizontal com-
ponent as is here assumed. Perhaps the agreement would have been better also in the vertical intensity
if we had used a form of the current-system analogous to that given diagramatically in fig. 187. We
believe, moreover, that much of the disagreement may be due to earth-currents,
which would have the effect of increasing the horizontal magnetic force-components,
while reducing the vertical. It is possible that these currents played the most im-
portant part. We must further draw attention to the uncertainty that may be con-
nected with the observed values of Pv. We see this with special distinctness in
Charts III and VII — X for the I5th February, in which there seem to be powerful
perturbing forces in the vertical intensity at Uccle, while at the surrounding stations

—Val Joyeux, Wilhelmshaven and Munich — no particularly noticeable effect is found. The uncertainty
in the determination of the normal line is, as will be understood, rather great.

At Axeleen the observed vertical arrow is considerably greater than the calculated. This may
only be due to the great uncertainty which attatches to the statement of the scale value for Fat this place.

PART II. POLAR MAGNETIC PHKNOMENA AND TERRELLA EXPERIMENTS. CHAP. II. 439

92. By means of the long series of perturbations that we have now gone through, we have
succeeded in obtaining a more or less clear idea of the magnetic storms, and have classified them
according to their appearance and course. As, however, the material employed was large, it may be
advisable to go once more briefly over the principal results at which we have arrived in the preced-
ing pages.

The perturbing forces are calculated from the deviations from the normal daily course followed by
the magnetic elements on calm days, as represented in Article 14. On the charts, the horizontal
components are shown by current-arrows, of which the length is proportional to the size of horizontal
component of the perturbing force, and whose direction gives the direction of an electric current over
the- place, which would produce a magnetic force similarly directed. These current-arrows, however, are
only a geometrical representation of the perturbing forces, and indicate nothing whatever as to the
existence of such currents.

In a number 01 places, moreover, the vertical component of the perturbing force is given by a
line at right angles to the current-arrow, on the left of it — left of a person, standing on the earth and
facing the direction of the current-arrow — if P, is positive, that is to say if the force is directed towards
the earth, and on the right of it if the force is directed upwards.

The storms that are first described are those which exhibited the simplest conditions, while later
on, the more complicated perturbations are taken.

We succeeded, in this way, in first separating the so-called equatorial perturbations from the polar.
Each of these types of perturbation have their characteristic area of perturbation, which is clearly
apparent from the charts, as also from the comparison of curves which we made for each perturbation
studied.

We have considered that the perturbations should be divided in all into five different types,

1. The positive equatorial storms,

2. The negative equatorial storms,

3. The positive polar storms,

4. The negative polar storms, and

5. The cyclo-median storms.

Of these it is especial!}' the positive and negative polar storms, and the positive equatorial storms, that
are most frequently met with.

The chief peculiarities of the positive equatorial storm are as follows:

Everywhere in low and medium latitudes, positive perturbing forces are met with in the horizontal
intensity, while at the same time in declination no deflections, or only very small ones, are found. In
the vertical intensity, only small perturbing forces occur.

If we consider the conditions in rather lower latitudes, we find the strongest perturbing forces in
the equatorial regions, while the perturbing forces decrease in strength with increasing distance from the
magnetic equator.

440 ISIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

The deflections in horizontal intensity always increase at the beginning of the storm rather rapidly
and to a certain height, after which the perturbing forces remain more or less constant in strength for
a long period.

In the horizontal-intensity curve, there are always a number of very characteristic serrations, which
are found again at all the stations situated in low and medium latitudes, and these serrations appear at
any rate very nearly simultaneously all over the globe. This is also the case with the time of the
occurrence of the perturbation. We have made some determinations for the purpose of finding out
whether any differences in time could be proved in these at various stations. We have also found
differences of some minutes; but as, in many cases, the accuracy with which the time can be determined
is not as great as could be desired, we will not venture to express any certain opinion upon this foundation.

If, on the other hand, we approach the auroral zone, the perturbation-conditions alter to some extent.
We also find in declination deflections like those in horizontal intensity. A peculiar impulse at the
beginning of the perturbation, which was less noticeable in lower latitudes, now comes out distinctly,
this being that the deflections in horizontal intensity are not first in a positive direction, but in a negative;
and the current-arrow, or, if preferred, the perturbing force, oscillates here, at first quite distinctly,
through a more or less considerable angle. This condition is most distinct in the immediate vicinity «(
the auroral zone. Here too, we find again serrations to some extent similar to those at southern stations,
but often considerably larger.

At one station in polar regions, Kingua Fjord, in the only instance of such a perturbation found in
the material from 1882 and 83, we came upon a storm in which the perturbing forces, which \vc i
considerably greater strength, seemed to be distinct from the perturbations at the other stations.

Very frequently, perhaps as a rule, the positive equatorial storm is interrupted by the breaking in
upon it of a polar storm.

The two best examples we have of perturbations of this type are the storms of the 26th January,
1903, and the 151)1 December, 1882. Plates XIV and XXIV show very clearly the above-descrilx-d
characteristics of this type of perturbation.

Fig. 31, on p. 69 of Part I, gives an excellent idea of the perturbation-area of such a storm.

Figs. 167 & 168, pp. 406 & 407, show the area of perturbation about the auroral zone during a
positive equatorial storm. The characteristic turning of the perturbing force at the beginning of the
perturbation is seen on Chart I. The same peculiar condition is also shown in fig. 57, Chart I, p. 133,
at the two stations, Dyrafjord and Axeleen, where the movement is especially distinct.

Other instances of positive equatorial storms are found on the gth December and 23rd October,
1902, the 22nd and 3oth March, 1903, the 29th — 3oth and the nth — I2th October, 1902, and the 23rd
— 241)1 November, 1902.

We have sought for the cause of these positive equatorial storms in corpuscular rays, which \vi
imagine issuing from the sun, their main mass being gathered in the magnetic equatorial plane of the
earth. In fig. 37 we see cathode rays, under certain circumstances, may concentrate themselves in such
a manner. In this case, the rays go from west to east round the earth, in such a manner that cor-
responding current-arrows would have to be directed as in the negative equatorial storms. It is probable,
however, that the rays in the innermost parts swing round once or oftener, so that those nearest the
earth pass it from east to west. In fig. 38 b, we have shown how the rays can bend round before the
earth in this manner, and the nearest part will therefore produce on the earth a magnetic force-effect
directed northwards, which thus answers to a positive perturbing force in the horizontal intensity. It is
in rays of this kind, which turn round and pass nearest to the earth in a direction from east to west
(if they are rays with negative particles), that in our opinion the cause of these positive equatorial storms
must be sought. Fig. 39 shows a number of rays of this kind, lying in the magnetic equatorial plane,

PART II. POLAR MAC.NKTIC PHKNOMKXA AND TF.URELLA EXPKKIMKNTS. CHAP. II. 441

which SreRMKR has found by calculation. The rays answering to values of y between 0.3 and 0.9, are
specially noticeable.

In reality, the constitution of the current-system which produces the magnetic storms of this type,
is rather complicated, as there are at the same time perturbations in the north, which cannot be ex-
plained merely by an equatorial current-system. This is in perfect accordance with the conditions of
which the experiments give a hint. Fig. 38, a and b, gives, for instance, quite distinct information of
the existence of a connection between the rays which operate in the equatorial regions at a distance
from the earth, and those which come in a wedge close in to the earth in the polar regions, the latter,
in our opinion, being the cause of aurora polaris and the polar magnetic storms.

The patch of light in the polar regions, seen in fig. 37, is, we believe, connected with the powerful
and strictly local storm in Kingua Fjord, which we found during the perturbation of the i5th December, 1882.

Similar polar precipitation, of which the existence cannot be so directly proved, should, we believe,
be regarded as the cause of a number of apparently abnormal conditions that we found, for instance,
in the perturbations of the 26th January, 1903 (p. 67), the 22nd March (p. 128), and the 24th November,
1902 (pp. 273 & 274!.

The serrations that we find most strongly marked in the polar regions, must similarly be ascribed
to polar precipitation. Simultaniously with the change in the equatorial current-system which produces
the various serrations in the curve, slight polar precipitation will occur at places in the polar regions,
acting locally with comparative power, but its effect decreasing rapidly outwards.

These occurrances of slight polar precipitation will always accompany a positive equatorial storm.
For this reason, the character of the curves in the polar regions is very irregular in comparison with
those farther south. This may be seen, for instance, by comparing Axeleen with Bombay or Batavia
'•ii PI. XIV. We must thus, during the positive equatorial storms, imagine a constantly acting, more
itorial current-system, and a number of slight occurrence of polar precipitation in the north and south.
As these two systems are undoubtedly, as we have said, connected with onea nother, a change in the one
will always or at any rate as a rule be accompanied by a corresponding change in the other. We
shall demonstrate this more clearly later on in the experiments, which show that the rays may run for
a time more or less in the magnetic equator, but then intersect that plane at continually increasing
angles, after which they finally descend in polar regions.

We next have the polar magnetic storms. In these, the most powerful forces are found in the
polar regions, while the forces decrease very rapidly in strength with descent to lower latitudes.

In these storms, it will be possible, as a rule, to demonstrate in the polar regions one or more
more or less distinctly defined areas, within which the most powerful perturbing forces are gathered. It
appears that as a rule the character of the storm is mainly dependent on whether, in this area, there are
positive or negative deflections in horizontal intensity. When the former occur, we disignate the storm
as a positive polar storm, when the latter, a negative.

We will first look at the negative polar storm. It occurs very frequently, and often attains a very
considerable strength. In order to obtain an insight into the nature of the storm, we looked out the
vi.ry simplest of those contained in our material, and these were first discussed.

Among the chief peculiarities of the negative polar storm, it may be pointed out, in addition to
that already mentioned, that the character of the curve in the polar regions is generally much serrated
and irregular, which indicates that the acting forces, or current-systems, as we prefer to call them, must
approach comparatively near to the place under consideration, coming nearest to the earth, now in one
place, now in another. In lower latitudes, on the other hand, this disturbed character disappears, and
the course of the curves is fairly even and quiet, although considerable deflections occur.

442 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

Whereas during this type of perturbation, negative values of the perturbing forces in the horizontal
intensity were found in the polar regions, in lower latitudes at the same time positive values of this
component were found. Mere, then, we have a reversal of the component. The deflections in declination,
on the other hand, may at one time be easterly, at another westerly, according to circumstances.

We find the typical perturbation-area of a negative polar storm in its most perfect and distinct
form, shown in figs. 41 and 42. Areas such as these are constantly met during the negative polar
storms. In the auroral zone there are very strong current-arrows directed westwards, while south of it
the current arrows point in the opposite direction. In fig. 40, p. 86, we have endeavoured to give a
diagrammatic representation of an ideal form for the typical perturbation-area that appears during the
negative polar perturbations. The large vertical arrow, A, is supposed to coincide with the direction
of the current arrows found in the most perturbed area, the so-called 'storm-centre'. The entire lines arc
the lines of force for the horizontal magnetic forces that occur upon earth ; while at right angles to them
are the dotted potential lines, or, as we have called them, current-lines. It is the right half of this figure
that should correspond with the field represented, for instance, in figs. 41 & 42. For the sake of the
general idea, we called the line that coincides with the arrow A in fig. 40, or along the current-arrow
in the storm-centre, the principal axis of the system, and the line at right angles to it the transverse axis.
It will be seen that we have supposed the area of perturbation upon the two sides of the principal axis to
be exactly symmetrical, but in reality this will never altogether be the case, but only approximately.
As a rule there are occurrences all over the polar regions of strong or slight polar precipitation, which
easely effaces the traces that we might expect to find of such a condition. When the storms are
particularly simple and well-defined, however, indications may to a certain extent be found of a pertur-
bation-area on the other side of the principal axis, that is more or less symmetrical with the first. We
believe we have found a condition such as this in the perturbation of the I4th & I5th February, 1883,
where there is a simple, well-defined negative polar storm with storm-centre in the north of Europe, of
which the principal axis lies more or less along the auroral zone in this district, there being no storms
of any marked strength at the same time at other places round the polar zone. We here have some
stations more or less symmetrically situated on both sides of the principal axis; and in the description
on pp. 363 & 364, some conditions are pointed out that, although possibly only slight, would seem to
confirm this assumption. In figs. 152 & 153, the current-arrows at Kingua Fjord and Godthaab indicate
that such an area actually exists in the regions to the north of the principal axis.

On the transverse axis there are two characteristic points that are enclosed by the current-lines.
The horizontal components of the perturbing forces in the regions round one of these points, are directed
straight in towards the point, while in the other all the horizontal forces point straight out from it. In
the points themselves, the horizontal force is zero.

The first of these points we have called the system's point of convergence, the second its point
of divergence.

The storm-centre during a magnetic storm does not remain in the same place all the time. As a
rule, a more or less distinct movement of the various storm-centres can be traced. In the polar regions
this can best be seen from the horizontal-intensity curves, where a more or less distinct difference in
the time of the beginning, maximum, and conclusion of the deflections at the various stations is found.
We may also refer here to the perturbation of the 151)1 December, 1902, where this condition conies
out with unusual clearness when we look at the horizontal-intensity curves for Dyrafjord and Axeleen,
on PI. X. There seems no doubt that the storm-centre here was at first situated in the vicinity of
DyraQord, and afterwards moved eastwards along the zone, so that at the end of the perturbations, it
was situated nearest to Axeleen. This is also apparent on looking at corresponding charts. At first
the current-arrow at Dyrafjord is the strongest; but it then decreases, while the current-arrow at Axeleen

' PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. II. 443

increases. While in the polar regions, such , movement of the storm-centre can be demonstrated, the
current-arrows in southern latitudes will turn a certain angle, clockwise or anti-clockwise, and always in
such a manner as to make it seem likely that it is produced by a movement of the whole perturbation-
area in the same direction as that in which the storm-centre in the polar regions moves. Thus, simultane-
ously with the movement of the storm-centre the whole pertubation-area in lower latitudes will move in
the same direction. As it appears from the character of the curves that the acting current-systems must
come near to the polar stations, while they must be comparatively distant from the stations in lower
latitudes, and also on account of the evident connection existing between the pertubations in high and
low latitudes, we have considered ourselves justified in drawing the following conclusion :

During the negative polar storms, a current-system of some kind or other will be formed in the
pi'lar regions, the magnetic effects of which will be the primary cause of the perturbation-area formed.

According to this, the magnetic pertubing forces in low latitudes must be considered for the most
part as very distant effects of this polar system of precipitation. The direct magnetic effect of this system
then, we believe would be the primary. There might moreover be imagined a number of secondary
effects, such as, in the first place, induced earth-currents, in the next, electric currents in the atmosphere
occasioned secondarily by the ionisation which, especially in the upper strata of the atmosphere, must be
thereby occasioned simultaneously.

The question which next comes up is: How must this polar current-system be supposed to be
constituted? Here too, we believe the cause should be sought in corpuscular rays coming from the sun.
These rays, when the}' come under the influence of the magnetic field of the earth, will be drawn in in
zones round the magnetic axis. A single ray, considered by itself, will, if not under the influence of other
corpuscles, move in a spiral path in towards the earth, then turn, and leave the place in a similar
manner. We must thus imagine the corpuscular current as a whole, descending towards the earth in
paths that are more or less vertical, then turning when near the earth, and once more leaving it, unless
they are absorbed in the earth's atmosphere. How the rays, as a whole, will behave in the vicinity of
the earth, is a question that cannot be decided in advance. It is a problem that requires special treat-
ment. We have succeded in throwing much light upon the question by placing screens of various sizes
and shapes upon our terrella. These, when the terrella is irradiated with cathode rays, will cast shadows,
and from these shadows the course that the rays take near the earth can be directly measured. The
experiments will be described in Chapter IV of the present Part. The simplest assumption we can make
on the whole is that the rays in the vicinity of the earth turn round in an easterly or westerly direction.
The conditions round the auroral zone also show that during the negative polar storms, there are effects
like those of a horizontal electric current situated at a certain height above the earth.

Upon this basis, we have tried to find out how near we are to the actual circumstances when we
assume that the polar current-system that is formed during a negative polar storm, can be replaced by
a current-system consisting of two vertical infinite branches, which are connected by a horizontal piece
of current. In Article 36 (pp. 102 & 103), we have made an estimate of how the horizontal forces vary
when we move from the storm-centre outwards along the transverse axis of the system. This showed
that as regards the horizontal forces, in the principal features even a quantitative agreement could be
reached between the observed forces and those calculated as the effect of this ideal system. In the pre-
ceding Article, we have also made a minute calculation of the magnetic effects of such current-systems.
A direct comparison of these areas with the observed pertubation-areas of the negative polar storms,
show the close agreement that exists here. In fig. 186, for the sake of distinctness, we have placed a
pertubation-area observed in one of the most characteristic elementary negative polar-storms in our
material, by the side of that of such a linear current-system. In the horizontal forces, the resemblance,
as we see, is striking. In the vertical intensity, the direction is also the same, but the observed forces

444 HIKKKLAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

are at a certain place, Val Joyeux, considerably smaller than the calculated. The cause of this should,
we believe, be sought for principally in two circumstances. The first of these is that in our current-
system the horizontal portion of current may be more conspicuous than in reality it is. If a rather
different form of this had been chosen, e. g. if it had been assumed that the rays were more as if they
ran in towards the earth in a point, as shown diagrammaticaly in the figure 187, the agreement would
probably have been closer also as regards the vertical intensity. A system of this form would also probably
be more in accordance with the actual current-system. As, however, it is a question of a very rough
estimate, and the calculation of the first is considerably easier, we have employed this form.

In the second place, a no inconsiderable part of the perturbing forces observed will certainly be
due to earth-currents. These, as every one is aware, will, when they have the effect of increasing
the horizontal forces due to an external current-system, have the effect of decreasing the vertical
component. The magnitude of the vertical intensity has been employed, ever since Gauss's time, tor
the purpose of determining how great a part of the magnetic effects observed must be ascribed to exter-
nal forces, and how great a part to internal. In the chapter on earth-currents we shall look more closely
into this proportion as regards the magnetic storms. We must, however, expressly draw attention to the
great uncertainty that attaches to the determination of the perturbing force in the vertical intensity. We
may, for instance, refer to Chart III for the storm of the I5th February, 1903. Here, while at lYdr
there is a comparatively powerful vertical arrow, at the surrounding places, Val Joyeux, Wilhelmshaven
and Munich they are too small to be measured. The values of Pe, therefore, when small, must IK
considered as only approximately correct.

There is another circumstance that we may point out. In the negative polar storms about mid-
night, Greenwich time, the horizontal portion of current will as a rule fall between Axeleen and Kaa-
fjord, that is to say north of the latter station. In the most powerful storm we have studied, however,
namely that of the 3ist October and ist November, 1902, the current seems to have moved to the south
of this station, as there are now positive deflections in vertical intensity. In lower latitudes, at Wil-
helmshaven and Pola, we also find at the same time positive perturbing forces in the vertical intensity,
which however, we think should be considered as the effects of the negative equatorial storm, of which
there are also distinct effects.

The third of the principal forms of magnetic storms, is the positive polar storm, of which the follow-
ing are the chief peculiarities :

The form of the perturbation-area is on the whole the same as that of the negative polar storms;
but all the forces in that area, both horizontal and vertical, are in the opposite direction. In the polar
regions, in this type of perturbation, there are positive deflections in the horizontal intensity. We have
here employed the same terms as in the negative polar storms — storm-centre, principal axis, transverse
axis, and points of convergence and divergence. Whereas in the negative polar storms we found the
system's area of convergence to the south of the storm-centre when considering the conditions in the
northern hemisphere, in the positive storms we find the system's area of divergence in that region. As
a rule, the perturbing forces in the positive polar storms diminish just as rapidly in strength as those in
the negative polar storms; and we find here too a reversal in direction of the horizontal component <>t
the perturbing force at about the same distance from the storm-centre as in the negative polar storms.
Not infrequently, however, we meet with cases in which there are positive deflections comparatively far south.

In the matter of strength, the positive polar storms are as a rule somewhat weaker than the nega-
tive, and the character of the curves in the polar regions is not quite so disturbed in the former type
of perturbation as in the latter. The field of a positive polar storm appears most distinctly in fig. 34,
Chart IV for the gth December. In fig. 83 — charts for the 151)1 February, 1903 the form of the field

PART II. POLAR MAGNETIC PHENOMENA AND TERRELI.A EXPERIMENTS. CHAP. II. 445

of force also comes out quite distinctly. At Uccle, for instance, is seen the powerful positive vertical
component that is characteristic of the area of divergence.

It will be seen that the positive polar storms may be explained as effects of a current-system of
the same form as that which we assumed as the cause of the negative polar storms, if we assume that
the current flows in the opposite direction. In tig. 50, p. 105, we have given a diagrammatic representation
of a system of rays, of which the effect in the main will be equivalent to the current-system that we have
employed, and which possibly, on the whole, will be more like the actual positive polar current-system.

These two principal systems, the negative and the positive polar perturbation systems, rarely occur
quite alone. As a rule they occur simultaneously, but in different districts. It appears that they always,
on the whole, are grouped in the same manner in relation to the sun, and in the following manner:

On the morning and night sides of the globe, there is always a powerful, negative polar system
of precipitation, generally fairly extensive, in which the principal axis of the system falls, as a rule along
the auroral zone. This negative system continues westwards on to the afternoon side, but here the
principal axis of the system turns northwards to the districts north of the auroral zone, and it looks as
if the system also as a rule would be continued westwards until it joined the negative system on the
morning side. What the form as a whole, of the system of precipitation would be, cannot, however, be
determined; but it is conceivable that it is more or less analogous to the spiral luminous figures that are
reproduced in fig. 140 on p. 327. The positive polar system developes along the auroral zone, most
strongly in the southern part of the zone. It may sometimes be of very considerable extent, but as a
rule is much smaller than the negative system. In this way there will be a boundary-station in the
auroral zone, as a rule upon the evening side, which will be situated between the positive and negative
systems. Thus, while at the stations on the afternoon side in the auroral zone, the positive storm Is
the principal phenomenon, and on the night side the negative, and the perturbations here occur with
great distinctness and with well-defined deflections in a positive or negative direction, as the case may
be, at this boundary-station now one system, now the other, will prevail, causing the deflections in hori-
zontal intensity to be at one time positive, at another negative.

We have a very clear example of this circumstance in the perturbation of the i5th January, 1883
(Chart V, p. 336).

While in the district to the west of Little Karmakul, i. e. at Bossekop, etc., effects of a positive
polar storm are apparent all the time, and to the east, at Ssagastyr and Uglaamie the effects are ex-
clusively those of a negative polar storm, the current-arrow here oscillates backwards and forwards, is
at first, i8h 25m, very small, but increases rapidly with direction easterly, I9h 5m, then turns, and at the
last point of time, I9h 25™, is a powerful westward-pointing current-arrow.

At a station situated on the afternoon side a little north of the auroral zone, the northern negative
system and the southern positive system will counteract one another horizontally, but co-operate in
vertical intensity. Powerful perturbing forces, therefore, are very often found in vertical intensity. The
current-arrows for the horizontal perturbing forces there now point in one direction, now in another,
and are sometimes exceedingly small. In Jan Mayen, we constantly find this condition very marked (see
Charts V— VII for the I5th January, 1883, pp. 336 & 337; Charts V— X for the isth July, 1883, pp.
381—383; Charts V— VII for the 15* October, 1882, pp. 421 & 422).

This division of the negative and positive systems of precipitation will always appear in a more or
less complete form whenever polar storms occur.

This area of perturbation will thus, as a whole, be moved westwards in the course of the pertur-
bation, in a manner such as would be found if the systems of precipitation formed systems closely con-
nected with the sun.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903. 57

_j_j_6 BIKKKI.AM). Till: M IRWKC.I A N ACROKA POLARIS FXri'DITIOX, I QO2 1903.

In detail, however, we shall he able to find the perturbation-conditions somewhat different from
those we have here described as the tvpical. The forces will alwavs, as already stated, in the extended
negative area of precipitation, concentrate themselves about one or several storm-centres. At the same
time, the negative svstems that occur at the other places will more or less disappear. Frequently there
is a single, comparativelv verv limited, negative svstem of precipitation, while the rest of the negative
current-circuit has practically disappeared. This has verv often proved to be the case at about (ireemvich
midnight. At about this hour, we very frequently find a powerful, well-defined and comparatively very limited,
negative system in the north of Kurope, while at other places round the arctic /one, no negative systems
of precipitation are apparent, as far as we can see from our observation-material. For this reason the
storms that occur at this time exhibit particularly simple areas of perturbation. It is the simplest of these
that we have taken first, and therein' found the elementary type of negative polar storm.

With regard to the movement of the systems, it should be observed that it is only in its main
features that this takes place as stated above, differences being very frequently found in the details. We
have, for instance, just mentioned an example of the movement of an elementary negative polar system
eastwards along the auroral xone, simultaneously with the development of the storm. The cause of this
is, we believe, in a great measure to be found in the fact that the height of the sun above the magnetic
equator varies. In tig. 76 we have shown a curve that, according to Stormer's calculations, gives the con-
nection between the height of the centre of emanation above the magnetic equatorial plane, and the
deflection undergone bv the rav that goes to the origin, when we consider an elementary magnet
situated in that point, with its axis along the /f-axis, \Ve have thought that a similar connection must
exist between the height of the sun above the earth's magnetic equator and the position of the various
storm-centres, and that when this height of the sun alters, the various perturbation-centres will be moved
similarly to these "distinguished" rays in the calculations. These rays, however, will move now towards
the east, now towards the west, according as the height of the sun changes (see fig. 76 cS: Article 71).
\\V should therefore also expect to find similar conditions at the storm-centres. The finding of deviations
from the regular moving of the perturbation-systems towards the west, is thus only a conceivable con-
sequence of our theory. In the first storm in Part 11 (Article 83), we have made a comparison between
the positions of the storm-centres observed and the calculated areas of precipitation at the various times,
and their movement from time to time. We think, too, that we have found in some cases verv distinct
analogies, although of course there will be no question of any exact agreement.

In Chapter I of Part II, we have principally studied the occurence and development of the various
polar systems. In all the perturbations, we have not only again and again found the characteristic con-
ditions that are touched upon here, but a number of details have also appeared that are constantly found
in storms of most varied character. The manner in which the polar systems break in upon one another is
always exceedingly characteristic. We recall, for instance, the relation between the effects of the positive and
negative storms at Cape Thordsen in the afternoon. If we compare the afternoon storms at this station
on the i 5th and 2nd January, 1883, and the first November 1882 (see PI. XXY1, XXV cV XXIII), we find,
as proved in detail in our previous description of the storm of the 15th January, a negative storm from
1 2'' to i _).'', breaking in upon a positive storm of long duration. On January 2nd there is a similar
phenomenon from 14'' to 16'', but the positive storm is much less pronounced. On the ist November
also, there is a corresponding phenomenon from 13'' 30™ to i6h, but here the effects of the positive
storm have almost entirely disappeared. A slight indication of a similar circumstance is also met with
in the storm of the i st February, 1883. It would take too long, however, to go more minutely into
these matters here, and we will therefore only refer the reader to the description of two storms in which
the characteristic conditions are especially conspicuous. These are the perturbations of the 151!! January
and the 1 51)1 July, 1883, in which the perturbation-conditions are perhaps most easily surveyed.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. II. 447

A positive polar storm in the auroral zone will, as we have said, always, or at any rate generally,
be accompanied by a negative polar storm in rather higher latitudes. Some such idea as the following
might then seem probable as the explanation of this circumstance:

We know, according to the theory, that corpuscular rays that move in the earth's magnetic field
will approach the polar regions in paths that twist spirally about the magnetic lines of force. If
the rays possess great magnetic stiffness, the radius of these spirals will be comparatively great. If we
assume that such ray-spirals exist on the afternoon side of the earth, and that they lie close
together somewhat in the manner shown in fig. 188, the connection with the southern positive system
and the northern negative system, as regards the polar regions, can be ex-
plained quite simply. For rays of a stiffness answering to HQ = 7 X Io6> we
find in the polar regions, where //= about 0,5, Q = 1,4 X io7cm. The dia-
meter of these spirals must then be 280 km. The principal features of the
field in southern latitudes can probably also be brought out as effects of a

Fig. 1 88.

spiral system such as this. Judging from our experiments, of which the results

are clear enough, an explanation such as this, is not entirely satisfactory, and would at any rate have to
be considerably modified. According to those experiments, the rays in the positive and negative storm-
centres seem inclined to behave in a manner similar to that shown diagrammatically in fig. 50. The
above explanation cannot, at any rate, be applied to the night storms, in which there is only a negative
storm in the south.

We thought of showing two more types of perturbations, namely, the negative equatorial storm and
the cyclo-median storm. We have, however, only a few examples of these among our observations.

The negative equatorial storms are most powerful in the region of the equator, where the per-
turbing forces in horizontal intensity are negative. Their area of perturbation may be explained as the effect
of a current-system of which the greater part is situated more or less in the magnetic equator, as the
experiment shown in fig. 37 shows, and where the rays have a movement similar to those that are
calculated in the magnetic equatorial plane for an elementary magnet answering to values of y that are
- i (see fig. 39, p. 82). In order that these rays shall come comparatively near to the earth, their
stiffness must be comparatively great. More flexible rays would be deflected like the rays in the equa-
torial plane for y~^> — i, and thus glance by the other in the opposite direction. We believe we have
effects of rays such as these in the positive equatorial storms. The rays that we believe should produce
the negative equatorial storms must therefore be assumed to go round the earth and to be magnetically
more inflexible than those that produce the positive equatorial storms. In accordance with this, it is only
during very powerful storms that we have found these negative perturbation-areas. The fact that the
active rays during specially powerful perturbations have a greater magnetic stiffness than those in the
less powerful storms, is also indicated by the circumstance that has just been touched upon, namely, that
the storm-centres during the latter seem to move southwards. In particularly violent magnetic storms,
it is well known that the auroral zone moves southwards, so that polar aurora can be observed even in
very low latitudes. The simultaneously-occurring magnetic storms have also, in lower latitudes, a completely
polar character, which indicates that the acting current-systems come in to the immediate vicinity of the
place. But if the corpuscular rays come in towards the earth in such low latitudes, their stiffness must be
considerable. These circumstances will be explained fully in Chapter IV. The forces that occur in the
negative equatorial storms are also considerable greater than those found in the positive. Among our
observations, we have found only examples of negative equatorial storms, which occur simultaneously with
polar storms, and it is perhaps doubtful whether this type of perturbation on the whole can occur alone.
We have not sufficient material, however, for the formation of any well-founded opinion on the matter.

448 BIRKELAND. THE NORWEGIAN AURORA I'OLARIS EXPEDITION, 1QO2 — 1903.

We find the perturbation-areas in which the negative equatorial storm is most distinctly apparent,
during the perturbation of the 313! October, 1902, and the 8th February, 1903 (see figs. 107 — 116, with
description in Art. 66 & 67; and figs. 87 & 88, with description on p. 189). In the latter case, however,
we have suggested, at the foot of p. 189, another possible interpretation of the field.

The last cyclo-median type of perturbation, we have supposed would answer to effects of rays of a
degree of stiffness answering to the experiments shown in figs. 66 & 68, i— 6. How the rays in these
triangular figures move, is indicated in the lowest of the three figures 71, and in fig. 72. These should
be rays that came comparatively near the earth in lower latitudes, and which formed fields similar in
form to these figures, that is to say spirals in which the direction of the current-arrows was anti-clock-
wise. We find similar spiral fields in the areas of convergence in the negative polar storms. In the
cyclo-median storms, however, the forces in low latitudes must be more powerful in comparison with the
forces in the polar regions, than in the negative polar storms. We have only a few instances of such
perturbation-fields that can be characterised as rather well defined. We believe the perturbation of the
6th October is a storm of which the field of force should be explained as the effect of such a cyclo-
median system. In our discussion of the compound perturbations, we have also several times come across
fields that would naturally be due to cyclo-median systems, but in which nothing certain could be decided,
owing to the complicated character of the storm. Fields of this kind are to be found in figs. 78 and 79,
for the 25th December, 1902, and figs. 87 and 88, for the 8th February, 1903.

These five types of perturbation, however, as the above shows, must not be considered as com-
pletely separate phenomena. There will be a genetic connection between them, and this frequently finds
expression in the fact that when there are simultaneous effects of several systems, a change in one system
will be accompanied by a change in the other. This is especially distinct in simultaneous positive and
negative polar storms, but is also very prominent in simultaneous positive equatorial and polar storms.

For all the perturbation-areas we have studied, a natural and simple explanation of the main features
has been found by the aid of these five types of perturbation. In addition to the direct magnetic effect
of these corpuscular systems, there will also be effects of simultaneously-occurring earth-currents, and
possible atmospheric ionic currents and secondary cathode rays. There seems to be no doubt that the
first of these exert a considerable influence, and we shall study them more closely in a later chapter;
but what effect the atmospheric currents might have is a rather more doubtful question.

In Chapter IV of Part I, an estimate is made of the intensity of the corpuscular currents that appear
in the polar storms, and the amount of energy they carry. The making of such an estimate has been
made possible by the fact that we have two stations, Axeloen and Kaafjord situated one on each side of the
auroral zone, and that, as already mentioned, the current-systems form in the auroral zone, that is, between
the two stations. We have assumed that in the simplest perturbations the conditions up there can be
regarded approximately as effects of an infintely long, horizontal rectilinear current, situated between
these two stations. We can then, by the aid of the observations at the two stations, determine both
the strength of such a current, and its height. The question will indeed be over-determined, and we can
thus obtain a kind of idea of the approximation with which an assumption such as this can be employed.
In the simple cases that we have studied, the approximation, as a rule, must be considered as quite satis-
factory. We found the average strength of the current in the storms we investigated to be about io(i
amperes, and the average height about 400 kilometres. If we also used Dyrafjord and Matotchkin Schar,
we sometimes arrived at greater heights, up to more than 1500 kilometres; but we believe these are
probably due to the fact that our assumption in this case does not hold good.

We have further examined into the amount of energy which these current-systems must represent,
and have come, by estimating, to figures such as about 2 X IC)7 h- P-i if we assume that the systems are

PART II. POLAR MAGNETIC PHENOMENA AND TEKKELLA EXPERIMENTS. CHAP. II. 449

formed of ordinary cathode rays, about 5X IoH» if we assume/? rays with a velocity of 2.59 X io'0cm.sec.~'.
It is, however, reasonable to suppose — as we shall show in describing the terella experiments in a sub-
sequent chapter — that the rays in this case are considerably stiffer than these. If we assume a stiffness
10 times as great as the stiffest « rays, or answering to UQ = 7 X IO°> we obtain an amount of energy
of about io1:Jh. p.. From this we have inferred backwards and proved that we come, by assumptions
which are still indeed rather arbitrary, but not unreasonable, to values for the amount of energy emitted
from the surface of the sun in the form of corpuscular rays, that are as great as those of the energy
emitted in the form of light and heat. It does not therefore seem improbable that the disintegration of
the sun's matter which is undoubtedly taking place, and which must be assumed to be the cause of the
corpuscular rays observed, would be great enough to account for the emission of light and heat from the sun.

A POSSIBLE CONNECTION BETWEEN MAGNETIC AND METEOROLOGIC PHENOMENA.

93. If the view we have maintained is correct, namely, that the magnetic storms are due to cor-
puscular rays that are drawn in in zones round the magnetic poles, where they pass directly down into
the athmosphere of the earth, it is clear that these rays, especially in the upper strata of the atmosphere,
must be assumed to produce a strong ionisation in the air. In our expedition of 1902 & 3, atmospheric-
electrical measurements were made, which will be gone into later on ; but it may be remarked here, that
the result of these measurements showed that the "Zerstreuung" of the air at those stations averaged
about twice as much as in Christiania, indicating that the air up there is considerably more ionised than in
lower latitudes. In an expedition which I made, in company with my assistant, Mr. KROGNESS, to Kaafjord
at the time when Halley's comet crossed the sun's disc in May 1910, I had an opportunity of studying
this matter more closely.

Instead of, as before, making the measurements at places that are at no great height above sea-
level, 1 on this occasion investigated it at my old aurora-observatory on the top of Haldde Mountain,
about 910 metres above the sea. Here there proved to be sometimes tremendous variations. On the
2oth May, for instance, values were found that went up to about 500 times the normal. Unfortunately the
attempt was interrupted in the middle of these measurements; but I had an opportunity of making
insulation-tests twice at that time, which proved there was no perceptible leakage. If we can demonstrate
this circumstance with certainty, we presumably have before us a phenomenon that is closely connected
with the peculiar light-phenomena that LEMSTROM discovered in 1882 & 3 on a mountain-top at Sodankyla.

There is no doubt that such strong ionisations will have a very great influence upon atmospheric
conditions, especially upon the formation of clouds, and must thus be assumed to be a meteorological
factor of no small importance, especially for the districts in the vicinity of the auroral zone. I am of
the opinion that this is a very important connecting link between terrestrial-magnetic and meteorological
phenomena. I have therefore recently submitted to the Norwegian State authorities, a suggestion that a
permanent up-to-date-magnetic-meteorological observatory be established upon the top of Haldde, for the
purpose, if possible, of throwing light upon these interesting and meteorologically important matters.

There was another phenomenon, striking examples of which we had the opportunity of seeing on
this expedition in May, 1910, namely, the formation of what may be called auroral clouds. In addition
to the usual polar bands, which in a clear sky, could very often be observed in the form of several
evenly luminous arcs, of which, however one was especially conspicuous, exactly similar to parallel auroral
arcs, we very frequently found formations of cirrus clouds, which exhibited the most perfect argreement
with various auroral formations. Several times we had capital examples of the manner in which such
clouds are formed, how drapery-formations appeared in a short time, exactly in the same manner as an
auroral drapery. The first observer, who has called attention to this very interesting fact seems to be

45° HIKKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

ADAM POULSON('). As far as I know, no one has, however, studied this phenomenon in connection with
simultaneous magnetic registrations at the same place. This we had the opportunity of doing, and
the very interesting fact came out, that the formation of these clouds was always accompanied by
simultaneous magnetic storms and earth-currents; and there thus appears to be no doubt that these are
direct cloud-forming effects of the same rays that occur in the auroral phenomena. From this it seems,
that these cirrus-clouds are directly formed by the corpuscular rays which we suppose to be the cause
of magnetic storms and aurora. The first hypothesis that one naturally might form as to this phenomenon
is, that the clouds are due to water-vapour brought to condensation by the ions formed by the impact of
negative rays. It is however also a probability that some of the observed »auroral clouds« are not real
clouds, but merely a very strong concentration of corpuscular rays, which in the case of darkness might
appear luminous; in the daytime the concentration of corpuscles should have the effect of making the
places where they occur less transparent, and able to diffuse light,- and thus become visible. In such a
way also possibly certain faint polar bands observed in the polar regions might be explained. According
to circumstances these concentrations may disappear or give rise perhaps to real clouds.

(') Met. Zeitschrift 12, 161 (1895).

CHAPTER III.

STATISTICAL TREATMENT OF MAGNETIC DISTURBANCES OBSERVED AT

THE NORWEGIAN STATIONS 1902—1903.

INTRODUCTORY.

94. In the previous treatment of the perturbations given in the first part of this work, each
disturbance has been examined individually. This investigation led us to divide the perturbations into
groups, each of which possessed certain characteristic properties, especially with regard to the distribution
of the perturbation in space relative -to the earth.

In the following we shall proceed to study the variation in the time of the appearance at our four
arctic stations of the magnetic storms occurring during the period of our observations.

In order to solve this problem, it is necessary first to fix the unit by which we are to measure the
»quantity« of perturbation that has occurred during a certain interval of time. One way would be to
count the perturbations, e. g. those which exceeded a certain magnitude. Such a mode of procedure
is often employed to obtain a quantitative measure of phenomena of this kind; but the method is not
very exact, as perturbations count equally, even when their magnitude varies within wide limits. Further
we are met with the difficulty, or rather impossibility, of defining what is meant by one disturbance.

We have therefore decided to follow a more exact method, which can always be applied without
ambiguity. In this method the »quantity« of perturbation is measured by what we shall call storminess,
which is defined as follows :

We assume the perturbing force in any of the magnetic elements H, D or V in the time interval
o <] t <[ T to be found as a function of time. The determination of this function from experiments only
requires the possibility of finding the perturbing force at any moment, which can be done in the way
described in Part I of this work.

By the absolute storminess in one of the components— say the horizontal component— we understand
the quantity :

It is equal to the average perturbing force P,L if the latter is always taken to be positive.
It will also be of interest to consider separately disturbances in the positive and negative direction,
and for this reason we define the positive and negative storminess

T

T

- f
~T I

o
T

P"dt
o

where /J,f is any positive value of P,, in the interval, and P" any negative value. It follows:

niRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 1903.

S I = 9P 4- S1"

H ft \ W

Further we shall introduce a quantity representing the difference between the positive and the

negative storminess

i
1 C

', dt

For Declination and Vertical Intensity similar expressions are defined.

Finally, by the Total storminess in the same interval of time we are to understand the quantity.

ST= i\S

In accordance with the definition of storminess here given the positive and negative storminess
corresponds respectively to a positive and negative direction of the perturbing force.

There are two problems which will be dealt with in the following pages and form the main ol>jm
of our investigation, viz:

(1) The total storminess as a function of time.

(2) The distribution of disturbances in magnitude and direction at the different hours of the day or
the possible diurnal variation of the storminess.

For the practical carrying out of the calculation, the following mode of procedure has been adopted:
The storminess was calculated for each period of two hours, for all three components, and the positive
and negative storminess were taken out separately. The numbers for one day were placed in the same
horizontal line as shown in the first series of tables.

For each five-day period, the mean was taken of all numbers in the vertical columns corresponding
to the same hour-interval. This gave a horizontal line containing the distribution of the storminess at the
various hours for a period of five days. Taking the mean of the positive and negative storminess in
this horizontal line, we obtain the positive and negative storminess S1' and S" for a period of five days,
and their sum (•S'1-)- 5") gives the absolute storminess for the same period.

We think it of considerable importance that a continuous record should be given of the occurrence
of magnetic perturbations during the whole period of observation, believing that such a record will ^iv(
an idea of how far we have succeeded in the first part of this work in treating the most important of the
perturbations.

For our present purpose, however, it is the average values, that mostly concern us; and we have
therefore decided on publishing the following separate tables:

FIRST SERIES.

Tables for the continuous two-hourly records. These tables will be divided into groups of five days,
corresponding to each five-clay period. The numbers will be expressed in arbitrary units, which will
differ for the three components, but will be the same for all four stations. The factors of transformation
into absolute units will be given for each component.

SECOND SERIES.

Tables giving the distribution of storminess at the different hours of the day for each five-day period.
The periods will be divided into groups of 6. The mean value for each vertical column is taken for each
group and placed in a horizontal line, thus giving the distribution of storminess for 30 days, which will
be taken as one month.

Finally, we find the mean distribution for the whole period of our observations. For each station
there will be three tables, one for each component; and the numbers will be expressed in absolute
magnetic units.

PART. II. POLAR MAGNETIC PHENOMENA AND TERRE1.LA EXPERIMENTS. CHAP. Ill 453

THIRD SERIES.

Tables giving the record of storminess for each live-day period. There will be one table for each
station, containing the positive, negative and absolute storminess for each component, and one column
containing the total storminess. The numbers will be expressed in absolute units.

The method of calculating the storminess is very much the same as that employed for calculating
the perturbing force. The "normal line" is drawn on the magnetogram in the way described. During
the perturbations a number of areas are formed by the registred curve and the normal line. The areas
on both sides of the latter are taken out for each interval of two hours, and from them, knowing the
scale value and the length of the interval, we can find the positive and negative storminess. The relative
values given in the first series of tables are simply these areas given in centimetres and reduced to the
same sensitiveness for all four stations.

In taking out average values, it is necessary, as we know, to have a value for every two-hour
interval throughout the period. It will unavoidably happen that in some records short intervals of time
may be missing, but the blank interval due to the change of paper on the cylinder will generally be so
short that it will practically introduce no error; for the intermediate values can be found by connecting
harmoniously the two ends of the curve. If during a perturbation, the curve is invisible for a short
interval of time, we have employed the same method of completing the curve by harmoniously connecting
the two parts.

In the curves it has occasionally happened that records were wanting for several hours. If
considerable disturbances were occurring at the other stations during these intervals, we should have
to omit the whole five-day period; but as a rule we have been able to estimate thestorminess for the
blank intervals.

Values which are not found directly from the curves, and consequently cannot claim great accuracy,
will be put in brackets. These values may be found in various ways e. g. by completing the curve
for a short blank interval or by estimating the value from the curves of the other components at the
same place or from the curves of the neighbouring stations.

During such investigations it became clear that the great storms did not show the same properties as
the small ones with respect to distribution in space and time. It was therefore of interest to find the
average properties of the great storms separately.

The classification of the storms into great and small is of course to a certain extent quite arbitrary.
We have decided on the following procedure : To find the storminess of great storms, we take
that of every two-hour period for which the positive or negative storminess is greater than 15 y in any
of the components. If the condition for a great storm is fulfilled for a certain two-hour period in one
component, the corresponding storminess is counted in the case of the other components even when it
is less than 157.

Hirkeland. The Norwegian Aurora Polaris Expedition, 1902—1903. 58

454

HIRKELAND. THE NORWEGIAN AURORA 1'OLARIS EXPEDITION, 1902 — 1903.

FIRST SERIES.
RECORDS OF STORMINESS FOR EACH TWO-HOUR PERIOD.

The storminess in absolute units is found in the following way:

SH = 14-9 FH (in y). Si> = 9.17 FD (in y). Sv = 17.5 FY (in y).

Fa is the number given in the table for the storminess in the horizontal intensity.

FD — »— declination.

/•"V — >— vertical intensity.

The columns with the heading -|- contain positive storminess.

negative — » —

Matotchkin Schar.

TABLE LXIV.
Disturbances in Horizontal Force (/"//).

Gr. M.-T. 0-2

il

2-4

4-6 6-8

8—io

IO— 12

12 — 14

14 — 16

16-18

18 — 20

20 — 22 22 — 24

Date

r

—

+

_

•4-

_

4-

—

+

_

4

—

+

—

+

_

+

_

4-

—

+

—

+

_

October 3

0

O.I

o

O.I

(0.1)

(0.1)

0.1

o

O.I O

o-3

o

o

0

o

o.3

O.I

o

0

o.a

0

0.8

o

0.6

4
5
6

0
0

o

06

o.a
o

o

0.2

o

0.2

O.I
0

o

0-5
o

0.4

O.I
O.I

o

0.!
O.I

o.a
o
o

O.I

o

0

O.I
O.I

o

0.7

o.a
o

o
o

O.I

0.6
o
o.a

o
o
o

o.a
o
o.a

o

0

o

o

0

o

o

0

o

o

O.I

o

o

0

o

0

o
o

0.4
0.4

O.I

0

o
o

0.4

0

03

7

o

o

o

o

o

o

o

o

o

o

o

0

o

0

0

o

o

0

0

o

0 0

o

0.7

8

o

0

0

O.I

o

o

o

o

o

o

O.2

o

O.I

o

o

O.I

O.I

o

0.3

0.3

o

0.3

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9

o

O.I

o

o

0

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O.I

O.I

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2.1

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0.4

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2.3

2.0

0.5

6-5

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17.0

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6.7

12

1-4

0.3

0.7

0

0

0

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O.I

O.I

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O. I O. I

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0

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0

13

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0.6

o-3

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8.5

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i.5

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14 jl o

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0

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18

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0.2

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0

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O.2

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0

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0

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3.4

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0.8

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0.4

19

20

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1.0

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0

0.7

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O.I

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0

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0
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0
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0

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0

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21

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0

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O.I

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0.8

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01

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0.8

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22

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O.2

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0.2

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0

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23

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0

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0.2

2.4

24

0.9

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(0.4)

(O.I)

(0.3)

o

o

o

0

o

O.I

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03

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1.8

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0.7

1.4

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14-5

o

15-5

25

o

8.3

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1.5

o

o-4

o

o.a

0.4

o

i-3

o

2.0

o

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0-3

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0.6

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0.7

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1.9

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26

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0

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0

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0.8

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0.4

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0-5

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0.8

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4.0

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0.5

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5-5

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6.3

29

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0.2

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0

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0.3

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9.8

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8.9

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9.6

3°

0.4

o

0.2

o

O.I

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o

0.4

3-3

o

a.o

0.4

0

I.O

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0.4

o

0.5

o

3.3

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2.0

31

0

1.2

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0.5

O.I

i-3

1.4

0.2

5-2

0

la-5

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7.0

i-3

5-2

0.4

0.3

6.7

0

16.5

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16.0

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20.0

November i

0

7.0

0.4

0.9

1.5

o

0.9

O.I

1.4

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0.3

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O.I

o

o

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0.1

O.I

o

o

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0.6

O.I

o

2

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0

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O.I

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o.a

0

O.I

o

o.a

O.I

O.3

0.4

J -9

o

9-5

o

3-4

O.I

0.2

3

o

0-3

0

o

0

o

o

o

o

O.I

o

0

o

o

O.I

o

0.3

o

O.I

o

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0.6

0

O.I

4

(o)

(6.1)

(o)

(0)

(o)

(o)

(o)

(o)

(o)

(O.I)

(o)

(o)

(o)

(o)

(o)

(o)

(0.3)

(0.6)

(o)

(4-0)

(o)

(a.o)

101

(0.1

5
6

(o)
o

(O.I)

o

(o)

0

(o)
o

(o)

0

(o)
o

(o)

0

(0)

o

o
o

o
o

o

0

o
o

o
o

0

o

o

o

o

0

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o.S

0

o.S

O.I

o

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6-3

o

o

o

3-8

0

o

0
0.1

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELI.A EXPERIMENTS. CHAP. III. 455

TABLE LXIV (continued). FH Matotchkin Schar.

GD^T- °-* ""* <-6 6-8

8—io

IO— 12

12— 14

14 — 16 16— 18

18 — 20

ao — 22

22 — 24

+

—

+

—

-f

—

4-

_

4-

—

+

—

+

_

•f

4-

_

+

_

+

+

November 7

0.4

O.I

0-5

o

(o)

(o)

o

0

o

o

O.I

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o

o

o

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0

8

0

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0 0

O.I

o

0.3

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0

9

10. I I

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(o)

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O.I

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1-3

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1-9

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(o)

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(o)

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(ol

(0) 10) (0) (0)

(0)

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20

(o)

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(0)

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19.5

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23
24

5.0
15.0

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0.3

o

0.2

9

o

0

o

0

o

o

0-4

o o.a

o

O.I

o

O.I

0

0.3 o

1.2

0.9

0.8

o

0.3

O.I

o

O.I

10

o

O.I

O.I

o-3

0.3

O.I

0

o

o

0.2

0.6

O.I

0.6

o

0 0

o

O.I

O.I

0-7

O.I

0.7

o

0.4

it

o

o

0

O.I

o

o

0

o

o

o

o

O.I

O.I

o

O.I

o

1.4

o

0.4

o.3

O.I

1.9

o

2-3

12

o

O.I

O.I

o

o

o

o

o

O.I

0

o

o

o

o

O.I

0

0.5

o

(O.I)

0-5

(o)

d.6)

(o)

(2.01

'3

o

0.3

o

O.I

0 0

O ° 0

0

0

o.a

o

o

o

o

0.2

O.I

0.2

0

o

1.7

o

0.5

14

O.I

o

0

o.a

0 0

o o o o o

0 0

o

o

0

o.a

0

O.I

0

o

o

o

O.I

15

o

0.8

O.I

O.I

o

o

o o o o o

0

o

0

0 0

0 0

o.a 1.9

o.a

0.3

o

0

16

o

o

0

o

o

o

0

o

o

o

o

O.I

(o)

(o)

(o)

(o)

(o.a)

(o)

(O.I)

(ol

(o)

(1.5)

(o)

(0.5 1

17

(o)

(o)

(o)

(o)

(o) (o)

(0)

(o)

O O.I

o

o

o

o

o

o

o

o

(0)

(0.3)

o

0.4

o

o

18

0

o

o

o

o

0

0

o o o

o

o

0

0

o

o

o

0

o

o

o

O

o

0.4

19

0

0.2

o

0

o

O.I

o

o

o

o

0

0.2

o

0-4

o

O.I

0.3

O.I

o

I.I

o

'•9

o

O.I

20

o

o

o

0

0

o

o

o

o

o

o

o

o

o

o.a

O.I

o

O.I

o

o

o

0

o

o

21

0 , 0

o

0

o

o

o

o

o

o

0

o

o

o

o

o

o.a

o

o.a

0

O.I

o

o

o

22

o

o

o

0

0

o

o

o

o

o

O.I

o.a

0

o-3

o

O.I

°-3

o

0.2

o.a

o

4.7

o

9.0

23

o

6-5

o.5

2.5

0.3

0.5

0.2

o.a

3-5

o

3.6

o

7.3

o

5-3

o

I.I

a-3

o

'3-3

o

8.1

0.3

O.I

24

O.I

0.2

O.I

0.3

O.I

o

(o)

(o)

(o) (o)

(O.I)

(0:1)

(o)

(O.I

(o.a)

(o)

(0.4)

O.I)

(O.I)

i-5

(0)

(3.5)

(o)

(0.5)

25

(o)

(0.2)

(o)

(0.2)

(o) (o)

o

o

O O.I

o

0.4

o

O.2

o

O.I

O.I

O.I

o

a. i

o

0-4

o

0.9

26

O.I O.I

o

O.I 0 0

o

o

0 0

o.a

0 I

O.2

0

O.I

O.I

o

O.I

o i 0.7

o

3.8

o

2-3

456 H1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE LXIV (continued). F,, Matotdikin Schar.

Cr. M.-T. 0-2

II

2-4

4-6

6-8

8 — io

IO — 12

12 — 14

14—16

16-18

18-20

20 — 22

^^==:

+ !

0 2.0

22-

4
o

24

=

4.2

Date
December 27

+
o

O.I

+
o

O.2

+

o

o

+

o

O.I

+

0

O.I

+

0

0

4-

0. 1

o

+

o

o

+

O.3

0

-t-

0. 1

0.1

aS

o

1.4

O.2

o

0.2

0.2

O.I

0.2

0

0.6

O.I

0.2

o.a

O.I

03

o ; 0.3

O.I

o

o.i o j 0.7

0

O.I

29

o

0

0.4

o

0.4

o

0

O.I

o

o

0

0

o

o

o

O 0.2

O.I

O.I

0.2 O 0.3

0

0

3°

o

o

0.2

o

o

o

0

o

o

O.I

o

0.2

o

0

o

o | 0.5

o

o.a

O O.2 O

0

0.1

3i

o

o

0

o

o

o

o

o

o

o

0

0

0

0

o

o 0.2

0

O.I

0

0

o

o

O.I

January I

0

o

o

o

o

0

0

0

o

o

o

o

o

O.I

o

0 0

O.2

o

o

0

0

0

0.4

a

o

0.2

0

0

o

o

0

o

o

o

o.a

0

o.a

0

o

0 0

o

o

o

o

0

o

0.2

3

0

0

o

o

o

o

0

o

0

0

o

o

o

0

o

o o.a

o

0.4

O.3

0.3

0.2

o.a

o

4

o

O.I

o

o.3

o

O.I

O.I

0.2

0.3

0

O.I

o

o

o

0

O O.I

O.I

1.9

o

0

0.4

o

0.8

5

o

0.2

0-4

o

0.4

o

o

0.2

O.2

0 2

O.I

o.a

o.a

O.I

1.2

O O.2

4.8

o

1.2

o

1.6

0

o-5

6

o

0

o

O.2

o

0

0

o

o

o

o

o

o

o.a

o

0.3 0.2

o

0.3 0.2

o

1.8

0

0.2

7

o

o

o

0

o

o

O O.I

o

o

o

o.a

0

0.4

O . O. I O.I

O.I

O.I 0.3

o

o

o

o

8

o

o

o

o

o

O.I

o o

O.I

o

0.3

o

O.I

o

0.5

o 1.5

0

o 05

o

2.1

o

0.2

9

o

0

o

o

o

O.I

o

0.2

o

0

o

o

O.I

o

O.I

o , i.a

o

O.I

0 2

o

0.6

0

2.1

10

O.I

0.5

O.I

o

(o)

(o)

(o)

(O.I)

o

(o)

o

o

O.I

O.I

2.8

o 1.4

o

O.I

O.I

0

0.9

0

'•7

ii

o

0.4

o

°-3

O.I

o

o

o

o

o

o

0

O.I

o

0-3

o 0.3

o

0.6 i.i

O.I

I.O

0

°-7

12

o

o-3

O.I O

0

o

o

o

0

0

o

O.I

O.I

o

0.4

o 0.3

o

o i.a

o

0

0

0.6

13

o.r

°-3

O.2

0

o

o

O.I

o

o

0

o

o

o

o

o

o 0.8

o

°-7 1.3

O.I

0.6

o

0.3

'4

o

o

o

o

o

o

O.I

o

0

o

o

0

o

o

o

o

o

o

O 0

o

0.1

0

i.a

15

o

O.I

o

0

o

0

0

O.I

o

O.I

o

o

0

O.I

O.I

o

O.I

o

0 0.2

0

O.I

0

0

16

(o)

(0.1)

(o)

(O.I)

(o)

(o)

o

o

o

0.3

O.I

0

2.5

0

°.3

O.I

i-5

o

°-3 0.3

0

I.O

0

I.O

17

o

°-3

o

O.I

0

o

(o)

(o)

(o)

(O.I)

o

O.I

o

0.3

0

0.2

o

o

0 02

0

0.2

o

0.1

18

o

o

O.I

0

(o)

(01

(o)

(o)

(o)

(o)

0

0

o

O.I

2.0

O.I

2.3

0

1.2 0

0.5

o

o

O.I

>9

o

O.I

o

0.2

o

o

0

o

o

O.I

0

0.4

0.4

o

0.6

o.r

1.4

O.I

O.I O.I

0

I.O

lol

(0.31

20

(o)

(O.I)

(0)

(O.I)

(o)

(0)

0

O.I

O.I

o

o

O.I

o

O.I

o

02

o

0

O.I

o

o.3

O.I

0

0

21

0

0

o

o

o

o.a

o

O.I

o

o

o

o

0

0.4

O.I

O.I

o

o

(0.1)

(0.2)

0

0.8

0

2.2

22

0

I.O

O.I

o

o

0

0

o

o

o

o

0

o

O.I

o

O.I

o

O.I

o.i o.a

o

o

0

0.1

23

o

0

0

0

o

o

o

0

0

o

0.3

o

O.I

0

0-5

o

i.a

0.2

0-3 38

o

5-3

O.I

0.2

=4

o

o

O.I

0.2

O.2

o

o

O.2 o

o.a

o

0

o

O.I

0

0.2

0.6

0

O.I

0.6

o

0.6

o

0.7

25

(o)

(o)

(o)

(o)

(o)

(o)

(o)

(O.I)

o

O.I

0

0.2

o

O.I

o

O.2

o.a

O.I

o

o

o

o

o

0

26

0

0

0

0

o

0

o

o

o

o

O.I

o

0.5

o

O.I

o

o

(0.5)

0

26.5)

o 26.6

o

40.0

27
28

o
o

22.1
0.2

O.I

o

2.4

0.2

0.9

0

I.I
o

0.7

o

0.2

o

0.4

o

O.I

o

O.I
O.I

0.2

o

o
o

O.I
O.2

O.I
0

o

0

0.3

I.O

o
o

O.I

0.6

0.6

0.2

o 1.5

o 0.8

0
0

1.6

0

29

o

O.I

0

O.I

o

o

0

o

o

o

O.I

o

o.a

o

O.I

O.I

o

0

o o

o

o

0

0

30

O.I

o

O.I

o

O.I

o

o

O.I

O.I

o.a

0.9

0

2.9

o

3-4

o

5-o

o

2.1

0

0.3

0.1

0

0

3'

o

°-3

O.I

o

O.I

o

o

o

o

o

o

p

o

o

I.I

o

1.7

o

0.6

o

o

o

0

o

February i

o

o

o

o

0

o

o

o

o

0

0

o

o

o

o

o

0.6 o

1.0

o

O.I

0

0

0

2

o

O.I

o

o

0

o

o

o

o

o

0

O.I

o

O.I

o

o

o

o

0.2

0

0.2

0

0

0

3

o

o

o

o

O.2

o

o

o

o

o

o.i I o o.a

o

0

o

o

o

o

0

0 0

0

o

4

o

o

(o)

(o)

(O.I)

(o)

(o)

(o)

(o)

(o)

(o)

(0) (0)

(o)

(o)

(o)

(0.5)

(o)

(0.5)

(0)

(O.It (0)

(o)

101

5

0

o

O.I

O.I

o

o

0

o

o

o

O.I

0 0.2

0

0.4

o

1.2

o

0.6

0

o 0.3

o

0.1

6

o

0

0

o

O.I

O.I

O.I

o

o

o

o

o o

o.a

(0.2)

(o)

(0.5)

(o)

(0.4)

(o)

o

o

o

o

7

o

0

o

O.I

o

o

o

0

0

o

o

0 0.2

0

O.I

0

0.7

o

O.I

0 0

4.7

o

9.4

8
9

O.I

o

0.4

0.8

0.1
O.I

0.6
°-5

0.3

O.I

°-5
0.4

0.2
0.2

0.5

O.I

0.5

O.2

0
0

o

O.I

0

o

0.2
O.I

0

o

4.0

0

o
o

4.8

0.3

o
o

°-3
o.a

"•3

0.3

o

0

14.8
4.0

0.2

o

0.8

4.2

10

O.I

0.4

O.I

o

0

o

0 O.I

o

O.I

o

o

O.I

0

(0.2)

(o)

0

o

0

O.I

o

1-3

0

10.0

1 1

°-3

0.5

0.2

0

O.I

O O O.I

o

O.I

o.a o o.i

O. I

O.I

O.I

I.O

o

0.6

0.7

0

i-5

o

3-«

12
13

0

o

0.6
'•9

o

O.2

O.I
O.I

0

O.I

0
O.I

0 j O

o o.a

o

O.2

0

o

o

0.4

O.I
0

0

o.a

o

0

0

0.3

O I.I
0 O

o

O.I

0.5

0

1.2

3-7

o

0

3-3

0.5

0

0

1.0

I.I

'4

O.I

0.4

0.2

O.I 1 O

o

O 0

o

o

o

O.I

o

O.I

0.4

0 0

O.I

o-3

O. 7

o 1.5

0

3.0

1 1

i

i

PART. II. POLAR MAGNETIC PIIENOMKNA AND TERRE1.LA EXPERIMENTS. CHAP. III. 457

I'Al'.LE LXIV (continued). FH Matotchkin Schar.

Gr. M.-T. 0—2

2-4

4-6

6 — 8 8—io

IO— 13

12-14

14— 16

16-18

18-20

ao — 22 23 — 24

1

Date

4-

+

4-

+

4.

4-l-U

4-

+

4-

—

4-

_

4-

_

1- .-binary 15 o

o-3

o

O.I

o

0

0

O.I

O.I

0

o.i 1 0.3 0.6

0

3-7

o 0.8 3.6

09

o

o

0.3

o

0

16 o

0

o

o

o

0 j 0

o o

O.I

O.I O O.I

0

O.I

0 0.2 0.4

O.I

o-5

o

0.3

O | O.I

17 o.i

0.2

o

o

0

O. I i O

o o

o

O.I 0 O.I

O.I

o-5

O i O.2 0

0

o

o

o.a

o

O.I

18 o

04

o

o

o

0 0

o o

o

0 0

o

0

o

o

0 0

0

.-*

O.I

o

O.I

o

o

.9

o

0 0

0

o

o

o

o

o

O.2

o

0

O.I

0

o

0.3

o

°-3

0

O.I

o

o

o

O.I

20 (0)

(0.1) (0)

(0.2)

(o)

(0.2)

(ol

(0.2)

o

o

O.I

0

o

O.I

o

O.I

o

o

o

o

o

o

0

o

21 O

0 (0)

(o) (o)

(o) (ol

(0) 0

O.I

o

o o-4

0

O.3

O.I

0.5

o

o

o

o

o

o

o

22 0

0 0

1.4 o

1.8

o

3.0 1.0

0.2

2.3

0

0.6

o-5

O.I

O.I

o-3

o

O.I

O.I

o

0.4

0

0-1

23

o

O.I 0

o ! o

o

o

o o

0

o

0

o

O.I

o

O.I O O.I O.I

0.3

o

0.8

0

0.3

24

o

O.I 0

o

o

o

0

o

0

o

o

o

o

o

0

o 0.8 o

O.2

o

o

o

0

0

25

0

0

0

o-3

o

0.8 o.i

0.6

0.6

O.I

I.I O

O.I

O 2

o

0.3 o

o

o

o

0

0

0

0

26

0

O 0

0 0

0 O

o o

0

o

0

o

0

o

O.I 0 0

o

o

o

1. 1

o 0.5

2?

(01

(o)

(o)

(o.i) (o)

(0.2

o

o

o

o

o

0

o

o

0

0

o

o

o

0

o

o

0 0

28 0

0

o

0

o

o o

O 0

o

o

0

o

o

o

o

o

0

o

o

0

o

0

o

March I o

0 O

0

o

o o

O.I

O.I

0

o

0

O.I

o

o-3

0 2.O O.I

i-5

0

o-4

O.I

0

2-3

1

TABLE LXV.
Disturbances in Declination

Gr. M.-T. 0 — 2

2-4

4 — 6 6 — 8 8 — io 10—12

12—14 14—16

16- 18

18 — 20

3O— 22

22 — 24

Date

+

+

—

4-

—

+

—

4

—

4-

_

4-

—

+

—

4-

—

4-

-

4-

—

4-

-

October 3

0

o

0

o

o

o

o

0 0

0.3

O.I

O.2

o

o.a

O O.I O

0-3

O.I

I.I

0

0.4

0 0

4

o.a

0

o

o

0-5

O O.2

O.I O

°-5

0.4

O.I

O.I

O.I

0.3 O.I 02

0

O.I

o

O.I

O.I

O.I 0.2

5

O.2

O.I

0.3

0.2

o-4

0.4 o

o

O.2

O.I

O.I

o

0

0

0

o

o

o

O.I

o

O.I

O.I

o o

6

o

o

0

0

O.I

O.2

o

o

0.2

o

o

o

o

0

o

0.4 o

o

o

o

O.I

o

O.I

o

7

O.I

o

o.a 1 o

o

o

o

o

o

0

o

o

o

0

o

o

o

o

o

o

o

o

O.I

O.I

8

0.2

0

O.I

O.I

0

o

o

o

o

0

O.2

0

o

o

0

0

o

0

o

0.9

O.I

O.I

O.I

O.I

9

O.I

o

o

o

0 O

O.I

o

0

o

O.I

O.I

O.I

o

o 0.5

o.i 0.3

O.I

O.I 0

o

o

0

10

o

o

0

o

0 O

0 0

o

o

o

o

o

o o o

o

0 0

0 0

o

O.I

O.I

II 0

o

o-5

o

O.I j O.I

0 0.3 0.2

0

O.I

O.I

1-3

o

o-3

o

i-7

8.0 o. i

2.2

o

17.8

o

6.0

12 0.6

0.2

O.I

0-3

o o

0 0

O.I

o'1

O.I

o

0

0

0.1

O.2

O.I

0 0

o

o

o

o

o

13 o

o

0

0

0 0

o ! o

0

o

O.I

0.5

0

0.8

O.I 0.2

O.2

0.5 o

1-9

o

°-5

0 0

14 o

o

0

o

o

o

o

o ; o

o

o

o

o

0 O.I

o

0

0 O.I

O.2

O.I

0

0.2

O. I

15

o

o

o

0

o

o

O.I

o 0.7

o

0.2

o

o

o

o

o

0

0.2 0.3

o-5

o-3

0.2

0.2

0

16

o

0

o

o

o

0

o o o

o

0

o

o

o

0

0

0

0 0

0

o

o

o

O.I

'7

o

o

o

o

o

o

o

o

o

o

0

O.I

o

o

o

o

o

o

O.I

o

0

0

o.

O.I

,8

o

O.2

0.2

O.I

0.4

O.I

o

0

0.2

o

0

0

o

0

0

O.I

O.I

o

O.I

4-3

o

'.5

o

04

19

0

0.5

0.7

o

0.3

o

o

O.I

o

0

o

o

o

0

o

0

0.1

0

o

O.I

0 0

o

0

20

o

0

o

o

o

o

o

O O.I

0

0-3

O.I

o

O.I

o

o

0

o

o

o o 0.3 ! o. i

0

21

O 0

0

o

o

O.I

o

0

o

o

0

o

0

0

O.3 O

0.9

0.2 0. 1

0.4 o 0.4 o

03

22

o

O.I

o

O.I

0

o

o

O.I

0

o

o

0

o

o

o

O.I

o

o o

o

0

0 0

o

23

0

o

o

o

o

0

o

o

o

0

o

0

o

0

o

0

o

o

O.I

o

o

'•S

0. I

'•5

24

o

1.3

o-3

o

O.I

o

o

o

O.I

o

O.I

0

o

0

0.3

0

i-3

o

0.4

3-4 ^o

16.0

0

130

25

o

8.3

o

1.6

o

O.2 O.2

o

o

0.2

0.7

O.I

t-5

O.I

O.I

o-3

O.I

0.8 o

O.3 O

0.2 0

0 2

26

o

0.4

O.2

o

o

0 0

o

o

O.I

o

0.4

o

O.I

o-3

o-3

0.6

0.3 o

1.8

O.I

O.I

o

o-5

27

0

2.4

0.4

0.4

0.2

o

0.5

0

0.8

O.I

0

0.4

O.3

o-3

t.6] 0.5

0.7

2-5

O.I

6-3

o

33

o

6 I

28

o

0.6

o

o-5

O.I

0.3

o

O.2

0.3

o

o.i

o

o

o-3

0.2 0.3

O.I

o-5

o

3-0

o

a-3

o

1.2

29

O.I 0

0

o

0.3 : O

O.I

o

O.3

O.I

0.3

o

o

O.I

0 O.I

O.I

i-5

o

9-4

o 7.9

o

3-6

30

O.I 1.0

o

0-3

O.3

O.I

0.7

O.I

3-6

o

a.9

o

o

o

04 o

0.2

05

o. i 0.6

o 1.7

o.a

O.I

31

O.I

°-5

3-4

o

3-7

o

1.7 o

3-°

0

4-7

o

9.7

2.5

12.3 o

1-5

3-o

0 '3-3

o 26.0 o

21.3

November i

o

9-o

o

1.8

0.8

0

O.2 0.3

O.2

o

1

o.i ' 0.4

o

o

0 0

0

o

0 o

1

0. 1 O.2 O

0

458

BIRKKLAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

TABLE LXV (continued).

Matotchkin Schar.

Gr. M.-T. 0-3

2-4

4-6 6-8

8— IO i IO— 13

12—14

14 — 16

16-18

18 — 30

20 — 22

22-24

Date

- 4-

+

_

4.

—

+

—

+

—

)

4-

+

_ 4.

4-

=T=
4. _

November 2

0

o

o

o

0

o

O.I

o

o

O.I

o

0.4

O O.I

O.I

o

0.6

0.7 o

6.6

o

4.7

O.I O.I

3

O

0.4

o

o

o

0

O.2

o

o

o

0

o

0

0

o

o

O.I

O.I O

O.I

O.2

o

0 0

4

(0)

(0.1)

(o)

(o)

(o)

(o)

(O.I)

(o)

(0)

(o)

(o)

(0.1)

(o)

(o)

(o)

(o)

(o)

(o)

(o)

(o)

(o)

(o)

I'ol 101

5

(o)

(O.I)

(o)

(o)

(0)

(o)

(o)

o

o

o

o

o

o

o

0

o

o

0

o

O.I

p

O.I

0 0

6

o

o

o

0

o

0

0

o

0

o

0

o

o

o

0

o

0.7

0.2

I.I

4.0

o

4-7

o 0.5

7

0

0.4

o

0

o

o

O.I

o

o

0

o

o

o

o

0

0

o

o

o

o

o

o

0

O.I

8

o

0.7

o

0.2

o

o

O.I

0

o

o

o

o

o

o

o

o-3

O.I

0

O.I

O.I

O.2

0

0 0

9

0

o

(o)

(o) (o) (o)

o

o

o

o

o

Q

o

o

O.2

o

o

0

0

o

o

o

0 O.l

10

o

O.I

o

0 0

0 O.I

o

0.2

o

o

o 1 o

0.3

o

O.I

O.I

o

O.I

o

0-3

0.3

0.2 O.6

ii

o

o

O.I

0

o

o

o

0

o

o

o

o

0

o

o

o

o

o

0

o

o

o

o o

12

o

o

o

o

o

o

o

o

0

o

o

o

o o

o

O.I

o

o

O.I

o

0

o.5

0 1-5

13

(o)

(0.5)

(o)

(0.2)

10.11

(o)

(o)

(o)

(o)

(0)

0.3

o

0.9

O.I

O.I

O.I

o

0.6

O.I

0.4

o

o

0 0

M

o

o

0

o

0.6

O.I

o.a

o

O.2

o

0.4

o

I.O

o

1.4

o

0.7

0.4

O.I

0.7

O.2

2.1

0 1.3

'5

o

1.2

o

0.7

o

O.I

0

O.I

o

o

O.I

03

0-3

0

0.7

o

0.3

0.3

0-3

o-3

o.i 3.0

O I.o

16

o

0.7

o

0-3

o

O.I

o

0

o

o

o

0

o

0.3

o

0

o

o

o

o

o

o

0 0

17

0

0.8

O.I

0.3

0.4

O.I

O.I

o

o

o

o

o

o

o

o

o

o

0.5

0

0.4

o

O.I

0 0

18

o

o

o

0

o

o

0

o

o

o

o

0

0

o

o

o

o

°-3

o

0.7

o

1.7

O 2.1

19

o

0.6

o

0

o

o

O.2

o

o

O.I

°-3

O.I

O.I O.I

O.2

o

0.3

o

O.2

O.I

o

i-3

o 0.9

20

o

0

o

0

o

0 0

o

o

o

o

o

o

o

o

O.I

o.a

1.4

o

2.6

o

1.6

0 0

21

o

o

o

o

o

o

o

o

o

o

o

O.I

0

0.3

O.3

O.3

O.3

o-5

O.I

3-3

0

12.5

0

3-5

22

(o)

(i.o)

(o)

'0.5)

ro.a)

(o)

(o)

(o)

(0.2)

(o)

(i.o)

(o)

(i.o)

(0.1)

(2.0)

(0.3)

(1.5)

(5.0)

(o)

(5.5)

(o)

(8.0)

(o)

(8.0!

23

(0) (2.0 (0)

d.o) (0.5)

(0.5)

(i.o)

(0.2)

o-3

O.I

3.0

O.I

0.2

O.2

O.I

0.3

°-5

3.4

I.I

0.9

J-3

1.4

t-3

1 8.0

24

0 I 1. 2 0.3

7-4 1.3 O.I

1-7

O.I

1.7

o

a.o I o

4.0

O.2

IO.O

O.I

0.7

II. O

o

8.5

o

22.5

o

14.0

25

02 ; 5.2 0

1.2 O.2

°-5

0.6

O.I

I-3

0

3-°

0

3°

o

3.3

O.I

3.7

2.0

O.I

"•5

0

13-1

o

4.7

26

O

4.2 o

0.5

o

0.6

o

0.4

0.3

0

0

O.3

o

0

0.8

0.4

O.I

3-5

O.I

1.2

O.I

0.3

o

0.6

27

0. I

O.I

O.I

o

O.I

0.2

O.I

O.2

O.I

o

o

o

O.I

0

o

O.I

0

O.2

o

O.I

0

o

o

0

28

0

0 0

O.I

o

O.I

(O.I)

(o)

0

O.I

O.I

O. 1

0

0-3

0

o-3

o

0.9

O.I

O.I

o

0.2

o

o.a

29

0

O 0

O.I

0

O.2

0

o

o

o

0.4

o

O.I

O.I

o

o

o

o

0

0

o

o

o

0

30

o

0 . 0

0

o

O.I

0.2

o

o

O.I

O.I

O.I

0

0.3

0.2

O.I

o

1.3

0

1-7

0

I.I

o

0

December i

0

o ; o

o

o

o

0

o

0

o

o

0.3

o

o.3

o-5

O.I

o

3.0

o

1.7

o

2.4

o

O.I

a

o

0

0

0

O.I

o

o

o

O.I

0

0.8

o

O.I

0.2

0.3

O.I

(o)

(0.7)

(o)

(2.5)

o

o

o

0

3

0.1

o

o

O.I

0

o

°-3

o

o

o

0

0

0

o

O.I

O.I

o

o

0.2

O.I

o

O.I

o

0

4

o

0

o

0

o

o o

o

0

o

o o

o

O.I

o

o

o

0.7

0

3-i

o

0.3 o.i

0

5

o

0

o

o

0

0 1 0

0

o

o-3

O.I

0

o

0

0

o

o

o

0

O.I

o

0

O.I

0.2

6

0.3

O.2

0

o

o

0

o

o

o

o

0

o

o

0

o

O.I

0

0-3

0

0

o

o

0

0

7

o

o

0

o

0

o

o

o

o

o

o

0

0

0

o

o

0

o

(o)

(0.5)

0

'•5

o

1.4

8

o

0

o

O.I

o

o

O.I

o

o

O. I

0

o

0

0

o

o

0

o

o

O.2

o

I.O

o

O.I

9

o

0

o

0

0

o

0.4

o

0.4

0

0.5

o

O.I

o

0.2

o

I.O

0.7

o.a

I.O

0

0.6 o

0.2

10

O.I

o

O.2

O.I

0.4

°-3

o

o

O.I

o.a

O.I

0.3

0.5

0.2

o

O.I

o

o

0.3

1-3

0

1.5 o

0.4

1 1

o

O.I

0

0

o

0

O.I

0

O.I

0

o

0.3

O.2

o

03

o

0.4

1-5

0.4

I.O

0.8

1.5

o

3-3

12

0.1

0.2

o

O.2

0

0

O.I

o

o

o

o

o

o

0

O.2

o

(i.o)

(i.o)

(o.a)

(i.o)

(o)

(i.o)

(0)

(0.21

'3

O.I

O.I

o

o

o

o

0

0

0

O.I

o

0.4

0

O.2

o

O.I

0.4

4.0

0.3

O.2

O.I

1-5

o 0.5

14

o

O.I

o

o

o

o

0

o

0

0

o

o

o

o

o

o

O.I O.I

O.I O

o

o

O.I 0

15

O.I

O.I

o

o.a

o

o

o

o

o

o

0

0

o

0

0

0

o

0

o 0.8

o

0.3

O.I O.I

16

o

O.I

o

o

0

o

0.4

o

O.I

0

(o)

(0.3)

(o)

(O.I)

(o.i)

(o)

(0.4)

(1.51

(0.2)

(0.5)

(o)

(i.o

10.11 10.21

'7

(o)

(o) (o)

(o)

(0.1)

(o)

(o)

(o)

0

o

o

o

0

0

0

o

0

o

O.I

O.I

O.I

0

0 0

18

0

o o

o

o

o

o

0

0

0

o

o

O.I

0

o

o

0 0

0 0

o

0

O.I O

19

o

0 0

0

O.I

0 0

O.I

O.I

o

o

O.I

o

O.I

0

O.3

O.3

o o.i 0.7

O.I

[.a

0 0

20

0 0

o

O.I

.0.2

O.I O.I

o

o o

o

o

0

o

o.a

0.3

o

0

0 0

0

o

0 0

21

1

0

0

o

0

o

1

o

o

o

O 0

0

o

0

o

O.2

o

0.6

o

0.2 O

0

o

0 O

1

1

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III.

459

TABLE LXV (continued).

Matotchkin Schar.

Or. M.-T. 0-2

li

2-4 : 4-6

6-8

8 — IO IO — 12

13— 14

14— 16

16- 18

18 — ao

30 — 33

32—34

Date

+

_

+

_

-I-

—

+

+

+

+

+

+

+

+

_

December 22

o

0

o

0

0

o

o

o

o

o

O.I

o

0.9

O.I

o.a

O.I

0

o

0

I.I

o

33

o

5-5

23

O.I

4-3

I.I

O.I

0.7

o

O.I

0.4

I.I

0.3

3.3

o

1-3

0.9

1.1

o.a 0.7

3.9

o

9-5 o

9-i

0.3

O.I

24

0-3

O.I

0.4

0

O.I

O.I

(o)

(O.I)

(0.2) (O.I)

(0.3)

(O.I)

(0.4)

(0.4)

(0.5)

(o.i) (0.5)

(0.51

(0.2!

ll.O) (0)

(3.0)

(0.2)

(O.II

25 fo.i)

(0.5)

(0.4)

(01

(0.2)

O.I

o

0

0.4

0

0.3

O.I

O.I

o

0

0

o

o-3

0

I.I O.I

o

O.I

o

26

0

o

O.I

O.I

O.I

O.I

o

O.I

O.I

o

O.I

o.a

0.1

o.5

o.a

o.a o

I.O

o.a

O.I O.I

3-7

0.3

O.I

27

O.2

O.I

o

O.I

0

O.I

o

o

O.I

o

o

0.2

o

o

0

o

0.2

o

03

0.3 o

0.6

0.1

2.1

28 0.4 0.2

0.3

O.I

O.2

O.I

0.3

O.I

o.a

0.3

O.I

O.2

O.I

o.a

o

o

0

I.O

o

0.2 0.2

0.9

0

O.I

29 o o

O.I

o

0

o

o

0

o

o

o

0

o

o

o

o i o.a

0.9

0.3

0.2 O.I

o

o

o

30 o o

0

0

o

o

o

o

0

O.I

0

o

o

o

0

0 | 0.3

0.3

°-3

0 O.I

0

O.I

o

31 o.i o

o

0

0

o

o

0

o

o

o

o

o

0

O.I

o

O.I

O.I

o.a

0 0

o

o

O.I

1

January i o o

o

0

o

o

o

o

o

o

o

0

o

o

o

o

0.2

O.I

o

0.1 O

o

0.4

o

2 0

0.3

o

0

0

o

O.I

O.I

o

o

0.2

o

o

o

o

0

o

o

0

O O.I

o

o

0

3 o.i

o

O.I

0

0

0

o '• o

o

o

O.I

0

o

o

o

o

O.I

0

0.3

0.5 0.4

O.I

o

o

4 °

o a

O.I

O.I

0.2

o

0.5 0.2

0.4

o

0.3

o

O.I

o

o

0

O.I

o

0.4

07 0.3

O.I

o

O.2

5 °

0.6

o.a

0.2

0.2

o.3

o 1 i.a

O.3

0.5

O.I

0.2

o

0.6

o.a

0.4

05

a-5

o

1-5 (0.21

(O.I) 0

o

6 o.i

o

0.6

0

O.I

o

0 0

o

o

o

0

o

0

o

0.4

0

0-5

0

1-5 0.2

O.2 O.I

o

7 °

o

o

o

o o

o o

o

0

o

o

o

o

o

o

o

03

O.I

0.3 o

0 0

0

8 o

o

o

o

0 0

0 0

o

O.I

O.I

O.I

o

o

o

0

O.I

I.O

o

1.3 o

1.7 o

O.I

9 °

o

0

o

o

o

O. I O

o

O.I

o

O.I

o

o

O.I

o

o

i-3

o

1.9 o

1.4

o

2.1

IO

O

o.a

o

0

(o)

(o)

(o)

(o)

(o)

(o)

o

0

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O.I

0.4

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O.I

0.4

o

o

O.I

O.I

O.'I

0.3

ii

0.6

0

o

o

o

O.I

o

o

0

O.I

o

O.I

o

O.I

0

0.8

O.I

0.4

0.4

2-4

0.6

0.8

0.5

0

12

O.3

o

O.I

o

O.I

o

o

o

O.I

o

o

0

o

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O.I

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0

03

°-3

0.9

O.I

o

0.9

O.I

13

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O.I

o

O.I

o

o

o

0

o

o

o

o

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0

o

O.I

0.2

!-3

0.2

t-3

o

I.I

O.I

0

'4

O.I

o

o

o

o

o

o

o

o

o

o

0

O.I

o

o

0

0

0

o

0

0

o

o.a

O.I

IS

OS

o

o

o

0

0

0

o

0

O.I

o

O.I

0.3

O.I

O.3

0.3

o

0.4

O.3

0.2

o

0.2

o

o

16

(0.2)

(o)

(0.1)

(o)

(o)

(o)

(o)

(o)

o

0.3

o

O.I

o-3

0.6

o

0.7 | 0.1

0.6

O.I

0.4

O.I

O.I

O.I

0.4

17

O.2

o

O.I

o

0

o

(o)

(o)

(O.I)

(O.I)

o

o

o

O.I

o

o

O.I

O.I

o

I.O

0.2

0

o

o

18

O.I

o

o

o

(o)

(o)

(o)

(o)

(o.i)

(O.I)

o o

o

0

0.4

0.6

0.8

o.a

0.8

°-3

1.2

o

O.I

o

19

20

0.2
(0.1)

o

(o)

O.I

(o)

o
(o)

o

(o)

O.I

(o)

o

o

o
o

o
°3

o
o

0.2

o.a

°-3
o

O.I

o

O.I

o

0.9

o

o

0

0.6
o

0.9

o

o

0

o

O.I

O.2

0.7

(o)
o

(O.I)

o

21

O

o

0

o

0

O.I

o

O.2

o

O.I

O.I

o

O.I

0-4

o.a

I.O

0.4

O.I

(o)

(0.5)

0

0.6

0.6

o

22

o-3

0.2

o

0

0

0

o

o

o

o

o

0

0

o

o

O.I

O.I

O.I

o

0.9

0

0.9

O.I

o

23

o

o

0

o

(o)

(0.1)

(o)

(o)

0.1

o

O.I

0.3

O.I

03

O.I

04

0.2

3.3

O.I

3-5

0

5.4

°-3

°-3

24

0.2

o

O.I

O.I

0

o.a

o

o

0

O.I

o

0

0

O.I

o

O.3

o

1-3

O.I

I.I

O.I

0.3

O.I

O.I

25

(0.1)

(o)

(o)

(o)

(o)

(0.1)

(o)

(O.I)

o

o

o

o

0

o

o

°-4

0

0.9

0

0.2

0

0

o

0

26

0

o

o

o

o

o

0

0

O.I

o

0.3

0

0.6

o.a

o.a

o

(o.a)

(I.OI

(o)

15.0

o

18.1

o

28.0

27

0

17-5

0

4-7

0.3

1.4

0.7

O.I

O.I

O.3

o

O.I

o

o-3

o

0.3

o

'•3

O.I

0.6

o

0.7

o

0.5

28

0.1

0

0

0

0 O

o

O.I

o

O.I

O.I

0

o

O.I

O.I

0

0.4

1.6

O.I

0.4

O.I

o

0.8

0

29

o.a

o

O.I

0

o

o

o

0

o

o

o

o

O.I

o

O.I

o

o

o

o

0

0

o

o

0

30

O.I

O.I

o

0

o

o

o

O.2

o-5

o

3-i

0

3.9

o

32

o

4-4

o

0.6

o.a

o

O.2

0

O.I

31

O.I

0.2

o

o

o

o

o

0

o

o

0

o

o

o

0-4

o

1.4

O.I

0.3

o

O.I

0

o o

February i

o

o

o

o

o

o

0

O.I

o

o

o

o

o

o

O.2

o

0.6

O.I

0.2

O.3

O.I

o

0 0

3 0.2

0

o

0

o

o

o

o

o

o

O.I

o

0.3

0

O.I

o

o

O.I

0

o

o

o

o o

3

0

0

o

0

0 0

o

O.I

0.5

o

O.I

O.I

0.2

o

o

o

o

o

o

o

o

0

0

0

4

o

0

(o)

(o)

(o)

(0)

(o)

(o)

(o)

(o)

(0.1)

(o)

(O.I)

(o)

(o.a)

(o)

(0.5)

o.n

(O.I)

10)

(o)

(0)

(0)

(01

5

o

o

O.I

O.I

O.I

o

O.I

o

0

0

0.3

0

o

0

O.I

O.I

0.4

«-3

O.I

0.5

o-3

o

°-3

o

6

7

o

o

0
0

O.I
O.I

0

o

0.2 0.4
O j O

O.I
0

o.a

0

O.3

o

o
o

o

0.1

0
0

o

O.I

0.4

0

(O.I)

o

(o)
o

(o.a)
o.a

(0.6)

O.I

o

o
o

o o
o I 3.9

o

0

0

7.6

8
9

o
o

I.O

0.8

O.I
0.2

0.9
0.3

0.9 o

0.2 0.5

I.I

O.I

o

O.2

0

0

o

(O.I)

o

(o)

0

0:7

o

0

35

0

o

-

0,

I.I

O.I

0.7

O.I

6.5

1.6

o.a 15.3
o 3.4

0

o

2-5
2.7

460 B1UKKI.AND. THF NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

TABLE LXV (continued). F» Matotchkin Schar.

Gr. M.-T. 0—2

2-4

4-6 6-8

8—io

IO— 12

12—14

14-16

16— 18

1 8 20

2O — 22 22 — 34

Date +

_

+

_

+

—

+

—

+

—

4-

—

+

—

+

—

+

—

+

—

•4*

_

+

February i o

o 0.6

O. I

O.I

O.2

0

0.2

O.I

o

o

o

o

o

o

o

0 0

0

o

O.I

O.I

°-5

0

5.9

ri

O 1.2 O.2 O.I

0.4

0

O.I

0.2

0

O.I

°-3

O O.I

o

03

o 0.7

0

0.4

0.8 > o i.i

o

3.0

12

o. i 0.3 o o

o

0

0

O.I

0

o

o

o o

o o

0 O

2.0

O.2

2.4

0 3-4

o

0.8

13

O.2 0.6

0.4 o. i

O.I

0.3

0

0.5

0.2

o

0.3

O O.I

0.2 0

o

0

O.I

0

1.6

o.i 0.6

0

0.6

'4

0.2

0.2

O.I

O.2

o

o

O.I

0

0

o

O.I

0.2

O.I

O.I

O.I

I.I

0

o-3

O.I

O.I

O.2 0.5

0.3

0.7

15

0

0

o

o

0

o

0

0

O.I

0

0.4

o 0.3

o

0.8

2.7

o-3

6.3

o

I.O

o

0.2

0

0.2

16

o

0

o o

0

o

o

0

o

0 0

0 0

o

O.I

o

o

0.7

o

0.3

O.I 0

0

0

n

O.2 O

O 0

o

0.2

0

0

o

O.I

O.I

0 O.I

o

o

2.O

(O.I)

(0.31

o

0

0.2 0

O.I

0

1 8 O.2

o

o

0

o

o

o

o

o

o | o

0 0

0

O.I

o

O.I

o

o

0

0 0

o

o

19

o

o

o

o

0

o

o

o

0

o.a

o

0

0

o

0

O.I

o

0.2

O.I

0

0 0

0

0

20

(o)

(o)

(O.I)

(0.1)

(0.3)

(o)

(0.3)

(o)

o

0

O.I

0

o

o

0

0

0

o

0

0

o

0

o

o

21

o

o

(o)

(o)

(o)

(0)

(o)

(o)

o

o

O.I

o i 0.5

o °-5

o.a

O.I

0.2

o

0

0

0

0

0

22

0

o.i 0.3 0.3

I.O

O.I

1.3

0.2

i-3

o

2-5

0

I.I

0 O.I

O. I O. I

o.a

O.I

°-3

o

O.I

o

0

23

o o o o

0

o

0

0

o

o

0

o 0.3

0 0

o

O.I

O.I

°-3

O.I

o

03

O.I

O.I

24

o

0

0

o

o

0

o

o

o

o

0

o

o

o

0

0

0.2

O.I

0.4

0

0

0

0

o

25

0

o

O.2

o

'•3

0

2-3

0

1.8

o 1.7

o 0.7

O.I O.I

°-3

o

O.I

o

O.I

o

00 0

26

0

o

0

o

0

o

o

o

o

o

o

0 0

o

o

0

o

0

o

O.2

o

I.O 0 O.J

27

(o)

(o)

(o)

(o)

(0.3)

(0)

o

o

o

o

o

0 ; 0

o

o

o

0

o

0

0

0

0

0

0

28 o

o o o

0

0 0

o

o

0

o

o o

o

o

o

o

o

o.

0 O O

0

0

March i o o ! o o o o

o

o

o

o

o

o

°-3

o

°-3

o

1.0

o 0.7

0.6

0 O.2

o

a. i

TABLE LXVI.
Disturbances in Vertical Intensity

Or. M.-T.

0—2

2-4 4-6

6-8

8-10

10—12

12—14

14-16

16-18

18^20

20 — 22

22—24

Date

+

—

+

—

+

—

+

_

+

—

-4-

—

+

—

+

—

+

—

+

—

+

—

+

_

October 3 ; o

0

0

o

o

o

0

0

o

o

0

0

o

o

o

o

0

0

o

o

o

o

0

0

4 o

0

0

0

o

0

o

o

O.I

O.2

o

0.3

0.7

o

O.I

o

0

o

0

o

o

01

0

0.4

5

O

o

O.I

o

0.5

o

0

0

O.I

o

o

o

o

0

o

o

0

o

0

o

0

0.2

0

o

6

o

0

o

o

0

o

0

0

o

0 , 0

o

o

O.I

o

O.I

0

03

0

o

o

02

o

0.4

7

o

o

o

0

o

0

o

o

o

0

o

o

0

o

o

0

o

o

0

o

0

0

o

0.4

8

o

0

o

o

o

o

0

0

o

o

o

o

O.I

0

o

o

o

o

0-1

°-3

o

0.2

O O.2

9

o

0

o

0

0

o

0

o

o

o

o

0

0

o

I.O

o

O.I

O.I

0 O.I

o

o

0 0

10

o

0

o

o

o

o

0

o

o

0

o

o

o

0

O.I

o

0

0

0

0

o

o

0 0

1 1

o

0

0

o

0

o

0

o

0

0

o

o

o-5

o

o

0

O.I

3-3

° 93

o

5-4

<> 3.8

12

o

o

0

o

o

o

0

0

o

0

o

o

0

0

O.I

o

o

o

o

o

0

o

o

o

13

o

o

o

o

o

0

o

o

o

0

o

o

o

o

O.I

o

0.2

0.4

0 1.2

o

0.5

o

o

M

o

o

o

o

0

o

o

0

o

o

0

o

o

o

0

o

o

o

o 0.3

o

0.4

o

o.a

15

o

0

o

o

o

o

o

o

o

0

o.i

o

o

o

0

o

O.I O

0

I.I

o

04

o

o

16

o

o

o

o

o

0

o

o

o

o

o

0

o

o

o

o

0

o

0 0

o

0.3

0

0

'7

o

0

o

o

o

o

0

o

0

o

o

o

o

o

0

o

o

o

0

0

o

o

o

o

18

o

o

o

O.I

o

o

0

o

0

o

o

0

0

0

0

o

o

o

o

4.0

o

0.8

o

o

19

o

02

o

0.4

0

0.2

0

o

o

o

o

o

0

0

o

o

0

o

o

o

•o

0

o

o

20

0

o

0

0

0

o

0

o

o

o

o

o

0

0

0

0

o

o

0

o

o

O.I

0

0

21

o

o

o

o

o

o

0

o

0

o

0

o

o

o

o

o

0.3

o

0

o

O.I

0

o

I.O

22

0

0.2

0

0

o

0

0

o

o

0

o

0

o

0

o

o

0

o

o

"o

o

o

o

0

23

o

0

0

0

o

o

o

o

0

o

o

o

o

o

o

o

0

o

0

o

o

I.O

o

0.8

24

o

o

o

o

o

0

o j o

0

o

o

o

0

o

o

0

O.I

o

o

0.9

o

2.4

o

2.3

25

o

3-9

O.2

1.4

0.2

o

O.I

0

0.8

o

1-5

o

2-4

o

0.9

o

0.4

o

O.I

o

o

0.9

0

0.5

36

o

O.2

0

O.I

0

o

o

o

0

O O.2

0

0.5

0

1.4

0

0.8

o

O.I

0.8

o

0

0.2

0.1

27

0.1

0.4

o

I.I

O.I

0.4

o

O.I

0.2

0

0.4

o

0.6

o

0.4

4.5

0

5-5 o.i

1.8

O.I

1.4

0

3'3

PART. ii. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. in. 461

TABLE LXVI (continued). /•> Matotchkin Schar.

Gr. M.-T. 0—2

2 — 4 4 — 6 6 — 8 8—io 10— 12 12 — 14

14—16 16— 18 18 — 20 ao — 22

22 — 24

Date ' +

_

4-

+

—

+

_

4-

_

+ !-

4-

+

+

+

__

•f ! -

4-

October 28 o o

O.I

0.2

o

o

0 0

O 0 0 0

O 0 O

o

o

O.2 O 0.9

1
o 0.7

o

0.6

29 o o

0

o

o

0 0 O

o o o . o

o o o

o

o

0.6

o 4.5 o 4.4

o 1.9

30 o

o

0

o

o

O i 0. 1 O

1.3 o 0.6 o

o

0 O

o

0

o

o o. i o 0.8

o 0.3

3'

O

0.2

o

o

o. i o 0.9 o

1.6 o 0.4 0.6

o

2.0 0

2.0

o

2.O

3.0 0.6 9.4 o

4-9 o

November i

0.4

0.3

o

0.7

o

0.4

O.I O.I

O.I

o

o

o

(o)

(0)

(o)

(o)

(o)

(0.3)

(0)

(0.5)

(0)

(0.5)

(Ol (0)

2

0

o

0

o

0

0

o o

o

o

0

o

0

o

0-3

o

°-3

I.O

1.7 0.9

o.i 1.5

O.I

0

3

o

o

0

o

O O 0 0

0 O O O

0

o

o

o

°-3

O.I

O.I 0

o 0.8

O O.I

4 lo)

(o)

(01

(o)

(o) (o) (o) (o) ' (o) (o) (o) (o)

(0)

(0) (0.,)

(0) '(0.11

(0. II

(ol (o.i)

(o) lo.ai

(01 (0)

5

10)

(o)

to)

(o)

(o) (o) (o) o | o o o o

o

o o

0 0 O

0 O.I

0 O.2

o : o

6

0

o

o

o

o o

o o o o o o

0

o o

o o.i 0.8

o 9-5

o 3.6

O.I O.I

7

0

o-3

0

O.I

o

0

0

0

0 0

o o

o

0 0

0 0

0

0 0

0 0

o

o

o

0 O.I

0

0.4

o

0

0

o

o o

0 0

o

O O.I

0 0

°-3

0 O.I

o 0.4

o

o

9

o

o

o

o

0

0

0 0

0 0

o

0

o

0 0

0 0

o

o o o a

0 O.I

10

0. 1

0

o

0

0

0 0 0

o

0

0 0

0.2

O O. I

0 0

o

0 0 0 1.5

0 2.2

1 1

0

o

0

0

0

o

0

0

0 0

o

0 0

0 0

0 O

o

0

o

0 O

0 0

12

0

0

o

0

o

o

o

o

o o

0 0 O

0 0

0 0

o

0

o o 0.3

o 1.6

>3

10,

(0.2)

(o)

(o)

(0)

(o)

(o)

(o)

(o) (o)

0.4 o

2.4

0 O.I

0 0.2 0

O.I 0.3 0 O.2

0 0

14 o

o

0

o

0

0

o o

0 0

O.I O

0.3

o.i 0.3

O.2 O 0.7

0.2 O.I O.I 1.2 O.I 0.4

15 0

" 0.6

0

o

o

0

0 j 0

0 O

o o o

o 0.3

o 0.3 o

0 0.2 0 1.7

0 1.2

16 o

0.2

0 0

o

0 0

o

o

0

o

o 0.8

0 O

0 O

0

o | o o

0

o

0-3

17

o

0.6

O O.I

o

o

0

o

o

0

o

o

o

0 0

o

0.2

o

000

o

o

0

18

0

o

0 0

o

o

0

0

0 0

o

0

0

0 O

o

0.2

o

0 0.2

0

3-1

0

2-5

'9

o

0

0 0

o

0 0

o

o o

0 0

0.5

O O.I

O 0 O

O O.2 I O

1.6 o

1.2

20

o

0

0 0

o

0 0

o

o o

o

0

0

O O.I

0

0.5 i.o

0.2 1.6

o

0.7 o

o

21

o

0

0 0

o

0 0

0

0

0

O.I

O.I

O.I

o 03

0

09

1.6

0.9

0.8

1.8

3-6

0

17

22

(o)

<o)

(o) (o)

(0)

(o) (o)

(o)

(o)

(o)

(o)

(o)

(o)

(o» (o)

(o) (0.8)

(7.0)

(2.0) (2.0)

12. Ol

(2.0)

(o)

(4.0)

23

(o)

(i.o)

(0) (I.O)

(o)

(o) (o)

(o)

O.I

O.I

3-0

o

o

1.0 0

0.2 O.I 1.7

0 1.7 O.2

1.8

0

150

24

o

r5.5

o 11.5

o

7-6 o

5-°

O.2

0.6

o

2.4

o

ii-° , ° 15-5 3-° IO-°

5.8 0.2JI2.I

0

7-3

0

25

1-7

o

i-5 o

(o)

(0.5) (o)

(0.5)

0.2 0

0.6

o

0.4

O.I O.I

3.8 o 13.0

6.5 2.5 0.2

1.2

o

(r.7l

26

0

'3.0.1

O O.I

O.I

o o

0

O.I

o

0.2

o

o

o

03

33 °-1 ; 4-o

0.3 0.4 0.5

0

o

o

27

o

o

o

O.2 O

o

O.I

O.I O

0

0

o

o

o

0

o

O.2

0 0

O.I 0

0

o

0

28 0 0

0.2 o O

0

0

0 0

O O.I

o

o

0

0

o

0.2

0.5 O O.2 0

0

o

o

29

o

0

o o o

0

o

o"

o

o o

o

o

o

o

o

o

0 0

o

0

o

o

o

3°

0

o

00 0

o

o

o o

o o

o

o

o

o

0

O.I

0.5 0.5

0.2

0

O.I

o

o

December '

0

0

0

0 0

0

0

0 0

0

0

o

1-4

o

0.9

0

O.I

I.O

0

i-9

o

i-5

0

o

2

o

0

o

o o

o

o

0 0

0

O.2

0

o

0

O.2

0

o

2.7

0

o-S

o

o

o

o

3

o

°

0

O 0

o

0

0 0

o

o

o

0

o

°-5

0

O.I

0

0

0.7

o

°-3

o

O.I

4

o

0

o

0 0

0

0

0 0

o

0

o

0

o

o

o

0.2

0

o

1.9

o

°-5

o

o

5

0

0

000

0

o

o

o

o

0

o

o

0

o

o

o

o

o

o

o

o

o

0.7

6

o

0.4

o

o

o

0

0

0 0

0

0

0

0

0

o

0

o 0.3 o

O.2

o

o

0 O

7

0

0

O o O

0

o

0 0

0 0

Q

0

0

(o)

(o)

(0) (0) 0

(r.o)

o

2.5

O-2 O.I

8

o

o

000

0

o

0 0 0 0 0

o

o

o

o

0 O 0

°-5

o

1.4

O O. I

9

o

0

O 0 0

0

o

O.2 o

o.i 0.5 o

0

0

o-3

0

0.6

2.2 O.I

0.6

0

o-3

o

O.I

10

o

0

O.I

O O.I

O.I

o

O.I O.I

O.6 2.1 O.2

a. i

02

O.I

O.2

O.I

0.3 o

2.2

o

3.2

o

0.8

1 1

o

O.I

o o o

0

0

o

o

O O 0

0

o-i

o

0.9

0.4 o o

i-3

o

4-7

o

0.9

13

.
0.3

o

o

O.I O

o

0

0 0

000

o

o

O.I

o

0.6 o (o)

(i.o)

(o)

(4.5)

(o)

(1.0)

13

O.I

o

O O 0

o

0

O 0

o 0.4 o

0.2 O

o

0

O.2 2.4 0

1.6

o

2.9

o

0.7

14

o

o

o

0 0

0

0

0 0

o o o

o o

o

0

O.I 0 0

o

o

o

o

o

15

o

0.4

o

1.2

o

O.2

0

0 | 0

000

0

0

0

o

o

o

O.I

1.2

O.I

o

o

o

16

0

o

0

0

0

o

o

O 0

0 O 0

(o)

(o)

(o)

o

(0.3) (0.6) (0)

(I.O)

(0)

(2.0)

(o)

(0.5)

1

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903.

59

.j.62 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IC)O2 — 1903.

TABLE LXVI (continued). Fv Matotchkin Schar.

Gr. M.-T.

O — 2

2-4

4-6

6-8

8—io

10 — 13

12 — 14

14 — 16

16-18

18 — 20

20 — 22

22-

-24

Date

+

—

4-

_

4-

_

4-

—

4-

— 4-

—

4-

—

4-

—

4-

—

4-

- +

4-

.

December 17

(0)'

(o)

(o)

(o)

(o)

(o)

(o)

(o)

O 0 0

o

o

o

0

o

0

o

0.1

O.I 0

0.2 O

0

18

O

0

o

o

o

o

o

0

o

0 0

o

0

o

0 0

o o

o

0 0

0 0

o

'9

o

o

o

o o

0

o

o

o

0 0

0

0.3

o

0.8 o

0-3

o

o

I.I 0

1.5 o

0

20

0

o

o

o

o

o

0

o

o

o

o

0

0

o

0.6

o

o

o

o

o

0

0 O

0

21

o

o

o

o

o

0

o

0

0 O

o

o

0

o

0.2

o

0.5

o

O.3

o

0

o

0

0

22

o

o

o

o

0

0

o

o

o

o

O.I

O.I

o

o

O.3

o

o

o

o

I.O

o

2.5

o. r

2.5

23
24

o

0

3-4
o

o 3.7
o o

o | 0.5

0 0

0.4

(o)

O.I

(o)

(o)

O.I I.O

(o) 1 (o.a)

0

lo)

0.5
(0.4)

1.3

(o,

0

(O.I)

I.O

o

(0.5)

13.5

(o)

0

(o)

19.2
d.o)

o

(o)

9.0

".51

0

'0)

°-4

25

(o)

(01

(o) (o)

(0)

(o)

o

o

o

o

O.I

O.I

0

0 0

o

O.I O

o

i. a

o

0.2

0

0.4

26

o

0

0

0

o

o

o

o

O.I

o

O.2

O.I

I.I

o

r-5

0

0.4 o

0

0.4

o

3.8

o

I.Q

27

O.I

0

o

o

o

o

o

o

o

o

o

0

0

0

0

o

0.6

o

0.5

0

o

2.3

0

4-0

28

o

2.4

o

O.I

o-5

0.2

0.4

O O.2 O

o.5

o

'•5

o

o.a

o

0.6

o

o 0.3

o

I.'J 0

O.I

29

o

0

o

0

o

0

o

o

0 0 O

0

0

o

0

0

0.5

o-3

0

O.3

0

O.I O

o

30

o

o

0

o

o

0

o

o

o

o

o

0

o

o

0

o

O.I

O.2

o

o-3

o

o

o

O.I

31

o

O.I

o

o

o

o

o

o

o

o

o

o

0

o

o

o

o.3

0

O.I

o.a

O.I

o

o

o-5

January i

o

o

o

o

o

o

o

o

o

0

o

o

o

o

0

o

0.4

o

O.I

o

o

0

o

o.5

a

o

0.6

0

O.I

o

0

0

o

0

o

o

o

0

o

0

o

o o

0

o

o

0

0

0

3

o

o

o

o

o

0

o

o

o

o

o

o

o

o

o

0

o o

o

1-7

o

1.2

o

o

4

0 0

O.I

O.I

o

0.2

O.I

O.2

O.I

o

o

o

0

o

o

o

O.3 | O

0.2

0.6

0

I.O

o

0.4

5

o

0

0

I.O

0 1.3

o

0.2

1.6

o

0.9

o

0.9

o

i.7

o

o

4-5

o

2.2

0

1.5

0

0

6

o

o

o

o

O.I

o

o

0

0

0

o

o

o

o

0.3

0

0.3

0

0

1-5

0

2.8

o

0.8

7

o

o

o

o

o

o

o

o

0

o

o

o

o

o

0

o

0.2

o

o

I.O

O O.I

o

0

8

o

0

0

0

0 0

o

0

O O.I O

O.I

0

o

0.3

o

0.4

0.6

0

0.6

o 0.9

0

0

9

o

0 0

o

0 0

o

0

0.2 ; o 0.2

o

O.2

o

0.5

o

1.2

0.2

0.5

o.a

o 0.3

o

O.Q

10

0-5

O.I

0.3

o

(o)

(o)

(o)

(o)

(o.i)

(o)

0

0

0.4

0

3.5

o

1-3

o

O.I

0

o

1.2

o

1.6

1 1

O.I

o

0

o

o

0

o

o

0

o

o

o

o

o

0.5

o

0.5

o

0.3

33

O. 1

1.2

0

0.3

12

O.I

o

0

o

o

o

o

o

o

0

o

o

0

o

0.6

o

0.7

O.I

0

3-2

0 0

0

03

13

o

o

o

o

o

0

0

0

o

o

o

o

o

o 0.2

o

0.8

O.I

O.I

4-4

o 3.0

0

0.8

'4

o

o

0

o

o

0

o

o

0 0

0

o

0

o o o

0

o

o

o

0 0

O.I

0.8

15

o

o

0

0

o

o

o

o

0 0

o

o

O.2

o

0.8 o

0.4

o

0

0.5

0

o

o

O.I

1

16

(0)

(o)

(o)

(o)

(o)

(o)

o

O j O O

0.4

o

4-5

o 1.4

0

2-3

O O.2

O.I 0

O.I 0

o

17

o

o

o

o

o

o

(o)

(o) (o) (o)

o

o

O.2

o

0

o

O.I

O O.I

0 0

0.3 o

o

18

o

0

0

0

(o)

(o)

(o)

(o)

(o)

(o)

0

o

0

0

1.6

0.3

1.6

O.I O

2.2 O O. I O

o

19

o

0

0

0

o

o

o

o

o

0

O.2

o

0.5 j o 0.3

O.I

0,1

1.9 o

O.I O.I O.2 (01

(0)

20

(0)

(o)

(o) (o)

(o)

(o)

0

0

o

o

o

0

O O 0

o

o

o

o

0.4

0

I.O 0

0

21

o

0

o

o

o

0

o

o

o

o

o

o

0.5

o 0.8

O.I

O.I

o

IP)

(0.7)

0

I.I 0

1.5

22

o

1.2

o

O.3

0 0

o

o jo o

o

o

O O 0

o

o

°-5

0

2.3 o 0.3 o

o

23

o

o o o

o o

(o)

(o) o o

o

O.I

o

o.a i.i

o

O.I

1-5 0.3

2.9 o

5.0 o.a

O.I

24

O.I 0 O 0

0 0

o

0

0

o

o

o

O.I

0 0

0

O.I

0.7 , o

3-4

0

0.8 o

0.4

25

(o)

(0)

(o)

(o)

(o)

(o)

(o)

(o)

0

o

o

0

o

o o

0

O.3

0.8

0

O.I

0

0

o

0

36

o

o

0

0

0

o

o

o

0

0

o

0

o.a

0 0

O.I

o (3.0)

0.6

5-8

(0.5)

15.01

(0)

li.o;

27
28

(o)
o

(I.O)

o

(o)
o

d.o)

o

(o)

0

(0.5)

o

(o)
o

(o)

0

0
0

o

0

o
o

0.4

0

o
o

o 0.4
o o

0

o

0

0.6

I.I 0

0.8 0.3

1.4

0-3

o
o

I.O O

I.I O

1.6
0-3

29

o

0

o

o

0 0

0

o o

o | o o

0

0 0

o

o

0 0

0

0

0 0

o

30

o

o ! o

o

o o

o

o

0

0

2.O

o

3-3

o 2.5

0

0.4

3.3 O

1.6

o

0.2

0

o

31

o

O.I O

0

0 0

0

0

0

o

o

o

0

o 1.7

o

0.8

0.2 0.5

0 0

0

0

o

February i

o

o o

o

0 0

0

O 0

o o ! o

0

0 O

0

O.2

o.i 0.4

O.I 0 0

0

o

2

o

O 0

o

o o

0

0 O

o

O 0

o

0 0

o

O.I

o o

0000

0

3

o

o o

0

0 , 0

o

0

o

o.a

0

o

0

O 0

o

o

o o

0000

0

4

0

0 (0)

(o)

(o) (o)

lo)

(o)

o)

(o) (o)

(o)

(o)

(o) 10.4)

(o)

(0.3)

(O.I) (0.2)

(0) (0) (01 (01

1 \

(01

PART II. POLAR MAGNETIC PHENOMENA AND TERRELI.A EXPERIMENTS. CHAP. III. 463

TABLK LXVI (continued). Fy Matotdikin Schar.

Gr. M.-T.

o— 2 , 2 — 4 4—6 6—8

ill!

8—io 10— ra

is— 14

14 — 16

16— 18

1 8 — 20 20 — 22 aa — 24

Date

+

—

+

—

-t-

—

4-

—

-

—

4-

—

+ -

•+•

—

4-

4- -

4-

—

February 5

10!

(o.il o

O.2

o

o

o

0

0

0

0

o

O.I

o

0.9

o

0.8

0.4

O.I

0.9

O.I

0.6

0

0

6

o

0 0

0

0

O.I

0 0

o

o

o

0

°-3

o

0.3

o

10.41

(0.2)

o.a

0

O.I

0

o

o

1

o

0 0

o

o

o

0 0

o

o

o

o

o

0

o

o.a

°-3

O.I

O.I

o

o

3-9

o

8.4

8

0

0.5 o

0.9

o

1.6

0.8

°-3

o-5

0 (0)

(0)

a.o

o

0.8

0.7

0.7

2-7

0

5-9

o-S

24

0.4

0.5

9

o

O.I O.I

0.2

°-3

o.a

o I o.a

o

O.I

o

o

o

o

o

0

o

o.a

0

3-9

o

4.a

o

3-5

10

O.I

O.I O.I

o

o

o

0

0

o

o

o.a

0

0-3

o

o

o

o

0

0 0

o-3

i. a

o

4-4

i i

O.I

0.2 O.I

o

o .

o

0.6

0

0

O.I

°-3

o

O.I

o

o

o

o

08

o.a 1-9

o.a

0.5

o

1.4

12

0.1

O.I O

o

o

o

o

o

0 0

o

o

o

o

o

o

30

o

o 1.9

°3

0-5

0.1

0.1

'3

0.1

0.7 o

o

o

O.I

o.i

o

o

0

°-5

o

°-3

o

o

o

0 0

0.2 0.9

O.I

0.7

o

0.2

14

o.^.

O.I 0.1

o

0

o

o

0

o

o

0.4

o

0

o

I.O

0

o

o.a

o 0.6

o

a. a

o

2.8

15

o

0 0

o

0

o

o

0

o

0

0

o

0.4

o

1.2

1-9

o

17.0

o 0.3

o

0.4

o

O.2

16

o o o

o

o

o

0

0

o

o

o

o

0

0

0

0

°-3

0.7

o 0.7

o

O.I

o

O

'7

o ; o. i o

o

0

0

o

0

o

o

o

o

0.2

o

I.O

o-i

(o)

(o)

0 0

o

0-4

0

O

18

o

0 0

o

o

o

0

o

o

o

o

0

0

0

0

0

o

o

0 0

o

0

o

0

19

o

0 0

0

o

o

0

0

0

o

0

0

0

o

o

o

o

0

0 0

0

0

o

o

ao

(01

1.0 1 10)

(0.3)

(o)

(0.4)

(o)

10.3)

o

0

o

0

0

0

o

0

0

0

0 0

o

o

0

o

21

0

o lot

(o)

(o)

(0)

(0)

(°)

o

o

0

0

1.0

0

'•3

o

0.7

o

0 0

0

0

0

o

22

o

0 0

1.2

0

«-3

O.2

I.I

1.6

o

3.6

o

0.8

o

o

o

o.a

0 O.I 0

o

o

0

o

23

0

0 0

o

o

o

0

o

0

0

o

0

0.2

0

o

o

°-5

0

o.a o.i

o

0.4

0

o

24

0

0 0

o

0

o

0

0

o

o

o

o

o

o

o

o

0.5

o

o.a o

o

o

0

o

25

0

0 0.2

o

o

o

1.7

0

3.0

o

3-5

0

2-7

o

0.7

o

O.I

o

o

0.1

o

o

0

o

26

0

0 0

o

0

o

0

o

o

o

0

0

0

o

o

o

o

o •

o

o

o

i-3

0

O.I

27

(0)

(o) (o.i)

(o)

(o)

(0)

o o

0

o

o

o

o

o

0

o

o

o

o

o

0

0

o

o

28

o

0 0

0

o

o

0 0

o

o

o

o

o

o

0 0

o

o

o o

o

0

o

o

M:nvli l

o

0 0

o

0

o

o

o

o

o o

o

0.9

o

1.8

o

0.6 0.8

(0.2)

(0.2)

o

O.I

o

2.1

Kaafjord.

TABLE LXVII.
Disturbances in Horizontal Force (/'//).

Gr. M.-T.

I

0 2 2 — 4

4-6

6—8 8—io

IO — 12

13 14

14 — 16

16— 18

18 — 20

20—23

22 — 24

Date

4-

+

_

4-

—

4.

_

4-

—

4-

—

4-

_

4-

—

4-

—

+

—

4-

—

4-

—

September 3

O O.I

0.3 o

O.I

0

0

O.I

o

0

o

o

o

o

o

O.I

0

o

(0.1)

(o)

0.1

0

o

0

4

0 0

o

o

0.2

o

O.I

O.I

O.I

O.I

O.I

°-5

O.I

0

0.8

o

0.6

0

o

0

o

o

O.I

0

5

0

0

0

o

o

0 0

o

o

0

o

0 O.I

O.I

O.I

0

0

o

0

o 1 o

o

O.I

o

o o

0 0

0

O.I O

o

o

o

0

O.2 0

O.I

0

o.a

0

o.a

o-5

o

0

o

0

o.a

7

o.i 0.5 o o.i

o

0

o

O.I

o

o

o

O O. I O

o

0

o

o

0

0

0

0

o

0

8

o

0

o

o

o

o

0

o

o

0

o

o

o

o

0

o

0

0

o

0

0

o

o

o

9

o o o o

o

0

0 0

0

o

0

0 o O

o

o

0 0

0

o

0

0

0

o

10

0 0

0 0

o

o

0

o

0

0

O.I

0 0.2 O.I 0

o

0 0

0

o

o

o

o

0

1 1

o o

o

o

o

0

o

o

0.1 O

O.I

0 0.2

o

o

0

0 0

0

0.1

o

O.I

o

0.3

I 2

O.I 0.1

0 0

O.I 0

O.I

o

o

0

O.I

0.3 0.8

o 0.7

0

5-6 o

1-7

0.4

o

3-4 o

9-2

>3

O.2 0

o 0.3

0

O.2

o

O.I

0

O.I O

0 0

o

o

o

o

0

0

o

0

0

o

o

'4

O 0 0 0

O 1 0

o

o

o

0 0

0 o 0 0

0 o 0

0

o

o

o

o

o

15

o o o o

o

o

o

0

o

O 0

O.I 0.1 0 0

O.I o.i 0

0

o

o

O.I

o

0.7

16

o

o

0

o

0

o

o

o

o

O.I O

O.I O.I 0 0

o o o

o

o

o

o

o

0

'7

0

0

o

o

o

O.I

o

0

o

o

O.I

o o.i o.i 0.6

o

0.4 o

o

0

o

o

o

o

18

0

o

O.I

o

0.1

0

o

o

O.I

o

0.6

o

°-3

o

O.I

o

o

O.I

0

0-4

0.2

4-2

o

0.3

19

0

0.6

O.I

0

0

o

o

O.I

o

0.2

I.I

o

0.9

0

i-9

o

1.7 o

0.6

o.a

0

13-0

0

7-5

20

0

2.2

o 0.8 o. i

0.4

0.1

o.a

0.9

o.i u-5

o 0.5

0

0.2

o.a

O.2 0

0.9

0.7 o

8.5 o

3.9

'j i

0 O.I

o

o

o

o

o

0

O.I

0

o

0 O.I

O.I

o

0.5

0.2 0.1

0

O.I

o

0 0

o

22

0

o

o o

o

o

o

0

o

o

0

O.I

0

0

O.I

o

O.I O.I

O.I

0.4

0

0.7

o

5.1

1

464 I5IRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE LXV1I (continued). FH

Knaljord.

Gr. M.-T. o — 2 a— 4

ll

4-6

6-

-8

8 — 10

!O— 12

13 — 14

14-16

16-18

18-

-20 20 — 22

22-

— ^—

-24

Date

+

-t-

4_

+

+

_

4- -

-f

_

-1-

+

+

~

~

September 23

o

3.1

O 2.1

O.I

0

O.I

0

0

0

0 0

O.I O

0 0

0

0 O

1.9 o

-'.7 o

O.2

24

o

o

0 0

0

0

0

o

o

o

o o

o

0

o o

0

o o

o o

0 0

o

25

o

0 O 0

0

0

0

o

o

o

o

O.I

o

o.a

O.2 O

o

0 0

0 0

O 0

o

26

o

o.a o o

o

O 0

O.I

o

o

0

o

o

o

0 0

o

O 0

O.I

0

O. I o

o

27

0

0.2 0 0

0

o

0

o

0

o

o

0

0

0.3

o

0.3

o

o.a 0.4

0

0

0 0

o

28

o

0.5 o °

0

0

0

0

0

0

o

o

o

O.I

0 O

o

O.I O

0 0

0 0

o

29

o

O.I O 0

o

0 0

0

o

o

0 0

O.I 0

O O.I

o

O.I 0

O O.2

0.5 o

9.1

30

0

0.2 0 0

0

0 0

0

o

o

0 0

0 O

O.I O.I

O.2

o.a 1 o.i

1.4 o

8.0 o

8.4

October i

o

5.4 ° ]-8

0

0.1 0

o

o

0

0 0

O.I 0

o o

o

O 0

0

0

0 O

O.I

2

o

o o o

0

0 0

o

o

0

0

O.I

o.a o

O.I

0

o

O.I

0.1

0

0

0 O

0.2

3

O.I

0 0 O

o

0 0

o

0

0

o

o

O.I

o

0.2

o

0.3

o

O.I

O.I

o

0 I 0

0.2

4

o 03 o o

O.I

o o

0

0

O.I

O.I 0

o

0.3

0

0

o

o

o

o o

0 0

o

5

O O.I O O.2

O.I

O.I 0

o

o

0

0 0

0

0

0

o

o

o

O.I

0 0

0 0

o

6

I)

o o o

o

O 0

o

0

o

0 0

0 0

0

0

o

o

0

0 O

o o

O.I

7

o

0

o

o

o

O 0

0

0

o

0

o

0 0

0

o

0

o

o

0 0

0 0

O.I

8

o

0 O

0

o

0

0

o

0

0

O.I

0

0

0

o

0

O.I

o

O.I

o o

0 0

0

9

o

o o o

o

O 0

o

o

0

0 0

0

o

0

o

0

o

o

o o

o o

o

10

o

o o o

o

o o

o

0

O O 0

0 0

0

o

o

0

0

0 0

0 0

o

it

0

000

0

0 0

0

o

0

0 0

0.3 o.i

o

o

(o)

(o)

2.0

I.O O

13.8 o

5-5

12

0

0.6 o

o

o

0 0

0

0

o

0 0

O.I

0

O.I O

0 0

o

0

0

o

0

o

'3

o

0 0

0

0

0 0

o

o

0

O.I

O.I

0

o

O.I O.I

0 0

0

O.I

o

0

o

0

14

o

0 0

0

o

0 0

o

o

o

o

o

0

o

0 0

0 O

o

0 O

o

0

O.I

'5

o

o

o

o

0

0 0

o

o

o

o

O.I

o

o

0 0

0 0

o

0 O.I

0 i O

o

16

0

o

o

0

0

o o

0

0

o

o

o

0

0

0 O

0 0

0

0 0

0 0

o

'7

o

o

0

o

o

0 0

o

o

o

o

o

o

o

0 0

o o

O.I

0 0

0

o

0

18

o

o

O.I

o

0 I

0

o

o

o

o

o

o

o

o

0

o

O.I

0

O.I

O.2

o

0-3

0

0

19

o

0.8

0

0.9

o

o o

0

o

o

o

o

0

0

o

0

o

0

0

o

0

0

o

0

20

0 0

0

o

o

0 0

o

o

o

o

o

o

o

0 i 0

0 0

0

o o

o

O.I

o

21

0 0

0

0

o

o

o

o

0

o

0

o

0

0

0 0

O 0

o

0 0

0.4 o

0.4

22

0 0

o

o

o

0

0

o

0

o

o

0

o

o

o

o

o

0

o

o o

o

0

o

23

0 0

0

0

0

0 O

o

o

O : o

0

o

o

0 0

o o

0

0 0

2 I

O.I

I.I

24

o 0.3

O.I

o

0

0

o

0

o

0

o

0

o

0

O j O.I

0.6 o.i

0.7

O O.I

4-2

o

,3.8

25

o 9.4

0.1

'•5

0

0

o

0

o

0

o

o

0

0.4

o o.a

0 0.2

o

o

0.2

0

0

o

26 o 0.5

o

O.T

o

0

o

o

o

0

o

o

o

o

O O.2

O.I 0

0

O. I O

0 O

I.O

27

o 1.4

0

0.4

0.2

O.I

o

O.I

O.I

o

O.I

0

0.2

0

2.O 0

1.8 o

2.3

o.a o

2.2 O

7-3

28

0.1 O.I 0

0-3

O.I

0 O

o

O.I

0 0

o

O.I

o

O O.I

o o

0

1-5 0

2.4 o

3-9

29

o 0.3 o o

0.2

0 0

o

0

0 0. 1 I O

0

o o o

(0) 101

0

o 0.3

0.3 o

2.6

30 i o 0.7 o

O.I

0

0 ! 0

0.7

0.4

0.6 1.3 o.a

0

O.I O 0.2

O.I 0

o

o

o

0.8 o

I.I

31 o 1.7 o

0-3

o

1.2 O.I

03

1.2

0.2 7.3

0

12.7 o

15.3 o

3-7 0.8

0

12.7

0

18.8 o

18.6

November t

o 9.8 o.a

I.I

0.8

0

o

o

O.I

o

O.I

0.2

0

0

0 0

o

o

o

0

o

0.4

0

o

a

0 0

0

o

0

o

0

0

o

0 0

0

O.I

o

0 O.I

0.7

o

0.6

3-7

O.I

0.8

o

0

3

0 0

o

0

o

0 0

o

o

0 O O

0

o

0 0

o o

0

O O.I

0 0

0.3

4

0 0

0

o

0

0 0

o

o

o o o

o

o

o o

o

o

o

o

0

o

0

0

5

O 0

o

0

o

0 0

o

o

0 0 O

0

0

o

o

o

o

0

o

o

0

o

0

6

0 O

o

o

0

0

o

0

o

o

(0) : (o)

(o)

(o)

(o)

0

o

o

O.I

0.6

o

1-3

0

0.2

7

o.i 0.3

O.I

o

0

0

0

0

o

o

0 0

o

o

o

0

o

o

o

o

0

o

0

0

8

O O.I O , o

o

0

o

o

(o)

(o) 0 ; 0

o

o

0

0

o

o

0

0

0

0

0

0

9

o o 0,0

o

o

o

0

0

O O 0

o

o

o o

o

o

o

o

0

0

0

0

10

0 0

o

o

0

0

0

o

o

o

O 0

o

o

o o

o o

0

o

0.2

o-5

o

0.9

II

0

0

0

0

o

0

0

0

o

0

Q

0

o

o

o

0

0

o

o

o

0.2

0

0

o

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III.

TABLE LXVII (continued). FH

465
Kaa fjord.

Gr. M.-T.

o — 2 1 a — 4 i 4 —

-6

6-8

8— IO IO— 12

1

12— 14

14—16 16- 18

18 — 20

20-

M

22—24

Date

+

—

+

_

-t-

—

4-

_

4- —

4-

4.

_ 1 4.

+

+

4-

- 4-

_

November 12

0 0

0

o

o

o

o

o

O 0

0 O O

o

o

0 O

0

0

O O.I

O O.I

O.2

'3

0 0

0.2

0.7

0-5

o

0 ! 0

O O.I

0 [ 0-5

o

0.4

o

O.I O

0.2

O.I

O.I 0

0 0

o

M

0 0

o

o

o

O.I

o o

(o) (o)

(0) (O.I)

o

o

O.I

O.I 0

o

(o)

(o) 0.3

O.I 0

0.2

IS

o 0.6

o

o

o

o

o

o

o o

O 0

0

o

O.I

o o

0

o

0 0

1.2 O.I

0.3

16

o o

o

0

o

o

o

o

o o

o o

o

O.I

o

O.I 0

o

o

0 0

0 0

O.I

17

o 0.6

o

0

0

o

0

o

1

O 1 O.I

o

o

0

o

0

0

o

0

0

0 0

O.I

o

o

18

o o

0

o

0

o

o

o

0 O

o o

o

o

o

0 0

o

0

0 0

0.6 o

°-3

19

o o

0

o

0

o

o

o

o

0 0

o

o

o

o

0 0

0 0

0 0

0.3

0

0

20

o o

o

o

o

o

o

o

0

o o

o

o

o

o

O O.2

O.I O.I

O.I O.I

O.I 0

o

21

0 0

0

o

0

o

0

o

o

0 0

o

o

o

o

o 0.6

o

0.8

0.2 o

IO.O

o

2.1

22

0 0

0

o

0

o

O 0

0

o

o

O.I

O.I

O.I

0.2

^

o 1.6

0.8

1.2

0.3 o

4-4 o

2.8

23

0.4 o

0.3

0 O.I

o o.i 0.2 o.a

o 0.5 o.i

0.4 o.i 0.4

o 0.9

O.I

2.1

o 2.7

O 1.2

II. I

24

o 13.4

0

16.3 0.3

1.2 0.3 0.9 1.3

O \ 2.8 0

8.0 o 10.0

o 1.3

5-3

°-3

24 o

14.0 o

8.7

25

o 4.4

o

1.4

0.3

0.2 0.5 O.I 0

0.5 0.7 o 1.9 o 3.6

o 4.2

o.a

o

M-5 o

7-5 o

3-3

26

o 6.1

O.I

O.I

0.1

O.2 O O O.2

O O O. I J O

o

3-8

o

5-2

o

a.o

o 0.4

0

o

O.I

27

O.I O

0

0

o

O.I

0 O.I

0

O.I

O O.I

0

0

o

O.I

0

o

o

O O.I

o o

o

28

o o

O.I

o

o

o

0 0

0

o

o o 0:0

o

o

0

o

o

0 O

0 O

0

29

0 0

o

o

o

o o o

0

o

O 0 { O O

. o

0 0

o

o

0 0

0 O

0

3°

0 0

0

o

o

0 0 O.I

o

o

000 0.2

o

O.I

O 0

o

O.I

0

o o

O. I

December i

O i O. I

0

0

o

0

0 0

o

0

O.I 0

0

0.4

o

O.I

0.3

o

0

o.a

o

I.I

0

o

2

O O. I

o

o

o.3

0

O.I 0

0

o

o o

0

o

o.a

O.I

0.5

o

0

o

o

0

o

0

3

0 0. 1 i O

0

0

000

0

o

0 0 O

o

o

0

o

0

o

0

o

o

0

0

4

JO 0 I O

0

o

000

0

o

o o o o

0

0

0

O.I 0.2

O.I 0.2

o

o

o

1

5

o o o

0 O

0 0 O 0

o

0 O O

o

o

o

o

0 0

O 0

0

o

0.7

6

0 O.2

0

o

o

o

0 0

o

o

0 O

o

0

0

o

0

o o

0 0

0

o

o

7

0 0

0

0

0

o

0 0

0

o

o o

0

0

0

0

0

0 0.2

0

O.I

0

o

o

8

o o

O 0

o

o

0 0

o

o

O 0

0

0

0

0

0

0 0

0

O.I

o

o

o

9

o

o

o

o

O.I

o

O.I 0

o

0

0 0

0

o

0

o 2.7

o 0.9

o

0.2

O.I

o

O.I

10

o

o

0.3

O.I

o-5

o

o o

0

0

O.I O.2

0

o.a

0

O.I

o

0 0.2

O.I

O.2

O.I

o

O.2

ii

o i o

0

o.a

0

o

O 0

0

o

0 O.I

O.I

o

O.I

o

0.5

o 0.7

o

2.6

0

o

I.I

i

12

O.I

°-3

o

O.I

0

o

o

o

0

o

0

0

o

0

O.I

o

0.7 o

i-5

o

o

o

o

'3

0

o

0 0

O.I

o

O.I

o

0

o

O.I

O.I

O.I

0

o

o

o.i 0.4

O.I

O.I

O.I

0.9

O.I ; O.2

M

0

O.I

0 0

0

o

0

0

o

o

0 O

o

0

o

0

o o

o

0

o

0

0 0

15

0

1.4

O.I

O.I

0

0

o

o

0

0

o

o

0

o

o

o

0 O

O. I

o

0

0

(o)

(O.II

16

0

o

0

0

0

0

0

o

0

0

0

O.2 O.I

O.I

o

o

0.5

0

o

o o

0

0

0

17

0

0

o

o

o

0

o

o

0

o

0

o

0

o | o

0

O 0

o

o o

0

o o

.8

0

o

o

o

o

o

o

o

o

o

o

0

o

o

o

0

O 1 O

o

o (o)

(0. 1 1

O 0

19

0

0

o

o

0

o

0

o

O 0

0

O O.I

O.I

O.I 0 O.I 0

0-3

0 0

0.4

0 0

20

o

o

0

o

o

0

0

o

o

o

o o

o

o

o

O.I

0 0

0

0 0.

0

0 0

21

0

0

o

o

0

o

o

o

0

o

o

0 0

0

o

o

0 0

o.a

o

0

0

0 0

22

0

o

0

o

0

o

o

o

°-4

0

0.5

o

o

O.I

0

0.2

.O.I O

O.I

o

0

2.0

o 5.8

23

0

IO.I

0

1.5

o

1.2

0 I.I

0.3

O.I

0.9

O.I

3.6

o

°-3

O. I

3-4 o

0.3

2.3 o

4.6

O 0.1

24

o

0.5

o

o-5

0.2

o

0 0

0.2

O.I

O.I

O.I

o.a o.i 0.6

O O.2 O

0.6

O.I

o

0.4 o 0.6

as

0

o.a

o

o.a

0.3

0

o

o

(0.2)

(o)

(0.4)

(o)

(I.O) (O.I) (0.2)

(o.i) (0.9! 10)

(0.3)

(0.6)

(o)

12.01 10) (2.0)

26

(o)

(I.O)

(o)

(0.5)

(o.i)

(0.2)

(o)

(o)

o

o

o

0

o

O.I 0

O.I

0 O

o

o

0

0.7

0 2.0

27

0

o

o

o

o

0

o

o

o

o

0 0

0

0 0

0

o o

o

O.2

o

0.6

0 2.8

28

0

1.6

0

O.I

O.I

O.I

0.2

o

o

o

o.a ; o

O.I

O.I O.2

o

o 0.4

o

o

0-3

o o o

29

0

O 0

o

o

0

0 0

o

0

0 0

o

O 0

0

O.I 0

O.I

o

o

o o o

3°

o

o

0

0

0

o

o o

o

0

o o

0

o o

o

o

0

o

o

0

o o o

3i

o

o

o

o

0

0

o

o

o

o

o

0

o

0 0

o

O 0

o

o

0

0

o

o

466 BIRKELANU. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

TABLE LXV1I (continued). FH

Kaafjord.

Gr. M.-T. ; 0-2

2-4

4-6

6-8

8 — io

10— 12

12 — 14

14 — 16

16-18 18 — 20

20 — 22

22 — 34

Date ! 4-

—

+

—

+

—

+

—

+

—

+

—

-1-

—

+

—

+

—

4-

—

4-

—

4-

January i o

0

o

o

o o

o

o

o

0

o

0

0 0

0

o

o

o o

0

o

o

0

O.I

2 0

O.I

o

0

0 O

0

o

o

O O.I

o

O.I 0

o

o

o

0 O O

o

0

0

0

3 °

O.I

0

O.I

0 0

o o

O.I

O.I

0

o

0 0

o o

o

O O.I 0

0.2

0

0

0

4 °

0. 1

o 0.3

0 O.I

O.I 0.2

o

o

O 0

0 0

o

0

o

0 O.I

o

O.I

0.3

0

0.6

5

0

O.I

0.5 o.i

I.I

o-5

o

0

0

0.1

O.2

O.I

O.2 ; o

o

o

0.9

O.I O

o

O.I

o

0

0

1

6

o

O.I

O O.2 O

0

o

o

0

0

o

o

0 0

o

0

o

0 0

O.I

O.I O.2

o

O.I

7 °

o

o

0

0 0

0 0

o o

o

0

o

o

o

o

o

o

O. I

0.1

o

o

0

0

8 o

o

0

0 O. I O

O.I O

0 O

o o o o

o

o

0

0

o

O.I

o

0

0

0

9 o

o

O 0 o. I O

0 0

o

o

0 0 O. I O i O.I

o

o

o

o o

O.I

0.2

0

'•3

10

0

0.2

o

0.4 o

0

o

o

o

o

O 0. 1 O O. I

o

0-3

O.I

O.I

o

o

O.I

0

0

0.2

1 1

o

O.I

o

0.2 0

0

o

o

0

o

0

o

0 0

0

O.I

O.I

o

0.6

o

0.6

°-3

O.I O.I

12

o

O.I

O O.I O.I O

o

o

o

o

o

O.I

0 0

0

0

o

o i 0.3

o

o

o

0 0

13

0

O.I

o o o

o

o

o

0 0

0 0

0 0

o

o

o

o o

°-5

0

O.I

0 0

M

o

0

0 O O

0

0

o

0 0

0 0

0 0

o

o

0

O 0

o

o

0

o 0.9

15

0

0

000

0

o

0

o

o

0

o

0

o

o

o

o

o 0.3

0.2

o

0

O o

16

o

o

0 0. 1 ' 0 0

O 0 o 0

o

o o 0.3

o 0.2

o

000

o

0

0 0

17

(o) 1(0.1)

(O.I (O.I) (0) (0)

(o)

(o) o o

0 0

o o o o

o

O O 0

O.I

0

0 0

18

o

0

O O 0

0

o

o

o

o

0

o o o. i

0.4 o.i

0.2

O 1.2 O

o

0

(0)

10. 1.

'9

(o)

(O.I

(0) |(O.I) (0) (0)

(0) (0)

o

O.I

0 O.2

O.I 0

°-3

o

0.6

o : o. 1 1 o

O.I

0.2

o

0.2

20

o

0

o

0.3 o o

o

0

o

0

0 O

o

o

o

O.I

o

0 O.I

0

O.I

0

0

0

21

0

o

o

O o O.I

o

0

o

o

0 O

0

O.2

o

0.4

o

0 O

o

0.3

0

0

03

22

0 02

O O 0 0

o

o

0

o

0 0

O 0

o

o

O.I

O O.I

0

o

o

0

0

23

0 0

O O o O. I

o

o

o

o

O.I O

O.I 0

0

O.2

0.6

o 0.4

O.I

O.I

t-3

0

O.I

24

0 0

O O.2 o O

o

0-2

0

o

o o

O.I

o

O.I

o

0.2

o 0.3

O.I

O.I

0.2

0

O.I

25

o

0

o

0 0

O.I

0

o

o

o

o

o

o

o

o

o

0

o

o

o

0

0

0

0

26

0 0

0

0 0

o

o

o

O.I

o

o.a

o

°-3

o

0.2

0

0

O.I

0

3-3

o

1 I.O

0

-•-'•5

27

o 5.0

0

O.2 o O

0

o

o

0

o

0. 1

O. I O. I

O 1 o

O.I

O.I

0

O.I

o

0.9

o

0.7

28

0 0

0

o o o

o

o

o

0

0 0

o o

O | O

O.I

0

o

o

O.2

0

0

0

29

0 0

0

000

o

0

0

o o o

0 0

O O.I

o

o

0

o

o

0

0

o

3°

0 0

0

0 0

0

o

o

0

O.I

O 0

O.I

O.I

0.3 o.i

1.7 o

3-7

o

o

o

o

0

3"

O O.I

o

o

o

0

o

0

0

o

o o

0 0

o

O.I i 0.2

o

0

o

o

0 0

o

February I o o

0

o

o

o

o

o

o

o

O 0

o o

o

O O.I

o

O.I

o

o

0 0

0

200

0

o

0

o

o

o

0

0

0 O

0 0

0

o

o o

0

o

o

0 0

0

300

o

o

0 O

o

o

0

0

O O.I

O.I

o

0

o

0 0

0

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0 0

0

4

0 0

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0

o

O.I

o

o

0

o

0

0

0

0

0

0

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o

o

O.I

0

O.I

0

5

0 0

o

o

0

0

0

0

o

o

o

o

o

0

(o)

(o)

'o)

(o)

(o)

(o)

(o)

(o)

10)

(01

6

0 0

o

o

(0) (0)

(o)

(o)

(o)

(o)

(o) (o)

(0)

(o)

(o)

(o)

o

o

0

o

0

o

o

0

7

0 0

0 0

0

0

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o

o

0 ' 0

o ; o

o

o

o

o

0

o

o

1.6 o

4-4

8

o 0.3

O.I

1.3 o

O.2

O.I

O.I

0.1

°-3

I.O O.I

0.2 0.4

3.6 o

4-3

0

i-3

5.0

o

8.0 o.i

0.6

9

O.I

0.3

o

I.O

o

0.2

1 O

0

o

0

o o

0

o

0

o

0

o

O.I

O.I

o

1-9

0

3-a

10

o

0.5

0

0 | O

0

o

o

o

o

o i o

o

o

o

o

o

o 1 o

o

O.I O.I 0

6.1

1 1

o. i 0.3

O.I

O.I

O.2

o

0

O.I

o

0

O O.I

o

O.I

o

O.I

o

O O.2

O.I

o 02 o i--

12

0 0.2

o o

o

o

0 O 0

0

o

o

o

o

0.2

O O.I 0

1.7 o

0.3

o

0

O.I

13

0

3.7

0.6 o

0.4

o

O.I O O.I O.I

o

0.3

o

O.2

O.I

0

o o

I.I 0.1

O.I

o o 0.7

H ': o

0.7

O.I 01

O 0

i o

0

o o

O.I

O.I

O.2

0

°-3

0.2

O.I O

0.2 0

O.2

O.I 0.1

0.!

15 o o

0 0

o

o

o

0

o

o

o

0.6

o

0.3

0.8

o

2.O ' O.I

0 0

o

o

o

0

l6 | 0 O

0 0

o

0

. 0

o

O 0

o

o

o

o

(o)

(o)

(0) (0)

(0) (0)

(o)

101 101

101

17 lo) (0.3) (o) (o)

(0.2 | (0)

(O.I) (0.1

(o)

•o)

(o)

(o)

(o)

(o)

(o)

(o)

o o o o

O.I

0 0

0

18

0 0.2

0 0

o

o

o

0

o

o

0

o

o

o

o

0

o

o

0 0

o

0 0 0

19

o

o

0 0

o

o

o

o

O 0

o

o

o

o

o

0

o

o

0 0

o

000

1

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III.

'ABLE LXVII (continued). Fu

467
Kaafjord.

Gr. M.-T.

o—

-2

a—

-4

4-

-6

6-

-8

8-

IO

IO-

- la

12 —

'4

14-

16

16-

-18

18-

•3O

30—

-32

33-

-24

Date

+

-

+

-

+

-

+

-

+

-

4-

—

+

-

+

-

+

-•

+

-

+

-

+

-

•

-

25

0

0

o

O.I

O.I

0.2

o

O.I

o

0.2

0. 1

O.I

0

o.a

0

o

o

0

o

o

0

0

O

0

26

0

o

o

0

0

0

0

o

0

o

0

0

o

o

o

0

o

0

o

0

o

0.6

o

o-5

27

o

o

0

0

0

O

0

o

0

0

o

o

o

o

o

o

o

o

o

o

o

o

o

0

28

o

o

0

o

o

0

0

0

O.I

0

o

0

o

o

0

0

0

o

o

o

o

o

o

0

Marrli I

0

o

0

o

o

0

o

0

0

o

0

o

o

o

O.I

O.I

2-3

o

08

0

o

0-3

0

1.2

2
3

0

o

0.8
0.4

O.I
0

o

0

o
o

O.I

o

0

o

o
o

o

(o)

o

(o)

o

(o)

O.I

(o)

o

(o)

o

(o)

(o)
<o)

(o)
(o)

(o)

(01

(o)

(o)

i-4

(o)

o
(o)

3.1

(0.2J

0

lo)

I.I

(0.2)

O

(°.2J

4
5

10)
0

(o.i)
0.4

(o)
o

(o)
1.6

(0)
O.I

(o)

O.2

(o)
o

(o)

0

0
O.I

o

0

o

°-3

o
o

o

0

o

0

o

(I 0)

0

10)

0
1.2

0

O.I

0
O.I

0

O.I

o.a
o

0

o

O

o

0-5
O

6

0

o

o

0

0

O

0

o

o

o

o

0

O.I

0

O.I

0

O.I

0

o

o

0.3

0.3

O.2

0.4

7

0.4

0

0.2

o

0.4

O

°-3

0.4

o

1.2

O.I

O.I

o

02

0.8

0

i-3

o

0.7

O.I

o

o

O

0.4

8

0

'•7

0.8

O.I

0.8

O

O.2

o

o

o

o

o

o

1.0

0.4

O.I

2.7

0

0.6

0.6

O.2

64

O

IO.O

9

0.6

O.I

o

1-3

°-3

o

°.5

0

o

O.I

O.I

O.I

o

0

o

0

O.I

o

°-3

0

o

0.4

O

0.2

10

o

o

0

O.I

o

o

o

o

o

o

o

0

O.I

o

O.2

o

0.8

o

0.6

0

O.I

O.I

O

0.2

ir

O.I

0

0

o

o

o

o

o

o

o

o

o

0-3

0

O.I

O.I

O.I

0

0.4

O.I

0.7

o

o

0

TABLE LXVIII.
Disturbances in Declination (FD).

Gr. M.-T. 0-2

i!

2-4

4-6

6-8

8—io

IO — 1 2

12 — 14

14 — 16

16-18

18 — 20

20—22

22 — 24

Date 1 4- -

+

+

+

^.

+

—

+

—

+

—

+

—

+

—

+

—

+

-

eptember 3

O

O.2

O.2

O.I

O.I

o

0

O.I

O.2

0

O.I

o

O.2

0

O.I

o

0.6

o

(o)

(o.i)

o-3

o

o

O.I

4

o

0.4

o

0.2

o

0.3

1.0

O.I

0.8

0

O.I

0.2

0.5 o

o

0.4

0

0.4

o

O.I

O.I

O.I

O.I O

5

o

O.I

O.I

O.I

O.I

O.I

0

O.I

0

O.I

O.I

O.I

o

0.2

0

O.I

0

o

o

o

O.I

0

o 0.3

6

o

°-5

o

0.2

o 0.3

O O.I

0

O.I

o-4

0

O.2 O.I

o

O.I

o

o

o.t

0.3 o

O.I

O.I O

7

0

1.4

o

0.6

O. I O.I

O i O.I

o

O.I

0

o

O.I

o

o

O.I

0

o

o

o

o

o

o

0

8

0

o

o

o

o o

o o

o

o

0

0

o

0

o

o

O.I

o

O.I

0

o

o-3

0.3

O.I

9

0.4

o

O.I

O.I

o

O.I

O.3 O

o

o

o

0

o

0

o

O.I

0

0

o

O.I

o

0.7

0.1

o

10

0

o

o

0

O O.I

0

O.I

O.I

O.I

0.4

O.I

0.4

o

o

0.6

o

0.2

o

O.I

o

o-5

o

O.I

ii

o

0

0

O.I

0 O.I

O. I O. I

o.a

o

0.3

O | O.I

O.I

0

0.6

O.I 1 O

0.5

o-3

o

0.7

o

0.9

12

o

0.9

o

0.3

O j O 2

o 0.3

o

O.I

0.3

0

i-5

0

1.6

0

4-5

0

2.1

0

o

2-3

0

4.8

13

o

0.4 | o

0.4

o.i 0.5

o 0.8 o

O.I

o

0

O.I

o

o

O.I

o

o

o

o

O.I

o

O O. I

14

o

0 0

o

o o

o o 1 o

o

o

o

o

o

0

o

0

o

0

o

o

0

o

o

15

o

O.I

o

O.I

O.I

O. I

O.I

o o

o

0.2

0

O.I

O.I 0

O.I

0

o

O.I

o

O.I

0.8 ! o

1.6

16

O.I

0.2

o

O.I

o

0

o

o

0.3

o

0.3

o

o

0

o

°-3

o

o

o

0 0 0.4 O.I

o

17

O.I

O.I

0

O.I

o

0.5

O.I

O.I

O.I

0

0.3

0.1

0.3

O.I

O.I

O.I

0.6

o

0.6

0

0

o.a ; o

O.I

18

0

O.I

o

O.I

o

o

0

o

O.I

O.I

0.4

O.I

o

0.7

0

0.3

0

O.2

O.I

2.1

o

8.8 o

1-7

19

o

1-7

0

0.6

o

0.5

O.I

0.5

0.6

o

0.8

0.2

0.4

o

1.4

o

i-3

o

0.6

0.4 o

7-3 o

6.4

20

o

3.O

0

3.4 1 0.4

0.9

0.5

0.4

O.I

0.4

1-3

O.I

1.2

o

O.I

0.2

o.a

o

O.2

3-4 o-i

2.2 O.I

0.4

21

0

o.a

O.I

O O.I

O.2

0.2

O.2

0

O.I

O.I

O.I

1.3

o

O.I

0.4

O.I

0.5

0

0 0

0 0

o

22

o

o

o

o o

o o

o

O.I

o

O.I

O.I

O.I

O.I

O.I

o

o

0.9

O.I

1.9

o

1.3 o

2.1

23

o

4.2

o

1.2

o

0.3 0.4

O.I

O.I

O.I

O.I

0.1

o.a

0

o

O.I

0

0.6

O.I

0.6 o

2.0 0

O.I

24

o

0. 1

0

0 0

0 O

O.I j O.I

O.I

0

0.2 0.2

o

o

o

0

o

0

o

0

o o

o

25

O.I

0

o

O.I O

o

0

0

o

O.I

o

0.2 0.2

0

o

0.7

o

o

O.I

O.I

o

o o

o

26

0.3

O.I

0

O.I

o

0 0

o

O.I

o

o

O.I O

o

0 0

o

o

o.a

0.5

o

0.5 o

o

27 0.2 O.I 0

O.I

0

O.I O

O.I

O O.I

o

O.I

o.i 0.4

o

0.3

0 0

O.I

0.2

O.I O.I 0.2

o

BIRKFI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE LXVIII (continued). Flt

Kaatjord.

Gr. M.-T.

o — a

2-4

4—6 6—8

8 — 10

lo — ia

12— 14

14 — 16

16-18

18 — ao

ao

— 22

22

—~~—

-94

Date

f

—

4-

—

4-

—

.+

—

+

—

4

—

+ —

+ —

+

—

+

—

+

—

+

_

September 28

0.4

O.I 0

0.3

o

o

o

o

o

0

o

o

O.2 O.I

0 O O-I

o

O.I

O.I

O.I

0

0

0

29 0.2 0.2 o. r 0,1 o.i o.i o o o o

O.I 0

0.2 0

0 0. 1 O.2

0

o-3

o

0.4

0.4

0

5.o

30 o : 0.7 o o ! o o o o.i o.i o.i

0 0

O O.I

0.6 o 1.7

o

o.a

I. a

o

7.2

o

8.3

October i o

5.7 O 2.9 ' O O.I O.2 O O. I O

0.1 0

0 0

0 O.I O.I

o o.a 0.6

O.I

°-3

o

O.I

2 0

o o. i o 1 o o o o. i 0.6 ' o

O.I O.I O 0

O.2 0

o.a

o.a

o.a

o

o.a

o

0.2

0

3

O.I

0 | O.I

O.I

o

o

o

O.I

O.I

O.I

o.a

o.a

O.I 0

0 O.I

o

o

o

0.5

O.I

0.6

O.I

o

4

°-3

O.I O O

O.I

O.2 O.2 O

0 O

0.9 o

0 O.I

o

O.I

o

0 0

O.I

O.I

0

O.I

0.4

5

°-3

0 0.2 O.I

O.2 0.3 0 0.2 0 O.I

O.I 0

0 0

O 0 O.I

0 0

o

0.2

O.I

0

0.1

6

o

o o o

o

O.I

o o 0,0

O O.I

0 O

o o.a o

o

o

o

O.I

O.I

o

O.I

7

o

o

0

o

o

0

o

o

o o

0 0

o

o

0 0

o

0

o

0

O.I

o

°-3

0

8

0

o

o

o

0

o

o

o

0

O.I

0.4 o.i

O.I

o

0 O.I O

o

o

0.8

o

0-3

0

O.I

9

O.I

o

0

o

0 O

o

O. I O. I

O.I

0

o

O.I O

o 0.3 o

O.I

O O.I

o

o

o

o

10

o

o

o

0

o o

o

O O.I

o

O.I

o

0 0

0 0 O

0 O.I

o

0

0

O.I

0

1 1

o

O. I O.2 i O. I

o

o-3

0.2

0.1

O.I

0

0.2

O.I

0.5 o

O.I 0

O.I

(O) 2.2

!-3

O.2

12.6

0

6.2

12

o

O.I 0

0.4

0

0

O.I

o

O.I

o

O.I

o

O.I

0

O.I 0

0.3

0 0

o

O.I

0

0

o

13

o

0

o

o

0

o

0

o

0.2

0

0.7 o.i o jo

O.I O

O.I

o

o

0.6

o

1.0

0

0

1

M

0

0

o

o

O I O

o

o

O.I 0

0

o o o

0 0

°-5

0

0.7

o

O.I

o

0.5

0

15

O.I

0

0

o

0 0

o. r

O.I

O.I O

O.I

O.I 0 0

0 0

0

o

O.I

0.2

0

O.I

O.I

0

16

0

O.I

o o

0 0

o o

o

0

0

o o o | o o

o

0

o

o

o

O.I

o

O.I

17

o

o

0 0

0 0

o

o

0

O.I

0 O.I

•

o

o i o

o

o

o

o

0

o

0

0

0

18

O.I

o

0.2

O.I

O.I 0.2

O.I 1 O O 0

O.I j 0 O O.I

o

O.I

O.I

o

O.I

0.9 o

••4

O.I

O.I

19

O.I

0.8

O.I

o.a

0

o.5

o ' o.a o o o | o o

o

o

o

o

o

o

0.1 0

o

0

0

20

o

0

o

o

0 0

o

o

O O.I O.2 O.2 O i O

o

o

0 O

o

o o

0.4

0

O.I

21

0 O.I

O.I O.I

o o

0 0

O.I

O O 0 O O.I

O.I

o

o 0.6

o

O. I O. I

02

o

1.0

22

0 0

0 0.2

0 O.2

0 O.I 0

o

0

0 0

o

0

o

0

0

o

O O.I

O.I

o

O.I

23

o

0

0

0

0 O

0

o

0

O.I

0

o

0

o

o

0

0

0

O.I

o 0.6

0.7

O.I

0.6

24

0 I.I

0.4 o.i

0.3 o o o.i o.i o

0.4 o o

O.I

O.I O.I

0.8 o. i

°-5

0.4 o

5-°

0.8

9.0

25

o 1 1.8

O 2.6

o 0.5 o.i o.i o 0.4

o.i 0.5 0.4

0.2

0

°-3

o

O.I

o

O.I 0,2

O.I

0

0.2

26

0 0

o o

O O o

o

0

0

o 0.4 o

0.3

o-3

0.2

0.9

0

o

0.5 o. i

0

0.4

0.2

27

o . 1.9

o

i-5

0.2 0.4

°-5

O.2

O.I

0.3

0

i-3

O.I

0.5

i-9

o-3

1.6

0.8

0.6

°-3

o

0.7

o

4.0

28

o 0.3

o.i 03

O.I O.I

0 0

O.I 0

o 0.4 o

0.4

O.I

O.I

O.I

o

o.a

I.I O.I

1.0

o

4.0

29

O O.2

O O.a

O.2 O.I O.I O.I

0 O.I O.I 0 O.I

O.I

o

o

(o.i)

(o.a)

o

0.2 0

3.5

0

a.8

3°

O.I

0.9

o o.a

0.4 o

0.4

O.I

1.0 O.I

I-I

0. 1 O O

o

°-3

o 0.6

o

0.5 o

2.7

o

0.7

3'

o

3.6

0.4 0.5

2.7 o

1.8 o

0.6 o.i 1.9

o-i 3-3 J-3

8.5

0

15.7 o

!-7

3-a o

13-5

o.5

I2.I

November i

o.i 8.4

o ' 2.3

O.2 O.2

O.I O.2

0.4 o

0.2

o

0

o

0

o

0

0

o

0 0

0.4

o

O.I

1

2

0

0

0

o o

O O.I

o

O.I

0

O.I O 0

o

°-3

o

1.9

O.I

O.I

1.8

0

2.7

o

O.I

3

0

°-3

0

0.2 0

0 O.I

O.I

0

o

o

0 0

o

o ! o

o

0

o

o

o

0.4

0

0.7

4

o

O.I

o

0 0

0 O

o

o ! o

0

0 O

o

o o

o

o

o

0

0

o

0

o

5

o

0 0

0 0

0 0

0 0

o

0

0

o

o

o 1 o

o

o

o

o

o

O.I

o

o

6

o

0 0

0 0

0 0

o : o

0

(o)

(o)

(o)

(o)

(0) ! (0)

(o)

(o)

0

0.9

o

3-2

O.I

0.3

1

7

o

0.6 o

O.I 0

O.I 0

0 0

0

o

0

0

0

0

o

0

o

0

0

o

0

0

o

8

O.I

O.I 0

0.6 o

0 0

0 (0)

(o) o

o

o

0

O O.I

o.a o

o o

O.I

O.I

o

0

9

o

0 0

o o

0 0

0 0

0 0

O.I 0

O O 0

o

o

o o

o

0

o

0.2

10

o

0.2 O

O O O o. I O O O O

O O.I

0.1 0 O

o o

o

o

0.2

0.7

0

1.0

II

0

0.2 0

0 0

0 0

0

o

o

0

0 O

o

o

o

o

0

0

0

0

o

0

0

12

0

0 0

0 0

0 0

0

o

o

o

0 0

o

0

O.I

o

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0

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0

0.5

0

2-4

'3

o

0.6 0.3

O.5 0.2 0.2 0.3

0.4 o.i

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0

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0 j (O.I) (0) 0 0

o

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(o.a)

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(01

10.51

15

(o)

(0.3) '(o.i) (o.i) (0.1) (o)

(O.I)

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0 O.I

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16

0

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0

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PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III. 469

FABLE LXVIII (continued). FD Kaafjord.

Gr. M.-T. 0 — 2

il

2 — 4

4-6

6-8

8-10

10— la

13—14

14 — 16

16-18

18 — ao

20—33

23 — 34

Date

+

—

+

—

+

—

-K

—

+

_

-1-

+

4-

-1-

+

+

+

Vovember 17

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Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903.

60

i

>i..\ uis i:.x i>i I )ii u >

1902-1903.

Kaafjonl.

Cr. M.-l. 0-2 2 - , 4

— o 6 -- 8 8 10 i o — i 2 i L' -- i 4 i 4 - - i 6

16—18 1 8 — 20 20 — 22

22

-2;

Date r -*- H

+ j _ ' + I - 4- - ! + j .4-

4- ' -4- — 4- —

4

January o o o. i o. i o. i o

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0

20 0 0. 1 0 0. 1 O. I

O.I O O I o 0 O, 1 O 0 O. 1 0 O

0,0 o o o o

o

0

21 O O O. I O Q.2

O O 2 O O.I O O-4 O O.O O 0.5 O

O. I O. I O O O 0

o

O.I

2D 0 0. 1 O. 1 0.5 I .8

o L'.U o i .0 o o. 7 o 0.3 o. i o. i o

O.2 0 O. 1 O O O

O. I

0.2

23, O. I 0. 1 0 o (I. 1

0. 1 0 0 0 0 0 0 O.2 O. I O O

0.3 o 0.2 o o 0.6

o

o

0.5
o

, , . 0

'

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III.

471

:/\BLE LXVIII (continued).

Fo

Kaafjord.

Gr. M.-T. 0—3

2-4

4-6

6-8

8— 10

io— 13

12— 14

14 — 16

16-18

18-20

ao — aa

32 — 34

Date

.

—

+

—

+

—

+

—

+

_

+

_

+

_

•4-

—

+

—

+

—

+

_

+

_

Ki-bruary 25

0

o

0.2

O.I

0.9

0

2.2

0

0.4

o

0.4

O.I

04

o

o

°3

0

o.a

o

o

o

o

o

o

26

0

0. I

0

O.I

o

o

O

o

o

o

0

0

o

o

o

0

o

o

o

0

O.I

o.5

o

0.9

27

0

O.2

0

0.2

o

o

0

0

o

o

o

o

o

o

0

o

o

o

0

0

o

o

o

o

28

o

0

0

O

o

o

O

0

O.I

o

o

O.I

o

o

o

o

O.I

0

0

0

O.I

0

o

o

March I

o

0

o

o

o

0

0

0

O.I

0

O.I

0

O.I

o

O.I

o

0-3

°-5

o

0.6

o

o.a

o

a. i

2

0.3

0.6

0

0.2

O.I

o

0

0.2

0.8

0.3

0-3

o

0

o

o

O.I

o

0.3

O.I

0.2

(0.1)

(0.5)

(o.a)

'0.5)

3

(o)

(0.2)

(o)

(0.2)

(o)

(o)

(o)

lo)

(0)

(0)

(o)

(0)

(o)

(o)

(o)

(O.I)

(o)

(o)

(o.a)

(o.a)

(O.I)

(o.a)

(O.I)

(0.2)

•(

lol

(0.2)

(o)

(0.2)

(0)

(o)

(0)

o

0

o

o

o

O.I

o

o

0.2

o

o

o

o

O.I

o

03

0.4

5

0.4

0.4

0.2

0.7

0.2

O.I

O.I

O.I

(0)

(o)

(o)

(o)

(O.I)

(o)

(oj

(o)

1-3

0

1.0

o

0.4

o

O.I

0

6

0

0.2

0

O.I

O

o

0.2

0

0

0

O.I

0

0.4

o

o

o

O.I

o

0.3

0-5

o.a

0.9

0.4

0-5

7

O.I

0-3

0.2

0.2

04

0

0-5

o.a

0.3

o

«-a

0

1-3

o

0

0.8

0.8

0.2

O.I

0-3

O.I

o.a

o.a

0-3

8

O.2

°-3

0.2

O

O.I

o

O.I

o

0.4

0

09

0

0.6

O.2

1.0

0

07

0.9

04

1.6

o.a

3-1

0

7-2

9

o

1.7

0.6

0-3

1.6

0

0.6

O.I

o.a

O.I

O.I

0

o

0 I

o

o

O.I

0

O.I

05

0.7

O.I

o.a

o

10

0

o

0.3

O

0

0

O.I

O.I

O.I

o

0

o

O.I

O.I

o

0.6

O.I

I.I

o

35

O.I

i.i

03

0

1 1

O.I

0

O.I

O.I

o

0

0

o

0

o

o

o

O.2

o

o

0

O.2 O.I

°-3

0.8

O.I

0.3

0.4

o

1

TABLE LXIX.

Disturbances in Vertical Intensity (Fy).

Gr. M.-T. 0-2

2-4

4-6 6-8

8 — io

IO— 13

13 — 14

14— 16

16- 18

18—20

2O — 32

33 — 34

Date

+

+

+

—

+

—

4

—

+

_

+

—

+

—

+

—

+

—

+

—

+

—

v-jiirmbcr 3

(0)

(0.1)

(o)

(o)

(o)

(0.1)

(o)

o)

0

0

o

0

O.I

o

o

o.a

o

O.2

(o)

(0)

o

°-3

o

O.I

4

O

0

o

o

o

O.I

0

o

0.2

0

o.;

o

O.I

o

O.I

o

O.I

0

0

o

0

O.I

o

0

5

o

0

o

o

o

o

o

o

O.I

o

0

O.I

o

o

o

o

o

o

o

o

0

o

o

O.I

6

o

o

o

o

o

O.I

o

o

O.I

o

o

O.I

°-5

o

0.4

o

O.I

0

I.O

o

o

o

o

o

7

o

2.2

o

0.9

o

0.4

o

0

o

o

o

O.I

o

o

o

O.I

0

o

0

o

o

0

o

o

8

o

o

o

o

0

o

0

o

o

o

o

O.I

o

0

o

0

o

o

o

o

o

o.a

o

0

9

0

O.I

0

o

0

O.I

o

O.I

o

o

o

o

o

o

o

0

0

0

0

O.I

o

0.4

o

O.I

10

0

o

o

o

o

0

o

o

0

O.I

o

o

i. a

0

1-7

o

I.I

o

O.I

o

O.I

o.i

o

I.O

i [

o

O.I

o

o

o

o

o

0

0

O.I

o

o

o

O.I

o

o

o.a

0

0.4

O.2

0

0.4

o

I.O

12

0

0-7

o

o

o

o

o

o

0

o

o

0-3

o.a

O. I

i-3

o

J-3

o

1.9

0

1.5

O.I

1.8

4-7

'3

o

0.3

0

O.2

0

o-5

o

O.I

o

o

0

o

0

o

0

0

o

o

o

o

o

O.I

0

O.I

M

o

0

o

o

o

o

o

o

0

0

0

o

o

o

o

o

o

o

o

o

o

o

o

0

15

o

o

o

o

o

o

o

o

0

o

O.I

0

o

O.I

o

o

0

o

0

o

o

°-3

o

1-7

16

o

O.I

o

o

o

o

o

0

o

o

o

o

0

o

o

o

o

0

0

o

o

0

o

o

17

o

o

o

o

o

O.I

o

O.I

o

o

o

O.I

o

o

0.3

O.I

0.9

o

O.I

o

o

o

0

o

18

0 0

o

o

o

o

0

o

o

0

0.3

O.I

I.O

o

o.a

o

o

O.I

O.I

o

0.8

5-1

0

3.1

'9

0

0.6

0.7

0

O.I

o

0

0

o-3

O.I

0.6

o

°-5

o

i-3

0

2.O

0

O.I

1-3

O.I

8.3

0

5-3

20

0

2.0

o

i-5

o

0.4

0

0.1

0.9

o

a.o

o

1.2

0

O.I

O.I

O.I

0

O.I

2.O

0

4.8

o

5-4

21

o

0.4

o

o

0

0.1

0

o

O.I

0

0

o

0.3

o

0.2

o

0.2

0

o

o

o

o

o

o

22

0

o

0

o

o

o

o

0

o

0

o

0

o

0.2

O.I

o.a

0.9

0

O.I

3.4

o

3.8

0

7-i

23

0

6.0

o

2-3

o

0.4

o

o

o

o

o

O.I

I.O

o

O.I

0.2

0.9

o

°-3

1-3

o

4-3

o

1-3

24

o

0.4

0

O.I

o

o

o

o

o

o

o

o

o

0

o

0

o

o

o

o

o

o

o

O.I

25

o

o

o

o

o

o

o

o

o

0.2

O.I

O.I

o

0

0-3

o

O.I

o

o

o

o

0

o

o

26

o

0.6

0

o

o

o

o

o

o

0

o

o

o

o

o

o

O.I

o

0.5

o

o

0.6

o

O.I

27

0

0.3

o

O.I

o

o

o

o

o

o

o

0

0.2

o

o

o

o

o

O.I

0

0

o

0

o

28

o

0.8

o

0.4

o

o

o

o

o

o

O.I

o

O.I

o

o

o

O.I

o

o

o

o

o

o

0

29

o

0.3

o

o

o

o

o

o

o

0

o

0

o

O.I

o

O.I

o

O.I

O.I

o

O. I

0.8

o

11.7

30

o

2.5

0

o

o

o

o

0

O.I

o

o

O.I

o

o.a

o

0.3

1.8

o

I.O

O.3

0

5.6

0

8-5

O, -tuber i

0

8.4

0

6.0

o

a-3

o

o-5

o

o

o

o

o

O.I

o

0

o

0

o

O.I

o

0.3

o

0-3

2

o

o

o

0

o

o

o

0

o

0

o

o

o

o

0

o

o

o

O.I

o

0

0

0

O.I

472 HIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

TABLE LXIX (continued). Fv

Kaaijord.

Gr. M.-T. 0—2

il

2 —

4

4-6

6-8

8—io

IO— 12

12 — 14

14 — 16

16-18

1 8 — 20

20—22

22—24

Date

4

—

4

—

4

_

4

—

+

—

4

—

4

—

4.

_

+

4

+

+

October 3

O

O.I

o

0

o

o

o

0

o

0

o

O.I

o

o

o

o

o

o

0.2

0

0

0.6

° 0.!

4

O

0.4

o

0

o

o

o

0

O.I

o

O.I

o

o-5

o

O.I

0

o

o

0

o

o

0.2

o 0.7

5

o

0.2

o

0

O.I

o

O.I

o

o

0

o

o

0

o

o

o

o

o

o

0

o

°-3

0 0,

6

o

o

o

o

o

o

o

0

o

0

o

0

o

o

O.I

o

o

o

o

0

o

o

o 0.4

7

0

o

0

o

o

o

o

0

o

o

o

0

o

o

o

o

o

o

o

o

o

0

0

0.9

8

o

o

o

o

o

0

0

o

o

o

o

O.I

o

0

o

o

o

0

0.3

o

o

O.2

0

05

9

o

o

o

0

o

o

o

O.I

o

o

o

0

o

0

0.6

o

O.2

0

o

O.I

o

o

o

0

10

o

o

o

0

o

0

o

o

o

0

o

o

o

o

o

o

o

O.I

o

0

o

0

0

0

II

o

o

o

1.2

0

0

O.I

0

o

0

o

0

1.0

o

0.3

o

(o)

(o)

o

2.1

2.5

2.9

0

5.8

12

o

1-9

o

o

o

0

o

o

o

0

O.I

o

O.I

o

O.I

o

o

o

o

o

o

o

0

o

13

o

0

o

o

o

0

o

0

o

o

O.I

o

o

o

o

o

O.I

o

o

0.7

0

'•7

o

O.I

M

0

o

0

o

o

0

o

o

o

0

o

o

o

0

o

o

o

o

o

0

0

o

o

0.6

15

o

o

o

o

o

o

o

o

o

o

o

o

o

o

o

o

o

o

o

0

o

o

o

o

16

o

o-

0

0

o

o

o

o

o

o

o

o

o

o

0

o

o

o

o

o

o

0

o

0

17

0

o

0

o

0

o

o

0

o

0

o

o

o

0

0

o

o

o

o

o

0

o

0

o

18

o

o

o

o

0

O.2

o

o

o

o

o

o

o

o

0

o

o

o

O.I

0.5

o

0.9

0

0

19

o

1.0

o

0.7

0

O.I

o

0

o

0

o

o

o

o

o

o

o

o

o

o

0

0

o

o

20

o

o

o

o

o

o

o

0

o

0

O.I

0

o

o

0

o

o

o

o

o

0

o

0

0.1

21

o

o

0

o

0

o

o

0

o

0

o

0

o

o

0

0

0.4

0

o

o

0

0.5

0

2-3

22

o

0.4

o

o

o

0

o

o

o

o

0

0

o

o

0

o

o

o

0

0

0

O.I

o

O.I

23

o

o

0

o

0

o

o

o

o

o

o

o

o

o

o

o

o

o

o

O.I

o

2.6

o

4.2

24

o

1.0

o

o-5

o

o

o

o

O.I

o

o

o

o

o

O.I

o

1.2

o

i-3

o

o

3-5

O.I

3-6

25

0

7-1

o

4.8

o

i-3

O.I

O.I

0.6

o

1-7

0

2.1

o

1.2

o

°-3

o

0

o

o

0.3

o

I.I

26

0

0.3

o

0.3

o

o

o

o

o

o

o

0.2

o

o

.0.3

o

°-5

o

0.6

0

o

O.I

o

1-4

27

o

'•9

0

L5

o

0.8

O.I

O.I

O.I

0

O.2

0

0.7

o

i.S

O.I

1.9

o

0.8

o

o

1.6

0

28

o

1.4

o

O.I

0

O.I

o

O.I

o

0

o

o

O.2

o

o.5

o

0.4

o

0

2.1

o

3°

o

6.5

29

0

2.O

o

0.6

0

O.I

o

o

o

0

o

o

o

o

0

o

(0.2)

(O.I)

0

0.7

o

4.5

0

3.6

3°

o

2.O

0

o.i

0

0.4

O.I

0.4

1.5

0

I-3

O.I

o

03

O.I

o

O.I

O.I

0

0.4

o

2.3

o

3'3

31

o

4.8

o

4.6

o

4.8

o

'•9

'•3

0

1.6

0

o

6.3

0

8.2

o

6.8

4-3

0.5

5-9

0

3-9

i-3

November i

o

3-0

0

1.9

0.4

o

O.I

O.I

O.I

0

O.I

o

o

o

0

0

0

o

o

0

o

0.2

o

0

2

o

o

o

o

o

o

o

0

o

0

o

0

o

o

O.I

o

1.4

o

o.S

0.9

0

i.5

o

O.I

3

o

o

o

0

o

o

o

0

o

o

o

o

0

o

o

o

o

o

0

o

o

0.8

o

i-7

4

o

1.2

o

o

o

o

o

o

o

0

o

o

o

o

0

o

o

o

o

0

o

0

0

o

5

o

o

o

0

o

o

o

o

o

0

o

o

o

o

0

o

0

o

o

0

o

0

o

0

6

o

0

o

o

o

o

o

o

o

0

(o)

(o)

(o)

(o)

(o)

(o)

(o)

(o)

O.I

0.2

o

0.9

o

O.I

7

o

0.8

O.I

o

o

o

o

o

o

0

o

0

o

o

o

0

o

0

o

o

o

0

o

0

8

o

0.3

o

0-7

o

O.I

o

0

o

0

o

o

o

0

0

0

0

0

0

0

0

0.2

0

O.2

9

o

o

o

o

o

o

0

0

o

o

o

0

0

0

0

0

0

o

0

o

o

0

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1.2

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III.

TABLE LXIX (continued). Fv

473
Kaafjord.

Gr. M.-T.

o-

-2

2-

-4

4-

-6

6-

-8

8-

- IO

10

-12

la

-14

14-

-16

16-

-18

18-

-ao

ao

-aa

aa-

-24

Date

+

—

4-

_

4-

—

4-

—

4-

—

4-

4-

4-

4-

4-

+

4-

N"ovcmber22

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28

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29

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0

0

o

0

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o

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o

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0

o

0

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December i

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o

0

o

o

0

o

o

o

o

0

o

0

o

o

o

0

o

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0

o

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0

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0

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0

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21

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29

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January i

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(o)

(o)

(o)

(o)

(o)

(o)

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0

0

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9

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0

0.5

0

o

O.I

O.I

o

o

0.6

474

BIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

TABLE LXIX (continued).

Kaafjord.

Gr. M.-T.

o — a

2-4

4-6

6-8

8—io

IO— 12

12 — 14

14 — 16

16-18

18 — ao

20 — 22

22 — 24

Date

+

—

+

—

+

—

+

—

+

—

+

_

4-

_

4-

—

+

_

4-

_

+

4-

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0

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o

o

0

o

o

0

o

0

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22

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(o)

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31

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(o)

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February !

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0.4

0

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0

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18

0

O.I

0

o

0

o

o

o

o

o

o

o

0

0

0

o

o

o

0

o

o

o

0

o

19

o

o

o

0

o

o

o

0

o

o

o

o

o

o

o

o

o

o

0

0

o

0

0

0

20

o

o

o

o

0

O.I

o

0

o

0

o

o

0

o

0

o

o

o

o

o

o

0

o

0

21

o

o

o

o

o

0

o

0

o

o

o

o

0.2

o

o-3

o

0.4

o

0

o

o

0 0

0

22

o

o

0

2.1

o

•3-5

o

1.8

O.I

o-5

0.4

0

o

O.I

o

0.2

o

o

0

o

o

o

0

o

23

o

o

o

0

0

o

o

0

o

o

o

0

0

O.I

0

0

o

o

o

o

O.2

0

0

0.2

24

o

o

o

o

0

o

o

0

o

0

o

o

0

o

o

o

°-3

o

O.I

o

o

o

o

0

35

o

o

o

o

o

1.4

o

1.8

o

O.I

o-5

O.I

0.6

o

0

o

o

o

o

o

0

0

o

0

26

o

o

o

o

o

o

o

0

o

o

o

o

o

o

o

o

0

o

o o

0

0.7

o

3-3

27

o

°-5

o

0

0

o

o

o

o

0

o

o

o

o

0

o

o

o

o o

0

0 0

0

28

o

o

o

o

o

o

o

o

o

o

O.I

o

o

o

0

o

o

o

0 0

o

0 0

0

March i

o

o

o

o

o

o

o

0

o

o

0

o

o

0

0.4

o

3-°

o

2.5

o

O.I

0.1 0

•to

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III. 475

'ABLE LXIX (continued). /> Kaafjord.

<;,-. M.-T.

O — 2

2-4

4-6

6-8

8 — 10

IO 12

13—14

14 — 16

16 — 18

18 — 20

2O — 22

22 — 24

Date

+

—

+

—

+

—

—

+

—

+

—

+

—

+

—

+

_

4-

4-

—

+

March 2

O

1.8

0

o

0

o

O.I

0

0

0

0

0

o

o

o

o

1.0

0

1-5

o

0.9

o

o

3-0

3

0

2.O

o

°-3

0

o

o

o

o

o

o

o

O.I

0

0

0

0

o

o-3

o

(o.a)

(0)

(o)

(o)

4

0

(0.2)

(o)

(O.I)

(o)

(o)

(o)

(o)

o

o

o

0

0

0

o

0

0

o

o

o

0

O.I

0

1.6

5

O.I

0.8

o

0.7

O.I

°-3

o

o

o

a

o.a

0

(o)

(o,

4.0

0

o

o.a

o

0.3

O.I

O.I

0

o

6

O

0

o

0

0

o

0

o

o

o

o

O.I

o

0

o

O.2

o

o

o.a

o

0

2.6

o

2.0

7

O

1.4

o

0.6

0

1-3

O.I

0-5

0.4

o

o-3

0

1.4

o

1.0

o

1.6

0

1.4

0.1

0

1-4

o

0.8

8

0

3-5

o

3-1

0

0-5

O.I

0

O.I

O.I

O.I

O.I

1.6

o

1.4

o

I.I

0.6

o

2.4

0

65

06

4.2

9

0

2.1

o

2.9

0

3-5

0.6

i-3

O.I

o

O.I

0

O.I

o

0

o

0

0

0

o-3

o

0.8 o

0

10

0

O O O O

0

o

o

o

o

0

o

o

o

0.9 o

I.I

0

o 05

o

I.O 0

1.8

1 1

O

0.3 o o o ! o

0

o

o

O.I

O O.I

O.I

o

0 O

o

o

o 1.6

0

2.4 o

0.4

A xeleen.

TABLE LXX.

Disturbances in Horizontal Force (/•//)

Gr. M.-T.

o-

2

2 — 4

4-6

6-8

8-10

IO — 12

12 — 14

14 — 16

16-18

18 — 20

3O — 22

32 — 24

Date

4-

—

I 1 __

-t- —

+

—

+

—

+

—

+

+

—

+ 1 —

+ —

+

—

+

September 3

0.2

I.O

o 6.5

O 2.2

o

°-5

O.I

o

I.O

o

3-a

o

0.8

o

03

o.a o i.i o.a

1.2

o 0.4

4

O

0.7

o

0.6

o 0.5

o

i.5

1.2

03

o

0.6

I.O

0

2.6

o

03

1.6

o

21 0.5 0

0

o.5

5

0

0-3

0

°-7

O O.I

o

o.5

o

0.4

0.5

O.I

M

0

0.8 o

0

0.6 o

0.4

0.2

O

0.2

o

b

0

i. a

o

O.2

o

0.4

O.I

O.I

0.4

o

I.O

O.I

4.3

o

3.1

o

0.4

O.I

O.2

3.5

O.I

O.I

O

0.4

7

0

36

o

6.2

o 3-3

o

03

0

O.I

O. I

O.I

i. a

o

0.4

o

O.I

O.I

O.I

0

O.I

o

o.a

0

8

0

o-3

6.1

o.a

O.I 0

o

o

o

0.4

o

1.6

o

!-9

O

1.2

0

O.2

O.I

O.I

0.2

O.3

O.I

0.2

«

O

1.2 0 0.5

o o

o

O.I

0

i. a o

i-9

o

1.2

0.7

O.I

0.8

o

o

1.5

O.I

I.I

o

0.4

10

o

1.9

o

2.O O.I

0.6

0.1

o

0 0

4.9 o

7-3

O

4.6

0

I.O

0.6

O.2

0.9

0.6

O

o

0.9

1 1

o

i-7

o

2.7 o

1.8

o.S

o.a 0.6

0-3

i-3

o

0.7

O

i-7

0

0.4

0.6

O

1-9

0

O.3

o

2.1

12

o

3.4

o

1.7 0.2

0

O.I

o.i —

—

—

—

—

0.6

O.g

o

4-1

o

1.4

I.I

O

0.8

0.3

'3

O.I

O.I

o

1-7

o

1.8

0.4

o

o

o

o

0.4

o

I.O

0

0.6

0

°3

o

o

o

0-3

0

1.3

'4

o

O.I ° JO

o

o

0

o

o

0.4

o

O.I

o

o

o o

0

0

o

o

o

O

02

O

'5

O.I

O.I O j 0.3

o

o.a

0

°-3

O.I

O.I

O.I

0.2

O.I

o-3

O.I

03

o

O.I

o

0-3

o

35

O

4.0

16

o

0.7 o 0.3

0

o

o

o

0.2

o.a

0.7

O.I

O.I

0.3

0

O.I

O.I

01

O.I

°3

O.I

O.I

O.I

O.I

'7

o

0.4

0 1.5

O.2

i-9

0.2

O.I

o

o

o-3

0

,.a

0

2.1

0

O.I

0.4

o

O.2

o

0

O

O.I

18

O.I

o o

0.4

0.1

0.2

O

O.I

O.I

O.I

30

O

2.9

0

0.2

O.I

o

0.3 o.i

0-3

o

10.7

O.I

03

"9

0

i.o 0-6 0.6

0.2 0.3

0-7

O.I

3-1

o

4-7

O

2.1

0

I.I

0.9

O 0.9 0.3

3-i

0-3

33

0.2

1.9

20

0.4

i.i o.i ' 4.0 0.3 1.7

2.0

o.a

5-1

o

4-3

O

3.0 o

1.2

o

0.8 o o 10.9

0-3

0.9

O

4.0

21

o

I.I

° I.O

O.I

0.7

0.3 o.i

0.4

0-3

1-5

O

3-5 o

1.6

O.I

0.2 1.9 0

O.I

O.I 0

O

0.2

22

o

0.2

0 O.I

O

O

O

o

o

0-3

o

0.7

0.1

0.3 0.8 o o.i

0.9

O.I

8.3

o 6.3

o

6.6

23

0

6-3

0 5.7

0.2

0.6

0.3

o

0.6

o

2.9

o

6.3 O

i-7

o

0.9

0.8

0

3-3

o 5-5

o

3-a

24

o

3-°

o 0.8

o 0.5

o

0.8

o

0-3

o

'•5

O.I

O.2

o

O I

0 I

0 0

o

O.I 0

O.I

o

25

0

o

0 0.1

O.2

o

o.a

o

o

0.2

0.2

0.2

2.6

o

1.4

0.7

0.2

O.I 0

1-9

o

0.3

o

°3

26

o

2.9

0

3-4

O.I

O.I

0.2

o

o.a

0.1

O

0.2

0

0.6

0.2

O.I

O.I

0 O

0.6

o

3-5 o

I.O

27

o

0.2

o

i-5

0

0.2

o

0

O.I

o.a

o.i o.a

1-5

0

O.I

o.a

O

O.2 O

a. i

O.I

0.9

O.I

0

28

o

i-9

o

2.9 o.i

°5

0.2

0.2

O.I

O.I

0.5

O

O.T

0.3

o.a

0.2

O.I

I.I

O.I

0.6

O.2

'•5

I.O

0

29

0.2

°-3

o 0.3

0

0.2

O.I

O.I O'1

o

0.4

0 0.2

O.I

0.3

0

0

0.4 0.3

0

0-5

o 04

1.6

3°

°-4

0.4

O. I

o

O.I

O

O

o.i 03

o

O.I

O.I

O.I

O.I

1.2

o

0.6

2.2 O

4-5

0

4.9 o

8.0

<>,-(,, |>er i

o

7.0

o

5-6

o

3-3

O

I.O (0.0

(0.1)

0.3

O.I

0.3

0.2

O.I

3.3

0

3.1

o

3-5

o

0.7

o

I 2

a

o

0-5

o 0.9

O.I

0.2

O.I

O.I 0

O.I

0

o.a

O.I

0.3

0.8

0

o

I.O

o

1-5

O.I

O.I

O.I

O

3

0

O.I

0

0.4

o

0

o.i

O.I 0

o.a 0.4

0

O.I

o.a

0

0.4

0.2

O.I

0

1.4

o

0.8

0.1

0.6

4

O.I

0.7 °-9 o 0.2

0.2 0-2

0.3 o-1

O 2.1 0 I.I 0

o

O.I

O.I

O O

0-3

O.I

O.I

O.I

O.I

5

O.I

0.5 o 0.9 0.3 0.2 o 0.8 o

0.4 O O.2 O.2 O

o.a

O 0

0 O

O.I

0

O.I

0

0.4

6

o

O. I O o O O.I O O. I O O. I O O.6 O O*3

0.4

o o o o

o

0

I.O 0

1.2

7

O.I

0.3 o. 10 o o o o o o. 10 o o o

o

0

o o o

o

O.I

O 0 0.2

_^-O i'.IKKl LAND. Hit Nt>K\VK<;i.\N AURORA I'lll.ARlS EXPEDITION, T 9<32 — (903.

TABLK I. XX (continui-dl. /'"//

Axeleen.

o
o
o

o

0.7

-•7

o. i

O.I

5-

12.6 O. 1 1.3 O.12 O. | O.12 O

O =;.} o 3.1 O.I I .2 0.3 O.I 0.5 O.2

O.I 2.3

4.60 0.5 o 8.1 0.3 0.6 o.i 0.9

12.6 O.I 3-3 0.5 O.I 1.2 O I .-1 O

o.'-i

O.2

1.8

o. i

O.Q

0 4-3

0.3 ' o

O.Q O

O.2 O I

o.i 0,5

o 16.2

O. I O

O. 1
O. I
O. I

'•5

O.2

0.-\

I O.2

O. I

4-3

5-5
'•5

. r

0.5

i.. I
0.8

0.6 o

0.2 o. i

o. T o

o o. i

O. I O

o

o

o

O. I

o. i

O. I

0.3

0 3

6.0

1.8

0 o o o 0.6 o

2.2 I.I 0.1 25 o 1-3

2.3 O 2.6 0.3 I.O 2.0

1 .3 0.5 o 0.9 o 0.3

O.I O O.I O.I o O

O. f 0.7

0.1 , O.I

o i o. i

o , o

o.i 0.3

I

O. I O

O.2 O

o o

0.8 0.3

o ! o

1.4 I O. 1 O.3 O.2 O O. I

o I 1.7 0.2 1.6 o o

o i i .6 o 0.5 0.3 o

0.2 , 0.8 o 0.3 o. l o

O.12 O. I 0.3 O. 1 0.3 O. I

o

O.I

O.2
O.2

0.3

O.2 O

o o. i

O.I O

0.1 O

O.2
O.I

2, I

0.6
o
o
0-7

O. I

0.8
o

o
0.9

°0

0.4

o

3.8 o 6.2 o 7.6

6.7 I o.i 1.9 0.3 ; o.i

2.4 I O 4.3 I 0.2 ' 0.5

5.5 o 4.3 0.1 ' 5.2

O.I O. I 0.2 O ! O

o 2.3

O O.2

o o

o 0.6

O.I 12.2

0.7

1.6

o 3.7 o

O I.O I O

o o o o

O 1.2 O O.I

O.2 I .O O.6 O

O.i

o

o

O.2

o

o

O.I

0.3
0.3

O O 0.2

1.6 o ' 4.2

O O. I O

0.3 o ' 3.2

1.6 o.i o.i

0.9 o 1.6 o 0.5

1.2 0.3 1.6 0.3 1.4

O. I O O. I O i 0.4

0.9

1.6

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. 111.

TABLE LXX (continued). FH

477
Axeleen.

Or. M.-T. 0 — 2

|

2-4

4-6

6-8

8-10

IO — 12

la— 14

14— 16

16- 18

18 — 20

3O — 22

22 — 34

II

1

Date +

—

+

—

•+•

+

—

-t-

—

+

—

+

—

4-

—

•f

—

+

—

+

—

+

—

November 27 o. T

O.I

O.I

O.I

0-3

O.I

0.6

O.I

°-3

O.I

O.2

O.I

O.I

O.I

0

O.2

o

0.6

o

0.2

o

0

o

o

28 o o. I

0

o

O. I

o

°3

o

0-3

o

°-5

o.a

0.3

o

0.3

0

0

1.2

0

1.8 o

2.1 0

'•5

29 o r.o

O.I

0.2

O.I

o

o

o

O.I

0.3

O.I

O.I

o

O.I

o.a

O

O.I

O

o

0 0

0 0

03

3°

0

I.O

o

'•7

0

2.9

o

1.8

o

0.7

—

—

i. a

o

o

0.6

o

3-9

0

3.1 o

3.6 0

2.5

Dfi'cmlicr i

O.I

'•7

0.3

o

0

O.2

0

O.I

O.I

0

I.I

O.I

2-3

0

0-7

o

o

4.2

o

4.2 o

3.8 0

I.O

2

o

0.8

o

1.2

O.I

0.7

i-7

o

2.8

0.3

0.6

o | a. i

o

0.8

0.3 j o

5-8

o

2.2 0

I.O O

I.I

3 °

1.6

o

3-2

o

1.4

0

0.4

O.I

0.3

O.2

o 0.7

o

0.8

0 O.I

O.I

o

0.5 o

0.6 o

o

40 o.i

0

o

o

o

o

o

o

o

o

o

O.2

o

o

0 0

0.3

o

4.6 o

3.9 o

°-3

5 0.2 o

0

O.I

0

O.I

O.I

o

o

o

O.I

o

O.I

O.I

o

o

0

O.I

o

0 0

O.I 0

0.3

6 o 3.5

O.I

0

0

O.2

0

o

o

o

O.I

O.I

O.2

o

o

o.a

o

0.7

o

O.2 O

O.2

O.I

o

70 o

o

o

o

0

o

0

O.I

o

0.4

o

o.a

o

0.9

o

0.5

o

o

0.7 o

3.5

0

3-0

80 0.7

o

0.8

o.5

O.I

O.2 O.I

o

O.I

O.I

o

o

o

0

0

o

0

o

0.4

o

5-4

0

i-7

OO O.I

o

o

0.2

0

O 'O.I

O.I

O.I

0.2

o

0.8

o

0.8

0.4

o

2.5

o

3-5 o

3-'

o

2.O

lo o 1.4

0

1-3

o-3

0.9

0.2 O.2

I.I

O.I

2.3 o

3.3

0

1.4

o

O.I

o.a

0

1.6 o

3-°

o

I.I

11 O I .2*

0

2-7

0

°-3

o.i 0.3

O.I

0.3

0.1

0.2

0.3

o

0.4

O.I

o

3-°

o

4.0

o

8.8

0

0.8

12 0 0.4

O.I

0.6

o

0.5

o 0.5

0

O.I

0

0.8

0

0.7

o

O.I

o

3-o

o

7-3

0.7

0.3

0.4

0

13 o.i 0.4

o

0.6

O.I

o

O O.2

0

1.2

O.I

O.I

o.a

O.I

0.3

0.3

o

S.i

0

4.4

o

3-a

o

2.0

M

0

1.6

0.6

O.I

o

0

O.I O.I

o

o

o

O.2

o

O.I

0

0

o

0.4

0

O.I

0

o.a

o

0.2

'5

0

3-0

o

3.5

0.2

0

O.2 O

O.I

0

O.I

0.3

O.I

o

O

O.I

o

o.a

o

2.7

0

2.2

o

0.7

16

o

O.2

o

0.3

o

O.2

°-3

o

0.7

o

O.2

O.I

o

o.a

0.4

O.I

o

6-5

o

2-5

o

3-5

0

2.3

17

o

°-3

O.I

o-5

O.I

o

O.I

o

o

O.I

O.2

0

O.I

o

O

0

o

o

o

0.6

o 0.7

o

0.4

18

p

°-3

0

o

0

o

o

o

o

o

o

0.4

0

O.I

o

°-3

0

O.I

o

o

0 0

o

0.2

'9

o

0.9

O.I

°-4

0.2

o-5

I.I

o

0.8

O.I

O.I

0.3

0.9

o

o-5

0

0.6

0

0

I.O

o

1.6

O.I

o

20

o

O.I

0

0.4

O

0.4

0

O.I

0

O.I

O.I

0.2

O.I

0.2

0-5

0.2

0.4

0

o

0.2

0

O.I

0

o

21

0 0

0

O.I

0.2

o

o

o

0

o

O.I

o

o

o

O.I

O

o

0.7

o

2.O

O.I

0.4

0

O.I

22

o

0.3

o

o

O

o

0.3

0.2

0.7

o

'•7

O.I

0.4

o

0.7

0

O.I

0.6

o

1.2

0

0.6

o

2.8

23

0

2.9

o

14.4

O

9-7

0.5

2.7

3°

0

0.6 0.4

o

8.4

0.5

t.6

0

5-4

o

5.7

o

9.7

o

i-5

24

o 0.4

0

I.I

0-3

0.4

0.7

0

1.8

0.2

O.2 O.6

0.6

O.I

0.7

2.2

0

6.1

o

8.4

o

I.I

0

0.8

25 0

3-7

0

5-5

O.I

I.O

I.I

0.2

0.7

°-3

O.I

0.5

O.I

O.I

0.2

O.I

0.3

0.4

O.I

0.8

0

0.4

o

0.5

26

O.I

0-5

0.4

0.2

0.2

O.I

O.I

O.I

0.4

O.I

0.4

0.4

0.9

o

i-9

O.I

o

0.7

o

0.8

0

3-7

o

0.6

= 7

o

0.9

o

'•3

0.6

O.2

0.5

0.2

°-3

O.I

0.1

0.6

0.2

0.3

o

O

o

°-3

0

0.8

O.I

1.8

o

2.1

28

o

5-4

o

1.8

o

3.6

I.I

0.2

0.6

°-3

1.6

O.I

i-9

0

0.4

O

0

0-5

0

0.8

o

4.2

O. I

0.2

29

°-3

O.I

0

0.6

0.8

o

0.2

O

0.4

o

0

0.1

O.I

O.I

o

O.I

o

1.2

o

2-5

o

I.O

o

°-3

3°

o

0.6

o

0.2

O.I

O.I

0

0

O.I

o

o

o-3

o

O.I

O. I

O.I

O.I

0-7

o

0.4

0

O.I

0

0.6

3i 0.1

0-5

o

O.I

o

o

o

0

o

0

o

o

o

0

o

O

o

0.5

o

°-3

O.I

O.I

o

0.3

January I 0.2

0

O.I

O

0

o

o

O

O.2

o

o

0.4

o

O.I

0.3

O

O.2

0

O.I

0

o

0.3

o

0.6

2 O

1.4

0.8

O

0-5

o

0.3

O

0

0

0.3

O.I

O.I

o

O.I

0

o

O.I

0

O.2

o

O.2

o

0.2

3

o

0.7

o

0.8

o

O.I

0

O

O.I

o

°-3

o

o

o

O.2

o

O.I

O.I

0

2.2

o

3-5

O.I

0.2

4

o

0.6

0

2.4

0

1.9

0.7

0.7

0.8

O.2

0

0.4

o

0.4

O

0

O.I

0.3

0

2.1

o

a-5

0

'•4

5

o

2.4

o

9-3

o

5.5

O.I

1.6

I.O

0.4

O.2

0.9

0.7

0.2

0

I.O

o

5-°

0

2.7

0

0.6

o

0.6

6

0

I.O

0

2.7

O.I

0.6

O.I

O.I

O.I

0.3

o.a

O.I

I.O

o

1.2

o

0.7

o.a

o,

1.9

O.2

2.8

0

1.6

7 0.2

0.7

o

0.9

0

o-3

o

0.3

O.2

0

°-3

0

°3

O.I

0.2

0.2

O.I

o-4

o

2.1

0

1.0

0

I.I

8

o

1.2

o

I.O

O.I

o-3

O.I

0.2

°-3

O.I

0.4

o

0.8

o

0.6

o.a

0.4

0.3

o

1.4

0

a.o

0 j O.I

9

o

0,4

o

0.8

0.2

O.I

o-3

O.I

0.7

0

1-5

o

i-5

o

2.O

o

0.8

O.I

O.I

I.I

o I 3.3

0

O.2

10

o-3

°-3

o

4.2

o 1.3

0.6

0

0.2

o

o.7

o

I.I

o

0.4

i.i

o.3

0.4

O.I

0.7

o 1.7

0

1.6

1 1

o

1.8

o

0.7

o

0.6

o

0.4

0.4

o

0.3

o

0-3

o

0.6

0.7

O.I

0.6

o

4.6

o

1.9

o

2.6

12

o

1-3

0

0.8

o-3

o

0.3

O.I

0.9

o

O.2

O.I

0.6

o

i.i

O.I

O.I

0.7

0

3.7

o

0.5

o

I.O

'3

o

2.7

o

0.9

0

O.I

o

0

o

o

0

o .

O.I

0.1

0-3

O.I

0

'•3

o

10.9

o

3-6

0

1.0

14

0

o-3

O.I

o

O.I O

O.I

O.I

0

0.2

o

o

0.5

o

o.a

o

o

°-3

o

0

0

o

O.I

0.6

15

o

1.2

o

I.O

o 0.8

o

O.2

0.2

o

o-5

o

'•7

0

3-J

o

o.a

i.i

o

4.o

(o)

(1.5)

o

0.6

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903.

61

478 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE LXX (continued). FH

Axeleen.

Gr. M.-T.

O — 2

2-4

4-6

6-8

8—io

IO— 12

12— 14

14 — 16

16-18

18 — 20

20 — 22

22-24

Date

+

—

+

—

-f

—

+

—

+

+

—

+ —

+

—

+

—

+

—

+

_|_

January 16

O

0.4

O

I.I

O.2

O.I

0-3

0

o-3

o

O.2

o.a

0.8

o-7

I.I

o

o

2.0

o

3.5

o

i-H

O

0.4

'7

O

0.5

O

I.O

O

o-5

O.I

o

0.4

o

O

O.I

0.4

o

I.I O

O.2

O.I

o

0.2

o

I.O

o

O.I

18

O.I

O.I

O.I

°-4

O

0.4

o

O.I

O.I

o

0.3

o

o.a

O.I

O.2

3-6

0.3

2.1

o

5.3

0

0.7

o

O.I

19

0

0.5

O

0.6

0.6

o

0.4

O.I

0-9

o

0.7

o

2.8

o

0.4

O.I

o

3.7

o

0.7

o

0.9

0

0.3

20

O

0.3

O

L5

o

2.8

0.2

0.9

1.2

o

03

I.O

O.I

0,4

o.a

O.I

O.I

O

o

0.6

o

2.4

O.I

0

21

O

0.4

O

0.7

o

1.2

O.2

O.I

O.2

O.I

0.3

O.I

1.2

o

O.I

I.O

0.5

O

o

O.I

o

2.5

O.I

2-4

22

O

5-4

O.I

0.4

o

O.I

O

O.I

O

o.a

o

0.8

O

0.3

o

O.I

o

o.5

0

3-2

o

0.2

0

O.I

23

O

0.6

O

O.2

o

O.I

0-4

o

o-3

O.I

0.7

o.S

0.6

O.I

0.6

o

o

1.6

0

2.4

0

7-5

o

°0

24

O.I

0.4

O.I

0.8

0.5

O.I

0.7

o

0.8

o

0

o-4

o.5

o

0.5

O.I

o

1.6

0

4.7

0.5

I.I

o.i i. 5

25

O.2

O.I

O

0-3

o

0.3

0

O.I

O I

o.a

o

O.I

o.a

o

0.3

o

0

o-S

0

O.I

o

o

o

o

26

O

0

O

O

0

o

o

o

O.I

O.I

o-3

O.I

i-7

o

i. a

o

o

a-3

o

8.5

1.2

2.5

0.6

27

O

14.0

O

7.6

o

5-3

O.I

I.O

2.3

o

0.4

0.3

0.4

o

0.4

o

0

0.8

o

I.O

O.2

0.2

O.I

I. p.

28

O

0.8

0

0.3

o

o

0.1

o.a

O.2

0.2

0 I

o

O.I

o

0.3

o

O.I

1.6

o

2.5

O

2.O

0

M

29

O

°-5

O.I

O.I

o

0

o

o

O

o

O.I

o

o.a

O.I

0.2

O.I

o

o

o

o

0

O

o

0

3°

0

O.I

O.I

O.I

0

o

O.I

O.I

0.6

o

4.4

o

6.0

o

1.3

O.I

O.I

1.6

o

0.8

02

O

0

0

3i

0

01

O.I

o-3

0.3

o

O.I

o

o

O.I

o

0.5

0.4

O.I

O.I

0.6

O.I

2.6

0

1.6

O.I

0.9

0.2 o.i

February i

0.2

O O.I

O

0.2

0.2

0.6

o

0

o

o

0-5

O.I

0.3

0-5

0

O.I

0.6

o

I.O

0.2

o

0.4 o

2

O

O.I

O

0.7

o

o

o

o

o

o

O.I

o

O.I

o

0.6

o

0.3

0

o

o

0

o

0 O.I

3

O

0.8

0

1.4

o

05

o

0.8

0.2

0.5

0.6

o

0.5

o-3

O.I

O.I

o

0

0

o

0

o

o

0

4

O

O.I

O

0.3

o

0.7

o

0.2

o

0.6

0

0.6

o

0-4

O.2

O.I

O.I

o

o

0.6

0

o

o

1.5

5

O

0.2

0

O.I

0

O.I

o

0-3

o

0.5

0

0.4

o.5

o

1.8

o

0.3

I.O

o

1.8

0-5

'•5

0.2

o

6

O

0.6

0

0.6

o

'•7

O.I

2.4

o.5

o.a

°.3

o

1.6

0

1.8

o

I.O

o

0.4

0.2

O

o-3

0 O.I

7

O

O

0

o-4

o

0.3

o

O.I

0

o.3

o

0.7

O.I

O.I

O.I

o

O.I

0.8

0

0.4

0.3

0.3

O

3-7

8

0.4

O.2

0.4

5-0

o

5-3

o

3-3

2.1

o

2.2

O.I

2.2

o

o

4.1

o

5-3

o

'5.5

o

12.8

o

'•5

9

O.I

O.I

O

3-0

0.4

0.3

0.4

0.2

0

0.6

O.I

o.a

O.2

o

o-3

0

O.I

O.I

o

3-5

0.3

0.6

o.i

0.4

10

0

0.6

O

i.i

o.a

0.3

05

O

0.4

o

0.4

o

0-5

o

0.2

O.I

O.I

O.I

0

o

o

0-5

0

4-9

II

0

4.4

O

4-i

o

4-4

0.8

O.I

0.4

O.I

1.4

o

1.6

0

1.9

o

o 0.7

o

4.4

o

i.4

o

1.3

12

O

1.8

0

0.8

o

O.I

0.3

0

o

O.2

O.I

o.a

0-3

O.I

0.8

o

o.3

1.2

0

4.0

o

I.O

o

°-5

'3

0

2-5

O

i-9

0.2

1.2

0.6

O.I

o.5

O.I

0.7

O.I

0.3

0

0.6

0

O.I

O

o

0.7

0

1.8 0.3

0

14

O.I

0.9

O.I

0.9

0

0.4

O.I

0-3

o

0.5

0.3

o.a

o.a

O.I

0.8

O.I

0.3

o

o

2.0

o

1-9

o

1.9

15

O.I

O.I

0

1.6

0.5

O.I

°-4

o

0.7

O.I

I.I

o

i-7

o

o

3-2

0

13.0

0-5

0-3

o

O.I

0

O.I

16

O

O.I

0

0

O.I

o

0.2

o

o

O.I

O.I

O.I

0

0

o.3

0

o

0.7

o

4.3

O.I

o.S

0.4

0

17

O.a

O.I

O.I

0.4

0.4

o

O.I

o

0.2

o

o.5

o

i-7

0

0.4

I.O

0.4

0.6

O.I

o

0.3

1.2

o

0.6

18

O

I.I

O

O.I

0

o

O

o

0.5

o

O.I

o.3

O.I

°-3

0.2

o

O.I

O.2

0

I.O

O.I

0.2

0.2

0

19

O

O

O

O

o

o

0

o

o

o

o

0.7

0

0.7

o

03

o

0.4

0

L3

o

0

0

o

ao

O

°-3

O

0.3

o

I.O

O

0.4

O.I

o

0.5

o

o.a

O.I

o

o

O.I

O.I

O.I

o

o

O.I

0

o

21

0

0

0

O.I

O.I

O.I

O.I

O.I

0

o

0.3

0

2.9

0

2.4

o

o.4

o.a

o

O.I

o

O

0

0

22

O.I

O.I

0

1.9

o

5.2

0

6.5

0.2

0.9

1.8

0

2.9

o

1.2

o

0.6

o

o

0.4

o

0.4

0

0.7

23

O.I

0.9

O.I

O.I

O.2

o

0

0

O.I o

0.9

o

1.4

o

1.2

o

o.a

0.4

o

0.3

0.3

0

0.5

o

24

O

°.7

O

0.6

0

o

O.I

0

o

0

o

o

o.a

o

0.4

o

o

0.8

o

°-3

0

o

o

0.3

25

O

O.I

0

1.1

o

7.9

o

4.5

1.2

o

3-t

o

4-2

o

0.8

O.I

o

0.6

o

0.8

o

1-3

o

0.2

26

0

O.I

0

O

o.a

o

0.3

o

O.I

o

o

I.O

o

0.3

0

O.I

0

o

0

o.a

o

0.4

0

3-6

27

O

1.4

0

1.6

o

0.6

0.2

o

o

o

o

O.I

0.4

o

0

O.I

0

o

o

O.I

o

o

o

0

28

0

O

O

o

o

0

o

0

o

o

o

o

0

o

o

o

O.I

o

o

0

o

o

o

O.I

March i

O

O

O

O

o

o

O.I

o

0.6

o

O.2

o

1.6

0

1.8

o

O.I

'•7

o

4-7

o

o-7

0.2

I.O

2

O

2.2

0

'•7

o

2.8

O.I

1.6

O.I

I.O

O.2

o.3

o

o

O.I

0

O.I

o.5

o

4.8

O.I

O.I

0.2

0.8

3

O

4-4

O

2.6

o

i-5

O.I

0.2

o

O.I

o.a

o.a

0.2

0

O.I

o

O.I

O.I

o

O.I

o

o

O

O.I

4

O

O.I

O

0-3

0.4

o

O.2

O

o

o

o

o

0

O.I

O.2

O.I

o

o

o

O.I

O.I

O.I

o.a

O.I

5

O.I

0.7

0

2.9

O.I

2.7

o.i 0.3

0.5

o

2.5

o

2.8

0

M

4-2

o.a

3-9

o

2.3

o

0.2

o

O.I

6

O

0.9

O

O.I

o

O.I

0

0

0

0

0

O.I

0

o

o

O.I

o

0.4

o

I.O

o

6-3

o

2.5

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III. 479

1'ABLE LXX (continued). FH Axeleen.

Gr. M.-T. 0 — 2

2 — 4

4-6

6-8

8—10

1O— 13

13 — 14

14 — 16

16-18

18-20

3O — 33

33 — 34

Date

4

—

•f

—

+

—

4-

—

4-

—

-f-

_

+

_

4-

_

+.

—

+

_

+

—

4.

_

March 7

o

3-4

o

4.3

o

4.6

O.I

1.8

3.O

0

1.7

0

a.S

o

0.6

o.S

o 3.1

O.I

a. i

0.3

O.I

0

0.7

8

o

x'7

o

5-4

o

i-5

o-5

o

'•5

0

0.8

o

1.8

O. I

0.6

o-3

o 6.9

o

"3-3

O

10.5

0

2.5

9

O.I

0.8

o

5.4

o

9.0

o.a

1.3

0-5

O.I

I.I

o

0.6

o

0

0-5

0 0.1

0

1.4

0.3

a.o

o-3

0.3

10

0

°-5

0

2.6

o

0-5

o

0-3

O.I

O.I

O.3

o

I.O

o

1.8

O.I

o 3.4

o

7.3

O

4-0

o

O..|

1 1

0 1.3

0

1.6

o

0.6

O.I

O.I

o

O.I

0.5

O.I

1.3

o

1-3

o

o 0.7

O.I

3-a

O

'•9

0

0.3

13

0

3.6

o

2.2

o

4-3

O.I

i. a

J-5

0

0.6

0.8

3-0

o

0.7

o.a

0.3 0.4

0

0.6

0.4

0.4

O.I

9.1

<3

" :«

o

5-5

o 9.3

0.8

I.O

i .4 0.5

i-7

0.4

3.4

0

0.4

3-8

0 13-5

0

3.3

0.4

o

o

0.5

M

0 I.O

0

3.4

O.I

0-5

0.4

O.I

0.8

0.1

I.O

0

3.7 o

I.O

O.3

o 0.7

O.I

I.O

O

'•7

o

0.7

15

o 0.6

0

0.5

O.2

0-5

0.6

o

0-5

0

o-7

03

a.o

o

a-3

O

0.9 2.4

0

4-9

O.3

0

O.I

0.2

16

0-3

o

O.I

O.I

o

0-5

o

°-3

o

O.I

o

0.3

0-3

o

0.3

O

0 0

0

0-3

0

3-o

o

0.4

17

0

o

o

o

o

0

o

o

o

0-3

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o

o.a

o

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o

0 0.2

0

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0.9

0

0

18

0

o

0

o

o

o

0 0

o

0

0.1

O.I

O.I

O.I

0.4

o

0 O.2

o

0.4

O.I

o

O.I

1.2

1 9 o

2-3

o

1.7

o

0.8

o 0.6

O.I

O.I

0.4

0.1

0

o.a

O.3

o-3

0 1.2

o

6.1

O

3.9

0

1.6

20 o

1.5 o

0.5

o

0.8

O.I ! O.3

0.5

O.2

1.6

0.1

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O.3 O

0.6

O O.6

o

0.3

0.3

o

O.I

o.5

21 0

0.9 o

2.O

0

0.4

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0.4

0.1

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1.5

0-3

0.4 0.3

0.6

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0.6

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a.S

0

'•7

22 0

0.8

0

0.8

0

0-5

0.3 o.i

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0.2

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0-3

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0.7

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0-3

O-5 O.2

0.2

0-3

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0

8.9

23 o.i

0.4

o

'•7

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0.5

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0.3

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o

0.9

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O.I

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0-9

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0

0.6

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O.I

0

0.5

2,( 0

1.3

0.3

0.3

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O.I

o

0.2

2.0

0

i. a

o

0.7

O.I O

0-5

o 0.5

o

O.I

o

o

0

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25

o

o-3

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0.5

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0.6

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0

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0.1

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0

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26

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0

0

0.9

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o

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0

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0.4

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0.3

0

0.2

27

o

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0

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0

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o

0.4

0

0.6

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0

0

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0

2-5

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0.8

28

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0

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0

0

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0

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0.6

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0

0.5

0 I.I

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i-7

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0.2

29

o

0.2

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2.9

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1.9

0

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0

0.5

0.3

0.2

1-4

0

o

t-9

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0

0.2

o-3

o

30

o

1.9

0

4.6

o

I.O

0.4

0-3

i-5

o

0.6

0.6

O.I

0.4

0.2

o.5

o

0.7

o 1 0.5

O.I

0.7

o-7

0

3'

O.I

6.8

o

I.I

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O.I

0.4

0-7

0.2

1-5

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1-3

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I.O

0.2

o

5-1

o ' 1.8

o

3-2

0

1.4

April i

' o

1.4

o

2.8

O.I

0.7

0.3

O.I

o

O.I

1.3

o

3.4

0

2.9

o

1-4

o

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0

0.3

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o

I 1. 2

a

0

4-2

0

2-3

0.9

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o-4

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O.2

O.I

0.5

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1.6

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o

0.8

0

0.7

o

2.3

O

3-8

O.I

I.I

3 o

2.3

0

7-3

o

0.3

O.2

o

o

0.8

0.4

0

0.4

O.I

0.4

0.4

09

o

o

3-3

O

3.1

o

0.6

4

0

••3

0

3.6

o

i-7

o

0.3

0.3

0.3

O

3-t

0.3

I.O

0.2

O.I

o

0.8

0

3-a

O

0.6

O.I

0.3

5

O.I

1.2

0

3.4

o

7-1

o

3-4

0.6

0.5

o.3

I.O

2-9

0

O.I

5-1

o

3.2

O.I

0.8

o

1-5

o.5

0.2

6

0.9

0.6

2.4

2.5

1.6

8.9

0.8

0-7

3-5

0.2

o-5

7-2

o

16.5

O

3-3

o

3.6

0.4

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0.1

O.I

0.2

O.I

7

o

O.I

o

o.3

o

0.7

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o.a

0.8

0.2

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0.7

2-3

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3.6

o

0-5

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0

3-6

o

4-1

O.2

I.O

8

0.1-'

°-3

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0.3

0

0

o.3

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0-3

0-5

0

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1.9

0

0.4

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0.1

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0-5

o-3

3.8

9

0.3

9.0

I.O

2.5

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5-2

5-°

0.3

4-5

o

1.3

0.4

1-3

0

o.a

I.I

0

6.8

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I.O

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4.7

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8-3

10

0

2-5

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3.4

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0.5

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0.8

i.7

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0.6

0-5

t.6

0.6

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0.3

1.9

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4-7

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2.7

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1-7

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0.5

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0.4

o-7

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1-5

0

8.9

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0.7

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1.7

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0.6

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o.3

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0.7

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0

0-7

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0.6

15

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0.8

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5-8

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6.7

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0.6

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4.3

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3-5

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6.6

0

1-9

16

0.5

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0.3

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o

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O.I

o

o.a

(0.6)

(0.4)

'0.5)

(1.4)

(o.a)

(1.3)

(0.1)

(3.3)

(0.8)

(a.s)

o

1.3

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0.5

17

o

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o

o

o

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0.2

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0.3

0-3

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0.7

2-4

0.4

2.1

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6.7

0

4.8

o

'•7

o

0.6

18

0.3

0.4

0.2

0.3

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o.a

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O.I

0.8

O.I

3.O

O.I

2.3

0.5

0-5

1.8

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5-9

0.8

3-3

0.3

0.9

O.3

O.I

19

0.3

I.O

0

1.6

0.3

o.a

O.3

0.6

o

0.2

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0

0

0.3

o

0.3

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O.3

0.1

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0.4

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0.7

0

30

I.O

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0.9

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0.4

0

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0.2

0

0

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0

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0

0.8

0.3

0-5

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1.6

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0.6

0

0-5

21

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0.5

O.2

0.7

0

1-4

0-3

0

0-3

O.I

O

2.9

O

3.4

0.3

0.7

o

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1-7

0

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22

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0.4

0

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0

0.3

(0)

(a.o

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3.8

0

1-4

o '.3

o

1.3

0.3

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o

1.8

23

O.I

0.3

0

0.7

o.a

o.a

0.6

0

0

0

0.3

0.3

3-a

0

3-a

0

1-5 o

0.1

3.O

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0.6

0

0.3

24

0.3

o-3

0.4

0.3

0.4

0

0.7

o

0.1

0.6

O

2.2

O.I

0.6

o

0.3

0 I.O

o

3-6

o

1.6

o

0.4

25

o

t.J

o

3-1

o

0.7

0.6

o

0.5

0

3-8

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0-3

o

1.3

o 0.5

O.I

O.I

O.I

o

0.8

o

1

480 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

TABLE LXX (continued). F,,

Axeleen.

Gr. M.-T.

O— 2

2-

-4

4-

-6

6-

8

8—io

10 12

12— 14

14—16

16— 18

18-20

20 — 22

22-24

Date

1
+ i

+

-

f

—

+

—

+

—

+

—

+

-

+

.

+

-

.+

—

4-

—

4-

April 26

0.1 0.4

O.I

0.7

O.I

O.2

O.2

0.2

0.7

O.I

0

3-0

o 1.4

O.2

O.2

O.2

0.3

O I.I O.I

4-4

0.5

2.1

27

o 6.3

0.1

4-9

0

5.6

o

1.4

0.4

O.2

0.8

0.2

2.O O | O

1.8

o

1.6

o 0.5 o

0.7

O.I

O.I

28

o 0.9

o

1.6

0

0.8

O.I

0.2

O.I O

I.O

o i 3-1

o 5.0 o

3-7 o

O.2 O.2 O

°5

o

3a

39

O 2.1

O.I

i-5

O.2

0

0.2

o

0-5

o

0.6

I.I O.I

0.8 0.9

0 0

0.8

o 1.7 o

3-5

o

5.0

30 |i o 0.9

0

O.I

O

0

o

O.I

O.I

I.O

o

3-5 °

2.5 I.I

0.2

o

2.8

0

4-5

o

'•7

0

°-5

May i

0 O.2

0.2

o

O

o

O.I

o

0.3 O.2

o.a

1.8 1.4

o 0.3 o.i o 0.9

0 2.8 0

2.3

0

3.1

2

O 1.6

O

1. 1

0

0.5 o

O.2

o 0.8 o

0.7 o 0.9 o 0.4 1 0.5 o

0.4 o o.i

0.8

1.4

o

3

o.i 0.3

0.2

0

0,2

0 O

O.I

O.I O 0 0.1 O.I O.I 0.3

o 0.4

o

o.i 0.6 0.7

0

0.6

0

4

03 0.3

°-3

0.3

0

0.6

O.2

0.8

O.I O.2 I.O O.I 2.3 O | 2.2

o 0.3

0.7

0.4

0.2 0.5

4-4

O.I

5-1

5

1.0 !..(

0 ;I7-5

(J

10.5

o

3.6

0.8 0.3

0.1

o-5

o.a

0.4

3-4

o

1.1

o

0.2

0.7 0 2

0.3

O.2

02

6

o 1.8

0

3-1

o.5

36

o

6.1

0.5

0.8

-

-

7
g

9

10

- -

-

-

-

-

-

-

-

-

0.4

0.5

2.0

0

3.0 o

0.2 0.4

o 3.2 o

2.5

0

o.7

II

0.4 o

0.5

0

0

0.5

O. I

0.3

o

0.8 o.i

0.3 3.1 o

3.4 o

0.7 o

o 0.9

O.I

0.3

O.I

0.2

12

0.3 0.3

0.3

O.I

O.I

0.3

O.I

0.6

o

0.3 0.1

0.3

0.9

o

2.4

o

0.4 1 0.7

o 0.8 o

°-3

O.I

0

13

0.4 o

o

0.7

o

2.O

O.I

0.9

O.I

0.5 0.6 o.i 0.7

O 2.1 O

0.4 2.3

o 6.0 ! o.i

2.0

0.4

0.5

'4

0.5 o

O.I

0

0

0.9

o

2.1

0

1.2 2.8 O 2.7 O O.I 2.7 O.2 O.6

o.i 3-5 o

7.4

o

5-3

'5

o 5-4

o

1O.O

0

5.0

o

1.3

o

i-5 0.7

o ! o.i

O.I o.I

O.I O

o-3

o 0.8

0

3-5

0

1.4

16

0.2 O.I

0.4

0.3

0

0.6

0.2

0

0.6

o 0.5

0.8 1.5

0. 1

0.8 0.5

I.I

0.4

0 I.I 0.2

0.2

I.I

..3

17

2.9 0.4

1.3

0.8

0.1

3-2

O.I

1.2

0.5 O.2 3.9

0

5-i

0

2.O

0

0.2 O.2

I.O O.I 1.3

0

0.6

0.3

18 0.3 o

0.2

O.I

0

0.7

0.1

O.I

0.4 o o.i

0.5

0.2

O.I 1.2

0

0.7 o

0.3 0.5 o.i

0.2

O 1

O.I

19

0 0

0

t.o

0

0

0

0.5

0.3 o.i o

0.9

1-7

0.4

4.8

o

2.4

o

0.6

0 0

0-5

0

0.6

20

0 O

0.2

0

0

0

0

O.I

0

O.2

(0.1)

(0.5)

(1.0)

(0.2)

(i.o)

(o) (0.5) (o)

(0.3)

(0.2)

o-5

o

O.2

O.I

21

o 1.7

o

3-7

o

I.I O

0.3

0

0.2

0 I.I

O.2

0-5

3.0 o

0.7

O.I

0.2

I.O

O.I

0.8

0

I-'

22

0.9 o

°-3

o.5

o

O.2 O

0.8

O.3 0.3 O.I 1.3 0.4

O.I

2.2

0

i-3

0.2

0.4

0.5

0

0.6

°-3

0.7

23

o 0.6

o

4.2

0

5-7 o.i

2.8

3.7 o 8.0 o

3-7

o 3-3

o

O.I

I.O

O.I

'•5

0

'•3

0.4

0.7

24

07; 0.4

0.7

O.I

0-5

o 0.3

o

o

O O.I O.I 0.4

o 1.7

o

I.I

0

o

0.1

0.3

2.6

0.6

13

=5

O.2 0.8

o

4.8

o

0.6 0.3

O.2

3-7

o

3-1

o 7-5

o 7.2

0

2.8

o

0.5

5.5

0.2

3.0

°-3

O.2

26

o.i 0.3

o

5-4

0.2

0.6 O.2

O.I

O.3

o

2.0 O 4.3

0

2.1

o

1.6 o

'.7

0 O. I

0.8

O.2

0.2

27

o.i 0.9

0

1-3

1.2

O 1.2

o

o.S

O.I

0.3 O.2 4.6

o

4.2

0

4.0 o

o.S

1.4 o

2.0

0.4

0.3

28

o 3-7

o

7-7

o

14.0 o

8.4

0.5

°-5 3-3 o ,1.9,0 0.8

O.2 I 2.5 O

2.5

o 0,6

1. 1

O.I

-M

29

0.4 0.7

0

2-3

O.I

0.6 0.5

0.2

i .a

O 7.1 O i 1.9 O.2 0.8

0.3

0.4 0.9

o ' 4.4 o.i

4.0

0

4-'

30

o 4.7

0

4.2

0

6.2 0.5

'•3

3.8

o 8.7 o 10.0 o

4.1

o

1.4 o

O.2 I.O (0.2)

(2.0)

(o.a)

(i.5l

TABLE LXXI.

Disturbances in Declination (F/,)

Gr. M.-T.

0 — 2

2-4

4-6

6-8

8—io

IO 12

12—14

14 — 16

16-18

18— 20

20 — 22

22—34

Date

1
+ —

+

—

-f

+

—

+

—

+

+

4-

—

4-

—

4-

_

+

—

+

-

September 3

o 7.0

o

12.8

0

3.3

O.I

1-7

o

O.2

0.6

o

i-9

0

0.7

O.I

2-3

O

3-8

o

1.9 o 0.8

0

4

o.i 0.3

o

0.7

0

0.9

0

0.7

0.9

O

I.O

O.I

0.5

o

2.O

0

2.9

o

.3-4

O.I

1.5 o 1.2 O.I

5 . 0.3 0.6

O.I

"•3

o

0.2

0.3

0.2

0.7

O

O.2 O

0.3 o

0.2

o

o

o.a

O.I

O.I

o. i o 0.3 0.6

6

o 2.3

0

1-3

o

2.8

o

0-5

o.a

o

0.4

o

I.I j 0

0.8

O.I

1.2

o

2.6

O.I

I.I 0 1.0

0

7

o

3.8

o

3.1 o

3-2

0.2

O.I

o

O.I

O.I

o

0-3

o

O

0.2

0 0

O.I

o

o 0.3 o

0

8 | o.i

O.I

o

0.2 • 0

0 0 O

-

-

-

-

0

O.3

O.I

O.I

0.2

0

0.4

o

1.3

o. i 0.6

0

9

o

0.4 0.5

O

0.5

0

oa

0-3

—

—

—

—

—

—

0.2 0

O.I

o

0.8

O.I

0.2

0.4 0.5 o

10

0

0.6 o 1.6

o

1-3

O. I O.2

O.2

O.I

0.6

o

3.6 o

2.2 O

3-6

0

3-7

o

1.6

0 0.2

0.4

i i

O.I

0.3 o 2.9

o

2.O

0.5 ' o.i

0-4

O.I

0.6

o

o

03

0.2 O 2.0

o

3-1

0

I.O

0. 1 0.2

1.6

12

o

2.8 0

1-3

O.I

0

0.4 : o.i

1.2

o 0.3

2-3

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III. 481

A1SLK LXXI (continued). FD Axeleen.

(ir. M.-T. o — a 2 — 4 4 — 6

6-8

8—io

IO— 13 12—14

14— 16

16-18

|8 — 30

2O — 22

aa — 24

Date

4-

—

4-

—

4-

4-

_

+

_

4-

4-

-t- —

+

4-

4

4-

rptcmber 13

o

0.5

0

2.5

o

2.4

O.I

0.5

0.3

o

0

o

0.2 0

0 O

o

o.a

O.I

O.I

o

0-5

o

0.6

14

o

o

°'3

o

o

O

0

O.I

0

O.I

0 0

0 O

0 O O

o

O O.I

O.I

0.1

O.I

O.I

15

O.I

O.2

0 ! 0

O.I

0.3

O.2

O.2

O.I

0

o.a o

o 0.3

O.I O.I

O.I

o. i 0.9 o

1.3

O.I

0.3

2.2

16

0.3

o.3

O. I O. I

o

o

0-3

O

O.I

o

o.a o. i

o 0.3

o 0.7

0.1

0.3 0.7

o

0.3

0.3

0.2

O.I

'7

o.3

o.3

0 2.1

0

3-3

O.I

o.a

0

o

0.3

O.I

0.5 o.i

1.3

0.3

1.2

o

0.8

o

o

0.3

0.9

0

18

0-3

O

O.I

0.5

0.3

o.3

O.I

0.3

O.2

O.I

0.5

O.I

O.6 O.2

O.2

O.3

O.I

o-3

2.6

o

1.4

5.1

0

0.9

19

0.2

3.o

0.6

I.I

O.I

I.O

0.4

0.4

o.S

0.7

1.8

0

0.9 o

2.9

o 1.6

0.4

3-7

1.8

23

0.9

0.6

1.8

20

O

4-5

o

9.2

0.3

5-4

I.I

0.3

O.I

1.6

0.3

0.7

I.I 0. 1

0.3

0.4

1.8

o

4.0

3.3

0.8

27

0

29

21

O.2

0.7

O.I

0.4

O.I

0.6

o.a

0.3

O.I

O.I

0.3

0.3

0.9 o

O.I

0.6

o.3

I 2

o 0.3

o

0.3

O.I

O.I

22

0.4

0

0.4

0

o

O.I

0

o.3

O.I

O.I

O.I

O.I

O.I O.2

0.7

O.I

0.8

o

0.7

1.3

O.I

2.5

O.I

3-2

33

O

4-7

0

6.3

o

3-5

0.6

0-5

0.4

o

1.3

0

O.9 0.2

0.3

0.4

1.6

0

'•9

O. I

o-7

0.9

0

2.8

24

0

2-5

O.I

0.4 0.2

O.I

o

0-3

0.1

o

o

0

0.2 0

O.I 0.2

0

0 O 0 O

0 O.I

O.I

25

0.2

o

0.2

O.I 0

O.I 1 0

0.5

0

o.a

0.2

O.2

0.8 O.2 1.9 o

'•5

o 0.8 0.3 o

°-5

0.4

0

26

0

a i

O.I

1.7 o.i 0.3

O.I

0.3 0,1

03

0

O.2

o 0.3 o.i o

0.2

o.i 1.8 o 0.7

0.6

0

0.5

27

0.1

0.6

0

2.2 O

0.9

o

0.3 o

o

O.I

O.I

0.2 0.5 0 0.4

0.4

o.i 1.8 o 0.9

o

I.I

0

08

O.I

1.6

0

3.3

o

0.5

O.I

0.2 0.4

o

o.i 0.3

o 0.4 o 0.4

0.5

o. i 0.9 o 0.4

o.i | 0.6

0

29
30

O.I
1 .0

i.i

o. i 0.6

O.I
n r

05

0.3

O 2

O O.I

o

Q

0. 1 0.2

02 o.i o 0.4

05

O.I 0.3 O 1.3

0.1

0

4-5

w

Ortnbcr 1

—

O j O — . -

—

—

—

0.5 1 oi

o.i 0.6 0.5 0.8

0.5

o.i 0.6

0.4 o.i

1-3

o

0.9

2

0

0.3

o

I.O

O.I

03

O.I

O.2

o

0.2

0. 1 O.2

O.I

0-3 0.2

O.I

o

0.3 0.4

O.I

O.I

O.I

O.I

0.5

3

0

0.6 o.i

O.2 O. I

O.I

O.I

0-3

0.3

o

o.a o.a

o

0 o

0.2

0.1

0.3 i.o

O.I

0.4

0.3

o.a 0.2

4

O.2

1.2 1.0

0 O.I

09

0.5

O.I

0

0.5

0.9 o

0.3

0.5 0.2

O.I

O.2 O O

O.I

0.2

0.3

o. i 0.7

!

5

0-3

0.3 0.1

1.2 0.7

0.6

0.4 0.3

O.I

O.I

0.4 o

O.I

0 O.I

0

O O.I O.I

0 0. 1 0.4

0.2 0.3

6

0

°-3 o

0.4 o.i

0-3

o.a

O.I

o

o

O O.I

O.I

O O.I

0

o 1 o o.i

0

o.i 0.5

0 1.2

7

o

0-7

o

O.I

0

o

O.I

0

0

o

0

o

o

0 0

0

o o o

0

0

O.I

o

I.I

8

o

0.3 o.i

0.3 o

0.1

O. I 0. 1 O

O.I

0.2

O.2

o.5

0 0

O.I

0.1 O.I 0.5

O.I O.2 , O.S O

1-7

9

O.I

0.8 o

0.3 o

0.3

O.2

O.2

o.i o.a

O O.2

o

0.2 O.I

0.6

0.8 o.i i.o

O.I 0.2 0.3 i o

0

10

0

0 0.1

O.I O.2

o

0.3

0

O.I 0

o 0.3

o

0.5 o

O.I

o.i o 0.9

0

0.4 o

0.6

O.I

1 1

O.I

O.2 0

1.8

0-3

0.3

0.6

o 04 o. i

O.2

O.I

2.3

O.I I.I

o

4-8 o 5-5

o

2.2 3.O

o.a

2.7

12

o

3.0

O. I

'•3

O

03

0.4

O.I

O.I

o.5

0

0.3

O.I

0.2 o.i

O.I

O.I O.I 0.2

0 0. 1 O O

0

'3

o

0 0

o

0

O.I

0

0

0.1

o

0.9 o

o

O.I

0.5

0

2.2 0

2.5

O.2 O.3 ! O.6 0. 1

0.2

•I

0.2

0. 1 0. 1

o o

O.I

o

O.I

O O.I

0 0

o

0.1

O.I

0

0.9 o

1-4

0

1.3 o o

0.6

IS

O

1.2 0

0.4

o-i

0.2

0.8

0

—

—

— —

—

—

—

—

0.2

o

1.4

0

0.8 O.2

o

0.9

16

0

t.6

o

'•9

o

0.6

0

O.I

0.2

o

O.I

0

o

0

0

0

o

o

0.5

o

0.5 o

O.I

0.4

17

o

0.3

0

0-5

0

0.6

o

0.3

o.a

o

O.I

O.I

o

O.I

o

0

0

O.I

0.6

o

1.3 o

1.2

0

18

o.3

0.2

O.I

0.4

0.4

0-5

1-9

o

0.6

O.I

O. I O. I

o

0.1

o

O.2

0.3

o

3-3

o

0.3 0.7

0.7

0

'9

o

3-5

o

8.2

0.2

i.3

0.4

0

O.I 0

O.I o

0

O.I

o

0

O.I

0

0.3

0-3

O.I O.2

O.I

O.I

20

0

0. 1 0. 1

0.2

O.I

O.I

o.a

o

O O.I

0.3 0.3

o

O.I

0

03

o

O.I

0.3

0

0.3 o.i

o

o.R

21

o

I.I

O.I

I.I

O.I

O.2

o

O.I

0 O.I

o.i 1 o.i

o

0.3

0.2

O.I

0.9

o

0.4

0 I

0.7 0.6

o

2.7

22

o

2.1

o

1.8

0

'•9

O.I

0.3

0.3

o

O.I O.I

O.I

O.I

o

O.I

o

O.I

o

0

0

0.7

0

I.O

23

O.I

O

o

0.2

o

o

O.I

O.I

o

o

O.I

O.I

O.I

O.I

O O.2

o

O. I

0.4

O.I

0.4

0.6

0

1.8

-'4

o

3.9

O.I

1.9

0.3

O.I

O.I

o

0

0.2

o

0.3

O.I

o

1-5

o

3-9

0

5-6

0

2.1

'•3

1.2

3-0

25

o

6.9

o

6.7

O.I

2.4

1.2

0

0.3

0.5

O.I

0.6

0.6

0.4

0.4

O.I

02

O.I

0.3

0.2

0.6

0.4

o

1-3

26

o

a.o o

0-5

O.I

O.I

O.I

O.I

o

0.3

o

0.7

0.4

o

1.3

0

2.7

o

2.9

0

1.2

o

0.3

0.8

27

o

4-7

o

8.5

O.I

3-6

1.6

0.3

0.7

0.4

0.3

0.6

'•3

0.2

3-1

0

4-7

O.I

4.0

o

I.O

o.a

o

39

28

o

1-9

0.3

2.1

O.I

0.7

0.6

o

0.5

O.I

o-3

O.I

0.6

0.1

0-5

o

0.7

0-4

1.2

0-3

O.I

4.8

o

4.8

29

0

4-5

0

3-3

0.2

0.7

0.4

o.a

0.2

0.2

0-5

O.I

0.3

0.1

0

0.3

1.4

0-5

3.4

0.7

0.4

o-5

o

2.4

30

o

1-7

—

—

—

—

—

—

o

5-5

0.2

1-4

' O.I

0.4

0.1

O.2

°-5

0

2.1

o

0.5

I.O

0.3

I.O

31

o

6.2

o

13-0

O

8.0

o

4-3 o 4.1

0

4-'

0.5

1.6

3-9

o.t

n.6

0

1 1 . i o 6.0

0

1.3

3-°

November [

o

5-3

O.I

5-3

0.2

0.8

1.5

0 I.I

o

O.I

O.2

O.I

0.3

o

O.2

o

o

0 O.I 0.2

o.a

o

O.I

i

i

482 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 1903.

TABLE LXXI (continued). . F]t

Axeleen.

Gr. M.-T. 0-2

3-4

4-6

6-8

8—io

10 — la

13—14

14 — 16

16-18

18 — 20

20—22

— — — _

22-24

Date

+

—

4-

—

4-

—

4- 1 -

4-

—

+

—

4-

—

+

—

4-

—

4-

_

+

4

November 2

o

O.I

o

O.I

o

O.2

o 0.4

O.I

0

o.a

0

o.5

O

i-5

o

4.2

0

5-0

O

i-3

0.5

o

0.2

3

0

0.6

o.a

O.2

o

o.5

O.2

0

O.I

o o

o.a

o

0.4

O.I

o

0.4

o

0-4

0

0-7

° O.I 2.0

4

O.I

0.3

0.3

O

O.I

o

O

0

o o | o

o-

O.I

o

O.I

o

O.I

o

o

o

o

0 0 0

5

O.I

o

O.I

O

0

o

O

o

o o o

o

o

o

o

0

o.a

o

0.3

o

O.I

O.2 o 0.3

6

o

o

o

O

o

o

O

o

O O O.I

o

O.I

O.I

O.I O.I

1.8

o

2.O

5-9

0.7

0-7 o.i 0.6

7

o

2.5

o.a

1.4

O.I

0.6

o

O.I

O O O.I

0

o

O.I

o

0

o

O.I

O

O.I

0

0.2 o 0.2

8

o

1.8

o 3-7

o

o.5

o

o

O.I

0 O.I

O.I O

0.2

o

O.I

o

°-3

0.3

0

O.I

0-3 o o..|

9

0

0

o

O.I

o

0.2

o

0

o

o

O.I

o

Q

o o.a

o

o

0

O.I

o

o

O.I

o 0.8

10

o

1.2

o

0.4

0.2

O

O.I

0

0

o

O.I

0

O.I

O.I O.I

O.2

o

0.6

0

0.2

0.2

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PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III.

'ABLE LXXI (continued). FD

483

Axeleen.

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O.I

o

0.3

o

0.6

O.I

O.I

o

°-4

O.2

2.3

I.I

0.9

0.6

o

1O.O

27

O

13.3

o

12.4

o

9-7

o

3.9

0.2

0.3

0.3

0

0.3

O.I

O.I

0.5

O.I

0.3

0.3

0-3

0

0.6

o

i.a

28

O

0.9

o

O.I

0.2

o

0.3

O.I

°-3

o

0 I

o

O.I

0.3

0.4

o

1.4

o

I.O

o

0.3

O.I

0

I.O

29

O

0.8

O.I

0.4

O.I

0.3

o

0

o

o

o

o

0.3

0

O.2

o

o

o

o

o

o

O 0

0

30

O

0 0.2

0

O.I

0-3

0.4

O.I

0.4

0

o.a

0.6

33

O.I

5-3

o

4-0

o

30

o

o 0.4

0

0-4

31

o

0.6 o.i

0.6

o.a

O.I

0.4

0

o.a

o

0

o.a

0-5

o

°-7

0

1-5

O.I

I.O

o

o.a

1-3

o

o.S

February i

o

0.3 O.2

o

O.I

o.a

O.I

O.I

o

O.I

o

o

0.3

0

0.6 | o

i.i

0

o-9

o

o. i o.a

O.I

0.2

2

o

0.4 0.3

O.2

0.3

o

o

o

o

o

0.4

0

0.5

o

0.8

o

0.6

0

O.I

o

0 0

o.S

O.I

3

O.I

0.3 o

0.7

o.a

0.4

O.I

0.4

o.a

o

0.9

o

i.a

o

0.5

o

o

o

o

o

o |o

O.I

0

4

0.3

O O.2

02

O.I

0.4

O.I

0.5

o

o.a

0.4

O.I

0.6

o

O.I

o

03

o

0.8

o

O.I

04

o

0.7

5

0

O 0.2

0.3

O.I

o.a

0

o.3

O.I

0.3

0.6

O.I

0.8

o

1.3

o

1-4

o

1.6

o

0.9 0.2

O.I

0.3

6

0

0.9 o

3-0

O.I

3.8

0.3

0.3

0.4

o

0.3

o

o.7

0

0.8

o

0.8

o

0.5

O.I

0.5 o

o

0.2

7

0

O.I 0

O.2

0. I 0.2

o

0.3

O.I

o.a

0.3

o

0.8

o

i.i

o

1.5 o

o-5

o

I.I

0

O.I

2.1

8

o

2.2 0

7-5

0 1 0.0

O.I

a. a

o.5

I.O

1.6

0.7

2.5

o

5-i

o

2.5 o

3.1

4-9

'•5

4.6

O.I

0.6

9

O.I

0.7 o

3.o

o 0.4

o.a

o

0

O.I

0.1

O.I

o

0

o

0-

°.5

o

o

t.6

o.9

0.5

o

1-3

484 IJIRKK1.ANO. THF NORWKGIAN AURORA POLARIS EXPEDITION, 1902—1903.

TABLE LXXI (continued). Flt

Axeleen.

Gr. M.-T. 0-2

2-4

4-6

6-8

8- 10

IO— 12

12 — 14 14 — 16

16-18

18 — 20

-^ _.

20 — 22

—

22-24

Date l| 4-

4-

—

+

—

4-

—

4-

—

4-

—

4-

—

4-

—

4-

—

+

_

+

+

February I o

o

2.2

0

2.O

O.I

0.7

0.3

0.2

0.1

O.2

0.1

O.I

0.4

O

0.4

0

O.I

0

0-4

o

0.3

°3

°-3

5-0

1 1

0-3

1-7

o

5-0

o

3-6 o DO

O.I

0.2 0.5

o

I.O

o

1-4

o

i. a

0

0.6

o

0.6 o

o 0.6

12

o

2.1

o

1.6

o

0.5

o 0.5

o

0.4

O.I O

0.4

0

o.3

0

(1.0)

(o)

(2.0)

(o)

0.8

O.I

02 0.2

'3

0

3-5

o

0.2

0.2

0.4

o.a

0.4

0.3

0.2

0.5 o

0.2

o

0.4

0

O.I

O.I

I.O

0

O.I

I.O

0.6 , 0.2

M

o

2-3

0.2

1.2

O.2

0.2

o.3

O.I

0.2

O.I

0.4

O.I

O.2

O.2

0.4

0.3

o

0.3

O.I

1.9

0.6 0.6

O.I I.i!

15

0

r.8

O

29

O.I

0.4

O.2

o.a

0.4

o.a

0.4

o

2.4

O

2.5

o

3.0

2.4

O.I

0.4

0.4

o.:

O.I

0

16

0.2

O.I

O

o

O.I

O.I

0

O.I

0

O.I

0 0

o

O

0-5

0

0.9

o

0.6

i-5

0.2

0.7

O.I

o..i

i?

o

1.0

0

i-3

0.2

0.6

o ! 0.3 o

o.i 0.4 o

i-7

O

0.9

o

o-5

0.4

o

O.I

0.2

0.1

0.2

O.S

18

O.I

0.7

03

0.4

O.I

0.3

0.6 o

0.6

o i o.a o.i

O.I

O

o.S

0

O.I

O.I

O.2

o

o. i 0.3

o 0.4

'9

0

o

O

O.I

0

o

O 0

o

o

o o.a

O.I

O.I

O.I

0.1

o

O.I

o.a

o.a

o 0.6

O.I O.I

1

1

i

DO

O.I

o.3

O.I

0.3

O.I

i .0 o 0.3

O O.2

0-3

o 1 o

0.3

o

O.I

O.I

0

o.a

O.I

0.1

0.2

O.I

0

21

o

o

o.a

o

o.5

0

0.3 o.i

0

o-3

0.9

o

2.7

o

2.9

o

'•3

o

0.3

0

0 O.I

0.2

u

22

0.2

O.I

o

3-6

o

6.9 o 6.9

O

2-5

1.4

0.5

1-9

o

2.2

o 1.3

o

0.3

o.a

o 0.7 „

0.4

23

O.I

1.2

O.I

O.2

O.I

o o o

O O.I

O.I

0.2

0.4

o.a

0.6

o

0.4

o

0.6

0

O.I

O

O.I

0.9

24

0

1-3

0

0.9

O.I

0.2 i o

O.I

O O.I

o

O

o.a

o

0

o

0.6

o

0.4

0.2

0

0

O.I

0.!

25

O.2

0

O.2

0.9

0

6.7 o

3.6

°-5

O.2

1.6

O

2-3

o

0.7

0.2

0.4

O.I

O.I

O.I

o

0.6

0

OJ

26 i o. i

0.2

O

o i o. i

o o

O.I

o o

o 0.4

o

O.2 0

o

0

o

o.a

O

0.9

0.8

o

1.8

1

27 o

1.6

O

i.9

O.I

O.8 . O.2 O

o o

o o.a 0.1

O

o

o

o

o

O.I j 0 0

0.3

0

0.4

28 || 0

o

O

o

o

o ; o ! o. i

o o

o o ! o

0

0

o

o

o

0

0 0

O.I

0

0.2

March i o

o

0

o

o

0 0

O.I

O ! O

0.7

o

a.o

O 2.2

0

3-7

o

0.8

0.8

O.I

0.2

0.2

2.0

a

0

•3.8

0

1.8

o

2.5 0.4

0.4

0.9 ! O

0.2

o

0

O O.I

o

1-3

o

2.2

0.2

1-5

O

0.2

1.6

3

O

4.8

0

2.6

0

1.9 0.2

O.I

O i O.2

O.I

0.5 o.i

O.2 O

o

O.I

o

I.I

O

0-3

O

0

0.1

4

O.I

O.I

0

0.3

o

O.I O

0.3

o

0.3

O

o

O.I

0 ! 0

o

o

o

O

O

0

O.I

0.2

I.I

5

0.2

I.I

o

3-9

o

3'5 0.2

0.2

O.I

O.I

1.7

o

3-9

0 5-1

0

6.0

o

2.7

0

0.6

O

0

0.8

6

O

1-9

o 0.3

0.2

O.I 0.2

O

o

o

O.I

o

0.4

O O.I

o

o

0.2

i-5

0

1.2

0.2

0.5

1.8

7

O

3-8

0

6.4

0

5.2 o.i

1-9

I.I

0.5

0.6

o

2.0

0 3-0

o

3-3

0

2.8

0

0-5

0.2

0

0.8

8

O

3-5

o 7.2

0.4

1.7 i i .a o

I.I 0

I.O

o

1.6

o 3-i

o 2.7

0.6

3.6 0.8 3.3

0-3

1.2

1.9

9

0.1

1-9

0

9.0

o

8.0 o.i

0.8

0.6 o.a

0.4

O.I

0.2

O.I j 0

o.a o.a

0.2

0-3

0-7

0.3

1.2

o

1.5

10

O

'•9

o

2.6

0

0.3 o.a

0

O.2

0.2

0

O.I

0.6

0

1.8

o a. a

O.I

2.1

i-5

0.7

1.1

0

1-7

i i

O

2.6

0

2.9

o

0.8 0.2

0.3

o

0

o.7

o

0.6

0

0.2

0

1.2

o

i-5

0.4

O.2

I.O

o

i.i

12

0

2.8

0

3-1 o

6.0

°-5

O.I

I.I

0

0-5

O.I

I.O

O.I

I.O

o

3-9

o

i-3

o

2-3

O

0

4-5

'3

o

3-6

0

6.9 o

6.1

0.6

0.5 0.7

0.2

o.5

O.I

2.2

O.I

2-7

0.8

2.6

2.O

i-4

o

0-7

0.4

0.8

0.2

14

o

3-°

o 2.9

O.I

o-5

0.7

o 0.6

O.I

O.I

0.4

1-7

o

2.1

o

1.8

0

0.8

o.a

0.3

0.4

O.u'

0

15

0. 1

O.I

0.1

0.4

0.6

0.7

0.6

0.2

°-3

o

0-5

o.a

J-5

0

I.I

0.4

i.i

0.1

i. a

0.8

0-3

o

O.I

0.6

16

0. [

0.2

o

°-3

0.2

0

o.3

o.i 0.3

o

(o.a)

(O.I)

0

O.I

0

o

o

O.I

O.I

o

O.I

O.I

0

0.3

17

0

O

0

0

o

o

o

O O.I

0

0

o

O.I

0

O

0

o

o

o-S

o

0.4

O.I

0

O.I

18

o

0

0 0 0

o

o

O O.2

o

0

o

O.I

O.I

O

0

o

0

0.2

0

0.3

0.2

0

'.;

19

o

2.6

o 1-7 o

°-7

0.2 O.I 0.4

o

0.3

o

0.4

o

0.9

o

a.4

o

3-5

o

0.3

o.3

o

1.2

20

o.a

'•3

O.4 O.2 O.2

0-3

o o. i 0.3

0.3

1-3

0

0.6

o

O.I

o

o.a

0

0.2

O.I

0.4

O.I

0

i-3

21

0

I.I

O 3.0

0

5-0

o.i o.a o.i

o.a o.i

O.I

'•5

0

0.8

o

I.O O

0.6

o

'•3

0.3

o 3-3

22

0

1.4

o 1.6

O.I

0.5

0.2

0 0

O.I

o

0.3

O.I

0

0.4

0

i-3

o

1.3

o

1.6

o

2.8 0.4

23

0

7.0

0 1.3 0

2.4

o.i 0.5 o

0.4

o a 0.6

0.8

0

O.I

0

(o.a) (o)

(0.8)

10.11

10.4) (o.i)

0 11.01

24

(0.1)

(0.2)

10)

(0.3>j '02J

(o) | (0.31! (o.i) (0.3)

(o)

(0.4) o

(0.4)

(o)

(o.i)

(0.2)

(0)

(0.2)

10.21

0

101 (01

101

lo.l

25 lo.n

(0.2)

(o) (0.3) (0.2)

(o)

(0.3) (o.i);(o.8)

(o)

o o

O. I

O.I

o

o

o

o

O.I

0

0. 1 0. 1

0.4

0.2

26

O.I

0

o 0.3 o

0

o

O. I O

0

0.4 o

I.O

o

0.8

o

I.O

o

1.6

o

0.6 o

0

O.I

1

27

o

0.4

0

0.3

o

0

0

O O.I

0.4

1

O O.I

o

o

O.I

0

o.a

o i 0.9

O.I

0.4 0.2

O.I

0.4

28

o

O.2

o

O.I

0

o

o

0 0

o.i 0.8 o

1.4 °

0.5

o

O.I

o.i 11.9

0

0.3 o.i

0.6 o.i

29

0-3

O.I

0

4.0

0

2.5

0

1.6 o

O.7 O.I 0.2

0.2 0.2

2.O

o

3-5 o 4.5

o

0.7 o.i

0 1-7

3°

0

4.5

o

8.3

o

2.7

O.I

0.6 o

o.5

O.2 O.I

0.4

o

o.3

O.I

o 0.4 0.2

0.2

0.8 o.i

0.7 o.i

3i

O.I

8.0

0

2.9

o

2.0

0.4

i.o 0.3

0.7 0.5 o.a

1.8

o

2.4

o

2-3

0.4 2.9

o

0.8 i.o

1 1

.

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III.

ABLE LXXI (continued). FD

485
Axeleen.

Gr. M.-T. 0-2

L 1

2-4

4-6 6-8

8 — IO IO— 13 i 13 — 14

14 — 16 16— 18

18 — 30

3O — 33 32 — 24

D.it.- 4-

-I

+

—

+

—

4-

_

+

+

+

+

+

_ ' +

+

+ _

April i o 1.5

o 3.9 o.i

I.I

O.I

0.3

O.I

0.2

O.3 O.3

i.a o

0.4

0.3

o

0.7 o

o.a

0.5

O.I

o.i 5.1

3 0 3.7

o 3.7 0.3 o.i

O.I

0.8

0.5 o

0.5 o.i

0.9 0.2

0 I.O

1.8

o.i 1.6 o.a

a.o o

o.a i.i

3 ° -M

0 8.9 0.2

0.3

O.I O.3

0.6 o. i

0.3 o

0.5 o.i

o 0.4

O.I

0.2 0.9 0.3

i.a

O.3

o.i 0.3

.1 O

t.6

0

5-5 o 2.5

O.3 O.I

O.3

O.I

o 0.3

0.8 o

0.4 o

0.7

o 3.4 o

0.6

0

0.8 0.3

5 o

20

o 5.2 o

10.3

o.i 3.0

O.I

0.9

O.I

0.6

2.3 O.3

4.2 o

3.6

I.O I.O O

o.a

O.2

0.3 1.6

6 o.i

2-5

O.I

10. 0 O.I 8.3

0-5 0.5

0.6

0.5

0

6.6

0

8.9

1.2 2.1 1.8

O.I 1.3

O.I

0.8

0

0.7

O.I

7 °-3

O.I

o-3

o 0.5 o

0.6

O.I

O.I

0.6

0.1

0.8

1.3 0.2

2.3 O

1.8

o ; 1.4

o

3.7

0.2

0.8

i.a

8

O

'•3

o 0.8 o 0.4

0.3

o-5

°-3

o

0.3

o

O.I 0.4 1-3 0.2

0.4

0.3

2-5

0

3-3

O

1.3

3.7

9

0.4

5-3

0 7.O 1.3

4-3 3-9

3.1

'•3

4.0

0.9 0.3 a.o o a.o

O.I

5-3

0.3

S-2

0-3

3-0

O.I

o.i 4.5

10

0.3

1-3

O.2 2.1 0.3

0.4 0.3

0-7

0.2

o-7

0.5 o.i 1.9 j o.i

0.7

i.a

2.0

O.I

4-5

0

3-0

0.8

o 0.8

11

O.I

I.O

O.I

0.8 0.2

0-5

o.3

0-3

O.I

0-3

0.2

0.9

0.3 0.2

O.I 0

I.O

o

1.4 o

I.O

o a

0.4 0.2

1 2

'3

1 4

1 r»

16

0.3)

(0.4)

10.1) O.l)i(O.l) (0) (0.2)

(0.3)1 (0. 1)

(O.I)

(0.2) (O.I) (I.O) 10.3)

(2.0) (0)

(3.0) (o) (3.5) (o)

0.3

O.2

0 0.2

'7

0

O. I

0 O.I O.2

O 0.2 0.2 O.I 0.2

0.4 o 2.8 o 4.5 o

4.8 j o 6.5 o

0.9

O.2

o.a o.a

18

0-5 0.2

0.2 0.9 0

i.o 0.3

0

0.5 o

0.2 0.3 1.8 0.8 7.5 o

6.1

o 4.1 o

4-7

0

08 0.5

"9

0-4 0.8

o.i 2.8 o.i i.o 0.6 0.6

0 0. 1 O O

O.2 O O O

O. I

0 O.I O.I

0

0.2

0.2 o.a

20

0.3 o.i

o

0.5 o 0.7 0.3

0-3

0.8

0

O. I O.2

o 0.4

O.I

0.4

O.2

o.i 0.8

o

0.5

0

0.3

0.2

2 1

0.5 o.i

0.2

0.8

o.i 1.8 o.i

°-3

0.2

0-3

0. 1 0.2

O.2 O.I 0.9 0

0.6

0 I.I

0

0.6

0-4

0.3

0

22

o.i 03

o o 0.3 o o o

O.I

O.I

(o.i) (0.3)

O.2 0.3 O 0.3

0.4

0 1.3

0

I.O

°-3

0.3

'•4

•-"'.

o 0.6

O 1.2 ' O.2 O.2 0.7

0

o-S

0

O.2 O.I

1.9 o 3.1 o

3-2

o

3.6

0

1-5

o

0.4

0.2

24

o. i 0.5

o.i 0.5 o.i 0.5 o.i

0.3

O.I

O.I

o 0.8

0.8

0

0.6 o

I.I

o

1.2

o

1-3

0

0.4

0.6

25

o 2.5

o 6.4 o

1.8

o

O.I

O.I

0.2

0.2 0.3

0.8 o

I.O

o

04

o

0.3

o

0.4

0.2

o.a

°-3

26

0.3 0.8

O 2.O o

0.9

0.2

0.6

0.2

O.I

0.3

o

o 0.4

0-5

O.I

1.5

0

3-9

o

4-3

0.2

i.a

0.8

27

o 7.1

0

9.0 o 6.3 o

i.i

0.4

0

0.3 0.2 0.7 O

o

O.2

0

0.4

0.2

O.I

o-3

0.1

0

i.i

28

O 2. I

O

5-2 0

3-° 0.2

0.2

O.I

0.2 0 08

O I.O

O.2 O.2

1.3

0

1.4

O.I

0.8

0.2

o

'•9

29

o 4.0

0.4

2.9 o

2.O o

0.4

0.3

o i (o.a) (0.3)

(0.5) (0.4)

(I.O (0. 1)

1.7 o

3-5

o

i.a

O.I

0

i.a

3°

o 1.8

0

1.5 o

1-4

O.I

0-5

o

O.I

0.2 O

i-5 o.i

3-4 o

2.O 0

i-9 j o

0.3

O

o

0-3

May i

o 0.4

0

1.2

o

1-3 0.2

0-4

o-4

o

O.I 0.^

0.6 o.i

0.3 0.3 0.9

0

3.6

o

3-2

o 0.6

O.I

2 0 0.2

0

0.9

O.I

°-3

0.6

O

0.6

o

o. i o.a

o'6 o.i

0.5 o i.i

0

a.o

0

4-3

o 3.1

o

3

0.2 0.4

0 O.I

0

O.I

o

O.I

O.I

O.I

0 O.I

O.I

O.I

0.2 0

O.I

O.I

o.a

o

o-5

O.I

0.2

0.2

4 0.2 i.i

O.I

07

o

1.7 0.4

0.8

0.2

O.2

0.4 o

1.3 o

I.O O

O.3

0.3

2.3

o

3.7

0.4

I.O

0.8

s

04 3-5

o

.5.0

o 16.0

0

5-5

0-3

0.5

1.9 o

0.7 o

(0.5) (o.i)

0.8 o

a.o

O.I

1.3

o.i 04

0.6

6

0.3

1.6

0-5

1.6

0.9 2.O

0.4

3-4

0.3

I.O

o 4.1

(..5) 'o.O

(0.2) (0.2)

3-5

o

4-o

o

2-4

o.5

3-5

2.9

7

o.i 1.6

0

108

0.7 3.7 o.i

!-3

0.8

0.4

1.4 o

3-5 o

(0.2) (O.2I

(3.0)

(o)

3-0

o

°-3

0-4

O.I

0.8

8

o.i 1.3

0

i-9

o

0.4 O.3

0.8

0.7

O.I

0.3

O.I

O.I

03

0-3

0.3

1.3

0

1.5

o.a

3-4

o

0.6

0.6

9

o

5-°

o

8.0 o

3-6

O.I

O.I

0.1

0.4

0.8

0.3

0.7

0

0.5 o. i

(i.o)

101

(3-0)

(o)

0.8

O.2

0-7

0

10

0

'•7

0

'•3

o

0.8 02

04

0.3

O.I

0.7

o

(1.5)

(O.I)

(0-5)

(0.2)

(3.0)

(o)

(3.0)

(0)

3-3

0

0.3

o.3

i i

0.3

o-3

0.1

0-3

O.I

O.I

0.6

O.I

1-7

0

0.7

O.I

o

0.6

O

0.4

I.I

o

'•5

o

i.i

O

O.I

0.9

12

o

3-4

0

1-5

O.2

0.3

o-3

O.I

O.3

o

0.4

0

05

o

O.3

0

1-4

o

2.0

o

i.i

O

o

0.2

'3

0.2 0.3

o 0.7

o

1.3

0.5

O.I

0-7

o

0.6

o

05

o

2-3

o

37

o

6.2 O

2.7

O.I

o

1-9

'4

0.3 0.6

o 0.5

o

0.8

0:2

1.3

O.3

O.I

I.O

0

2.O

o

(1-5)

(o.i)

3.8

o

4.7 0.2

2.7

o

O.I

'•7

15

o

5-8

0

ri.8

9

5-3

0.3

°-7

0.6

O.I

0.6

O.I

O.2

0

O

O.I

0.3

0

'•5 o

i.i

O.I

o.a i.i

16

o

32

o

2.0

O.I

i-5

O.I

0.4

0.3

0.4

O.3

O.I

O.I

0.6

I.I

0.4

3.3 0

2.8 0

i.i

0

0.9

3-3

'7

0.8

0.6

I.O

3.6

O.I

2-5

O.I

0.8

0.9

O.I

o-3

0.4

O.I

0.6

0.9

O.I

1.4 o.i

1.2 O

1.6

O.3

0.6 0.6

18

0-3

0.3

o.i 0.5

o

0.4

0.4

O.I

o.a

O.I

0

0.4

.O

0.8

O.I

0.4

0.5 0.2 a. a o

I.O

O

04 o.i

'9

0.4

O.I

o 0.8

'0.4

o

0.2

O.I

(0.3)

(o.a) o.i

04

O

°-3

0.9

o 1.4 o 1.5 o

0.4

0

o.i o.a

20

0.4 o

0.3 o

0.4

O.I

O.I

o

o

0.3

(0.1)

(0.3)

(o)

(0.5)

(0.7)

(0.3)

(l.4) (O.I) (2.0) (0)

'•5

0

1.3 o

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903.

486 BIRKELAND. THK NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

TABLE LXXI (continued). FD

Axeleen.

Gr. M.-T.

0 2

2-4

4-6

6-8

8—io

IO— 12

12 — 14

14 — 16

16-18

18-20

20 — 22 22-24

Date '• 4- '

4- i

4 ' -

+

—

4 i

4- -

4 —

j

4 —

_L_ ,

4

4 - -1- _

May a i 0.2 0.8

o 4.1

O 1.2

0.2 0.3

o 0.4

0 0.2

0.5 o

3.4 o.i

o.i 0.7

2.3 o

5.0 o o 7 i.o

22 0.2 0.4

O 1.2

o.i 0.8

o 0.8

O.2 0.2

0 0.2

o.i 0.6

0.2 0.3

1.8 o.t

•-2.O O

°-t 0-3 4-° o.i

23

o.i 0.8

o 7.7

0 13-5

0

5-9

0 2.4

o 4.0

1.0 2.1

i-5 °

o.i 1.6

0.9 o.i

O-9 O.2 O |.^

24

o.i 2.4

o O.q

o.i 0.4

o

0.8

o 1 0.4

O.I 0.2

o 0.7

o.i 0.4

o 0.5

1.4 o

2.O 0.2 i .5 og

25

o 2.9

0 9.8

o 3-4

O.I

1-3

0

i-7

1.5 o

4.5 0.2

1.8 0.3

2.6 0

3.8 o.i

I.O O.I 08 0.3

26

0 I.I

0 8.2

o 3-5

0.2

O.I

O.I

o-3

0.4 o

0.2 0.2

o 0.3

°-5 o-3

1.8 o

0.3 0.4 0.7 i.o

27

o 3.0

o 3.9

o 0.7

o. I

0-5

I.I

0

0 I 0.2

O.6 O.2

0.4 0.7

1.3 o

1.9 o.i

O..S 0 2.0 O.j

28

O 6.2

0 12.0

o [5.0

o.i 7.3

0.5

I.O

0.6 o I

1.2 O

O.I O.2

O.2 0.4

0.7 O.2

0.6 0.8 o 3.0

29

0.6 3.3

o 6.9

o 4.1

o 1.8

0

1.0

0.7 i.o

O.2 O-5

1.2 0

1 .0 O

2.7 o

2.0 0.2 0.4 I.o

3°

° 5-9

O 1 I.O

o 7.0

o 2.3

0

2-3

o.i 1.8

2.6 0.2

3-2 o

4-4 o

6.0 o

1.1.01 101 10

TABLE LXXII.
Disturbances in Vertical Intensity (Fy).

Gr. M.-T. 0-2

2-4

4-6

6-8

8—io

IO— 12

13—14

14 — 16 16 — 18

1

18-20

20 — 22

Date 4

+

—

4

+

—

+

4

4

+

4

+

+

— 4-

September 3 '

0

2.7

1.3 2.8

4.4 o

3.0 o ! (o)

(o)

O.I

o

0.5 o

o

1.6

O.I

0.7

o

33 o

4-7

0.2 0

4

i-5

O 1.2 0

30 o

o. 7 o o

O.I

0

2.8

o o.a i o

0.2

0.7

0.8

0.4

2.4 o

2.8

o 1.8

5

o

3.2 o ' 2.3

O.2 0

0.1 O.2 O.I

O.I

O.I

0

O.I

0

0

O.2

1.2

o

0.5

0 O

O.I

0 1.2

6

0

2.8 O I.O

0 O.I

o 0.3 0.3

0

0

0

0.7

o

0.4

1.5

o

1.9

0.7

0.9 o

2.8

01 0.1

7

0

6.3

0.2 2.5

3.2 o

0.3 0.2 0.5

o

0

0

0

o.a

o

0

O.I

o

0

0

o

o

0 0

8

0

00 O

O 0

0 0 O

O.I

0

O.I

o

O.I O

0.4

o

0.3

o

i-5

o

2.2

0 0.2

9

0

0.9 o o.i

O O.I

O O O

0

0.6

o

O.I

O.I

o

O.I

0

O.I

0

0.2

o 3-4

0 0. 1

10

0

0 0

o

O 0

0 O 0

O.I

0

a. 8 0.3 o.a

0.5 0.6

I.O

O.I

0.4

°-5

o 0.6

O 2.1

ii

0

1.5 o.i

0.5

I.O

0

0.6 o o

O.I

O.I

o

0

0.5

0

'•3

o

0.5

0

2.1 0 1.3

o 4.7

_ (. f

12 u

13 o

3.0 o

O O I

o

i-5

o

2-4

0

1.4 o o

o

o

o

0

0

0

o

0

o

o

0 I

^•-f '-'.u
o 0.7

o 0.5
o.i 1.3

'4

0

0

o

0

o

0

o

o o

0

0

o

0 0

0

o

0

o

0

0

o

o

0 O.I

15

o 0.5

o

0 O-I

o

°-3

o

0

o

0

o

O.I O

O.I

O.I

0

0.9

0.5

0.3 0.4 I.I

0

5.5

1 6 o.i o.i

0.4 O O.2

o

0 O

o

o.a

0

°-3

0

0.3

o

1.5

0

0.8

0

o o 1.7

O.I

0

17 06 o.i

0.3 1 O.2 2.4

o 1 0.7

o

0

o

O.I

O.I

o

1.6

0

2.3

0

0.6 o

O.I O.I 0

0.4

o

18

0 0

O.I

O 0. 1

O.2 O

0.2

0

0.4

0

1-7

0.8

o

o

0.4

o

o.a o. i

0.2

o

9.5

O.I

4-3

19

o 3.1

0.3

O.2 O.I

0.2 O.I 0.4

0

3.5

o

I.O

o

3-o

0.2 0.8

0

2.3 O

7-4

o 23.5

0

16.2

20

o 1 1. 6

o

13.8 o

2.6 O

1.2

0.8

2.8

7-3

o

2.7

0.2

0 2.8

O I.O 3.6

5-7

o 9.1

o 0.8

21

0.5 o.i

0.2

0 I.I

o 0.3

0.2

o

o.a

0

0.4

I.I

O.I

0.4

°-3

2.7

0.6 o

1.2

0

O.I

O.I

0

23

0 O

O

0 0

O ' O

o

o

O.I

0

O.I

o

o.a

0.2

0.9

O.I

°-3

0.5

5-2

0

7.7

0

13.0

23

0 12.8

1.6

4-5 4-6

o 1.3

05 o.i

O.I

o-3

0.4

0.6

o.a

0.3

0.3

0.9

1.8

o

6.8

0

9.6

o

5-3

24

0 3-3

0

0.2 O.I 0. 1 O

O 0

0

0

0 0

o

o

0

o

o o

0

o

0

o

0

25

0 0

0.1

0 O 0 I O O O. I

o

o

0.3 ! 0

0.6

0.8 o

1.8

O O.I

I.O

0

1.6

0

O.I

26

0 3-4

o

1.3 o o o o o.i

o

o

0 O.I

o

0 0

0.3

o 0,5

°-3

O.I 4.6

o

1.0

27

o 2.3 o

0.2 000

0

O.I

o

o

0

O O.I

0. 1 o

0

O I

o

2-5

o 2.7

0

0

28

o 3.0

o

2.2 O 0. 1 O

0.8 0.5 0.2

0

O. I O O O O

I.O

0

0

0.3 0.3 0.2

O.I

0

29

0 I.I

O.I

0.4 o.i

O. I O

o o o

O.I

O.I O

o 0.6 o.i

0.3

0.3

o

O.8 0 1.2

o 14.0

3°

o 1.6 o.i

0 0

o o

o.a o.i o

o

o o

o i.o o

8.7

o

i-3

5.0 o 15.6

o 19.6

October i o 19.6 o

I I.O 0.5

O.3 0.9

o

O.I O.I

O.I

0.3 o

O.2 O.I O.I

2.8

o

0.4

0.8 o

i-3

0 1.2

20 o

0

O. I O O O

0

o 0.2

0.1

o

O.I

O O.2 O

O.I-

o

0

I.O O

1.8

0 0.1

1

30 o. i o o o.i

O.I O.I O.2 O O

o

o

0.6

o 0.8

o

0

o

O 1.2 0 1.3

0

0.7

4

o

3.8 o

o.i 0.7

o 0.6

o

O.I

O.I

0.4 o.i

0.3

o o.a

o

o

o

o

O.I

o

1.6

0

2-7

5

o

0.8 o.i

0.2 ! O.I

0.4 o

o

O.i

o

0 O

0

o o

o

o

o

O.I

o

o

0.8

0

0.8

6

o

O.I 0

0 O.I

o o

o

0

0

o o

0

0 O.I

0.1

o

0

o

o

o

2.8

o

1.6

7

o

O.2 O

O 0

o ! o

o

0

o

o o

O

o

0

0

o

0

0

o

o

o

o

1.8

PART II. POLAR MAGNETIC 1'HEXOMKNA AND TF.RRELLA EXPERIMENTS. CHAP. III. 487

ABLK LXXII (continued). Fr Axeleen.

(ii-. M.-T.

0—2

2 — 4 4 — 6 6 — 8 8— 10 10— ra

13 — 14 14 — 16 : 16— 18 !

18 — ao ao — 33 22 — 24

Date

-

+

—

+

—

4-

— + — +

_

-f

— 4-

—

+

- ;

4-

—

+

-U

( ), -tolicr 8

O

0

0

o o o o o o o

O.I

o

0 0

0 0

0 0

01 0.5

o a. i

o 3-5

9

o

0

0

000

O O. I O O

o

o

O.I 0

2.5 o

3.3 o

1.4 o

o 0.6

O 0

10

O

o

0

0

0 0

o o o o

o

o

0 0

0 0

O.I O

0 0

0 0

O.I I 0.2

i i

o

O.I

o

000

o 0.2 o o i o.a

o

4.1 o

2.0 0

5-7 o

0.3 i.o o ,15.0

o 9-3

12

0

2-5

o

O.I 0 0

0 0.2 O.I 0 | o

o

O.I O

O.I O.I

0 0

0 O.I

0 0

o o

13

0

o

0

000

o

0

0 0

O.I 0.2

0.3 o

O.2 O

O.I O.I

0.6 34

o 5-5

0 I.O

'4

o

0

o

0

o

0

0

0 0

0

o

0

o

0

O

O 0

O

o

'•5

o

1.9

0

3-o

'5

o

2.2

0

0

0

o

o

O 0

o

0-3

o

o.a

0

O

0

o

°-3

0.8

0-5

0.6

0.1

0.3

°-3

16

0

0.2

O.I

o

0.5

o

o

o o

o

o

0

o

0

O

o

o

o

o

0

o

2-3

0

'•5

'7

o

0

0

0

o

o

o

0 O.2

o

o

O.I

o

0

0

o

o

0

0

o

O.I

0.1

0

0

18

o

0.2

0.1

0.2

3-1

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i-7

0 0

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0

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o

0

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o

o.a

o

0.1

3.9

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5-4

0

o

'9

o

1.0

0.3

I.O

5-0

o

3-0

o 1.3

0

i.a

o

o.a

0

o

o

o

o

0 03

0

1.2

o

°3

'JO

o

O

0

o

o

o

0

0 0

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0

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o

O.I

o

o

0.1

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o.g o

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I.I

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0.9

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0

0. 1

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O.2

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0.2

o

0 0

o

o

0

o

0

o

o

O.I

o

o.i 02

o

I. a

o

7-5

22

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0.9

o

0-3

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0.7

0 0

0

0

0

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0

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0

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0 0

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33

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o

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0 0

0

0

0

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0

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0

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0

0 0

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4-7

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10 O

-'t

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5-4

0

2.6

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o

0

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0

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0

o

0

0.9

0

5-1

o 0.8 o. i

o

1 1.2 0

13.6

»5

0

17.8

o 7.7

0.4

0.5 0.4 o.i o

O.I

0.4

O.I

5-1

0 '

0-3

o

O O.I

o 0.5

o

1.3

0

3-7

26

0

1.6

o

o.a

o

0-3

o

O.I O

O.I

o

o

o-5

0

4.1

0

0.8

o

o 3.7

0

2-3

o

2.1

27

o

6.4

0.2

5-°

3-5

O 2

0.0

O 1.2

O.I

O.3

0

3-3

0

3-4

0.8

1.2

I.I

o 30

o

5-0

o

13.0

28

0

3-7

O.I

3-3

1.2

o

o.a

03 o

O.I

0.2

o.i

°-3

o

3-a

0

09

o

o.i 6.0

o

4.6

0

'°-5

29

0

4.0

O.I

0.8

I.O

o

0.5

o.i 0.3 j o.i

03

O.I

O.I

0

o

0

0.9

°-3

o.i 7.8

o

1O.O

o

6.9

H°

0

5-1

O.I

O.I

°-5

O.I

0-3

0.5 3-3 0.1

4.6

o

O.I

0

o

o

'•9

o

0.9 0.9

o

8.3

o

7-3

3'

0 1-1--'

o 14.2

0

12.6

o.a

3-3

o-5

0 i-5

o 0.6

4.0 o

1.5

0

7-3

o 13.0 o

31.2

o

21. 1

< >\ ' mbcr I

o 16.7

o 7.6

0

I.O

o-3

o

M

o 0.4

0

0

0

o

0

o

0

o

o

0

0-5

o

0

a

o o

0

o

0

o

o

o

O.2

o o

o o

o 0.3

0

0.2

0.3

0

3-9 °

8-5

o

0.9

3

0.3 o

0.6

o

0

o

o

0

0

o o.i

o o

0 0

o

0.1

o

o.a

0 0

2.8

o

3-7

4

0

'•9

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o

o

o

0

o

0

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0 0

0 0

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0

o

o

o

o

0

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0

5

o

o

0 0

o

0

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0

o

o o

0 0

0000

o

o

0.3 °

1-3

o

O.I

6

0

o

O 0

o

o

o

o

0

o o

0 0

0 0

o 0.5

O.I

0.9

10.3

o

9-7

o

4-7

i

7

o 6-6

o

i-5

0-3

0.2

0

o

0.2

0 O.I

0 0

0 0

o

0 0

0

o

0

0

0

0

8

0 1.0

0

a. i

o o o

o

0

o o

O o O O

O O.I O

O.I

0.3 o i.i

o

o-7

9

0 0

0

o

O 0 0

o

0

o o

O o O O

0 0 0

o

000

o 1.6

10

0

1.0

O.I

O.I

o o o

O.I

o

o o

o o.a o j 0.3

O O.I 0.2

o

o.i o 3.0

o 7.8

ii

o 0.8

0

0

0 0

o

o

0

o

o

0

o

0

0

o o o

o

0

o

o

0 0

12

0 0

0 0

0 0

o

o

0

o

0

0 O.I 0 0.2

o 0.6 o

09

0

o

0 1

0

6.8

'3

0 1-1

o 6.7

4.1 o

'•7

o

0.2

0.2 0.7

o 3.3 o o.i

o 0.4 o

o

46 o 6.5 o 4.2

'4

0.3 o.i

1.9 o

4.2 o

4-3

o

1-4 I.O °

1-6 0.2 0 02 0-1 1.2 0

o.a

0 0 2.0 0 I.O

'5

o 4.0

0.7 o

3.8 o

3.0

0

0.9 o o

o-4 o o-9 o.i 0.2 o o

0

o.i o 4.7 o 4. a

16

o 0.8

O.I 0

o

O.I 0

0.3

o

O.I 0

o 2.4

o 0.5

0

O.I 0.2

o.a

o

0

O.I 0

2.0

17

o 8.1

0-5 1.2

2.1 0 1.6

o

0.6 o o

0 0

0 0

o 0.4 o

°5

o

0

1.2 0

o.a

.8

0 0

o o o o o | o

O 0 0

o o o o

0 O.I 0

o

O.I 0

3-3

o

5-3

'9

o 0.3

0.3 o i 0.5 o o.i

O.I

O O.I 0

o-a o.i o.i i.o

o 0.5 o

O.I

o o 1.6

O.I

2.O

20

0 O.I

O 0 O.I 0 0.1

0 O.I O.I O.I

0 O O O.I

o 0.9 o.i °.8

3.5 o.i 1.7 o

1-4

21

o

0.4

0

o

o

0 0

0 O.2

o

0

0 O.I 0-4 1-5

0 2.8 0

O.I

I.O

0

ii. 6

0

8.9

22

O.I

i-3

0.4

o

0

0 0

O.I 0

0 O.I

0 O.I

o.a 1.9

0 1.2 0.8

0.3

8.1

o

4-6

o

11.'

23

o ; 1.8

0.5 0.3 o.i o.i o

0.4 0.3

0.7 8.5

o 1.8

o o

0.3 23 1.2

O

2-5

1.9

4-2

I.I

14.3

- t

o

23-7

0 19-5 ° 7-7 : *•"

a.o 5.0 0.3 o.i

o.a o.i

04 0.3

°.6 o.i 8.3

o

9-"

o

24.4 o

16.6

as

O 12.1

o 8.0

o 5.4 o.i

0.5 o.a o.i 0.8

0.5 1-7

0.4 o

'.a o 9.0

o

19.1

o 19.4 o 13.0

26

0

14.8

o 4.7

0.2 0.9 o

O.2 0.2 0.3 O

0 O.I

o 4-3

°.l 4.4 1.5

0

3.3

0.4 0.7 o 0.6

488 HIKKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1 902 — 1903.

TABLE LXXI1 (continued). FY

Axeleen.

Gr. M.-T. o — 2 2—4 4 -

6

6-8

8—io

IO— 12

12 — 14

14 — 16

16-18

18-

-20

20 — 22

22-24

Date

_

4-

1

4-

—

+ - +

—

4-

—

+

—

-f

—

+

4-

+

~

Movembcr27

O

0.4 o : 0.2 i o

°-3

o

O.2 | O 0.2

o

o

0

o

o o

o

0 0

0 0

0

0

0.5

28

O

0.3 o o

0.2

o

0.8

o

o

o

O.I

0.8

0

1.4

o 0.4

1.2

o.i 1 4.6

0 (ol

(01

101

10.51

29

(o)

(0.6) (o) (o.i) (o.i)

(0.1) (0.3)

(0.1)

(0) (0.1)

O.2

o

0-3

o

ooo

0 O.I

0 0

o

0

0

30

(o)

(0.6) i (o) (o.i)

(0.1)

(o.i) 0.2)

(o.i)

(o) (0.1)

10. 1)

(0.6)

0.2

O.I

0.3 O j O.2

O.I O.i

3.4 o

4.0

0

1.6

December i

o

I.O 0

o

0

o

o

o

o

o

0

I.I

'•3

0.2

I.I

o

0

2.0 0.4

2.3 o.i

4.2

O.I

0.4

2

o

o.i o 0.3 o.i

O.2 O

1.9

o 3.3

0.7

o

0.6 o.i

0.7 o 1.5

0.5 0.3

I.I 0

0.8

o

2.5

3

0

2.1 O.9 O.I 3.2

o 0.5 o

0 O.I

o

o

o o

ooo

0 0

0.5 o

i-3

0

0.3

4

o

o o o o

o o

0

0 0

o

0

0

o

o

o

0.5

0 'O.I

I.I

0 1.9

0

0.8

5

o

ooo

o

ooo

0

o

0

0

o o

0

o

o

o o

0

o

o

o

0.8

6

o

2.1

o o

0

ooo

0

0

o

0

0

0

o

o

o

o

0

o-3

0

0.1

o

0

7

o

o o o o

o

0

0

0

0

o

o

0

o

o

0 0

o

o

0.9

0

3.5

0

3-0

8

O 2.O o O.2 O

o o o o o

o

o

0

0

0

0 0

o

0

o

o 4.6

o

2.4

9

0 0 0 0 0

O.I O.I O.I O O

o o

o o

0

o 3-1

o

2-7

o 2.5 o.i

O.I

0.4

10

o

1.4 o 1.3 ! 0.8

0.4 o.i

O.2

o 0.8

o

O.I

0.5

O.I

0.6

0 0

0

0.2

0.9 o 5.9

0

4-4

II

0

1-7

0

1.6

t-3

o

o

o

o

o

0

0.3

0.2

0

o

o

0.8

0.2

0.3

1-4

I.O

4.6

0

3.2

12

o

1.5 o o.i o

0 0

0

0

o

(0.2)

(o)

(0) (0)

03

o o

1.2

o

4-7

o 3.6

0

2.0

'3

0

1.4 o i.i o

0 00 (o) (o)

0.5 o

o o

lo.i)

(o) (o)

(0.5)

O.I

0

lo) 11.41

0

11.31

14

0

(2.0) (o) (1.3) (0)

(o) (0) (o) (o) (o.i)

0.5 o

0 0

o

O 0

o

0

ooo

o

o.|

15

o

4-9 o 4-°

o

0

o

0

O O.I

0 O

0 0

o

0 0

o

o

i-3

o 0.3

0.3

0

16

O.2

o

0

0

0

0

o

o

0

0.2

0 0

0

o

0-3

0. I

2.0

0.9

o

0.6

O.I

2.8

o

2.8

17

0

0.3 o

0

0

0

0

0

0

o

0

0

o

o

0 0

o

o

o

0

0

I.I

0.1

0. 1

18

o

o (o)

(o)

(0.2)

(0) (0)

(o) (o)

(o)

0.4

o

0

o

o o o o

o

ooo

o

'•5

19

o

°-5

o

0

0-5

0 O. I O O.I

o

o

0

0.7 o

1-7 o 0.6 o

o

0.9 o 6.5

o

13

20

o

°-3

o

0

O.2

o

0

o

0

o

0

0

I.O

o

3.5

o

1.8

0

1.8

o 0.3 o

0

0

21

0

o

o

0

0

0

0

o

o

o

o

0

0

o

o

o

0.7

0

0.3

0.8 o i.o

0

0.4

22

O.I

0

o

o

o

o

O.I 0

o

0.6

0.2

0-3

1.4

0

4-3

o

4.0 o

3.3

0

0.2 0.3

o

6.1

23

0

4.6

2.6

2.5

6.2

O 7,2 O II.O o

10.5

o

9.0 o

IO.O o 2.2 0.3

O.I

3-5 o 13.8

o

3-9

24

o

2.6

O.I

i-5

0.6

0 0.3 O O O.I

°-5

o

0.3 0.3

2-5 O.I 2.2 0.8

35

0.7

o 1.5

0

0.1

25

o

M

o

3.6

0.6

o o

0.2 0.3

o

0

O.I

0 O

O o O O

o

2.1

o

-M

0

2.8

26

o

1.2

o

0.2

0

0.1 0

O.i

o

0.1

o

o

1.4

o

3-1 o

2.O O

1-9

o

O.2 6.4

o

3-3

27

o

0.4

o

o-3 o

O.I

0 0

0 0

0

o

o

0

0 0

0

0

o

0

o

1-3

0

5-3

28

0

6.2

o

1-5 1.8

O.2

3.0 o 0.4 o.i

1.3 o

1.8

0

0.5 o

0 O

o

o o.'j 1.7

0

i.5

29

o

0.7

o

0 0

o

0 O O O O O

0

0

0 0

O O.I

o

O.6 O O.2

0

0

3°

o

o

o

0 0

0

0 O O 0

o

o

o

o

0 0 0.2 O.I

0.4

O.I O O.I

o

0.6

3'

o

o

o

0 0

o

o o o o

o o

0

o

0 0

0 0

o

o

O.I 0

0

O.I

January I

o

o

0

0 0

0

o o o o o

0

0

o

o

0

O.I

0

o

o

o

0

o

1.)

2

o 0.8

o

o

o

0

O O. I o O O

o

0

0

0 0

0 0

O.I

o

O O. I

0

o

3

0 0

O.2

0 0

o o o o o o

0

0

0

0000

0

I.I O.I 2.6

0

O.I

4

0

O.I

o

0.8 1.5

o 0.9 o.i 0.7 o o

0.6

i-7

o

0.5 ooo

o

O.I 0 2.0

0

0.9

5

0

O.I

O.2

'•9 3-5

o

0.5 o.i i.o 0.7 0.8 o

I.I

o

3.9 0 2.O

O.I

o.5

0.3

o

'•5

o

0.5

6

O.I

O.2 0.4

o

o

o

o o o o

0 0

0

o

0 0 0.2

o

o

0.7

o 4.4

o

2.1

7

ooo

0 0

0

0000

0 0

0

o

ooo

o

o

i.o o 0.3

0

o

8

o

o

o

0 O

0

0

0 00

0 0

0

O.I

O.I

0 0

o

0

o

o

[ -

0

O.I

9

o

o

o

o

o

o

0.2

0

0

o

o 0.7

o

O.I

0.5 o 0.5

o

o

0.6

0.7 1.3

0

3-1

10

o

2.9

o

3.1 o

o

0

o

0

0

o o

1.2

0

38

o 4.0

0

0-3

o

o 0.5

0

2.0

1 1

o

I.I

o

0.5 o

o

0 0

0

0

o

o

o

o

0

0 0

o

0

2-7

0

2.6

o

4.3

12

o 3.7 o

2.5 o

O.I O O 0 O

0 0

0

O.I

O.I

O.I 0

0

0.8

0.6

0 0

o

[.I

13

0 2.1 ' 0

O.I 0

o o o o o

o o

o

o o

0 0

o

1.4

0.6

0.2 1.2

O.I

1.2

14

O O.I

o

0 0

0

0 0

0

o

o

o

o

o

o

0 0

o

o

o

0 0

0

.'

15

0 I.O

0

0.3 o

0

o

o

o

0

0

0

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0.6

o

o 3-5

0

2.O

o

lo) (i.o)

0.4

0

1

1'AKT. II. POLAR MAGNKT1C I'HENOMENA AND TEKKELI.A EXPERIMENTS. CHAP. III.

'ABLE LXXII (continued). /•>

489
Axeleen.

Or. M.-T.

O — 2 2 — 4

4_6 6-8

8-10

IO— 12 | 13 — 14

14 — 16 16— 18 18 — 20

ao — 22

22 — 34

Date '' - +

— ,

+

—

+

_

+

—

+

_

4.

4-

+

_

+

—

+

_

4.

_

-,.

January 16 o o.i

o

o-3

0.9

o

I.I

o

O.I O

0.4 o

4.0

o

I.O

0 0

0.6

o-3

O.I 0

0.5

0

1.2

17 o-5 °-5

0

o

o

0

0

0

0 0

0 0

o

O O.I

0 0

0

0

0.5 o

2.5

o

o-3

18

O O

o

0

0.7

o

0.3

o

° 0

o

O.I

0-3

o 0.6

o 4.8

O I

o.a i.o 0.4

0.4

0.8

o

'9

o 0.4

o

o.a

0.4

o

O.I

0

o

0.4

0.5

o

2.0 o a.o

o i 1.8

o.a

0-5 o 0-5

0.6

o

0.6

20

o

0.4

o

2.2

0.6

0.4

0.3

0.7

° i 3.6

o

o

o

o

o

I.I 0

0.9 o

O.6 0.3

'•3

o.a

0

21

o

0

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0

1.6

0

0.8

o

0 O.I

3.O

o

7-7

o

1 1.8

o 3.0

o

(0.2)

(0.4) (0.2)

(1.0) 0

(1.5)

22 0.[) (0.8)

(o)

10.51

(0.6)

(o)

(0.4) (o.i) (o.i) (0.4)

0 0

(o)

(0)

fo)

(o) (o)

10)

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7.8

490 BIRKELANl). THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE LXXII (continued). />

Axeleen.

Gr. M.-T. 0-3

3-4

4-6

6-8

8—io

IO— 12

12 — 14

14—16

16-18

18 — so

20 — 23

33-24

Date

—

+

—

+

—

4-

- 4-

—

4- -

4-

—

4-

—

4-

— 4-

_

4-

-f

March 7

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5.7

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0.5

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o 2.5 o

a.o

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8.0 o

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16.0 o

16.8

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6.8

0.5

0.6

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o o. i o 0.3

o

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III. 49!

•

'ABLE LXXII (continued). Fr Axeleen.

(ir. M.-T. 0-2 2-

-4

4-

6 ' 6-8

8 — io

10 — i a

12 — 14 14—16

16-

•t8 18 — 20

ao—

22

23-

-24

Date

1

*

—

_t-

+

— I +

—

+

—

-f 4-

-

+ +

+

-

+

April 26 0.3 0.3 o

0.3

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14.6

27 , o 26.0 o

20.7

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o.a o 03

0

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o

28

0 2.0 0

3-2

o

0.2 O.I 0

O O.T

o o

0 O.I 2.O 0 2.6

o 1.4 o

0

'•4

0

5-7

29

o 0.9 0.4

0

o

0.2 0 0

O 0

O 0

10.41 KII II. i) lo. ii 3.6

o 0.8 0.3

0

7.6

0

7.3

3°

O O.2 O.I

o

O.2

o 0.3 o

o

o

0 0

0.4

O 1.7 O 2.O

o 1.3 o.i

o

O

0

o

May i

000

o

0

0

0 O.I

0

o

O.I

o

0

o. i o o 0.6

o 1.5 o

O.I

,.6

0

4-7

2

o 0.6 o

o

O. I

0

0 0

O 0

0

o

O.I

o o o 0.7

o 1.7 o

O.I

5'°

o

4-2

3

o 2.9 o

o

o

O

0 0

0 0

0 0

o

o o o o

0-3 o 1.3

0.3

o

0.3

o

1

O.2 O.2 O

o

O. I

O.I

0.2 O.I

0 0

O.I O

O O O. 1 0. 1 O

0. 1 0 I .O

o

11.7

0

18.5

S

o ^3-5 °

32.0

O.I

13-7

0.5 0.8

0.7 0.2

(5.0) (o) Uo.o)

0 (1.5) (0) |<0.5) (0.3) I.O 0.2

12

o

0.8

O.I

6

o 1.5 0.4

O.2

0.9

2.4

1.3 0.7

4.0 0.8

6.7 ! o

(0.5) lo.il 11.5) (ol 0.6

0 O.I O.I

O

6.5

0

95

7

o 9.6 o

i '-5

0.1

0.7

0.3 o.i

O.I

o.a

o.a 1.3

o-3

0

(1.5) (ol 13.0)

loi 12.5) (ol

0.2

o

o

0-5

8

o 0.3 o

0

O. I

O.I

o.a 0.3

O.I

0-5

0 0.2

0

O.I

0.7 o.i

2-4

o 3.0 o

O.I

4.0

0

4.8

Q

o 1.9 o

2.2

I.O

O-5 > O.2 O

o 0.5

0.3 0.3

o

o.a

0.6 o

3-3

0 2.8 0

O

o

O. 1

0

1 O

0 O.I 0

0

0. I

O

o 0.3

O O.2

O.I O.I

I.I

0

3.9 o

3-2

o 0.7 0.6

1-9

0.5

o

2.0

1 1

O o. I O

0

0

O

0.1 o.a

0

0

o

0

0.6

o

0.9

0

1.6

0 0.2 0

0

0

O.I

O

12

000

0

o

O.2

0 0

o

o

o

o

o

0.2 0.4

0.4

1-7

o 0.4 o

o

0

o

O

13

0 00

o

0

0

O.2 O

0

0

o

0

0

o

1.7

o 5-7

0 4.2 0

o

0.9

o

I.O

'4

O.I 0 0

o

o

0.2

o 05

O.I

O.I

0.6

0

3.0 | 0

(1.5)

(o) 5-°

o 1.6 3.2

o

13.0

o

7-5

'5

0 8.2 0

5-7

0.6

0.2

0.9 o.i

0.7

o

0

O.I

0

o o a.o

O 2.3 O

0

4.0

0

2.4

16

O 0.5 O. T

0

0

O.I

O.I 0

0

o

o

o

0

0

o o

0.8

o 1.8

0.4

0

1-5

0

6.4

'1

0 1 I.I 0

10.2

o

6.0

0.7 0.3

0

1-5

o.a

o

1.7

0

4.0

0

4-1

o 0.6

0-3

O.I

0.5

0

4.8

18 o o o

O.I

o

0

o 0.4

o

°-3

O O.I

0 0

I.O 0 3.3

o 1.6

0

o

0.7

O.T

0.2

19

O. I O O

°-3

o

o

o 0.5

0

O.I

o o

0.2 0 3.8 0 0.8

O.I 0

I.O

I.I

o

o

O

yo

000

0

O.I

0

o o

o

o

(o)

(0)

10.5 11 (o)

(I.O)

(o)

(i.o)

(o) (0.5)

(0.2)

0

o

o

O

21

O I.O O

1.2

o

O O O.I

o

o

0 0

o o

4.1 o

6.1

o 3-°

0

33

0

o

7-8

22

o 1.7 o

0

o

01.30

0.5 o

0 O.I

o

0

0.4 o

1-7

0 I.I

0

0.2

o

0.9

0-5

23

o 3.1 o

7-3

o

9.6 0.4 1.4

0.2

O.I

4-4

o

16.2

o

12.4

o 6.0

° '-5

o

0-5

0

0

4-9

24

o ,1.7 o

0

0

O.I O i O.5

O.I

o

0.2

0

o o

0

0

I.O

o 1.4

0

0

6.0

o

107

25

o 15.7 o

5.8

O.I

O.I O.I j O

O.I

0.4

O.2

0

4.0 o

3-7

o

0.5

0-3 °3

3.8

O.I

I.O

o

3.7

26

0 35 °

3.6

O.I

0

o o

0.2

o

0

O.2

0.7

0.4

o.a

0-3

3-7

o 0.6

o

O.I

0.6

o

5-9

27

o 6.6 0.2

2-3

0.2

o

O O.I

O.I O

O.2

O.I

0

0.3

o

1.6

0.7

o.i 1.5

0.3

O.I

I.O

O.I

3-4

28

o 6.6 o

12.7

0

16.6 4.5 o.i

5-i

o

4.0

0

4-4 °

0.2

O.I

0

o 0.6

0.3

0.6

i-7

0

4.0

29

o 5.0 o

1.9

O.I

0.3 O.2 O.2

05

o

2.6

0.4

4.5

o

0.4

0.3

0.4

0.2 0.5

'•7

°-3

9-3

0

8.3

30

o 9.3 o

8.0

1.6

o.i 0.5 o.i

o 0.3

5-6

0

7., o

4.4

o

2.3

0 O.I

5-4

o

3-°

(o)

<5.o>

Dy rafj ord.

TABLE LXXIII.
Disturbances in Horizontal Force (Fa).

Gr. M.-T. 1 0—2

2—4

4—6

6-8

8—io

10 12

13—14

14-16

16-18

18— 20

ao — 32

22—34

Date | 4- ! -

+

+

+

+

_l_

+

+

4.

4-

+

—

4/

_

December 2 o 2.8 o

2.0

0.3

0.8 0.7

o

o

0.5

O.I

o.a o.a o.a i.o

O.2

2.4 o

O.2

o

0

0

0. 1

03

3 0.7 i.o

O.I

0.4

O.I

0.3 o

O.I

o

0

0

o

O.I O

o

0.2

O O.I

0-3

o

O.3

0

O.I

0

400

o

0

o

0 0

o

o

o

0

0

0 0

o

O

0.3 o

i-9

o

1.6

0

0.4

O.I

5

0 JO

o

0 0

0 0

0

o

o

0 0

0

o

o

O O

o

o

o

O.I 0

0.3 2.9

6

0.9

1.8

O.I

0 O

000

o

o

o o

o

o

o

O O

o

o

o

0 0

o o

1

7

0

0

0

0 0 O

0

o

o

o

0

0

0 0

o. t

O

o

o

0.4 o

0.5

O.I

1.6

0

8

o

2. 1 O

0.4 0 O

o o

o

O.I

o

o

0

o

O 0. 1 O

o

0.3 o

O.I

0.2

0.5 0.1

9

O.I

0 0

0 O.I

0

O.I O

O.I

0

o o.a

o

0.4

0.3 0.3 3.8

o

1.9 o

0.3 o.i

o 0.6

10

0

3.1 o.i

3.0 o

0.4

0

O.I

0

1-4

0.5 0.5

O.I

0.5

o.a o 0.3

°-3

0.5 o

0.8

0

0.1 1.5

it

o 4.0 o

5-5 o °-2

0 0

O 0

0 O.2

O.I 0

o.i o.i 1.3

o

'•5 °

1.9 o

0.9 4.0

492 BIRKELAND. THE NORWEGIAN AURORA POKARIS EXPEDITION, I QO2 — 1903.

•

TABLE LXXIII (continued). FH

Dyrafjord.

Gr. M.-T. 0-2 2 — 4 4—6

1! i

6 — 8 8—io

IO— 12

13 — 14

14 — 16

16-18

18 — ao

2O — 23

~

22-24

Date

+

— + — +

— +

— +

—

4-

—

+ : —

4- —

-f

—

_l_ !

4-4-

December 12

O.I

4.4 o.i 0.3

0

O.I

0

o

0

0

o o

0 0

0.4 o

3.6

o

3-7

0

O.I

0.6 o

.1 O.I

'3

o

0.4 o

0

°-5

o

0

o

0

0.3

o.i 0.5

0 0

O.I i O.I

0.3

0

0.3

0

M

0.2 o.g 0.4

M

0-7

°-3

O.I

0

o

o

o

0

o

o

0 0

o o

0 0

0

0

o o

O.I

O O.2 O.I

'5

0

1 1.6

0.7

2.3

I.O

0

o

o

0

o

0 0

0 0

0 O.I

o

o 0.6 o

0.4

0 0

0.1

16

o

0

0

0

0

o

o

o

O.I

o

o

0.2

o 0.8

0.2

o

2.4

o

o

O.I

0.2

O.I 0

.2 0.2

'7

O.I

O.I

O.I

0 0

o

0

o

0

o

0 0

0 0

o

o o

0 O

o

O.I

O.I 0

0

18

0

0

o

o

o

o

o

o

0

o

o o

0 O

o

o

o

o o

o

o

0 0

.1 0

>9

o.a

O.I

O O.2

0-3

0.8

O.I

o

0

o

0

O O.2 0.3 | O.I

O.I

0.4

o

o-5

o

0.6

0 0

0.1'

20

o

0

O O.I

0

°-5

0

o.a

o

o

0

o

o o o

o

O.I

0

0 O.I

o

0 0

0

21

o

o

o 0.5

0

o

o

o

o

o

0

o o o i o

o

O.I

o

0.8 ! o

0.2

0 c

o

22 0

0.1

0

o o

O.I

0.2

O.I

0.6

O.I

0.3

o.a

0.3 o.i

0.4

o

0.8

0

0.9

0

0.7

0.6 o 6.1

23 o

14.8

o

8.8 o

'°-5

°-5

3.9

—

—

—

—

— — — _

—

°-3

0.9 2.6

0.8 0.5 0.8

24

o

5.2

0

5.0 0.1

0.4

O.I

o

o

o.5

0.4

0.2

o.i 0.8 o.i

O.I

0

0.2 0.7

o.i 0.9

0.2 0 5.8

25

o

2.8

o

8.8 j o

I.I

0

o o

O.I

0

0.5

o 0.5

O.I

O.I

o

o.i 0.5

O.I O

0.2 0

2.8

26

0

0.9

O.I

o

0

o

0

o.i | o.a

o

o

O.I

o 0.5

O.I

O.I

0

O.I 0.2

0.5 0.9

O.2 O.I 6.4

27

O.I

0.4

o

1.6

o

0.2

o

0.7 o

O.I

o

o

O.I O.2

0

o

O.I

0.2

0.2

0

I.O

o. i 0.3 5.5

28 o 6.4 o 2.6 o

5.2 I.o

0.2 03

O.I

0.4 o.i

o. i 0.3

0.5 o

0.2

0.4 o

O.I

0.6

o o. i 0.8

29 o 0.7 o o. i o. i

o

o

O.I O.I

0

0 0

o o i o o

o

O.I 0.2 O.I

0 O.I 0 O.I

30 o 0.5 o o.i o

0 0

0 0

O.I

0 0

o o o o

o

O.I O.I

O.I

0

o 03 o.i

3r o

O.I O

0 0

0

0 0

0

0

0

o

0

0 O.I

0

O.2 O O

o

000

o

January i

0

0.2 0

0

0.1

o

0 0

0

o

o

o

0

O.I O

o

O O 0

o

000

•9 0-5

2

0.4

0.8

0.2

o

0

0

O o O O

0

o

O.I

0 0

o

O 0 0

0 — 00

3

o

I.O

o

O.I O

o

0 0 O O

0 O

0

0 0

O.I

O | O.I O.I

O.I O o O. I O

4

o

0.9

°-3

6.8 o. i

6.7

0.9 0.7 0.4 o

0 0.1

0

O O.I

0

o.a o.i 0.5

O 0.4 o O.2 O.I

5

o.a

4.4

0

6.1 o.i

060 o 0.6

O.I

0.2

0.4

0.2 I.I

o

a. 5 o

o

O.I O.3 0.3 0 0.2

6

o

2.5

0

,,

0

0.2

o o

0 0

0

o

o

0 O.I

O.I

O.2

O.I

O.I

O.I

O.I

0.4 o

.i 0.6

7

o

O.2 O, I : O.I O

o o o o o

0 0

o

0 0

o

O O O. I O O O 0

0

8

o

o o o o

O.I O.2 O.I O.I O.I

O O.I

0

O.I O.I

0

O.3 0 0.9 JO 1.2 0.2 0

0

9

0

0 0 O.I 0.2

o o.i o. i 0.2 o

0 0

O.I

o 0.5

o

0.4 o o. i o

I.I 0 0.7 ".-'

10

O.2

I.O O

82 0.3

0.1

0 0

0

o

0 0

O.I

0 1.3

o

1.9 o.i

o

0.5

0.9 o o

0.0

1 1

°-3

I.O O

4.1

O.I

0.3 o.i 0.3

o o

O O.I

0.2

o

0.4

0

0.4 o 2.3 o

i .9 0.3 o

.1 0.3

12

O.I

I.I O.I

1.7 O.2

0.5 ° i-5 o-3 o

o 0.4 i o

O 2

O.I

O.I

O.I O.I

0.5 o

O 0 0

.6 0.5

'3

°-7

0.3 0.2

O. I O

o o o o o

0 0 O

o

O.I

o

0 O

0.5 o.i 0.3 o o

.1 0

H

O.I

O. I O O O

o

0 O O O

0

o

0

o

0

o

0 0

0.5 o 0.6 0.3 o

IS

O.I

0 0

0 0

o

0 0

o o

O.I

o

O.2

o

0

o

o o

o

O. T O O 0

•3 °

j

16

O.I

0.4 o. i

0.9

o

o

o o

0.3 0.2

o.i 0.3

0.9

o.a

°-3

o

O.I

O.I

o

0.4

0.6 o o

.8 0.3

'7

0.3

0.3 0.4

0.2 O.I

O.I

0 0

O.I O

0

o

o

o

o

o

O.I

O.I

o

0

0 0 0

0

18

o

O.I O.I

O.I 0

o

O.2 O.I

0.7 o

O. I O

0.1

O.I

0.5

O.I

i-3

o

4.8

o

0.3 0.3 o

. i o.a

19

o

1.3 o

2.6 O.I

o

0 0 O.I O.I

o 0.5

O.I

o

0.8

0-3

0.6

o

o

0.2

0.6 o o

.3 °-6

20

O.I

0.5 o

5-8 o

2.8

o

0.7

1.2

o

0 0

O.I

O.I

0.3 o.i

o

0.3

o.a

O.I O./ O 0

0.1

21

o

0.2 O

0.4 o

1.6

O. I

O.I O

0

0 O.I

0

0.4

O.I O.I

°-5

o.i 0.4

o

1.3 o.i o

J.s

22

o

5-8 0.3

0 ! 0 j 0

0

0 0

o

0 O O.I

0

O.I O

0.2

o

O.I

O.I

000

1 0.1

23

O.I

o o o o

0.4

O O.I O.I

o.3

0.4 o.i 0.3

°-4

0.4

o.a 1 1.9

0

1.5 o a.8

o 0.5 0.6

24

0 2.6 O 3.6 : O.I

O.2

O.I

O.2 O.I O I

0

O O.I

O.2

0.2

o.a 0.6

0

o.i o.i 0.7

O.2 I

.0 0

25

° 0 O.I 0.2

0.2

O.2

O.I

o

O.I

O.I

0

O.I

O.I

O.I

O.I

O.I

O.I

0

0 0

0

0 0

0

26

o

o

o

0

o

o

0

O 1 O.I

o

O I

O.I

O.2

0.2

o

0.2

O.I

O.I

2.2 0

1.6

-•7 °

9.7

27 ; o 13.2 o 14.3

0

6.0

o

3-2

1.3 o

0.7

o

o.a

O.I

0.2

0

0.7

o

0.7 o

I.O

0.4 I

4 °

a8

O.I O.2 O o

o

o

o

0. 1 O O

O 0

o

O.2

O.I

0

1-4

o

0.3 0.2

0.6

O.I O

6 o

29

o.i o.a o.i o.i

o

o

0

O -1 O

o

0

o

0

o

o

O.I

o

o

000

0 0

0

3°

o

0.4 O O.2

O.I

O.I

O.I

0.2

O.I

o.3

o

0.6

1.4.

O.I

2. a

0

6.5

o

5-8 o

O.I

0 0

0

i

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III. 493

ABLE LXXIII (continued). FH Dyrafjord.

Gr. M.-T. 0-2

2 — 4

4-6

6-8

8-10

IO— 13

13 14

14—16

16-18

18 — 20

ao — 32

23 — 34

Date

+

—

+

—

+

—

-4-

—

-t-

—

+-

—

+

_

4-

-i-

—

-t-

—

+

_

+

_

January 31

O

2.5

0.2

0.9

O.I

O.2

O.I

O.2

O.I

O.I

o

o

o

O.I

0. 1

0

I.O

0

0.3

o.a

o

O.I

o

o

ebruary i

0

0

0

0

o

O.2

o

O.I

o

o

o

o

O.I

O.I

O.I

o

°-3

0

O.3

o

O.I

o

0.3

o

a

O

1.9

O

0

o

o

o

o

0

o

o

O.I

O.I

O.I

0.2

o

o.a

o

o

o

o

o

o

0.4

3

0

I-5

0

0.8

O.I

o.a

O.I

O.I

o.a

o

o.a

o

°-3

O.2

O.I

O.I

o

o

o

o

o

o

0

o

4

O

o

0

0.3

0

0.6

0

0.2

0

O.I

O.I

O.I

O.I

0

O.I

o

O.I

0

o

O.I

0.5

o

0-5

o

5

O

o

O

0

o

0

o

O.2

O.I

0.3

O.I

O.I

o

O.I

0.5

o

I.I

o

0.5

o

O.I

0.3

0.4

o-3

6

O

2.2

o

3-4

O.I

1.0

O.I

o-3

o

o

o

o

o

O.I

0.3

o

O.I

O.I

O.I

o.a

o

o

o

o

7

O

o

o

0.4

0

0.2

o

O.I

o

O.I

0

O.I

O.I

o

o.a

0

°-3

0.1

O.I

O.I

0.8

1-3

O.I

4-5

8

O

a. a

0

9.1

o

13.8

0.9

4.0

1.0

0-5

2.8

0.2

i-5

o.a

5-2

0

6.0

o

2.9

5-5

0.2

5-3

3-5

o

9

O.I

2.3

o

7-5

°-3

0.2

O.I

0-3

o

O.I

O.I

O.I

0.1

O.I

O.I

o

O.I

0

O.2

O.I

0.4

1.4

0.3

3.9

10

O

3-6

0

1.9

o.a

o-5

O.I

0.2

O.I

o

o

o

O.I

0

o

O.I

0

0.2

O.2

O.I

0.6

o

O.I

6.8

II

0

3-3

0

4-7

o

3.7

O.I

0.7

°-3

O.I

o

0.5

O.I

0.6

O.I

O.I

0
n f\

o

—

—

—

—

—

—

1 2
13

0

8.2

0

a. i

O.I

0.9

0.7

O.I

1.3

o

0.2

o

o

0.2

O. I

O.I

o

O.I

O.O
0

O.I

4-9

2.0

o

0

3-5
0.7

o
o

0.3
0-3

0.7
0.6

«4

—

—

—

—

—

—

—

—

—

—

0

0.6

o

°-3

0.4

0

0.4

o

o

O.2

I.O

0

—

—

15

0

1.9

o

4.2

0.4

o.a

0

0

0.2

O.I

o

0.2

0-3

0

2.5

o

4-3

0

0.2

o.a

O.I

0.4

o

0.4

16

0

0

0

o

o

o

0

0

0

o

o

o

o

o

o.a

o

O.I

0

O.I

0

O.I

o

o

O.I

'7

O

1.2

o

1.4

o

o.a

o

o

0

0

o

O.I

O.I

O.I

O.I

o

0

0.7

o

0.8

O.I

O.I

o

0.7

18

0

3-4

O.I

O.I

o

o

o

O.I

O.I

o

o

°-3

o

o

o

o

0

0

0

o

o

o

o

o

19

0

o

0

o

o

o

0

o

0

O.I

o

O.I

O.I

0 2

o

O.I

O.I

O.I

o

O.I

o

O. I

o

0.3

20

0

1.4

0

0.4

o

i.i

o

0.2

0

0

O.I

O.I

O.I

0.2

o-3

0.2

0-5

03

O.I

O.I

o

O.2

0

O.I

21

O

°5

0

14.3

0

2I.O

o

19-3

0

5-2

0.2

2.0

o

i-9

o

0.6

O.I

O.I

O.3

O.I

o

0

0

o

22

O

o

0

0

o

O

O.I

O.I

0

O.I

o

O.I

O.I

°-3

O.I

0.3

0.2

0

o

o

O.I

O.I

0

O.I

-:-;

0.3

O.I

o

o

o

0

0

0

O

o

o

o

O.I

O.I

O.I

O.I

O.I

0.2

O.2

0.4

3-3

o

0.9

O.I

24

O.I

lf.\

0.4

o

O.I

o

o

O.I

0

O

o

0

o

O.I

O.I

o

0

O.I
O I

o

O. I

(O.I)

(O.I)
O I

(O.I)
O« I

(O.I)
O I

(O.I)
O. I

(o.a)
o

35

36

27

IOI
O.I
O

O.I

3-°

0

o

o

2-5

o
o

o

i-3

o

O.I

o

O.I

O

o

o
o

o
o

o
o

o
o

0

o

o

0

0.5

0

o

o
o

o

0

o

O.I

o
o

0.7

o

0.9

o

0.3

o

0.7
o

28

O

o

o

0

o

o

o

o

o

0

0

o

o

o

o

o

o

o

o

o

o

o

o

o

March i

O

0

o

o

o

o

o

o

0

o

o

o

0

0

o.5

0

3-7

o

5-5

0

0.3

0.5

o

3.4

2

O

IO.2

0

i-5

o

3-6

O.I

2-7

O.I

O.I

o

0.4

o

0.2

O.I

o

2.31 °

3-6

o

3.1

O.I

o

3°

3

O

6-3

0

1-9

o

1.4

0.4

0

0

0

o

O.I

o

0.2

O.I

o

o-3

0

0

0

O

o

o

0

4

O

0

0

°o

o

0

0

o

o

o

o

0

o

o

0

o

o

0

O.I

0

0.3

o

0.4

1.4

5

0.2

i-9

o

12.1

o.a

3-a

0.2

o

o

o

O.I

O.I

3.7

o

10.8

o

7-3

o

3-4

0

I.I

o

I.O

o.a

6

o.a

0.4

O.I

O

o

o

o

o

o

o

o

0

O.I

o

O.I

o

0.2

0.3

I.I

0

0.3

0.6

O.I

2-4

7

O.I

3-9

o

9.I

O.I

3-9

o

4-4

O.I

3.4

0.4

O.I

0.3

0.4

4.3

O.I

5-0

o

4.6

0

3-3

o

O.I

i-9

8

o

13-5

o

I2.O

O.I

1.4

0.3

O.I

0

O.I

o

O.I

1-7

o

2-3

o

5-4

o

7-1

O.I

1.6

'•5

o

59

9

O.I

3-3

o

15-3

o

IO.3

1.3

0.8

0.3

O.I

O.I

O.I

o

O.3

°-3

o

°-3

0

o

0

0.4

0.3

°-3

o.a

10

°-3

0.7

O.I

1.9

O.I

O

o

0

O.I

O.I

0

o

0.4

O.I

1-3

o

2.9

o

5-4

o

5-1

o

o-9

I.O

1 1

o

3-2

O.2

0.4

O.I

O

0.2

O.I

0

o

0

o

o

o

o

o

I.O

o

1.2

o

°3

0.9

O.I

o.a

12

o

a-3

0.2

i-3

o

7.4

0-3

O.I

o.a

o

o.a

o

°-3

o

0.4

o

4-3

o

a. i

o

1.6

0.4

o.a

7.8

13

o

3.8

o

21. 0

O.I

14.2

1.4

o

0.6

o.a

0

o.a

i. a

0.4

3-5

O.I

4.1

O.I

0.6

0.9

0.3

0.3

o

1.4

M

o

2O.O

o

3.6

O.I

O.I

o

O.I

o

0-3

o

0.6

0.6

O.I

1.6

o

1.8

0

0.3

0

o

O.I

O.I

O.I

15

o

0

o

1.4

o

i-7

o

O.I

o

O.I

O.3

o.a

0.7

o

'•7

o

0.6

o

1.6

0

O.I

O.I

O.I

0.3

16

O.I

O.I

0

0.2

0

°-3

O.I

o

O.I

O. I

o

O.I

o

o

O.I

o

o

O.I

O.I

o

O.I

O.I

0

0

n

o

o

o

O.I

o

0

0

o

o

o

o

o

0

o

o

o

o

O.I

O.I

O.I

o

o

o

0

18

o

o

o

O

o

0

o

o

o

o

o

o

O.I.

O.I

0

0

O.I

o

0-5

o

1-3

0

°-5

I.I

19

o

3-i

0

1.3

O.I

o.a

O.I

O.I

O.I

O.I

o

O.I

o

o

0.9

O.I

1.5

o

4.0

0

i.a

o

O.I

4-1

20

o

8.0

°-5

O

o

o-5

o

o.a

o

0.8

°-3

O.I

O.I

0.3

o.a

o

O.I

o

0.4

o

o.a

o

0.3

1-3

21

o

2.5

o

3-8

o

8.3

0.4

°-5

0.3

o

o

0.1

o.a

0

o

o.a

o.a

o

0.9

o

0.7

1-3

o

3-5

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903.

63

494

B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE LXXIII (continued).

Dyrafjord.

Gr. M.-T.

O — 2

2-4

4-6 6-8

8—io

IO— 12

12—14

14—16

16-18

18 — 20

20 — 22

22-24

Date

+

_

+

_

+

—

+

—

+

—

-t-

—

+

—

+

—

-4-

—

+

—

4-

_

+

_

March 22

0

0.9

O

o-3

o

0.5

0

O.I

o

0

o

0

O.I

0

0.7

0

2.2

o

1.4

o

i-5

3-a

O

9.0

23

O

2.O

O

4.1

O.I

0.2

o

o

0

o

O.I

o

O.2

0

0

0

0.3

o

0.2

o

0.5

o

0

3-a

24

O

5.8

O.I

O.I

o

0-3

o

0.9

0.2

o

o

O.I

0.1

O.I

0.3

o

O.I

o

O.I

o

0

o

0

0-1

25

O

O.I

0

O.I

o

O.I

o

o

o

o

o

0

0.3

o

o

o

o

o

O

o

o

O.I

0

°-3

26

O

O.2

O

O

o

o

o

o

0

o

o

o

O.I

o

O.I

o

O.2

O.I

O.I

o

o

o

o

o

27

O

O

O

O

o

0

o

0

0

o

O.I

0

O

o

O.I

o

O.I

o

0.8

o

°-3

o

0

O.I

28

O

O

O

O

o

o

o

o

o

o

o

o

O.I

o

0.3

o

O.I

O.I

°-3

o

o

o

O.I

o

29

0

I.I

0

9.1

o

2.O

o

0.8

0.3

O.I

o

O.I

0.2

o

2.8

o

8.2

0

9.8

o

3-2

O.I

0.2

3°

0

5-1

0

6.4

1.9

o.a

2.1

o

0.6

o

o

0.2

0-3

o

0.4

0

0.2

0.1

0.2

O.I

1.4

o

0.8

O.I

31

O.I

15-5

O.I

0.8

O.2

0.3

O.2

0.6

I.I

o

°-5

o

1.9

o

2.1

o

4.1

o

2.0

o

'•3

1.6

0

5-5

April i

O

3-o

O

4.0

0

o

o

o

o

o

o

o

0

o

O

o

0

o

O

0

°-5

o

0

8-5

2

0

9.5

O

4-5

°-5

0

0

I.O

o

0.5

o

o

°-5

o

0

o

4.0

o

5-0

o

2.0

o

°-5

a-5

3

O

15-5

O

I2-5

3.0

0

0

o

o

o

0

o

0-5

o

I.O

0

0.5

o

3-o

o

2.0

o

°-5

1.8

4

O

4.0

0

6.0

0

2-5

o

°-5

o

0

0

0

°'5

0

0-5

o

i-5

0

3.5

o

°-5

0

o

I.O

5

O

4.0

0

S.o

o

14.5

0

6-5

o

o

o

0

i-5

0

8.5

o

7-°

o

I.O

0

0

o

0.5

0

6

°-5

2.O

O

26.5

I.O

21.0

i-5

°-5

°-5

3-°

3-°

2.O

o-5

5-°

2-5

o

a.o

o

I.O

0.5

o-5

o

o

°-5

7

O

O

O

o

o

o

o

o

o

i-5

0.5

O

2-5

0

3-°

0

i-5

o

!-5

o

2-5

o

I.O

0

8

0.5

0.5

0

0

-

—

-

-

—

•—

-

—

0.5

0

1-5

o

0

o

I.O

o

I.O

o

0.5

10.5

9

0

13-5

O

IO.O

o

I I.O

o

13.0

I.O

2.O

i-5

O

i-5

0

3-°

o

6.0

o

5-o

0

0-5

i-5

0

21.0

10

0

3-°

O

6.0

o

o

0

I.O

o-5

°-5

°-5

°-5

I.O

°-5

3-°

o

3-5

o

3-o

o

I.O

5-o

0

2.0

ii

O

2.O

O

I.O

o

1-5

o

o

°-5

°-5

o

o

2.O

0

0

0

o

o

o

o

o

0

0

4.0

12

0

9.0

O

17.0

o

2.O

o

o

o

0

o

o

O

0

0-5

o

'•5

o

2.5

o

i-5

i-5

o

13.0

'3

O

7.0

O

4.0

o

0.5

o

i-5

o

0-5

0

0

O

0

0

o

I.O

o

1.5

0

2.O

o

o

I.O

H

0

1.0

O

'•5

o

o

o

o

o

o

o

o

0-5

o

I.O

o

0.5

o

o

o

O

0

o

°-5

15

0.5

0-5

0

o-S

o

o-5

0

o

o

i-5

i-5

o

4-5

o

3-°

o

"

"

~"

TABLE LXXIV.
Disturbances in Declination

Gr. M.-T. 0 — 2

Ii

2-4

4-6

6-8

8 — io

IO— 12

12 — 14

14 — 16

16-18

18— 20

20 — 22

82 — 84

Date || +

_

+

_

+

_

+

_

+

+

—

4-

—

+

_

-t-

—

+

—

+

—

4-

_

December 2

0

O.I

O

O.2

o

0-7

O.I

O.I

o

o

O.I

o

°-3

o

°-3

o

o

0.7

O.I

0

o

o

0.4

o

3

1.2

o-3

0.3

°-3

0

O.2

O.I

O.I

O.I

O.I

o

o

°-3

o

o

O.I

o

o

o

O.I

o

o

o

o

4

0

0

0

o

0

o

o

O.I

o

O.I

o

o

o

o

o

o

0

o

O.I

O.2

O.2

0.2

I.I

0.2

5

O.2

o

o

o

o

o

o

O.I

O.I

o

o

o

o

o

o

o

o

0

o

0

0

o

o-7

I.I

6

0.9

°-3

o

o

o

o

0

o

o

o

o

o

o

o

o

o

o

o

o

o

o

0

o

0

7

0

0

o

o

o

o

o

o

o

o

o

o

o

0

O.2

0

o

o

0

O.I

O.2

O.3

o-9

0.7

8

0.9

o-3

O.I

0.2

O.I

O.I

0.2

O.I

O.I

O.I

o

0

o

o

o

0

o

o

o

o

O.I

O.I

I.O

0.3

9

O

O.I

o

O

O.I

o

O.I

0.2

O.I

O.2

o

0

O.I

o

o

0.4

O.2

0.8

o

0.9

o

0.8

0.2

0-3

10

o

O.I

0.2

°-3

°-3

0-7

0.2

O.I

0

O.I

0.2

O.2

o

O.I

o

o

O.I

O.I

O.I

O.I

0.3

I.O

1.2

0.4

II

°3

o-3

O.2

o.a

O.I

O.I

o

o

0

o

o

0.3

O.2

0

O.I

o

O.2

O.2

0-4

0.2

O.I

0-5

2.O

O.I

12

0.6

O.2

O.3

O.I

0

o

O.I

O.I

o

0

0

o

o

o

O.2

o

O.I

0.9

0-3

0.5

0

0.2

0

O.I

'3

O.I

O.I

O.I

o

o

O.I

O.I

0

o

o

o-9

o

o

o

O.I

O.I

o

0.2

o-i

0

0.4

2.4

0.8

0-3

14

0.4

O

O.I

O.I

o

o

o

0

0

0

o

o

o

o

0

o

0

o

o

o

o

o

0.2

o

'5

0.9

I.I

0

0.8

o

o

o

0

o

O.I

o

O.I

o

o

o

o

0

0

o

0.4

o

0.4

0

0.2

16

o

0

o

o

0

o

0

0

O.I

O.I

o

o

0.4

o

o

o

0.4

0-3

0

0

0

0.2

O.I

0.6

17

O.I

O.I

o

0.3

o

o

o

o

o

o

O.I

O.I

o

0

o

o

o

o

o

o

o

O.2

o

O.I

18

o

0.2

0

O

0

o

0

0

o

o

0

0

o

o

o

0

o

0

o

o

0

o

o

I.O

19

O.I

O.2

o

O

o

I.O

0

O.I

O.I

o

0.2

o

0.2

o

O.I O

o

O.I

o

°-3

0

I.O

o

O.I

20

o

O.I

o

o

O.I

o

o

0.3

O.I

O.I

0

0

o

o

0

O.I

o

O.I

o

O.I

o

o

0

0

21

o

0

O.I

o

0

O.I

O.I

o

o

o

o

o

0

o

o

o

0

o

O.I

o

0

O.2

0

o

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III. 495

ABLE LXX1V (continued). FD Dyrafjord.

Gr. M.-T. 0—2

2 — 4

4-6 6-8

8—io

IO— 13

la— 14

14 — 16

16-18

18 — 20

ao— aa

32 — 24

Date

4-

—

4-

—

4-

—

+

—

+

—

4

_

+

_

4-

_

4-

—

4-

_

+

+

December 22

o

0

o

o

O.3

0

o.a

o.a

°-3

O.I

0-3

0.3

0.3

o

o

O.I

o

0.3

o

o

1-3

o

3-5

o

23

o

5-7

0

3.4

O

3-3

I.O

o.3

—

—

—

—

—

—

—

—

—

—

'•5

0.6

1.8

0.8

O.I

O.I

24

i-3

O.I

1-3

O.I

0-3

O.I

O.I

O.I

O.3

O.I

O.I

O.I

O.I

o

0.4

O.I

o-3

0.3

o

1.4

o

0.6

0.8

O.I

25

0.4

0.3

0.2

0.7

O.I

0.4

o

0.1

O.I

o.a

O.I

0.3

O.I

O.I

O.I

O.I

o

O

o

0.8

o

0.3

i-3

O.I

26

O.I

0.2

o.a

O.I

O.I

O.I

0

O.I

O

o.a

o.a

0-3

o

O.I

o

o

o

0

0.3

o

o

I. a

3-5

o.a

27

0

o.3

0-3

O.I

O.I

o.a

O.I

O.I

O.I

O.I

O.I

O.I

0.4

o

o.a

o

o

O

o

o

O.I

1.4

3-5

0

28

1.9

0

O.I

0.8

o

a-5

O.I

0.7

O.I

0.6

o.a

o

0.3

O.I

O.I

O.I

o

0

o

O.I

0

0-3

'0.4

O.I

29

°-5

0

O.I

0.4

O.I

0.3

o.a

0.3

O

O.I

o

o

o

o

o

0

o.a

O.I

O.I

O.I

O.I

O.I

O.I

O.I

3°

O.I

0

O.I

o

O.I

o

o

O.I

O.I

o

O.I

O.I

0.4

o

o

o

o

O.I

O.I

o

0

O.I

O.I

I.I

3'

o

0

o

o

o

o

o

0

O

o

0

o

o

0

o

O.I

o

O.I

0

o

o

o

o.a

O.I

January i

O.I

O.I

o

o

O.I

O.I

o

O

O.I

O.I

0

o

O.I

o

o.a

0

O.I

O.I

o

O.I

o

0.8

o.a

0-3

2

0.4

O 2

o

0.3

o

0

O.I

O.I

o

o

o

O.I

o

o

o

o

o

O

o

o

o

o

o

o

3

°-3

0-3

O.I

O.I

O.I

O.I

o

o

o

o

o

0

o

0

o

o

O.I

O.I

o

O.I

O.I

0.3

O.I

o

1

O.I

O.I

o-7

O.I

o

0.3

I.O

I.I

0.4

o

0-3

O.I

o.a

o

o

o

0.1

O.I

o

O.I

O.I

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o

0.4

5

2.3

O.I

O.I

0.9

O.I

I.I

0.8

o

3.9

0

i-7

O.I

0.8

0

0.9

o

0.2

0.6

0.1

o

O.I

O.I

o

O.I

6

O. I

0

0.8

O.I

o

O.I

o

o

o

o.a

o

o

o

0

O.I

O.I

0-3

o

0

O.I

o

3.1

0.5

0.6

7

o

O.I

o

o

o

0

O.I

o

o

O.I

O.I

o

O.I

o

O.I

0

O

o

0

O.I

o

O

0

o

8

o

O.I

o

0

O.I

0

O.I

O.I

O.I

o.a

O.I

O.I

O.I

O.I

O.I

O.I

o.a

o

o

0.6

0.1

1.4

o

0.3

9

o

0

o

O.I

O.I

0.3

O.I

0.6

0.3

o

O.I

o

0

O.I

1.2

0

O.I

O.I

o

o

O.I

o-3

1.9

0.7

10

I.O

0.2

0.8

0.7

0.2

O.I

0.3

O.I

O.I

o

O.I

o

O.I

o

0.4

0

I.O

o

0

O.I

o

0.4

0.4

0.7

ii

o-5

O.I

0.8

o

O.I

O.I

O.I

O.I

0

O.I

O.I

o

0.3

o

0.2

o

O.I

O.I

0

i-3

o

2.1

o

1-9

12

l.i:

0-3

0.6

o.a

0.3

o

0.4

o

0.3

0

0-5

o

0-3

o

O.I

O.I

O.I

O.I

o

0.5

o

0

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0.2

'3

0.2

0.8

O.I

o

o

O.I

0

0

o

0

o

o

O

o

0-3

0

0

o

0

0.8

O.I

0.3

O.I

O.3

14

O.I

O.I

O.I

0.2

0

o

0

0

o

o

0

0

o

O.I

O

O.I

o

o

0

o

a.o

0.8

0.4

0-3

15

o

O.2

o

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0

O.I

O.I

O.I

0.3

o

o.a

0

0.4

0

O.I

o

0

o

o

0

0

O.I

o

0.3

16

0.2

O.I

0.4

o

o

o

O.I

o

0.5

0

o

0.7

o

0.6

o

o

o

O.I

O.I

o

o

0.3

I.O

0.4

17

I.O

O.I

O.I

O.I

o

o

O.I

o

o

0

o

o

O.I

O.I

o

0

o

o

o

o

o

o

0

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18

O.I

0

o

O.I

o

o

0.3

O.I

O.I

O.I

o

o

O.I

o

0.3

o

1.6

o

O.3

0.4

0.3

o

o

0

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0.5

O.I

0.7

o

O.I

o

o

O.I

o

0.3

°-5

0

O.I

O.I

0.7

o.a

0.4

0-3

O.I

o

o

0.3

o.a

O.I

20

o

0.2

0.2

°-3

0.3

0.9

0.5

I.O

i-3

o

0-3

0

O.I

O.I

0.2

o

0

0

0

o

o

O.I

o

0

21 0

O

o

o

o

0.5

O.2

O.I

0.2

o

o

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O.I

0

O.I

0

o.a

o

o.a

O.I

O.I

O.I

O.I

0.4

22

o

1-4

O.I

o

o

0

0

o

o

o

o

0

o

O.I

O

o

O.I

o

o

o.a

o

0

o

0.3

23

o

0.2

o

o

0.2

o

o

0.8

0.7

o.3

O.I

0.5

O. [

O.I

O.2

O.I

O.I

o.a

0.5

O.I

O.I

1.8

o

0.6

24

O.2

O.I

0.7

o

o

O.I

o

O.I

o

o.S

0

O.I

O.I

0

O

O.I

0

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9-3

O.I

O.I

o

I.O

25

O

0

0.3

o

o-3

o

O.I

0

O.I

o

O.I

O.I

o

o.3

0

o

0

O.I

—

—

—

—

-

—

26

—

0.4

0.6

3-0

O.I

3.9

4-7

27

o.5

6.1

o.a

5.5

o

4.1

O.I

2.4

0.6

0.3

O.I

O.I

o

o

o

0

o

O.I

o.a

o

o

0.9

o.a

0.7

28

O.I

0.3

O.I

o

o

o

O.I

O.I

o

O

o

o

o

o

o

o

O.I

o

O.I

O.I

o

o-3

o

0.6

29

O.I

0.4

O.I

O.I

0

O.I

o

o

o

O

o

O.I

O.I

o

o

o

o

0

0

o

o

o

o

0

30

o

O.I

0.2

o

o

O.I

o

o.a

0.5

O

0.6

o

o.5

O.I

a. i

0

3.7

o

0.4

0.4

o

o

o

0

31

O.I

°-3

0

0.3

o

O.I

O.I

o.a

o.3

O

o

O.I

o

o

O.I

O.I

0.2

O.I

O.I

o

o

0

o

O.I

February i

o

o

O

o

o

O.I

O.I

o

o.a

O

0

o

O.I

o

O.I

O.I

O.I

O.I

°-3

o

o

o

o

0

2

0.5

O.I

O

o

o

o

o

0

o

O

0

o

O.I

o

O.I

o

0.1

O.I

o

o

o

o

o.a

o

3

O.I

0.2

o

0.2

O.I

o.a

0.2

o.a

o

o.3

0.4

0

O.I

o.a

O.I

O.I

0 I

O.I

o

o

o

o

o

o

4

o

o

O.I

0

0.2

O.I

o

o.a

O.I

O.I

O.I

o

O.I

o

O.I

O.I

o

o

O.I

o

o

o.a

O.I

0.6

5

o

O.I

O.I

o

O.I

0

O.I

O.I

0.3

O.I

O.I

o.a

o

O.I

O.3

O.I

o.a

0.3

o

o.a

o

0.6

o.a

O.2

6

0.4

0.3

0.2

0.9

o

i-3

o.a

O.I

0

O.I

o

O.I

o

o

O

O.I

O.I

o

o

o

o

o

o

0

7

o

0

O.I

o

0

0 I

o

o

o

0.3

O.I

0

O.I

o

O.I

O.I

o.a

o

O.I

o

0.3

I.O

3-8

I.I

8

o

0.6 o.a

3-3

O.I

5-3

o

4-4

'•3

0.4

3.7

O.I

a.o

O.I

1.8

O.I

0.4

0.3

6.4

o-5

6.5

o

0.8

0.4

9

o.3

O.2

0.8

O.2

0.3

o.a

o.a

0.3

O.I

O.I

0.3

o

o

O.I

O.I

O.I

O.I

O.I

o.a

°3

o.a

0.8

3.8

o.a

496 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE LXXIV (continued). FD

Dyrafjord.

Gr. M.-T.

0 — 2

2-4

4-6

6-8

8—io

IO— 12

12 — 14

14 — 16

16-18

18 — 20

20 — 23

22—24

Date
February 10
ii

12

4-
0.7
O.I

0.3

I.I

+

O.I
0

O.I

0.8

4-

O.I
0

0.5

2.2

4-

0

I.I

O.I
O.2

4-
0.1

0.4

O.I
O.I

4-

O. I

0.2

o

O.I

4-
0
O.2

O
O.I

4-
o
o
o.5

o

O.I

o

+
o

O.I

4-

O.I

O.I

4-
o

0.5

+

2.2

'•3

0.3

o

o-5

o-3

O.I

0.6

0.8

O.I

'3

0-7

°-3

0.3

0.8

O.I

0.6

o

o-5

o

0.9

O.I

0.3

O.I

O.I

o. r

o

o

o

O.I

0.6

o

o-3

0.3

0.2

14

—

—

—

—

—

—

—

—

—

—

O.I

O.I

O.2

O.I

O.I

O.I

O.I

O.I

o

O.I

O.I

0.6

—

-

15

o

0.4

0.3

0.2

o

0.4

°-3

O.2

0.4

o

1-3

o

I.O

0

0.9

o

o

2-3

o

O.I

o

0

o

0

16

o

0

o

O

o

0

o

o

o

0

o

0

o

o

0.3

o

o

O.I

0

0.4

O.I

O.I

O.I

o.:

17

O.I

o.5

O.2

O.I

O.I

O.I

o

O.I

O.I

O.I

o.a

o

0.2

o

0.3

O.I

O.I

O.I

o

o

o

O.I

0

0.2

18

0

1.2

O

O

o

0

o

o

O.I

O.I

o

0.2

O

o

0

O.I

0

o

o

o

o

O.I

o

0

19

o

O.I

O.I

O

o

o

o

o

0.3

o

O.I

o

0.2

o

o

o

O.I

O.I

O.I

o

o

o

O.I

o

20

O.I

O.I

O.I

O.I

o

0.5

0

O.I

o

o

o

o

O.I

o

0

o

O.I

o

o

O.I

0

o

0

0

21

o

o

O

O

O.I

o

O.I

O.I

0

O.I

O.I

O.I

0.3

o

0.6

o

°-5

0

o

o

O.I

0

o

0

22

o

0

0.8

i-5

o

8.7

0

7-i

O.I

0.8

2.1

0

i-5

0

O.I

o

O.I

o

o

o

O.I

O.I

O.I

O.I

23

0.4

0.4

o

o

o

o

o

Q

o

o

Q

O.I

O

Q

O.2

0

Q

O.I

Q

O.I

o

O.I

O.I

O.I

o

0.4

0.4

0.6

O.I

24
25

0.5

o

°_

0.3

o

o

O.I

0

o

o

O.I

o

0

26

0

O.I

o

o

o

o

O.I

0

o

O.I

O

O

O

o

o

0

o

o

o

o

0.7

0

°-5

0.7

2?

O.I

0-4

O.I

O.2

O.I

O.I

O.I

o

o

o

O

o

0

o

0

o

0

o

o

o

o

o

o

0

28

0

o

o

O

o

o

o

o

O.I

O.I

O.I

0

0

o

o

o

0

0

o

o

0

0

0

o

March i

—

—

—

—

—

—

—

—

o

O.I

o

0.2

O.I

O.I

O.I

o

O.I

0.3

o

1.6

O.I

0.4

°-3

o-3

a

O.I

2.1

0. I

O.2

0.2

0.5

0.2

0.8

o.S

o

O.I

O

o

0

o

o

0

0.2

o

°-3

I.O

0

1.6

1-3

3

O.2

1.4

O.I

0.9

O.I

0.4

0.5

o

o.a

o

o

O.I

o

o

o

o

o

o

o

0.2

o

0

o

0

4

o

o

O.I

O

0

o

o

o

o

0

o

o

o

o

o

o

o

o

o

o

O.I

o

0.6

0.8

5

0.6

O.I

O.2

1.9

O.I

1.2

o

0.3

o

O.I

0.7

O.I

1.8

o

0.9

0

0.7

O.2

0.2

O.I

O.I

O.I

I.I

O.I

6

O.2

0.8

O.I

O

O.I

o

o

o

0

O.I

o

O.I

o

o

0

o

0

o-3

O.I

°-3

0.4

0.7

4.1

0

7

1.4

0.7

0.4

2.O

o

3-i

o

3-3

a. a

o

3-3

o

2.8

o

0.8

o

I.I

0.5

O.I

°-3

O.I

0.3

I.I

0

8

1.6

0.8

o

i-7

o

1.0

O.I

o.a

O.I

o.a

I.O

o

1.2

o

0.8

o

0.3

0.6

M

0.6

8.3

O.I

4-3

0.6

9

1.2

0.8

0.8

2.4

o

4.9

o.5

0.5

°-3

o.a

o

O.I

O.I

o

O.I

o

o

o

0

0.3

O.I

I.O

0.6

0.4

10

0.4

O.I

o

1.4

o

o

o

O.I

O.I

O.I

o

o

o

o

O.I

o

o.a

O.I

O.I

0.6

0.2

I.I

1.9

°-5

1 1

0.8

0

O.I

O.I

O.I

o

O.I

o

o

O.I

o

O.I

O.I

o

o

O.I

o

0.2

O.I

1.2

O.I

0.3

O.I

0.2

12

3.O

o

O.I

O.I

o

i-7

O.I

I.I

0.5

o

°-5

0

I.O

o

O.I

o

0.6

0.3

o

0.3

3-5

O.I

2.7

3.7

13

0.8

0.6

1.9

2.2

O.I

IO.O

1.0

O.I

0.9

O.I

0.4

O.I

1.9

0

i.a

o

O.I

1.6

O.2

O.I

0.3

O.I

0.7

O.I

14

2.8

o.3

O.I

0.4

O.I

o

O.I

o

O.I

0.4

O.I

O.I

0.4

o

0-5

0.3

o.a

o

o

O.2

o

0

0

O.I

15

o

o

O.I

O.I

O.I

0.4

o

0.3

o

0.6

O.I

0.6

o.a

O.I

O.I

O.I

0.2

0.2

0

o-5

O.I

0

O.I

O.I

16

0

o

o

O

o

0

o

O.I

O.I

0.2

O.I

0.2

o.a

o

O.I

0

O

0

o

O.I

o

0.7

o

0

'7

o

o

O.I

o

o

o

o

o

o

O

0

0

o

o

o

o

O

o

o

o

o

0.2

0

0

18

o

o

o

0

o

0

o

o

o

o-3

o

0.2

o

o

o

0

O

O.I

o

o

o

°-3

I.I

O.I

19

O.2

0.5

o

0.2

o

o-3

O.2

O.I

o

O.I

O.I

o-3

o

0

o

O.I

O

O.2

o

1.2

o.a

0.3

1.6

0.3

20

2.1

0.9

o.a

0

O.I

0.2

°-3

O.I

0.6

O.I

0.6

0

O.I

O.I

o

0

o

o

o

O.I

O.I

o

0.4

0.3

21

O.I

O.I

O.I

O.I

O.I

1.0

0.2

0.5

O.I

O.I

O.I

O.I

o

O.I

o

O.I

o

O.I

0

o

0.5

0.2

i-7

O.I

22

O.I

O.I

o

O.I

o

0.2

o

0

o

O.I

O.I

O.I

O.I

O.I

o

o

O.I

0.2

O.I

O.I

1.6

0.3

5.3

O.I

33

o

O.2

O.I

°-3

o

0.2

o

o

o

0.2

o

O.I

O.I

o

o

o

o

O.I

o

0

O.I

O.I

1.2

0.3

24

O.I

1.2

O.I

o

o

0.2

0.5

O.I

0.4

O.I

I.I

0

o.a

o

O.I

0

o

O.I

0

0

o

0

o

0

25

o

O

o

o

o

o

o

O.I

o

o

O.I

o

o

O.I

O.I

0

o

o

o

O.I

o

O.I

O.I

O.I

26

o

O

o

o

o

O.I

0

o

o

O.I

0

0

o

o

o

o

o

o

O.I

O.I

O.I

0

O.I

0

27

o

O

0

o

o

o

O.I

o

O.I

O.I

o

O.I

o

0

o

o

o

o

o

0.6

0.2

0.2

0.2

O.I

28

o

0

o

O.I

o

o

o

o

o

o

0

0

o

o

o

o

0

O.I

o

O.I

o

o

0

0

29

o

0.2

0

J-5

o

2-4

o

1.0

0.6

0.3

O.I

0.2

0.2

o

o.a

o

O.I

0.4

O.I

0.8

0.7

0.3

I.I

0.0

3°

0.8

0.8

o

2.5

o

o-9

0.3

0.3

0.6

O.I

T.O

o

0.2

o

o

o

o

O.I

O.I

O.I

O.I

O.I

0.1

O.I

31

0.1

4-4

0

0.5

o

o-5

0.9

0.3

i.i

o

0.4

0

O.2

o

O.I

0.7

o

i-5

o

0.4

0.7

I.O

3-3

0

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III.

fABLE LXXIV (continued).

497
Dyrafjord.

Gr. M.-T.

0 2

2-4

4-6

6-8

8—io

IO— 13

12 — 14

14 — 16

16-18

18 — 20

20 — 22

"

22 — 24

Date

4-

+

+

i

4-

_

4-

_ +

_

4-

4-

+

4-

_

April i

0-5

0

o

I.O

0

0.5

o

o

o

0

o

o o

0

0

o

o

o

o

o

0.5

o

I.O

I.O

2

O

I.O

o

0

0-5

0

o

o-S

o

0

0

o 0.5

0

o

o

o

o

o

o

2.O

0.5

3.0

0.5

3

I.O

1.5

o

3.0

0

o

o

o

o

0

0

O 0

0

o

o

o

o

o

o-S

o

°-5

O

o

4

I.O

0

o

0

o

o

o

o

o

0

0

0 0

0.5

o

o

o

0

o

0.5

o

o

I.O

o

5

o

0.5

o

0.5

0

3-0

—

—

—

—

I.O

o j o

05

o

a-5

0.5

I.O

I.O

o

o

o

O

0

6

°.5

0.5

o

i-5

—

—

—

—

o.5

0.5

o

8.5 o

IO-5

I.O

o-5

4-0

o

4.0

o

1.5

0

0.5

o

7

o

0

o

o

o

0

o

0

o

0.5

0.5

o 0.5

o

0

0.5

o

o

0-5

o-S

I.O

1-5

I.O

0

8

o-5

o

o

0

0

0

o

0

o

0

o

o

0

o

o

0.5

o

o

o

o

o-5

o

0-5

o

9

I.O

0.5

o

6.0

0

3.0

I.O

2.5

o-5

o

0-5

0.5

o

o

o

I.O

o

0.5

I.O

I.O

3-5

o

—

0.5

10

o

0

0

i.5

0

0

o.5

o

0.5

o

0-5

o

I.O

o

—

—

0.5

o

o

o

I.O

o

o

o

ii

0.5

0

0

o

0

o

0

o

o

o

o

o

o

o

o

0

o

0

o

o

0

0

1-5

o

12

o

0 0

i-5

0

o

o

0

o

o

o

0

o

o

o

o

o

0.5

o

0.5

I.O

0.5

2.0

o

'3

o-5

0.5 o

0-5

o

o

o

o

0.5

0.5

o

o

0

0

o

o

0

o

0

o

o

o-S

o-5

o

M

o

o o

o-5

0

o

0

o

o

o

0

0

0

0

o

o

o

o

o

0

o

o

°-5

0

15

o

o

0

o

0

o

o

o

o

o

o.5

o

o-5

0.5

o

—

—

—

— •

—

—

—

—

—

TABLE LXXV.

Disturbances in Vertical Intensity (FT/).

Gr. M.-T. 0-2

2-4

4-6

6-8

8—io

IO — 12

12—14

14—16

16-18

18 — 20

20—22

22 — 24

Date I 4-

_

+

—

4-

—

+

—

4-

_

-t-

—

4-

—

+

—

4-

—

4-

—

4-

—

4-

—

December 2

O.g

o

o

0.8

o

o-3

o

O.2

o

O.I

o

0.5

o

O.I

0.4

o

0.8

o

0.3

O.I

o

0

o

0

3

O

1.6

o

i-3

o

O.I

o

0.3

o

O.I

o

0

o

o

o

o

0

o

o

o

o

o

O.2

o

4

O.I

o

o

o

o

o

o

o

o

o

o

o

o

0

0

o

O.I

0

0.3

O.I

0.6

o

O.I

O.I

5

o

0

o

o

o

0

o

o

o

o

o

o

o

o

0

0

o

o

o

o

o

o

o.a

1-3

6

o

1.8

o

o

0

0

0

o

o

o

0

o

0

0

o

o

0. 1

o

o

o

o

o

o

0

7

o

0

o

o

o

o

0

o

o

o

o

o

o

0

0

o

o

0

O.2

o

0

O.I

o

2.1

8

O.I

0.3

O.I

o

0.5

o

0

o

o

o

o

o

o

o

0

o

o

o

o

O.I

O.2

o

o.a

O.I

9

o

o

o

o

o

o

o

o

o

o

0

o

o

o

O.2

0

0.7

0.5

i-S

o

1.3

o

0.2

o

10

o-7

0

O.2

I.O

O.2

O.I

O.I

o

0.3

O.I

i-5

o

1.9

o

O.2

o

o

o

O.I

O.2

o

i-5

0

3-°

II

O.I

I.O

0

2.2

o

o

o

O.I

0

O.2

o

o

o

o

O.I

o

O.2

o

o

0.6

o

4.9

I.O

1-3

12

I.I

O.I

0

O.I

o

O.I

o

O.2

o

o

o

o

o

0

O.2

0

I.I

o

0.3

O.I

o

0.4

o

0.2

'3

o

0.2

o

o

o

o

o

o

o

O.I

O.I

O.I

0

O.I

O.2

O.I

0.5

0

0

O.I

o

3-0

o

i-5

H

o

1.6

o

O.I

o

o

o

o

o

o

o

o

o

o

o

o

o

o

o

0

0

o

o

0.4

15

°-5

1-4

o

1.8

1.4

0

O.I

o

o

o

o

o

o

0

o

0

o

0

O.I

O.I

O.2

o

0,1

o

16

o

o

0

0

0

o

o

o

o

o

o

o

0.3

o

o-3

o

1.3

0

0.5

o

o

o

o

O.I

17

0

O.2

o

O.2

o

o

o

o

o

o

o

o

o

o

o

o

o

o

O.I

o

O.I

o

o

0.2

18

o

0.2

o

o

0

o

0

o

0

o

o

o

o

o

o

o

o

o

o

o

o

o

O.I

O.I

19

o

O.2

o

o

o

I.O

0

0.5

o

o

o

o

O.2

o

O.I

o

o

o

O.I

O.I

o

O.3

O.I

o

20

o

O

o

O.I

o

0.6

o

0.4

o

O.I

o

o

o

o

0

o

o

O.I

o

O.I

o

o

o

o

21

o

0

0

0.4

o

o

o

o

o

o

o

o

o

o

o

o

o.a

o

I.O

o

O.3

o

o

0.3

22

o

O.I

o

o

o

0.2

o

1-3

o

0.8

O.I

O.I

o

o

o

o

o

O.I

O.I

O.I

0.3

0.5

0.7

0.4

23

5-o

O.2

0

4.0

o

5-5

o

9.6

—

-

—

-

-

-

-

—

—

-

0

2.4

o

4.5

O.2

0.2

24

i-3

0-3

0.5

0.6

O.2

O.I

o

o

O.I

0

0.8

o

0.6

o

O.I

o

O.2

o

°-5

o

0.5

0.2

a-5

0

25

0

O.I

0.6

0.4

o

0.5

o

o

0

0-3

o

O.2

o

0

o

O.I

o

o

0.2

O.I

O.2

o

o

1.9

26

o

0.7

O.I

O.I

o

o

o

0.2

o

0.3

o

o

o

o

o

o

o

o

O.3

o

O.I

1.4

0.4

0.6

27

o

0.6

o

0.7

o

O.I

0

0.9

o

1.3

o

O.2

o

O.I

o

o

o

0

O.I

0

0

1.4

1.9

I.O

28

0.8

O.2

o

1.4

o

2.1

o

1.4

o

1.3

o

0.3

o

0

0

O.I

O.I

0

0

O.I

o

o.a

O.I

o.a

29

O.I

O

O.I

o

o

o

o

0.5

0

O.I

o

0

o

0

o

o

O.I

o

O.I

O.I

o

o

O.I

0

30

o

0.2

o

o

o

o

o

0

o

o

o

0

o

o

o

o

o

o

o

O.I

o

o

o

0.8

31

o

O.I

o

0

0

o

0

0

o

o

o

o

o

o

0

o

o

o

o

0

0

o

o

o.a

498 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.

TABLE LXXV (continued). F-,

Dyrafjord.

Gr. M.-T.

o— a

2 — 4

4-6

6-8

8—io

10— 12

12—14

14— 16

16-18

18—20

20 — 22

22-24

Date

+

_

+

—

+

—

+

-

+

—

+

-

+

—

+

—

-t-

-

-t-

-

+

- +

_

January I

o

0.3

o

0

o

o

o

(1

o

o

o

o

0

o

o

o

o

o

o

o

o

o

0

3.2

a

o

1.6

o

0.2

o

0

o

0

o

o

o

o

0

o

o

0

0

o

o

o

o

o

0

0

3

0

i-7

o

I.O

o

O.I

o

o

o

o

o

o

o

o

o

o

o

o

O.I

o

O.I

0

0

o

4

O.I

o

0.4

o

0

O.2

o

3.5

O.I

o

o

0

o

O.I

O.I

o

O.I

o

0.4

o

o

I.I

o

0.7

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PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III. 499

ABLE LXXV (continued). FY Dyrafjord.

Gr. M.-T.

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4

0-5

I.O

I.O

o

o

0.5

o

o

0

0

o

o

o

0

o

o

I.O

o

I.O

o

o

o

I.O

o

5

i-5

o

0.5

o

5-o

a.o

o

7.5

0

0.5

o

o

0.5

0

2-5

o

i-5

o

o

o

o

o

o

o

6

2.O

o

I I.O

o

6.0

o-S

1.5

o

i-5

0.5

3-°

I.O

o

I2.O

o

6.0

o

1-5

o

o

o

0.5

o-5

0-5

7

0

o

0

o

o

o

o

o

o

°-5

o

I.O

0.5

o

o

0.5

o

o

0

0.5

o

4-5

o

3^°

8

O

0.5

0

0

o

o

o

o

0

o

o

o

0

o

o-S

o

0.5

o

o

o

o

°-5

5.0

0.5

9

4.0

0

I I.O

o

o.S

a.o

a.o

2.0

o

I.O

o

o

o

o

2.O

o

0.5

o

o

3-°

0.5

3.5

0-5

2-5

JO

I.O

o.5

i-5

o

o

o

o

o-5

—

0.5

0

o

0-5

o

2.O

0

o-S

o

o

0.5

3.5

I.O

o

0.5

500 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE LXXV (continued). FY

Dyrafjord.

Gr. M.-T.

o — a

3-4

4-6

6 — 8

8 — io

10 — 12

la — 14

14 — 16

16-18

18— ao

20 — 22

22-34

Date

4-

—

4-

—

+

—

+

—

+

—

+

—

4- —

4.

—

4-

—

+

—

+

—

+

April ii

o

I.O

o

0.5

o

o.S

0

0.5

o

0

0

o

0-5

o

o

0

O

o

0

0

0

0.5

o

'•5

12

4.5

0

0-5

a-5

o

2.O

o

0

o

o

o

o

o

0

o

o

1.5

0

I.O

o

o

I.O

3-5

0

13

o

°-5

0

i-5

o

0-5

o

I.O

o

i-5

o

o

o

0

o

o

0.5

o

I.O

o

o

i-5

o

I.O

14

o

0

o

°-5

o

0

o

o

o

o

o

o

0

o

0.5 I o

0

o

0

o

o

o

o

0

TABLE LXXVI.

SECOND SERIES.
DIURNAL DISTRIBUTION OF STORMINESS.

Matotchkin-Schar.

Sa in y

Hour

o— a

2-4

4-6

6—8

8-10

IO 12

12 — 14

14— 16

16-18

18—20

20 — 22

23—24

Period

4-

—

4-

—

+

—

+

—

4-

—

+

—

+

—

-\-

—

+

—

+

—

4-

—

+

—

Oct. 3-7

o

2.7

0.6

1.2

1.8

3.1

0.9

0.6

0.6

0.6

3-6

0-3

2.4

o

1.3

1.2

0-3

o

03

0.6

o

5-i

0

6.0

8-12

4.2 1.2

2.1

°3

o

0.6

0.6

0-3

0.3

1-5

0.9

2.4

7-5

0.6

4.8

0.6

7-5

6.9

3.1

31. 0

o

51-9

o

31.3

i3-n

o 0.3

0

O

o

1.2

o

0-3

0.6

o

1.3

°-3

o

°-3

0.3

1.8

1.8

0.9

0.6

37.O

0.9

5-i

0.3

1.8

18 — 22

°-3 3-9

O

3-o

0.9

0-3

0-3

0.6

0.9

0

1.2

0-3

o

0.6

o-3

0.9

3.0

o

0.6

10.5

o

5-4

0

7.2

23 — 27

a-7 3°-3

2.7

6.6

1.2

2.4

o

i. a

3.7

0.6

4.2

1.8

9.0

0.9

13-5

4-5

9.6

IO.2

2.4

24.3

o

75-6

0.6

91-5

Oct. 28 Nov. i

1.8 |27.9

3.1

5-4

6.0

4-5

6.9

3-9

3°-3

0.6

44.1

3-6

21.6

8.1 16.8

2.7

2.1

37.0

o

98.7

o 99.9 0.3

92.7

Mean value

1.5 11.1

1.3

2.8

1.7

1.9

1.5

1.2

5.9

0.6

9.2

1.5

6.8

1.8

6.2

2.0

4.1

7.5

1.0

30.4

0.2 40.5 0.2

36.8

Nov. 2 — 6

o

i-5

o

0

o

0.3

o

0.3

o

1.3

o

°3

o

0.6

0.6

0.6

4-5

9.0

0.6

59-4

o 29.4 0.3

i-5

7-11

'-8 1.5

1.8

o

o

o

0

o

0.6

0

0.3

o-3

o

o-3

o

0.6

0.6

0.6

0-3

0.3

o

4.8 o

6.6

12— l6

1.8

4.3

0.6

o

1.8

0

03

0.3

o

1.3

0.9

1.8

10.5

0.6

10.3

o

5.1

0.9

2.7

i-5

1-5

15.0

0.9

7.8

17 — 21

o 2.7

i-5

°-3

0.6

o

0.3

0

°-3

0-3

0.6

0-3

o-3

0.6

0.9

o

7.2

3-6

0-3

31.3

o

72.0

0-3

15-0

22 — 26

°-9 5a.5

o-3

4.8

0.6

2.1

o

0.3

13.3

O

35-5

o-3

29.4

0-3

40.8

5-7

3.7

64.8

2.1

75.o

1.8

84.0

o

78.0

•Jov.27Dec. i

o 1.8

0.6

0.3

°-3

0.6

0.6

o-3

0.9

O

0.9

o

r-5

o-3

5-4

0-3

5-1

0.9

O

7-2

o

7.5

o

1.8

Mean value

0.8 10.7

0.8

0.9

0.6

0.5

0.2

0.2

2.5

0.5

4.7

0.5

7.0

0.5

9.7

1.2

4.2

13.3

1.0

27.5

0.6 35.5

0.3

18.5

Dec. 2—6

0.6 3.4

0.9

0.6

0.6

0-3

o

o

0

0.3

0.9

°-3

°-3

0.9

1.8

0.3

2.1

3-9

0.3

6.6

0.3

'•3

0

4-3

7-n

o 0.6

0.3

1.2

0.9

0.3

1.3

o

0.6

0.6

2.1

0.6

2.4

o

1.3

o

7.8

3-0

3-9

5-i

1.8 15.0

o.3

10.2

12 — l6

°-3

3-6

0.6

1.2

o

o

O

o

0-3

0

O

0.9

o

o

0.3

0

3-3

o-3

2.1

7.2

0.6

'5o

o

9-3

17 — 21

o

0.6

0

0

o

0.3

O

o

0

°-3

O

0.6

0

1.2

0.6

0.6

«-3

0.6

0.6

4.2

0-3

6.9

o

L5

22 — 26

O.6 21.0

1.8

9-3

1.2

1.5

0.6

0.6

10.5

0.3

9.0

a.4

22.5

1.8

16.8

1.2

5.7

7.8

0.9

53-4

0

58.5

0.9

38.4

27—31

o 4.5 2.4 0.6

1.8

0.6

o-3

1.3

o

3.4

0-3

i. a

0.9

0.3 0.9

O

4.2

0.6

i-5

1.2

0.6 9.0 o

13-5

Mean value

0.3

5.5

1.0

2.2

0.8

0.5

0.4

0.3

1.9

0.7

2.1

1.0

4.4

0.7

3.6

0.4

4.1

2.7

1.6

13.0

0.6 17.7 0.2

12.9

Jan. 1-5

o

i-5

1.2

0.9

1.3

0.3

0.3

1.3

i-5

0.6

1.2

0.6

1.2

0.6

3-6

0

i-5

'5-3

6.9

4.2

0.9 6.6 0.6

5-7

6— 10 j 0.3

i-5

0-3

0.6

O

0.6

o

1.2

0.3

0

0.9

0.6

09

a. i

IO.2

1.2

13.2

o-3

1.8

3-9

o

16.2 o

12.6

11-15 0.3 3.3

0.9

0.9

03

0

0.6

o-3

o

°-3

O

o-3

0.6

o-3

2.4

0

4-5

0

3-9

11.4

0.6

5-4 o

8.4

16 — 20

o 1.8

0-3

1-5

o

o

0

o-3

°-3

1-5

°-3

1.8

8.7

i.a

8.7

2.1

!5-3

0.3

5-i

1.8

2.4

6.9 o

4-5

21 — 25

o 3.0

0.6

0.6

0.6

0.6

0

1.2

o

0.9

0.9

0.6

°-3

3.1

1.8

1.8

6.0

1.3

1.8

14.4

0

20. 1 0.3

9.6

26—30

0.3 67.2

0.6

8.1

30

3-3

2.1

0.9

i-5

0.9

39

0.6

10.8

o-9

II. I

0.3

18.9

i-5

8.4

81.9

0.9

87.0 o 124.8

Mean value

0.2 13.1

0.7 2.1

0.9

0.8

0.5

0.9

0.6

0.7

1.2

0.8

3.8

1.2

6.3

0.9

9.9

3.1

4.7

19.6

0.8

23.7 0.2 27.6

Jan.3iFebr.4

o

1.2

°-3

0

1.3

o

o

o

o

o

o-3

°-3

0.6

°-3

3-3

o

8.4

o

6.9

o

1.2

0 0

o

Febr. 5 — 9

°-3

3-6

0.9

3-9

i-5

3.0

i-S

1.8

3.1

o

0.6

o

2.1

0.6

14.1

o

22.2

0

4.8

35-4

O

71.4

0.6

43-5

10— 14

i-5

11.4

a. i

0.9

0.6

°-3

o

1.2

0.6

0.6

1.8

0.6

1.2

0.6

3-0

0.3

6.3

0.6

4.3

17.4

0

24.3

o

5'-3

15-19

0.3

2.7

o

°.3

o

0-3

o

o-3

o.3

0.9

0.9

0-9

2.7

°-3

12.9

0.9

3-6

13.9

3-o

2.1

O

2.4

o

0.9

20 — 24

o

0.9

o 4.8

o

6.0

0

6.6

3-0

0.9

6.9

o

3-0

2.1

0.9

1.2

4.8

0.3

1.3

1.3

0

3.6

o

2.1

Feb. asMar. i

o

o

o

1.2

0

3-0

0.3

3.1

2.1

0-3

3-3

o

0.6

0.6

0-9

1.3

6.0

0-3

4-5

O

1.2

3-6

o

8.4

Mean value

0.4

3.3

0.6

1.9

0.5

2.1

0.3

2.0

1.4

0.5

2.3

0.3

1.7

0.8

5.9

0.6

8.6

2.4

4.1

9.4

0.4

17.6

0.1

17.7

Oct. 3 March i

0.6

*•;

°-9

2.O

°-9

1.2

0.6

0.9

^•5

0.6

4.0

0<?

•f-7

/ o

6.}

I.O

6.2

/•<*

^•/

19.9

o.;

27.0

0.2

ii.l

i

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III. 50!

TABLE LXXVII. S,, in y Matotchkin-Schar.

Hour ! 0-2

2-4

4-6

6-8

8—io

10— la

la — 14

14 — 16

16-18

18— 30

ao — aa

33 — 34

Per

f

—

+

_

+

_

+

_

-4-

_

+

_

-f

—

+

—

+

—

+

_

+

_

+

—

Oct. 3-7

0.9

0.2

0.9

0.4

1.8

i.i

0.4

o.a

0.7

1.6

i.i

0-5

0.2

0-5

o-S

i.i

0.4

0.5

o-S

a.o

0.5

i.i

0.5

05

8-12

1.6

0.4

'-3

0.7

0.2

O.2

0.2 0.5

°-5

o.a

0.9

0.4

-•o

O

0.7

1.3

3-4

14.9

0.4

5-8

O.3 32.2

0.4

I 1.2

13-17

0

°

o

O

0

0

0.2 0

'•3

o

0.5

II

o

1.4

0.4

0.4

0.4

'•3

o-9

4-7

0.7

'•3

0.7

0-5

18-22

o

1.4

1.6

0.4

I.I

0.4 j o 0.4

o-5

o

°-5

o.a

o

o.a

o-4

0.4

a.o

0.4

0.4

8.6

O

4.0

O.3

'•3

23 — 27 o

22.3

1.6

36

0.5

0.4

1.3 o

1.6

0.7

1.4

1.6

3-i

0.9

4.1

a.o

4.9

6-5

I.I 21. 1

0.2

38.0

o.a

38.4

lot. 28 Nov. i 0.5

20. 0

6.1

4-7

9.2

0-7

4-9

i.i

13-'

o.a

14.6

0.7

17-5

5-2

23.3

0.7

3-4

9-9

O.3

47.3 o.a 68.6

0.4

47-2

Mean value

0.5

7.4

1.9

1.6

2.1

0.5

1.2

0.4

3.0

0.5

3.2

0.8

3.9

1.4

4.9

1.0

2.4

5.6

0.6

14.9

0.3 24.2

0.4

16.5

Nov. 2-6

o

i.i

o

o

o

o

0.7

0

o

O.2

0

0.9

o

o.a

O.2

o

2-5

1.8

a.o

19.4

0.4

17.1

O.3

i.i

7 -it

o

2.2

O.2

0.4

0

o

°-5

o

0.4

O

o

o

o

0.4

0.4

0.7

0.4

0

0.4

o.a

0.9

o-S

0.4

1.4

12— l6

0

4 3

O

2.2

1-3

°-5

0.4

O.2

0.4

O

1.4

0.5

4.0

0.5

4.0

0.4

1.6

3-3

i.i

3-5

0.5

IO. I

O

6.8

17 — 21

o

2-5

O.2

0-5

0.7

O.2

o-S

O

o

o.a

0.5

0.4

0.2

0.7

07

0.5

1-3

4-9

o-5

12.8

0

31-0

0

11.7

22 — 26

o-t

42.5

0-5

I9.I

3-8

3-i

5-9

1.4

6.8

o.a

14.4

0.5

14.8

0.9

27.4

2.0

11.7

43-o

2.3

49-7

2-5

81.5

3.3

81.5

X"ov.27Dec. I

0.2

0.2

O.2

o-t

0.2

i.i

0.7

0.4

o.a

0.4

I.I

0.7

0.4

1.8

1-3

i.i

o

9-7

0.3

6-5

o

6.7

o

0-5

Mean value

0.1

8.8

0.2

3.8

1.0

0.8

1.5

0.3

1.3

0.2

2.9

0.5

3.2

0.8

5.7

0.8

2.9

10.3

1.1

15.2

0.7 24.5

0.5

17.2

Dec 2-6

0.7

0.4

o

O.2

0.2

o

°-5

o

o.a

05

1.6

o

0.2

0.5

0.5

o-5

o

3-1

0.4

10.4

o 0.7

0-4

o-4

7-n

O.2 O.2

0.4

0.4

0.7

0.5

i.i

o

i.i

°-5

i.i

0.9

1.4

0.4

0.9

o.a

3.5

4.0

1.4

7-2

1.4

II. 0

o

7-9

12 — 16

0-5

i.i

o

0.7

O

0

0.9

0

o.a

o.a

0

I.I

O

0.5

°-5

0.2

3-4

11.9

1.4

4-5

O.3

6.8

0.5

1.8

17 — 21

O

o

o

O.2

07

0.2

o.a

0.2

o.a

o

o

0.3

0.2

o.a

0.7

O.g

1.4

o

0.7

1-4

0.4 2.3

0.2

o

22 — 26

0.9

8.3

3.6

0.4

a.o

0.5

O.2

I.I

3-2

0.7

5-4

0.7

38

3-4

4-7

I.I

2 a

8.5

0.7

23.0

0.4 33.6

1.6

10.4

27-31

i.:-;

o.5

0.7

0.4

0-4

0.4

°-5

0.2

o-S

0.7

O.2

0.7

O.2

0.4

0.2

O

1-3

4-°

1.8

i-3

0-7

1.4

0.4

4.1

Mean value

0.6

1.8

0.8

0.4

0.7

0.3

0.6

0.3

0.9

0.4

1.4

0.6

1.0

0.9

1.3

0.5

1.8

5.3

1.1

8.0

0.5

9.1

0.5

4.1

.Ian. 1 — 5

o.a

2.0

0.7

°.5

0.7

0.5

i.i

2.7

i.i

0.9

i-3

0.4

0.2

i.i

o.4

0.7

1.6

4-7

i.i

5-°

1.8

0.5

0.7

0.4

6— 10

0.2

0.4

I.I

0

o.a

0

0.2

o

o

0.4

0.2

0.4

o.a

o.a

0.9

0.9

0.4

6-3

o.a

9.0

0-5

6.1

0.4

4-5

11-15

2.7

0.2

0.2

O.2

O.2

0.2

0

o

0.2

O.2

O

0.4

0.7

0.9

0.5

2-3

0.5

4-3

2.O

8.6

i-3 3-8

1.8

0.4

16 — 20

1-4

O

°-5

O

o

0.2

O

o

0.9

O.g

0.7

0.7

0.7

i-4

23

2-3

2.9

3-2

2.3

4.0

2.9

1.8

0.4

°-9

21 —25

I.I

0.4

O.2

0.2

o

0.9

O

°-5

O.2

0.4

0.4

0.4

0.4

1.4

0.5

38

'•3

8-5

0.4

II. 2

o.a

13.0

2.O

°-7

26-30

0.7

3'-7

O.2

8.5

°5

2-5

i-3

0.7

'•3

°-5

6-3

0.2

8.3

i.i

6-5

0.4

9.0

7-2

1.4

29.2

0.2

34-2

1.4

5i-5

Mean value

1.1

5.8

0.5

1.6

0.3

0.7

0.4

0.7

0.6

0.6

1.5

0.4

1.8

1.0

1.9

1.7

2.6

5.7

1.2

11.2

1.2

9.9

1.1

9.7

Ian. 3 1 Febr.4

o-5

0.4

0

o

o

o

. o

0.4

0.9

o

°-5

o.a

0.9

o

1.6

0

4-5

o-7

I.I

0.4

0.4

o

O

o

Kebr. 5 — 9

o

3-2

I.I

2-3

2-5

1.6

3.5

0.7

0.9

o

0.9

o

1.4

0.7

6-7

0.3

5-°

6.5

1.8

iS-5

0.9

37-6

0-5

230

10— 14

09

5-2

1.4

0.9

i-3

o-5

0.7

1.6

0.4

0.2

'•3

0.4

05

0-5

0.7

a.o

i-3

4-3

i-3

9-0

0.7

I I.O

°-5

1 8.0

i5-'9

0.7

o

o

o

o

0.4

0

o

O.2

o-5

0.9

o

0.7

o

1.8

8.6

0.9

13-5

o.a

2-3

0.5

0.4

0.2

0.4

20 — 24

0

O.2

0.7

0.7

2.3

0.2

3.9

0.4

2-3

0

4-9

o

3-4 °

i.i

°-5

0.9

i.i

'•4

0.7

0

0.7

O.3

O.2

Feb. 25 Mar. i o

O

0.4

0

3.9

o

4.1

o

3-3 0

3-i

o

1.8

o.a

0.7

0-5

1.8

o.a

'•3

1.6 o 2. a

O

4-3

Mean value

0.4

1.5

0.6

0.7

1.5

0.5 1.7

0.5

1.3 0.1

1.9

0.1

1.5

0.2

2.1

2.0

2.4 4.4

1.2

4.9

0.4

8.7

0.2

7.7

Oct. 3 March i

O.J

/•'

»..V

1.6

/./

0.6 ' /./

0.4

1.4

0.3

3.2

"•J

2.J I O.?

)•*

1.3

2.4

6.3

I.O

toJ

0.6

'>•}

0.6

11. U

Birkeland. The Norwegian Aurora Polaris Expedition, 1903 — 1903.

502 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

TABLE LXXVIII. 5y in y Matotchkin-Schar.

Hour

O— 3

2—4 4—6

6-8

8—io

IO — 13

12 — 14

14— 16

16-18

18 — 20

20 — 22

22-24

Period

4-

4-

+

—

+

_

+

—

4-

—

+ -

-4- —

4-

-l +

—

4 -

+

_

Oct. 3-7

o

0

0.4

0

1.8

o

0

0

0.7

0.7

O I.I

2.5 0.4

0.4 0.4

0

..i! o

0

o

1.8

0

4.2

8-12

0

0

0

0

o

o

o

o

0

o

o

o

2.1 0

4.3 o

0.7

11.9 0.4

34-0

0

19.6

o 14.0

13-17

o

o

o

o

o

o

0

o

o

o

0.4

0

0 0

0.4

o

i.i

1.4

o 9.1

o

5.6

o 0.7

18 — 22

o

1.4 o

1.8

0

0.7

0

o

0

o

0

0

0 0

o

o

i.i

o

o

14.0

o-4

3-2

0 3.5

23-37

0.4

15.8

0.7

9.1

I.I

1.4

04

0.4

3.5

o

7.4

o

12.3 o

9.5

,5.8

4.6

19-3

I.I

12.3

0.4

20.0

° 7 24.2

Oct. 28 Nov. i

M

1.8

0.4

3-2

0.4

i-4

3.9

O 4

10.5

0

3.5

2.1

o 7.0

o

7.0

0

10.9 10.5 123. 1

32.9

22.4

17.2 q.8

Mean value

0.3

3.2

0.3

2.4

0.6

0.6

0.7

0.1

2.5

0.1

1.9 0.5

2.8 1.2

2.4

3.9

1.3

7.4 2.0

15.4

5.6

12.1

3.0 9.4

Nov. 2-6

o

o

o

o

O

o

o

o

o

o o

0

0 0

1.4

0

2.8

7.0

6.3

37-1

0.4

22.1

°-7

0.7

7-n

0.4

1.4

o

1.8

O

o

o

o

o

o

o

0

0.7 o

0.7

o

0

i.i

o

0.4

o

6.7

0

8.1

12— l6

o

35

o

o

0

o

o

o

o

o

1.8

O

12.3 0.4

a-5

0.7

1.8

2.5

I.I

3.1

0.4

'1.9

0.4

12.3

17 — 31 o

3.1 O

0.4 o

o

o

0

o

o

0.4

0.4

2.1 0

1.8 o

6.3

9-1 3-9

9-8 I 6.3

31.5

0

18.9

22 — 26 60

68.3 5-3

44.1 04

28.4

o

193

3.1

2.5

13.3

8.4

1.4 42.4

1-4 179-8

14.0 125.051.1

23-8 52-5

'7o

25.6

72.5

Nov. 27 Dee. i

o

0

0.7

o.7

O

o 0.4

0.4

O

o

0.4

o

4-9 o

3-2

o

2.1 7.0 1.8 8.4

o

5.«

0

0

Mean value

1.1

12.6

1.0

7.8

0.1

4.7

0.1

3.3

0.4

0.4

2.7

1.5

3.6 7.1

1.8

13.4

4.5 25.3 10.7

13.6

9.9

15.9

4.5

18.8

Dec. 2 — 6

o

1.4

o

o

o

0

0

0

0

0

0.7

o

o o

2.5

o

i.i

10.5

0

n.6

o

2.8

o

2.8

7-n

o

0.4

0.4

0

0.4

0.4

o

I.I

0.4

2.5

9-1

0.7

7.4 ; i.i

M

4.1

3-9

8.8

0.4

19.6

0

42.4

0.7

7.0

12 16

1.4

M

o

4.6

0

0.7

o

o

o

o

1.4

o

0.7 o

0.4 o

3-9

10.5

0.4

16.8

0.4

32.Q o

7-7

17—31

o

o

o

o

0

o

0

o

o

0

o

o

I.I O

5-6 0

2.8 O I.I

4.2 o

6.0

0

u

22—36

0

11.9

0

9-5

o

1.8

M

0.4

4-9

0.4

5.6

I.I

7.0

4.6

9-5

3-5

3.5 47-3 o

79.8 o

59.5

0.4

18.2

27-31

04 8.8

o

0.4 ' 1.8 0.7

M

o

0.7 ! O

1.8

o

5-3

0

0.7

o

7.4 1.8 2.1

3.5 0.4 12.6

o

'6.5

Mean value

0.3

4.0

0.1

2.4 0.4

0.6

0.5

0.3 1.0 0.5

3.1

0.3

3.6

1.0

3.4

1.3

3.8

13.2 0.7

22.6

0.1

26.0

0.2

8.7

I

Jan. 1-5

o

3.1

0.4

4.2

o

5-3

0.4

1.4

6.0

o

3-a

0

3-2

o

6.0

0

2.1

15.8 i.i

15-1

0

13.0

0

3-2

6— 10

1.8

0.4

I.I

o

0.4

0

o

0

i.i

0.4

0.7 0.4

2.1

0

16.1 o

1 1.9

3.8 2.1

1 1.6

o 1 8.6

o 11.6

11-15

0.7

0

0

o

o

0

o

0

0

o

o

o

0.7

o

7-4

0

8.4

0-7

1.4

39.6

0.4

'4-7

0.4 8.1

16 — 30

o

O O

o

0

o

o

0

o

o

2.1

o

18.2

o

1 1.6

1.4

14.4

7.0

I.I 9.8 0.4

11.9

0 0

21—25

0.4

4.3 o

0.7 o

o

o

0

0

0

O

0.4

2.1 0.7

6.7

0.4

1.8

13.3

I.I

32.9 o

25.2

o.7 7."

26 — 30

o

3-5 o

3-5 o

1.8

0

o o

o

7.0

1.4

II.9 O 1O.2 0.4

3-5 24.9 ! 3.2

31.9 1.8 25.6

0 10.2

Mean value

0.5

1.7

0.3

1.4

0.1

1.2

0.1

0.2

1.2

0.1

2.2

0.4

6.4

0.1

9.7

0.4

7.0

10.6 1.7

23.5

0.4

18.2

0.2 6.7

Jan. 31 Feb. 4

o

0.4

o

o

o

o

o

o

o

0.7

o

o

0

0

7-4

o

4-9

1.4

3-9

0.4

o

o

o 0.3

Fbr. 5-9

o

2-5

0.4

4.6

I.I

6.7

2.8

1.8

1.8

0.4 o

0

8.4

o

6.7

3.2

7-7

12.6

1.4

37-5

2-5

38.9

i-4 43-4

10 — 14

3.1

4.2

I.I

0

o

0.4 2.5

o

o

0.4 4.9

o

a-5

0

3-5

o

10.5

3.5

1.4

18.6

3-2

17.9

0.4 3>-a

15-19

O

0.4

o

o

o

0 0

0 0

o

o

o

2.1

o

7-7

7.0

i.i

62.0

o

3-5

o

3-a

o 0.7

20—24

0

o ! o

5-3

o

6.7 0.7

4-9 5-6

0

9.1

0

7.0

o 4.6

0

6-7

o

1.8

0.4

o

i-4

o

0

Feb.2sMar.i 'i o

O I.I

o

o

o 6.0

o

10.5

o 12.3

0 12.6

o

8.8 o

2.5 2.8 0.7 i.i o

4-9

o 7.7

Mean value 0.4

1.3 0.4

1.7

0.2

2.3 2.0

1.1

3.0

0.3 4.4

0 5.4 0

6.5 1 .7

5.6 13.7 1.5 10.3 1.0 11.1

0.3 13.8

|

Oct. 3 March i o.j

4-J °-4

j-i

0.)

1.9 0.7 l.o

1.6

O.j 2.X

o.j- 4.4

'•9

4-7

4.1

4-4

14.0 ).}

/;./ 3.4

16.7

i.ti a.;

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III.

503

(ABLE LXXIX.

Kaafjord.

SH in y.

Hour

I

2

a-

-4

4-

•6

6-

8

8—

10

10-

•la

13-

-'4

'4-

16

16-

-18

18-

-20

3O-

•aa

33-

-34

I'ericill

+

_

-f

—

+

—

1

_

+

—

+

_

+

+

+

+

+

+

.

Sept. 3-7

°3

1.8

0.9

o-3

0.9

0.3

03

0.9

°-3

0.3

°3

2.1

0.9

06

3-7

0.9

1.8

0.6

1.8

o

03

0

0.6

0.6

8 12

°-3

0-3

0

0

°-3

0

°-3

0

0.3

o

0.9

O.g

3-6

03

3.1

o

16.8

0

5-'

3.4

0

10.5

0

28.5

13- '7

0.6

0

0

0.9

o

0.9

0

°-3

0

0.6

o-3

0.6

0.9

°-3

1.8

°-3

«-3

o

o

o

o

°3

0

2.1

18 22

o

8.7

0.6

2.4

06

1.3

°-3

0.9

3-3

0.9

12.6

°-3

5-4

"•3

6.9

3.1

6.6

0.9

4.8

5-4

0.6

79.3

o

47-1

23-27

0

io-5

o

6-3

0-3

O

°-3

03

0

0

0

0 3

°-3

i-5

0.6

0.9

o

0.6

i. a

6.0

o

8.4

o

0.6

Sep. 28 Oct. 2

o

18.6

o

5-4

o

0-3

o

0

o

0

0

°-3

I 2

°-3

0.6

0.6

0.6

i-5

0.6

4.2

0.6

35-5

o

53-4

Mean value

0.2

6.7

0.3

2.6

0.4

0.5

0.2

0.4

0.7

0.3

2.4

0.8

2.1

0.6

2.5

0.8

4.6

0.6

2.3

3.0

0.3

20.7

0.1

221

Oct. 3-7

°3

1.2

0

0.6

0.6

°-3

o

o

0

°-3

0.3

o

0.3

o.g

0.6

o

0.9

O

0.6

°-3

0

03

o

1.3

8-12

o

1.8

o

0

o

0

°-3

o

o

o

°-3

o

1.2

°-3

°3

o

°-3

o

6.3

30

o

41.4

o

I6.5

'3- '7

o

o

o

0

o

o

o

o

o

o

°-3

0.6

O

0

°-3

°3

o

0

0-3

°-3

0.3

o

o

°-3

18-22

o

2.4

03

2.7

0.3

o

0

0

o

o

o

0

O

o

o

o

°-3

0

o-3

0.6

0

2.1

°-3

1.3

23-27

o

34-8

0.6

6.0

0.6

0.3

o

°-3

°-3

o

°-3

0

0.6

1.2

60

'•5

7-5

0.9

9.0

0.9

0.9

35.5

03

69.6

d't.aS Nov. i

0.3

37-8

0.6

54

3-3

3-6

0-3

3-°

5-4

3.4

36.4

1.2

38.4

03

45-9

0.9

11.4

3-4

0

43.6

0.9

68.1

0

78.6

Mean value

0.1

13.0

0.3

2.5

0.8

0.7

0.1

0.6

1.0

0.5

4.6

0.3

6.8

0.5

8.9

0.5

3.4

0.6

2.8

8.0

0.4

22.9

0.1

27.9

Nov. 2 — 6

0

o

o

o

o

o

o

o

o

o

o

o

°-3

o

o

0.3

3.1

o

3.1

13.9

06

6.3

0

'•5

7-u

03

1.2

°-3

0

o

o

o

o

o

o

o

o

o

o

o

0

9

o

O

o

1.2

'•5

0

2.7

13— l6

o

1.8

0.6

2.1

i-5

03

o

0

o

03

o

1.8

o

i-5

0.6

0.9

0

0.6

0-3

0-3

1.3

3-9

0.6

2.4

17 — 21

o

1.8

o

O

o

o

o

o

o

°-3

o

0

o

o

o

o

2.4

°3

2.7

0.9

0-3

33-o

o

7-2

22 — 26

1.2

71.7

1.2

53-4

2.4

4.8

2.7

3.6

5-i

1-5

I2.O

0.9

31.3

0.6

54-°

o

39-6

19.2

16.8

51-6

9-3

77-7

3.6

78.0

S""V.L>7 Dco.i

°-3

°-3

03

o

0

°-3

o

0.6

o

°-3

o-3

°-3

o

1.8

0

0.9

0.9

o

O

0.9

o-3

3-3

o

0.3

Mean value

0.3

12.8

0.4

9.3

0.7

0.9

0.5

0.7

0.9

0.4

2.1

0.5

5.3

0.7

9.1

0.4

7.5

3.7

3.7

11.1

2.2

21.0

0.7

15.4

Deo. 2-6

0

1.2

o

0

0.9

0

°-3

o

o

o

o

o

o

o

0.6

°3

:-5

0.3

0.6

0-3

0.6

o

o

3.1

7-n

0

O

0.9

0.9

i-5

o

°-3

o

o

o

°-3

0.9

03

0.6

o-3

°-3

9.6

o

6.0

0-3

9.6

0.6

o

4-3

is — 16

0.3

5-4

0.3

0.6

°'3

o

03

o

o

0

o-3

0.9

0.6

°-3

°-3

o

3-9

1.2

5i

03

i. a

2.7

"•3

0.9

17 — 21

0

0

0

o

0

o

o

o

o

0

0

0

o-3

°-3

0-3

03

0.3

O

1-5

o

o

1-5

o

0

22 — 26

o

35-4

0

8.1

1.8

4-3

0

3-3

3-3

0.6

5-7

0.6

14.4

1.3

3-3

1-5

13.8

O

3-9

9.0

0

29.1

0

31-5

Dec. 27 — 31

0

4.8

0

°-3

0-3

°'3

0.6

o

o

o

0.6

0

°-3

o-3

0.6

o

o-3

1.2

0.3

0.6

0.9

1.8

o

8.4

Mean value

0.1

7.8

0.2

1.7

0.8

0.8

0.3

0.6

0.6

0.1

1.2

0.4

2.7

0.5

0.9

0.4

4.9

0.5

2.9

1.8

2.1

6.0

0.1

7.9

Jan. 1-5

0

1.2

1-5

'•5

33

1.8

0.3

0.6

o-3

0.6

0.9

°3

0.9

o

o

0

2-7

0.3

0.6

0

1.3

0.9

o

2.1

6— 10

0

o.g

0

1.8

0.6

o

"•3

0

0

o

0

03

o-3

°-3

°-3

0.9

°-3

0.3

°-3

0.9

0.9

1.2

o

4.8

11-15

0

0.9

0

0.9

°3

0

o

o

o

o

0

0.3

o

o

o

°-3

°-3

0

3-6

2.1

1.8

1.3

o-3

3-0

16 — 20

o

0.6

0

1.8

o

o

0

0

Q

o-3

o

0.6

°-3

1.2

2.1

i. a

3.4

o

4.2

O

0.9

0.6

o

0.9

ai-35

o

0.6

o

0.6

0

0.9

0

0.6

o

o

0.3

o

0.6

0.6

0-3

1.8

2.7

o

2-4

0.6

i-5

4-5

o

i-5

26-30

0

'5-0

o

0.6

o

0

o

o

°-3

0.3

0.6

0.3

'•5

0.6

1-5

0.6

5-7

0.6

II. I

10.2

0.6

35-7

o

69.6

Mean value

0

3.2

0.3

1.2

0.7

0.5

0.1

0.2

0.1

0.2

0.3

0.3

0.6

0.5

0.7

0.8

2.4

0.2

3.7

2.3

1.2

7.4

0.1

13.7

a 11.31 Kcbr.4

0

°-3

o

o

o

o

o-3

o

o

o

o

o-3

0-3

o

0

°-3

0.9

o

0-3

0

°-3

o

0-3

o

Kebr. 5-9

0.3

1.8

0.3

6.9

o

1.3

°-3

0.3

0.3

0.9

3-0

°-3

0.6

1.2

10.8

o

13.9

o

4-3

15-3

o

34-5

°-3

24.6

10-14

0.3

13.2

2.4

0.6

1.8

O

03

o-3

°-3

°-3

0.3

'•5

0.6

0.9

1.8

0.9

0.6

o

9.6

0.6

a. i

i. a

°-3

34.6

J5-I9

0

'•5

o

0

0.6

O

03

°-3

0

0

0

1.8

0

0.9

3.4

o

6.0

0.3

o

0

°-3

0

0

o

SO — 24

•"cb. 25 Mar. i

o

o

o

°-3

°-3

0.6

o

°-3

°-3

0.6

0.3

°-3

0

0.6

0.3

0-3

6.9

o

2.4

o

o

3-7

0

5-i

Mean value

0.1

3.4

0.5

1.6

0.5

0.4

0.2

0.2

0.2

0.4

0.7

0.8

0.3

0.7

3.1

0.3

5.5

0.1

3.3

3.2

0.5

7.7

0.2

10.9

Mari-li a — 6

o

5-i

03

4.8

0-3

0.9

o

o

°3

o

0.9

o-3

°-3

0

3-3

o

3-9

0.3

4-5

o-3

8.4

0.9

4-5

3-3

7-11

3-3

5-4

3.0

4-5

4-5

o

3-°

1.2

0

3-9

0.6

0.6

i. a

3.6

4-5

0.6

150

o

7-8

3-4

3-°

30.7

o

32-4

Sep.3March i

O.I

7-*

O.J

}•'

0.6

0.6

0.3

0.4

0.6

0.)

1.9

"•;

2.9

n.6

4.3

"•>

•f-7

0.9

3 •'

4-9

1.1

14.)

0.1

16.J

TABLE LXXX.

BIRKKLAND. THE NORWKGIAN AURORA POLARIS KXPEDITION, igO2 — 1903.

SD in y

Kaafjord.

Hour

o—a

2-4

4-6

6-8

8— IO IO— 12

12 — 14

14—16

16 — 18

18—20 2O — 22

— — — _
22-24

Period

+

—

4-

—

+

—

+

—

4- —

+

— 4-

—

4-

—

4-

—

+

- 4-

+

Sept. 3-7

o

4.7

0.5

3.2

°-5

1.4

1.8

o.g

1.8 0.5

'•3

0.5 1.8

0.5

o.a

i-3

I.i

0.7

0.2

0.9

0.9 0.4

°4

°-7

8-12

0.7

1.6

O.2

O.g

o

0.9

o-5

0.9

0.5 0.4

1.8

o.a

36

O.2

2-9

2-3

8-5

0-4

4-9

0.9 o 8.1

°-7

10.6

i3-n

0.4

1.4

0

t-3

0.4

2.O

0.4

1.6

0.7

o.a

i-3

o.a

0.7

0.4

O.3

i.i

i.i

0

1-3

0

°-4 2-5

02

32

18— aa j

o

7.3

02

5-6

0.9

2.9

1.4

2.O

1.6

i.i

4-9

i.i

5-2

I.4

3-i

1.6

2-9

2.9

1.8

14.0

0.2 35-3

0.3

191

23-27

I.I

8.1

0

2.7

o

0.7

0.7

0-5

°-5

°-7

0.2

i-3

i-3

0.7

o

2.0

o

I.I

0.9

2-5

0.2 4.7

0.4

O.L:

Sep. a8 Oct. 2

I.I

13. 1

0.4

5-9

0.2

0.4

0.4

0.4

1.4

O.2

o-5

o.a

0.7

0.4

1.4

0.4

4.1

0.4

1.8

3-4

l.,| I|.L-

°-4

14.]

Mean value

0.6

5.9

02

3.1

0.3

1.4

0.9

1.1

1.1

0.5

1.7

0.6

2.2

0.6

1.3

1.5

3.0

0.9

1.8

3.6

0.5 10.9

0.4

9.7

Oct. 3-7

1.3 0.2

o-5

0.4

o-5

i.i

0.4

°-5

0.2

0.4

2.2

°-5

O.2

0.2

o

0.7

O.2

o

o

i.i

i.i

M

O.g

i.i

8 — za | 0.2 0.4

0.4

0.9

o

°-5

°-5

0.4

0.7

0.4

1.4

0.4

1.4

O

0.4

0.7

0-5

0.2

4.1

4.0

°-5 23.2

o.a

1 1-3

13-17 .

O.2 O.2

o

o

o o

O.2

O.3

0.7

o.a

I.4

°-5

0

0

o.a

o

I.I

O

1.4

1.4

0.2 2.2

I.I

0.2

18 — 22

0.4 1.6

0.7

I.I

o.a 1.6

O.2

°-5

0.2

o.a

°-5

0.4

O

0.4

O.2

0.2

o.a

I.I

O.2

2.0

0.4 3-8

0.2

2-3

23-27

0 36.6

0.7

7.6

0.9 1.6

I.I

0.7

°-4

1.4

0.9

4.0

0.9

2.0

4-i

1.6

5-9

1.8

2.2

2-3

1.6 11.7

-•3

26.8

Oct.28Nov.i

0.4 24.1

0.9

6.3

6.5 0.7

4-3

0.7

3-8

o-S

5-9

i.i

6.1

3-2

"5-5

0.7

38.6

1.4

3-4

90

0.2 38.0

°-9 35 5

Mean value

0.4

8.9

0.5

2.7

1.4 0.9

1.1

0.5

1.0

0.5

2.1

1.2

1.4

1.0

3.4

0.7

6.1

0.8

1.9

3.3

0.7 13.4

0.9 12.9

Nov. 2-6

o 0.7

o

0.4

0 0

0.4

o.a

O.2

0.2

o.a

0

o

o

°-5

o

3-4

0.2

0.3 4.9

o 11.5

0.2

1.8

7 — II O.2 2.0

0

1-3

o o.a

0.2

o

0

O

o

o.a

0.2

0.2

o

0.2.

0.4

O

O

o

°-5 '4

12 — l6

o 2.7

0.7

i.i

0.7 0.4

O.g

i-3

0-5

0.2

i.i

o

1.4

I.I

0.2

1.8

o.a

o-9

O

1.6

04

36

0

7-9

17 — 21

0.5 2.0

0.2

0-5

0.4 o

O

o-5

O.2

0-5

J-3

o.a

0.7

O

I.I

o

i.i

25

0.7

3.2

0.2 15.8

o 9.-

22 — a6

o 42.7

0

31.4

i.i 4.1

4-5

0.9

4-i

1.4

10.4

0.4

'3-'

0.2

16.0

3-i

14.3

10.3

5-9

22.3

'-4 39.8

^Jov.37 Dec. i

O.3 0.4

O

0.4

0

0.4

O.2

0.4

o

o-5

0.9

0.4

i.i

0.9

0.4

o-S

i.i

o-7

1.6

O

°-5

._: _,

1

O..S 0.2

Mean value

0.2

8.4

0.2

4.2

0.4

0.9

1.0

0.6

08

0.5

2.3

0.2

2.8

0.4

3.0

0.9

3.4

2.4

1.4

5.2

0.5

12.4

0.3 12.6

Dec. 2 — 6

0.4

1.6

o

0.9

0.2

0.4

0.9

o.a

0

0.9

1.6

o

°5

O.3

o-5

o

0.4

o-7

o

29

0.4

i.i

O.2

i-3

7-ji

0.2

o.a

0.7

0.4

0.7

0.2

0.9

0.4

0.4

0.9

°-7

0.7

0.7

0-5

0.4

0.5 1.8 1.4

o-S

5-8

o-5

11. a

0.4

12 — l6 2.2

2.2

O.2

1.8

02

O

0.4

0.2

o-5

°-5

i.i

0.7

0.7

0.4

i-4

o o H.o

0.9

4.0

0.9

2-7

O.2

2.5

17 — 21 o

o.a

0.9

o

0.5

0.2

0.4

o

0

o

0.2

o

o

0.4

o-5

0.2 I.I

o

o.a

*-a

'4

1.6

°4

°-l

22 — 26 1.3

IO.I

1-3

4.1

4-9

0.2

2.5

°-5

0.9

2.O

3-2

1.8

4-5

'•3

6.1

0.2 3.1

2.2

1.4

8.1

o

22. 0

1.8

'5-'

27 — 31 I 0.2

6-5

O.2

1.4

o

0-9

0-5

°-5

o

I.I

0.4

0.9

0.2

o-5

0.2

0

0.9 1.3

0.7

i.i

0.4

43

0.)

6.1

Mean value

0.7

3.5

0.6

1.4

1.1

0.3

0.9

0.3

0.3

0.9

1.2

0.7

1.1

0.6

1.5

0.2

1.2

2.8

0.6

3.9

0.6

7.2

0.6

5.1

Jan. 1—5

0.7

0.7

1-3

0.9

°-5

2.9

'•3

o-5

o-5

2.2

2-3

o

I.I

O.2

0.4

0.7 L4

23

0.4

5-8

2-5

2.7

2.0

05

6— 10

0.4

o.7

0-5

O.2

I.I 0.2 1.3

0

0.7

O2

0.7

0.2 0.7

0.4

2.7

0.3 a.o

1.6

04

3-4

0.9

3-4

o-5

3-8

11-15

i-3

1.8

i.i

0-5

i-4

o

0.5

o

0.2

0.4

05

0.4 1.3

0.4

1.4

0.4

1.6

t-a

°-5

8.1

'•3

2-5

0-5

2.2

16 — 20

0.9

0.4

0.9

0.4

O.2

0.2

o-5

o.a

O.g

0.4

1.8

0.4

2.2

O

a. a

1.4

i.i

3-4

'•3

2.7

'•3

3-8

I.I

"•3

21—25

0-5

1.8

1.3 °

O.g

0.2

0-5

0.4

0.7

0-5

2.0

o

1.8

O

0.9

0.9

o-7

4-0

°-5

7-o

O.2

10.3

°-5

2-5

26 — 30

0.2

3-4

0.2

o-5

0.2

0

O.2

0.2

0.9

°-5

1.8

0.5 4.1

o-5

2.7

°-5

32

1.8

2-3

7-7

°-4

18.4

0.2

-'2-5

Mean value

0.7

1.5

0.9 0.4

0.7

0.6

0.7

0.2

0.7

0.7

1.5

0.3

1.9

0.3

1.7

0.7

1.7

2.4

09

5.8

1.1

6.9

0.8

5.5

Ian. 3 1 Feb. 4

0.2

0.4

0.2

0

0.4

0.2

0.2

o.a

o.a

0.4

0.9

o.a 0.7

o

o.a

0.4

0.7

0.4

°-5

0.4

o

o..(

0

0.0

Feb. 5-9

0.4

a.o

i-3

5-2

0.4

5-°

O.2

i-3

°-5

0.7

3-1

0.4 1.3 0.5

4-5

0.4

2-3

3-4

1.8

8.1

°-9

21.3

0

214

10— 14

!-3

7-6

I.I

1.8

0.7

0.2

0-5

i.i

0.4

0.7

1-4

°-5

0.7

0.3

0.2

0.7

o.a

2.0

0.9

7-2

0

7-6

0.4

12.2

15-19

1.6

o.a

0.2

0.2

O.2

0.2

02

0.2

0.7

0-7

1.4

o

I.I

O

0.4

4.7 0.2

8.6

0.2

i.i

O.2

!-3

02

0.4

20 — 24

O.3

1.4

0-4

1-3

4.0

°-5

5-°

o.a

2.O

0

2-3

o

2-7

0-5

I.I

°-5 i-3

0.4

°-5

0

O

I.I

0.2

1.4

Feb.25Marchi

O

°-5

0.4

0.7

1.6

o

4.0

o

I.I

o

0.9

0.4

0.9

O

O.2

0-5 °-7 j '-3

o

I.I

0.4

'•3

O

M

Mean value

0.6

2.0

0.6

1.5

1.2

1.0

1.7

0.5

0.8

0.4

1.7

0.3

1.2

0.2

1.1

1.2

0.9

2.7

0.7

3.0

0.3

5.5

0.1

7.0

March 2 — 6

i-3

2.9

0.4

2-5

0-5

0.2

o-5

0-5

1.4

°-5

0.7

o

I.I

0

o 0.7

a.5

°-5

a-9

1.6

1.6

2.9

2.0

2.9

7-n

0.7

4-1

2.5

I.I

3-8

0

2-3

°-7

1.8

O.2

4.1

0

40

0.7

1.8

2.5

3-4

4.1

1.6

10.3^ 2.2

8.6

2.0

i3-5

Sep. 3 Marchi o.f

/.o

»•/

2.2

0.9

o.y

j.i

O.j

o.S

06

'•7

o./ i.S

0.5

2.0

0.8

•z 7

2.0

1.3

4.1 1 0.6

9-4

O.f

.v.v

1

PART. II. POLAR MAGNETIC PIIENOMKN A AM) TKKRKLI.A EXPERIMENTS. CHAP. HI. 505

AIJI.K LXXXI. Sy in y Kaatjord.

Hour

O — 9

2-4

4-6 6-8

8 — 10 10 — ia 13 — 14 j 14 — 16

1

16— 18 18— ao 20— 22 32—34

Period

-1-

_

4

_

+

—

+

— +

\

-

4-

+

-1-

+

4-

<-pt. 3-7

0

8.1

o

3-a

0

3.5 o

o 1.4

o

0.4 I.I

a-5

0

1.8

I.I

0.7

°-7 3-5

o

0

1-4

0

°-7

8-12

0

3-2

o

o

o

0.4

o

0.4 o

0.7

o 1.4

4-9

0.7 10.5

0

9-1

o 8.4

i.:

5-6 4-2

63

33.8

13-17

0

1.4

o

0.7

o

2.1 0

°-7

0

o

04 0.4

o

0.4 0.7

0.4

3-3

0

0.4

o

o 1.4

o

6-3

18-22

o 10.5

3.5

5-3

0.4

1.8

o

0.4 4.6

0.4

10.2

0.4

10.3

0.7 6.7

I.i

11.3

0.4

1.4

2O.O

3.3 73.2

o

69.7

23 — 27

o 25.6

o

8.8

o

1.4

o

o o

0.7

0.4 0.7

4-3

O

1.4

0.7

39

o 32

4.6

o 172

o

5-3

•p.28 Oct. 2

o 42.0 o

22.4

o 8.1 o

1.8 0.4

o

0.4 0.4

0.4

1.4

o

1.4 6.7

0.4 4.2

I.I 0.4 33.1

o 72.1

Iran value 0 15.1

0.4

6.7

0.7

2.7

0

0.6 1.1

0.3

2.0

0.7

3.7

05

3.5

0.8

5.8

0.3

3.5

4.5

1.5

20.1

1.1 29.7

Oct. 3 — 7 o 2.5 o

o

o.4

o

0.4

o 0.4

o

0.4

04

1.8

o

0.7

o

o

o

0.7

o

o 3-9

o 7.7

8—12 0 6.7

o

0.7

o

o

0.4

0.4 o

o

0.4 0.4

3-9 °

3-5

o

0.7

0.4

i.i

7.7

8.8 10.9

O 22. 1

i3-'7

O 0

0

o

o

O 0

0 O | O

0.4 o

o

o

o

o

0.4

o

o

3-5

o 6.0

o 2.5

l8 — 22 O ).O

0

3.5

o

I .1 0

0 O o

<M

o

0

o

o

o

1.4

0

0.4

1.8

° 53

o 8.8

23-27 o 36.1

o

24.9

o 7.4 0.7 0.7 2.8 o 6.7 0.7 9.8 o 10.9

0.4 '3-7

o

9-5

0.4

o 28.4

0.4 62.0

01.28 Nov. i o 46.2

0

25.6

1.4 18.9 0.7 8.8 10.2 o 10.5 04 0.7 23.1 2.1

28.7 2.5

24-5

"5-1

13-0

30.7 35-0

13-7 51 5

lean value 0 16.1

0

9.0

0.3 46 0.4 1.7 22 0 3.1 0.3 2.7 39 2.9

4.9 3.1

4.2

4.5

4.2

4.9 14.9

2.4 25.8

\[>V. 2 — 6

o

4.2

0 O

o

o o

0 O

0

o

0 0

o

0.4

o

4-9

o

2.1

39

O I 1.2

o 6.7

7-11

0

3-9

0.4 2.5

o 0.4 ! o o o

0

0

0 0

o

o

o

0

o

04

o

0.7 2.8

o 12.3

12— 1 6

o 7.7

o 9.1

o 7.0

o ! 4.2 o 0.4 o o 4.9

0

2.8

1.4

0

o

O

0

6.0

0

3-5 7-7

17 — 21

O 2.1

o o

OOOOOoOOO

0

I.I

0

2.1

0

3-5

o

04 6.3

o 8.1

22 — 26

o 24.5 o 15.8

o 11.2 o 6.0 o o i.i o 1.8

0.7

2.1

1.4

2-5

2.8

4.2

4.6

3.9 7.0

0.7 17.2

iv. 27 Dec. i

o

O

o o o

0 0 0 | O

0 0

0 O

o

0

0

O

o

0

o

0

0

0 0

Iran valnr

0

7.1

0.1

4.6

0 3.1

0

1.7

0

0.1

0.2

0

1.1

0.1

1.1

0.5

1.6

0.5

1.5

14

1.7

4.6

0.7

8.7

>cc. 2-6

o

0.4

o

o

0

o

o

o

o

o

0

0

o

0

O

0

0.4

o

o

0

o

o

0

0.4

7- I"

o

o

0

O

o

o o

0

0

o

0

o

0

0

0

0

o

o

o

o

o

o

o

o

12 — l6

0

o

0 0

0

0 0

o

o

o

0

0 O

o

0

o

0

0

o

0

0 0

0

o

17 — 21

0

o o o

O 0 O

0

o

0 0

o

0

o

0.7 o

0.7

n l.|

0.4

o 39

o

0.7

22 — 26

07

37-3 i ° 23-'

o 12.3

o

4.6

0.4

o

3-5

o

1 1.9

o 13-3

o

IO.3

°-7 39

13.7

o 31-3

o 42.4

27—31

o

1 1.6 o 0.7

0.4 0.4

I.I

o

0

o

0.4 o

a. i

o 0.7

o

3-9

o

3-9 o

1-4

1.8

o 10.5

Mean value

0.1

6.6 0 4.0

0.1

2.1

0.2

0.8

0.1

0

0.7

0

23

0

2.5

0

2.5

0.1

1.5

2.4

0.2

6.7

0 9.0

.Ian. I 5

o

0.4

o

4-2

2.8

0

o

a. i j o

1.4

0.4

0.7

o

4.9

o

3-5

1.8

o

4-9

o

3.5

3-a

O.| 1.4

6—10 0.4

0.7

0.4

0.7

0 0

o

O 0

0 0

o

o

0

3-3

I.I

6.0

o

1.8

0.7

i.i

9.8

o 4.6

11-15 0.4

3-9

I.]

"•1

0.4 o

0

o 0.4

0 I.I

0.4

3.1

o

4-9

o

1.8

0.4

6.0

4.3

2.1

2.8 o 13.0

1 6 — 20 o

1.4

0

o

o 1.4

o

0.7 o

0 0

0.4

6.0

0.7

8.4

1.8

14.0

o

8.4

0

1.8

2.8 o | 5.3

21-25 °

7.0

o

0.7

o

I.I

o

0.7 o

0 0

o

1.4

o

3-5

0

6.0

0.4

5-6

1.8

I.I

8.1

o 13.0

26 — 30 o

6.7

o

0.4

o

0

0 0

0

0.4

0

0

1.8

o

3-5 o

8.8

o

7-4

18.9

0.7

28.7

o 50. i

Mean value

0.1

3.4

0.3

1.1

0.5

0.4

0

0.6

0.1

0.3

0.3

0.3

1.9

09

3.9

0.8

6.4

0.1

5.7

4.3

16

92

0.1

14.6

n 31 Febr.4 o

o

o

0 0

0

o

o

3-3

o

o

1.4

0.4.

o

i.i

o

5-3

o

0.7

o

o

0.7

o

1.8

rebr. 5 — 9 o

13-7

o

9.1 0.4

14.0

0.4

a.i

0.4

'•1

2.5

0.4

1.4

0

1 1. 3

0

1 6.8

0

6.0

26.6

o

56.7

o

58.1

10— 14 o

34-3

o

5.6 i.i

0.7

1.4

0

o

o

I.I

o

o

0.7

I.I

0

3-9

o

11.6

1.8

a. i

6.0 o

445

'5-19

o

i.i

o

0.4 o

o

o

o

0

o

1.4

0

2.1

o

1 6.8

0

6-3

i-4

i.i

0

o

1.4 o

i.i

20 — 24

o

0

o

7-4

0

12.6

o

6-3

0.4

t.8

1-4

o

0.7

0.7

i.i

0.7

2.5

o

04

o

0.7

O 0

°-7

eb.ajMv.i

0

1.8

o

o

o

4.9

o

6.3

o

0.4

2.1

0.4

3.1

o

M

o

10.5

o

8.8

o

0.4

a.8 o

23.8

lean value

o

8.5

0

3.8

0.3

5.4

0.3

2.5

0.7

0.6

1.4

0.4

1.1

02

5.5

0.1

7.6

0.2

4.8

4.7

0.5

11.3 0

21.7

arch 2 — 6

0.4

1 6.8

o

3-9

0.4

I.I

o

o

o

o

0.7

0.4

0.4

o

14.0

0.7

3-5

0.7

7.0

i.i

4-a

9.8

o

33.1

7-n

o

25.6

o

23.1

o

18.6

2.8

6-3

a. I

0.7

1.8

0.4

n.a

o

1 1.6

o

'3-3

a.i

4-9

17.3

o

43.4

3.1

25.3

cp.3 March:

0

<i.4 n. i

4.8\ o.)

}•*

O.I

'•)

o.7

O.2

'•)

'•J

3.1

0-9

,'.-•

1.3

-*•/

0.9

).6

j.6

/.<V

//./

"•-

lS.2

506

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE LXXXII.

Axeleen.

SH in y

Hour

O — 2

3 — 4

4-6

6-8

8 — io

IO 12

12— 14

14 — 16

16-18 18 — so

20 — 22

22-2.|

Period

+

—

+

—

+

—

+

—

+

—

•f

—

+

_i_

+

—

+

—

+

Sept. 3 — 7

0.6

20.4

o

42.6

o

19-5

0-3

8.7

5-i

2.4

7-8

2.7 33-3

O 2O.I

o 3-3

7.8

0.9

21.3 3-3

3-9

'•= 3-9

8-12

o

25-5

o-3

a i. 3

1.2

7.2

2.1 1.3 3.1

7.2 23.1

13.2 30.0

11.7 22.8

6.6 6.6

16.5 0.9

17.4 6.0

4-5

2-7 11.7

'3 — '7

0.6

4-3

0

11.4

0.6

11.7

1.8 1.2 0.9

2.1

3-3

2-4

4.3

4.8 6.6

3.0 0.6

3.7 0.3

3.4

0-3

8.7

0.9 16.2

18 — 02

'•5

10.2 2.1

18.3 2.1

8.7

9.0 i 1.5 26.1

3.1 40.5

2.1 34-8

0.9 14.7

3-3 3-3

I3.O

1.3

68.1

2.1

63.3

0.9 39.0

23-27

o

37.2 o

34-5 1-5

4.2

2.1 3.4 2.7

3.4 9.6

6.3 31.3

3.4 to.a

3-3 3-9

3-3

o 33.4

0.6

30.6

o.b i3.s

Sept.28Oct,2

1.8

30.3 0.3 [29.1 0.9 12.6

1.2 4.5 1.8

0.9 3-9

1.3 | 3.4

3-0 7.5

7-5 2.1

20.4 0.9 30.3

2.4

21.6

Mean value

0.8 21.3 0.5

26.2 1.1 10.7

2.8

3.3 6.5

2.9 14.7

4.7

22.7

3.8

13.7

4.0

3.3

10.5

0.7

27.2

2.5

22.1

1.8 19.5

Oct. 3-7

0.9 5-i 3-0

3-9 • 1-5 1-5

0.9 3.9 0.3

2.4

7.5

2.4

4.2

1.3

1.8

i.S

0.9

0.3

o

5-4

0.6

6.0

°-6 7o

8-12

o 6.3 o

8.7 0.3 1.8

0.9 1.2 2.4 2.7 6.6

1.2

14-7

3.4

•7.3

!-5

0.6

10.8

o-3 20.4

1.2

16.8

1.8 7.2

13-17

0.3 10.5 o

6.3 0.6 2.1

0.3 1.8 0.3 1.5 2.4

0.6

1.8

i.a

0.6

1.8

0-3

7.3

0.6

35-7

°3

12.9

0.6 7.5

18 — 22

o 18.9 o

27.6 0.9 13.2

1.8 1.5 0.9 0.6 2.7

0.6

5-'

0.6

2.4

0.6

0

3-6

o 11.7 0.3

12.9

0.3 17.1

23-27

o 42.0 0.3

39.3 0.6 18.6

3.6 3.9 11.7 0.6 15.9

0.9 18.6 2.1 7.8 24.3

1.8

52.8 o 28.8 1.8

27.0

Oct. 28 Nov. i

o 59.1 0.6

69.0 2.7 40.2

6.0 4.2 6.9 10.2 7.5

17-4 39 50-4 0.9 37.2 o

55-8 o 55.5 0.6

507

Mean value

0.2 23.7

0.7

25.8

1.1

12.9

2.3

2.8 3.8

3.0

7.1

3.9

8.1

9.7

3.5

11.2

0.6

21.8

0.2

26.3

0.8

21.1

1.2

19.7

Nov. 2 — 6

o 7.2

o-3

30

0.3 1.8

1-5

o 0.3

0.6

03

0.9

1.8

i.a

0.6

2.1

0.3

IO.2

0.3

45-9

0.6

20.7

1.8

._.,

7-ir

0.6 11.4

1-5

11.7 0.6 2.7

0.3 0.6 0.9 0.9 0.6 3.3 0.9

1.8

O.9 1.2

0.3

3.7

0.3 0.6

0-3

5-1

12— l6

1.2 12.6 O

30.0 o 17.7

4.8

8.4 11.4

4.8 10.8 5.4113.9

3.4 8.1 2.1

0.6

5-4

o 14.1

1.2

15.6

17 — 21

O 14.7 1.2

7.2 1.2 1.8

0.9

2.7 2.1

1.5 3.4 2.7 6.6

0.3 7.3 0.3

1.3

17.4 o 29.7

0.6

42.9

0.9

34-8

22—26

o 50.4 2.7

81.3 9-3 33-9

[2.6

12.6 19.2

5.4 6.9 13.2 5.4

34.6 3.4

63.3 o 128.7 o 85.2 i.a

78.9

o 128.1

Nov.27l)ec. i

0.6 11.7 1.5

6.0 1.5 ! 9.6

a. 7 ; 6.0 2.4

3-3 6.6 1.5 11.7 0.6 3.6 24 0.3

29.7 o 27.9 o

22.5

Mean value

0.4 18.0

1.2

23.2

2.2

11.3

3.8

5.1

6.1

2.3

4.6

4.5

6.6

5.2

3.8

12.0 0.5

32.9

0.1 33.9

0.7

31.0

0.7

36.3

Dec. 2 — 6

0.6 18.0

0.3

'3-5

0.3

7-2

5-4

1.2

8.7

1.8

30

0.3

9-9

0.3

4.8

'•S

0.3

2I.O

0

32.5

o

14.4

o-3

4-5

7-11

O IO.2 O

14-4 3-° 3-9

1.5 a.i 4-2

1.8 9-3

0.6

138

o

10.5

1.5

1.8

I7.I

o

30.6

o

71.4

0

35.8

12— l6

0.3 l6.8 2.1

'5-3 0.9 2.1

1.8 2.4 2.4

3.9 i.a

4-5

0.9

3-3

[.8 1.8

0

45.6 o

51.0

2.1

29.7

1.2

'5-6

17 — 21

o 4.8 0.6

4-2 1.5 2.7

3.6 0.3 2.4

0-9

1.5 2.7

3-3

0.9

3-3 i-5

3-o

2.4 o

11.4

8.4

0.3 2.1

22 — 26

0.3 23.4 1.2

63-6 1.8 33.6

8.1 9.6 19.8

1.8 9.0 6.0 6.0

35.8

I2.O

13. 0

1.2

39.6 0.3

50.7

0

(6.5

o 180

27 — 31 j 1.2 22.5 o

12.0 4.5 11.7

5.4 ; 1.2 4.2

1.2 5.1 3.3 6.6

i-5

1.5

0.6

o.3

9.6 o

14.4 0.6

21.6

0.3 10.5

Mean value

0.4 16.0 0.7

20.5

2.0

10.2

4.3 2.8 7.0

1.9 4.9

2.9

6.8

5.3

5.7

3.2

1.1

22.6 0.1

30.1

0.5

32.0

0.4

12.9

Jan. i —5

0.6 15.3 2.7

37-5

'•5

22.5

3.3 6.9 6.3

1.8

2.1

5-4

2.4

3.1

1.8

3.0

1.2

16.5

°-3

21.6

o

21.3

0.3

9.0

6— 10

1.5 10.8 o

28.8 1.2 7.8

3-3 2.1 4.5

1.2

9-3

03

14.1

0-3

13.3

4-5

6.9

4.3 0.6

21.6

0.6

29.4

o 13.8

11-15

o 21.9

0.3

IO.2

1.3 4.5

1.2 2.4 4.5

0.6

30

0.3

9.6 0.3 15.9

3.7

1.2

I2.O

0

68.1

o

-2-5

0.3 17-4

16 — 20

0-3

5-4

0.3

•3.8

2.4

11.4

3-0 3-3

8.7

o

4-5 3-9

13.9 i 3.6 9.0

11.4

1.8

20.7

o 37.9

o

18.9

0.3 2.7

21 — 25

0.9 20.7

0.6

7.2

i-5

5-4

3-9 0.9

4.2

1.8

3.o 5.7

7-5

1.3 4.5

3-6

i-5

12.6

o 31-5

1.5

33-9

0.6 13.5

26 — 30

o

46.2

0.6

24.3

0 15-9

0.9 3.9 9.6 0.9

15.9

1.3

35.2

0.3 9.9 0.6

0.6

18.9

o 38.4

4.8

14.1

2.1 0|.K

Mean value

0.6 20.1

0.8

20.3

1.3

11.3

2.6 3.3

6.3 1.1

6.3

2.8

12.0

1.3

9.1

4.3

2.2

14.2

0.2

34.9

1.2

23.4

0.6 20.2

Jan.3iFebr.4

0.6 3.3 0.6

8.1

1.5

4-2

2.1

3-0

0.6

3-6

2.1

4-8

3-3

3-3 4-5

2.4

1.8

9.6

o

9.6

0.9

2.7

1.8 5.1

Kebr. 5-9 1.5 3.3 1.2

27-3

i.alas.i 1.5

18.6

7.8

4.8

10.8

4.2

13.8 0.3 rs.o

13.3

4.5 21.6

1.2 64.2

33

4<5.3

0.9

17.1

10-14 0.3

30.6 0.3

26.4

1.2 19.2 6.9

1.5

3-9

2-7

8.7 1.5

8.7 0.6 12.9

0.6

2.4 6.0

o 33-3

o

19.8

15-19 0.9

4.2 0.3

6-3

3.0 0.3 2.1

o

4.2

0.6

5-4

3-3 IO-5 3-o 2.7

'3-5 L5 44-7

1.8 20.7

1-5

6.0

20 — 24 0.6

6.0

0.6

9.0

0.9 18.9 i 0.6

2I.O

1.2

2.7

10.5 o

33.8 ! 0.3 15.6

o 39 4-5

0.3 3-3

0.9

'•5

15

.:"

Feb. 25 Mar. i | o

4.8

o

8.1

0.6 25.5

1.8

'3-5

5-7

o

9-9 33

18.6 0.9 7.8

0.9

0.6 , 6.9

0 17-4

o

7--

0.6

14-1

Mean value 0.7

8.7

0.5

14.2

1.4

15.2

2.5

9.6

3.9

2.4

7.9

2.9

13.0

1.4

9.3

50

2.5 15.6

0.6 24.8

1.1

14.0

1.3

11.3

March 2 — 6

0-3

24.9

o

22.8

1.5

21.3

1-5

6.3

1.8

3-3

8-7

1.8

9.0

0.3

5-4

13-3

1.2 14.7

o

24-9

0.6

UO. I

1.2

10.8

7-11

0.3

22.8

0

57-6

o 48.6

2-7

IO.2

12.3

0.9

12.9

0-3

32.3 | 0.3

12.9

5.1

o 39.6

0.6 81.6

1.2

55.5

0.9

1 2.,-;

13 — ]6

0.9

22.5

0.3

32.1

0-9 45-3

5-7

7.8

12.6

2.1

12. 0

4.8

31.3

o

13.8

12.6

3-3 Si.o

0.3 27.0

3-°

12.3

0.6

17 —21

0

I4.I

o

12.6

o

16.8

0.3

3-6

3.0

3.1

6.9

5-4

3.1

2.7

2.7

4.5

O I2.O

O 22.2

1.5

22.8

0.6 15.0

22 — 26

o-3

8.4

0.6

10.8

0.3

5-'

i-5

1.2

7-5

0.9

3-6

6-3

3-o

3-3

0.9

5-1

1-5 5-7

0.6

45

3-4

4.2

0.6 *8.8

27-31

0.3

27.9

o

26.4

0.6

9.0

1.5

5-4

6.6

4.8

7.8

5.1

7-2

3.4

8-7

2.1

o 24.6

0-3

21.3

0-3

34.9

3-0

7--

Mean value

0.4 20.1

0.2

27.1

0.6 24.4 2.2

5.8

7.3

2.4

8.7

4.0

12.5 1.5

7.4

7.1

1.0 24.6

0.3

30.3

1.5

23.3

1217.8

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III. 507

ABLE LXXXII (continued). SH in y. Axeleen.

Hour 0—2

2-4

4-6 .

6-8

8—io

10—13

13—14

14 — 16

16-18

18 — 20

20—33

22 — 24

Period

+

—

4-

—

+

—

+

—

+

_

4-

_

+

—

+

4-

_

+

- i +

__

pril 1—5

o.3

31.2

o

594

3-0

29.4

2.7

11.7

5.'

7-2 13.3

32.8

3-6

10.8

19.3

6.9

i i.i

0.6

28.8

0.6 34.0 3.1

40.2

6— 10

4-a

37.5.

IO.2

23-7

5-'

459

18.9

6-3 32.4 a.7

7.2 30.3 ; 15.9

54-9 17-4

16.5

3-3

36.9

1.5

33.0 0.6 42.3 3.4

47-7

11-15

0.6

20.4

2.7

31.8

8.4

3-9

87

i-5 14-4

4-2

26.7 8.7 28.5

9-3

11.4 |i3-3 24

17.7

0.9

27.6 1.2 26.7 15

'5-0

16 — 20

6.0

4-8

4.2

5-4

2-4

1.8

1-5

3-3

30

2.1

8.7

6-3

10.2

20 4

3-3

18.2

'•5

49-8 3.3

36.9

1.8 13.5 2.7

5-1

21—25

1-5

8.7

1.8

14.1

2.1

7.2

6.6

0.6 2.7

3-0

I2.O

23-2

13.2

18.3

10.5

10.5

4-5

12.3

06

25.8

0.9 9-9 2.4

9-9

26 — 30

o.3

31.8 0.9

26.4

O.g

19.8

i-5

5-7 , 5-4

3-9 7-2 23-4

15-6

14.1

31.6

6.6

11.7

16.5 0.6

24.0 0.3 32.4 1.8

327

I- .111 value 2.2

•22.4 3.3

26.6 3.7

18.0 6.7

4.9

10.2 3.5 11.5 17.4

17.7

20.1 12.5

13.9

5.1

24.1 1.3

29.4 0.9 248

2.2

25.1

May i-s

4.2

1 1.4

a-i 56.7

0.6

34-8

0.9 14.1

3-9

4-5 3-9

9-6

I3.O

4-2

18.6

<-5

8.7 4.8

3-3

12.9

4-5

33.4

6.9

25.2

6 — 10

(3.01(30.0)

(3.ol(45-o)

(7.5)(54.o)

(o) (45.0)

(7-5)

(9.0) (6.0) (7.5) (30.0

(3.0X45.0) (3.01

(9.0) I6.o)

(1.5) (30.0) (1.5X36.0)

(3.0) (15.0)

1 1 — 16

4.8 17.1

2.7 32.4

0.3

26.1

0.9

15-6

0.3 12.9 12.9

2.1 22.5

0.3

21.3 8.4

5-t

11.7

0.3 36.0 0.6 40.5

1.8 22.2

17 — 20

10.2

1.5

6.3 6.6

13-5

1.2

5-7

5-4

1.5 10.8 8.1

28.5

2.4

20.4 1.5

14.7

1.8

6.3 5-7 6.3

2.7 6.0 7.2

21—25

54

10.5

3-° 39-9

i'-

22.8

2.1 '12.3

22.8

i-5 33-9

7-5 36.6

1.8

52.2 o

18.0

3-9

3.6 25.8 1.8

24.9 4.8 21.0

26 — 30 1.8

30.9

o 62.7

4-5

64.2

7.2 30.0

15.6 1.8 64.2

0.6

67.8

0.6

36.0 1.5

297

2.7

14.7 30.4 3.0

-'9-7 --7 -'5.5

I'-au value

4.9

16.9

2.9 40.6

2.5

35.9

2.1 20.5

9.3 5.2 22.0

5.9

32.9

2.1

33.8

2.7

14.2

5.2

5.0

21.8 3.0

26.2 4.2

19.4

•]i 3 May 30

i. a

tS.6

'•'

i6,(,

I-2

6.4

6.7 2.7 y.y

i-4

'4-7

5.6

,„,, ;.„

« '?'"

0.9

rf-7 t.j

24.2 I.f

,0*

ABLE LXXXIII.

Sf, in 7

Axeleen.

Hour 0 — 2

2-4

4-6

6-8

8 — io

IO— 13

13—14

14 — 16

16-18

18 — 20

2O— 22

32 — 34

Period

+

_

4-

—

+

_

4-

_

4-

—

4-

4-

4-

4-

+

4-

4-

Sep. 3-7

0.7

25.2

0.2 41.8

o

I87

i.i

5-8

3-2

0.5

4.1

o.a

7-4

o

6.7

0.7

ii-5

0.4

1 8.0

0.5

8.3

0.5

5-9

i-3

8-12

0.4

7.6

0.9 ro.8

i.i

5-9

2.0

1-3

2.7

0.9 5-4

o

00

3.2

6.1

O.2

13-3

o

18.0

0.2

9.5

i.i

3-2

7-7

I3~n

[. :

2.3

0.7 8.5

0.2

9-0

i-3

1.8

0.9

0.3 1.3

0.4

i-3

1-3

23

2.0

2.5

I.I

4-5

0.4

2.7

2.3

2.7

5-4

18-22

2.O

14.8

2.2 2O.2

1-4

'3-3

3-a

3.9

1.8

4.7 5-4

2.0

6.5

0.9

7-6

2.3

8.3

3-4

19.8

10.3

8.3

20.7

1-4

1 6.0

23-27

0.5

17.8

0-7 19-3

0-5

8.8

'•3

3-4

i.i

0.9 2.7

0.9

3-8

2.2

4-3

1.8

6.7

0.4

"•3

0.7

4.1

3-6

3.9

6.1

:p.a8OcLa

2.7

7.6

1.4 8.8

o.7

4.1

1.6

i.i

'•4

0.5 1.8

i-4

0.7

2.9

3-i

3-1

3-6

i-4

S-o

1.6

4.1

3-6

1.6

13-5

lean valur

1.3

12.6

1.0 18.2

0.7

10.0

1.8

2.7

1.9

1.3

3.5

0.8

4.8

1.6

5.0

1.7

7.7

1.1

12.8

2.3 6.2

5.3

3.0

8.3

Oc-t. 3-7

0.9

5-6

2.2 3.4

1.8

3-4

2.3

1.4

0.5

i.i

2.7

0-5

0.7

0.9

0.7

0.5

0.5

o-7

2.2

0.4

1-4

2.9

0.9

6.3

8-12

0.4

5-9

0.5 6.8

0.9

1.8

2.9

0.7

1-3

1.6 0.7

3.O

5.2

1.8

2-3

1.6

10.6

0.5 14.6

0.4

5-6

6.3

1.4

8.1

I3-I7

0.4

5-8

0.2 5.0

0.2

2.9

1.4

0.9

i.i

0.2 2.2

o.a

0

0-7

'•3

o

5-9

0.2 II.5

0.4

7-4

1.4

2.5

3-8

18 — 22

o-5

12.6

0.5 21. 1

1.4

7.2

4-7

0.7

1.8

0.5 1-3

i.i

0.2

1-3

0.4

1-3

2-3

0.4 7.7

0.5

2-5

4.1

1.4

8.3

23 — 27

0.2 29.7

0.2

32.0

I.I

II. 2

5-6

0.7

1.8

2.3 0.7

4.0

4-5

i.3

II. 2

0.5

30.7

o.5

23.8

o.S

9-5

4-5

2.7

19.4

ct. 28 Nov. i

° 35-3

0.9

52.3

I.I

21.6

5-4

9.0

3-3

22.7

3.0

10.6

2.9

4-5

8.r

1-3

25.6

1.6

30.2

3.0

13.0

11.7

2.7

20.3

M< an value

0.4 15.8

0.8

20.1 1.1

8.0

3.7

2.2

1.6

4.7

1.6

3.1

2.3

1.8

4.0

0.9

10.9

0.7

15.0

0.7

6.6

5.2

1.9

11.0

Nov. 2-6

0.4

1.8

I.I

0.5

0.2

i-3

0.4

0.7

0.4

0

°-5

0.4

'.3

0.9

3-2

o.a

12. 1

o

i3-9

10.6

S-o

3.5

0.4

5.6

7-n

o

II. 0

o.S

10.1

0-5

2-3

0.4

o.a

o.a

0

0.7

0.2

O.2

0.7

o.5

0.3

0

1.8 0.7

o.S

0.5

3.3

0

7.0

13 — 16

O.2

II.O

0

28.4

O.2

19.8

0.5

3.4

5-4

0.4

2.7

0.7

4-7

1.6

2-9

1.8

2.O

1.6

2.9

3.0

a. a

2.7

I.I

II. 3

17 — 21

O.2

14.9

O.2

10.4

0.5

4.1

0-5

2.7

0.4

0.9

i.i

0.9

2.3

0.4

3-2

o.9

6.5

T.4

"•3

I.I

a.a

13.2

0.9

I4.3

22 — 26

o 40.5

O.3

48.6

1.4

27-5

r-3

17.1

1.6

9.0

0.9

13-3

8.3

1.6

14.4

2.0

32.6

7-9 25.0

7-6

13.0

33.9

1.6

47-5

ov.27 Dec. i

o.5 4-5

i.r

1.6

2.0

4.1

1.8

2.O O.9

1-3

i-3

I.I

0.9

2.0

0.2

a-7

2.O

3.3

4-3

3.3

2.5

4-9

0.7

6.1

Hean value

0.2

14.0

0.5

16.6

0.8

9.9

0.8

4.4

1.5

1.9

1.2

2.8

3.0

1.2

4.1

1.4

9.2

2.5

9.7

4.0

4.2

7.9

08

15.3

.)ec. 2 — 6

O.2

11.2

0.2

10.4

0.5

8.1

1.6

0.7

1.4

0.5

3-8

o

5-3

0.2

2.3

0.4

3-6

0.9

3-4

3.3

0.9

2-9

0.3

6.5

7-n

0.4

9.0

0.9

IO.I

2.2

1.4

2.5

0.9

0.9

1.6

4-3

o

2.5

0.4

1.4

1.6

2-3

o.9

5-o

II-5

4-5

n.S

o.5

17-3

13— l6

0.4

I7.8

I.I

9.4

0.7

1.4

3.O

0.5

0.7

0.4

0-5

1.6

0.7

2.3

1.8

o-S

6.8

i-3

3.7

13-3

3-'

6.7

0.7

6.3

17 — 31

I.I

3-5

3.O

2-5

2.9

0.9

3-2

0

1.6

O.3

0.9

o

1.4

0.2

1.6

o.S

0.9

o.5

3.3

0.9

1-3

1.4

0.3

3.9

32 — 36

0.7

15-7

I.I

28.3

2.2

14.2

4-9

4-7

5-6

i.r

2.5

3-4

4-'

1-3

9-9

2.O

10.3

5-4

15-7

a.9

7.3

2.7

O

14.4

27-31

1.3 8.5

3.6 5.0 j 3.3

8.1

5-9

0.4

3-1

i.i

0.9

o

0.9

O.2

8.5 o

2.2

0.9

4-3

i-3

3-4

3.4

3.3

8.1

Mean value

0.7 10.8

1.5 11.0 1.8

5.7

3.4

1.2

2.2 0.8

2.2

0.8

2.5

0.8

4.3

0.8

4.4

1.7

56

5.4

3.4

5.8

0.6

9.3

-

- - . . - I

- - — ** *r **

5=«» »* *

*--

T **

5* *^
T» i« i -

B«.

U

a I s*
2« 19

•«j --•»

«.= ««-• *

itf *S

*r 5-*
*» *•«

: --

c».a: « cg^r

- »*'

• - '-•

a* B

: !

~«3. = *Br » <J r-^a *,— ana BJ; «^»r

3=~= 5^5 :

.

-

-. .

> ~ -

f *.a -^

_

—
B^r obr«ca

m «7

: -..- '•

PAKT. 11. KULAK MAGNETIC PHE5OMEXA AXD TEK*JE1_LA 1 II • •MTWTK.

FABLE LXXXIV (continued). Sr in 7

our, HI. ' • -
Axdeen.

| 0-2

3-4

4-6

6—8 8—io io—i2 13 — 14

14—16

l6- l8 l8 — 30 30 — 23 33 — 34

Period

4,

Oct. 3-7 175

0

I.I

0.4

1.8

3-5

0.7 3.5 04 0.7 04 14 o 3-8

«M

»9

-.

O 46 0-4 32-8 O 36.6 O

8-13 91

o

0-4

0

o

o

i-8 o o 0.4 o i.i o 15,1

04

10- 1

o 31'5 56 6.3 fnja o 45.5 0-4

13-17 8-4

o

0

0-4

0

1-8

o ' o o 0.7 i.i i_4 o 1-8

o

0-7

1

0-4 18.9 4JO 34.7 3.5 20.3 I.I

18-22 7.7

0-4

60

t*

0-7

32.3

o '1819 0.7 4^6 07 4-3 0-4 0.7

-.

o

0

14 II.6 3931-9 04 '31.5 04

23 — 27 109.2 04

54-3

o-7

3-5

•3-7

0.7 33-9 i-i 4.2 04 3.1 o 31,3

2.8

30-5

4-2

249 23.1 2-8 854 0 1414 0

jWf.38Xov.i 1530

o 91.0 i.i

48.0

9-5

*4-»| 5-3 i-l '9-3 0.7 34^ 14-0 39

- •

11-3

3&6

130 97.0 39 156.1 o 160-0 o

.

01

ma

0.7

90

10.1

29 94 04 54 04 57 24 03

15104

54114264 37055 05704 03

Xor.a-6 6.7

i.i

°

2.1

il-I

'4

a* 50-4 39 7*-' * 3*9 o

32-9

o

'3-o

0-4

0-7

i.i

04 o o 0.7 o 04 o 0.7

•

II

'--

0.7 14 04 144 o 354 o

12—l6 21.0

I.I

23-5

9-5

0-4

42-4

0.7 31.2 4,6 8-8 7.0 2.5 32 sue

i-i

39

0-7

8.1 16.5 4-6 46.9 o 637 •»

o

4-3

3-8

o

9-5

0-4 6.3 0.7 - 3-3 0.7 0.4 1-6 0.7

-.

9-1

04

16.5 16.1 5.3 67^6 0-4 62.3 0-4

22-26 188.0

o

1138

3-2

494

i.i

1 1-2 39 49 20.0 2.5 333 35 133

7-7

33-8

72-8

_'-..- - - - - s - .

<ov.27 Dec. I 10.2

o

1-4

o

1-8

1-4

14 4-6 14 o 8-8 14 6-0 6.3

14

4-9

49 30jO t?-2 28.7 04 10.5 0-4

Mean vah* 483

0.4

260

34

87

93

24 7.7 20 56 32 64 24 7J»

17

7.2

144

10241.4 5570.4 15464 04

Dee.3— 6 15.1

0

1-4

3-2

0-7

1 1.6

6.7 1-8 8.4 o o 2.5 0-4 3.1

o

2-5

7X> 10.5 1-4 L4-4 0 154 o

7-n 17.9

o

109

o

UB

7-*

i.i 0.7 28 o 14 o 0-4 2.5

•

3.1

-'

: - - ----- .

13— 16 34.3

07

22L8

o

o

0

0-40 14 o o 4-2 o o

2-5

:-

- - - ------ - - - - •

17-21 39

o

o

0

o

3^2

o 04 o 04 o 14 o 6-0

0

: -

-,

109 6uO 74 30.1 i.i 11-6 0-4

22 — 26 35-4

04

27.3

9-5

0-4

i.i 36-6 2-8 39-£ 04 39-2 i.i 42-4

69-7

: :-

36-4 33.1 30-8 854 1-4 00^9 o

: 2^6

o

6-3

o

U

6-3

o 10.5 04 i-4 o 46 o 6.3

o

1.8

0-7

0.7 3.5 :_4 Iij6 i.: 26.3 o

Meaa rake 220

92

115

21

07

9-1

14 67 26 63 03 87 03 94

01

16-1

27

126 126 88 39-2 27 307 03

Jan. 1-5 35
6 — 10 IOJ9

0

0-4

9-S

10.9

»-*
1-4

.

.. ,

i.i 49 2.5 6-0 3,1 3-8 o 9-8

L

:s

-.

7-4 5.3 3-1 21.7 0-4 io_2 o
16,5 8.1 i.i 38jo 3.5 25* o

1 1 — 1 5 3o-O

16 — 20 49

uO

1 1.9

9-5

o

3.1

:-

3.5 6.3 10.5 04 04 3-3 o 22,1

0-4
39

130

"-

6*

12.3 f3-7 M-7 '6^ 0,7 31-5 !••
«3-i 7-7 3-5 «** 39 7-4 3.5

21—25 1 1-3

0.7

6.0

0-4

0

"

3J 4-9 6.7 i-« 2-8 0-5 39 r,M

1-4

47-6

33

I :J) 20-0 2-8 38.7 4j6 36.3 o

26—30 109.2 o 536

o

23-1

o

070 5-3 o o -.oi-i iSu6

5*

IO.I

-

*-* 3** 35 55-3 «4 136.5 o

Mean vabe 280

05

ICJ

05

43

57

1.2 28 4.2 13 13 34 1.4134

14

184

24

133 157 44 282 21 394 04

:in.3iFebr_4

i^ 14

o

-,

o o

o

04

D

: - •

i i

* l**l* l**l* Is*! Ml**l *7I "

Febr.5-9

231

o 338

04

i8x>

3-5 9-i

iJt

:

O IO-3

o 2.5

o 15.1 2.1 19,3 29,: 4^ 74^9 o 75.3 o

10—14

392

r A ft

0-4 9^5

0-4

0

4-2 0.7

:

i.i

-.

1-8 o

i8 04

O_tf T «

o 5j6 o 35 49 32 «** o 44.5 35

O_tf f ^LA « _2 f ^— A 6-3 * -4 6 " O ^ %_4 O

15 J9
20—24

I O.O

° 5-3
i-i 259

o
o

37-1

74 «7 3

0-7

39

I.I 13.3

**4 »-4
SI 6.7

u-4 IVAA^ 4-2 »^4 %*-3 *^ *^-l **-4 ^-J *-

0-4 8.1 a ioj6 o 6.7 2.1 0-4 6.3 «

Feo-asMa.-.:

: - -

o 8_,

0

I3»

o 11.9

o

o-7

:

OQ MO

>6 32

14 2-50 7-40 7jo 6.7 o 31-5 o

163

04124

01

115

25 82

84

13

12

14 47

22 24

0.4 77 1.1 125 67 5.4 184 47 28.4 03

Mar<*2-6

o ao-4

o

°

t«-0 0-4

8-8

tjt

- -

o V6

o 38.7

o 64.8 o 055 5.3 30.5 37.8 130 50.4 39

IO2-6

i-« 96-3

0-7

ao-4

M 3.5

231

i-«

18-6

o 8-8

04 19,3

i-i 33-1 Hj9 16.5 71-4 8.1 137^9 1.1 139.5 o

12— 16

8oJ>

<X7 fn ft

o

44-1

: : .

88

1.1

* 1 4^1

i-i 137

04 45-5 5-3 6»» 2ijo 30.3 34-7 »4 7»-4 3-2

17-21

•>-> ^

25^

iJ& 6-0
_ £ n

84 o

Iij6

o

0.7 1-8

• 1 **!

0-4 7-4

O XI

o 9-*|» 1 7-* 17-5 '•» 57-1 o 73.5 o

O ^-2 O 4 O * _-0 « j iflLjO O ""3L.I O

30-3

35-0

o o o
o 31-5

°4

: -

:

I -

2.1

I.I O

o 0.7

o 17.9 o 336 4j6 6jO 354 o 25j6 o

Mean raloe

517

47352

15

128

55 07

94

1.1

57

03 34

03114

0327.1 2432420211.4534 24703 12

April 1—5 86.1
6—io 105-0
11-15 38-9
16-20 35
21—25 !6-i
36—30 102.9

Mean value 583

o 65-8 0.7

1-4 I IO-6 o_4

o 3a9 o

0.4 2-5 o

: . - _ : -

i.i 84-7 1-8

06528 0.6

13.6 9-i o 333

72-8 14 8-i 1 1.9

1-8 04 0.7 5.6

04 0-4 i-i 0.7

0.4 i-i o o

12-3 °-7 0-7 2-5

167 22 14 94

Biriceiand. The Norwegian Aurora Polaris

o 28.7 :o-9 9.5 i-i 17.5 35 36.1 1-4 »i-o 22-4 0-8 53^ 1-4 «a 7

4-9 130 1-8 52-9 0.7 76.7 o :o6 I 17.3 46-9 5:.! 33,1 62.3 I4JO 129.5

0-4 7.7 o 34.9 o 44.5 o T«L« o 82-6 0.7 36.1 34.7 «-4 4«*

0-4 O 0-4 14 JO O 3O-8 O 70-0 O 788 I-« 335 60 4-3 32

o 4-3 6.7 10-3 15* 7-7 6uo 13.3 o 37.5 0-4 33.3 oj I«9 i»9

0.7 0-4 0-7 o 0-4 1J» 1-4 19-3 0.7 329 3.5 17^ 68.3 o 96.3

11 94 3.4 186 3J 307 18 533 32 50J 13.1 237 383 53 985 23

-..:.

^10 lURKIJ.AM). 1IIK NOIUVI r, 1A \ ATKOKA I'nl.ARlS KXl'KDITIUN, 1902—1903.

I'Ani.K I, \.\X1\' icuntimied). Sy in 7

Axeloen.

Jlunr o--2 2- 4 4 — 6 6 8 8 io 10 — 12 12 14

14- 16

16- 18

18

— 20

20

— 22

22-

"24

| ;

~

-=

4- —

-t- —

4

__ _^_

Mav i 5 05,2 0,7 112.0 o (8.3 i.i 3.5 2.5 0.7 2.5 o 18.2 0.4 35.)

o. ( 5.6

2.5 6.3

8.8

M-7

64.1

6.0

96.3

3-0

o io 16.0 o 187 i.| 1 3.0 7.7 4.0 7.0 7.7 i | 7 6.7 25.6 1.4 . 6.7

0.4 25.2

o 43.8

5

31-9

38

5

7-7

58.8

0-4

1 ] 15 2O, 1 0.) 20. 0 0 2.1 2.1 2.8 1-2 O.I 2.8 O..} 2.1 0.7 I Q.I

I. -I 15-8

o 56.0

I I.

2

3°.i

(59

2

0

38.2

<M

io 20 |0.o o.| 37.1 0.4 21.4 o. | (.2 2.8 0.7 o 0.4 0.7 o i 8.4

o 30.8

0.4 35.0

1 6.

7

15.8

Q

5

4.2

39-9

04

-'i 25 81.12 o 50.1 o 3,1-3 °-4 7-° 7-° ' ^'' 3-- °-4 16.8 o 70.7

o 72.1

1 • 1 53.6

r3-

3

25.6

24

5

14.4

93 i

3-*

.:6- 30 108.5 ° o0-1' °-7 5°.5 7-° '.8 '"•- '•! -° 7 -'5 43'4 -• ' 58-5

8.1 18.2

I.I 24.5

27.

o

I 1. 6

54-6

3-9

89.6 ! o 4

M,-au value 66.9 0.3 61 .3 0.429.8 3.1 4.0 7.0 3.1 7.3 1.717.8 0.831.5

1.7 28.0

09 36.5

11

i;

21.6

41

7

6.0

69.3

1.5

~v p.;', Mav 30 /;.A ".; Ji/.~ I./ lli./i '..A j. A f,.; 2.,- /.'/ J.I A.; I .<> l; /

j.i iif.n

">•

7

9.9

+

7

3.}

™

i."

Dyrafjord.

llniir 0 — 2 2 -4 | 4 -o 0 — 8 8 — io 10 — 12 12—14 i|— 16 16 -18

18

— 2O 2O

- 22

22 — 24

Period 4- + • 1 4- 1 1 4 +

4_

1

— 4-

+ _

N"\ . 23 26 0 105.O 0 1 |[.0 3.0 63,. O 0 3O.O 0 12.0 O . 3.0 30 3.0 27.0 O 66. 0 12 O

45-0

33.0 12.0

54-o

o 78.0

N"\ .-', I ><•<•. i 0.3, 16.2 o |.2 0.3 oo 3,. 3 0.6 3.9 o 0.6 o.o 1.2 1.5 2.1 O.Q 4.8 0.3

2. 1

0.6 8.1

0.3

0.6 8.7

Her. 2 — 6 4.8 16.8 06 7.2 1.2 3,. 3 :•. i 0.3 o 1.5 0.3 06 o.o 0.6 3.0 1.2, 8.1 0.3

7.2

0 5-7

0

2.4 9.9

1 1 03 27. t) 0.3 26.7 0.3 1.8 03, 0.3 0.3 4.5 1.5 2.7 O.6 2.7 2.1 1.2 I.5.Q O.Q

13.8

o 10.8

1.2

7.2 18.6

12- 16 2-1 50.1 2.7 7.8 )-5 0.3, 0 , O 0.3 O.O 0.3 2.1 O 2. | 2.1 O.6 15.Q O

,3.8

0.3 6.6

2-7

4-2 2.7

17—21 o.o 0.6 03 2.) O.Q 3.0 03 0.6 o o o o 0.6 O.Q 0.3 0.3 1.8 o

3-9

0.3 2.7

°-3

0.3 0.6

22 20 0 71..) 0.3 67.8 0.3 36.3 2..| 0.3 3.0 2.7 2.7 3.0 1.5 7.2 2.7 1.2 3.0 I..5

7.8

4-8 15.3

6.0

1.8 62.7

27 3 1 0.3, 24.3 o 13.2 0.3 10.2 30 3.0 1,2 O.Q 1.2 0.3 0.6 1.5 i .8 o i .5 , 2.4

'•5

O.Q 4.8

0.6

2.1 19-5

Mean vain, 1.5 31.8 0.7 209 1.3 10.3 1.4 2.3 0.8 1.8 1.0 1.6 0.7 2.6 2.0 0.8 7.7 0.9

8.0

1.1 7.7

1.8

3.0 19.0

Jan. i 5 1.8 21.0 1.5 30.0 O.Q 6.6 4.5 2.1 1.2 1.8 0.3, o.o 1.5 0.9 3.6 0.3 8.1 , 0.6

r.8

O.6 2.1

0.9

3.6

2.4

o— io • 0.6 ri.i 0.3 30.3 1.5 1.2 o.o 0,0 OQ 0.3 o 0.3, 0.6 0.3 5.7 0.3 8.4 0.6

3-6

i .8 9.9

1.8

2.4 5-i

11 — 15 3.0 7.5 OQ 17.7 09 2.4 0.3 5.4 O.Q o 0.3 1,5 1.2 o.o 1.8 0.3 1.5 0.3

11.4

0.6 8.4

1.8

4-8

=.4

16 — 20 1.5 7.8 l 8 28.8 0.6 8.7 0.6 2.^ 7.2 o.o o.o 2.4 3.6 1.2 5.7 1.5 6.3 1.5

'5-°

2.1 6.6

0.9

3-6

3-3

21—25 0.3, 25.8 1,2 12,6 OQ 7.2 OQ 1.2 O.Q 1-5 1.2 O.Q 1.5 3.3 2.7 1.8 O.Q' 03

6.3

0.6 14.4

0-9

4.8

"•7

-'0 30 O.O ,)2.O 0.3, -13,8 0.3 18.3 03 10.5 4.5 O.Q 2.4 2.1 5.4 1.8 7.5 O.Q 20.1 0.3

27.0

0.6 9.9

9.6

6.0

29.1

Mean value 1.5 19.4 1.0 302 0.9 7.4 1.3 3.7 2.6 0.9 0.8 1.4 2.3 1.4 4.5 0.9 10.1 0.6

10.9

1.1 8.6

2.7

4.2

9.0

Ian. 31 l-eltr.j o 17.7 0.6 6.0 0.6 3.6 06 1.8 O.Q 0.6 O.Q 0.6 1.8 1.5 1.8 0.3 4.8 o

'-5

0.9 1.8

0.3

2-4

1.2

K'-'ur. .5 0 0.3 20.1 o 61.2 1.2 42.6 3.3 14.7 3.3 2.7 q.o 1.5 5.1 1.5 18.6 o 22.8 O.6

11.4

n-7 4-5

24.6

9-9

23.1

10 - 1 1 0 60. 0 0 3,6.O 1.2 15.0 3.0 3.0 6.O O.6 O.Q 4.5 O.Q 4.5 3.0 O.Q ' 3.0 O.Q

24.0

1.2 21.0

o

3-0

30.0

1.5-IQ 0 105 0.3 17.] 1.2 1.2 0 0.3 0,0 0,6 0 2.1 1.5 O.Q 8.4 0.3 13.5 2.4

0.9

3-3 °-9

1.8

0

4-5

20 — 24 '•- 72 o 14 j o 06.3 0.6 58.8 o 150 o.o 6.6 1.2 7.8 1.5 3.6 30 1.8

1.8

2.1 10.2

1 2

3-°

1.5

:• clir,25Mar. i 0.3 0,3 o 7.5 o 7.8 0.3 0.3 o o o o o o 1.5 1,5 11.4 0.3

17.1

o-3 3-3

4-5

0.9

12.3

Mean value 0.3 22.3 0.2 28.7 0.7 22.8 1.3 13.2 1.9 3.4 2.0 2.6 1.8 2.7 5.8 1.1 9.8 1.0

95

4.3 7.0

5.4

3.2

12.1

Man-li2 o i. 2 50.4 0.3 48.0 0.6 24,6 2.1 8.1 0.3 0.3 0.3 1.8 8.4 1.2 33.3 o 30.3 0.6

2 1 .6

o i 1.4

2.1

4-5

2I.O

7 -i' '-5 78-8 0,0 i i (i.i 1.2 465 5 i 16.2 1.2 8.1 1.5 O.Q 6.Q 2.1 2 (.3 0.3 43.8 o

54-°

0.3 2Q.I

6.0

4-2

27.6

'- '" o-3 7!!'6 0.6 705 o.o 71.1 54 o.o 2.7 2.1 1.2 3.3 8.4 1.5 21.0 0.3 32.4 0.6

14.1

0.6 6.3

3.o

1.2

28.5

'7 •-' ° l"-8 i-5 15-3 03 26.7 1.5 2. | o.o 27 o.o o.o 1.2 1.2 1.2 0.9 5.7 0.3

n.7

0.3 10.2

3-9

2-7

30.0

22 26 0 270 0.3 [;.;» 0.3, 33 0 3.0 0.6 0 0.3 0.3 2.1 0.3 3.3 o 8.4 0.3

5-4

o 6.0

9-9

O

37-8

-7 3' 0.3 65.1 0,3 48.0 6.3 7.5 60 4.2 6.0 0.3 1.8 O.Q 7.5 o 16.8 o 38.1 0.6

39-3

0.3 18.6

5-i

3-3

3°-3

Mean value 06570 0.753.6 1.630.0 3.5 5.8 2.0 2.3 1.0,1.4 5.8 1.116.8 0.326.5 0.4

25.5

0.3 13.6

5.0

2.7

29.2

April 1—5 ° 108.0 o 06,0 7,5 51.0 o 24.0 o 1.5 o ' o oo o 30,0 o 30,0 o

37-5

o 1 5.0

0

4-5

39°

6- 10 3-° 57-° ° 1L>75 3° oo.o 4.5 43.5 6.0 21.0 160 7.5 18.0 16.5 3Q.o o 390 o

34-5

1.5 16.5

19-5

4-5 I02>0

''~ "5 '-5 58.5 o 72.0 o 13.5 o 4.5 1.5 7.5 1.5 o 21.0 o 13.5 o 12.0 o

15.0

0 13-5

6.0

o 600

!'• -.2Mar-lrjl ,,:, ,-.../, :,.,, ,.,..,. ,., ,;.,, , . ,, ,,._, ,..V _,., ,.._, ,.; _.y, ,,, -.; ,,.? , ;. ; „-

/ y i

I.-, <>.-<

i-7

;-; >ri

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III. 511

I'ABLE LXXXVI. Sz> in y Dyrafjord.

Hour o— 3

2-4

4-6

6-8

8-10

IO— 13

13— 14

14-7- 16

16- 18

18 — 20

ao — aa

33 — 24

Period

+

—

+

—

4-

—

4-

—

-4-

_

4-

4-

+

+

+

+

—

H-

Nov. 23 — 26

3-6

9°

o

1 8.0

1.8

19.8

3.6

9.0

36

o

o

o

O

0

3-6

o

12.6

7-2

234

5-4

16.3 3.6

18.0

5-4

N'ov.27 Dec. i

O.2

a.o

o.a

o

o

2.7

0

3-2

0.9

o-5

o.a

0.3

O.g

0.4

0.7

o

o.a

°-5

0.5

05

0.7 3.O

'•3

3-4

Dec. 2 — 6

4.1

'•3

0-5

0.9

0

1.6

0.4

0.7

0.4

0.4

o.a

0

I.I

o

0-5

O.3

o

i-3

0.4

0-5

0.4 0.4

4.0

2-3

7- ii

2.2

1.4

0.9

'•3

i.i

1.6

0-9

0.7

0.4

0.7

o-4

o-7

0-5

O.3

0.5

0.7

0.9

a.o

0.9

2.3

'•3 4-7

9-5

3-2

12 — l6

3°

2-5

0.7

1.8

o

0.3

0.4

O.3

O.3

0.4

1.6

O.3

0.7

0

0.5

o.a

0.9

2-5

0-5

1.6

0.7 5.8

3.0

1.8

17 — 21

0.4

I.I

0.3

04

o.a

3.0

O.3

0.7

0.4

o.a

o-5

0.3

0.4

0

O.3

o.a

0

0.4

o.a

0.7

o 3.5

O

2 2

22 — 26

3-2

"•3

3-1

7-7

i-3

7.0

2-3

'•4

1.4

'•4

1.6

2.0

i.i

0.5

I.I

0.7

0.7

0.9

31

5-0

5-6 5-a

166

0-9

27-31

4-5

0.5

I.I

2-3

°-5

5-4

1.4

2.0

0.5

1.4

0.7

04

3.O

O.3

0-5

0.4

0.4

°5

0.4

0.4

°-4 34

7-7

2-5

Mian value

3.0

30

1.1

2.4

0.5

3.0

0.9

1.0

0.6

0.8

0.8

0.6

1.0

0.2

0.6

04

0.5

1.3

09

1.8

1.4 3.7

6.6

22

Jan. 1 — 5

5.8

1-4

1.6

2.5

o-5

2.9

3-4

2.2

6.1

O.2

3-6

0.5

3.0

0

3.O

• I

0.9

1.6

1 0.3

°5

0.5 3.7

05

1.4

6 — 10

a.o

0.7

3.9

1.6

0.7

0.9

i.i

1-4

0.9

0.9

0.7

0.2

o-S

0.4

3-4

0.4

3.9

o.a

o

1.6

0.4 7.6

50

4.1

11-15

3-6

2-7

2-9

1.6

0.7

°-5

i.i

0.4

i.i

0.3

i-4

O

1.6

o.a

1-3

0.4

0.4

0.4

o

4-7

38 5-8

i.i

5-2

16 — 20

32

0.9

2-5

0.9

°-5

1.6

1.8

2.3

3-4

0.7

1.4

«-3

0.7

1.6

3.O

0.4

3-6

0.7

°-7

0.7

0.4 1.3

2.3

0.9

21—25

0.4

3-r

a.o

0

0.9

i.i

°-5

1.8

1.8

1.4

04

1.4

o-5

0.9

0-5

0.4

0.7

0.7

1.4

1.4

0-5 38

O.2

4-7

26 — 30

1-4

13-0

0.9

IO.I

0

7-9

0.4

S.o

3.3

0.4

i 3

0.4

i.i

O.3

3-8

o

5-0

0.3

2.0

2.0

5.4 2.3

5-6

108

Mean value

27

3.6

2.1

2.8

0.6

2.5

1.4

2.2

2.6

0.6

1.5

0.6

1.1

0.6

2.2

0.3

2.3

0.6

0.7

1.8

1.8

3.9

2.4

45

|an.3[ Febr.4

i-3

i.i

0.2

0.9

0.5

0.9

0.7

i.i

i.i

0.7

0.9

O.3

0.7

0.4

0.9

0.7

0.9

0.7

0-9

o

o

0.7

0.5

i-3

Febr. 5-9

'•3

2.2

2-5

7-9

0.9

13.4

0.9

8.6

3-1

1.6

5-6

07

3-8

°-5

4.0

0.9

1.8

1.3

13.1

1.8

13.6

43

'37

3-4

10— 14

4-5

5-"

J-3

5-o

0.5

9-9

3-a

2-3

1.4

3-2

i.i

I.I

i.i

0.7

1-3

04

09

0.5

1.6

2.5

0.5

4-5

8.1

4-5

15-19

O.2

4.0

i.i

0.5

0.2

0.9

0.5

0-5

1.6

0-4

u.O

0.4

2-5

o

3.7

0.4

0.4

4.7

0.2

0.9

o.a

0-5

0.4

0-5

20 — 24

1.8

O.g

2.O

2-9

o.a

16.7

O 2

IS-'

O.2

1.8

4.0 0.5

3-4

0.3

1.4

o

1.8

o.a

O.3

o.a

i-3

I.i

1.4

0.4

'•Vki'5 Mar. i

0.4

i-3

0.4

o-5

0-4

0.4

0.5

o

0.4

0.7

o.u 0.5

o.a

0.3

05

0

o.a

°-7

O

2.9

1.4

0.9

'•4

1.8

Menu value

1.6

2.4

1.3

3.0

0.5

6.9

1.0

4.3

1.3

1.4

2.5 0.6

I

2.0

0.3

1.8

0.4

1.0

1.4

2.5

1.4

2.7

2.0

4.3

2.0

March 2 — 6

2.0

7-9

i.i

5-4

0.9

3-8

i-3

2.O

'•3

0.4

1.4

o-5

3-2

o

1.6

o

i-3

'•3

0.5

1.6

2.9

1.4

'3-3

4.0

7-n

9-7

43

23

'3-7

0.2

1 6.2

i-3

7-4

4.9

i.i

7-7

0.4

7.6

o

32 0.2

3.9

2-5

3-6

54

•58

5°

14-4

3-1

12— 16

10. 1

1.6

4.0

5-0

0.5

31.8

2.3

2.9

2.9

a-3

3.3

1.8

6.7

O.3

3-6 0.7

a.o

3-8

0.4

3.3

7.0

I 6

6-3

7-2

17 — 21

4.3

2-7

0.7

o-5

0.4

2.7

1-3

1-3

i-3

I.I

1.4

i.i

o.a

0.4

o

0.4

o

0.7

0

3-3

M

i 8

8.6

1.4

22 — 26

0.4

3-7

0.4

0.7

o

i-3

0.9

0.4

0.7

0.9

2-3

04

0.7

0.4

0.4

o

O.3

0.7

0.4

0-5

3-2

09

1 2.1

0.9

27-31

1.6

9-7

o

8.3

0

6.8

2.3

2-9

4-3

0.9

2-7

°-5

i.i

0

0.5

i-3

O.3

3-8

0.4

3-6

3-'

3.9

8-5

2.O

Mean value

4.7

4.8

1.4

5.6

0.3

8.8

1.6

2.8

2.6

1.1

3.0

0.8

3.3

0.2

1.6

0.4

1.1

2.1

0.9

2.6

5.6

2.3

10.5

3.1

April 1 — 5

4-5

54

o

8.1

0.9

6.3

o

0.9

o

o

1.8

0

0.9

1.8

0

4-5

0.9

1.8

1.8

1.8

4-5

1.8

7-2

2-'

6— 10

3-6

1.8

o

1 6.3

o

5-4

2.7

4-5

2-7

1.8

3.7

16.2

2.7

18.9

1.8 5.4

8.1

0.9

99

3.7

13-5

3.7

3-6

0.9

11-15

1.8

0.9

0

4-5

o

p

o

o

0.9

0.9

o.g

o

0.9

0.9

o

o

o

0.9

o

0.9

1.8

1.8

8.1

o

i '( v.2March3

}.o

/•/

'•>-

1-4

O.J

S-)

1.3

2.6

/.*

l.o

1.9

0.6

I.S

o-J

'•!

" 4

1.2

' -/

'•)

'•9

3.9

l-o

6.O , 2.<)

TABLE LXXXVII.

in y

Dyrafjord.

Hour

O— 2

2-4

4-6

6-8

8—io

IO— 12

12 — 14

14-16

16-18

18—20

ao — aa

22 — 34

Period

+

+

_

+

+

+

4-

_

4-

_

4-

_

•

—

4-

—

+

—

4

-

Nov. 23 — 26

45-5

3-5

28.0

0

31. 0

3-5

3-5

17-5

o

10.5

O

o

0

o

3.5

7.0

35

56.0

3-5

70.0

7.0

84.0

17.5

a 1.0

N'ov.27 Dec. i

0.4

8.4

o

1.4

O

8.1

o

6.7

0.4

2.5

0

0.7

0

0.7

0

o

3-5

0.7

0.4

3-5

0.7

IO.3

0

5-6

Dec. 2-6

3-5

11.9

o

7-4

O

1.4

o

1.8

o

0.7

o

1.8

0

0.4

1.4

o

3-5

0

1.8

0.7

a. i

0

1.8

4-9

7 — I"

3-3

4.6

I.I

I 1. 2

2-5

0.4

0.4

0.4

0.7

I.I

5.3

0

6.7

o

1.8

0

3-3

1.8

63

3-2

5-3

23.8

49

228

12— l6

5-6

n.6

o

7.0

4-9

0.4

0.4

0.7

o

0.4

0.4

0.4

I.I

0.4

2.5

0.4

9.8

0

3-2

i.i

0.7

II 9

0.4

7-7

17 — L'I

o

2.1

o

2-5

0

5-6

0

32

o

0.4

0

o

0.7

o

0.4

0

0.7

0.4

4-2

0.7

i.i

0.7

07

2.1

22 — 26

32.1

4'9

4-2

17.9

0.7

22.1

o

38.9

0.4

7.0

4.6

1.4

2.8

o

0.4

0.4

i.i

0.7

3-5

9.1

3-9

33.1

133

10.9

27 — 3'

3-2

39

0.4

7-4

0

7-7

0

9.8

o

9.1

o

1.8

0

0.4

0

0.4

0.7

0

0.7

i.i

o

5-6

7-4 7-7

Mean value

6.3

6.5 1.0

8.9

1.4

6.3

0.1

9.1

0.2

3.1

1.7

0.9

1.9

0.2

1.1

0.2

3.2

0.5

3.3

2.7

2.2

10.7

4.8 94

512

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

TABLE LXXXV1I (continued).

n

Dyrafjord.

Hour

0 — 2

2 — 4

4-6

6-8

8—io

IO— 12

12 — 14

14—16

16-18

18-20

2O — 22

23-24

Period

4-

—

+

—

+

—

4-

—

+

—

+

—

+

—

+

•+•

—

-r

_

+

+

Jan. 1-5

2.8

15.8

1.4

13.0

0

56

o

10.9

0.4

3-9

O

1.8

0

i.i

1.4 o

4-9

0

2.5 o

0.4

4.2

0

10.2

6— 10

0.7

9-i

0.7

10.9

o

28.7

o

6.7

0.7

0.7

0

o

0.4

0

3-9 0-4

6.0

o

i.ij ..4

I.I

37-5

0

23-8

11-15

2.1

16.8

2.5

2.1

a.8

0.4

I.I

I.I

1.4

0

o

0.7

0.4

0

0 0

0

0.4

4.3

2.1

1.8

17.9

I.I

8.4

16—20

0.4

13.0

r.i

8.8

0.4

6.0

o

10.9

0.4

4-9

0

I.I

0.4

0.7

2.1 0.4

3-5

2.1

3-5

2.1

i.i

2.8

0

I8.9

21 -25

0.4

10.9

0

9-5

0.4

5-6

0.4

1.8

0.4

2.8

0.4

0.4

O

0

0.4 ; o

2.5

0

2.8

2.8

2.1

228

0.4

11.2

26 - 30

39-2

5-6

17.2

3-2

2.1

39

o

i5-i

0

'9-3

o

4.6

3-5

o

6.0 o

8.8

0.7

2.1

21.7

I.I

13-7

41-3

6.0

Mean value

7.6

11.9

3.8

7.9

1.0

8.4

0.3

7.8

0.6

5.3

0.1

1.4

0.8

0.3

2.3

0.1

4.3

0.5

2.7

5.0

1.3

16.5

7.1

13.1

Ian. 31 Febr.4

2.1

5-6

0.4

5-6

o

3-5

0.7

1.4

o

0.4

0.7

o

0.7

0.7

0.7

0.4

6.0

o

56

0.4

0.4

i.i

0.4

2.5

Febr. 5 — 9

7.0

39

8.4 5-3

5-3

7-4

1.8 JI4.4

o

9.8

1.4

i.i

1.4

0.4

i.i

0.4

0.7

2.8

0.4

26.6

o

399

2.1

40.6

10 — 14

26.3

5-3

o 18.6

0.7

19-3

2-5

n-5

1.8

5-6

o

1.4

0

I.I

o

O

1.4

o

5-6

1.8

i.i

4-9

1.8

'93

15-19

a. i

13-7

o

11.9

o

3-2

0

o

0.4

o

0.4

0

3.1

o

4.6

O

4-9

1.4

2.8

0.7

i.i

i.i

0.7

i.i

20 — 24

0.4

5-3

6.0

4.6

0.4

16.5

o

43.4

o

31.2

o

15.4

0.4

4.6

1.4

0

7-7

0.4

2.1

o

0

5-6

0.4

4-2

Keb.25Mar.i

1.4

1.8

o

7-7

o

17.9

0

37-8

o

14.7

o

5-6

0.4

0.4

0.4

o

3-5

o

7-7

0.4

1.8

6.7

2-5

14.0

Mean value

6.6

5.9

2.5

9.0

1.1

11.3

0.8

18.9

0.4

10.3

0.4

3.9

0.8

1.2

1.4

0.1

4.0

0.8

4.0

5.0

0.7

9.9

1.3

13.6

Harch 2—6

4.9

16.5

16.1

7-7

o

14.4

o

15-4

0.4

2.8

0

o

2.8

0

2.8

o

4-9

o

4.2

°-7

0.7

20.3

i.i

37-1

7-«

12.3

13.0

21.4

9.8

1.8

22.4

0-4

28.7

0

24.9

0.4

7.4

4-9

I.I

4-6

1.8

7-4

1.4

1-4

23.1

0

59'9

1.4

51.1

12— 16

22.4

13-3 16.5

13-3

o

3°-5

o

15-1

o

11.9

0

6.0

1.8

I.I

5-6

2.8

6.3

4-9

6.0

3'2

o

'5-4

1.8

14.4

17 — 2:

0.4

n-5

0

7-4

o

13-3

o

10.5

o

4-2

o

2.8

0.4

1.8

0.4

o

3-9

o

6.7

0.4

3.2

6-3

1.8

18.9

22 — 26

2.1

7-4

0.7

5-3

o

3-9

0

6.0

0

S-2

o

0.7

o-7

0

0.4

o

2.8

o

i.i

o

0.4

6.7

3-9

1 6.8

27-31

27-3

0.7

132

2.8

I.I

9.8

0.7

13-7

o

9.8

o

2.1

1.4

o

7-7

o

'3-3

0.4

0.7

35

o

17-5

7.0

12.6

Mean value

11.6

11.4

11.3

7.7

0.5

15.7

0.2

149

0.1

9.5

0.1

3.2

2.0

0.7

3.6

0.8

6.4

1.1

3.4

5.2

0.7

21.0

2.8

25.2

April 1—5

35-o

14.0

18.3

8.8

19-3

12.3

0

28.0

o

5.3

0

o

1.8

0

'0-5

o

,5.8

o

8.8

8.8

0

2I.O

7.0

35"

6— 10

24-5

3-5

82.3

o

22.8

8.8

12.3

8.8

5-3

8.8

10.5

7.0

3-5

42.0

15.8

22.8

5-3

5-3

o

14.0

10.5 31-5

2I.O

24-5

11-15

15-8

5-3

1.8

17-5

O

12.3

0

5-3

o

10.5

o

3.5

5-3

o

5-3

O

8.8

o

8.8

o

o

12.3

14.0

>°o

)ec.2March3i

8.0

&9

4.6

8.4

l.O

10,4

0.4

12 .7

o i

7.0

0.6

2.4

1.4

0.4

2.1

0.3

4-5

0.7

3.8

4-i

1.2

14.}

•/•"

';-,-

THIRD SERIES.
THE STORMINESS AS A FUNCTION OF TIME.

Matotchkin Schar.

TABLE LXXXVIII a. (Unit y)

Interval.

sfa

S»a

si

t

on

ST

Sep. 3-7

_

—

_

_

—

—

8-12

—

—

—

— -

-

—

-

l8 — 22

—

—

—

—

I

—

23 — 27

—

—

—

—

—

—

Sep.28Oct.2

-

-

-

—

—

-

_

Month.

—

-

-

-

-

—

-

Oct. 3-7

l.O

'•7

0.7

0.8

0-5

0.8

3-3

8 — 12

2-5

9i

l.O

5-7

0.6

6.6

15-2

13 ~ '7

0-5

3-3

0.4

o-9

0.2

1.4-

4-3

18-22

0.6

2.7

0.6

1.5

O.I

2.1

4-5

23 — 27

4-i

20.8

1.7

n-3

3-5

99

31.1

Oct.28Nov.i

I l.O

31-3

7.8

17.2

6.7

7-4

5I-I

Monlh. i 3.3

115

2.0

6.2

1.9

4.7

18.2

Kaafjord.

TABLE LXXXVIII b. (Unit ;-)

Interval.

si

c"
o//

SpD

SnD

SPy

crn
Of

8T

Sep. 3-7

09

0.7

0.9

1.2

0.9

1.6

3-6

8-12

25

3.6

2.O

2-3

3-7

3.0

100

13-17

0.4

05

0.6

1.2

0.4

1.2

2-5

18-22

3-5

125

1.9

7-9

4-2

"S3

27 o

23-27

O.2

30

0.4

2.1

i.i

5-4

7-7

Sep.28Oct.2

o-3

9-2

1.2

5-a

l.O

14-5

19-3

Month.

1.3

4.9

1.2

3.3

1.9

6.8

11.7

Oct. 3-7

°-3

0.4

0.6

0.6

0.4

1.2

2.2

8—12

0.7

5-3

0.9

3-5

r.6

4'i

9-3

i3-n

O.I

O.I

0-5

0.4

O.I

09

1.4

18 — 22

O.I

0.8

°3

1-3

O.2

2.O

2.8

23-27

2.2

n.8

1.8

7-3

4-5

13-4

24-5

Oct.28Nov.i !

II. I

20.5

6.4

10. 1

6.5

23.0

46.2

Month.

2.4

6.5

1.7

3.9

2.2

7.4

14.4

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III.

513

Matotchkin Schar.
TABLE LXXXVIII a (contin.). (Unit y)

Kaafjord.
TABLE LXXXVIII b (contin.). (Unit y)

Interval.

si,

si

SPD

c"

•J D

OP

0 K

<?"
OK

ST

Nov. 2 — 6

0.5

8.7

0-5

3-5

i.o" 5.6

12.0

7-n

»•»

'•3

°-3

0-5

O.2

1.6

2.6

12 — 16

3-°

2.8

1.2

2-5

1-7

2.8

8.2

17 — 21

I.O

9-7

0.4

5-5

i-7

6.0

14-5

22 — 26

9.8

3°-7

7-7

27.1

14.4

44-3

794

\ov.27 Dec. i

1-3

1.8

0.4

2-5

I.I

1.8

5-1

Month.

2.7

9.1

1.8

6.9

3.4

10.4

20.3

Dec. 2—6

0.7

1.8

0.4

1.4

0.4

2.4

4-1

7-ij

1.9

3 i

I.O

2.8

2.O

7-3

1 1. a

J 2 — 16

0.6

3-1

0.6

3-4

07

6.2

8-5

17—21

°-3

1.4

0.4

o.5

O.g

0.9

2-5

22—26

5-9

16.4

2.4

7.6

2.7

19.8

33-2

27-31

i.i

2.9

07

1.2

1.8

3-7

7-i

Month.

1.7

4.8

0.9

2.6

1.4

6.7

11.1

Jan. 1-5

i-7

3-1

0.9

1.6

1.9

5°

8.7

6— 10

a-3

3-4

0.4

2-4

3-i

38

9.4

11-15

1.2

2.6

0.8

1.8

1.6

5-3

».:•;

16 — 20

3-4

2.O

1.2

1-3

4.0

3-5

8.8

21 —25

I.O

4-7

0.6

3-5

i.i

7.0

107

26 — 30

5-i

3i-5

3-i

14.0

3-i

8.6

42.0

Month.

2.5

7.9

1.2

4.1

2.5

5.4

14.7

Jan. 3 1 Feb.4

1.9

0.2

0.9

0.2

1-4

o.a

2.8

Feb. 5-9

4.2

I3.6

2.O

7.6

2.9

12.6

25-5

10— 14

1.8

9-1

0.9

4-5

2.7

6.4

15-2

15—19

2.0

2.1

°-5

2.2

09

6.4

88

20 — 24

i-7

2-5

'-7

0.4

3-°

1.6

6-5

Feb. 25 Mar. i

1.6

1-7

1.6

08

4-5

1.4

7.2

Month.

2.2

4.9

1.3

2.6

2.6

4.8

11.0

March 2 — 6

—

—

_

_

_

—

7— ii

—

—

—

—

—

—

—

Oct. 3 March i

2-S

1-6

1.4

•#•/

*•}

6.4

If. I

Interval, j filjj

on
&H

si

cm

o#

•s"i-

fn

*v

NT

Nov. 2 — 6

0.4

l H

0.4

1-7

0.6

a.a

4.1

7-n

O.2

o-5

O.I

0.6

0.1

1.8

2.2

12 — 16

0-4

1-3

°-5

19

1.4

3-i

5-4

17 — 21

°-5

36

°5

a.8

°-5

i-4

5-6

22 — 26

14.9

30-3

6.0

i'6.7

'•3

7.6

5i-3

Mov.27 Dec. i

o.a

0.8

°-5

0.6

o

0

i-5

Month.

2.8

6.4

1.4

4.1

0.7

2.7

11.7

Dec. 2 — 6

0.4

0.4

0.4

0.9

o

O.I

1-5

7-n

2.4

0.7

0.7

2-3

0

o

4.2

12— 16

i.i

I.O

0.7

2.3

o

o

3-6

17-21

O.2

o.a

o-5

0.4

o.a

0.4

i.i

22 — 26

3-9

10.4

3.6

5-6

3-7

13-3

23-5

27-31

0-3

i-5

°-3

a. i

1.2

3.1

4-4

Month. 1.4

2.4

0.9

2.2

0.9

2.6

6.4

Jan. 1—5 i.o

0.8

i.a

1.6

i.i

1-7

4.4

6— 10

°-3

I.O

I.O

1.3

i.i

i-5

3°

11-15

o-5

07

I.O

i-5

i-7

2.1

4-7

16 — 20

0.8

0.6

1.2

1.3

3-3

1.2

5-3

21—25

0.7

I.O

0.9

2-3

i-5

3.7

5-5

26-30

1.8

n. i

1-4

4.7

i-9

8.8

17.8

Month.

0.8

2.5

1.1

2.1

1.7

3.0

6.9

Jan.3i Feb.4

O.2

O.I

0.4

0.3

0.9

°-3

1.4

Feb. 5-9

2.8

7-3

1.4

5-8

3-3

152

22.3

10— 14

1-7

3-7

0.7

3-5

1.9

7-8

II.8

15-19

0.8

0.4

0.6

i-5

2-3

0.5

3-6

20— 24

o

0

1.6

0.6

06

2-5

(3.9)

Feb. 25 Mar. i

0.9

0.9

0.9

0.9

2.1

3-4

6.0

Month.

1.1

2.1

0.9

2.1

1.8

4.9

82

March 2— 6

2.2

1-3

1.2

i-3

2.6

4.8

8.5

7-n

38

6-3

2-5

3-8

4.2

i3-5

21.3

Sep. 3 March i

1.6

4.1

1.3

2.9

I-i

46

99

Axeleen.
TABLE LXXXIX a. (Unit y)

Dyrafjord.

TABLE LXXXIX b. (Unit y)

Interval. ,S';'/

ll

'ST,

CrP

<5/>

on
«/>

S"v

si

ST

Sept. 3-7

6-3

II. I 5.6

8.0

160

7-6

32-3

8-12

8.2

I2.O

6.0

3-2

12.3

i-7

26.2

13~ 17

i-7

5-9

1.8

2.9

6-5

3-2

13.2

18 — 22

n-5

19.1

5-7

9-3

49.6

6.6

65.6

23-27

5-2

13.6

3-3

5-5

199

4.1

3'.8

Sep.28Oct.2

2-5

16.2

3-3

4.1

3°-7

5-8

41.4

Month.

5.9

13.0

4.1

5.5

22.5

4.8

35.1

Oct. 3-7

1.9

3-4

1-4

2-3

6.4

i-3

10. 0

8 — 13

3-°

6.8

39

3-i

10.4

5-9

20.3

13-17

0.7

7-4

3.8

1.8

7-i

i-3

12.6

18 — 22

1.2

9-1

3.1

4-9

7.6

5-7

18.2

23-27
Oct.28Nov.i

5-4

2.6

23.2
40.8

6.8
7-9

8.9
16.1

35-4
639

12.0 57.5
7.6 84.9

Month.

2.4

15.1

4.2 i 6.2

21.8

5.6

33.9

Interval. . SP,,

0«

OH

OP

OD

si

Spv

oil
Of

ST

Sept. 3-7

—

—

—

—

—

—

-

8-12

—

—

. —

—

—

—

—

13-17

-

-

-

-

—

-

-

18 — 22

—

—

—

—

—

—

—

23 — 37

—

—

—

—

—

—

—

Sep.28Oct a

—

-

-

-

—

-

-

Month.

—

—

—

—

—

—

—

Oct. 3—7

_

—

_

—

—

—

—

8-12

—

—

—

—

—

—

—

J3-I7

—

-

—

—

—

—

—

18 — 22

—

—

—

—

—

—

-

23-27

-

-

-

-

—

-

-

Oct.28Nov.i

—

—

—

—

—

—

-

Month.

-

-

-

-

-

-

-

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Axeleen.
TABLE LXXXIX a (contin.). (Unit y)

Dyrafjord.
TABLE LXXXIX b (contin.). (Unit y)

Interval.

SPH

si

C.P

VD

o«

OD

CrP

Oy

O n
o Y

ST

Nov. 2—6

0.7

8.4

3-2

3.0

14.2

I.O

•8.5

7-n

0.6

4.8

0.4

3-o

8.3

o-5

10.8

12— l6

4-4

"•3

2.1

7-i

15.8

ii. i

32.4

17 — a i

2.O

13.0

2.4

5-3

15.5

4-6

26.2

22 — 26
Nov.27Dec. i

5-0

3.6

58.8
11.4

8.4
'•5

205
2.9

81.7

8.3

11.5 116.6
3-5 18.9

Month.

2.5

17.9

3.0

6.8

23.9

5.4

37.2

Dec. 2-6

3.8

8.9

J-9

3-7

6.2

2.7

'5-7

7-n

3-7

15-°

2-3

6.0

13.4

4.2

26.9

12— l6

I 2

16.0

1.8

5-1

11.9

1.4

22.8

17 — 21

i-7

3-5

1.6

I.O

4-3

4.1

10.2

22 — 26

S.o

27.6

5-4

8.0

20. 1

26.8

57-8

27-31

a-5

92

3-2

3-i

6.2

2.8

16.1

Month.

2.8

13.4

2.7

4.5

10.4

7.0

24.9

Jan. 1-5

1.9

13-6

2.9

4-3

4-7

5-6

19.9

6 — 10

4.6

104

3.1

4-3

7-2

3-5

18.5

11-15

3-1

136

2.8

4.1

8.8

2-5

21.3

16 — 20

36

10.3

3-7

2.9

6.2

7-5

20.5

21 — 25

3-5

11.5

3.8

39

9-4

9.9

24.8

26 — 30

5-8

19.1

4.2

8.9

36.0

4-5

49-3

Month.

3.6

13.1

3.1

4.7

12.0

5.6

25.7

Jan. 3 1 Febr.4

'•7

5°

2.7

'•4

1-5

2.0

8.6

Febr. 5-9

5-0

20.3

5-7

80

31-5

4.8

39-0

10—14

3-9

M.O

2.9

6.5

10.3

1.9

235

15-19

3-0

8.7

2.9

2.9

3-8

3-0

14.7

20 — 34

5-0

5.9

3-4

4.6

9-4

5-7

20. 2

Feb.2sMar. i

3-8

8.6

2.6

3-7

8.0

2.2

17.3

Month.

3.7

10.4

3.4

4.5

9.1

3.3

20.6

March 2 — 6

3.6

13-7

S-i

5-4

146

19.7

39-4

7-n

5-5

27.9

71

1 1.6

48.7

10.7

70.7

12— 16 7-1

20.9

6.2

7-5

27.6

14.6

52.4

17 — 21

1.4

II. 2

3-0

3-9

IS-1

5-3

24.9

22 — 26

1.9

7.0

2-9

3-0

9-9

1. 1

15.4

27-31

3-o

>3-4

4-9

7-5

11.4

5-i

26.4

Month.

3.6

15.7

4.8

6.5

21.2

9.4

38.2

April 1 — 5

S.o

33.1

5.0

I I.O

26.6

14.2

52.1

6— 10

9-9

3i-5

10.2

12.9

47.0

29.7

92.7

11-15

9.0

14.9

4-9

4-1

is-1

23.6

44.7

16—20

4-1

14.0

9-2

2-3

1.6

1 8.6

29.4

21-25

4-9

11.9

5-0

3-7

7-3

IO.O

25.6

26 — 30

5-7

19.8

5.5

9-5

31-0

6.9

48.0

Month.

6.4

19.2

6.6

7.2

21.1

17.2

48.8

May 1 — 5

5-8

16.9

6.4

8.2

36.0

8.1

5'-7

6 — 10

(9.8) (23.6)

8.5

9.6

19.1

14-3

50.6

11 — 15

6.1

18.8

7-7

6.3

13.8

10.3

37-3

16-20

r°-5

4-9

5-5

4.1

'3-9

8.3

28.6

21 — 25

15-5

14-3

7-1

12.2

25.6

22.3

59-6

26 — 30

2O.6

22.6

6.5

I8.4

38.0

17-3

74-4

Month.

11.4

16.8

6.9

9.8

24.4

13.4

50.4

Sept.sMayso

4-1

IJ.O

4-3

6.2

tS.J

S.o

)j.o

Interval.

oP

OH

SKH

OP

«Z)

O»
»1>

Sp?

on
0 V

,S'T

N 6

7 — 11

TO T/>

13 — ID
17 — 22

_

—

_

—

23 — 26

13.°

45-3

7.2

6-5

ii. i

22.8

68.7

Nov.27Dec.i

M i mt 1 1

3.3

3-7

0-5

I'3

04

4.0

7.6

1I1UI11I1.

Dec. 2-6

3-0

3.5

I.O

0.8

1.2

2.6

7-7

7-n

4-5

7-4

1.6

1.6

3-5

5.7

'5-3

12— l6

4.4

5-8

I.O

1-4

2.4

3.5

12.1

17 — 21

I.O

0.8

0.2

0.9

0.7

1.5

3-0

22 — 26

3-4

22.9

3-4

3.7

48

1 1.4

3'-7

27-31

1-5

6.9

J-7

1.6

I.O

4.6

10.7

Month.

3.0

7.9

1.5

1.7

2.3

4.9

13.4

Jan. i — 5

2.6

6-5

3-1

i-3

1.2

5-5

12. 1

6 — io

2.9

5-a

1-7

1-7

1.2

9-9

14.2

11-15

3-°

3-4

1.6

1.8

1-5

4-2

9.2

16 — 20

4-4

5-1

i-9

i.i

I.I

6.0

I2.3

21—25

3-8

5-7

0.8

M

0.9

5-7

11.7

26 — 30

7-5

13-3

2.4

4-4

I O.I

7.8

28.3

Month.

4.0

6.5

1.9

2.0

2.6

6.5

14.6

Jan. 31 Febr 4

J-5

2.9

07

0.7

15

1.8

57

Febr. 5 — 9

7-5

17-5

5-2

3-8

2-5

127

30.6

10—14

5-5

13-1

2.1

33

3.4

7-9

22.4

15-19

3-3

4-5

I.I

i.i

1.6

2.8

8.4

20—24

2.0

18.1

i-5

3-2

1.6

10.9

24.0

Feb. 25 Mar. i

2.9

3.7

o.5

0.8

1.5

8.9

12.4

Month.

3.6

10.0

1.9

2.2

2.0

7.5

17.2

March 2 — 6

9-5

13.7

2.6

2.4

3.2

9-6

269

7 — 11

14.6

24.8

6.1

4.9

4-7

20.4

48.0

12— 16

7-9

22.5

4.0

4-3

5-0

I I.O

35-4

17 — 31

3-7

10.5

1.6

1.4

1.4

6.9

16.7

22 — 26

2.2

8.0

1.8

0.8

I.O

4 2

[i,8

27-31

12 I

13.6

2.1

3-6

6.0

6.1

29.0

Month.

8.3

15.5

3.0

2.9

3.6

9.7

27.9

April 1 — 5

11.9

26.6

i-9

2.9

9-7

ii. i

44.0

6—io

15-4

41.0

4-3

6.5

17.8

14.8

66.0

11-15

6-9

,8.5

I. a

0.9

5-o

6.4

27.9

16 — 20

—

—

—

—

—

—

-

21 — 25

-

—

-

—

-

-

-

26 — 30

—

-

-

—

-

-

-

Month.

-

-

-

-

—

—

-

May 1 — 5

-

-

-

-

-

-

-

6T _
— IO

11 — 15

I O — 3O

21 — 25

_

—

—

—

—

—

—

26—30

-

-

-

—

—

—

-

Month.

-

—

-

-

-

-

-

Dec. 2 Mar. 3 1

4-7

1O.O

2.1

2.2

2.6

?•'

18.)

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III. 517

THE TOTAL STORMINESS AS A FUNCTION OF TIME AND ITS RELATION TO SOLAR

ACTIVITY.

95. The main object of the investigation with regard to the total storminess was to find any possible
regularity in the occurrence of magnetic storms, especially as regards a monthly period. The existence
of such a period has been recognised by many authorities, but various opinions are held with regard
to its length.

Mr. E. W. MAUNDER (l), from records made at Greenwich, deduced a period of 27.275 days. Mr. ARTHUR
I IARVKY (2), from a study of storms at Toronto, found independently about the same period namely,
27.246 days. Dr. AD. SCHMIDT (8), however, from observations at Potsdam, deduced a period of 29.97 days.

A period of about the same length - - about 26 days(4) --is found for most magnetic elements,
lor atmospheric electricity and northern lights, and for a great variety of phenomena connected with
meteorology. All these periods may in some way be related; but it is not my intention to overload
the problem by treating such possible connections. We shall in the following pages confine our atten-
tion to the treatment of the period for the »polar storms«, as this period has actually manifested itself
during the period of our observations.

The variation of total storminess at the Norwegian stations is given in tables 88 and 89 and graphically
represented by the curves fig. 189. As might be expected, the curves for the four stations show almost
exactly the same variation, there being merely a difference as regards absolute magnitude. If, for one
station, the absolute storminess for each component were represented by curves, we should see — what
seems almost a matter of course -- that the storminess varies in very nearly the same way for all
three components.

We notice that a period of about one month is extremely well marked at all four stations.
The maxima seem to fall into two groups, the first of these having the first maximum at the end of
September, and the last at the end of January, while the second group has its first maximum at the
beginning of February and the last observed maximum at the beginning of May.

If we do not divide the maxima into groups, but consider the two occurring at the end of January
and the beginning of February as belonging to the same maximum, we deduce a period of 30.7 days as
the average of 7 periods, the first period beginning with the maximum on September 30 and the last
one ending with the maximum on May 3.

Considering each group separately we get :

From the first group 30.0 days, mean of 4 periods
— » second — 28.3 » » 3

Mean 29.2 days.

I1) E. W. MAUNDER: The .Great" Magnetic Storms, 1875—1903, and their Association with Sun-spots, as recorded at the

Royal Observatory, Greenwich. Monthly Not. 64. 1904.

,,Magn. Disturb. 1882 — 1903, etc." Monthly Not. 65, 1904.

.The Solar Origin of Disturb, of Terr. Magn." Astron. Nachr. 167. 1904.

,,Magn. Disturb, as recorded, etc." Monthly Not. 65, 538-559 and 666-681, 1905.

.The Solar Origin of the Disturb, of Terr. Magn." Astroph. Journ. ar. 1905.

Journ. Brit. Astr. Assoc. 16. 1905.
I-) Nature. Vol. 83, p. 354. 1910.

(3) AD. SCHMIDT: Ergebnisse magnetischer Beobachtungen in Potsdam im Jahre 1907, p. 29. Published 1910.
(4l ARRHF.NIUS: Lehrbuch der kosmischen Physik p. 146.

Hirkflaiul. The Norwegian Aurora Polaris Expedition, 1902—1903.

=;i8 HIRKFI.AM). TIIF NORWFI.IAX At:RORA POLARIS KXPKDITIOX, igO2 1903.

These numbers are deduced from the curves giving the storminess of each five day period. In
these smother! curves there may be an error in the determination of the actual time of occurrence of
the maxima.

In curve . /, tig. 190 the variation of storminess is represented for each (lay during the period of
observations. The curve represents the n/isoliilc storminess S"t or .S'w lor Axeloeii. The curve for the
total storminess would not he essentially different.

In the following table are given the most marked maxima, the principal maxima belonging to the
two groups arc- marked in the third column.

I'AliLK XC.

Time
Sept.

,f Max.
95

Prineipa! Principal

Si/e ot" Max. . . ii • i •!•• ,- -VT
Max. Period 1 line ot Max.

arbitrary unit.
Group I Days

10.7 Jan. 29.5

Principal Principal
Si/e ol Max.
.Max. Period
arbitrary unit.
Group 11 Days

6-5

«

i 1-5
19.2

8-5
16.8

Kebr. 7-5
10.5

-5-1 1
No. i"

"•3 >

„

22.2

'5-9

'4-5

0-8

Oct.

3O.O

lo-5

i i.f> No. i'
7-8

a i. 5

95
10.8

28.9

„

2 ,.2

,2.3 [ 30.5

March 1.5

7-°

-

20.6
30-5

20.7
32.1 No. 2'

7-5

,. 12.2

IQ.8 \

10.6 \ '

Nov.

5' 5
13.0

6.4
9-5

2-,0

3' o

8.2

10.6

28.1

a

-3 5

33-0 No. 3' April 5.4

22.4 \ T „ >

Her.

0.5

7-o

8.6

22.1 /

10.5

29-- „ 1 1.5

9.T

'5-2

7-3

M-5

73.6

29.1

22. 7

27.0 No. -('

„ -'6.5

i i . r

-7-5

Q-5

May 4.5

,8.0 |

Jan.

4-5

'3-4

34-3

'

12.5

8.8

»

26 o

.5-4 No- 5'

Mean Period of (irou[> I -0.5

Mean Period ot' Group II 28.7

The two groups show a characteristic difference; each of the maxima of the first group consists
mainly of a single top, those of the second group consist of pairs. This fact must strengthen the
assumption that the maxima within each group are closely related to one another. In the fourth column
are given the intervals between successive maxima. The average period becomes 29.1 days, or about
the same as found from the five-day curve-. There seems no interpretation of the results possible leading
to a period of less than 29.1 days.

Ihi period found is very nearly equal to one synodic month, as the time from one opposition of
the moon to the next is 29.53 days. This coincidence would naturally suggest a connection between
the polar storms and the position of the moon in relation to the sun.

On the other hand we know that the polar storms are closely connected with the conditions existing
on the sun, and this connection mu>t point to the rotation of the sun about its own axis as the cause

PART II. POLAR MAGNETIC PHENOMENA ASH TERREI.LA EXPERIMENTS. CHAP. III.

519

of the monthly period of polar storms. Now it has been found that different parts of the sun rotate
with a different angular velocity. The least synodic period of rotation is about 26.04 days> which is the
period of facula near the equator; the period, however, becomes longer as we get deeper into the sun's
layers, or towards its pole. In the table below is given the synodic period for faculae, for sun-spots, and
for the photosphere.

TABLE XCI.

Heliographic
Latitude

Kaculae
iStratonofl")

Sun-Spots
(Carringtonl

Photosphere
(Duncri

0°

26.0 days

26.8

27.4

•5°

27.1

=7-3

28.4

30°

27.8 —

28.6

29.8

45°

39.5 -

29.8

32-7

The numbers in table XCI, are taken from ARRHENIUS' Cosmical Physics ('). They indicate that for
equal heliographic latitudes the period of rotation increases towards the interior. According to PRINGSHEIM
the angular velocity of faculae, photosphere and sun-spots(2) should be the same for the same latitude.
However this may be, it is commonly assumed that the angular velocity decreases from the photosphere
towards the interior.

We notice that the period found for the storminess cannot be explained merely by the time of
rotation of the sun-spots. The greatest number of sun-spots are found betwen 15° and 20° heliographic
latitude. From this we should expect a period corresponding to that latitude, or about 27.3 days. This
is a_bout the period found by MAUNDER and HARVEY. Such a period of disturbance may well exist, but
it is too small to explain the essential feature of the variation of storminess in our case. If the period
of polar storminess is to be explained by the rotation of the sun, we shall either have to go to points
deep down in the sun's layers, or to points near the poles, for the source of magnetic storms.

As both the moon and the sun give rise to a period such as that found for the magnetic storminess,
the problem of finding out by exact methods the cause of the period becomes a rather difficult one; and
it is hardly possible, by means of purely statistical methods, to decide from which of the^two sources
the monthly period originates. At any rate, if a statistical method could give any answer to this question,
we should have records covering a long period. 1 think, however, we can get a step further by utilising
our knowledge about the physical conditions which might produce the observed changes of storminess.

ON THE POSSIBLE INFLUENCE OF THE MOON UPON MAGNETIC STORMS.

96. There are two main sources of influence to consider :

1 1 1 The moon is the seat of a magnetic field.

(2) The moon is the source of primary or secondary "electric radiation".

It is well known that the direct influence of the moon's magnetic field must at any rate be extre-
mely small, and would cause variations of quite another type than those considered, in the magnetic
storms. But there is still a possibility of an indirect influence, as the presence of the moon's magnetic

i'l ARRHENIUS: Lehrbtich der kosmischen Physik p. 125.
r-'i K. PKIXGSHEIM: Physik der Sonne p. 61.

U1RKELAND : THE NORWEGtAH AURORA POLARIS EXPEDITION, 1902 — 1903.

field will produce a change in the orbits of the cathode-ray particles coming from the sun. It lias been
found by STORMKR that rays which are to arrive at the earth must start in directions that lie within very
narrow limits. Now the magnetic field of the moon might change the direction of the rays, and thus a
number of rays may reach the earth, which otherwise would escape from it. At present, mathematical
investigation has not been carried so far that the magnitude and variation of such an effect can be exactly
calculated.

From a simple consideration, however, we are able to estimate the character and magnitude of tin-
indirect effect of the moon's field, compared with the direct effect of the radiation from the sun.

The earth and the moon are put into an almost uniform field of electric radiation. Let us imagine
a sphere (S) drawn with the earth as centre and with a radius equal to the distance between the earth
and the moon. The radiation which must consist of very stiff" rays, will enter mostly on one hemisphere
and pass out of the sphere on the opposite side. On the surface of this sphere there will be a number of
spots a\ .a->... . a,t where those rays enter that reach the earth.

Let us first consider the case of the moon being so far from the areas a\ a., . . . an that ii>
magnetic field at those spots is very weak. This only requires the distance from the moon to the spots
to be of the order of the radius of the sphere, because we know that the direct magnetic effect of the
moon upon the earth is very small.

On this assumption, the moon has no appreciable influence on the rays that come directly from
the sun to the earth; but we nevertheless have to consider the effect of those rays which pass near
to the moon and are so greatly deflected that their previous history, so to speak, is totally wiped out
so as to leave the moon in every variety of direction. The earth will be exposed to the action of t\y.
fields of radiation, one from the sun and the other from the moon. But the rays, of which the history
is effaced are scattered in all directions, so that the field of radiation from the moon must be extremely
weak as compared with that from the sun. As the plane of the moon's orbit forms a comparatively
small angle with the ecliptic, the directions from the moon are distributed very nearly in the same way
in relation to the earth's magnetic field, as the directions from the sun ; so that on an average the magnetic
effects produced by the two fields must be in proportion as the intensities of the radiation.

A ''similar consideration will show that the effect of any secondary radiation caused by the impact
of electric radiation on the moon must be very small compared with the direct effect from the sun.

If, however, the secondary electric rays are caused by radiations such as light or y rays which do
not produce- magnetic effects themselves, or if the moon is the source of primary electric radiation,
are a priori unable to say anything definite about the order of magnitude of the effect of the moon as
compared with that of the sun. We shall have to look at the observed magnetic effects for information
regarding this point, and, in fact, the diurnal distribution of disturbances will give us some information
in this respect.

In the case of the moon being near to the areas a\ a.> . . . an the effect of the rays of which the pre\
history is wiped out, will be of the same order as before, but now the moon may have an appreciable
effect on the rays which would otherwise have reached the earth. The moon's field in this case
act as a shield for the rays, and thus be able to diminish the effect of an already existing radiation. It
might be possible that the perturbations consisted in a diminution of a radiation which was constantly
being given out; effects of this kind are not impossible. But we cannot suppose that the great polar
storms here considered have been caused in this way. That the polar storms are due to something
positively occurring is evident from the connection with aurora borealis and sun-spots, and besides great
storms are found in the most varied positions of the moon.

I'AKT II. POLAR MAGNKT1C P1IKNOMKXA AND TKRRKI.l.A KXPFRIMK.N TS. CHAP. III. 521

THE SEAT OF THE RADIANT SOURCE.

97. The eruptive character of the occurrence of magnetic storms, indicates that the period might be
explained by a periodic change in the intensity of the source, just as certain periods have been found
for the eruption of geysers.

But such an explanation cannot be maintained; for, owing to the rotation of the sun, the radiation
would have to issue from a number of sources, and it is hardly conceivable that a large number of
sources would vary with the same period and be in the same phase.

The only possible explanation left, seems to be that the period of storminess is the synodic period
of revolution of some layer of the sun. From this view it follows, that if the storminess is to show only
:>ne distinct monthly maximum, there must be a fairly limited region of the sun, the activity of which
as a radiant source, is predominant, and we see from the curves fig. 190 that it must maintain its pre-
dominance during several revolutions of the layer to which the source is attached.

If such a source on the surface of the sun gave out electric radiation from a surface element
according to the same law as for the radiation of light, the storminess due to such a source ought to vary
approximately according to a sine or a cosine law, or

ST = A sin "in -_

in which T is the time of revolution of the source ; and in which it is to be remembered that only positive
values have a physical interpretation. We should get a number of separate waves according to this
sine law, the effect of the predominant source would be felt during half the period, or 14.6 days. I he
effect would increase somewhat rapidly, but in the neighborhood of the maximum it would keep nearly
constant for several days.

The curves of storminess, however, show a very marked difference from the sine form. The effect
of the predominant source, far from being felt during half a period, is generally only felt for a few
days at the time of the maximum, which occurs suddenly, and assumes a very pointed form.

How can this discrepancy be explained? There are only two possible explanations,

1 1 1 That the suddenness is due to an eruptive character of the source, or

(2) That the radiation is greatly predominant in certain directions.

In view of the violent changes observed in the upper layers of the sun, great and sudden changes
in the ray-emission will probably take place and influence the character of the phenomenon; but such
changes alone are insufficient to explain the character of the variation in storminess. Above all, it can
hardly account for the comparative regularity with which the maxima occur.

On an average., the source must be quite as active when it is turned away from the earth as when
it is turned towards it. If the maxima were solely determined by the eruptive changes, there would be
far greater changes in the length of the period of storminess than are actually observed. We see, from
the curves, that the periods within each group of maxima only show comparatively small differences. It
is, of course, conceivable that there might be a period of variation of the source, which could produce
the observed effect; but from a physical point of view it is scarcely probable that a period of eruption
would be so regular, and farther that it would coincide with another quite independent period - • the
period of the sun's rotation.

On the other hand, the second assumption, namely that the radiation is greatly predominant in
certain directions, gives at once a simple explanation of the variation of storminess.

According to this view, the radiation would be mainly restricted to certain narrow pencils starting
from the source.

When the earth comes sufficiently near to such a pencil, there will be a perturbation.

522 FilRKELAND. THK NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Let us suppose, that the position of the source is such that the pencils strike the earth and produce
a perturbation. Let at the moment considered the heliographic longitude of the centre of the sun's
disc be io, and that of the source L To explain the observations we must assume that the angle
A. — /.„ cannot vary greatly for the various pencils of rays which strike the earth; for if the pencils
could start from the source in the most varied directions in relation to the surface of the sun, the effect
would be the broadning out of the maxima, or the causing of an enormous variation in the interval
between successive maxima. As long as the maxima keep their pointed form, and occur at fairly
constant intervals we are justified in assuming that the final directions of the pencils relative to the
sun's surface are, roughly speaking, the same.

As the only singular direction from a plane is its normal, and as there is only one predominant
direction of the pencils, I think there can be little doubt that the radiation starts almost perpendicular to
the surface of the sun. If, after starting, the rays were not exposed to any deflecting field of force
from the sun, A — /.<, would be nearly equal to zero.

It has been found by many observers, that there is a lag, or interval between the passage of a
sun-spot across the central meridian, and the occurrence of the magnetic storms.

On the assumption that sun-spots act directly as a source, and the velocity of propagation of the
radiation is at least as great as that of ordinary cathode rays, the lag would mean that /. — /.„ had a
positive value. In order, then, that the radiation, starting normally, shall reach the earth, the existemv
of deflecting forces is necessary. Assuming that the deflection is due to a magnetic field, and knowing,
from other considerations, the stiffness of the rays, I have recently (') calculated the intensity of magne-
tisation of the sun, that would account for the observed lag.

The active area must be comparatively limited, for it is very seldom that a storm lasts for more
than 24 hours. Very often several storms occur in succession at the time of the maximum, which indi-
cates that the active area is more like a group of active spots.

The theory of the confinement of the electric radiation causing magnetic polar storms, to certain
sources, which send out narrow pencils of rays, was deduced as a natural consequence of the character
of the variation in storminess, and is the one that I have adopted in my previous works on these
matters, as, for instance, in "Recherches sur les Taches du Soleil", read before the Christiania Videnskabs-
selskab on Feb. 24, 1899, where, on page 2, the view is clearly expressed in the following terms:

"Dans un me'moire inse're' aux Archives des sciences phys. et. nat. Geneve, juin 1896, j'ai chcrche
a expliquer la relation existant entre les taches du Soleil d'une part, et les aurores bor6ales et les
perturbations magnetiques de 1'autre. Dans mon hypothese le Soleil 6met de longs faisceaux de rayons
cathodiques, qui sont en partie 1'objet d'un succion dans 1'atmosphere terrestre de la part des poles
magnetiques, chaque fois qu'un des faisceaux cathodiques en question frole notre planete d'assez pres.'

It is a matter of great interest that subsequently Mr. MAUNDER, from a study of perturbations
observed at Greenwich, was led to the very same conclusions.

Nor does the physical side of the question present any serious difficulties. In the corona and the
comets' tails, we are actually examining radiations having definite directions. The difficulty in this
respect is not that we are in want of a possible explanation, but rather that we have too many
of them.

In order to explain the properties of the corona and the tails of comets, it has long been supposed
that the sun should possess an electric field, in which case the cathode rays might leave the sun in a
direction perpendicular to its surface, just as, in a vacuum-tube, the cathode rays start perpendicularly tc
the cathode surface.

(') K. UIRKEI.AND: C. R. 1910.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. III. 523

Further, in the pressure of light, we have a force that would also be able to carry small dust-
particles, charged or uncharged, away from the sun. This force undoubtedly plays an important part in
the economy of the universe, and has been utilised by ARRHENIUS to explain aurora borealis and
magnetic disturbances. Our hypothesis does not, however, require the influence of radiant pressure.
If the rays are suddenly brought into being e.g.as cathode or £ rays of great penetrating power, and
consequently with a velocity very nearly equal to that of light, the influence of the light-pressure on
the orbits of the rays will be insignificant.

The recent discovery by HALE of strong magnetic fields, existing in the neighborhood of sun-
spots, furnishes us with a new possible explanation; for it has been found that the lines offeree are
nearly normal to the surface of the sun, and in order to get out, the rays would have approximately to
follow the lines of force.

The most usual way of obtaining a beam of nearly parallel rays, is to let the radiation from the
source pass through an aperture. Applied to the sun, it would mean that the radiation originating mostly
from the interior, could only get out through an aperture in the sun's upper layers.

We are not in possession of sufficient data to tell which of these is the right explanation. It may
even be that all of them may be present and play a part in the phenomenon. I think, however, that a
discussion of the various possibilities will be necessary, if we shall hope to attain to a more intimate
knowledge of the mechanism of the solar activity giving rise to the magnetic storms and aurora ; for it
is through the conclusions drawn from each hypothesis that we are able, by comparison with experi-
ments, to test it.

The last purely mechanical explanation by means of apertures is really a very simple and a very
fascinating one, which I think is deserving of attention. The advantage of the "aperture hypothesis" is
that it not only explains that the radiation escapes in a certain direction, but also the fact of its being
confined to narrow pencils. Through the sun-spot-hypothesis of Mr. WILSON, we have long been familiar
with the idea of apertures in the sun's outer layers, and recently EMDEN, in his theory of the sun, has
assumed the existence of vortices with their vortex-filaments ending on the surface of the sun, so as to
form a kind of opening into the interior; and the existence of vortices has been brought to full evidence
trough the spectroheliographic researches by HALE at the Mount Wilson Observatory.

The length of the period of storminess leads us to suppose, that the source, if situated near the
photosphere, would have a latitude of about + 30°. As the sun's equator forms quite a small angle
with the ecliptic, and since the radiation, as we have seen, most probably issues in narrow pencils
perpendicular to the sun's surface, radiation from sources in this latitude would not strike the earth at all.
It it can be taken as a general rule, that the time of rotation increases towards the interior, the source, if
situated nearer the equator, would be below the photosphere, which is what would be expected if the
radiation were limited by apertures.

If we do not accept the assumption of apertures, the question then arises, how are the rays able to
penetrate the great layers of matter above the source? The rays, which produce the magnetic storms
and aurora must have a great penetrating power compared with that of other known electric
radiations; but still they are unable to penetrate more matter than the earth's atmosphere. In
order then, that the radiation from a source situated below the photosphere shall get out, the source
must produce radiation, as a kind of secondary effect, from matter nearer the surface of the sun.
One possibility is, that the source is sending out active matter of some kind, which floats above the
source. We expect that important information in this respect may be obtained from the spectrohelio-
graphic observations of the sun's disc.

The distribution of calcium is especially interesting from the fact that this metal at high temperatures
is found to give out a large amount of corpuscles.

524

HIRKKLAND. THE NORVEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

SUN-SPOTS AND STORMINESS.

98. In fig. 190 the storminess is compared with the occurrence of sun-spots. The storminess is
that of the horizontal Component at AxelOen put up for each day. The sun-spot curves B, C and D are
deduced from the "Results of Measures made at the Royal Observatory, Greenwich, of Photographs of
the Sun taken at Greenwich, in India and in Mauritius".

The curves D give the total visible area of sun-spots for each day during the period of our
observations.

If the radiation started perpendicular to the surface of the sun, it would not be the total visible
area of sun-spots that would be significant with regard to magnetic storms and aurora ; but only the
spots which at the time under consideration were near to the central meridian of the sun. Curve ('
represents for each day the number of sun-spots for which 7S — /.„ <; 10°, where )., is the heliographic
longitude of the sun-spot centres as given in the Greenwich records. The dotted curves in (' and I)
represent the area of the umbra, the curves drawn in ful indicate the area of the whole spot.

Finally the graph B represents the time of passage of the central meridian of the various groups
of sun-spots given in the Greenwich records. At the time of the passage, an ordinate is drawn whose
length is proportional to the largest total area which the group has attained during the time it lias been
observed. Thus the graph does not give the area that the group actually had at the time of the passage.
We have even gone so far as to put up groups, which have not been visible at all at the passage of
the central meridian. The reduction to central meridian has been done by interpolation, or if the group
only appears on one side of the central meridian, we have extrapolated by means of the synodic period
of the revolution of sun-spots.

A comparison between magnetic storms and sun-spots shows thai the af>/>earcnce of Inrgf i;m/<f>s n/
sun-spots (foes not take place so regularly as the principal maxima of storminess. Very often large maxima
of storminess are not accompained by any sun-spots at all.

In the following table are given a number of sun-spot groups for which there seems to be an
undoubted coincidence with magnetic storms.

TABLE XCII.

Sun-spot Group

Time of passage of
Central Merid.

Time of Max. of ,
Mag. Storminess

4980

Sept. 19.8

Sept. 22.2 & 19.2

0.9 days

4981 & 4982

„ 28.2 & 28.0 „ 30

'•9 »

4983

Oct. 10.3 Oct. 10.5

0.2 „

4986

„ 24-9

26.6

'•7 *

4987

i, a9-6

n 30-5

°-9 „

4990

Nov. 20.0

Nov. 23.5

3-5 «

4999

Jan. 1.7

Jan. 4.5

2.8 „

5001

n 24-7

26.0

'•3 „

5002 & 5003
5013, 5014, 5016

„ 29.0 & 28.9
March 27.1, 28.2, 39.1

n 29.5
March 31.0

0.6 „
1-9 „

5015

April 2

April 5.4

3-4 „

5017 „ 8-7

8.6

— O.I „

Mean of the Lag :

+ 1.6 days

PART II. POLAR MAGNETIC PHENOMENA AND TERREL^A EXPERIMENTS. CHAP III. 525

In those cases for which a coincidence exists, the storms, as usually found, occur somewhat later
The average lag 1.6 days gives /„ — /„ equal to 21°, where i, and 10 are respectively the longitudes
of sun-spot and central meridian at the time of the maximum of storminess. The lag here found is
only half as large as that found by Ricco (') for a number of very great storms.

As regards the principal maxima, those of September, October and November coincide with quite
large and distinct groups of sun-spots. After that a marked maximum of storminess reappears quite
regularly at the end of December; but the sun-spots have disappeared. Nor do the great principal
maxima of February and March coincide with sun-spots. Not until April does there seem to be an
apparent coincidence.

Regarding the connection between sun-spots and storminess, it seems improbable that the sun-spots
can be the direct cause of the magnetic storms; for the sun-spots appear to be rather irregular in their
occurrence and with a somewhat different period of revolution than the source of electric radiation. If,
then, the source were formed in any way by sun-spots, we should hardly find the variation of stormi-
ness so regular as it was actually found to be during the period of our observations. The results
suggest that sun-spots and magnetic storms are both of them manifestations of the same primary cause.

The storminess seems to go on whether there are sun-spots or not. But also from our point of
view we shall expect to find that the passage of sun-spots is accompanied by magnetic storms; for the
existence of sun-spots is to be considered as a visible sign of a great activity of the primary source.
The effect will undoubtedly in a number of cases be the same as if the sun-spots themselves were
sending out pencils of electric radiation. The strong magnetic fields near the sun-spots show that violent
currents of electricity are actually operating in the sun-spots, and these currents may only be another
effect of the same electric activity which produces the magnetic storms and aurora.

As we saw, the existence of one well-defined monthly maximum would require that there were
one single complex of sources which was greatly predominant with regard to emission of electric
radiation. It must, however, by no means be regarded as a matter of necessity that the same source
should always maintain its predominance; but it is quite possible that the intensity of one source may
diminish, and that of another increase so as to take the lead for a certain number of revolutions of the
sun, until a new one is called into play to become the principal source.

In fact we saw that the results of our observations were best explained by dividing the principal
maxima into two groups, and in view of the previous considerations these two groups correspond to two
different complexes of sources. The first group has its last principal maximum at about January 28 and
the second one its first principal maximum at about February 7, consequently the difference in helio-
graphic longitude of the two sources should be about 120°.

This change in position of the source must be taken into account when we are dealing with the
determination of the monthly period of storminess. In fact, if the period were deduced in the ordinary
way from material covering a great many years, the shifting of the source would have the effect of
masking the "real" period, or the period deduced from a very long interval of time might be quite
different from that here found from the intervals between successive maxima. It is really no wonder
then that various authorities have found a different monthly period.

(') Nature 82, p. 8. 1909.

Birkeland. The Norwegian Aurora Polaris Expedition, 1903-1903. 67

.S26

P.IRKKLAM). IHi: NOKWKC.IAN AURORA POLARIS KXPKI >1TION, 19O2--I9O3-

ANNUAL VARIATION OF STORMINESS.

99. Observations have not been made for a .sufficiently long time for an exact determination of
the annual inequality. The longest period of observations, that of Axeloen, only covers a time of about
nine months.

The average total stonm'ness at Axeloen for each month during this period is given in the
following table.

TABLK XCII1.

Month

ST

L

Sept

-+- 1 o°

<><-t

33-9° »

"*~ 5-5

Nov

-

Dei- . . .

Jan

25-71 .

- 4-5

Fcb

6 6

Maivli

• • 38.18 „

-6.9

April

48.75 »

— 5-4

May

5°-37 »

~o

The numbers indicate two maxima, one in the autumn and one in the spring, or about the same
type of variation as found (or the annual variation of aurora borealis. Under the heading L is given
the average latitude of the centre of the sun's disc for each month. \Ve notice that the main feature
of the variation of S follows that of the absolute value of L; but the maxima and minima of ST seem
to occur somewhat later than the corresponding ones for L.

It thus seems as it tin- annual inequality may be explained by assuming that the intensity of this
electric radiation on an average is weaker at the sun's equator than at some distance from it; for if the
radiation leaves the sun perpendicular to its surface, and if the sun's magnetic axis forms an insignificant
angle with its axis of rotation, the rays which at any time shall reach the earth must start from points
having about the same hcliographic latitude as the centre of the sun's disc. It must however also be
taken into account that the pencils consisting of diverging rays from the solar spots of radiation are
probably somewhat bent towards the magnetic equator of the sun. We shall return to this question
in the chapter on the results of the experimental investigations with a magnetic cathode-globe in
vacuum-cases.

A resume of the above investigations on "Storminess" at our four polar stations has already been
published in a communication to the Congres de Radiologie in Brussels, 1910. See also Arch, de
(ieneve XXXII, August, 1911, pp. 97 — 116.

Since writing the above, I have seen a paper by Ur. BIDLINGMAYRR, published by the Kaiserliches
Obscrvatorium at YVilhelmshaven (Berlin, 1912), in which the author has introduced the idea "terrestrial-
magnetic aetivitv", which has certain points of resemblance to that of "storminess" introduced here.
I >r. Bidlingmaver has employed the idea for observations from Wilhelmshaven in the year 1911.

It is a highly interesting fact that Dr. CIIRFJ: in his most valuable "Studies in Terrestrial Magne-
tism", London, 1912, Chap. XVII, makes some reflections concerning sunspot relations that agree well
with the results obtained by our analysis.

Our results on storminess here given were printed as early as 1910, and only the last two pages
have been reprinted in 1913, two lines having been removed and a few lines added in conclusion.

Diurnal Distribution of Storminess

Matotschkin Schar

--\

\

V

\

V

\

X

\

\

\

J^

V

7

\v

\

Z

i...-—-

\

12 16 20

tV 12 16 20

.J?

S 12 16 2O

Diurnal Distribution of Storminess

Kaafjord

\

•s
5:

\

V

•

Fig. 193.

Diurnal Distribution of Storminess

AxeloenFl.I

\ .

5

V

\

fN

r±

12

16

20

\

\

8 12

Fig. 193.

16 20

\

\

\

72

16

20

Diurnal Distribution of Storrniness

AxeloenPl.H

7

S3

\

\

\

V

\ Vi

0 •

L.

-10 -
-15 -
-20:
-25 -

7

Fig. 194.

Diurnal Distribution of Storminess

Dyrafjord

V.

z\

\

V

S 12 16 20

Diurnal Distribution of Storminess

(Dec. 2 to March 1)

I
6

-20 ~
-25 —

2

\

CT.M.T.

Z

6 8 10 12 « 16 18 20

? 4 6 8 10 12

16 18 20 22

/\

fi 10

Fig. 196.

Vector Diagrams lor ,,the Average Polar Storm"

N ^

Matnlrfilfiii -

Kaaftonl

v~

Gr.M.T

Axelcicw

Dyra/jurd/

Cr.MT.

Sr.-ilc ,„

, , , , 1 . , -, , l 0

Fig. 197.

Birknnd. The Norwegian Aurora Polaris Expedition, 1902 — 1903.

536 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

ON THE DIURNAL DISTRIBUTION OF STORMINESS.

100. The distribution of storminess in the various hours of the day is represented in the plates
(figs. 191, 192, 193, 194 and 195).

The arrangement will be seen from the plates. Curves are given for each thirty days' period, and
also one series of curves at the bottom of each plate giving the mean storminess-distribution for the
whole period of observation.

For each period the following curves are given :

(1) The positive storminess Sp is represented by ordinates going upwards from the bottom line
which is taken as the time-axis.

(2) The negative storminess S" is represented by ordinates going downwards from the top line
which is taken as the time axis.

(3) The values of S? — S" = Sd are represented by ordinates taken positive upwards, and these
curves are drawn in full on the diagrams, while SP and S" are dotted lines. The vector S'1 whose
scalar quantity is equal to

.A8

has a very simple physical interpretation. It gives at any hour of the day the perturbing force for the
average magnetic storm for the period considered To fix the ideas let us assume that all storms
occurring during a certain period took place on the same day, but in such a way that the hour of the
day was unaltered. We should then get a certain disturbance, the perturbing force of which at any hour

would be given by the equations :

P - „ Sd
J- i, - -Jj,

Pd = n SD

P, = n S"v

where « is the number of days in the period in question.

On looking at the curves, we notice immediately that the storminess shows a very marked diurnal
variation. Comparing curves for the same station and the same magnetic element we see that for
different monthly periods they show very nearly the same course.

The absolute magnitude of the storminess may vary from one month to another, but the type of
variation is always the same, namely that which is represented by the average curve at the bottom of each
plate. This constancy of distribution of polar storminess is a matter of great interst. It shows that tin
amplitude and form of the average curve is by no means an accidental one, for the same type is found,
and almost equally well marked, for curves representing a very short period.

POSITIVE AND NEGATIVE STORMINESS.

101. The positive and negative storminess is defined quite arbitrarily from the sign of the com-
ponent of the perturbing force. There is then no necessity of any connection between, say, the positive
storminess of the various components for the same station.

And further, in view of the local character of the storms near the auroral zone, the distances
between the stations are fairly large, and therefore, even for the same magnetic element we may not get
correspondence in positive or negative storminess at the various stations. The regularity actually shown
by the elements at the various stations is rather to be considered as a strange coincidence than as
a matter of necessity.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. Ill

537

With only a few exceptions, the positive storminess shows the same type of curve for all three
elements at the four stations. The negative storminess also, with the exception of a few cases, shows
roughly the same type of variation at all stations and for all elements.

The cases that do not follow this rule are especially the vertical components for Axeloen and
Dyrafjord. For Sv at Axeloen the diurnal period is extremely well marked, but conditions are reversed.
S"Y for Axeloen varies in a way which corresponds to that of the positive storminess; and S^for AxelOen cor-
responds to the negative storminess found elsewhere.

For Dyrafjord the storminess in H is greatly predominant. For Si> the amplitudes are very small,
and for 5> the curve of negative storminess shows two distinct maxima, one of which corresponds to the
maximum of the positive, and one to that of the negative storminess of the horizontal force.

The reason for these similarities in the variation of the two types of storminess, as well as the
exceptions mentioned, will become clear through the treatment of the "average storm".

As a result of the comparison of curves, it appears that at the four stations there are mainly two
types of storminess, which we shall call P and N storminess, and which, with the few exceptions men-
tioned, correspond respectively to the positive and negative storminess.

P AND N STORMINESS.

102. The diurnal period of the P storminess is less marked than that of the N storminess. The
P storminess sets in gradually, and gradually disappears. The N storminess begins and ends more
suddenly, and obtains a much greater maximum value than that of the P storminess.

While the time of the maximum of storminess is usually well denned, the exact hour of minimum
is difficult to tell. In fact the minimum is more to be characterised as a calm period lasting for several
hours. As a rule there will be small P storminess when the N storminess has its maximum, and a small
.V storminess during the interval of great P storminess; but this is merely what should be expected,
and it shows that at the time of day when one type of storminess is operating, there will be little
storminess of the other type. What is more remarkable, however, is the existence of an interval which
is absolutely calm, where both N and P storminess are small.

The time of occurrence of the maxima of P and N storminess, and the interval of calmness, are
given in the following table. The numbers are taken from the average curves at the bottom of each
plate, which give the mean for the period of observation.

TABLE XCIV.

Gr. M. T.

Longitude

Local Time

P Storminess

A' Storminess

Calm

Period

Maximum

%

SD

5y

Mean

s*

fo

Mean

Interval

Mean

P. st. N. St.

Matotchkin-Schar
Kaafjord

15

17

'3

18

'5
'7
19

15
17
17

'5
'7
163
18

21

22.5
19-1-27

a

2.2

21
22

27

20
23

23

20.7
22.5
24-3

2.2

3.6* E
1-5 »

I.O „

1.5 W

8-13''

7-'4
7 — 10

8.5-125

10.5''

85
10.5

i8.6l< 0.3''
18.5 o.o
173 i-3
16.5 0.7

Dyrafjord . . ' . .

Mean

17.7'' O.6'1

538

HIKKEI.AND. THE NORWEGIAN' AURORA POLARIS EXPEDITION, 1902—1903.

For Dyrafjord it is only in the horizontal force that the two types are well separated; for the
other two magnetic elements the storminess is much smaller, and each group of storminess is divided be-
tween the positive and negative storminess, so that the TV and P groups get mixed up. In consequence the
time of maximum has been determined from the horizontal force only.

For AxelDen S'^ has a large value during a long interval, and has in fact two maxima. The
number given is the mean of the time for the two maxima.

The calm period is long and well defined for Matotchkin-Schar and Kaafjord, for Dyrafjord shorter
and not so quiet, while for Axeloen it has more the character of a minimum than that of a quiet
interval.

We see from the table that in spite of the rather large differences in longitude of the stations, the
TV storminess for the various stations has its maximum very nearly at the same local hour, about half past
twelve at night. Also the P storminess has its maximum at the same time of day about six o'clock in the
evening, and the calm period is always found in the forenoon. Except at Axeloen, the middle of the
calm interval is at half past ten in the morning.

Tin's result shows that the storminess near the auroral zone follows the diurnal motion of the .•;//;/.

PROPERTIES OF THE "AVERAGE POLAR STORM"

103. To obtain comparable numbers we must consider the storminess for a period common to all
four stations. The storminess for the three months December, January and February, is given in table
XCV and graphically represented in fig. 196. As we have already mentioned SJ can he considered as
a vector representing the perturbing force of the average polar storm, and in the usual way it can be
represented by a vector diagram of some sort.

TABLE XCV.
Mean Storminess for the Period December 2 — March i.

*

o -

-2

2-

-4

4-

-6

6-

8

8-

-10

IO-

-12

Gr M T

4-

-

+

-

+

-

+

-

+

-

+

SH

0.25

7.27

°-73

2.03

0.72

1-13

0.38

1.05

1.28

0.60

1.85

0.68

Matotchkin-Schar . . .

•Syy

0.67

3-°4

0.62

0.87

0.8 1

0.48

0.90

0.47

o-95

°37

1. 60

o.37

S,

Q-37

2.31

0.25

1.82

O.2I

1.36

0.85

°o3

1.72

0.27

3-22

0.22

Sj,

0.06

4-79

0-33

1.47

0.68

0.52

O.20

°-33

0.28

0.22

0.72

O..SI

Kaafjord ,

c

-

g.

f,-

T ,16

**

1.13

O.O4

°'34

°'57

° '

SY

0.08

6.13

0.08

2-93

0.28

2.64

o. 16

1.27

o 37

0.30

0.77

O.3I

sa

|
o-53

14.90

0.65

1833

'•57

12.22

3-13

5.22

5-72

,.78

6-35

2.85

f-

088

D

°-59

9-94

°-93

11.77

2.13

2.77

1.78

1.24

SF

22.24

0.40

I3-58

°-93

5.48

5-77

3-63

3-3°

4.04

3 13

I-I3

5-T

%

1.07

24.48

0.62

26.57

o-93

13-48

1.30

6-37

i-7S

2 02

1-25

1.83

T eft

*D

3.44

1 49

3.71

°-55

4.11

2.46

..48

°-93

1.50

s>

6.8 r

8.10

241

8.59

1. 12

8.65

0.40

u 93

°-37

6.22

0.74

2.08

PART ii. POI.AK M.\(;M.;TIC PIIKNOMK.NA AND i KURKI.I.A EXPERIMENTS. CHAP. in.

TABLE XCV continued.

539

Station

Gr. M. T.

12 - 14

14—16

16-18

J8-20

20—22

22 — 24

+

-

+

-

+

—

+

-

+

-

+

-

Sa

3-27

0.88

5-35

0.62

7-52

2.73

3-43

1397

0.6.0

19-57

0.15

19.38

Matotclikin-Schar .

SD

1-39

0.73

'•73

1-39

2.37

5-ii

1.16

8.02

0.70

9.22

0.62

7.16

Sv

5-'3

0.36

6.49

I. II

5-45

12.48

1.29 18.79

0.50

18.43

0.22 9.74

sa

1.18

°54

i-55

0.50

434

0.34

3-3°

2.41

1-25

6.99

0.09

10.79

•s/»

1.40

o.33

'•45

0.68

1.26

2.62

0.73

4.21

0.65

6.49

0.50

583

sv

!.78

0.39

394

o.34

5-49

u. ID

3-99

3-78

0.77

9.06

O.O3

15.08

s«

10.55

2.67

7.98

4-i3

1.92

17.42

0.25

29.90

0.93

23.10

0.73 14.78

SB

4-83

0.58

6.34

o-59

6.38 1.27

58:

4-31

3-23

4-59

0.68 ! 8.79

s»

1.29

8.62

0.79

13-95

1.90 12.82

11.67

6.26

28.59

1.84

32.89 ! 0.66

%

1.58

1. 10

4.10

0.90

9-1-7

0.82

943

3.12

7.72

3-28

1
3-47 7-67

Sr,

sr

1.16

°57

1.58 0.15

3-83

0-59

3-34

'4 22 || 1.39 12-35

4.40

12.02

Vector diagrams of the horizontal component of S1* are given in fig. 197 for the four stations. The
vectors are drawn from points on a time-axis for every second hour.

At Matotchkin-Schar, Kaafjord and Dyrafjord, there is an interval of several hours in the forenoon
with very small forces corresponding to the quiet period. At Axeloen the interval is very short. In the
afternoon the perturbing force increases, and assumes at each station a nearly constant direction towards
the north-west, which is maintained for several hoiirs. Then, all of a sudden, the perturbing force
turns round, takes up a direction nearly opposite to what it was in the afternoon, and assumes a com-
paratively large value.

If the average storm is represented by current-arrows, we should for each station get two typical
current systems.

(1) One system with maximum about six o'clock in the afternoon with its current-arrows turned
eastwards along the auroral zone.

(2) A second type with its current-arrows turned westwards along the auroral zone, and with its
maximum about midnight.

In the following table is given the time-interval for a small perturbing force, and the times of
maximum of the horizontal component of the perturbing force of the average positive and negative storms.

TABLE XCVI.

Station

Local

Time

Small Force

Maximum

Interval Mean

Pos. Storms

Neg. Storms

Matotchkin-Schar . . .

7-'4 '°-5
6—14 10.0
8— 10 9.0
7-12 9.5

18.6
18.5
14.0
1 6.0

24.6

24-3
23.2

255

Mean

16.8 24.5

540 BIRKELAND. THE NORWECilAN AURORA POLARIS EXPEDITION, 1902 — 1903.

The positive and negative average storms have respectively their maxima at about the same time as the
P and TV type of storminess. The two types of storminess are merely another aspect of the existence of
the two types of polar storms. It is, however, by no means a matter of course that the maxima of
storminess should fall on the same hours as the maximum of perturbing force of the average storm; for
from the equation S^ = S''H — S'IH it follows that Sd might be small even when both Sp and S" are large.
The coincidence regarding the occurrence of maxima of TV and P storminess on the one side, and the
perturbing force of the positive and negative average storm on the other, is a consequence of the fact
that the occurrence of the two types of storms does not greatly overlap, but that each type is mainly
restricted to its own time of day.

Some fields of the average storm are represented on the four charts, fig. 198.

The first chart gives the field at 13'' om (Gr. M. T.) corresponding to the beginning of the posit iv<
storm. We notice that it is breaking in from the north-east. It is strongest at Axeloen and Matotchkin-
Schar. The current-arrows are directed eastwards along the auroral zone. For Dyrafjord, Kaafjord and
Matotchkin-Schar, the vertical component of the perturbing force is directed downwards, but upwards
for Axeloen, showing that the current goes to the north of the three former stations, but to the south of
the latter.

The second chart gives the field at 17** om, when the negative storm is on the point of breaking in
from the east. At Dyrafjord only the effect of the positive storm can be noticed. At Kaafjord the arrow
is slightly turned, and at Matotchkin-Schar even more so. At Axeloen, however, it is almost completely
turned to the west. It looks as if the force at Axeloen should at this hour be mostly due to current-
systems different from those producing the effect at the other stations, and as we shall see later, this
is also the case.

On the third chart for 2ih om, the negative storm dominates at Axeloen and Matotchkin-Schar and
almost completely at Kaafjord; but the effect of positive storms is still most prominent at Dyrafjord.

On tlie last chart for ih om, the negative storm dominates at all four stations; but it is now
strongest at Dyrafjord. The vertical component is directed downwards for Axeloen and upwards for
the other three stations, showing that the currents on an average at this time are running above the earth's
surface, and between Kaafjord and Axeloen.

Through the treatment of separate perturbations we were led to the assumption of two types of
polar storms, which we called the positive and the negative polar storms. The statistical treatment of the
whole material shows exactly the same two types.

The average storm in the afternoon has the properties of a typical positive polar storm ; the midnight
average storm has the properties of a negative polar storm; and we see that the predominant part of the
storminess, at least at the three southern stations, is made up of these two types.

The cause of the singular character of Sy and Sy for Dyrafjord and S\ for Axeloen, will now become
evident. The reversal of the conditions of storminess of Sy for Axeloen only means that the storm-
centres of the two types of polar storms, positive as well as negative, pass between Kaafjord and
Axeloen. The small amplitude in the SD curve for Dyrafjord shows that the current on an average is
nearly perpendicular to the magnetic meridian at this place. The storminess of the vertical intensity
at Dyrafjord shows that the current-systems usually pass near the zenith, usually somewhat to the north
of the station.

PART II. POLAR MAGNETIC PHENOMENA AND TERRF.LLA EXPERIMENTS. CHAP. III.

541

COMPARISON OF STORMINESS AT THE FOUR STATIONS.

104. In the following table is given the total storminess for the months December, January and
February, and the mean of the whole three months' period. S« is the storminess expressed in relative
numbers, the total storminess of Kaafjord being put equal to one.

6 is the angular distance to the magnetic axis.

TABLE XCVII.

Dec.

Jan.

Feb.

Dec. 2 — March i j

ST c:
^11

ST | 5,

ST SR

Sr

tf

Katotchkin-Schar .

ii. i / 1.73

14.7 ;- 2.13

11.0 y 1.36

12. a

1.72 25.3°

KaaljonI ....

6.4 „ i. oo

6.9 „ i. oo

8.1 „ 100

7-1

i.oo 34.7

Axelncn ....

24-9 „ 3-89

25-7 n 3-73

20.6 „ 2.54

23-7

3-34 16.3

Dyrnfjord

13.4 „ 2.0g 14/6 „ 2.12

17.2 „ 2.12

I5-I

2.13 18.1

The magnitude of the storminess follows in the order Axeloen, Dyrafjord, Matotchkin-Schar, and
Kaafjord. The two stations Axeloen and Dyrafjord with the smallest angular distance 0 have the greatest
storminess. The storminess, however, is not quite symmetrically, arranged with regard to the magnetic
axis, for Kaafjord, with an angular distance of 24.7° has only about half the storminess of Matotchkin-
Schar with a still greater angular distance ; and both stations are situated to the south of the auroral
zone. Dyrafjord and Matotchkin-Schar have nearly the same storminess, although their angular distances
are greatly different.

The relative stopminess of AxelOen is the most remarkable. Although the great storms have their
centres between Axeloen and Kaafjord, and generally quite as near to the latter station as the former,
the storminess at Axeloen is more than three times as great as that at Kaafjord.

One possible explanation of the great storminess at Axeloen is, that besides the large storms with
their centres between Axeloen and Kaafjord, there are a number of smaller storms which have their
centres nearer to the magnetic axis. If so, we should expect the principal maxima of storminess — which
are mostly due to the occurrence of large storms — compared with the average storminrss of the stations
to be smaller for stations situated near the pole and the magnetic axis.

The distinctness of the principal maxima is illustrated in the following table.

TABLE XCVIII.

ST

5f

5»

S'«/ST

5"Vsr

' |

I II

I II

I

II

I II

I II

Matotchkin-Schar .

12.2 ;' 15.1 ;•

8.0 y 8.8 y

33-6 /

46.3 ;•

3.8 3.1

4-3 5-2

Kaafjord ....

7-1 „ 9-9 n

4-3 „ 5-6 n

ai.a „

28.8 „

3.0 2.9

4-9 S.i

Axeloen .... 23.7 „ 35.0 „

18.7 „ 28.6 „ 48.7 „

67.0 „

2.1 I.g 3.6 3.3

Dyraljord . . .

I5-I n 18.3 „

I2.I „ II.2 „

3°-2 „

45-5 n

2.0 2.5

2-5 4-1

The columns (I) correspond to the period of three months common to all four stations. The
columns (II) correspond to the whole period during which observations have been made at the various
stations.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903. (J'J

542

HIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, lgO2 — 1903.

S"' is the average storminess for the principal maxima. There is one principal maximum for each
thirty-day period, and for each principal maximum we have taken the storminess of the five-day period,
which contains the principal maximum, and which will be the same for all stations.

Sf represents the total storminess left when the maximum five-day periods are taken out. We have

T _

— m S

« — m

n is the total number of five-day periods in the interval, m is the number of those five-day periods which
contain the principal maxima.

If all storms, large and small, had their centres distributed around the same zone, we should expect
•S'"lsT t° be about equal for all stations. We see from the table, however, that the values of S"'/5T show
great differences, and in such a way that the ratio is smallest for Axeloen and Dyrafjord with the smallest
angular distance 6.

Consequently in beliveen the principal maxima there are a number of storms which have their centra
situated nearer the magnetic axis than those of the great storms producing the principal maxima.

Thus the very great storminess at Axeloen compared with that of the other stations is partly dm
to a number of storms, generally quite small, which have their centres to the north of the auroral zone.

Axeloen also takes up a singular position with respect to the diurnal variation. To show this we
shall introduce a quantity, -which we shall call the calmness of the station (c), and which is defined as
follows :

c =

and

ST is the total storminess

Sj » » » » for the calm period only

/ is the length of the calm period expressed in hours.

TABLE 1C.

Station

ST

•Jc

V

/

(

I II

I II

I

II

Matotchkin-Sehar .
Kaafjord

2.7 ;< 3.2 ;'

2.O „ 2.5 „

3-5 3-7
2.6 3.0

5»

7

17.5
18.2

18.5

21. 0

Axeloen

"•5 n M-o „

4.2 „ 5.O ~

i.i 1-5
2.6 2.7

3

4

3-3
10.4

4-5
10.8

The numerals 1 and II have the same meaning as in table XCVIII.

The calmness is about equal for Matotchkin-Schar and Kaafjord. For Dyrafjord it is about half
the value of the two former stations, and for Axeloen only about Va °f tnat value.

It is very remarkable that this peculiarity in the position of Axeloen — as will be seen from the
curves, fig. 196 - - is almost entirely restricted to the negative storminess in the horizontal force, while
the storminess in the vertical direction follows the same characteristic course as that found for the

PART II. POLAR MAGNETIC PHENOMENA AND TERRELI.A EXPERIMENTS. CHAP. III. 543

southern stations, the N storminess in vertical intensity showing only ow well-defined maximum at
midnight local time.

The negative storminess in H, however, shows two instead of one maximum. There is one maximum
four hours before midnight, and one four hours after midnight. The occurrence of these maxima is not
accidental, but they are repeatedly found for each monthly period (see figs. 193 and 194).

It is to be expected that the effects of storms with their centres chiefly in the maximum zone of
aurora would be felt during a longer time-interval of the day at a station situated nearer the pole. This
will be evident from the fact that a place near the pole and magnetic axis will have about the same distance
to the centre of the average storm at any hour of the day. Consequently we should expect for Axeloen
to get a broadening out of the maxima. But we cannot in this way explain the occurrence of the two
distinct maxima at Axeloen ; for at the time they occur, we have no corresponding maxima at Kaafjord,
which is just on the opposite side of the auroral zone and situated almost on the same meridian. The
two maxima of SJJ for Axeloen must therefore be caused by systems of a very local nature, in other words
by electric currents near the station. The effect of those systems dies away so suddenly towards the
south, that even at Kaafjord their effect is inappreciable.

Remembering that the auroral zone passes between Axeleen and Kaafjord and nearest to the latter
station, we conclude that these local current-systems occur at a considerable distance to the north of this
/.one, and much farther north than the somewhat great midnight storms, which have their centres usually
midway between the two stations.

We see that also through the study of the diurnal distribution of storminess we are led to assume
the existence of local storms wif/i their centres to the north of the auroral zone.

These centres of local storms occurring in the vicinity of the poles, show quite another diurnal
distribution than the greater storms in lower latitudes. At Axeloen they are strongest and most frequent
at eight o'clock in the evening and four o'clock in the morning; but small local disturbances are here
frequently found also during the day-time.

Thus we come to the following conclusion : The great storminess and the very small calmness of
Axeloen compared with the other stations is chiefly due to local disturbances with their centres nearer
the poles, and showing another diurnal distribution than the greater and usually more universal storms,
which have their centres in the auroral zone.

To judge from the direction of the horizontal component of the perturbing force, these small
disturbances should belong to the type of negative storms, because the current-arrows are turned towards
the west. 1 think, however, it will be best to restrict the class of negative polar storms to those which
have their centres near the auroral zone; for it is evident that it is only at some distance from the pole
that we may expect to find distinct types of positive and negative storms.

Further, when we compare the storminess in the vertical direction, the similarity between the negative
storms and these northerly local storms will be difficult to maintain.

Comparing the curves of storminess for Axeloen we find for Sy no sign of maxima corresponding
to the two distinct maxima of S",. Thus the local centres near tin's station produce practically no
disturbance in the vertical direction,

The simplest explanation of this fact is that the station is placed near a horizontal current-sheet,
in other words that the currents producing the local disturbances extend over an area, which has great
dimensions compared with the smallest distance between the station and the current-sheet.

The storminess Sr at Axeloen follows exactly the same diurnal distribution as that shown by the
storminess at Kaafjord, which indicates that the storminess Sr for Axeloen is mainly due to the positive
and negative storms passing between the two stations, and which we found to be caused by currents
mostly restricted to a comparatively small cross-section.

544

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPED1TJON, lgO2 — 1903.

TABLE C.

Matotc

likin-Schar.

Kaa fjord

Date

Great Storms

All

Small

Great

Storms All

Small

(5a

(•^((•S'T),

'/

•sr sT-sTg

(5S,

(5*).,

on), sr, 5'

Sr-sJ

Dec. 2- 6 . . . .

I.I3J'

0-997

1-707

2.26;'

4-"7

1-857

07

07

0

07

1.48;-

7-n ....

331 ft

2-03 „

7-'8 „

8.'6 „

"•23 ft

3-07 ,

'•59,.

0.89 „

0

1-83 „

4-23 ,

240n

12-16 ....

2-34 n

'•59 „

5,48,

6.16,

8-45 ft

2.29 ,

0.82,

1. 12,

0

1-39 ft

3-59 ft

2.20,

17 — 21 ....

0-75 n

0.29,

°-75 n

1. 10,

2-54 n

'•44ft

o .10 „

O.I4,

0.32;'

0-36 «

[.!«„

0.76,

22-26 . . . . 19.64 „

8.03 „ 20.69 «

29-63 „

33-18 ,

3-55 «

11.00,

5-77 ft

14.14 ft 18.82,

23-54 ft

4-72 ft

27-31 .... 2.12,,

0-49 ft 3-33 ft

3-97 n

7-°7 ft

3-'o ft

'•24,

1.24 „

1-80, 2.51 „

4-4' n

'•90 n

Jan. t- 5 . . . .

3.91 „

093ft

532,

6.04,

8-74 ft

2.70,

0-33 «

o-oSft

1-23 ft 1-27 ft

4-35 ft

308,

6— 10 ....

4-02 „

'•33 «

4.81,

6-4' ft

9-40 „

2-99 «

o-37 «

0.23 „

0.84 „ 0.95 ,

3-56 „

2.6, „

11-15 ....

'•59 n

I.OI „

4.60,

4-97 „

8-25 „

3-28,

0.52 „

0-58,

'•37ft '-57 ft

4.69,

3-'2 »

16 — 20 .

2.80 „

°-75 n

4-85 ,

5-65 „

8.82,

3-'7 ft

0.60 ,

0.28,

2.57 „ 2.66 ,

5-25 «

2-59 *

21 — 25 ....

3-93 „

2-18 „

5-86,

7-38 ft

1 0-65 ft

3-27 „

o-45 ft

0.64 „

1.70,, 1.87,

5-5' «

3-6.1 „

26 — 30 ....

34-27 n '5 93 n

'°-33 ft

39-17 ft

42.04 „

2.87,

"•97 «

4-69 „

8-87 „ 15-62,,

'7-79 ,

2.17ft

Jan. 31 — Feb. 4 . .

0.70 „ 0.38 „

o-74 »

i-o5n

2.76,

1-7' ft

°-05ft

0-05 ,

0-44 ft ! 0.44 „

'42ft

0.98 „

Feb. 5 — 9 . . . .

'5-90 « 7-54 «

'3 04 ,

2I-32ft

25-50 ,

4.18,

890ft

5-77 «

16.42 , 19.54 ft 22.17 ft

2-63,

10—14 ....

8.13, 3.39,

6.60,

11.00,

15-15 ft

4-'5 ft

3-75 n

1.62 „

6-95 « 8.06, n. 80,,

3-74 »

15-19 ....

'•94 n '-Si „

6.18,

6-72,

8-78 „

2.06,

o-72 „

0.67 „

1.58, i .86, 3.62,

1.76,

20 — 24 . . . .

2.24 „ 0.82 „

3-oi „

3-84 „

6.46,

2.62,

-

o-75 ft

2-'5 „

—

Fcbr. 25 - March i

2-27,, I- 77 ft

4-94 ft

5-7' ft

7.18,

'•47 ft

'•27 „

0.84 „

4-52,

4-77 «

6.03ft

L36,

Mean

9-477

13.24;'

. 2.77;'

Mean

4.9I7

7-337

2.42;'

AxelOen

Dyraljord

Date

Great Storms

All

Small

Great

Storms All

Small

(S$t

( o » . 1 1 O w, J

•sf

ST

(•s^jt^Us^

C"7" C"T

II

s"' v

Dec. a— 6 . . .

8-87;' 3.10;' 6.62;'

"•497

15.717

4.22;'

4-437

0-447

2-57 7

5-M7 7-737

2-597

7-n . . . .

15.50,,; 6.34 „ 15.84,

23-02 „

26.92 „

3-90 „

9-36 ft

1.22 „

7-44,

12.02 „ 15.28,

326,

12--16 ....

13.98,, 4.50, 12.13,

19-05 «

22.80 „

375ft

7-55 ft

0-99. ft

4-24 n

8.72, 12.06,

334ft

17 — 21 ....

1.86 „ 0.44 „ 6.45 „

6.72,

'0.23 „

3-5' ft

0-40 „

0.17 „

0.58 , 0.72 , 3.02 „

2-3° B

22 — 26 ....

28.96, 10.93, 45- '5 ft

54-74 «

57.81 „

3-07 «

21-49 ft

4-33 «

12-72 „ 25.34, 31.65,

6-31 r

27 -31 ....

7.23 „ 3.08 „ 7.90 „

11.14,

16.05 ft

4-9' «

5-48 ,

t-77 ft

3.90, 6.96, 1 0.66 „

3 7° ft

Jan. i — 5 . . . .

11.67, 4-84 « 8.52,

'524 ,

'9-94 n

4-70 „

6-56,

1.91 „

5-3° « 8.65,, 1 2.1 1 „

3-46 ft

6 — 10 ....

9-59 « 3-63 „ 9-54 n

14.00 „

18.47,,

4-47 «

6.21 ,

'•63 ft

9-40 „

11.38, 14.21 „

2.83 „

11 — 15. - - -

13.84 ft 3-92 n 10.24 ft

16.88,

21-25 n

4-37 ft

3-83 „

'•26ft

3-55 «

5-37 „ 9- '8,

3 Sift

16 — 20 ....

9-'4 „ 3-33 n 9-07,,

'3-30 ,

20.53 «

7-23 ft

5-4' ft

0-92 „

4-20,

691 « 12.25,

5-34 n

21-25 - • - - 9-74 „ 3-5' ft 15-63 «

18.75 „

24-75 ft

6.00,

6.04 ,

0-76,

4.11 „

7-34 ft "-7' „

437ft

26-30. . . . 22.05, "-'9ft 39-37 n

46.50 ,

49-33 ft

2-83 „

18.28 „

4-73 n

'5-79 n

24-61 „ 28.33 „

3-72 n

Jan. 31 -Feb. 4 • • '-84 „ 0.60 „ 2.04,

2-8lft

8-57 «

5-76 „

1.98,

0.17 „

'-58,

2-54 n 5-65 „

3->i«

Feb. 5 - 9 . . . .

20.98 „

10-34 « 24.76 „

34-06 „

38.95 n

4.89ft

21.98,

7-47 «

'3-5' n

26.86, 30.59,

3-73 ft

10— 14 ....

'3-5' r 5-98n

'0-53 ft

18.14 „

23-53 n

5-39 ft

"•52ft

r-79 ft

6-00,

13.11 „ 22.40,

9-29 n

15-19 ....

7-87,

3.40 „ 6.04 „

10.49 ft

'4-73 ft

4-24,

4-69,

085 «

2-75 ft

5-5' ft 8-37 ,

2.86 „

20— 24 .

7-40,

5-50,

I3-7I n

16.52 „

20.24 ,

3-72,

no' ft

3-37 «

"•25ft

21.08 „ 24.02,

2.94 ,

Feb. 25 — March i

10.33 n

5-'6 „ 97',,

'5-02 „

17-28 „

2.26,

5-54 «

032ft

9-50 „

II.OI „

12-36 ft

i -35 ft

Mean

'9-337

23-737

4.407

Mean

11.29;' 15.09;'

3.80)'

1'AKT II. POLAR MAGNF.TIC PHENOMENA AM) TKRRKLI.A EXPKRIMF.NTS, igO2 — 1903.

TABLE CI.

545

O — 2

2 — 4

4—6 6-8

8 — 10 10—12 12—14 14 — 16

16-18

18 — ao ao — aa 33—34

4-

-

+

-

-f.

-

+

—

4-

—

•+•

+ ';

+

-

4-

-

Mat.-Schar

L

Great . . I o
Small . . ,| 0.3

O I.I O 0.6 O 0.3 O.g O 1.2 O 2.4 O 4.3 O

0.7 i.o 0.7 0.6 0.4 0.7 0.4 0.6 0.6 0.7 0.9 0.9 0.9 0.6

Great . .

Small .

0.7

1 Great . . o
Small . . II 0.4

Kaafjord

PH Great .

i „ Small .

'/< Great .

„ Small .

'y Great .

„ Small .

Axeleen

'// Great . .
„ Small . .

""ft Great . .
,. Small . .

>r Great . .
,. Small . .

Dyrafjord

';/ Great
, Small .

o
0-7

o

O.I

o
°5

2-3
0.7

«.1

0.6

4.0
0.8

1.6
0.7

5-i
i.i

o 0.6 o

O.2 0.2 O 0.5

I.O

0.8 o.i 1.3 0.5

0.6 0.3 0.8 0.3 0.7 0.4 0.5 0.4 0.6 0.4 0.6 0.6 0.5 0.9

2.3 o 3.6 0.3 4.5 0.6

I.I O.3 1.5 O.I 2.0 0.5

O 1.4 O 0.7 0.3 O.2 1.4 O

0.2 0.4 0.2 0.6 O.5 0.3 0.3 0.3

0.5 0.2 0.3 o 0.2 oooo 0.6 o i.i

0.3 I.O 0.5 0.2 0.2 O.I 0.3 0.2 0.7 0.5 0.5 0.5 0.5

o 0.5 0.4 0.3 0.5 o o o o o 0.3 o 0.6 o

I
0.5 0.7 0.6 0.4 0.6 0.3 0.6 0.7 1.5 0.4 i.i 0.3 0.8 0.7

O 2.1 0.2 2.3

o.i 0.9 o.i 0.4

o 0.9 oooo 0.7 0.3 2.4
0.2 0.4 0.3 0.3 0.8 02 i.o o.i 1.5

4-9 2.3 '•' i3-° ° '8-1 o 17.0

2.6 0.5 2.3 i.o 0.6 1.5 o.i 2.4

1.3 3.6 0.3 7.0 o 8.8 o 6.7

0.9 2.5 0.9 i.o 0.7 0.4 0.6 0.5

a.8 10.6 o.i 1 6.8 o 16.8 o 8.1

2.7 1.8 1.2 i. g 0.5 1.6 0.2 1.6

3.1 o.i 3.1 a.o 0.5 6.1 o i i.o

1.2 o.i i.3 0.4 0.8 0.9 o.i 0.6

0.6 i.o 0.3 1.5 o 4.3 o 4.9

0.6 1.6 0.4 2.7 0.7 2.2 05 0.9

3.1 O.I 3.0 3.0 O 7.5 O 13.8

3.4 o.i 2.0 0.8 0.8 1.6 o 1.3

11.9 o 15.0 o 9.9 i.i 3.6 • 2.8 0.4 3.7 o 8.0 1.4 5.5 2.6 0.6114.1 o 36.9 0.2 ai.i o 9.7
2.9 0.6 3.4 1.6 2.3 2.1 1.6 2.9 1.4 2.7 2.8 2.6 1.3 2.4 1.5 1.3 3.3 0.2 3.0 0.7 2.0 0.7 5.1

o 8.0 o 9.7 o.i 6.7 0.5 1.8 0.6 0.3 i.i o 3.3 o 4.9 o.i 4.0 0.8 2.6 3.9 0.3 3.7 o 7.3
0.6 i. 9 0.9 2.1 1.2 1.5 1.6 0.9 1.2 0.9 1.5 0.9 1.5 0.6 1.4 0.5 2.4 0.4 3.2 0.4 2.9 0.8 0.6 1.6

20. 8 o 12.8 0.5 5.2 4.4 3.1 3.7 1.5 2.7 0.2 4.7 0.3 8.2 0.5 13.3 1.6 1 1. 1 10.7 4.0 27.6 i.i 31.7 0.3
1.4 0.4 0.7 0.4 o.a 1.4 0.6 0.6 2.6 0.5 0.9 i.o i.o 0.4 0.2 0.7 0.3 1.8 i.o 3.3 i.o 0.7 1.2 0.5

O.I 22.2 O 24.8 0.2 II.5 O 5.6 O.6 1.4 0.6 0.3 0.5 0.4 2.2 O 7.3

i.o 2.3 0.6 1.8 0.8 2.0 1.3 0.8 i.i 0.6 0.7 1.5 i.i 0.7 1.9 0.9 1.8

6.9 I.I

4.2 2.4 1.3 11.7

0.8 3.5 i.i 3.5 0.9 3.3

'D Great . . 0.8 3.5 o.i 2.2 o 3.2 o 1.8 0.5
„ Small . . ;j 1.6 0.5 1.4 0.5 0.5 0.9 i.i 0.6 i.o

'I Great . .
, Small .

0.3 0.7 O 0.3

0.7 0.9 0.6 i.i

o 0.6 o 0.8 0.3 0.9 o.a ( 1.5 1.9 2.9 1,8
0.3 0.9 0.4 0.4 0.8 0.4 1.4 0.5 1.3 1.5 i.i

5.1 6.8 1.6 6.7 0.5 6.9 o 9.9 o.i 5.3 0.4 1.2 0.6 0.2 0.9 o 2.8 o.i 1.6 3.0 0.5 n.i 3.6 10.
1.7 1.3 0.8 1.9 0.6 1.8 0.4 2.0 0.3 0.9 0.4 0.9 0.5 0.3 0.7 o.i i.o 0.5 1.7 1.2 0.9 1.3 0.8 1.9

546

HIRKF.I.AND. TIIK NOKWKGIAN AURORA I'OLARIS EXPEDITION, igO2 — 1903.

SEPARATION OF GREAT AND SMALL DISTURBANCES.

105. The separation of perturbations into great and small storms has been performed according to
rules given in the introduction to this chapter, and for the period of three months common to the four stations.

In table C is given the storminess for great and small storms for each five-day period.

The quantity S — ST will be taken as representing the storminess of small storms.

The storminess of small storms only shows small and quite irregular variations from one Five-day
period to another, showing that the cause of small storms is almost constant!}' present. In view of our theory
this would mean thai almost at any time pencils of electric rays from the sun (ire striking the earth,
and we have to suppose a great number of sources of electric radiation spread over the surface of the
sun. On the ground of this fairly constant supply of disturbance, the great storms, from the principal
sources of the sun, are superposed.

TABLE CII.

C T-

_ H Sr-

Sm

CM

Sm

&,

•Jl

5

Si*

CT~ cr

All

Great

Small

All

Great

Small

All

Great

Small

Matotchkin-Schar . .

3-12

7-97

4 ^6

5.36

2.62

33-57

30.04

1 1 OQ

3-53
3.18

4.21
4.64

5.61
7.85

'•35
i 40

18 TJ

14 18

4 =,6

d8 TO

q.6o

2.60

3.18

°-75

Dyra fjord ....

2.97

12.07

8.43

3-64

30.19

25.60

4-59

2.50

3-°4

1.26

The ratio of the storminess of great storms to that of the small ones, given in table CII, is seen tu

vary between 2.05 for Kaafjord and 4.39 for Axel&en, or, in other words, most of the storminess is due to storms

_5
belonging to the group of great storms. The ratio "-'T is considerably greater for the group of large

•->!

storms than in the case when all storms are counted.

The distribution over the day of large and small storms is given in table CI, and graphically
represented in fig. 199. Comparing these curves with those in fig. 196 we notice tinat the characteristic
diurnal period found from the treatment of all storms is even more marked for the group of large stiirmt.
We further notice that the greater part of the calm period of the day is due to small disturbances,
Table CIII gives the conditions for the period of four hours during which the large storms have the
smallest storminess. We notice that the quantity I is greatly increased in the case in which the small storm-
are left out.

TABLE CIII.

5T_5

r

€ v

cr ^r

Station

Calm
Period

/ o r\ / o / \ £i i

ST

5r

.S j ,,
CT

All

Great

o

Matotchkin-Schar .
Kaafjord

Gr. M. T.

8 — i2h

0.81 ;' 1.83 ;' 2.58

9-47 ;'
4-91 »

3-74
a.68

10.7

00

0.23
0.33

AxelOen

8 — i an

S.74 » =; 08 „ i i.^s;

IQ.O

i. 08

2.36

0.19

Uyrafjord .

!2.64

6.13

0.25

is the total storminess of great storms for the calm period

\<Jc/s -

- small

PART II. POLAR MAGNETIC PHENOMENA AND TERREI.LA EXPERIMENTS. CHAP. Ill 547

The result for Kaafjord of the separation of small and large storms is the most remarkable.
If 33 °'u of small storms are removed, the quantity v becomes infinitely large, that is to say that out of
the 67 "'u of storms greater than a certain value, no oiif appears during the calm period.

For the other three stations .1' has a finite value. The reason for this is partly the fact that the
percentage of small storms taken out is smaller for these stations.

For Matotchkin-Schar £ has the large value of 10.7, although the small storms removed only make up
23 % °f tne whole storminess. If we were to increase the upper limit for small storms so as to
make the percentage a little greater, we might expect to find perfectly calmness.

Also for Dyrafjord and Axeloen 2 increases rapidly with the percentage of small storms taken out
but not quite so fast as for the two former stations.

The rapid increase of .T for great storms shows that the storminess of the calm period is almost
entirely due to comparatively small storms showing a diurnal distribution somewhat different from that
of large storms.

The two maxima for Sf, at AxelOen, one four hours before, another four hours after, midnight,
follow the group of large storms. Thus in spite of the fact that these storms are so limited in their
sphere of action that they produce practically no effect at Kaafjord, they appear at Axeloen as fairly great
storms. I think this will clearly show that the current-systems causing the disturbances carry a compara-
tively small amount of energy, so that they can only produce the great effect at AxelOen by passing
near to the station.

THE DISTRIBUTION OF STORMINESS AND THE SOLAR ORIGIN OF POLAR STORMS.

106. The existence of a well marked diurnal period of polar storms was already shown in my
previous work "Expedition Norvegienne 1899 — 1900". See p. 16, and PI. II. The type of variation is
tumid for Hossekop for the period 1899 — 1900, and for a number of other stations for term days during
the polar year 1882—83. The diagrams are in good accordance with the present results found from a
more complete statistical treatment.

From the study of the occurrence and motions of the perturbing fields, I was led to the conclusion
that these fields followed the diurnal motion of the sun (See: "Exp. Norv. etc." p. 29), a result which
has been brought to full evidence through the present investigation.

The diurnal distribution of perturbations shows immediately that some part of the storminess, in
some way, must be connected with the sun.

One of the most interesting features of the diurnal variation is the existence of a well-marked
calm period. I think this is a property of the storminess which may serve as an important test for an}'
possible explanation, and we shall subsequently see how far it is in agreement with our own theory.

The properties of the diurnal distribution of storminess for a certain interval of time can be ex-
pressed in the following simple way: At any moment there is a region of the earth with great distur-
bedness. This region is not symmetrical with respect to the axis of the earth, but is mainly restricted
to the night and evening side, and extends from places near the magnetic axis to places some distance
to the south of the auroral zone, where the storminess rapidly diminishes. At the night end of the
disturbed area we have negative, at the afternoon end positive storms, and nearest the pole we have an
area of very local disturbances. On the evening side, between the two types, there is no calm region, but
the two types will to a certain extent overlap.

From the diurnal distribution we can draw some interesting conclusions regarding the amount of
storminess which is a direct effect of the sun.

Suppose part of the storminess was produced by something showing a period different from 24
hours; the storminess from such a cause would be evenly distributed over all hours of the day.

548

BIRKKLAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

We are consequently justified in assuming that the total storminess due to causes other than the
sun, cannot be greater than the storminess of the calm period. In other words, the quantity 5r jn table
CIII is an upper limit for the sum of all the storminess of the place that is not due to the sun, and
Sr~S^ is a lower limit for the sun-storminess. The quantity 1" given in table CIII will then in each
case give a lower limit for the ratio of the sun-storminess to that which is due to any other cause.

We can also express the sun-storminess in percent of the whole amount. In table CIV the
lower limit for the percentage of sun-storminess is given for all storms and for the great storms
separately.

TABLE CIV.
Lower Limit for Sutt-stormintss.

All Storms

Great Storms

Station

ST-ST

TOO e

«5H5J), i *sr(s3,

Sf S'1'

Matotclikin-Schar .

79 percent

91.5 percent 70.5 percent

Dyrafjord

•ja „

86 „ 63 „

The first column gives the limit for sun-storminess of all storms as a percentage of total storminess.

The second column gives the limit for sun-storminess of great storms as a percentage of the total
storminess of great storms.

The third column gives the sun-storminess of great storms as a percentage of the total storminess
of all storms.

The second column shows that nearly all the storminess of great storms is caused by the sun.

Comparing the first and third columns, we notice that the sun-storminess of great storms forms
about as large a portion of the whole total storminess as that given in the first column, which is
calculated from the diurnal distribution of all storms. If, then, the numbers in the first column represent
the true value for the sun-storminess, it would mean that almost all the small storms were not of solar
origin; but this is certainly not the case.

In calculating the values in the first column, it was assumed that the storminess of the calm period,
consisting mostly of small storms, was entirely due to causes other than the sun. But we know that at
least part of this storminess must be of solar origin, and through the knowledge gained about the pro-
perties actually shown by the magnetic disturbances, we are able to estimate a lower limit for the sun-
storminess of the calm period.

We know from the treatment of separate storms that a polar disturbance with its centre near the
auroral zone will be accompanied by small disturbances at considerable distances from the storm-centre.

To fix the idea suppose it is 8 o'clock in the morning Gr. M. T. At that time Kaafjord will he
situated in the calm region. But on the opposite side of the magnetic axis polar storms are operating
which are bound to produce a certain effect at Kaafjord.

We found that the elementary polar storm produced a field of a fairly regular type (sec p. 86,
Part I). We are justified in assuming that points situated symmetrically with respect to the axis ol the

PART II. POLAR MAC.XETIC PHKXOMKX A AMI TKKRKI.I.A KXI'KRIMKNTS. CHAP. III.

549

eld, will have perturbing forces of the same order of magnitude. Thus if we had a storm-centre at
tyrafjord, we should find that this storm would produce about the same strength of field in south
iurope as at a place on the opposite side of the magnetic axis and with angular distance equal to that
f Dyrafjord.

Table CV gives the ratio (•/) of the strength of the field near the centre to that in southern
lurope (San Fernando and Munich) for a number of polar storms.

TABLE CV.

Storm

Remarks

Dec. 15 .
Keb. 10 .
March 31 .
„ 22 .
Dec. ->6 .
Feb. 15 .

Oct. 27

23

12

17
I I

n

12

13

13

Calculated from the fields at i h and i'1 15"' p. 90

table XVI
field at

oli 45

23"

Table XXXII

107
123

'35
]43

184
205

- ' -

Mean

14.6

The quantity /. varies between 23 and n. The larger value corresponds to an elementary storm when
he ratio is taken for the storm-centre and a point near the transverse axis of the field. If the principal
ixis is turned more towards the south, as on the 22nd of March, it will have the effect of making -/.
.mailer; for, at equal distances from the centre, the forces will be greatest along the principal axis,
•"iirther, the ratio /. is smaller for compound than for elementary storms, which is easily understood if
vc take into account the local character of storms near the centre.

The effect produced at our stations by storms on the opposite side of the magnetic axis will be
smallest for those stations which have the greatest angular distance from that axis. In view of the results
expressed in the table, we can put

For Matotchkin-Schar and Kaafjord . . . / <^ 20
•» Axeloen and Dyrafjord x <C 15

The greatest storminess in the disturbed region for the period of our observations is known only
or that part of the auroral zone extending from Dyrafjord to Matotchkin-Schar; but from the treatment
if storms from the polar year 1882 — 1883, we have seen that storms occur with about equal strength
ind frequency all round the auroral zone.

Let |S)' represent the diurnal maximum of total storminess. This quantity is very nearly equal to
.he maximum perturbing force of the average storm. For the three-month period considered we obtain

For Matotchkin-Schar . . . (S)m = 30 y

„ Kaafjord „ = 20 „

„ Axeloen » = 43 >,

„ Dyrafjord „ = 29 „

Mean 30.5 y

At the time when one of the Norwegian stations has calmness, we can assume the maximum strength
jf the average storm on the opposite side of the pole to be at least 30 /.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903.

70

55°

KIKKK1.AN1). THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902-1903.

As an upper limit for the storminess which is not of solar origin we obtain

For Matotchkin-Schar a = 5'J - 3%0 = 1.1 y

„ Kaafjord §. . . a = Sf - *%„ = 0.4 „

„ Axeloen a = S^ - %„ = 9.4 „

„ Dyrafjord a = Sf - »/15 - 2.2 „

In table CVI is given the lower limit of sun-storminess (5<? — a) as compared with n and also
expressed in percent of the total storminess.

TABLE CVI.
Loivcr Limit for Sttn-stonniness.

Station

a

iooSr-rr

Matotchkin-Schar . .

9.2

91 per cent.

AxelOen

1.5

60 „

c.q

86 „

The quantity a cannot be entirely due to storms which are not of solar origin. In the first plan it
is not impossible that every now and then we also have centres of polar storms on the morning and
forenoon side of the earth. At the southern stations Matotchkin-Schar and Kaafjord, forenoon centres of
any magnitude are seldom observed; but nearer the magnetic axis and the north pole, at Dyrafjord and still
more frequently at Axeloen, centres of fairly small and local polar storms are also found on the fore-
noon side.

In the second place a contains some storminess due to disturbances which do not belong to the polar
type, but may still be of solar origin. In our opinion the equatorial storms as well as the cyclo-median
perturbations are effects of the same solar agency as that producing the polar storms; but at the polar
stations these storms show quite a different diurnal distribution from that of the polar storms. Thus the
equatorial storms would produce about equal effects all round the auroral zone, and the cyclo-median
perturbation in the instance investigated was strongest on the day side.

In view of these facts, table CVI shows that at the three southern stations practically all the s/ontif
which occurred during the interval of our observations were caused by some agency coining from the .<«;;.

The fact that the lower limit of sun-storminess is smaller for Axeloen than for the other stations,
must not lead us to the conclusion that a smaller part of the storminess should be of solar origin at
this station. It only means that by the method used we are unable to prove the solar origin of a great
part of the storminess at Axeloen. The efficiency of the method depends on the calmness of the station.
On account of the character of the distribution of storms on the earth's surface, it is, on the northern
hemisphere, merely at stations on the southern border of the auroral zone that we can expect this calm
period to be well marked.

For a place in a lower latitude the storminess will be due mostly to distant systems with their
centres near the auroral zone. In the night the disturbed region would be on the same side of the pole
as the place considered, while in the day it would be on the opposite side of the pole; but for places
far from the poles the difference in the effect of the day and night systems would be diminished,
is in accordance with the fact that the great polar storms are accompanied by disturbances in lower

PART II. POLAR MAGNETIC PHENOMENA AND TERRELI.A EXPERIMENTS. CHAP. III. 551

latitudes, which are not by any means restricted to the night side. Also if we go to regions near the
poles and the magnetic axis, we shall find a rapid diminution in the calmness.

As regards Axeloen, we found the small calmness to be due, not so much to its more northerly
position, as to a number of centres of local storms which showed their own characteristic diurnal
distribution; but judging from the very great diurnal maxima of these storms, they must be mainly of
solar origin, and moreover we must suppose that stations so near each other as Kaafjord and Axeloen
have disturbances of essentially the same origin.

The result of this investigation regarding the amount of sun-storminess has an interesting bearing
on the question regarding the possible influence of the moon on magnetic disturbances. If the agency —
of whatever kind it was— came from the moon the effect should show a period of a lunar day, different
from 24 hours. Then the moon storminess must be contained in the quantity a, and thus be extremely
small compared with that of the sun.

It ought to be remembered that the alorniiiifss only contains variations of a somewhat abrupt and
irregular character. Then if the sun or the moon gave out a magnetically effective agency at a constant
rate, the effect of such an agency would not enter into the quantity we have called storminess.

APPLICATION TO THEORY.

107. The previous results regarding the amount of storminess due to the sun are obtained without
any assumption regarding the mechanism connecting cause and effect. We have merely made use of
facts actually found for the distribution of storms with regard to time and space.

The next question is: How do the properties found agree with our theory ?

Tin- characteristic properties to be explained are mainly the following:

|i) The great storminess on the night and evening side of the earth, and in the region near the
auroral zone.

(2) The calm region on the day side.

(3) For the somewhat great storms, with their centres passing between Axeloen and Kaafjord, we can
distinguish two types, which we have called positive and negative polar storms.

(4! A number of local storms occur in the vicinity of the pole to the north of the auroral zone.

We found during the treatment of separate storms that the main features of the field of an elementary
storm could be explained by a system consisting of a vertical current coming in from space, and bending
round in the direction of the auroral zone at a height of some hundred kilometres above the surface
of the earth, and leaving the earth as another vertical branch. Now we have seen that the average
storm, which is made up of numbers of such systems, is almost entirely caused by the sun. There
seems then no escape from the assumption that these current systems-coming in from space, are currents
directly produced by electric radiation emanating from the sun.

We can also use another line of argument. In order that the sun-effect shall mainly make itself
felt only within narrow regions on the earth's surface, and almost entirely on the side turned away from
the sun, it is necessary that the sun-agencies descend in comparatively narrow streamers, and are de-
viated in some way by some field of force possessed by the earth.

Now electric rays from the sun, diverted by the magnetic field of the earth, will be just what
is necessary to explain this very peculiar kind of solar action. Regarding this point I must refer
to the publications of my experiments with the magnetic terrella in a vacuum-tube.

Corresponding to the disturbed region near the auroral zone, we have areas of precipitation of
cathode particles on the terrella, forming bright spots or bands along a certain magnetic parallel which

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

in a striking way corresponds to the auroral zone. The bright areas on the terrella usually show the
characteristic property of being restricted to the side turned away from the cathode or the source of
the radiation.

The existence of a calm period is a mere consequence of the distribution of storm-centres on the
night and evening side, and the rapidity with which the magnetic effect diminishes with the distance from
storm-centre. As we have seen, both these properties were consequences of our radiation theory, which
will then also explain the calm period, which is especially well marked on the southern border of the

9

auroral zone.

The existence of two types of polar storms, each restricted to its own time of day, is I think a matter
of the greatest interest for the question regarding the cause of magnetic storms.

In order to find whether the P and N storminess could be explained from our theory, I have
tried by means of screens placed in various positions outside the terrella, to trace the direction of tin-
rays before they strike the terrella. In this connection it was of special interest to regard the direction
of motion of the horizontal component of the corpuscles just before they struck.

It is of course difficult, not to say impossible, to reproduce in the limited space of a vacuum-tulir
exactly the conditions that govern the formation of magnetic storms. We have, however, been able to
show from the terrella experiments the existence of two types of precipitation which I think will show tin-
way in which the two types of storms are to be explained.

In one type most strongly developed on the night side, the horizontal components of the vrloclti.
the corpuscles are turned towards the east; and at the same time, with a proper adjustment of rnagnrtki-
tion and stiffness of rays, we get precipitation on the evening side with the horizontal component of iimtimi
turned towards the west.

I think these two types correspond respectively to the negative and positive polar storms. Thus
the typical distribution and direction of the two types of storms can be explained when we assume- the
polar disturbances to be a direct effect of electric radiation from the sun.

The local storms with their centres to the north of the auroral zone, which had a great effect at
Axeloen, will, I think, be explained by our radiation theory, when we remember that the precipitations
approach the magnetic axis when the rays become softer, and we should merely have to assume that the
sun gives out rays of different stiffness.

We found that the large storms usually had their centres in lower latitudes than the small storms.
This indicates that probably the rays given out by the very powerful sources in the sun, are stiffen
than those from the many small sources producing the small storms occurring between the great maxima.

When the corpuscular currents strike the atmosphere, secondary processes may be called into play;
but if these secondary processes, of whatever kind they might be, are to produce magnetic effects of the
same order as the impinging rays, they must follow quickly after the primary action. For if secondary
effects of the same magnitude and frequency as the primary effects were present, and these secondary
effects could show up several hours after the sun agency had left the place, it would be difficult indeed
to explain the existence of a calm period and the great rapidity with which the negative storms erase
after midnight.

We saw that the typical field of polar storms could be explained by a current-system coming in
from space corresponding to the precipitation of electric rays from the sun. This would strongly
support the view that by far the greater part of the disturbance effect observed is caused ilirecllv by the
currents of sun-radiation.

CHAPTER IV.

EXPERIMENTS MADE WITH THE TERRELLA ESPECIALLY FOR THE PURPOSE
OF FINDING AN EXPLANATION OF THE ORIGIN OF THE POSITIVE AND

NEGATIVE POLAR STORMS.

108. In the following pages, we shall describe a series of experiments that were made for the
purpose of gaining a clear idea of the course of the rays about our magnetic terrella.

It is, of course, of great importance to calculate, as STORMER has done, the separate possible paths
that electric corpuscles from a distant cathode may describe about an elementary magnet, under the
influence of the magnetic forces originating from the magnet; and in so doing he has thrown much
light uppn my earlier experiments, and, on some essential points, has supported the theory which it
is my intention to work out. But as long as the mathematical problem is not entirely solved, so that
the distribution of nil paths in space is found, the utility of such calculations as an endeavour to
explain, lor instance, the positive and negative polar storms, is very limited. The experimental investi-
gations with a magnetic terrella in a large discharge-tube are another matter. There it is possible, by
various means, to see how the rays group together round the terrella, and even to photograph the
phenomena.

It is apparent that in this way a full, clear idea of the phenomena may be obtained, so that the
results, as we shall now see, may be successfully transferred to the relations between the sun and the
earth, as regards the various terrestrial-magnetic and auroral phenomena that have been observed.

We can, as will be seen, guard against the liability of our discharge-tube, owing to its compa-
ratively narrow proportions, having any injurious influence upon the range of the conclusions that can
lie drawn from any of the results, and those who will closely follow the entire series of elaborate ex-
periments which have been made, will end by seeing how great difficulties resolve themselves into
nearly perfect lucidity. Some of the experiments last described, were made some time after the first
series; I have not, however, on that account, omitted any of the previous results, as I considered it
best that the method adopted could be plainly traced.

The experiments now to be described have nearly all been made with the machine shown in
lig. 67 (Section I), generating a direct current with a tension of up to 20 ooo volts. The arrangemen
of the sets of apparatus was also similar to that shown in the figure, but the discharge-tube now was not
cylindrical but prismatic, composed of flat plates of glass, so that the photographs taken of the terrella
should not be contorted by the passage of the light through the curved glass of unequal thickness. The
prismatic discharge-tube, which is shown in fig. 200, was formed of plates of glass, 20 mm. in thickness,
cemented together with »cementium«, and finished outside with »picei'n«. There was no great difficulty
in keeping the tube air-tight, even if it were exhausted down to a pressure answering to 0.0005 mnl-
of mercury ; but with a low pressure such as this, there was vapour in the discharge-tube, of which
the pressure may well have been several times as great as that mentioned above; but in the experi-
ments here described it had no disturbing effect upon the results, as we generally worked with greater
pressure.

554

P.lRKF.I.AXn. Till: XOKWKGIAX AI'ROKA POLARIS KXPKIMTIOX, I QO2 - —

In order to obtain clear phenomena in the experiments, it is important that the discharge-tube
shall have been exhausted for several days, and that during this time the terrella shall have been
frequently magnetised, thus becoming' heated and giving off gases. The discharges, moreover, must
have taken place abundantly, so that superfluous gas is removed from the electrodes and the inner
surfaces of the discharge-tube.

One drawback in the photographing <>l tin- various light-phenomena was the rather bright, dis-
turbing reflections trom the plaU -glass sheets. They have been to some small extent removed in the
retouching of the prints.

Fig. 200 is a photograph taken during an experiment with a terrella No. 5, which was 5.5 cm. in
diameter, and suspended in such a manner that the magnetic axis coincided with the axis of rotation,
The first series of experiments in the following pages, until stated otherwise, have been made with this ter-
rella, of which the magnetic moment fur different magnetising currents is given graphically in fig. 70 (Part I).

In the experiment shown in tig. 200, the terrella is provided with two fixed screens, one hori-
zontal round the equator, anil one vertical. On the horizontal screen moreover, there are fixed 5 short
thick pieces of metal wire, coated, as are also the screens and the terrella, with tungstate of lime. The
picture is interesting in that it shows how the rays from the cathode are thrown upon the walls of the
discharge-tube; and it also shows how the rays are drawn in towards the terrella in the form, previ-
ously often mentioned, of two luminous horns near the poles. The dark space between these luminous
horns widens greatly if the magnetisation of the terrella is increased. The rays are thrown down in
abundance upon the under surface of the discharge-tube, and similarly up towards the top surface. The
rays are moreover thrown forcibly against the left side surface, looking from the cathode towards the
terrella; and the terrella is magnetised with the south pole uppermost. On the right side surface there
is no appearance of any corresponding great precipitation of rays. It will be seen that here no perceptible
rays reach the back surface of the discharge-tube.

A great number of experiments have been made with terrella No. 5, and photographs have been
taken trom various points simultaneously, during each separate experiment. Such photographs have been
taken, tor instance, of 12 different positions, with the vertical screen tui'iu d right round, 30° each time.

PART II. POLAR MAGXKTIC PHENOMENA AM) TERRKLLA EXPERIMENTS. CHAP. IV.

555

Fig. 20 r,

556 B1RKKLAXD. THE NORWEGIAN' AURORA POLARIS KXPKDITIOX, 1902 — 1903.

It has not been necessary, however, to reproduce more than a few of these photographs, as other ex-
periments that have subsequently been developed from the above, more easily show clear results.

In the following pages we speak of the north and south sides, i. e. respectively the upper and
under sides of the horizontal screen, and the east and west sides of the vertical. We calculate the
angle between the vertical screen and the centre line between the terrella and the cathode positive
eastwards from o° to 360°.

In order to have an unmistakable manner of indicating the angles which we have occasion to
mention in the following pages, we shall refer them to the axis about which the terrella ran be
rotated -- which, in these experiments, is always vertical - - and a horizontal plane through the centre
of the terrella.

We employ the designations easterly hour-angle and declination to indicate the position of a place.
The hour-angle is then calculated in the horizontal plane eastwards from the centre line between the
centres of the cathode and of the terrella, to the projection of the place upon the horizontal plane, and
the declination is an angle with its vertex in the centre of the terrella, and one side passing through
the place in question, and the other through the projection of the place upon the horizontal plane. The
northern declination is positive, the southern negative.

In the eight photographs reproduced in fig. 201, the experiments were made under a pres-
sure of about 0.002 mm., with 25 milliamperes through the discharge-tube, and 30 amperes upon the
terrella.

In Nos. i and 2, the easterly hour-angle of the vertical screen was 330°, No. i being photographed
90° east of the screen, and No. 2 90° west of it. The terrella, it will be noticed, is seen very little from
above. In Nos. 3 and 4, the easterly hour-angle of the vertical screen was 30", No. 3 being taken 90°
east of the screen, and No. 4 90° west of it. In Nos. 5 and 6 the hour-angle of the vertical screen
was o°, the photographs being taken as before, but from a place with a declination of 25°, so that tin
terrella is seen from considerably above.

It should be remarked that the light-figures here seen upon the northern side of the horizontal
screen are of course exactly repeated upon the southern side, since the axis of the magnet coincides
with the axis of rotation; but they are not visible here.

In Nos. 7 and 8, the hour-angle of the vertical screen was respectively 300° and 60°, and the
photographs were taken respectively 120° and 55° east of the screen.

With regard to the luminous precipitation upon the phosphorescent screens, that upon the vertical
screen shows that a very considerable part of the cathode rays are deflected towards the left before
they reach the terrella, and then, as we have seen, thrown against the left side surface of the discharge-
box, looking from the cathode towards the terrella (fig. 200).

This phenomenon, in which a large proportion of the rays arc carried past the terrella, and arc
nearest to it some way out on its afternoon side in a direction opposite to that of the earth's rotation,
must be regarded as very important. We shall frequently return to it in the course of the experiments.
It is deflected rays from the sun such as these, that we have previously assumed to be the principal
cause of the positive equatorial storms. We shall also return to this ray-phenomenon in discussing the
diurnal variation of the terrestrial magnetism and the zodiacal light.

In photograph No. 5, there are two places, A and B, in which rays descend upon the horizontal
screen, and it is these two instances that we shall first consider here. We shall see that the more abundant
of the two, which we will call A, and whose eastern boundary is very nearly a straight line, is due to rays
which, if not arrested by the screen, would travel round the terrella in a direction from west to east, oscillating
alternately above and below the plane of the magnetic equator, and most of them descending at last in "the
auroral zones"; but they never seem to come into contact with the terrella to the north of the northern

PART II. POLAR MAGNETIC PHENOMENA AND TERREL1.A EXPERIMENTS. CHAP. IV. 557

auroral zone or to the south of the southern auroral zone. The smaller precipitation, B, is due to quite
another class of rays, which, unlike those of A, operate close to the terrella north of the northern
auroral zone or south of the southern auroral zone.

The aim of the experimental investigations here described, is to obtain a clear idea of the general
course of these two classes of rays. We shall first show, by numerous experiments, how the rays
forming A curve round the terrella, rising and falling above and below the equator, when not arrested
by the screens. In the next place, the rays forming B will be investigated by an altogether different
series of experiments. We shall see, among other things, that rays of the first class will give us a
natural explanation of the negative polar storms, while the rays belonging to the second group will
help to explain the positive polar storms. In the following pages we shall speak of these two classes
of rays as rays of group A and rays of group B.

In fig. 202, eight more photographs are given, representing various experiments. No. i of
these answers to No. 5 of fig. 291, the only difference being that here the terrella is magnetised with
10 amperes instead of 30. Otherwise everything is the same. Only the effect of the precipitation A is
visible, that of B, for reasons that will be made clear later, being no longer found on the horizontal
screen. Some of the rays forming A now fall upon the terrella, and we obtain a figure upon the front
of it that resembles the luminous figures shown in figs. 66 and 68 in Section I.

Photograph No. 2 also shows conditions similar to those of No. 5 of the preceding Plate, except that
the hour-angle of the vertical screen is 180°. In the precipitation B there appears the shadow of one
of the cylindrical pegs. In some of the experiments it sometimes happens that two shadows of the same
peg are seen, one of them being cast by rays of the precipitation A, the other by B.

Photograph No. 3 was taken for the purpose of examining the sharp line of precipitation that forms
the eastern limit of A on the horizontal screen. The experiment was made under the same pressure
and with the same discharge-current as before, and the magnetising current to the terrella was of 30
amperes. The hour-angle of the vertical screen was 90°, and the photograph was taken 45° to the
west of it. The experiments were made by turning the terrella in such a manner that the vertical screen
came near the line of precipitation on the horizontal screen. If the vertical screen were turned ever so
little more to the east than the line of precipitation on the horizontal screen, no precipitation was found
upon the vertical screen. On the other hand, if it were turned less to the east than that line, precipita-
tion appeared upon the vertical screen in the form shown in this photograph. We at once get the
impression that the rays bend down towards the line of precipitation, where, if they could get through
the horizontal screen, they would cross one another, so that the rays that at first were above the screen
would go below it, and vice versa. It is then a natural proceeding, if we wish to study the rays in A,
to experiment, as we have done, with a horizontal screen alone, in which there is a slit parallel with the
powerful line of precipitation; and also with a vertical screen alone, containing a radial slit at the mag-
netic equator. This vertical screen must be so bent that the line of precipitation, right from the terrella,
can be made to fall upon the slit in the screen, along the entire length of the line, so that all the rays
can get through the slit simultaneously. The arrangement of the experiments is also clearly seen from
their accompanying photographs, which will soon be described. A preliminary experiment was made,
and this is shown in No. 4 of fig. 202. Here a slit was made in the horizontal screen, which, however,
the first time, was not given the right direction along the line of precipitation. Next, a hole was made
in the vertical screen, near the auroral zone. We at once discover that close to the slit in the horizon-
tal screen, the rays leave the under side and form a second precipitation upon the north side of the
terrella, while the rays from above go through the screen, and form corresponding precipitation upon
the south side of the terrella. We have thus brought out the second of the remarkable instances of
precipitation represented in fig. 68, Section I.

Hirkdanil. The Norwegian Aurora Polaris Expedition, 1902—1903.

558

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

Fig. 202.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV. 559

We will now pass on to mention some experiments that were made gradually, first with three
round holes in a horizontal screen, next with two slits and then with three, in the horizontal screen, as
it appeared that when a part of the above-mentioned marked line of precipitation belonging to A fell
across a slit, a second line of precipitation appeared, which was also almost a right line, at an angular
distance from the first of 110°. When this second line of precipitation was also placed over a second
slit, the rays once more passed through the screen and formed a third line of precipitation, which was
also turned about 110° in relation to the second line of precipitation.

These experiments were both troublesome and lengthy, for every time an alteration was to be
made, the bottom had of course to be taken out of the discharge-box, and after the alteration had been
effected, the glass box had once more to be exhausted for several days, with frequent discharges, as
already mentioned, before it was again in perfect order.

Photographs 5 and 6 refer to an experiment in which 3 holes were bored in the horizontal screen,
with their centres situated radially, as the figures show. The experiment was made with a pressure of
about 0.002 mm., with a discharge-current of 23 milliamperes through the tube, and a magnetising
current of 8 amperes upon the terrella. The eastern hour-angle of the vertical screen was 240°; and
the photographs were taken respectively 120° and 60° to the west of the screen.

By this slight magnetisation, beautiful precipitation was obtained on the terrella, when the hole
farthest in on the screen was brought over the first line of precipitation. It was easy to prove by a
slight displacement, that it was the rays that came from above and passed through the hole, that formed
the precipitation on the south part of the terrella, and vice versa.

It will be seen that the precipitation does not only fall upon the terrella, but continues in the
second line of precipitation across the horizontal screen. By the employment of n amperes, the rays
through the first hole formed the western part of this precipitation upon the terrella, while, if the rays
were allowed to pass through the second hole — by a slight turn, so as to bring the first line of preci-
pitation over the second hole — they formed the eastern part of the precipitation upon the terrella, with
a continuation in the second line of precipitation on the horizontal screen. In these figures, 5 and 6,
we see distinct shadows of the pegs that are fixed in the horizontal screen. Much can of course be
concluded from the directions of these shadows, with regard to the course of the rays; but as the same
thing comes out more distinctly in another manner in subsequent experiments, we shall here only make
a few remarks. The shadow of the peg that stands on the first line of precipitation is faint, but often
extends some distance, and is curved almost like an arc of a circle with its centre in the centre of the
terrella. The shadows of the three pegs standing close together point outwards, and are formed of rays
belonging to precipitation B, which, however, is not distinctly outlined in the figure.

Photographs 7 and 8 are taken with the same pressure as before, with 20 milliamperes through
the discharge-tube, and with 16 amperes on the terrella.

There are now two slits in the horizontal screen, which here too have not been given quite their
correct form and position in relation to the first and second lines of precipitation. The angular distance
between the slits is, as will be seen from the precipitation, somewhat too small; for the slits could only
be determined by successive approximations, as the second line of precipitation does not appear until
the first slit is correctly cut, and the third line of precipitation until the second slit is correctly placed.
In the next experiment with three slits in the horizontal screen, however, the position and shape of the
slits are correct.

In this experiment, Nos. 7 and 8, both the second and the third precipitation came out distinctly upon
the terrella, but not so well as in fig. 68 in Section I. The photographs are taken from places with an
hour-angle of 90° and 270° respectively. Although the first line of precipitation lies on the west side of
the first slit, the second line of precipitation, it will be seen, falls a little to the east of the second slit.

560 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

It should be remarked that the position of the various lines of precipitation upon the horizontal
screen, depends somewhat upon the magnetising of the terrella. If, for instance, the current upon the
terrella is increased from 8 amperes to 30, the first line of precipitation will move back (westwards) a
little, with a parallel movement. The second and third lines of precipitation move at the same time; but the
angle between the first and second, and between the second and third lines of precipitation continues more
or less to be about uo° — 100°. This angle, however, also diminishes somewhat under stronger magnetisation.

In this experiment, another circumstance was also investigated. A thin screen, about 3 mm. in
height, formed of a strip of copper, was placed on its edge upon the terrella, and running from the
latter's north pole a little way down a meridian. The screen was then divided into three branches, and
was also coated with tungstate of lime. It was so placed that the rays which came through holes i and
2 would strike the terrella in the polar regions just where the little three-armed screen was. The in-
tention was to determine the direction in which those rays moved which struck the terrella in its polar
regions. It appeared from the experiments that the rays in the second polar precipitation, which belonged
to the very northernmost part of the precipitation up in the auroral zone, come fairly perpendicularly in
towards the terrella, though with some slight movement eastwards, while the rays both in the south-
western and south-eastern parts of the precipitation on the terrella to the north of the horizontal screen,
had a strong tangential movement, with direction from west to east.

STUDY OF THE RAYS OF GROUP A.

109. Experiment in which the Terrella had only a Vertical Screen. We shall begin by
describing a series of experiments which were made with the same terrella as before, in which the
magnetic poles coincide with the geographical; but the terrella now has only one screen.

This screen, which maintains a vertical position during the rotation of the terrella, was produced
by an abrupt bending of the former vertical screen, so that the latter comes to consist principally of two
plane portions, which intersect one another at an angle of about 100° in a vertical line, which is in
contact with the terrella in its magnetic equator. We will call the screen the vertical screen. The photo-
graphs here reproduced give a sufficiently clear idea of its form.

Fig. 203 shows 12 pictures from experiments with this arrangement with a vertical screen pro-
vided with a horizontal slit.

Nos. i, 2 and 3 are from experiments in which the terrella was magnetised with 8 amperes, the
discharge-current was of 25 milliamperes, and the pressure answered to o.ooi mm. The outer plane
part of the vertical screen formed an angle of 45° with the central line between the centre of the ter-
rella and that of the cathode. We shall simply, in the following pages, express this by saving that tlu-
screen had an hour-angle of 45°, referring only to the outer plane part of the screen.

The photographs were taken in a horizontal plane through the centre of the terrella, from places
with hour-angles of respectively 90°, 180°, and 270°.

When the screen here has an hour-angle of 45°, it does not to any great extent shut oft' the rays,
and the light-figures on the terrella (Nos. i, 2 and 3) are very much the same as if there had been
no screen. We recognise them from fig. 68 in Section I.

Photographs 4, 5 and 6 are from experiments made under very nearly the same conditions as the
preceding, except that the hour-angle of the screen is 135°. The photographs are taken from the same
positions respectively.

We here obtain a capital representation of the way in which the screen acts when the slit does
not fall near one of the lines of intersection of the rays, those lines which, on the horizontal screen,
we called lines of precipitation.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV.

561

Fig. 303.

Here only a narrow pencil of rays falls through the slit in the screen. These rays continue their
course round the terrella, undulating above and below the plane of the magnetic equator. There are
distinct nodes and loops visible in the light-figures upon the terrella, which resemble vibrating strings.
These figures become fainter according to their number, exactly like those in the preceding photographs;
and by magnetising the terrella more highly, they disappear from the equatorial regions, a circum-
stance which is in accordance with what we found with regard to the light-figures in fig. 68. The
reason of this must be that the corresponding rays, on higher magnetisation, go farther out from the
terrella, while those that were nearer turn right round, some of them striking against the terrella.

562 ISIRKKI.AND. TllK NORWKGIAN AURORA POLARIS KXPKDITION, 1902—1903.

Photographs 7, 8 and 9 were taken under the same physical conditions as the previous ones, only
lhat now the hour-angle of the terrella screen is 175", so that it nearly coincides with the first line of
intersection of the rays.

We see at once that now the majority of the rays pass through the slit in such a manner that the
second and third light-figures upon the terrella become very much as they were in Nos. i, 2 and 3, where
the screen did not act perceptibly. It will be seen, indeed, that something is wanting in some of the
uppermost polar percipitation in the second and third light-figures here, and this probably arises from the
slight precipitation of rays seen on the screen in No. 7 ; for it is certain that the rays that keep nearest to
the magnetic equator in their journey round the terrella, have not exactly the same lines of intersection
as those rays which intersect the equator at large angles. The angular distance between the consecu-
tive lines of intersection of the former rays is greater than that of the latter. The rays that form pre-
cipitation in the auroral zone, however, are just such rays as, in their discursion above and below the
magnetic equator, intersect that plane at great angles.

In these light-figures there are nearly always 110° between corresponding points in the precipita-
tion when 8 amperes are employed as the magnetising current. The rays in the third precipitation,
which are farthest up in the polar regions, intersect one another at the equator at an hour-angle that
is smaller by from 15° to 20° than that of the rays belonging to the more equatorial parts of the precipitation.

When a stronger magnetising current is applied to the terrella, several instances of secondary precipita-
tion appear on it, as we shall see; but there will always be three principal districts of precipitation in the
polar regions, lying about no0— 100° from one another. The fact that the position of these districts is
so independent of the magnetising conditions, is an exceedingly important one, as we may thus venture
to transfer the results to the earth, where the magnetic moment is so enormously great. There is, in
fact, on the earth, with regard to aurora, something which distinctly points to these fixed districts of
precipitation in the polar regions. In the north of Norway, for instance, from about 9 to 10 p. m., and
sometimes also between 4 and 5 a. m., there is a distinct culmination in the aurorae. Whether there is
any aurora at about 2 in the afternoon it is impossible to say, on account of the light-conditions; but at
any rate, during the darkest time of the year I have observed aurora several times at 4 in the afternoon
rom the top of Haldde in 1899 — 1900, aurora which grew fainter and disappeared, only to return again
later in the evening with increased strength. I think we are justified in concluding, from analogy with the
experiments, that the rays that descend in the auroral zone are just those that come most perpendicularly
down to the earth, and therefore those that make their way farthest down into the atmosphere.

Photographs 10, n and 12 in fig. 203 were taken during experiments in which the terrella was
magnetised with 28 amperes. The pressure, indeed, according to measurement, was somewhat lower than
before, namely, 0.0005 mm- 1 Dut '* was subsequently proved that the statements of pressure here below
0.002 mm. are very unreliable, as there was vapour in the discharge-tube, which we had not troubled
to condense, as it was of little consequence, in these experiments, whether it were there or not. A cur-
rent of 23 milliamperes was sent through the discharge-tube, and the hour-angle of the screen was 155",
The photographs were taken as before.

Photograph 10 shows distinctly how the first line of intersection of the rays falls just over the
slit. The continuation of the line of light is seen upon the screen in a lengthening of the slit.

Photograph n shows the second principal precipitation and the beginning of the third; but be-
tween them are two instances of secondary precipitation, which are especially distinct in the polar
regions.

Photograph 12 shows distinctly the third principal precipitation, and in addition a number of others,
fainter, and following one upon another, closer and closer, with increasing hour-angle. We have occa-
sionally been able to count nearly 20 of them, fairly distinct.

PART II. POLAR MAGNETIC PHENOMENA AND TKRREU.A EXPERIMENTS. CHAP. IV.

563

Fig. 204.

564 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Nos. i, 2 and 3 of fig. 204 were obtained under the same conditions as the three preceding photo-
graphs, except that the hour-angle of the screen was 265°. No. 2 shows that it is the second principal
line of the rays' intersection that falls upon the screen. Two secondary precipitations are also seen upon
the screen ; but we shall return to these later.

The last two experiments show that the angles 155° and 265° correspond to the first and second
lines of the rays' intersection with the horizontal plane (the magnetic equator), when the magnetising
current is 28 amperes. By other experiments, the angles corresponding to the first three lines of inter-
section were found to be 155°, 265° and 365°, for the same magnetisation, and the angular distance
between the second and third lines of intersection is thus only 100°.

By experiments with a magnetising current of 8 amperes on the terrella, the angles were found
to be 168°, 272° and 370°

In experiments with the terrella highly magnetised, it was very interesting to watch the changes
in the phenomena as the terrella became warm and gave off" gas. To begin with, 8 distinct secondary
precipitation-figures were once observed upon the night-side of the terrella, partly overlapping one
another, and coming closer together towards the morning-side. The number of the patches of precipita-
tion increased as the terrella grew warmer and gave off" more gas, and finally there appeared continuous
polar bands, answering to the north and south auroral zones.

Nos. 4, 5 and 6 were obtained under the same conditions as the preceding photographs, except
that the hour-angle of the screen is now 250°, and therefore somewhat less than what would answer
to the second line of intersection of the rays. It is also clearly seen in photograph 5 that the rays
have not yet drawn together so that all pass through the slit. The third patch of precipitation on the
terrella in No. 6 also bears evident signs of this.

The next six photographs are from a series of experiments that were made with the screen in the
same position, but with pressures of 0.0009 mm., 0.0019 mm., 0.0052 mm., 0.012 mm., 0.02 mm. and
0.05 mm. The only pressures represented here are 0.0009 mm. and 0.012 mm. In the cases of the
lowest pressures, vapour has certainly, as already mentioned, played an important part.

Nos. 7, 8 and 9 are from experiments with a pressure of 0.0009 mm- ar)d the screen at an hour-
angle of 40°. The photographs were taken from the same three positions as before, with respectively
90", 180° and 270° east hour-angle.

The strength of the current through the discharge-tube varied from 18 to 22 milliamperes, and the
tension between the electrodes from about 4500 to 3500 volts. The current magnetising the terrella
was of 28 amperes.

No. 7 shows precipitation of returning rays upon the screen. In No. 8 the second precipitation is
seen solitary, but with the third precipitation there are several secondary patches.

Nos. 10, ii and 12 were taken under a pressure of 0.012 mm., with a current of 24 milliamperes
through the discharge-tube, a tension of about 2500 volts, and a magnetising current of 28 amperes.
The figures give a hint of the transition to the continuous band of light round the poles of the
terrella, which appears with softer cathode rays; and it will be seen that the parts about the magnetic
equator become more and more free from precipitation.

Experiments were made for the purpose of determining what tangential motion in relation to the
terrella those rays had which formed the precipitation in the polar regions on the night and morning
side of the terrella. The experiments were made with various pressures, and both the primary and the
secondary precipitation was examined by means of the screen. It appeared in every case that the rays
had a motion parallel with the auroral zone in a direction from west to east. Corresponding precipitation
upon the earth would thus give rise to negative polar storms, as the various cases of secondary preci-
pitation summed themselves up in their magnetic effects very much as shown in the case of tin rays in
the diagrammatic figure 50 a, in Section I.

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV. 565

It will be seen that almost everywhere the uppermost, polar part of the light-figures on the
terrella, consists of the point of intersection of two strips of light which intersect one another at often
a considerable angle, sometimes, indeed, more than 90°. It was interesting to see that the corre-
sponding angle between the strips of light when they fell upon a vertical screen, was always much
smaller than on the terrella, being quite acute. It was enlarged on the terrella by the oblique projection
of the strips of light from west to east. The apex, when it touched the vertical screen, looked like a
section of the wedge of light or the horn, often seen in the air about the auroral zone during
experiments.

Figures 7 — 12, when considered as a connected group, give an indication of the reason for the
appearance of all these secondary precipitations when the rays are soft and the magnetic force great.
We receive the impression that some of the rays in the great bundle of rays that is working its way
round the terrella from west to east, turn back once or oftener near the polar zones, describing some-
thing that resembles an epicycloidal curve. The stronger the magnetism, the more loops do the rays
make, and the steeper the incline at which they intersect the magnetic horizontal plane. We shall return
to these cases of secondary precipitation in the next section of the experiments.

We shall now in passing mention some experiments that are closely connected with the preceding
ones, but which nevertheless originally formed the transition to the study of rays of group B.

When the screen had an hour-angle of about 90°, there might sometimes be noticed on its east
side a remarkable shadow of the wire that conveyed the current to the terrella, this being caused by
rays that have come over the polar regions of the terrella, and have then turned right round so that
they come near the earth in the auroral zone with a tangential motion from east to west.

Nos. 13, 14 and 15 of fig. 204, are from experiments such as these. In both experiments the pres-
sure was o.oi mm., 21 milliamperes passed through the discharge-tube with a tension of 3200 volts, and
25 amperes were employed for magnetising. The positions of the screen were with hour-angles of
82° and 87°; and in both cases the photographs were taken from places with hour-angles of 130° and 310°.

Nos. 13 and 15 show distinctly how the shadow of the metal wire at a distance of 3 or 4 centi-
metres to the east, is thrown upon the screen in the form of two lines meeting in a point, which runs
farther in towards the terrella in No. 13 than in No. 15. No. 14 gives the corresponding view of the
phenomenon from the opposite side. What is particularly interesting about this last-mentioned photograph
is that part of the conducting wire coated with phosphorescent matter is distinctly seen above the
screen, illuminated by the rays, and thus casting a shadow back upon the east side of the screen. The
rays which cause the formation of the shadow of the conducting wire come from above and strike a
part of the wire that is more than 2 cm. above the north pole of the terrella. They then shoot down
and bend westwards, coming in contact with the screen as the photographs show. It is a striking fact
that in spite of the bending and twisting of the separate rays, the pencil of rays succeeds in throwing
relatively clear shadows.

Several experiments of this nature were made without photographing them, and the particularly
sharp shadow of the conducting wire, with the characteristic point directed towards the auroral zone
was always noticeable. The experiments were, as we have said, an introduction to the study of what
we called rays of group B, which give us the foundation for the explanation of the positive polar storms.

In photographs 13 and 15, the characteristic light-figures on the east side of the screen will have
been noticed. These are of another kind than the precipitation upon the east side of the vertical screen,
which we saw when the hour-angle of the screen was small. Upon closer investigation it appeared that
a slight precipitation of returning rays also took place upon the east side of the screen when the hour-
angle of the latter was about 250°. It would thus seem as if this phenomenon could be obtained in
three positions of the screen, although the last, with 250°, was certainly very inconspicuous.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902-1903.

566

lilRKEI.AND. THK NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

An endeavour was made to determine the positions of the screen in which the precipitation in
these three cases was nearest to the terrella at the equator.

The first precipitation was nearest at an hour-angle of about 30". In the second precipitation it
was not easy to determine the position, as the precipitation became much fainter as the screen was
turned; but it appeared to be at from ioo"to 120". The position in which the third precipitation was nearest
to the equator was hardly capable ot determination, but it must have been somewhere between 250°
and 310".

Finally, it was observed that when the screen had a position answering to an hour-angle of 153°,
there was very marked precipitation upon its east side, nearest the corner where the screen is bent.
This is also visible in No. 11 of lig. 203. It consists of returning rays. It is possible, as we have
said, that they turn right round and give rise to the secondary precipitation upon the terrella. There
is yet another circumstance which we will mention here. When there was comparatively much gas in
the discharge-tube, there appeared, as already mentioned, continuous, luminous polar bands. These were
not closed circles, but were somewhat spiral in form, as they la}' at a higher latitude on the day-side
than on the night and morning-side. This circumstance we have previously shown in photographs, but
it is also applicable here where the magnetic axis is the axis of rotation.

110. Experiments in which the Terrella is Surrounded by a Horizontal Screen. The terrella
was surrounded by a horizontal screen of aluminium after the vertical screen had been removed. The
new screen, which is shown in fig. 205, had three holes or slits cut in it, so situated in relation to one
another that the angle between the median lines of the first and second slits was no", of the second and

third no", and of the third and first consequently 140°.
To the terrella itself were attached two almost
radially projecting wires, as fig. 206 shows. They,
were placed there in order that conclusions might be
drawn, from their shadows upon the terrella and screen,
respecting the course of the rays.

Nos. i , 2 and 3 of fig. 206, are from an experiment
in which the pressure was 0.0012 mm., the discharge
current 20 milliamperes, the tension 3600 volts, and the
magnetising current 8 amperes. All the photographs of
experiments with; this screen were taken from positions
in which the screen was viewed from above at an angle
of 20". The first slit is so placed that its median line
forms an angle of 147° with the central line between the
centres of the terrella and the cathode. For the sake of
brevity, we will say that the hour-angle of the median
line was 147". The photographs were taken from posi-
tions with eastern hour-angles of 90", 180" and 270°.

It will be seen that the first line of precipitation falls quite to the east of the slit, with the result
that no second or third precipitation appears on the terrella. Nos. 4, 5 and 6 are from an experiment
where the pressure was 0.0018 mm., the discharge-current 22 milliamperes, the tension 2800 volts, and
the magnetising current 8 amperes. The first slit is placed so that the hour-angle of the median line is
155°, and the photographs were taken from positions of which the hour-angles were 60°, i8ouand3io°.
The first line of precipitation falls more or less over the first slit, so that the rays pass through it

205.

PART II. POLAR MAGNETIC PHENOMENA AND TERKELLA EXPERIMENTS. CHAP. IV.

56?

bo

E

568 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, I QO2 — 1903.

and form a new line of intersection above the second slit, through which the rays also pass. We
see all three precipitations upon the terrella, and the third line of precipitation upon the horizontal
screen could also be distinguished, although faintly, during the experiment. It fell on the margin of the
third slit.

Some interesting experiments were made for the purpose of throwing light upon the origin of
the secondary precipitation, of which frequent mention has been made in describing the experiments
with a vertical screen (see figs. 203 & 204), and which was found again here under different conditions.

Nos. 7, 8 and 9 are of experiments with a pressure of 0.0014 mm- a discharge-current of 18.5
milliamperes, a tension of 3300 volts, and a magnetising current of 24 amperes. The photographs were
taken from places with hour-angles of 90°, 180° and 270°.

Slit i was placed at 125°, just so that a small pencil of rays fell through the screen at the end
nearest the terrella. This little pencil of rays which thus passed through the screen, at once gave rise
to a distinct, but faint, precipitation upon the terrella. Even the third precipitation was single, without
any secondary precipitation; but there is a strange precipitation upon the horizontal screen in which our
attention is especially attracted by a line of precipitation almost parallel with the first line of precipita-
tion, and only a few millimetres east of it.

That this secondary precipitation on the horizontal screen is produced by rays that have passed
through slit i at the end nearest the terrella, is apparent from the fact that if the terrella is turned so
that the first line of precipitation falls either entirely on the west side of the slit, or entirely on its east
side, the secondary precipitation completely disappears in both cases.

The next experiment was to let the rays of the secondary precipitation through slit i at the same
time as the first main precipitation came through it; for the distance between the two precipitations was
rather less than the width of the slit.

It appeared that as soon as the secondary precipitation also passed through the slit, new precipi-
tation made its appearance both on the horizontal screen and on the terrella, a secondary precipitation
suddenly appearing in the polar regions on the night-side, similar to the primary precipitation lying
immediately to the west.

Nos. 10, ii and 12 are from an experiment which shows this. The pressure was 0.0008 mm., the
discharge-current 17 milliamperes, and the magnetising current 24 amperes. The photographs were taken
from the same positions as the preceding ones.

We see distinctly that the third polar precipitation consists of two consecutive precipitations. That
on the east is the secondary.

The experiment was repeated several times without being photographed. Again and again it
appeared that when the first secondary precipitation upon the screen passed through the slit, a new
precipitation was formed nearer the second slit, the innermost part of it falling through that slit at the
end nearest the terrella, thereby producing the secondary precipitation upon the night-side of the ter-
rella, in the polar regions, farther out on the night-side than the first, which was there already.

It was distinctly seen that the second secondary precipitation upon the horizontal screen formed
a much smaller angle with the first precipitation than did the second principal precipitation. It was the
outer part of the first secondary precipitation which, by passing through the first slit, produced a new
line of precipitation not more than 50° farther east upon the horizontal screen. Only because the end
of the second slit nearest to the terrella was comparatively wide, did a pencil of rays from this preci-
pitation pass through there, and occasion the secondary precipitation after the second polar precipitation
upon the night-side.

We have previously touched upon the possibility that the connected polar precipitations upon the
terrella (in the auroral zone) were composed of a whole series of close-lying secondary precipitations

PART II. POLAR MAGNKT1C PHENOMENA AND TERRELI.A EXPERIMENTS. CHAP. IV. 569

(see p. 552); and we assumed, after discussing our experiments, that the rays again and again looped
back on themselves and described curves that more or less resembled epicycloids. Rays such as these
would be able to pass at the equator and nearest to the terrella with a velocity-component from east to
west, i. e. a direction the reverse of that of the primary rays.

It is interesting here to call to mind (cf. pp. 82 & 83, Section I) that the negative equatorial storms
were explained by the bending round of rays in the vicinity of the magnetic equator, so that they encircled
the earth from west to east, while the positive equatorial storms were explained by rays with a compo-
nent motion from east to west, nearest the earth at the equator.

We are not able to see, in the photographs as reproduced here, any distinct signs of shadows
cast by the two parallel wires upon the terrella, although, during the experiments, such shadows were
easily discernible, though always faint.

In both precipitations, A and B, upon the horizontal screen, there occurred in certain positions of
the terrella, curved but parallel shadows of these wires. These shadows have been especially useful in
investigations for the purpose of coming to an understanding regarding the rays of group B, as we shall
presently see.

111. Equatorial Rings of Light. In connection with the ray-phenomena just described, belonging
to group A, we will discuss a phenomenon which has already been mentioned several times, and called
equatorial rings. The phenomenon is described in "Expedition Norvegienne 1899 — 1900", p. 41 ; but un-
fortunately on that occasion the luminous rings were not photographed. There is, however, a photograph
of one in Section I of the present work, p. 80, fig. 37.

The equatorial ring is formed of rays that curve round the terrella from west to east. Under spe-
cially favourable experimental conditions, the concentration of rays near the plane of the equator is so
great that the rarefied gas is rendered luminous. It is not only rays that move exactly in the plane of
the equator that form the ring, but more especially rays that move alternately above and below the plane
of the equator in its immediate vicinity. We will here point to photographs 5 and 6, fig. 203, where
ust such rays as these are made distinct by their precipitation upon the terrella about the equator. Even
the rays that come nearest to the terrella in the polar regions, and which thus, in their passage through
the plane of the equator, intersect it at large angles, will perhaps serve to produce the luminous ring, as
they bring about a powerful concentration of rays just at the magnetic equator. We have seen indeed
that the rays from one primary pencil, have numerous lines of intersection in the equator. When
such rays, by a suitable proportion between the magnetism and the stiffness of the rays, are free to move
a great many times round the terrella near the equator, the gas there becomes luminous, and we may
have the equatorial ring. As may be expected from what has been stated, the appearance of the ring is
almost a chance phenomenon; it is unstable, and many fruitless attempts may be made to induce it to
show itself.

The three photographs forming fig. 207 were taken several years ago, and the experiments on
that occasion were made with a powerful influence-machine. The strength of the current with these
machines, however, is so small that the phenomena are not bright. The rarefied gas itself, moreover,
plays a very important part if the phenomenon is to be successful. It seems as if impurities were an
assistance. The experiments were made with a tension of about 6000 volts, and with the employment
of about 10 amperes upon the terrella — No. 2, with a diameter ofiocm. The magnetic moment with this
current-strength was about 50,000 C. G. S. The ring is distinctly seen to be rather thin and broad, its
outer margin often extending far beyond the terrella. The inner margin of the ring often comes right
up to the terrella; but I have several times observed the ring standing unattached in the gas, with a
dark interval between it and the terrella.

Fig. 207.

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV.

571

Fig. 208.

Of late, I have made these experiments partly by the employment of high-tensioned electric waves,
produced by DUDELL vibrations, through the discharge-tube. It seems to be a comparatively easy way
of producing them. I have, however, preferred a direct current from the previously-mentioned 2o,ooo-volt
machine (fig. 67), and have employed discharges of up to 35 milliamperes through the receptacle.

The four photographs in fig. 208 were taken from experiments such as these. The terrella No. 4
employed was 8 cm. in diameter, and a current of from 10 to 12 amperes was employed upon it
(M = 28000 C. G. S.). The magnetic axis was set at an angle of about 30° with the axis of rotation,
and the magnetic equator was drawn in pencil upon the terrella, as we were to see whether the ring
coincided with the magnetic equator in all positions of the terrella. The first two photographs were taken
while the magnetic north pole (below) had an hour-angle of o°. They were taken from places with hour-
angles of 90° and 270°.

It will be seen that although the angle between the magnetic axis and the axis of rotation is made
so great, the equatorial ring lies fairly parallel with the magnetic equator. The ring here is most
powerful!}' developed farthest from the cathode.

572 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

The next two photographs were taken during another experiment, from positions with hour-angles
of 90° and 180°.

The equatorial ring has not come out particularly well here, but on the other hand the polar rings
are quite distinct. We shall give better illustrations of the polar phenomena, however, later on, and will
therefore not dwell upon them now. These earlier photographs were taken during experiments in which
the discharge-tube was cylindrical, and not with the prismatic discharge-receptacle, which we used sub-
sequently. In No. 3, there are indications of the equatorial ring having been brighter out from the
terrella than close to it.

As will be seen later on, in the chapter on zodiacal light, I easily succeeded in producing these
equatorial rings round a magnetic globe, which itself served as cathode. It was sufficient to employ a
difference of a few hundred volts in the tension between the electrodes, in order to produce the discharge
under these conditions.

It is therefore not impossible that these rings in every case occur owing to the magnetic globe
having become negative in relation to its nearest surroundings in the discharge-tube.

In the meantime it is a fact that a considerable number of rays move round the terrella, from west
to east, close to the equator; this has been demonstrated by nearly all the numerous experiments which
have just been described.

STUDY OF RAYS OF GROUP B.

112. We now pass on to experiments made with terrella No. 5 provided with a vertical screen over
its north pole, the plane of this screen passing through the axis of rotation, which still coincided with
the magnetic axis of the terrella. The screen was placed thus in order that the course of the rays in
the polar regions over the terrella could be studied. At the same time, the former horizontal screen
was retained (see fig. 205), now, however, entire, without the three slits, in order to prevent the formation
of polar precipitation by rays of group A.

The two radial wires, about 4 cm. in length, standing out from the terrella, were also retained, in
order that their shadows thrown upon the screens might give information as to the course of the rays.
The photographs that are reproduced here distinctly show the position of the screens and wires. At first
a round hole was made in the vertical screen, and later on a slit was added.

It now appeared that when the plane of the vertical screen formed an angle of about 30° with the
line of direction from the centre of the terrella to the cathode, characteristic precipitation became visible
upon the screen, extending far over the screen towards the axis, when the terrella was magnetised with
8 amperes. When, on the other hand, 25 amperes were employed upon the terrella, the precipitation
had moved right out to the right margin of the screen, seen from the cathode. With the employment
of 14 amperes, the precipitation was so situated that its innermost edge lay farther in than the above-
mentioned hole in the screen.

The nine photographs in fig 209 represent various results of the experiments made.

Nos. i and 2 represent experiments in which the hour-angle of the vertical screen was 30°, this
angle being reckoned to the wing of the screen in which was the hole. The photographs were taken
from positions with hour-angles of 300° and 120-°, and looking from above at an angle of from 15° to
20° with the horizon. The pressure was 0.0014 mm-> the discharge-current 24 milliamperes, and the
magnetising current 14 amperes.

Nos. 3 and 4 are of a similar experiment, in which the vertical screen, with the terrella, is turned
160°, in order to obtain clearer precipitation. We say then that the hour-angle of the screen is 190°
and the photographs were taken from places with hour-angles of 310° and 90°. The pressure and
magnetising current were as before, but the discharge-current and the tension were respectively 20 milli-
amperes and 2700 volts.

PART ii. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. iv.

573

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903.

73

574 filRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

We distinctly see the shape of the precipitation upon the vertical screen, answering to a magne-
tisation of 14 amperes. The lowest curved edge of the precipitation upon the west side of the vertical
screen lies higher than the uppermost edge of the precipitation upon the east side of the screen. For
the sake of comparison we would observe that in photographs 7, 8 and 9—10 which we shall return
later — the precipitations are seen with very low magnetisation, namely 6.5 amperes.

In the above-mentioned experiment with 14 amperes to the terrella, it was ascertained that
precipitation B upon the horizontal screen, had disappeared in the position given to the vertical screen
of an hour-angle of 190°, but the western part of precipitation B appeared when the vertical screen was
turned 15° or 20° either west or east. This shows that the cathode rays which produced this part of
precipitation B, were stopped by the vertical screen in the position shown in the photograph, but that
the rays slipped past and descended upon the horizontal screen as soon as the vertical screen was turned
a little. It still appeared that if the vertical screen were turned eastwards to an hour-angle of about 230°,
the luminous line of precipitation bounding the easternmost part of precipitation B upon the horizontal
screen, also made its appearance.

Photographs 5 and 6 were taken from an experiment with a pressure of o.ooi mm., 14 amperes
to the terrella, 3200 volts tension, and 19 milliamperes to the discharge-tube. The vertical screen has
an hour-angle of 240°, and the photographs are taken from positions with hour-angles of 310° and 90°.

The rays here are fairly stiff, but the westernmost part of precipitation B is seen sufficiently
clearly, while the easternmost has not come out distinctly in the photograph.

Experiments were made with 8 and 24 amperes to the terrella. With low magnetising — 8 amperes
- the precipitation on the day-side (that turned towards the cathode) of the vertical screen was of great
extent when the screen had an hour-angle of, for instance, about 200° (or 180° less, see, for example,
Nos. 7 — 9 of fig. 209). On turning the screen eastwards, so that the angle became greater, the preci-
pitation moved out; but there was still a little left on the uppermost right corner of the screen, look-
ing from the cathode, right until an hour-angle of 260° had been reached (see No. 5).

With a magnetisation of 24 amperes, the precipitation was always far out on the screen, and had
already disappeared with a turning of the screen to an hour-angle of 220°.

When the terrella was turned so that the vertical screen had an hour-angle of about 225°, all
precipitation of light disappeared from the day-side of the screen when the magnetisation was 14 amperes,
and did not return to that side until the screen had been turned about 135° farther, i. e. when the
hour-angle of the screen was about 360°, and the former night-side was about to become the day-side.
It was otherwise with the night-side of the screen. There was at first no light there either, when the
light had disappeared from the day-side, with an hour-angle of 225°; but after turning the screen 75°,
there was the maximum of a faint precipitation upon the night-side on the wing of the screen in which
was the hole, and which then had an hour-angle of 300°. This precipitation is closely connected with
the small, faint half-ring of light that passes through the pole (see fig. 134 and p. 298 in Section I).

Further experiments were made for the purpose of explaining precipitation B upon the horizontal
screen, when employing 8 amperes to the terrella. It was observed that precipitation B originated in
rays which, if the vertical screen were in a suitable position (an hour-angle of about 15°) and caught
them, fell near the lowest, curved border of the precipitation of light. Precipitation B could be partly
or entirely removed from the north side of the horizontal screen, by adjusting the vertical screen in a
suitable manner. At the same time, as was to be expected, the corresponding precipitation B on the
south side of the horizontal screen was in all cases unchanged and just as bright, as there was no
vertical screen in the south polar regions.

It should be remarked that while the terrella was being turned, a distinct shadow of the right edge
(looking from the cathode) of the vertical screen often appeared in precipitation A upon the north side

PART II. POLAR MAGNETIC PHENOMENA AND TKRRELLA EXPERIMENTS. CHAP. IV. 575

of the horizontal screen. Precipitation A is in direct connection with the first precipitation upon the
terrella (see fig. 66, p. 151, Section I).

Photographs 7, 8 and 9, from three experiments, were taken from one position with an hour-angle
of 320°, and from above at an angle of 15° with the horizon. The experimental conditions were the same
in all three experiments, except that the hour -angle of the screen was respectively 70°, 50° and 40°.
The pressure in all three was 0.0105 mm > the magnetising current 6.5 amperes, the discharge-current
22 milliamperes and the tension 2600 volts. The photographs were taken for the purpose of studying
the shadows of the two vertical wires upon the vertical screen.

No. 7, with the hour-angle of the screen 70°, shows two distinct shadows, comparatively far down
in the precipitation. If the angle were made greater than 70°, the shadows sank still lower, and suddenly
also made a partial appearance in precipitation B on the horizontal screen. It was, as we have said,
quite clear that the lowest rays on the right of the vertical screen were rays that would have fallen
upon the horizontal screen -- precipitation B -- if they had not been intercepted by the vertical screen.

No. 8 shows two coincident shadows of the two wires. A plane through these wires, in this posi-
tion, passed approximately through the centre of the cathode. The impression given was that the rays
which threw the shadow upon the vertical screen in this position, fell normally upon the screen. For
the next experiments, therefore, a slit was cut in the screen in very much the same direction as that
in which the shadow fell.

No. 9, which is taken with the hour-angle of the vertical screen 40°, shows that the shadows have
now gone towards the left margin (looking from the cathode) of the precipitation. If, during the ex-
periment, the angle were made less than 40°, the shadows drew up towards the edge, and became
very long. The rays here evidently soon bend straight up, and they are seen to strike against the
roof and floor of the discharge-box (see photograph of this during discharge, fig. 200).

In order to investigate more closely the rays that went in at right angles to the vertical screen, a
slit was cut, as we have said, at the place in question. A new wing was moreover added to the
screen at an angle of about no° with the original screen, and in the manner shown in the photograph,
where it appears with sufficient distinctness. The purpose of this enlargement of the screen was to
catch the returning rays that had passed through the slit that had just been cut. The terrella was
moreover furnished with a small movable screen, also to be seen in the photographs. This screen could
be turned from outside by magnetic means, and also served in the investigation of the course of
those rays which passed through the slit. The way that the rays went, however, made it difficult to
observe them upon this movable screen; at any rate no photograph was obtained that could be of any
use, so this small, movable screen on the whole did little service.

Nos. i, 2 and 3 in fig. 210 were taken during experiments with a pressure of 0.0095 mm-> a
discharge-current of 20 milliamperes, and 6.5 amperes to the terrella. The photographs were taken
from places with hour-angles of 130°, 180° and 320°.

Precipitation of returning rays that have come through the slit, is distinctly visible in No. i. A faint
continuation of the luminosity upon the screen nearest the terrella is observable; a clear wedge of light
could be seen running right in towards the surface of the terrella. The position of this precipitation
answered to about j p. in., and the precipitation was of such a kind that these returning rays of group B
could very well have given an explanation of the positive polar storms. (Compare also the previously-
described beautiful experiments shown in Nos. 13—15, fig. 204, in which 25 amperes were employed
for the terrella.)

At Kaafjord, however, positive storms, with sharply-defined maximum occurred at 6 p. m , during
the six winter months for which we have the material for judging of the conditions there, (See Chap.
Ill, Table XCVI, p. 539).

576

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV. 577

It now, however, appeared to be impossible to obtain, by means of rays through the slit, any
precipitation on the terrella at a place answering to 6 />. in., even if the magnetisation of the terrella
were altered, as long as the magnetic axis coincided with the axis of rotation.

It is possible that if the discharge-box had been much larger, returning rays of this kind might have
been made, by high magnetisation, to descend upon the terrella in places answering to 6 p. m. This
question will be taken up again for thorough investigation, later on. In the mean time, experiments
were made in letting the magnetic axis of the terrella form an angle of about 20° with the axis of
rotation, once so that the south pole turned towards the cathode, and another time so that it turned
away from the cathode. This latter position must answer more or less to the condition of the magnetic
axis upon the earth in winter. Experiment showed that if the magnetic south pole were turned towards
the cathode, the precipitation from the rays through the slit was nearest the terrella in places answering
rather to earlier hours than 3 p. m. than to later.

On the other hand, the experiments showed decidedly that when the magnetic south pole was
turned away from the cathode, an abundant precipitation fell upon the terrella in places answering to
6 p. m.

Nos. 4, 5 and 6 were from an experiment in which the pressure was 0.0012 mm., the discharge-
current 21 milliamperes, the tension 2100 volts, and the magnetic current to the terrella 7 amperes.
They were taken from places with hour-angles of 90°, 180° and 330°.

The screen, with the slit and the hole in it, had a position answering to an hour-angle of 80°.
The magnetic axis formed an angle of 20° with the axis of rotation, and the south pole was in the
position of a place having an hour-angle of 180°. No. 5 shows how the rays through the slit and the
hole have turned back and strike the screen.

We have seen that in all the numerous experiments mentioned here, the rays divide into two
groups, which we have called A and B. The first group comprises rays whose course is about the
equatorial plane, and which turn alternately up and down, above and below that plane, twisting about
the terrella in a direction from west to east. The boundaries of the group upon the terrella are formed
of those rays which turn so far out from the equator that they form polar precipitation. We have
assumed that corresponding precipitation upon the earth forms what we have called the negative polar
storms.

The second group of rays approaches the terrella in the north and south polar regions, and the
rays descend in the polar belt with a velocity-component tangential to the terrella in a direction
opposite to that of the rays of group A.

We may therefore assume that rays of this kind on the earth glance off into the auroral zone
with a movement from east to west, and thus occasion what we have called positive polar storms.

That the rays about the equator must curve in the reverse way to those over the polar regions
of the terrella, is a consequence of the fact that the magnetic lines of force run in opposite directions
in the two places.

We will now go on to the further experiments that were made for the purpose of studying the
polar rays.

Photograph 7 was taken from a place with an hour-angle of 180°, with the screen at 85°. It
shows a bright precipitation of rays that have returned after passing through the slit and the hole.
The pressure during the experiment was 0.0014 mm., the discharge-current 21 milliamperes, the tension
3000 volts, and the magnetising current 7 amperes.

Nos. 8 and 9 were taken under similar conditions, except that the position of the screen had an
hour-angle of 90°, and the photographs were taken from places with hour-angles of 180° and 320°.

578

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

Fig. 211.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV. 579

A great difference is discernible between the precipitation in Nos. 7 and 8, although the position of the
screen is very little changed.

Nos. i, 2, 3 and 4 of fig. 211 were taken in order to determine more exactly the position of
the ray-precipitation now under discussion. In i and 2, the conditions are the same as in 8 and 9
respectively of fig. 210, except that the hour-angle of the screen is 75°; and in Nos. 3 and 4, they are
also the same, except that the hour-angle of the screen is 60°. The white wedge of light on the hori-
zontal screen (Nos. i & 3) is a patch belonging to precipitation B, formed by rays which have passed
through the slit.

It will be seen from all these photographs that under these conditions the precipitation is well
defined on the eastern side, and its strength is greatest on the terrella at a place answering to between
5 and 6 p. m.

Nos. 5, 6, 7 and 8 were taken from a series of experiments, made for the purpose of finding out
whether rays that come in towards the polar regions of the terrella from the left side, seen from the
cathode, could also form precipitation of the same kind as the rays that came through the slit on its
right side, looking from the cathode.

It appeared that with the highest magnetising that the terrella could stand, a quantity of rays were
drawn in towards the terrella on the left side too, descending fairly perpendicularly, so as to give the
distinct impression that even the large discharge-box of sheets of plate-glass, which was employed
in all the experiments described here, was not large enough, i. e. high enough above the poles, to
allow of the position of the precipitation upon the terrella being accurately determined, as it might
have been if the rays could have moved towards the terrella, unhindered by the sides of the discharge-
box. A great many experiments were made, however, so the results described below may be considered
sufficiently certain.

Photographs 5 and 6 are of experiments in which the pressure was o.ooi mm., the discharge-current
20 milliamperes, the tension 3000 volts, and the magnetising current 25 amperes. They were taken from
places with hour-angles of 250° and 315°. The hour-angle of the screen was 115°. With this high
magnetisation of 25 amperes, and still more with 35 amperes, which was used subsequently, the small
luminous patch, described in Section I of this work at the bottom of page 298, came out. In the present
case, this little ring became a rather compressed oval, a great part of it being visible upon both sides
of the screen. In No. 5 we distinctly see the one part, but in No. 6 the continuation of the precipitation
is no more than just visible. With 33 amperes and rather softer rays, this half of the oval was just as
bright as the other part on the other side of the screen (see No. 5).

In this photograph there is also distinctly seen in the precipitation, the shadow of the conducting-
vvire for the current to the terrella. The shadow shows how the rays descend almost perpendicularly
towards the terrella; but a twisting of the rays can also be proved resembling that of a helix.

Photographs 7 and 8 show results of experiments made with a pressure of 0.009 mm., a discharge-
current of 22 milliamperes, and a magnetising current of 30 amperes. The screen has an hour-angle of
70° (it is still the wing with the hole in it from which the angle is measured), and the photographs were
taken from places with hour-angles of 180° and 320°.

In No. 7 we see the continuation of the precipitation which produced the oval in No. 5. The pre-
cipitation now entirely disappears from the vertical screen where there had previously been precipitation
from the returning rays that passed through the slit.

The shadow of a conducting wire is now seen in the precipitation, showing that the rays have
curved round from the left side of the screen, looking from the cathode, to far back on the right side.

580 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

EXPERIMENTS FOR DETERMINING THE TANGENTIAL COMPONENT OF THE POLAR
PRECIPITATION IN RELATION TO THE SURFACE OF THE TERRELLA.

113. In the preceding pages, it has frequently been stated that the polar precipitation in the
neighbourhood of the auroral zone was produced by rays that came in to the terrella fairly perpendicularly.
By the previous investigations, therefore, it was not made clearly apparent how the tangential component
in the precipitation was directed at the various places on the surface of the terrella.

By the experiments illustrated in fig. 212, however, the matter has been give n, by special ami
ments, all possible clearness, and it will be seen what a remarkably striking analogy comes out betv
the situation and direction of the various instances of precipitation upon the terrella, on the one side,
and the situation of the positive and negative districts of precipitation during the polar magnetic storms
on the earth, described in Chapter I of the present part, on the other.

The photographs of which these illustrations are reproductions, were unusually successful. As tln-v
were to make clear one of the most important points in the theory, they were chosen with care from
a great number of more or less good ones. Any one with experience of similar experiments, will easily
understand the labour that this entailed.

The experiments were made with terrella No. 4, with a diameter of 8.2 cm., which was sns/>i'ii</i'il
by the magnetic equator, so as to give the best possible opportunity of photographing the polar precipi-
tation from the side of the discharge-box. Upon one magnetic pole — in this case the south pole—
a star-shaped screen was placed, consisting of 8 branches of a height of about 15 millimetres, standing
on their edge.

Nos. i, 2 and 3 were taken from an experiment in which the discharge-current was 24 milliamp
the magnetising current 20 amperes, and the tension 2500 — 2300 volts. The pressure was 0.006 mm.

The first two photographs were taken, looking towards the centre of the terrella, in a plane with
an easterly hour-angle of 270°, the first with a declination of + 24°, the second with —24°. The
third photograph was taken in the plane of the horizon from a place with an hour-angle of 240°.

Nos. 4, 5 and 6 were taken during a similar experiment, in which the discharge-current was 23
milliamperes, the magnetising current 20 amperes, and the tension 2500 volts. The pressure was 0.009 mm<

The terrella was turned 15°, so that the line from the centre to the magnetic south pole had an
hour-angle of 285°. The photographic apparatuses were in the same position as before. It was intended
that the conditions should answer more or less to the position of the earth in summer.

Nos. 7, 8 and 9 are of a similar experiment with a discharge-current of 24 milliamperes, a magnet-
ising current of 20 amperes, and a tension of 2400 volts. The pressure was 0.009 mm- 1 h's ume'
however, the terrella was turned 15° in the opposite direction, so that the hour-angle of the line to the
magnetic south pole was now 255°. The purpose of this was similarly to make the conditions answer
to some extent to the position of the earth in winter.

At the top of all the photographs, there is a hook, which has nothing to do with the suspension
of the terrella, and ought not to have been there at all, as it has nothing to do with the present experi-
ments. The cathode in the discharge-tube is, as will be understood, on the right of the terrella. The
left side will therefore answer to the night-side. For the purpose of easy reference, we will number
the eight branches that form the star-shaped screen, beginning with the middle branch on the right of
the picture — the branch which, as we have said, points towards the cathode -- and continuing in the
reverse direction to the hands of a clock.

It will at once be noticed that the principal precipitation on the three branches, 4, 5 and 6, on the
night-side, is found on the west side of each branch. There is no precipitation on the east side, but
a dark, narrow shadow is to be seen in the polar band of light on the terrella itself. In No. 2 there i:

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV.

Fig. aia.
Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903.

74

•ea

-

i

582 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

even a little light coming under the branches of the screen, as they do not lie close to the terrella bi
leave a millimetre here and there open between themselves and the terrella. These shadows and stripe
of light tell us the average straightness with which the rays descend towards the terrella. We sha
return to this, as the figures in fig. 221 are meant for such investigations.

What we here first of all substantiate is that the precipitation on the night-side of the terrella i
the polar band has a tangential component eastwards. The magnetic effect of corresponding precipitatio
over the earth would thus be a positive current directed westwards, just as we have always found th
current-arrows directed in the -negative polar storms in the auroral zone.

It is not only on the night-side of the terrella that we find precipitation on the west side of th
eight branches, but right round the connected luminous spiral, which we shall briefly call the auror;
zone. Even at the beginning of the spiral nearest the pole, where, in fig. 140, p-327, we saw a sudden ciirv
in the luminous band, we now see precipitation in two places on the west side of screen i, which point
towards the cathode; (see Nos. 2 and 8). But it is the precipitation on the night-side that is the st
and which comes out better, even when there is no precipitation on the day -side (see fig. 204); and
also has comparatively the greatest tangential component. This is thus in accordance with the fact tha
the negative polar storms are generally found on the night-side of the earth.

It is also easy, however, to demonstrate in our photographs precipitation upon the screcn-branche
exactly analogous to the precipitation on the earth which occasions positive polar storms. With regan
to branches 3 and 2 especially (see, for instance, photograph 3), we also find on their east side a grea
precipitation of rays, which, close up to the terrella, has a strong tangential component westwards.

The magnetic effect of corresponding precipitation over the earth would thus be a positive cum
directed eastwards along the auroral zone, just as we have always found the current-arrow directed
the positive polar storms. The time of day also suits these cases of precipitation exceedingly well, Co
the positive polar storms occur with a maximum in the afternoon, and, as is seen, branch 3 just answ
to a place on the terrella corresponding to 6 p. m.

At the extreme end of branches 5 and 4 also, there is precipitation on the east side similar
that on 3 and 2, but not going down so close to the terrella. It occurs in much lower latitudes, \v
on branches 3 and 2 it has come quite up to the auroral zone.

The photographs show plainly that the precipitation on the east side of branch 4 occurs in a m
more southerly latitude than that on the west side. On branch 3, too, the precipitation on the east
is farther south than that on the west side; but the two are considerably nearer to one another than 01
branch 4. On branch 2 they are still nearer to one another, looking as if they to some extent cover
one another. These conditions correspond in an astonishing degree with those on the earth duri
magnetic storms. We have frequently, indeed generally, seen that while there is a positive polar sto
in the southern part of the auroral zone, there is at the same time a negative polar storm in t
northern border of the zone. (See p. 445). These storms counteract one another in a horizontal direc
tion, and may sometimes neutralise one another's effect in the case of stations lying between the tw-
precipitations; but in a vertical direction the two storms art together. This has often been shown
discussing the observations from Jan Mayen, for instance.

In the preceding pages, we have repeatedly put forward the opinion that this precipitation ofra;
with a tangential component westwards along the auroral zone, was due to rays of group B, that i:
say, rays that are first drawn down towards the terrella in its polar regions, and then deflected a
some of them thrown back. That certain rays have such a course is evident from the experiments
are described with photographs 13, 14 and 15, fig. 204. The distinct shadows of the conducting w
that are thrown upon the screen cannot be interpreted in any other way; and the experiments describe
in Art. 112 are also very conclusive.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV. 583

According to the above, however, it is also conceivable that some rays of the group called A,
whii more especially bend round the terrella above and below the plane of the magnetic equator may
alscbe made partially responsible for the precipitation found upon the east side of the branching
scnns; for we have seen that some of these rays will loop upon themselves, and it is then clear that
ow)ranch of the ray-trajectory will be turning back. This branch may then just occasion precipitation
on ie screen in more southerly latitudes of the terrella with a tangential component the reverse in
diretion of that to which the ray would originally have given rise.

iN AN INTIMATE CONNECTION BETWEEN RAYS OF THE TWO GROUPS A AND B.

114. In continuation of the experiments which have last been described, I have succeeded at
lenjh in obtaining complete clearness as to the relative connection between rays of group A and those
of joup B.

Further experiments were first made with an eight-armed star-screen with arms 3 centimetres in
hi-i^it instead of 1.5 centimetres as they had previously been, the purpose being to see whether the
preipitation and shadows on the two star-screens corresponded.

The first eight photographs of fig. 213 show the conditions. The first four are from an experiment in
whii Nos. i and 3 were taken from directly opposite the magnetic poles, north and south, from posi-
tion with hour-angles of 90° and 270° without elevation, while No. 2 was from a position with hour-
ang 235° and 24° declination, and No. 4 with an hour-angle 295° and 24° declination. The discharge-
curint employed was 22 milliamperes with a tension of about 3000 volts and a magnetising current of
20 nperes to the terrella. The pressure sank from 0.022 mm. before the experiment, to 0.043 after it.

The next four photographs were taken from the same respective positions, with discharge-current
of :, milliamperes and tension about 3000 volts, while the magnetising current was 36 amperes. The
prt-Hire was 0.012 mm. before the experiment, and 0.066 mm. after it.

A comparison with the phenomena represented in fig. 212, in which the star-screen was about
1.5 n. in height, shows, on the whole, a similarity. One difference that may be mentioned is that the
posive precipitation does not extend so far down towards the terrella itself, as when the height of the
scrtn was less. The negative precipitation, on the other hand, extends right in, and the polar ring on
the ;rrella itself is now quite as well formed as with the lower screens. One especially characteristic
feafe is that the dark shadows in the ring of light on the terrella just behind the screening branches,
an; 10 longer now than when the screens were only 1.5 cm. high, but are, if anything, narrower. This
shos that the rays do not strike so straight down towards the terrella as might be thought from the
is experiments, but that rays that come in contact with the higher parts of the screen first move
a Hie away from the screen, and then turn in towards it again.

It will further be observed from the extremely interesting negative precipitation on the screens
(froi which an idea can actually be formed of the manner in which the rays approximately move from
the orthern polar light-ring to the southern, see Nos. 4 and 8), that the precipitation nearest the terrella
s (inter and thinner than farther out. This suggested the thought that possibly one of the eight
brarhes of the star-screen might cast a shadow upon the neighbouring branch, that again upon the
nex and so on. In order to determine this question, one of the branches was cut off, as shown in
Nosg and 10. The positions here are similar to those in Nos. 2 and 4, and the discharge-current employed
in t; experiment was of 23 milliamperes. It will at once be seen from the photographs that the already-
meroned narrow precipitation of light nearest the terrella upon the branching screens is not caused
by ie casting of the shadow by one branch upon its neighbour.

Photographs n and 12 were taken in two experiments, both in the same position as in No. 2. The
exp-iments were made very much as before, but with 10 and 20 amperes to the terrella. The tension

Fig. 21;

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV. 585

in both cases was about 2500 volts. The photographs show the important fact that the more highly the
terrella is magnetised, the farther does the positive precipitation reach towards the evening side. There is
no precipitation on branch 3 with 10 amperes' magnetisation of the terrella, but it is there with 20 amperes.

With conditions corresponding to those on the earth, where the spherical diameter of the auroral
ring may be put at about 45 °, the positive precipitation might reach far on into the evening side of the
terrella.

Nos. 13—16 are from experiments in which two additional small screens were introduced. One of
these was square, and placed at right angles to branch 3. It was pierced with a hole, and extended
1.4 cm. on each side of the branch. The other small screen was also square, was furnished with a foot,
and placed radially in relation to branch 5.

The purpose of these small screens was to find out whether the rays forming the positive precipi-
tation on the branches are only such as come by way of the poles (see the experiment in fig. 204,
Nos. 13—15 and Art. 112), or whether that precipitation is due to other rays belonging to the system
of rays that first intersect the magnetic equatorial plane several times.

In Nos. 13 and 14, the positions are similar to those in Nos. i and 3. The conditions are very
much the same, with from 2800 to 3000 volts between the electrodes, and about 25 amperes to the
terrella-magnet.

In Nos. 15 & 1 6, the position is the same as in No. 2. The magnetising current to the terrella is
lo and 20 amperes respectively, with 22 milliamperes at 3000 volts in the discharge. The absence of
positive precipitation on branch 3 in No. 15 will be understood on comparing that photograph with
Nos. ii and 12.

Some experiments were made without photographing, the magnetising of the terrella being changed
from 5 to 15 amperes. It then appeared that the little screen at the pole was illuminated from the right
when the magnetising current was 5 amperes, the light gradually moving nearer to the pole as the
magnetising was increased to 6, 8, 9, 10, &c. amperes. On branch 3, positive precipitation first appeared
with about 12 amperes, and when the magnetising current was weakened, moved out from the extremity
of the branch on to the left flap of the small additional screen, and finally disappeared.

It will be seen that these experiments did not throw much light upon this circumstance; but we
shall now see how the facts of the case stand.

Fig. 214 shows eighteen photographs and fig. 215 sixteen photographs of a series of experiments
made with this object in view.

Nos. i, 2, and 3, fig. 214, are from experiments made with a larger screen attached at right angles
to branch 3, the positions being similar to those in Nos. i, 2 and 3 of fig. 213. The magnetising current
to the terrella was about 25 amperes, and the tension in the discharge about 3000 volts.

It will be noticed, in No. i, how the light falls upon the upper side of the new screen, with its
lower edge more or less sharply defined. It should also be observed that the shadow of the suspending
wire, visible in the polar light-ring shows that the rays that come into the ring seem to have passed
above the new screen, that is to say at some considerable distance from the terrella's equator.

In No. 2 we first notice that the positive precipitation on branch 3 is not affected in any special
degree by the new screen. On the other hand, it will be seen that part of the negative polar ring is
lost behind the screen, showing that on that side the screen has been high enough to intercept some of
the rays that would have helped to form the polar ring.

No. 3 shows the same shadow in the negative precipitation, and also a peculiar light-effect to the
right of branch 3, and on the terrella behind the screen. This may perhaps be foreign light produced
by a discharge at a point on the terrella itself, a discharge that was found out during these experiments,
and was the occasion of their being broken off.

586

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, lgO2 — 1903.

A new arrangement of screens for the terrella was now carried out, as the succeding photographs
distinctly show. A vertical annular plate, coated with tungstate of lime, was soldered to the ends
of the eight arms of the star-screen.

Nos. 4 and 5 were taken from positions with hour-angles of respectively 235° with 15° declination
and 180° without incline. The magnetising current to the terrella was only 6 amperes, and the discharge-
current was 23 milliamperes with a tension of 3000 volts.

In No. 4 are seen continuations of the positive precipitation on branch 2, and this continuation seems
to be formed from the same rays that formed the first line of precipitation on our earlier equatorial scnrn.
When the magnetising is increased, the precipitation spreads over the screen farther from the terrella.

No. 5 shows one of the characteristic luminous triangles that we saw in fig. 68 of Section I; but
here there are also shadows of the suspending and current-conducting wires.

The position in No. 6 answers to an hour-angle of 90°. It will be observed that the polar ligh
has been reduced, and we see two peculiar lines of precipitation on the vertical screen to the left,
magnetising current was 10 amperes, the tension 2800 volts. The shadow of the suspending wire in
the polar ring of light seems to show that the rays forming the latter pass above the screen.

The conditions in No. 7 are similar to those in No. 6, except that the magnetising current is
amperes. In this case, with the slighter magnetisation, the peculiar lines of precipitation on the vertical
screen have moved anti-clockwise, and the polar ring of light is even fainter than before. This shows,
as we have already seen, that with slight magnetisation the rays go closer to the terrella at the equator.

No. 8 was taken during the same experiment as No. 7; but the hour-angle of the position is 270°.
Here too we see, as in No. 4, the very remarkable continuation on the annular screen of the
positive precipitation on branch No. 2.

Nos. 9 — 12 are all from one experiment, in which the magnetising current was 20 amperes, and
the tension in the discharge 2900 volts. The hour-angles of the positions were 90°, 235° (with 15'
declination), 270°, and 295° (with 20° declination). The polar ring of light on the night-side is fainter
in No. 9; but the shadow of the suspending wire is very clear. No. 10 shows the positive precipitation
upon branches i, 2 and 3; but there is no distinct negative polar ring.

There is a faint negative polar ring in No. u. In this photograph, the great peculiarity is perhaps
the shadows behind branches 6 and 7.

In No. 12 there is scarcely any of the usual negative precipitation on branches 4 and 5.

Nos. 13 — 18 are from a very important experiment with a very small terrella of only 2.5 cm.
diameter. The iron core in it was cylindrical, and measured 10 mm. in diameter, and was wound round
with 240 turns of 0.4 mm. copper wire covered with silk.

This terrella was placed in the middle of a flat screen, in such a manner that the magnetic axis
was at right angles to the screen. The object of the experiments made with this tiny terrella in the
vacuum-box of 22 litres, was to prove that the lines of precipitation that appeared on the screen had
nothing to do with the enclosing plates of the vacuum box. It was possible that our former terrellas
were too large in proportion to the vacuum-box; but it will be seen that the experiments with this little
terrella show our previous results to be unaffected as far as the distribution of the rays nearest the
terrella are concerned.

No. 13 shows the terrella with screen seen edge-wise. The hour-angle of the position was 180°.
The luminous ring outside the terrella is only from the cathode in the background.

No. 14 shows discharge without magnetisation of the terrella, the hour-angle of the position being
270°. There are shadows behind the terrella. The discharge took place with 2700 volts and 23
milliamperes.

No. 15 shows the conditions with a magnetising current of 2 amperes, 3000 volts.

Fig. 214.

588 B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

No. 16 shows the conditions with a magnetising current of 4 amperes, 3000 volts and
milliamperes.

No. 17 shows the conditions with a magnetising current of 6 amperes, 3000 volts and 23 milli-
amperes. The pressure fell from 0.014 mm. to 0.022 mm.

Lastly No. 18 shows the conditions with a magnetising current of 10 amperes and a discharge
current of 23 milliamperes with 3000 volts. The pressure fell from 0.017 mm- before the experiment,
to 0.021 mm. after it.

It is a noticeable fact in all these experiments, that the remarkable occurrences of precipitation that
we have previously designated A and B, are also found here when the magnetisation is sufficiently strung
(see No. 18). Their shape is so exactly the same as that with the larger terrcllas, that we may conclude
that for these experiments at any rate, the vacuum-tube was large enough in our earlier experiments.

In addition to these distinct, characteristic instances of precipitation on the afternoon side of terrella
and screen, we find upon the morning side that the pencil of rays is sharply defined, although the rays
evidently only graze the vertical screen. In reality it is, as we shall see, the greater part of the rays
from the cathode that are bent downwards in front of the terrella. This is immediately seen if the
screen is turned a little, so that the rays strike at an angle. This will be illustrated in the next plate.

These experiments will be of service to us, as a subsequent paragraph will show, in explaining the
zodiacal light.

In order to find out what became of the luminous patches upon the screen, when the plane o
latter no longer passed through the centre of the cathode, the screen was turned 23° in a positive
direction, and photographs were then taken.

Nos. i — 4 of fig. 215 were taken from places with hour-angles of 90° and 270°. Nos. 2 and 4
show how the rays that turned off in front of the terrella, and only grazed the screen in its former
position, form a strong, sharply-defined precipitation in the new position. This shows that while the
rays near the magnetic equator almost follow that plane, those outside the equator curve more and more
away from it. We have seen this before, having found a bright precipitation of rays respectively above
and below the two magnetic poles, upon the floor and ceiling of the vacuum-box (fig. 200).

Nos. i & 2 are of experiments with a magnetising current of only 1.5 amperes to the terrella.
A discharge-current of 23 milliamperes at 2800 volts. The pressure about 0.015 mnl-

Nos. 3 & 4 are of a similar experiment, the only difference being that the magnetising current
was 5 amperes.

Nos. 5 — 10 are of important experiments in which a small screen was introduced in front of the
south pole of the terrella, at about right angles to the magnetic axis. The introduction of this si
was for the purpose of studying more closely the above-described precipitation of light. The large screen
was turned back 23° to its original position.

The hour-angles of the several positions corresponding to these photographs were 90°, about 210°,
and 270°. The first three are of experiments in which the magnetising current was 2 amperes, the
discharge-current 22 milliamperes with 2900 volts. The pressure was 0.017 mm-

Nos. 8 — 10 are of experiments like the above, with the difference that the magnetising current was
10 amperes and the tension 3000 volts.

It will be noticed that the precipitation on the small screen moves outwards with increased mag-
netisation.

When we compare Nos. 7 and 10 here with Nos. 4 and 8 in fig. 214, full light will be at once
thrown on a hitherto somewhat obscure point. We perceive how it is thai rays of group B and rays of
group A, before they have reached the terrella, fortn a single coherent group, but that the rays which come
nearest to the poles of the terrella when this is sufficiently magnetised, are thrown round and acquire

Fig. a 1 5.
Birkeland. The Norwegian Aurora Polaris Expedition, 1903—1903.

75

590

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

a retrograde motion. In the course of this they have an opportunity of positive precipitation on our star-
screen and of the precipitation which we have called B on the equatorial screen in our earlier attempts.
When we after this look back on the photographs from earlier experiments — take for instance fig. 204—
we shall be able to see and understand them with much greater clearness than before. Look at the
admirable pictures in the first column (Nos. i, 4, 7, 10 and 13). We see directly how much of the
spherical triangular light pictures are wanting, it is rays that have turned before they have struck out
for the terrella, and we find them again in the precipitation on the eastern side of the vertical screen.
The more highly the terrella is magnetised, the greater will be the number of the rays of what we call
group A that will be converted into rays of group B. We have also seen that the end of the first line
of precipitation on the equatorial screen has moved away from the terrella, when this is magnetised to
an exceptionally high degree, the bulk of the rays nearest the terrella in the line of precipitation, have
been obliged to turn completely back.

It is interesting to observe that in Nos. 7 and 10 we have a section of the ray-masses over
the poles at right angles to that shown in fig. 209, Nos. 3 and 7.

We may now conclude by analogy that it is not only rays belonging to the first triangular figure
of precipitation that can be made to turn round by stronger magnetisation.

We have mentioned that such precipitation appeared three times on the eastern side of the vertical
screen when the screen was turned in a positive direction through 360°. The first precipitation was
strong and well defined, the second less strong, and the third slighter still. It is in this way that the
bulk of the rays in the middle of the three triangular figures of light disappear from the terrella, tin
rasy being thrown back before they reach the terrella, when the magnetism is sufficiently strong.

Applying this fact to the earth, we should expect that a
station of medium latitude, for instance 65 °, would not only have
powerful positive magnetic storms attaining a maximum at 6
p. m., but would also have slighter ones about i a. m., and a very
slight one about 8 a. m. (see p. 566). I hope to have an opport-
unity later on to investigate this matter.

Nos. ii — 16, fig. 215, are of experiments with a small
eight-armed screen, placed above the south pole of the terrella.
In the first three of these, the magnetising current was 10 am-
peres, the discharge-current 23 milliamperes, and the tension
2400 volts. The positions have the same hour-angles as before.
In the last three photographs the magnetising current was
20 amperes. Discharge-current 22 milliamperes with a tension
of 2700 volts. In the record of these experiments, the follow-
ing account is given: "Experiments were also made with a current
of 12 amperes to the small terrella. With this arrangement of
an equatorial screen there was no trace of negative precipitation
on the night-side. Great positive precipitation, on the other hand,
was found on branch 2, but on none of the other branches"

Subsequent experiments have also proved that if the equatorial screen is large enough, the nega-
tive precipitation on the night-side in the polar light-ring disappears.

In Nos. 14 & 16, precipitation A and B are exceedingly distinct upon the screen, and exactly as
with the large terrella (figs. 201 and 202). As we have already remarked, the circumscribing surfaces
of the vacuum-box have therefore nothing to do with the shape of this precipitation.

Fig. 2 1 6.

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV.

Fig. 216 shows some results with the small terrella after the removal of the large screen through
the equator.

Nos. i, 2 & 3 were all taken from a position with an hour-angle of 90°. In No. I the magnetic current
was 10 amperes, in No. 2 there was no magnetisation, and in No. 3 the current was 20 amperes. The
full development of the polar ring of precipitation in No. 3 will be observed.

In Nos. 4 — 9, the arrangement was the same, except that the magnetising current was 10, 20 and
30 amperes respectively for Nos. 4 and 7, Nos. 5 and 8, and Nos. 6 and 9, and the tension 2700, 2600
and 2700 volts respectively.

Nos. 4 — 6 were taken from a position with an hour-angle of 270°, and Nos. 7—9 from a position with
hour-angle 235° and declination 24°. The positive precipitation on branch 2 of the star-shaped screen is
seen, whereas no positive precipitation appears on branch 3. Some experiments where made without
photographing, for the purpose of studying this circumstance more carefully; and it then appeared that
at the end of the positive side of branches 4 and 5, precipitation also occurred on our tiny terrella.
When this result is also compared with that obtained when there was a large equatorial screen, it will
be understood that it can hardly be only the rays that come in right across the polar regions of the
terrella that produce positive precipitation.

ON THE SIZE OF THE POLAR RING OF PRECIPITATION.

115. We will now pass on to describe experiments that were made for the purpose of determining how
the size of the rings of polar precipitation was dependent upon the magnetising of the terrella and the
magnetic stiffness of the cathode rays employed. The intention of the experiments was to procure a basis
for the judgment of the magnetic flexibility of the corpuscular rays coming from the sun and producing
aurora and magnetic disturbances upon the earth in the manner we have supposed them to do.

In the experiments from which the photographs in fig. 217 were taken, the discharge-current in
every case was about 25 milliamperes, and the pressure in the discharge-tube 0.046 mm. The tension
difference between anode and cathode was 1800 volts in the experiments represented in the first and second
rows, and it went from 1800 to 1700 volts in those in the third row. The tension remains comparatively
constant here, because the pressure was so high that the amount of gas disengaged during the experi-
ment did not alter the conditions as much as it does when the pressure is small to begin with.

The magnetising current in the three experiments was respectively 10, 20 and 30 amperes.

The position of the terrella -- No. 4 -- was unchanged during the three experiments, this being
with the magnetic axis horizontal and at right angles to the central line to the cathode. The magnetic-
south pole had an easterly hour-angle of 270°, and photographs i, 4 and 7 were taken from a place
outside with the same hour-angle, photographs 2, 5 and 8 from a place with an hour-angle of 180°, and
photographs 3, 6 and 9 from a place with an hour-angle of 90°.

In fig. 218 there are 9 similar photographs from 3 experiments in which the discharge-current
was again about 24 or 25 milliamperes throughout, and the pressure in the discharge-tube about 0.008
mm. The tension in the three experiments was respectively 2400 volts, from 2400 to 2300, and from
2500 to 2300 volts, while the magnetising current was 10, 20 and 30 amperes. As will easily be under-
stood, our endeavours were aimed at keeping the tension constant in each series of experiments; in the
first series the tension aimed at was about 1800 volts, and in the second series about 2400 volts.

From the two series of photographs answering one to 1800 volts and the other to 2400 volts, we
find in the first place that the stiffer the rays employed and the less the magnetisation of the terrella,
the larger are the polar precipitation-rings. The idea originally was to magnetise the terrella so strongly
that the polar precipitation-ring would acquire a spherical diameter of 45°, very much as one imagines the

592

BIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

PART II. POLAR MAGNETIC PHENOMENA AND TERREU-A EXPERIMENTS. CHAP. IV.

593

Fig. 218.

^g^ H1KKI LAM>. II I K XnKWIX'.lAX AURORA I'OI.AKIS KXI'KIHTIOX, IQO2 — I 903.

auroral /one on the < arth, forming almost a circle round the point of intersection of the elementary
magnetic axis with the earth's surface. The terrclla employed, however, could not he magnetised suffi-
ciently strongly, hut, a^ \ve shall see, \ve can easily form an idea as to how much the terrella must be
magnetised in order that the ring shall have its correct si/.e. It is also no doubt possible that by se-
lecting a somewhat stronger iron core lor the terrella than the one here employed, and employing a
stronger magnetising current, a precipitation-ring with a diameter of 45 , might be obtained, which would
remain long enough to allow of its being photographed before the terrella became too hot. Indeed I
have already, as will be seen below, realised the conditions necessary for this purpose.

There is another result which may also be directly deduced from our photographs, a result which
we have moreover demonstrated many times under the most varied conditions.

It appears that the more /lie trnrlla is magnetised, the narrowr or thinner docs the hand of light in
tin- ri/ii; I'l-cninc, and the smaller the number of rays that arc drawn in towards the terrella in the pre-
cipitation-ring. This last circumstance may be at any rate partly accounted for 1>3' the fact that the
discharge-tube was not large enough for the highest magnetising of the terrella, as the rays describe large
arcs before they go in towards the precipitation-ring.

With reference to photograph No. 2 in fig. 218, \ would point out, as being of interest in this
connection, that aurora that occurs in low latitudes on the earth, must, according to our theory, be due
to stiller rays than aurora that only occurs in the ordinary auroral /.one; and the farther the northern aurora
extends towards southern latitudes, the greater will he its width and we should expect that it will be seen simul-
tanenelv in the xenith over a greater area of the earth. Theory, in this case, is in harmony with experience.

In order, as we have said, to obtain an estimate of the extent to which the terrella must be mag-
netised to give the precipitation-ring a spherical diameter of 45 , the magnetic intensity was measured
at the poles of the terrella by means of a LKXARD spiral. An intensity of 1600 C. G. S. answered
to a magnetising current of m amperes, 2400 C. G. S. to 20 amperes, and 2800 C. (1. S. to 30 amperes.
The relative proportions of the intensities were controlled by induction experiments with a small, flat
coil, which was also placed at the pole, exactly where the LKXARD spiral had been used.

The sixc of the precipitation-rings was then measured from the photographs, and their spherical
diameter calculated in the various experiments, measuring along the middle of the band of light, the
middle photographs, Nos. 2, 5 and 8, in figs. 217 and 218, being taken for this purpose. In this way
the following values were obtained for the spherical diameters:

Answering to 1800 volts, 73°, 68°, and 63";
» 2400 , 88°, 72°, 66°,

for magnetising currents to the terrella of respectively 10, 20, and 30 amperes.

From these values we may conclude by extrapolation that with cathode rays answering to 2000
volts and a field-intensity of 4500 C. G. S. at the poles of the terrella, we should certainly obtain a
small precipitation-ring with a spherical diameter of about 45°. The error in this determination is prob-
ably no greater than that in the assumption that the auroral zone upon the earth has a spherical dia-
meter of 45°. We shall later on have an opportunity of controlling experimentally the result of this
extrapolation.

We will now assume that with the above-mentioned magnetisation of the terrella, corresponding to
4500 lines of force at the poles, and with rays of 2000 volts, we obtain a comparatively correct idea of
what lakes place when the earth is irradiated by corpuscular rays from the sun; and upon this basis we
will see what degree of stiffness these rays from the sun may then be assumed to possess. We pre-
suppose then, that the magnetic field of force round the earth is similar in form to the field of force
round our terrella, and that thus the magnetic field at great distances from the earth is not in any very
essential degree aftected by possible current-systems outside the earth.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV. 595

We have then on the one hand a magnetic terrella with a radius of 4.1 cm., near whose poles
the magnetic intensity amounts to 4500 C. G. S., and round which circle cathode rays whose velocity
is T*j c, answering to 2000 volts, when c indicates the velocity of light (cf. LENARD, Ann. d. Physik, 1903,

317. P- 732)-

On the other hand we have the earth, with a radius of 6.4 X io8 cm., and with a magnetic inten-
sity in the neighbourhood of the magnetic poles that may be put at 0.68 C. G. S., and round which
circle corpuscular rays with a velocity of $c,

I now believe, that when the terrella is so strongly magnetised that the polar light-rings have the
same spherical diameter as the auroral zone on the earth, the cosmic ray system about the earth, which
occasions aurora and magnetic storms, is similar to the cathode ray system around the terrella. Thus all
details can be elaborated from our terrella-experiments and the results be applicable to the earth with a
suitable proportional factor. We shall also make repeated use of this important proposition.

Now jf the conditions in the one case are, so to speak, a true copy of those in the other, the
radii of curvature of the corpuscular rays at all corresponding places must be as much larger than those
of the cathode rays as the proportion between the radii of the earth and those of the terrella. Thus

Qo 4.1

The proportion between the magnetic intensity at sets of places in the vicinity of the earth and in
the vicinity of the terrella will be

H 0.68
7T0 = 4500

Now we have, as is well known,

„• m . u
' ' • a = -
e

where // is the intensity of the magnetic field, Q the radius of curvature of the rays, m the mass of
the electric particle, e its charge, and u its velocity.

For the corpuscular rays round the earth we have therefore

and for the cathode rays round the terrella

From this \ve obtain the important relation,

fJQ = 2.35 X 10< HoQo= 3 j x 10°

Even from this we may conclude that the rays in question must be unusually stiff magnetically.
HQ must be between i and io millions. We know only slightly penetrating positive rays which have
approximately so great an inflexibility, as H.Q for u rays from radium may have a value of 4 >( io5.

W. WIE.N observed that on the negative side also of the magnetic spectrum of kanal rays, there
was a slightly deflected patch of fluorescence. These may possibly be almost inflexible negative
ion-rays.

The y rays hitherto not magnetically deflected are presumably very much like Rontgen rays in
their nature. The opinion has been put forward that they are exceedingly stiff/!/ rays (PASCHEN), or that
they consist of neutral corpuscles (BRAGG). Possibly the corpuscles are not absolutely neutral either.
Even rays in which H . Q equals ten millions, there is hope of being able to deflect perceptibly by means

596 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

of gigantic magnets. I shall soon have at my disposal a 3o-tons magnet, with which, for a distance of
from 1.5 to 2 metres. I can hold a field strength of 20,000 C. G.S.; and with this I shall try if it js
possible to deflect rays such as these.

From the equations given, we obtain

JL. JL,p,4l.iM<

Ha QO m0

Further by the aid of the values for -=- and — > we obtain -—•£«• 1.82 X 103

tia y0 ma

If we now assume that our corpuscular rays are formed of ordinary electrons, and that we may-
venture to employ LORENTZ'S formulae (') for the extreme case we have before us, then

m 1

from which we obtain

— /J = -jJL= = 1.82 X 103.
': m0 ^ yi_ pz

If we here say that fi = 1 - .we obtain approximately

X

x = 1.82 X 103 or x = 6.7 X 10° .
2

We thus find that the velocity of the corpuscular rays should be u — p . c — c — — < i. e. only 45

metres less than the velocity of light. The transversal mass of the corpuscular rays, m, equals 1.82 X io:l »/„,
and is thus of an order one thousand times as great as the mass of an electron with small velocity (-).

Recently LsNARD(3) has also treated this very important question, and has arrived at similar conclusions
as to the stiffness of the cosmic corpuscular rays.

Although we may probably take it for granted that LORENTZ'S formula in this extreme case no
longer holds good, we may nevertheless conclude that the corpuscular rays from the sun, which should
be capable of giving rise to such precipitation-phenomena upon the earth as are manifested in aurora
and magnetic storms, must be extraordinarily penetrating and exceedingly inflexible to magnetic forces-
As, on this earth, we are not acquainted with any rays possessing such properties, the above result
must at first sight seem discouraging; but if we look into the matter, we soon find several observations
that are in complete harmony with it.

We know, for instance, that in the polar regions aurora very frequently descends to within
50 kilometres of the earth, indeed there are good observations of its descending to within 10 kilo-
metres and considerably lower. Auroral rays may sometimes be seen with a length of 30 kilometres.

It is thus clear that the rays which produce auroral phenomena, and which we assume to originate
in the sun, must be capable of penetrating considerable strata of our atmosphere. They must be sup-
posed capable of penetrating a layer of mercury more than 100 millimetres in thickness, if the rays follow
the law, Equal penetrability for equal masses. This moreover agrees with the idea that these same
rays, before reaching the earth, have been obliged to penetrate a certain stratum of the solar atmos
phere, since they issue from the regions in the vicinity of the sun-spots.

(') A. H. LORENTZ, The Theory of Electrons, 1909, p. 212, equation 313.

(2) BIRKELAND, Sur la deviabilite magnetique des rayons corpusculaires provenant du Soleil. Compt. Rend, de 1'Academie
des Sciences, Paris, le 24 Janvier, 1910.

(8) LENARD, Ueber die Strahlen der Nordlichter, Heidelberger Akademie der Wissenschaftcn, Jahrgang 1910, 17. Abhandl.

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV. 597

At present we are acquainted with (1 rays, which pass through about i millimetre of mercury;
md they are accompanied by y rays, much more penetrating still.

LENARD(') has made investigations for the purpose of finding a relation between the velocity of an
electron and the coefficients of absorption for corresponding rays in different substances.

He arrived at the result that the absorption increases more than a million times when we pass
rom /? rays of radium to cathode rays with a velocity equal to a hundredth part of that of light.

It seems probable, however, that the penetrability of our rays should be much greater than that
)f the p rays of radium; but no simple law has yet been found that can be employed for calculating
he absorption when the velocity is known.

Several physicists have found that the p rays are absorbed according to an exponential law, and
hat the velocity does not change when the rays pass through matter; but it would appear that these
•esults are not certain.

We can point to yet another circumstance that indicates that the corpuscular rays coming from
he sun must be extremely inflexible. After HALE'S discovery of the comparatively powerful magnetic
ield that is found round the sun-spots, it is an obvious conclusion that the sun on the whole is magnetic.
This conclusion is also obvious for other reasons. The corona's rays in the polar regions of the sun
lave led several investigators to believe that the sun is magnetic, with poles near those of the axis of
•otation.

It now appears that no rays can emanate from the equatorial regions of the sun out into space, if
he sun is assumed to have a magnetisation that can be compared with that of the earth, and the rays
ire supposed to be no more inflexible than the hitherto known corpuscular rays, i. e. if Rontgen
•ays and y rays are not corpuscular rays.

It is another matter altogether when we assume that the rays actually have the inflexibility that
,ve have above inferred that they must have, from aurora and terrestrial magnetic phenomena on the
;arth. We are then even able to give a plausible explanation of a phenomenon that has been studied
:>y Ricc6(-), and which has to do with magnetic storms. Ricco has observed that there is a difference
)f time of from 40 to 50 hours between the passage of a large spot to the central meridian and the
naximum of a magnetic perturbation that it produces on the earth. He concludes from this that the
velocity with which the corresponding rays are propagated ought to be between 900 and 1000 kilo-
netres per second.

It is easy, by quite simple calculations, to determine the path that a corpuscular ray going straight
)ut, with the velocity of light, from the sun's magnetic equator will describe when the stiffness of the
•ays is that assumed above, and the sun is supposed to act upon the rays like an elementary magnet
with a definite moment M.

I have calculated from ST6RMER*s(3) formulae that the sun should have a magnetic moment of order
to28, or about 150 times greater than that of the earth and inversely magnetic, in order to deflect our
•ays by an angle corresponding to this retardation of from 40 to 50 hours.

The probable existence of such corpuscle-rays from the sun as those here treated of, is
;ven now admitted by several men of science, and it will certainly be soon acknowledged that these
lew solar rays, which I have thus discovered, enter deeply into many terrestrial conditions, even if they
-annot compare in importance with the wondrous rays we have hitherto been acquainted with. Owing
o the magnetic condition of the earth, the new solar rays, as we have seen, principally enter the polar
•egions.

(') Annalen der Physik, t. XII, 1903, p. 714.

(-) Nature, November 4, 1909.

(3) Archives des Sciences physiques et naturelles, Vol. XXIV, Chap. IV, 1907, p. lai.

Birkeland. The Norwegian Aurora Polaris Expedition 1902 — 1903. 76

598

I3IRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

116. A new glass box was constructed to contain more than 70 litres, in order that all discharge-
experiments might be made with a terrella so strongly magnetised that the cathode-ray system round
it would be similar to the corpuscular-ray system round the earth. The thickness of the plate-glass
sheets was 22 mm.; and in order to guard against the great external pressure, the sheets forming the
ends of the box were specially strengthened. The sheets that were perforated were double. The
internal dimensions of the box were 36 X 36 X 55 cm. The terrella employed was 8 centimetres in
diameter, and was constructed with the object of procuring more than 4500 lines of force per centimetre
across the poles when the strongest magnetising current was employed. The iron core was 3 cm. in
diameter, and was closely wound round with well-insulated layers of copper wire, of which the total

Fig. 219.

resistance was 2.6 JL'. The wire could, without injury, be charged for a few seconds with 40 amperes
thereby imparting to the terrella an amount of energy equal to between 5 and 6 horse-power.

The magnetic moment M for 10 amperes was found to be 61300. At a distance of 4.5mm. from
the terrella, immediately above the- pole, the number of lines of force with 10, 15 and 30 amperes'
magnetisation was respectively 2075, 2760 and 4200. At a distance of 7.5 mm. from the pole of the
terrella the measurements were H = 1647, 2460 and 3280 with 10, 15 and 20 amperes respectively of
magnetic current. These measurements were taken with a Leduc apparatus. To ascertain if it were
correct, this apparatus was compared with a Lenard's bismuth spiral which gave the following correspon-
ding sets of values:

H by Lenard spiral 575° 5600 4800 3550

H by Leduc apparatus .... 5950 5650 5040 3720

As will be seen, the respective values correspond fairly well and the records of the Leduc
apparatus must thus be considered reliable. From this it must be supposed that immediately above

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV. 599

he pole of the terrella with 20 amperes magnetisation the H has been approximately equal to 4100.
f we then calculate the stiffness of the corpuscle-rays on the earth in the same manner as above, we
;hall see below that we are finding very nearly the same values as before.

The new terrella was first placed in our former smaller vacuum-tube (fig. 200), but it appeared that
he cathode rays were thrown in such numbers against the walls of the tube, that hardly any reached the
errella, and the above-described large vacuum-box was therefore, with much labour, constructed, and the
errella placed in it as shown in fig. 219. A number of test experiments were also made with these
ipparatuses, but unfortunately no photographs were taken except the one here reproduced, in which
he magnetising current was 20 amperes and the tension about 2000 volts. This shows exceedingly well
low the polar ring approximates the proper dimensions as compared with the conditions on the earth,
he angular diameter of the ring being here 49°; and with a magnetising current of 30 amperes we
ibtained a polar ring with about the same angular diameter — judging by the eye — as the auroral
:one on the earth, i.e. rather less than 45°. There is, however, no photograph of this magnetisation. A
ew days later, a leak appeared in the vacuum-box, which a couple of months' work failed to stop. In
:ase anyone should hereafter like to construct such a large vacuum-box, I would advise the use of glass
sheets of 25 mm. thickness and not as here 22 mm. as the enormous pressure is liable to bend thinner
elates too much.

There are two important conclusions that we can draw from the polar light-ring here photographed.
•"irstly, we can by this experiment control our earlier calculation of Hq for the cosmic corpuscle-rays
iround the earth. If we then by a very little extrapolation calculate the stiffness of the corpuscle-rays
m the earth corresponding to a circle with a diameter of 45° in the same manner as above, we find that
'/o = 3.1 X 10", or exactly the same value as before. The second important question we can now
solve is that of the breadth of the band of precipitation on earth of the rays which occasion the
>olar magnetic storms. For various reasons I have hitherto assumed (^ that the width of this zone of
precipitation between Kaafjord and Jan Mayen is less than 500 kilometres. The measurement of the
•vidth here on the night side of our terrella gives for these somewhat stiff rays that the breadth is
2.5° which corresponds to 280 kilometres on the earth.

The photograph reproduced shows an experiment (pressure o.oi mm.) in which the south pole of
he terrella is turned directly towards the observer. The two horns of light that are drawn in towards
he polar regions of the terrella are here seen coincident with one another. In the photograph in fig.
200 the poles were above and below, and these two in-drawn horns of light were separate.

In this photograph we also see the exceedingly interesting manner in which the greater number
jf the rays are thrown in a direction away from the terrella on the morning side. It is this collection
if rays which, in my opinion, plays an important part in occasioning the zodiacal light seen in the
norning. In our photograph, on the other hand, the rays that cross one another in what we have
:alled the first and second lines of intersection, or lines of precipitation (see figs. 201 — 207 and 214
i 215), are not visible. I think we should easily get the regions about these two lines of intersection —
he first by preference — • self-luminating in the vacuum-tube, if we so arrange it that the rays that go
•ound the terrella on the evening side are sufficiently intense. This can be attained either by bending
he cathode slightly upwards, so that several of the rays pass above the terrella, or by the equally
simple method of making the cathode exceedingly large, almost as large as the vacuum-box permits,
n the latter case, the conditions will be as nearly as possible like those between the earth and the
sun, as the pencil of parallel rays will be the largest possible.

As will appear later on, I consider the first line of intersection (line of precipitation) of the rays
3n the afternoon side to be of importance in connection with the zodiacal light visible in the evening,

I1) Expedition Norvegienne de 1899—1900, p. a6, a°.

600 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

while I consider the fainter collection of rays that cross one another in the second line of intersec-
tion to be the primary cause of the nocturnal zodiacal light-phenomenon known by the name of "Gegenschein"

EXPERIMENTS FOR THE DETERMINATION OF THE SITUATION OF THE POLAR ZONE
OF PRECIPITATION IN VARIOUS POSITIONS OF THE MAGNETIC AXIS.

117. The experiments are made with the object of obtaining more detailed material for judging
whether the situation of the zone of precipitation on the terrella in the various instances can serve
a guide for understanding the occurrence of the auroral draperies in the polar regions, and the situation
of those polar precipitations which give rise to magnetic storms on the earth.

We shall first go through the different conditions under which the pictures i to 16 of fig. 220 are t

Nos. i and 2 are taken in the course of an experiment, in which the discharge-current was 26
milliamperes, the tension 2500 to 2300, and the magnetising current 20 amperes. The pressure
0.008 mm. The south pole of the terrella lies in the plane of the horizon through the centre, with an
hour-angle of 290°. The photographs are taken from places with hour-angles of 290° and 110°, situated
on the prolongation of the magnetic axis. The pictures 3 and 4 are taken under the same experimental
conditions, only that the hour-angle of the south pole is 250°, and the photographs are again taken from
places on the prolongation of the magnetic axis with hour-angles of 250° and 70°. We see at once from
these 4 pictures, how the so frequently mentioned luminous patch is round and lies within the ring o
light when the magnetic pole turns towards the cathode (i and 4), while the patch is drawn out and
merges with the ring of light in the positions 2 and 3, in which the pole turns away from the cathodi

One thing in connection with this patch of light is particularly deserving of attention, that is, that
the rays which cause it are rays that have gone the shortest way from the cathode to the terrella. I
figs. 200 and 219 the rays which form these polar patches will be seen, showing themselves in the rarefied
gas, like two luminous horns, as we repeatedly have mentioned.

This circumstance is of importance when we imagine the conditions transferred to the earth. 1
sudden flare-up or eruption of corpuscle-rays take place in the sun, these would make themselves felt
on earth first by a precipitation corresponding to the above-mentioned polar patch of light.

Stations on the day side of the earth which happen to be near this first precipitation, will therefore
receive from it a first impulse announcing a coming magnetic storm.

When then, an instant later, the polar precipitation on the night side of the earth or the equatorial
ray-formations are produced, it may appear as if there was a noticeable difference in time at the different
stations on the earth for the commencement of the one and identical magnetic storm. In reality there
are several impulses which act in places very locally. I believe that perhaps some observations
that have been made when magnetic storms were commencing, can be explained by the view here set forth.

The pictures 5 and 6 are again taken from places on the prolongation of the magnetic axis, bi
the south Dole is now given a declination of 19°, and the hour-angle is 270°. The conditions of I
experiment are the same as before, the tension, however, being 2500 volts and the pressure 0.006 mm.

In the pictures 5, 9, u and 15, it will be seen that the phosphorescent coating on the terrella
has a defect uppermost by the luminous ring. Something like a shadow appears there which has nothing
to do with the precipitation.

The pictures 7 and 8 are taken under exactly the same conditions as 5 and 6, but with the magneto
poles reversed.

The pictures 9 and 10 are taken under similar conditions as before, but the tension is 2700 to
2500 volts and the pressure in the discharge-box 0.006 mm.

The magnetic axis is turned, so that the north pole has an hour-angle of 285° and declination 19 •
No. 9 is taken straight out from the north pole, and No. 10 out from the south pole from places on th
prolongation of the magnetic axis.

Kig. aao.

602

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

The pictures n and 12 are taken under similar conditions to 9 and 10 but with the magnetic
poles reversed, moreover the tension is now 2900 — 2500, the pressure being 0.005 mni-

The pictures 13 and 14 are taken during experiments where the hour-angle of the south pole was
255° and declination 19°. The pictures are taken from places on the prolongation of the magnetic axis,
the tension was 2600 — 2400 volts and the pressure 0.006 mm.

The pictures 15 and 16 are taken during similar conditions, but the magnetic poles are reversed
(the terrella re-magnetised) and the tension was 2700 — 2300, under a pressure of 0.007 mni-

The magnetising current for the terrella was, as will have been understood, 20 amperes in all the
experiments, and the discharge-current about 25 milliamperes.

It is also seen by the 4 last pictures how the luminous patch referred to takes different shapes in
different positions and encroaches upon the luminous ring.

The most striking result of these experiments is that the polar spiral of light always forms itself,
in surprisingly nearly the same manner around the magnetic poles without regard to whether the position
of the magnetic axis is altered at all in relation to the central line between the terrella and cathode. The
difference between the spiral round a magnetic north pole and the spiral round a magnetic south pole
is easily recognised, as the spiral seen from above a north pole winds itself in the direction of the hands
of a clock, while the spiral over a south pole winds the opposite way.

On the other hand, the position of the polar luminous patch is more sensitive to changes in the
position of the magnetic axis, as the light patch with such alterations had changed place and shape to a
certain degree.

When we apply the results described above to the earth, we would expect to find that similar
spirals of precipitation to those here depicted formed around the magnetic poles or perhaps nearest
around the points in which the magnetic axis of the earth intersects the earth's surface (see p. 58 of
this work, Section I, and STORMER'S Memoir in Arch, de Geneve, I.e. § 17).

These spirals of precipitation must in the course of the daily rotation of the earth, swing round
the true poles of the earth, while they, however, always retain their direction in relation to the line of
direction to the sun, and their position in relation to the magnetic poles.

As we have seen before, the north pole spiral can, as regards the earth, with some degree of
resemblance be' compared with a circle of from 40 to 45° spheric diameter and with the centre in a point
with latitude 78° 20' N, longitude 71° u'w. (New year 1903) which was the northern point of intersec-
tion with the axis just mentioned. If the corpuscle rays from the sun happen to be specially flexible,
the spherical diameter can be less than 40°.

It is obvious what ample opportunity is here afforded for testing the correctness of our theories
The theoretic positions of both the precipitatons which occasion polar magnetic storms and the preci-
pitations which occasion auroral arcs, are, as may be seen, hereby ascertained by a simple construc-
tion, after which it is merely necessary to observe the hour and place.

We get a theoretical daily and annual motion in these phenomena, by which the theory can be
controlled.

Owing to the relation of the auroral spiral to the direction towards the sun, the spiral will, when
compared with a fixed point of observation, appear to turn with the sun, in addition to also periodically
shifting in relation to the spot in other ways.

A thorough study of these questions will be made and the results be made known in the second
volume of this work. By that time other new experiments will be made as to the correct size of the
polar ring of precipitation (45° angular diameter), and the situation of this at the various positions of
the terrella will be determined with the utmost possible precision.

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV. 603

On a preliminary comparison with the investigations of the ordinary position of the auroral arc at
several polar stations, it appears as if these arcs have the direction corresponding to the experiments,
and the translatory motion of the arcs in a corresponding manner also makes its appearance.

INVESTIGATIONS REGARDING THE ANGLE FORMED BY THE PRECIPITATED RAYS

WITH THE MAGNETIC LINES OF FORCE.

118. We will now proceed to the description of the experiments represented in fig. 221, and
discuss the facts resulting from them.

The experiments were made in order to make it somewhat clear how steeply towards the terrella
the rays are precipitated in the "auroral zone" under the different experimental conditions, especially when
the magnetic stiffness of the rays is modified in proportion to the magnetisation. The plate is unfortunately
not so good as could be desired.

These investigations are of great importance to our present theory on the auroral draperies, as
we suppose that the auroral rays in the draperies are formed by those pencils of rays which come as steeply
as possible towards the earth, where they are entirely absorbed by the atmosphere after having rendered
the air luminous over a more or less wide expanse.

This is to some extent a modification of the opinion I have previously expressed, as I formerly
supposed that the rays of an auroral drapery were formed by secondary beams produced in the atmo-
sphere by the influence of the primary cosmic and corpuscular current which forms the auroral arc
itself. In a certain degree, something valid will remain in this older theory ; but it seems more
natural to suppose that rays with such tremendous power of penetration as that dealt with here,
must be the same stiff rays that we suppose to be emitted from the sun. The state of the atmosphere
of the earth is hardly such as to permit the formation of such stiff rays. I have therefore been
brought to take a different view of the matter, which was further confirmed by my terrella experiments,
namely, that auroral rays are formed by the rushing in of distinct pencils of cosmic rays towards
the earth almost exactly along the magnetic lines of force, without any turning, worth mentioning
about those lines These cosmic rays, which thus penetrate the atmosphere, are entirely absorbed,
and therefore never return into space.

During the experiments about to be described, the terrella maintained an unaltered position in
the discharge-tube, the line from the centre to the magnetic south pole being in a horizontal plane
with an eastern hour-angle of 270°. The photographs have been taken from a place in that plane
which also has an hour-angle of 270°, so that the eight branches of the screen are seen edgewise.

The discharge-current, during all the experiments, was about twenty milliamperes. The photographs
i, 2 and 3 were taken with a magnetisation current of 10 amperes, the first at a tension of
2800 — 2600 volts and a pressure of 0.009 mm., the second at 2200 — 2100 volts and a pressure of
3.017 mm., ar>d the third at 1800 — 1700 volts and a pressure of 0.05 mm. The photographs 4, 5 and 6
ire from experiments during which the magnetisation current was 20 amperes and the tension respectively
2500— 2100 volts, 2200 — 2000 and 2000 — 1800 volts, and the pressure respectively 0.007 mm , 0.017 mm.
>nd 0.025 nim. The photographs 7. 8 and 9 are of experiments during which the magnetisation current
,vas 30 amperes and the tension respectively 3000 — 2600 volts, 2400 — 1800, and 1700 — 1500 volts,
.vhile the pressure was respectively 0.007 mm-> 0.022 mm. and 0.026 mm.

In some of the photographs, for instance Nos. 4, 6, 8 and 9, on the left of the third branch of
he screen, the shadow of the brass rod from which the terrella was hung in the magnetic equator
.vill be observed. We have seen this shadow rather more clearly on a large number of the previous photo-
graphs, and it immediately gives us an idea of the steepness with which the rays here pass through the plane

604

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Fig. 221.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV. 605

of the equator to be precipitated in the "auroral zone". It was this shadow of the suspension rod
that first suggested the idea of constructing the high eight-armed screen and making these ex-
periments which have been of such great importance to the theory of the positive and negative polar
storms, as seen in Article 113. Such screens, placed on the edge above the polar regions of the terrella,
have already been used previously, but the results of the experiments were not so clear (see fig. 136,
page 302, Section I), because the screens were far too low.

The illustrations show us the angle at which the most perpendicular rays fall towards the
terrella. The shadows behind the branches of the screen show, further, that the rays are most perpen-
dicular in the middle of the "auroral zone". On the southern edge of the zone, the rays fall most obliquely,
and on the northern edge more obliquely than in the middle, but less so than on the southern edge.
It appears moreover, although not positively, from the photographs, that the rays, at about the same
tension, descend somewhat more perpendicularly towards the terrella with strong than with slight
magnetisation. With the same magnetisation, the rays are also somewhat more perpendicular with low
than with high tension; but the difference does not appear to be so great. There are here, however,
several things to be taken into consideration. It must not be forgotten, for instance, that the shadow-
producing part of the screen does not remain the same in all cases, a fact of which proof is found in
the form of the precipitation on the western side of the screen-branches (see fig. 212, Nos.i, 4 and 7).

We have endeavoured in the foregoing pages, by numerous experiments, to show how the rays
move round our terrella. It would have been of great interest if these experiments had been repeated
with our last terrella No. 7, which was highly magnetic, in the new large discharge-box measuring
70 litres, as we might then have chosen the magnetic conditions so that the luminous polar band would
have had an angular diameter of 45°. We could then at once have transferred the results to the
earth, and in particular determined the perpendicularity with which, according to the theory, the auroral
rays might be expected to come towards the earth. We propose to make these more extensive experi-
ments, and the results obtained will be published in the second volume of the present work.

In a general way, it can even now be established as a fact, that rays which are finally precipi-
tated in the "auroral zone", have first passed round the terrella, oscillating above and below the plane
of the magnetic equator.

In the foregoing pages, we came, as a consequence of our experimental results, to the conclusion
that the continuous luminous ring in the "auroral zone" was produced by a countless succession of secon-
dary precipitations overlapping one another in such a manner that the luminous ring appeared to be
continuous. We remember, for instance, having once counted, on the night side of the terrella, about
20 distinct secondary precipitations, of which those of a higher order lay to the east of those of a
lower. The number of these precipitations was greatly multiplied in proportion to the increase of the
magnetisation of the terrella. It is this opinion of the constitution of the luminous ring which we shall
firmly maintain in endeavouring to develope a theory as to the formation of auroral draperies.

The rays which are precipitated, for instance, on the night side of the terrella, a little eastward of
the place where other contiguous rays, originally from the same bundle of rays, are precipitated, will
thus have travelled considerably farther than those rays which are precipitated on the west side, close
by. They may, in fact, have been deflected below the level of the equator towards the south pole, and
then have risen again and been precipitated in the northern "auroral zone". It will consequently be
observed that the rays in the precipitation-zone are formed from separate, relatively small groups of rays
which have intersected the plane of the equator several times, before they are at last precipitated. We take
then first a group of rays in the northern "auroral zone", which have passed n times through the
equator. The nearest companion group which had nearly been precipitated in this zone, has subse-

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903. 77

6o6

HIKKKLANl). THE .NORWEGIAN' AL'RORA POLARIS EXPEDITION, IQO2 — 1903.

qurntly to pass through the equator once more, viz. u -\- i times in all, and is afterwards precipitated
in the southern "auroral zone", while a corresponding bundle of rays, which had nearly been preci-
pitated in the southern "auroral zone", passes through the equator and is precipitated beside the
bundle of rays which had passed ;/ times through the equator. The next contiguous group of rays has
passed through the equator 11 + 2 times before being precipitated in the "auroral zone". As the rays
now fall symmetrically above and below the magnetic equator, the corresponding process of selection
will have taken place in the southern "auroral zone", so that in the northern and southern zones
auroral rays will be produced successively one after another, each one having passed through the
equator mice oftciii'r than the nearest preceding auroral ray.

Aurora boreaiis observed at Bossekop on the 6th January, 1839, ai/cordin^; to Bravais.

Although it is not our intention to deal with the auroral phenomena until we come to Volume II
of the present work, where we shall see how the different forms of auroral light are to be explained,
ue shall, however, now show, as an illustration connected with the terrella experiment just described,
how the formation of auroral draperies is to be understood. As a characteristic feature of this perhaps
the most peculiar form of auroral light, we would remind the reader that the aurora borealis frequently
appears as a vertically hanging curtain consisting of densely co-ordinated parallel rays. The curtain
has most frequently its longitudinal direction in the magnetic east and west.

As further characteristics we would mention that the auroral curtain is frequently formed from east
to west, or vice versa, in such a way that the rays, one after another, seem to be precipitated from the
sky, and this so rapidly that the curtain can be completely formed and extend right across the heavens
in a few seconds.

Another phenomenon, which is most closely related to the above, is that of the so-called luminous
riWiV.v which may rush through the auroral drapery. The rays blaze up and go out, and the phenomenon is
repeated successively on every ray from one end of the curtain to the other, the wave appearing to
pass through the entire length of the drapery. The waves move most frequently from west to east, but
also \ ery otten in the opposite direction.

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV. 607

The auroral curtain may have characteristic undulating folds and eddies; and from one fold luminous
waves may pass along the curtain eastwards and westwards simultaneously (!).

We will now try to combine these facts with the experimental results at which we arrived through
our terrella experiments.

First we must suppose that the auroral rays do not exactly follow the magnetic lines of force,
but that, in what we call negative precipitation, they form a small angle towards the east with the
lines of force, while in what we in analogy with the polar storms call positive precipitation, they
form a small angle towards the west with the lines of force. We shall subsequently show how these
angles towards the east and the west are to be understood. The angles, however, are very small,
because the auroral rays are only formed by those rays from space which fall as vertically as possible
along the lines of force, and they penetrate, therefore, most deeply into the atmosphere and create
the auroral rays.

There are unfortunately not many observations which can be referred to with regard to this sup-
posed inclination between auroral rays and magnetic lines of force, but in the well-known work of PAUL
GAIMARD, "Voyages en Scandinavie, en Laponie etc : Aurores boreales", page 505, we note the following
remark: "We certainly are justified in stating that the rays are not always strictly parallel with the line
of inclination".

In the same work BRAVAIS makes the following remarks: "We admitted one of the two following
hypotheses: either the average orientation of the auroral arcs is not perpendicular to the magnetic
meridian, or the average direction of the rays is not strictly parallel with the line of inclination".

We shall now see that both these hypotheses must be assumed at the same time.

CARLHEIM GYLLENSKIOLD recapitulates, 1. c., page 69, his result as follows:

"The disagreement in our observations is rather great. When not taking into consideration the
doubtful positions, the difference of the average position is, in two cases, 22° 54' and 20° 31'; it
exceeds 10 degrees in eight others. The average difference is 6° 34' and the probable error of the
average is + 42'.!. The members of the French expedition on board the corvette "La Recherche"
have made, at Bossekop, 43 observations of the centre of the corona; the average difference is 5° and
the probable error of the average is o° 30'. The greatest difference is 15°; it exceeds 12° in two
other cases. Our observations consequently agree less with each other than those of the French
expedition. However, our observations are probably not in reality less exact than those made at
Bossekop; we are inclined to believe that the position of the corona is subject to greater variation in
a latitude of 78 degrees than in Finmark".

Mr. SIRKS OF DEVENTER(2) arrives, through 16 observations made in Europe during the great aurora
borealis on February 4th, 1872, at the result that "the corona in almost all places was some degrees
inferior to the magnetic inclination; the azimuth of the corona was also less than the magnetic decli-
nation".

When discussing the angle made by the auroral rays with the magnetic lines of force, the angle
always meant is that between the tangents of the magnetic line of force and the axis of the auroral ray
through the foot-point of its orbit.

Such an angle will generally have a projection on the plane of the magnetic meridian, through the
foot-point, and on a plane through the tangent of the line of force perpendicularly on the meridian.

(') See CARLHEIM GYLLENSKIOLD: Aurores boreales. Observations faites au Cap Thordsen, Spitzberg, 1882 — 1883. Stock-
holm, 1886, Vol. II: i, p. 136.
(2) POGGENDORFF'S Annalen, Band 149.

608 B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

When we mention above an angle to the east, we mean an angle whose projection on the latter
plane falls to the east.

Rays of group A which have intersected the magnetic equator must, according to the theory and
in conformity with the observations made by Mr. SIRKS, be supposed to form auroral coronae situated
some degrees lower than the magnetic zenith. We refer to the form of the precipitation on the west
side of the screens, fig. 212, Nos. i, 4 and 7, and fig. 213, Nos. 4 and 8.

Rays of group B, on the contrary, would be expected to create auroral coronae situated higher
than the magnetic zenith.

Thus we see that the theory gives reasons explaining that the different observations vary as to
the situation of the auroral coronse, as stated by BRAVAIS and CARLHEIM GYLLENSKIOLD. We shall return
to this important question in Volume II.

Another question which we shall soon deal with is this: Can we suppose that the cosmic rays
which produce the luminous auroral rays can return to space, or are they at once absorbed by the
atmosphere?

We will suppose that they are at once absorbed, because if the cosmic rays should return, then
this must take place in and from the foot-point of the auroral ray nearest the earth. But as H.Q
for the cosmic rays is between i and 10 millions, the lowest value that the radius of curvature can have-
namely when the ray moves perpendicularly to the lines of force above the magnetic poles of the earth-
will be between 15 and 150 kilometres. The thickness of the aurora at the foot-point should then be be-
tween 30 and 300 kilometres. Now we know that even in the aurora which approaches to within a
couple of kilometres^), or very close, to the surface of the earth, the rays have a proportionally small angular
diameter at the foot-point. GYLLENSKISLD states the value to be between 10' and 3° (1. c., page 132).

It must consequently be considered as certain that the cosmic rays which come vertically towards
the earth in such way as to form auroral rays, are entirely absorbed by the atmosphere.

Let us now see to what our experimental results will lead us, when they are applied to the
auroral curtain formed by the auroral rays.

The cosmic rays approach the earth in the same manner as our cathode rays approach the terrella.
We must now suppose that the auroral rays are formed by just such distinct, proportionally small groups
of cosmic rays, which successively detach themselves from a larger bundle of rays after having passed
through the magnetic equator, n, (n -+- 1), (« -f- 2), (n + 3), etc. times.

It is relatively easy, from our experiments with the terrella, to calculate, in some measure, the
difference of time which in this manner should correspond to the entrance into the atmosphere of the
«"' and (n -\- p)'h auroral rays at the moment when the auroral curtain is formed, provided that the velocity
of the cosmic rays be known. This will be done later on in Volume II, but even now we may form
an idea to the effect that we shall be led to results which are not in contradiction with the experience
which we have now acquired.

Supposing that H . Q is between i and 10 millions, and that the velocity of the cosmic rays is equal
to that of light, we can conclude from the experiments that it is only a question of a fraction of a
second between the formation of one auroral ray and the next one.

We proceed in the same manner as regards the so-called luminous waves which pass through an
auroral curtain. If the original bundle of rays from the sun suddenly increases or decreases, this increase
or decrease will be shown successively through the rays, one after another. If the rays produce pre-
cipitation corresponding to that found on the night side of our terrella, the wave will move from
west to east; if the precipitation corresponds to the so-called positive precipitation, the wave should go

(') ADAM PAULSEN: Aurores boreales observes a Godthaab 1882 — 1883, pages 8 and 13. Copenhagen, 1893.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. IV. 609

from east to west. GYLLENSKIOLD indicates about 39' as an average of six observations of the
angular velocity of the luminous wave. Supposing the thickness of the rays to be 10', we obtain about a
quarter of a second as the time which the corpuscular rays take to pass from near the southern to the northern
auroral zone, and vice versa. We suppose here rays of a certain rigidity. In reality, rays of a somewhat
different rigidity will, of course, occur, and the conditions will then be correspondingly more complex.
We will not here enter more closely into the theoretical problems as to the explanation of the so-called
folds and whirls in an auroral curtain. We will only say that we suppose that where such phenomena
occur, the angle between the rays and the magnetic lines of force is nearly o, or the angle lies in the
magnetic meridian.

We have taken for granted that the auroral drapery is formed by negative corpuscular rays of a
kind similar to ft rays, and have thus assumed that a or other similar positive rays take no part in the
formation.

There might in itself be much that would lead one to think of « rays in connection with auroral
draperies, but there are decisive points that to my mind contradict such an assumption.

In the first place the auroral draperies appear, as a rule, in the time between the positive polar
storms in the afternoon and the negative storms at night, i. e. just at the time when the negative
corpuscular rays fall most vertically and farthest in towards the earth. During the positive storms in
the afternoon, the rays are bent westwards along the auroral zone, and in the night, during the negative
storms, they are bent eastwards, always supposing that our results from the terrella experiments can be
transferred to the earth.

A precipitation towards the earth of a rays or other positive rays from the sun, would come in
on the morning side of the earth, not on the evening side as the negative rays do; and it would be a
remarkable coincidence if the positive rays were to go right round the earth and descend farthest into
the asmosphere on the evening side, at the very place where all experience would lead us to expect the
lowest precipitation of negative rays.

The way in which the phenomena are here compared, furnishes an explanation of an observation
that is sure to be made whenever bright draperies are seen near the zenith in the neighbourhood
of the auroral zone. The magnetic needles in the magnetometers then always, as far as I can
learn, oscillate backwards and forwards, with alternately great positive and negative deflections.

From these points of view, it will be easily understood that the connection between the magnetic
perturbations and aurora cannot be either simple or direct. Very early observers have proved that they
are not the very same conditions that give rise simultaneously to the most powerful magnetic storms
and the brightest aurora; but it is certain that when one of these phenomena manifests itself with great
intensity, the other infallibly occurs, although there is not on that account any easily definable proportion
to be found between their intensities.

During the last couple of years, attempts have been made in different ways, upon the basis of the
corpuscular rays, to obtain a plausible explanation of the formation of the auroral curtains.

VILLARD(I) has tried, upon the basis of some beautiful experiments, to conceive the auroral
drapery as formed by cathodic rays emanating from cirrus clouds, and afterwards drawn towards a
terrestrial magnetic pole, e. g. the north pole, whence the ray returns after having penetrated far into
the atmosphere and formed an auroral ray. He conceives then that the ray returns and goes towards
the south pole, where the same ray penetrates far into the atmosphere and forms] a southern auroral
ray. The ray then returns again and goes towards the magnetic north pole, and forms there a new
auroral ray by the side of the first one, and so on, times out of number.

(') VILLARD : Les rayons cathodiques et 1'aurore boreale. Paris, 1907.

6lO BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

On account of the absorbing power of the atmosphere, it does not appear that this theory can be
maintained.

Other reasons telling against this theory are advanced by STORMER (!) in his well-known essay,
'Sur les trajectoires des corpuscules 6lectris6s dans 1'espace". The only circumstance that ST&RMER
finds in favour of VILLARD'S theory and against mine, is that the auroral zone has a diameter ot
about 45°, while according to his own calculations it should be much smaller (4 to 12 degrees for
cathodic rays and /?-rays of radium, and for a-rays 24 to 36 degrees). In order to explain this
disagreement, STORMER takes up for discussion the idea that the terrestrial magnetic field outside
the earth is greatly modified by exterior currents, especially by the equatorial ring discovered
through my experiments. This supposition is less natural, it appears to me, than the one advanced by
me as to the rigidity of the rays, viz. that H .Q must be between i and 10 millions.

LENARD also makes the same suggestion in a recent paper on this subject, as stated on p. 596.

Further, ST6RMER, in the same essay, paragraph 19, has advanced a very interesting theory on
the creation of the auroral curtains based upon his mathematical studies on my theories.

In admitting an average value of H . Q of 315 for cathodic rays, he finds (1. c., page 119), the
theoretical dimensions of an auroral drapery. He arrives, for instance, at a length of 275 kilometres
corresponding to a thickness of 72 metres.

In going through the same calculations and choosing H.Q = 3.1 X 10°, I find the length of the
drapery almost unaltered, while the thickness has to be multiplied by 10. It will consequently be quite
700 metres. Nothing has here been added for the thickness of the auroral rays, as is done by STORMER.
It cannot be conceived here, in fact, that the auroral rays can be formed as STORMER supposes, as
in that case they would have a thickness of about 100 kilometres, which is contrary to all experience.
It will be observed that the dimensions, calculated in the manner indicated above, do not fit so
badly to a real auroral drapery; but it must be remembered that STORMER has here only calculated
the space in which the rays going to the centre of the elementary magnet, approach the earth. He
presupposes that the rays which in reality occur in the auroral curtains keep close to such rays through
the centre. We have seen from the experiments, however, that the cosmic rays lying nearest to those which
penetrate the auroral curtain, can swing entirely underneath the magnetic equator and penetrate the
southern auroral zone.

From certain positions of the magnetic axis of the terrella in relation to the cathode, we observe,
however, that the luminous spot which always occurs on the afternoon side to the north of the luminous
ring, stretches itself into a ribbon (see fig. 220). These spots are formed by rays which are drawn
directly towards the polar regions of the terrella without swinging above or below the equator, and it is
perhaps these rays which are most likely to agree with the bundle of rays in STORMER'S interesting
calculation.

I1) STORMER : Archives des sciences physiques et naturelles, juillet, aout, sept, et Oct. 1907.

CHAPTER V.

IS IT POSSIBLE TO EXPLAIN ZODIACAL LIGHT, COMETS' TAILS, AND
SATURN'S RING BY MEANS OF CORPUSCULAR RAYS?

119. Zodiacal Light. In several of the experiments with a phosphorescent terella with different
screens, in a large discharge-tube, we have come upon phenomena which appeared capable of serving as
starting-points for an explanation of Zodiacal light.

Zodiacal light is the name given to a brightness which appears in the western sky after sunset,
and in the eastern before sunrise, nearly following the line of the ecliptic in the heavens, and stretching
upwards to various altitudes according to the season of the year.

Moreover, at certain periods of the year, what is called "Gegenschein" (discovered by BRORSEN),
occurs almost directly opposite to the position of the sun.

Accurate observations have now shown that the axis of the zodiacal light diverges somewhat
noticeable from the ecliptic, and recent work has assumed that it is rather a question of the sun's
equator, than of the ecliptic.

The great cosmologist, CASSINI, concluded after only ten observations — the first detailed obser-
vations ever made — that the axis of the zodiacal light has a relation to the sun's equator, rising and
sinking with it.

Before I proceed further with the elucidation of this question, I will here mention a peculiarity of
the zodiacal light, which no attempt has ever been made to explain in anything approaching a satisfactory
manner by the various theories that have been advanced. This is a pulsation in the intensity and
shape of the light which has at times been noticed, a pulsation which surely testifies to an electric origin;
and I am therefore of opinion that the phenomenon is akin to the pulsation which is sometimes seen in
auroral lights and the oscillations in terrestrial magnetism.

HUMBOLDT writes: "I have occasionally been astonished in the tropical climates of South America,

to observe the variable intensity of the zodiacal light When the zodiacal light had been most

intense I have observed that it would be perceptibly weakened for a few minutes, until it again sud-
denly shone forth in full brilliancy" (Cosmos, vol. I).

Mr. BIRT, Kew Observatory, noticed in March, 1850, "One evening there was a sudden brightening
of the light for an instant, and also variations in its lustre of an intermittent character. These inter-
missions of brightness were observed on the same evening by Mr. LOWE at Nottingham" (Am. Journ. of
Sc., XV, second series, p. 121).

The Rev. GEORGE JONES, a most diligent observer of zodiacal light, relates in March, 1854: "I was
surprised, one evening, at seeing the zodiacal light fade sensibly away, dimmed to almost nothing, and
then gradually brighten again. This was repeated several times; but the effect, after all, was to leave
me only in amazement and doubt. Subsequent nights, however, gave abundant exhibitions of this kind,
of which, with the times and changes, I have made ample records with the particularity that the case
required. — — —

6l2 ISIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

"My records, however, will show that there is a regularity of appearance and the closing off of
these pulsations, which proves that they do not belong to so uncertain a cause as atmospheric changes
but to the nebulous substance itself. They seem to intimate a great internal commotion in the nebulous
matter, for they were too rapid to be occasioned by irregularities in its exterior surface.

"I noticed them again the following year, but must refer the reader to my records and charts.
The changes were a swelling out, laterally and upwards, of the zodiacal light, with an increase of bright-
ness in the light itself; then in a few minutes, a shrinking back of the boundaries, and a dimming of the
light; the latter to such a degree as to appear, at times, as if it was quite dying away; and so back
and forth for about three quarters of an hour; and then a change still higher upwards, to more perma-
nent bounds". (Observations of the zodiacal light by JONES, vol. 3 of the Report on the United States
Japan Expedition, 1856, page XIII).

The pulsations of the zodiacal light thus recorded cause one involuntarily to think of the regular,
often almost sinusoidal magnetic pulsations and simultaneous oscillating earth-currents which so frequently
occur, and markedly in the month of March. (See Part III of this Section.)

As an example, I shall quote an observation of JONES, not, it is true, from March, but from the
evening of the 3Oth January, 1854, "The pulsations of the zodiacal light were very distinct". At the
end of his series of observations we find: "7h 54™, its boundaries had risen to b again and .... bright:
7U 55™ at a ar)d very dim: 7h 56™ at b, and bright: 7h 57™ at a, and very dim: 7h 58^™ at b and
bright: 7h 59^m still at b and bright: it seemed now to be permanent at b".

Here we have plainly a period of about 2 minutes.

From another observation of JONES: "These lateral changes of the whole body of the stronger
zodiacal light are very remarkable. I cannot see any room for mistake, as there might have been, had
the light been more inclined to the horizon. But the horizon and ecliptic made nearly a right angle".

For comparison I shall adduce that, at the Haldde observatory, in March, 1900, I observed beautiful
magnetic oscillations with a period of 128 seconds.

In May, 1910, I again registered at Kaafjord beautiful magnetic waves and simultaneous earth-
current oscillations of very nearly 119 seconds, as will be seen in the subsequent part of this volume.

I quite perceive that it is easy to imagine that what are called magnetic elementary waves, which
have specially been studied by ESCHENHAGEN, have their origin in oscillations of electric ray masses.

It may be worth mentioning in connection with this, that the earth in March and September is at
the farthest possible distance from the nodes of the sun's equator.

It appears to me very probable, in view of the properties above described, that the zodiacal light
must be primarily occasioned by electrical phen6mena.

We shall now further analyse the most important attributes that the zodiacal light has been ob-
served to possess, and see if they can be put together and explained by the supposition of an emana-
tion of corpuscular rays from the sun. The question whether the axis of the zodiacal light is situated
in the ecliptic or in the equator of the sun has been carefully considered in two important treatises by
ARTHUR SEARLE. In the first of these, "The Zodiacal Light" (Proceedings of the American Academy of
Arts and Sciences, 1883) as well as in the second, "The Apparent Position of the Zodiacal Light", 1885,
he has made extensive researches by making special use of numerous observations from the classic and
admirable volume by JONES.

In the following pages I shall endeavour to interpret all the results of observations with which I
am acquainted, by starting with the supposition to which I shall subsequently come, in order to explain
the diurnal variation and the origin of terrestrial magnetism, viz: that the corpuscle-rays continually radiate
from the sun's surface (see Section I, p. 314). But these continuous rays must be assumed to possess
properties somewhat different to those of the very stiff corpuscle-rays that radiate in short periods from
the sun-spots, and which, we supposed, specially occasioned magnetic storms on the earth.

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 613

I now assume that these corpuscle-currents, which are continuously given out and probably most
strongly from the neighbourhood of the sun's equator, are somewhat less stiff as regards magnetism than
the rays which come in eruptions from the portions in greatest activity around the sun-spots. The
constant rays are thus less penetrative through matter, and come probably from lesser depths in the
atmosphere of the sun.

I have recently in a note(') in C. R. de 1' Academic des Sciences, Paris, in explanation of certain
phenomena in the magnetic storms, advanced the opinion that the sun is magnetic, with a magnetic
moment of the order io2s or about 150 times as great as that of the earth.

If this is the case, the corpuscles which are constantly given out will principally issue both from
the regions near the magnetic poles of the sun, and moreover the rays will to a very great extent be
concentrated and form a ring in the plane of the sun's magnetic equator, which probably only forms a
small angle, or is perhaps identical, with the heliographic equator.

There is no reason, as we shall see further on, to suppose that the sun's magnetic axis should
not be identical with the axis of rotation, as there can hardly be magnetisable masses with permanently
fixed positions in the sun.

In the plane of the sun's magnetic equator the corpuscle-rays will doubtless, as an elementary study
shows, bend comparatively sharply, near the sun; but they will keep constantly in the plane.

This question, the examination of how the corpuscle-rays move in the magnetic equator of a mag-
netic globe, I have investigated experimentally and have obtained very successful results. See fig. 223.

By allowing a smooth magnetic sphere (without phosphorescent coating) to be the cathode in a
discharge-container, a wonderfully developed luminous ring is easily obtained around the globe.

The photographs here reproduced have been taken with a magnetic ball of 8 cm. in diameter in the
smallest of the prismatic discharge-containers. It was seen that the ring expanded immensely with the
stiffness of the rays and with the magnetic globe's magnetic momentum. I was unable in this instance
to attain a difference in the tension between anode and cathode of more than 700 volts, when the
brass ball was the negative pole; but even at this tension and a magnetising current of 21 amperes
from an isolated storage battery the ring became so large that it at times reached to the glass
walls of the container. I shall repeat the experiment with my largest discharge-box, when I get it
repaired again, for I am convinced that I shall be able to obtain a perfectly flat ring of light of 30 cm.
diameter around my strongest magnetic globe No. 7, which is also of 8 cm. diameter.

If I were in possession of sufficient quantities of pure radium-bromide, I would coat the equatorial
portions of my strongest magnetic globe with that substance. It would be of interest to see if rings of
(i and a rays could then be made visible.

I will here observe, that when I have on previous occasions produced a luminous ring round my
terrella by cathode rays from a somewhat distant cathode, it is possible that I have been mistaken. It
may be that the magnetic ball has been sufficiently negative compared with the surroundings for an
emanation of negative rays to take place at the same time as the ball is illuminated and surrounded by
cathode rays from the real cathode. There are two reasons for this. In the first place, it was, as
already mentioned, only under quite exceptional circumstances that the ring was formerly produced, while
it is now produced in the way here described never wanting, and in the second, the difference in the
tension need only be very small before the negative radiation from the ball occurs, so that such
a difference in tension can very easily have taken place in the course of the earlier experiments.

But this condition does not, of course, affect our previous main results, in which, by the aid of
various screens, we have proved how, amongst other things, rays from the cathode circulate around the
terrella, bending above and beneath the plane of the magnetic equator.

(') C. R. 24 Jan. 1910.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902— 1903. 78

614

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

Fig. 223.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 615

All the trials represented on the adjoining figure have been made with terrella No. 4 of a
diameter of 8 cm. or perhaps 7.8 cm. when without the phosphorescent coating, and weighing 977 gr.
The resistance of its magnetising coil is 1.72 £. The magnetic momentum at 10 amperes magnetising
current was 27 200.

The first experiment (see fig. 223) was made with a discharge- current of 20 milliamperes under
pressure of about 0.005 mm' a"d with a magnetising current of 21 amperes.

In addition to the equatorial ring, discharges will be seen from the northern polar zone. This
polar discharge is easily produced if there are any sharp points or unevennesses, but, on the other hand,
it is difficult to obtain it when the surface is smoothly polished, as was the case in all the other
experiments represented on the plate.

The picture No. 4 has been placed beside this for the sake of comparison. It is a view of the
sun during an eclipse, May 1701, 1901. The picture is drawn by H. R. MORGAN from the negatives.
I will, later on, by the aid of points in the magnetic polar regions, both N. and S., produce a more
perfect example corresponding to photograph No. i, as this is obviously of great interest.

Photographs 2 and 3 are from an interesting experiment seen from the side and from above, in
which the pressure was brought as in the first experiment, but the discharge-current was only 2 or 3
milliamperes and the magnetising current 26 amperes.

The tension was 1500 volts before the magnetisation of the spherical cathode, and the radiation
from it could be seen to take place evenly from the entire surface of the sphere. After the magnetising
current was put on, the tension sank immediately to 600 volts and the radiation then took place only
from the equatorial regions of the spherical cathode. This could be plainly observed from the minute
glowing spots from which the rays issued, near the metal ball's equator.

In the experiment represented in photograph No. 5 the pressure was as before, the magnetising
current 21 amperes, and the discharge-current 3 milliamperes.

Photographs 6 and 7 are from an experiment with a magnetising current of only 2 amperes. The
ring is seen from the side and from above. Pressure 0.02 mm. and the discharge-current was 5 milli-
amperes. It is the low magnetising current that occasions the ring to be broad and small in extent.
A dark band is plainly visible between the magnetic sphere and the ring. It has happened on several
occasions that the luminous ring has been divided into two concentric rings by a dark circular band.

We can find the conditions for electric radiation's getting out towards infinity from the surface of
a magnetic sphere.

Suppose a magnetised sphere is giving out electric radiation of some kind. In the regions near
the poles the radiation will be able to get out by passing nearly along the lines of magnetic force.

For rays in the magnetic equator, however, the magnetic force is perpendicular to the orbit of
the ray-particle, and unless certain conditions are fulfilled the radiation will not be able to emerge in
this place.

It will be of interest for a number of questions in cosmic physics, to find the exact conditions
for rays in the place of the equator emerging into space.

Let R and cp be polar co-ordinates in the plane of the equator with the centre of the sphere
as origin.

We suppose the magnetic force to be perpendicular to the plane of the co-ordinates, and outside
the sphere given by the relation

6i6

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQOS — 1903.

This relation is the same as that which determines the fields of an elementary magnet. We can
then apply the results of STORMER'S mathematical analysis of the orbits of corpuscles in the field of an
elementary magnet.

According to STORMER, the orbits are determined by the following equation:

(I)

is the length of the orbit, y is a constant of integration.

c =

M
Haot

HOQO is a quantity which depends on the stiffness of the rays. QO is the radius of curvature of
the corpuscular orbit, when the magnetic force perpendicular to the orbit is H0-

Introducing the angle 6 which the direction of the orbit forms with the radius vector we get

' R + 3T»

From the condition that sin 6 must have values between — i and + i, STORMER finds that for
each value of y the orbits must be restricted to certain regions of space.
Suppose at first y is negative and numerically greater than i, or

yt = — y, where

In this case we shall have an interior and an exterior region for the orbits.
The inner region is limited by the two circles,

The exterior region goes from infinity to the circle

^3 = c (y, + 1/yl

(2c)

If y, is less than unity, the exterior circles R% and R3 cease to exist.

The rays issuing from points on the equator circle can have any direction inside the two quad-

rants 0 < 6 < •'- and 0 > 0 — f.

*- Ci

It is of special importance for us to examine the range of those rays which reach the greatest
distance.

It will be those going out in a direction corresponding to sin 6 = + 1 or for these rays:
R = a when sin 6 = + 1, which give

R! = a = c
If the rays shall not go towards infinity

- y,).

y, > 1 or

(3)

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 617

If condition (3) is fulfilled, the range of the radiation will be R-, as given by equation 2 b.
We suppose a to be constant and let c vary.

When c decreases towards -=- , Rz will increase and approach the value R-, = c.

y2 — 1

The greatest range which the rays can have without going towards infinity will be

R-i = -, a-— = 2.414 a.

\2— I

We then get the very simple result:

If electric radiation starting from the surface of a sphere in the plane of the magnetic equator, and
only subject to the influence of the magnetic field of the sphere, reaches a distance from the centre
greater than 2.414 times the radius to the sphere, the radiation will not be able to return to the sphere,
but will pass on towards infinity. This result will hold independent of the magnetic moment of the
sphere and the stiffness of the electric rays.

This result supposes that relation (i) holds good close up to the surface of the sphere. This relation
actually holds good provided the sphere is uniformly magnetised or it will be more or less true for
any magnetisation which makes the magnetic force in the magnetic equator a function of the distance
from the centre.

If the radiation shall return to the sphere, the following condition must hold:

c> 2.414. a or

iw-

M > 2.414. a.

This result corresponds to the rays starting in the direction 6 = -

2

If we consider the radiation starting normally we get

^2,max.,= 2rt,

or if radiation starting normally reaches a distance greater than 2 a from the centre, it will pass on to
infinity.

If the radiation starting normally shall return to the sphere, we must have

c > 2 a or

M

^ M

Application to the sun.
In order that radiation shall emanate from the sun

.86X 10** Ho,

when starting in the direction B = - and

m

when starting normally.

For the stiffest ft rays starting normally we get

.9 X
and for a rays

X IO27.

When M is of the order io28 as estimated by me in C.R. Jan. 24, 1910, it supposes that
o > 5 X io5 for normally starting rays if the rays shall be able to emerge into infinity.

6i8

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 -1903.

Fig. 224. Nebulous ring, with the Earth for its centre, according to Jones.

luminous and is capable of ... ; •...';•::':;•:

absorbing and scattering solar . ••; ..-.':•; :':\-i;/;>^£i

light. When treating of the
formation of the tails of comets,
we come back to the same idea.
Possibly krypton, which seems
to cause the well known auro-
ral line in the auroral spec-
trum is thus emitted from the
sun, and that we may be
able in this manner to answer
a question put by RAM-
SAY(!): "Is there any process
which will tend to increase the
relative amount of krypton in
the upper regions of the atmo-
sphere?"

120. We now return
to the radiations emanating
from the sun. From my
experience obtained from
the experiments, I regard
it as very possible from a
physical point of view, that
a ring of radiant matter
has been formed round the
magnetic equator of the
sun, the dimensions of this
ring being greater than
those of the earth's orbit.
We must recollect that in
the case of the sun, it is
a question of corpuscular
rays of very great stiffness,
as the mathematical calcula
tions also have shown. I
assume that these corpuscu-
lar rays from the sun
partially consist of atoms
and molecules, and not
merely of electrons, thus
that the radiant matter in
thick layers is both slightly

(') RAMSAY: The Aurora Borealis. "•'

Essays Biographical and Chem-
ical p. 314. London 1908. Fig. 225. Space round the Earth into which the radiant matter from the Sun does not enter.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 619

Let us now see how we can explain the characteristics that have been observed in the zodiacal
light, by supposing that in the sun's equatorial plane there exists a flat ring of radiant streams of
matter, consisting principally of primary rays and streams of atoms from the sun, and perhaps also of
secondary rays emitted from cosmic dust moving in the same plane and which are irradiated by the
primary beams from the sun.

If these corpuscle-rays and streams of atoms either themselves emit luminous rays or scatter
the light of the sun, we will, as we shall soon find, be enabled more satisfactorily than ever to explain
the characteristics of the zodiacal light.

It will be at once observed that my idea of this flat ring about the sun has a certain resemblance
to what is called the meteoric theory, as it also presupposes that a ring of cosmic dust exists which
encircles the sun, more particularly in the plane of the solar equator.

The idea perhaps equally resembles the theory advanced by MAIRAN in 1731, that the zodiacal light
is reflected from the sun's atmosphere, stretched out into a flattened spheroid or lenticular shaped body
revolving with the sun; an idea which LAPLACE has for ever set at rest by demonstrating that the sun's
atmosphere "can extend no further than to the orbit of a planet whose periodical revolution is performed
in the same time as the sun's rotary motion about its axis, or in twenty-five days and a half; that is
only as far as 8/ao of Mercury's distance from the sun".

We shall, however, soon see that my theory has an equally great resemblance to an entirely
different view of these phenomena, namely, to the idea arrived at by JONES after discussing the results
of his excellent observations : "I offer now, as a last conclusion, the hypothesis of a nebulous ring with
he earth for its centre". In reality my theory combines the advantages of all earlier hypotheses, and
it succeeds in explaining phenomena which none have elucidated previously, for instance the phenomenon
of the counter-glow — Gegenschein — and the pulsations in the brightness and outline of zodiacal light.

From what we have learnt from our experiments we can foresee what will happen when our
nagnetic earth advances in the assumed ring of radiant matter that surrounds the sun.

The earth magnetism will cause there to be a cavity around the earth in which the corpuscles are,
;o to speak, swept away, a space around the earth from which a portion of the radiant matter has
disappeared.

This cavity round the earth is doubtless not circular in such a way as JONES supposes with his
lebulous ring hovering about the earth in the sun's equatorial plane, but the space has a somewhat
lifferent form which we can describe and note particulars of very closely, owing to our earlier expe-
dients as will be seen in the following.

Diagrams showing a section of JONES'S and my spaces respectively round the earth, spaces that
ire free from corpuscles, will be seen in figs. 224 and 225.

We shall now easily understand that we have here an explanation of "the brightness in the east
>efore sunrise", owing to the streams of corpuscules from the sun, when they approach the earth suffi-
•iently, becoming deflected in the same manner as the rays shown in the fig. 219, and as it is further
>lainly shown on the morning side of the picture No. 16, fig. 215, which is as seen taken from the
outh pole.

In like manner it makes it easy to explain naturally "the brightness which appears in the western
ky after sunset" by referring to numerous pictures with the ist sectional line, also called the ist line
>f precipitation, of the rays; this is in a manner a boundary-line along which the cathode rays begin to
ravel around the terrella in curves regulated by the stiffness of the rays and by the magnetic condition
>f the terrella. See particularly the same picture 16, fig. 215, on the evening side.

620 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

In transferring the results of the experiments to the earth, we must recollect our above-mentioned
supposition, that the rays are approaching the earth from the sun, forming a flat ring of radiant matter
travelling in the sun's magnetic equator.

If these corpuscle-rays either emit luminous rays, or the radiant matter scatters the solar light, the
brightness in the western sky will appear, because we see into the deep layers of radiant matter situ-
ated in the sun's magnetic equator, and the brightness will disappear at the boundary line where the
rays spread out to travel round the earth over and under the earth's magnetic equatorial plane as
mentioned in the preceding pages.

We may now in analogy with our experiments conclude that the rays round the earth, after
spreading on the first sectional line, will gather again to a second sectional line (the 2nd line of preci-
pitation), in which, however, the density of the rays will be much less than in the first sectional line-,
but nevertheless considerable.

In the course of our experiments we have seen that the concentration in this second sectional
line is greatest by far when the magnetic axis of the terrella stood perpendicular to the direction of the
rays from the cathode.

The position of this second sectional line has been somewhat varied, according to the terrella':.
magnetisation, but it is always approximately on the magnetic equator of the terrella, and originates and
is most powerful not far from the direction opposite to the cathode.

We shall closely point out below to what a high degree the results of these last terrella experi-
ments, transferred to the earth, serve to explain the hitherto known characteristics of the counter-gl<>
Gegenschein.

JONES, in his work which we have quoted, has mentioned this phenomenon, which he, however, at
first did not believe to be zodiacal light. It was not till after his return from his long journey that it
became clear to him that this counter-glow was a phenomenon of the zodiacal light, which was first
observed by HUMBOLDT in 1803 ; but he supposed the phenomenon to be only a reflection from the
western zodiacal light, then shining with exceeding brilliancy (See Astronomische Nachrichten No. 989!.

In No. 998 of the same journal is another paper on- this subject by BRORSEN of Serptenberg in
Germany, who calls this eastern evening light by the appropriate name of "Gegenschein", and informs
us that he had seen it regularly at that place during the two previous years. His paper concludes as
follows: "The Gegenschein is visible, not only at the vernal, but also at the autumnal equinox; at
the former time more distinctly. A faint trace of it becomes visible in January, from which time it
grows stronger till March, when, and in April and the early part of May, it is quite distinct and broad.

"A much smaller and fainter Gegenschein appears in September, October and November. I have
become convinced, by frequently repeated observations, that in both cases the brightest part of the
Gegenschein is directly opposite the place of the sun, so that a calculation of the greatest light frequently
coincides to a degree with the point of opposition to the sun.

"The observations proved that the vernal Gegenschein about the middle of April, joins the westerly
zodiacal light by a stripe or belt of light, which is at first very faint, but becomes by degrees more
luminous; the autumnal Gegenschein appears, in the first part of November, to be elongated along the
ecliptic by a faint zone of light as far as the western horizon, which zone of light is by degrees trans-
formed, by increasing luminosity and more distinct basis, into the well-known phenomenon of the western
zodiacal light."

We shall, before we go more into the theoretical comparisons with our terrella experiments,
further quote data respecting the counter-glow from a particularly important work by ARTHUR SEARLE -
"The Zodiacal Light, discussed by means of the Records of Harvard College Observatory".

TART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V.

621

In this paper we find a very interesting table of collected results from observations of Gegenschein
U various stations by BRORSEN, SCHMIDT, HEIS, EYLERT, BUSCH, GRONEMAN, BACKHOUSE, LEWIS, BARNARD,
ind at Harvard College.

TABLE CV1I.

Jan.

II

Feb.

Mar.

April

May

June

July

Aug.

Sept.

Oct.

Nov.

Dec.

No. Obs. . .

i

40

45

31

7

3

29

5'

17

4

Mean A ...

134

144

174

20.4

327

334

353

22

45

74

Mean Jl . .

4-3

- 4

— 2

+ i

— a

+ 4

o

0

— I

— a

Mean f> . . .

+ 4 +2

+ 2

+ 2

o

0

0

O

+ i

— 2

Ext. 1 . . . .

20 14

13

15

IO

ii

16

IO

Ext. /?.... 8 8

IO

I I

7

9

12

7

6

The first line gives the total number of observations.

The other five lines give the longitude, its excess over that of the point in opposition to the
,un, and the latitude, of the observed light, with its extent in longitude and latitude, so far as this can
>e estimated by means of the sketches or descriptions. These quantities are given only in entire
tegrees.

From northern stations, it appears from the table that Gegenschein has most frequently been seen
n October, but the number of observations in February and March is also relatively large. According to
•xperience at the Harvard College Observatory, the phenomenon to be observed is often difficult to
listinguish, in March, from a part of the luminous band crossing the ecliptic nearly at right angles on
he borders of LEO and VIRGO, while in October, as in the other autumn months, it is perceptible only
s a reinforcement or as an extension of the band from Aquila to the Pleiades.

During February and March the observed light has a position a few degrees preceding the point
n opposition to the sun, generally north of the ecliptic.

In the autumn of 1886 the general remarks made by BARNARD and those made at Harvard Obser-
•atory concur in describing Gegenschein as only a very elongated patch of light, instead of a round or
lliptical spot.

BRORSEN'S above-quoted observations may thus in the main be said to be confirmed by all subse-
[uent researches.

We shall now see that these results of observations of counter-glow (Gegenschein) in nature can be
xplained by the results of my terrella experiments.

Just about the time of the equinoxes the "second sectional line" of the corpuscle-rays round the
arth, should, in analogy with the experiments, be most strongly present and as it moreover will fall in
he earth's magnetic equatorial plane about 180 degrees from the direction to the sun, it will also fall
omewhat in the plane of the ecliptic or near the sun's equatorial plane.

The experiments referred to concerning the second sectional line, are those described on pages
,60 to 564. The vertical screen used in these experiments consisted principally of two plane
iortions which intersected one another at an angle of about 100° in a vertical line. When, therefore,
: is recorded that the second sectional line, with magnetising currents 8 and 28 amperes respectively,
ell on the screen when its hour-angles were 272° and 265°, it must be remembered that the plane part
if the screen nearest the terrella and, passing through the magnetic axis had then a length of about
92° and 185°.

Uirkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903. 79

622 BIRKK1.ANM). I UK NORWEGIAN Al'RORA POLARIS EXPEDITION, 1 QO2 -1903.

The commencement of the sectional line, where by far the most of the rays cross each other, would
then from the centre of the terrella he seen with lengths of 192° and 185' respectively. These angles
must however he calculated along the magnetic equator of the terrella.

If it he further remembered that all three sectional lines referred to, by stronger and stronger
magnetisation of the terrella, draw back somewhat, being pushed outwards almost parallelly with a quite
slight reduction in length, it will be evident that with so intense a magnetisation as to correspond with the
conditions on earth, the second sectional line would begin and be most strongly developed at a length
but a few degrees less than .180° reckoned on the magnetic equator.

Returning now to the earth, supposed to be travelling in the ring of radiant matter round the sun

At the equinoxes we shall see the places where the corpuscle rays are intersecting each other in
the "second line of precipitation" in a line with the ring of radiant matter in the sun's magnetic equator,
which ring must be assumed to continue also beyond the earth's orbit.

In this manner we shall be able to see through the radiant matter into a considerably thicker stra-
tum opposite the sun, as shown diagramatically in fig. 225, and more light will be diffused, by reason of
which Gegenschein may be imagined to be caused.

121. We now pass on to mention how the spectral analysis investigations which have been made
of these phenomena look in view of the theory advanced here.

The spectrum of the zodiacal light has been observed for man}1 years, but owing to its faintness
the observations are very difficult to make. Among the first observers were LIAIS('), YOGICL(-), PIA//I-
SMYTH l:ll, and WRIGHT | '). LIAIS at times suspected dark lines, but could not be certain of their exist-
ence. WRIOIIT detected the presence of the atmospheric band at }. 5780. Other observers had thought
the bright aurora line at /. 4571 a part of the zodiacal light spectrum, but the work of the last three of
the above-mentioned observers seems quite conclusively to show that this belongs to the aurora alone,
although it ma}7 at times appear superimposed upon the spectrum of the zodiacal light. This fre-
quently occurs if the aurorse are at all common at the place of observation. HAI.L(:'), observatory in
Jamaica, found the spectrum continuous even when using a slit sufficiently narrow to show absorption
lines in the spectrum of daylight. In other respects, all observers agree in finding the spectrum conti-
nuous with an intensity curve quite similar to that of daylight.

The fact that the intensity curve of this spectrum closely resembles that of the sun, and the exis-
tence of from 15 to 20 per cent of polari/ed light, as shown by the careful observations of WRIGHT!'),
are in accordance with the meteoric theory ("). The above-mentioned observations were all visual.

The first successful attempt to photograph the spectrum of the zodiacal light is described by PATH,
Lick Observatory Bulletin No. 165, from which the above-cited resume is taken. The results are
summed up as follows.

"Upon developing the plate a spectrum was obtained which resembles the solar spectrum exactly, in
so far as can be judged from so small an object.

"Two absorption-lines could be seen with certainty. A comparison of the plate with one of the sky
spectrum taken with the same slit-width showed these lines to be C and the blend of // and A of the
solar spectrum.

I1) Comptes Rcmlus 74, 262, 1872.

l-l Astl'nn. Nach. 79, 327, 1872.

I3) Mont. Not. 32, 277, 1872.

(Ji Amor. Journ. of Sci. Srr. 3 8. 39, 187).

I •"'! Observatory 13, 77, 1890; Mon. YWatlirr Kcv. 34, 126, 1906.

ir'i Amcr. Jonrn. of Sci., Scr. 3, 7, 451, 187;.

('I O. SEAKI.E, Mem. Amcr. Acnd. 11, 135, 1888.

„ SKK'.ICFK, Munch. Bcr., 31, 265, 1901.

„ (iEF.i.MUYiiK.N, Bulletin Astron., 19, .) )6, 1902.

PART. II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 623

"These are the only two lines shown in the sky comparison plate within the spectrum obtained on
the zodiacal light. Thus in so far as spectra of such low dispersion and resolving power can be trusted,
we would seem to have good evidence to support the claim that the zodiacal light is reflected sunlight".

After these results we must ask: Is it conceivable that radiant matter can reflect sunlight as we
have supposed in our theory of the zodiacal light?

Although analogies may often be misleading, there will undoubtedly be a certain value in the
recollection that the atmosphere, even in quite clear weather, diffuses the daylight to so great an extent
that even the most powerful stars are invisible. The light is sent back either from the air-molecules
themselves, or from microscopic dust-particles that are found in the atmosphere, as by the blue of the sky.

Physical investigations of the power of electrically luminous gases to absorb and diffuse sunlight,
have not, as far as I am aware, been made on any large scale; but during the last few years some
very interesting results have been obtained, which will be discussed in these pages. With regard to
direct experimental research into the properties of radiant matter in the above respects, I do not think
anything has been ascertained.

In the meanwhile, I have made some observations at Kaafjord in Finmarken, which will possibly
afford us some guidance in the question.

1 have in broad daylight and at times in sunshine been able to observe rapidly-changing "clouds"
formed like draperies with radiant structure appearing at that time of the evening in which, in winter,
corresponding draperies of aurora are frequently seen.

I have thought that these must be, not real clouds, but auroral rays scattering the sunlight and
therefore appearing like clouds. At all events it seems to me little likely that the condensation of
moisture could take place so rapidly in the highest regions of the atmosphere, and a moment afterwards
revert to vapour again (see page 450).

I have found in literature certain investigations by R. LADENBURG and R. W. WOOD, of the optical
conditions in electrically luminous gases and in vapour, which are of great importance to the questions
we here touch upon. LADENBURG, in a treatise entitled "Ueber Absorption und Magnetorotation in
leuchtendem Wasserstoff "O), demonstrates that the number of absorbent "dispersion-electrons" is pro-
portional to the amplitude of the transfluent current. Now the intensity of the light is also proportional to that
ot the current, and the number of ions at constant pressure is proportional to the strength of the current.
All this should confirm the hypothesis that the bearer of the spectral hydrogen-series is the positive atomion.

WOOD, after a number of interesting investigations of "Die vollstandige Balmersche Serie im Spektrum
des Natriums"(-),"Die selective Reflexion monochromatischcn Lichtes an Quecksilberdampf"(3), and "TheUltra-
violet Absorption, Fluorescence and Magnetic Rotation of Sodium Vapour"(4), is of opinion that the Balmer lines
and the accompanying spectra are produced by atoms that have lost one, two, three, four, and so on, electrons.

There is now certainly very good reason for supposing that in the radiant matter which we assume
to have been radiated from the sun, there is comparatively a very large number of dispersion-electrons
that can take up and be in resonance with light-waves from the sun, and that possibly here too, this
number of dispersion-electrons is proportional to the enormous electric current-intensity that emanates from
the sun in (lie. manner here assumed.

It will perhaps after this no longer be considered improbable that the mighty strata of radiant
matter we have imagined we could see into when we observe zodiacal light, are capable of diffusing suffi-
cient sunlight to occasion this slight brightness in the sky. Subsequent spectroscopic investigations may
possibly prove that the zodiacal light also contains a weak light of its own, which some observers have
thought to show, and thus does not merely reflect sunlight.

(') Physikalische Zeitschrift. 10 Jahrgang, 1909; p. 497.

(-> . „ p. 89.

I3' . . „ p. 4»5.

I4' ., . „ p. 913-

624 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

It would be natural here, under the theory of the zodiacal light, to lay great weight upon undoubtec
electric evaporation of the sun's surface, which must be assumed to accompany the emission of cathodt
rays in accordance with our experience of electric discharges from a cathode in high vacuum.

In the following articles on comets' tails and Saturn's ring, due consideration has been paid tc
these conditions. Experiments have shown that considerable quantities of matter are in this way flum
out into the plane of the equator. It can be imagined that these grains of dust, moving under the
influence of gravitation and electromagnetic forces, become massed together by collision into greater am
greater globules.

This brings us to the assumption of a dust-ring round the sun, undergoing constant renewal fron
the central body ; and we thus come nearer to the hypothesis most current at the present time, namelv
the so-called meteoric theory.

That the spectrum of the zodiacal light suggests reflected sunlight can then also be explained b\
the reflection of the light from these tiny particles originally produced by the radiant matter.

.ertakci;

122. Appendix. Since the above was printed, I, together with Mr. KROGNESS, have undertaker,
a journey to Egypt and the Soudan, for the purpose of beginning to make personal observations of the
zodiacal light.

Of the expenses of this expedition one tenth was borne by the University, one tenth by my friend
Mr. SCHIBSTED, and eight tenths by myself.

For the time being, our object was to find out whether the pulsations in the light discovered by
JONES were accompanied by simultaneous magnetic pulsations.

During two months, March to May, 1911, observations and attempts to photograph the ligh
were carried on at Assouan by Mr. KROGNESS, and at Omdurman, near Khartoum, by myself.

As the then much discussed question of the simultaneity of certain abruptly-beginning magnetic
disturbances seemed likely to be also of importance in connection with these observations, I publishc
in "Nature" for March 16, 1911, (No. 2159, p. 79), a letter requesting other observatories, especially
near the equator, to take "quick-run" registrations at the same hours at which we did so.

At Assouan the instruments were set up in the depths of an ancient Egyptian tomb, in which the
temperature was fairly constant. Thanks mainly to Mr. KEELING, the superintendent of the Khedivial
Observatory at Helouan, we enjoyed all the facilities for our work that we could desire.

Our observations of the zodiacal light were made every evening and night in favorable weather,
from camps out in the desert west of Assouan and south of Omdurman, where the light from the towns
in no way hampered the observations. It was a strange occpuation these observations every dark night
in the Soudanese Desert, accompanied only by a chance Abyssinian servant.

The time however was not favorable, according to the general opinion of several inhabitants. The
zodiacal light could often be seen much brighter there than we saw it.

As a rule the desert wind raised fine sandy dust, which caused the air to become thick, especially
near the horizon. Venus, moreover, at that time was very bright, and was situated near, and sometimes
in the very middle of, the cone of zodiacal light, where its presence was highly embarrassing. It was
impossible, for instance, to be sure of the pulsations in the zodiacal light, although we thought now and
then that we saw slight, rather sudden changes.

Only on the 3oth April, the last day I was in Khartoum, just as I was about to leave it, the light
was unusually strong and right up in the zenith, and I was almost sure that I could see decided changes.

I had no opportunity of noting the exact times of these changes when I unpacked my photographic
apparatus; but during that last hour at the railway-station before leaving, I succeeded in getting the best
photographs of the light that we took throughout the expedition.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 625

It has subsequently appeared, after all the magnetic curves have been developed, that an unusual
magnetic calm has happened to prevail during all the times at which we obtained serviceable observations
of the light; there were hardly any perceptible magnetic changes at those times. Only on the 3oth
April did it appear that there had been a magnetic storm during the hours in which the observations of
the zodiacal light were made on my departure from Khartoum.

Our attempts to obtain good photographs of the zodiacal light were at first without result. We
tried altogether five or six combinations of lenses, some of the lenses being very expensive. At last
\v<: succeeded, by telegraphic order, in obtaining from Cairo and Dresden some simple cinematograph
lenses, which gave fairly satisfactory results.

We then took, both at Omdurman and Assouan, at exactly the same hours, two dozen plates each
evening during the last few days of our stay.

The times were photographically recorded from an electrically illuminated watch upon each plate
at the beginning and end of each exposure.

There is at present nothing more to say about our results here, but it was at any rate ascertained
that it was possible to obtain good photographs with our simple cinematograph lenses, by employing
HaufTs "Ultra-Rapid" plates, which ought by preference to be illuminated in before the exposure accord-
ing to Wood's method (]).

It is my intention as soon as possible to continue these investigations, perhaps with two stations,
in the Andes in South America. By photographing the zodiacal light simultaneously from two such
stations, it might be possible to obtain a parallax determination. According to HUMBOLDT, the conditions
there should be especially favorable, for in his "Cosmos", Vol. I, he remarks: "I have seen it shine with
an intensity of light equal to the Milky Way in Sagittarius". Judging from our photographs, this
should answer to an intensity of the zodiacal light from 5 to 10 times greater than that which we observed
in Egypt and Soudan.

As we thus obtained a negative result with regard to the pulsations of the zodiacal light by our
observations, we determined instead to study the magnetic curves at Greenwich for the period during
which JONES had carried on his observations. This observatory is presumably the only one in which, as
early as 1853, continuous magnetic registerings were made.

On going through JONES' observations, we find a considerable number of days on which he seems
to have noticed pulsations of light. On two occasions he is absolutely convinced of their existence,
namely, on the 3oth January, and the 2;th March, 1854. On tne first of these we read, in italics :
"There can be no doubt that there are pulsations in the zodiacal light"; on the second he remarks:
"It certainly does pulsate".

The curves at Greenwich are drawn by instruments with great sensitiveness and comparatively long
time-periods, so that possible magnetic pulsations would be more easily discovered than by the ordinary
daily magnetograms. But the curves have been faint and have been gone over with ink, and have thus
lost something of their character.

There are here reproduced four plates with magnetograms from Greenwich, first, two answering to
the above-mentioned dates, the 3oth January and the 2yth March, 1854, belonging to JONES, next, two
answering to the 2jth February and 25th April of the same year, when in JONES' observations too,
distinct pulsations are recorded. This comprises the most certain pulsations observed in the zodiacal light.

We have further chosen 5 days with light-pulsations, for which we have copies of the curves at
Greenwich, which distinctly show magnetic pulsations simultaneously with those observed in the zodia-
cal light.

(') Phys. Zeit. 1908, p. 355.

626

BIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

PART II. POLAR .MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V.

627

6'j8 HIKKKLA.ND. TI1K NORWEGIAN AURORA 1'OLAKIS F.XI'EI HI 'ION, 1 9<32 1903.

It slunild be stated, however, that on several occasions when JONKS believes he has seen pulsations
no corresponding magnetic pulsations were traceable at Greenwich. Whether the reason of this is that
the original photographic curves have been much obliterated, can scarcely be determined.

On the Plates, where Gottingcn mean solar time is employed, the time is marked when JONES has
observed pulsations in the xodiacal light (Z. L. P.).

It will be seen that this period — that for the 271)1 March — falls at the end of a series of exceedingly
distinct magnetic pulsations, which are in quick-run magnetograms usually called Escherihagen
oscillations. These are especially distinct in //, but thev would also certainly have been distinct in D
in the original curve. 1 lere, however, they have been fainter, and the curve has been drawn principally
as a mean line, whereby these oscillations have been eliminated.

On the 30th January too, the pulsations occur at the end of a series of particularly characteristic
magnetic pulsations. The latter are especially distinct in the period immediately preceding Jones' observa-
tions, but also undoubtedly seem to continue, although less powerful, during that period. The curves
here, however, have been somewhat obliterated and are difficult to follow in detail.

In the magnetic curves on the other two Plates, there are rapid oscillations of comparatively long
duration. These, however, are not such typical elementary waves as the preceding ones.

We finally append JONES' notes from the first two days mentioned, a, />, and d here indicate the
special boundaries of the zodiacal light, which are given in the figures in his work.

JANL'ARV 3oth 1854: KVK.MM,. Lat. 26° jo' N. Lon. 127° 42' 1C.

Sun set 51' 38' om.

Stronger Light 7'' 50"'. <Vc: Diil'nse, (7)11 =;om.
Sim's Lon. 310° 20'.

There can lie no doubt thai there arc pulsations in the Zoihacal Light. I noticed them last evening
(the sky being very clear); but, it being Sunday, made no particular record of them. They were,
however, distinctly to be seen; and when 1 called the attention of one of the quartermasters to them, he
very easily made them out. His language about the Light was: "Now it seems to be dying away";
"now it is brightening again", «.Vc. All this applied, however, only to the Stronger Light: it occurred
between 7'' 30™ and 8 o'clock. This evening 1 was on the careful lookout for them, and, with watch
in hand, made record of the changes and their times. Clouds interfered till 7'' 50'", when, this part of
the sky having cleared up, I got observations. The pulsations were very distinct; observable, however,
only in the Stronger Light. This, at /h 50™, had its boundaries as in the line /; (see chart), and was
very bright: 7'' 52'" it had sunk to the boundaries marked a and was very dim: 7" 54'" had risen to b

again, and was bright: 7'' 55'" at a, and very dim: /h 56™ at b, and brigth: 7'' 57'" at a and very
dim: 7'' 58' '.>'" at h, and bright: 7'' 59' V11 still at b, and bright: it seemed now to be permanent at b;
but clouds soon after spread over the sky, ami shut out everything from sight.

These pulsations, in order to be seen, seem to require that the ecliptic should be at a high angle
with the horixon ; at which time the Stronger Light is very brilliant.

MARCH 27th 1854: LVKNING. Lat. 35° 26' N.: Lon. 139° 42' 1C.

Sun set 6'' 12' ;>m-

( -jh 30m ^

Stronger Light | gh 3Qm j Dilluse at 7!' 30™, &c.

Sky remarkably clear. The following are my notes: — 7'' 15'" a whiteness running up with the
Zodiacal Light boundaries as far as the Pleiades, but its limits are not distinct: 7'' 24'", the light more
decided, but its boundaries not reliable : 7b 30'", got boundaries of both Diffuse and Stronger Light— the
latter, then, strong up to /;, and gradually tapering, dimming off to c.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V.

629

At 7 35, at <?, and dim.

7 38, do. do.

7 39, at /;, and bright.

7 43, do. do.

7 44, at a, and certainly dimmed.

7 45, at b, and bright.

7 47, at a, and dim.

7 48.1, do. do.

7 49, brightening.

7 50, at b, and bright.

7 51, at 6, and quite bright.

7 52], dimming.

7 52^, at rt, and dim.

7 53-i> brightening.

/;. in.
At 7 54.jr, at b, and bright.

7 55j> at ^i ar|d quite bright.

7 57?> at fl> ar|d quite dim, as if dying away.

7 58} do.

do.

do.

7 58! , brightening.

7 59.}, at A, and bright.

8 o, do. and quite bright.

8 3, brighter than at any time yet, and has clear-
ly ascended to the Milky Way by lines d d.
8 \\, dimmed and sunk to b.
8 7, brightening.
8 8, very bright, and at dd.

8 15, still as last, and seems to be permanent now.

9 30, boundaries to x.

I think I can know when it is going to be permanent, by the upper portion of the Light brightening more
than at any time previously in the evening, and the strong brightness ascending higher. The first
appearance of the Zodiacal Light seems to be a white light — ;'. r. when the twilight has not quite gone;
afterwards it changes to a warm yellowish light. The reverse of this happens in the morning. The
Diffuse Light is now very dim; in the morning it is very strong, for it.

This evening was remarkably fine for observations, and in my notes is the remark: "It certainly
does pulsate".

123. Only one abruptly-beginning magnetic disturbance occurred in the period when we were ob-
serving with "quick-run" registrations in Assouan, namely, the gth April.

I have, unfortunately, not received any intimation of quick-run registrations having been taken
except in Samoa, where Prof. Dr. ANGENHEISTER commenced the registrations on April 10, /'. e. one
day too late. Mr. TITTMA.NN, superintendent of the U. S. Coast and Geodetic Survey, has been good
enough to send me some copies of slow-run registerings for April 9 from Cheltenham, Porto Rico,
Tucson, Sitka and Honolulu. Of these, the curves from Honolulu (158° W) and Porto Rico (65° W)
are of special interest, because these stations, together with Assouan (33° E) form a particularly happy
distribution of stations about the Earth.

Figure 228 shows that on this day an equatorial perturbation occurred, the character of which is
very similar at the three stations. The times of commencement in H are as follows:

Honolulu Porto Rico Assouan

loh 2o'», 7 p. m. Gr. M. T. 20>», 8 20'" 44*

The changes in D at the same time were very small, as might be expected would be the case
with this kind of perturbation.

The first notices of time are given in a letter from the Coast and Geodetic Survey, - - the last
value is found by the "quick-run" magnetograms from Assouan as shown by the magnetogram.

The last time-determination is given in seconds, because of the greater accuracy that can be
reckoned upon in "quick-run" registerings.

The time-marks here, which refer to the central point for the obliterated parts, are certainly cor-
rect to one second, but a greater uncertainty arises when it is a question of determining when the

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 —1903. 80

630

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

perturbation shall be said to have commenced. I consider we may be safe when we estimate the pos.
sible error at + 4 seconds. But the values of the slow-run magnetogram lie within this mar "in nt
Honolulu and Porto Rico, where, however, the readings are naturally not so trustworthy as those of the
quick-run magnetograms from Assouan.

The curves from Sitka, Tucson, and Cheltenham show that the perturbations in those places have
had a somewhat different character from those at the three first-named stations, for it appears as though
a magnetic polar storm interferes. The curves for D and V show the same thing.

The times we have been given from the Coast and Geodetic Survey for these stations are:
for Sitka 10** 21"', Tucson io'i 20"', and Cheltenham io'» 2i»», 9, and these refer to the "larger displace-
ment" in //. This occurs shortly after the first abrupt beginning, and the times are, as may be seen
with the exception of Tucson, slightly greater than the others.

\

Honolulu

furtoSico

Assouan.

slow Tim.

Silku

•v

Tucsu

Cltcltcii-
lunn

Ci-.M.T.

1Aju: M

Fig. 228.

As regards Tucson, we notice that the first time-mark is considerably smaller than the later ones;
for this reason, I think, this value should perhaps be taken with some reservation.

In Trondhjem, under the direction of Professor S^LAND, "quick-run" registerings were made simul-
taneously with our observations at Assouan, though not between 10 and midnight, Greenwich mean
time. As the above perturbation occurred just in this period, we unfortunately have only "slow-run"
registerings from this station.

At this station the polar character of the storm is distinctly apparent, as might be expected from
so high a latitude.

On the occasion of the magnetic storm we are here studying, the similar sudden changes occurred
around the terrestrial equator simultaneously, within the limits of error in the observations.

When several observations of such magnetic storms around the equator obtained by quick-run
registerings, are available, as I hope may soon be the case, this important question of simultaneity v
be finally determined.

It may be of interest in connection with this to call to mind that in 1900, quick-run registerings
were taken simultaneously in Potsdam and at my observatory at Haldde, near Bossekop. In my \
"Expedition Norv6gienne de 1899 - 1900 pour 1'etude des aurores boreales" (Christiania, 1901), photo

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 631

graphs of these registerings are given, which show that corresponding small sudden alterations in 1)
were simultaneous within three seconds in Potsdam and Bossekop.

According to my theories of magnetic storms, it might be expected that sudden similar magnetic
,-lianges which occur in different parts of the earth arise rather simultaneously. When the sun suddenly
nds forth a strong pencil of cathode rays towards the earth, this pencil, owing to earth-magnetism, will
ae broken up in such a way as to form different partial systems of magnetic impulses -- polar and
equatorial. The various groups of rays have to travel different way-lengths in space before reaching
:hrir nearest to the earth, and may arrive at very different regions of the earth for the different groups.
But the difference in time between the various impulses affecting any particular locality on the earth
ran scarcely be more than a couple of seconds, while the difference in the intensity of the effects can
je very considerable. We know of corresponding phenomena in the case of Aurora, which will be
.reated later on.

COMETS' TAILS.

124. The theory here set forth, of the emanation of electrical corpuscle-rays from the sun, might
be thought to present a new point of departure in the study of the physical nature of comets, and more
(.•specially of comets' tails.

It seems evident from their spectrum that comets consist of an accumulation of cosmic dust, with
various carbonaceous substances, concentrated about one or more nuclei, which are surrounded by a
highly rarefied vaporous envelope in which possibly carbonaceous gases are comparatively strongly
represented.

As regards more especially the particular phenomenon of the comet's tail, it has been found that
it docs not make its appearance until the comet aproaches the sun, and is most highly developed a little
vvhile after passing the perihelion.

If, now, this vaporous envelope surrounding the more solid part of the nucleus, be ex-
losed to the radiation of a multitude of corpuscle-rays from the sun, it could easily be imagined
.hat in their passage through the exceedingly rarefied gas, these rays would change their nature. The
simplest assumption one is inclined to make is that some of the corpuscles that pass through the coma
lave acquired an appendix of gaseous atoms or molecules, which have thereby become luminous. As
.hese rays may be supposed to continue their way in more or less the same direction as before, but
A-ith a different velocity and mass, this would be a comparatively simple explanation of the luminous tail
if the comet, which is almost always directed away from the sun.

AKRHKNIUS has also, as we know, maintained a similar theory, only that instead of electric corpuscle-
ays of the kind here considered, he imagines rays of electrically-charged atoms, moving under the
nfluence of light-pressure.

It is possible, however, that there are also other, just as natural, ways of looking at the matter.
It might be imagined that after great heating by direct insolation, the comet is charged negatively by
-athode-rays from the sun, and that the charging reaches so high a potential that the comet dis-
:harges itself electrically, so to speak in the direction of its own shadow. These discharges may also
)e imagined to be due to some extent to an emission of secondary rays from the cosmic dust of the comet.

I have been led to this thought by experimental analogies which will be described farther on.
Answering to the idea that a comet is an accumulation of carbonaceous cosmic dust almost without atmo-
sphere, I have carried out experiments in which the cathode in a vacuum-tube consisted of a carbonaceous
naterial. The most recent investigations of the comet-spectrum seem to indicate that the radiation from
i comet may be compared to that from a cathode in a Crookes' tube (DESLANDRES, FOWLER).

I'.IKKI I. AM). 1111 MimVI-.CIAN Al'KOKA l'(jl.AKIS I XI'F.I HI I< IN , IQO2— 1903.

TABI.K C'Ylll.

i 803

IV. Passage

if IVrili

clion Ni

V. 0

,862 III. Pas

sage ot

Periheli

>n Aug. 22

Nov. Nov.

Nov. ' Nov.

Nov.

Nov.

Nov.

Dec.

Aug.

Aug. Aug.

Aug.

Aug.

Aug. Aug.

Sept.

12 13

i J [5

i 7

22

25

3

l6

l8 21

24

27

29 31

12

t 0.700 o, 7 i i

0,714 0,71 7

0,721

0,725

0.755

0,778

O,968

0,965 0,963

0,963

0,967

0,970 0,975

1,028

a 18 ,80 .|80,|7

48 ,23 48' ,08

4«",or

49 ,27

50°,84

.0 ,-
56 ,76

34°, 10

3°°,55 -6°. 17

22°,5,

1 9", 92

1 9 '. 1 9 ' 9 .36

32", 78

;>' o ,79 2 '.99

5.i<> 7 .36

i i ,03

21 ,79

27°, 42

4° ,53

39 ,59

36!',77 32°, 99

29 ,'7

25^,05

22°,37 '9°, 78

4°. 45

,r 0,010 0,037

0,06^ 0,09-

o, l 40

0,280

0,358

o,55°

0,6 1 7

0,578 0,524

0,469

0,409

0,369 0,330

0,080

/ 0,053 0,042

0,050 0,095

0,08 i

o, 148

0,028

0,03 |

0,01 o

0,062 0,069

0,1 14

o, 1 66

0,134 0,054

0,021

1 86 1

II. Pas^a^c of Perihelion June 1 1

1800 III. Passage o

Perihelion June 16

June lulv

July July

Julv

July

July

July

June

June lime

July

lulv

lulv J,,lv

Julv

30 2

4 6

8

1 O

I 2

'4

24

25 28

2

6

8 n

12

/• 0,897 0,912

0.929 0,946

0.965

0,98)

I ,005

1,026

o,147

0,470 0,543

0,647

0.751

0,803 0,880

0,006

« 1,15 o°,8o

9°.97 13°,. 2

16 ,23

19', 27

22", 2 (

25 ,ro

•|6 ,79

O o

42 ,30 31 ,87

23 .94

21 .53

21°, 88 23°, 4 7

24°,25

,./ 7",i8 io=,27

1 3°, 26 J o°, 1 3

i8°,8g

21 ,56

2| ', 1 2

26°,57

42°,76

38' 50 27°,68

l6°,97

9,i7

6°,oi ' i°,98

o°,78

,r o, 112 o, 1 63

0.2 1 3 0,203

0,3 1 2

0,302

0.4 1 I

0,459

0,304

0,202 0,252

0,189

0, 1 2O

0,084 0,030

0,012

/ 0,277 0,470

0,445 "o°5

0,369

0,375

0.2Q7

0,1 86

0,262

O,l89 0,164

0,063

0,042 0,007

0,004

'85

8 V.

'assage

of Perilu

lion Sept. 30

Sept. Sept.

Sept. Sept.

Sept

Sept

Sept.

Oct.

Oct.

Oct. Oct.

Oct.

Oct.

Oct. Oct.

10 19

22 24

26

28

30

2

4

6 8

1 1

'4

16 i9

r 0,058 0,620

0,606 0,594

0,580

".580

0.579

0,580

0,586

0,594 0,606

0.629

0,658

0,680 0,716

« 88n,23 70°,34

69°, 92 03 ,44;

56°, 92

5° ,53

44°.3«

3»".74

33°,89

30", 22 28 ,08

0°

28 ,02

3'°,2i

34°, 50 40°, 17

.•? o l °, l 6 62", 56

61 ,80 60 ,06

57 .20

53°,63

4 9°. 39

44", 73

39",84

34", 87 29' ,94

22 ,77

I6°,05

i i ",87 6°,o8

.'' 0,576 0,558

0,534 °.5'5

0.492

0,467

0,439

0.408

o,375

0.340 0,302

0,243

0,182

o, i 40 0,076

/ o, i 85 o, i 77

o, i 72 o, 166

o, l 40

0,26 i

0,323

o,37i

o,355

0-471 o.472

0.543

0,319

o, 1 02 0,068

1857 V. Pass, n

' Penh. Sept. 30

'85.

i III.

^assage

ot Perihelion Sept. i

1811 I.

Pass of Perih. Sept, 12

Sept. Sept.

Sept. Sept.

June

Aug.

Aug.

Aug.

Aug.

Aug. Aug.

Aug.

June

Oct. Jan. i

12 15

,7

2O

3

20

23

25

26 28

30

I O

15 "812

/' 0,694 0,658

0,036 0,503

1,566

0,838

0.470

0,4 l o

0,374

0.358 ' 0,331

0.313

1,8,5

1,173 2

005

" (8 ,59 55 ', i 6

73°'74 89°.77

1O5 ,21

109 ,68

84°,49

73';.96

65°, 69

59°,95 48°, 43

34°, 63

1 I I ",62

67°,86 I250,3o

,.->' 58^,82 00°, 14

Oon,22 56°, 64

290,83

•I6", 35

59°.37

o

5 i > ' '-

52°,55

49°, 1.5 40°. 07

28°,3°

• 22C,52

73°, '6 3

2°, 10

.'.' 0,591 0,571

0,552 0,495

o,779

0,606

0,405

o,344

0,297

0,271 ' 0,213

0,148

0.695

i , 1 23 i

066

/ 0,013 0,029

0,058 0,008

0,004

, 0,0 1 i

0.035

0,117

o, i 70

o, 174 o, 18 1

0,203

0,6 --0,75

,847

I. 1 'assa^e of

Perihelion Man

h 30

1618 III. P

assage of Perihelion Nov. 8

March March

March March

March

March

March

March

Nov.

Dec. Dec.

Dec.

Dec.

Dec Dec.

Jan.

5 8

o i o

15

16

1 7

18

29

i 9

17

22

24 29

7

/' 0,900 0,823

o.797 0,770

0,629

0,599

0,569

o,537

0,669

0,708 0,864

i. 01 7

i.iii

1,148 1.240

1,400

" 57 ,9( 58 ,48

58 ,55 5^ >6~

58^,60

58°,39

58°, 1 8

57°, 79

|9",88

2i°,3° 25°, 3 1

20', 86

2 7°,. 7

27°, 16 27°,07

27°,o8

rf |i°,84 .,,°,5o

1 1 ',38 | i ,24

|0°,28

O

40 ,01

39°, 7 i

39 ,36

3°,28

5°, 12 io",o8

i.r,3°

16 ,07

i6°,67 17°,97

I9°,8i

,'• o,Oo l 0,545

0,527 0,508

o, 107

0,385

0.363

0,341

0,038

0,003 0,160

0,252

0,308

0.329 0.382

o,47(

/ 0,00 1 0,008

0,01 i 0.013

0,028

0,054

0,060

0,064

0.28 —

0,205 0,43

o,37

0,072

0.3 • 5 °,45

0,125

o.35

i 769.

Passage

of Perihelion Oct. 7

Airj;. Aim;.

Aug. Aug.

Sept.

Sept.

Sept.

Sept.

Sept.

Sept. Oct.

Nov.

Nov.

Nov. Nov

Nov.

9 24

27 3°

2

3

1

5

7

9 25

i

8

15 !7

31

i' i ,554 i ,200

i , i 98 1,1 3.-,

1,008

i ,046

1 ,023

i ,00 1

0,955

0,908 0,655

0.835

,
r ,00 1

M55 '.'98

,,280

•i 4 [",98 30 ,8 i

28 ,42 29°, 4 2

24^,63

24°,20

o
23 ,59

23!',oo

22°,36

2^,31 io8°,32

iof,?,6

i oo°,56

i I2",35 H3°,3i

n5°,4°

ft 5'- 57 3 '° 1

2C,3,8 ic,64

o ,8 i

o°,5'

O ',2 1

- o", 1 2

- o",82

- i':,59 43°, 03

42C,93

42°, 52

(2°,o6 4i°,93

4i°,68

.'• o, i 5 i 0,067

0,050 0,032

°,° ' 5

0,009

O|OO.]

- O,OO2

— 0,0 i i

— 0,025 o, (47

0.569

0,676

0,774 °,8o°

0,851

/ o, i 99 0,06 i

0,225 0,335

0,480

0,52 |

o,533

0,621

0.618

0,566 0,070

0.270

o, i 07

0,063 O, IO2

o, I 14

PART II. POLAR MAGNETIC PHENOMENA AND TKRRKLLA EXPERIMENTS. CHAP. V.

633

In this connection it would be natural first to find out whether the length of a comet's tail has any
special relation to the distance of the comet from the plane of the sun's equator, since we have seen,
in treating of the zodiacal light, that it must be assumed that there is a ring of radiant matter round the
sun in that plane.

Table CVIII gives the results of a series of calculations that have been made in order to
make this matter clear. Here fi is the comet's heliocentric latitude, x its distance from the plane of the

J* I* 4G it IJO. «

Fig. 229.

sun's equator, r its distance from the sun, / the length of its tail, and a the angle between the radii
vcrtores of the comet and the earth, r, x, and / are measured in radii of the earth's orbit, / being only
approximate, as the tail is imagined to extend radially out from the sun, which in this connection is
sufficiently accurate.

The orbit-elements employed in the calculations are taken from PH. CARL'S "Repertorium der Cometen
Astronomic".

The angle between the plane of the sun's equator and the ecliptic is put at 7°, in accordance with
Arrhenius' "Lehrbuch der cosmischen Physik " (p. 153); and the angle between the line of intersection
of these two planes, and the line of equinox is put at 70°, also in accordance with the last-named authority.

634 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

It is impossible, however, to discover from the above Table any distinct increase in the length of
the tail when the comet is in the vicinity of the plane of the sun's equator. The greatest length of tail
is always found after the passage of the perihelion, and this indicates that a prominent part is played by
evaporation of the constituents of the nucleus, brought about by the radiant heat of the sun.

It would appear, however, from the graphic representation (fig. 229) of the variation with time in
the length of the tail, that it is not the passage of the perihelion alone that is decisive. The passage
of the perihelion is marked P, the time when /? 0 is marked Z?j or Bz, answering respectively to the
first and second intersections with the plane of the equator. Finally we have the point of time, A, at
which the angle « has its minimum, in those cases in which this point falls within the period of time
under consideration.

It may be remarked as a general characteristic, that the curves about the maximum of length of
tail have very steeply ascending and descending branches. Further, this maximum sometimes occurs a
comparatively short time after the passage of the perihelion - e. g. the comet 1862 III — and sometimes a
comparatively long time after — e. g. the comet 1861 II. On the whole, the length of this interval varies
considerably, and there does not appear to be any simple connection; the impression is rather, that the
great development in the length of the tail about the maximum takes place at the time when the comet
is passing certain especially favorable strata or zones. This is especially marked, for instance, in the
comet 1862 III.

There are two other circumstances in particular to be considered here, namely, whether the light
of the moon can obliterate the faint light of the comet's tail, and whether, during the period under con-
sideration, the tail of the comet has moved much farther from, or much nearer to, the earth.

In only the first of the cases considered is it noted that the light of the moon has interfered, and
this is shown in the curve.

With regard to the second of the above-mentioned circumstances, it is easy to estimate from the
angles a and r whether the distance from the tail of the comet varies so greatly as to have any signi-
ficance in judging of the light. In no case does it appear to exert any real influence during the period
about the various maxima.

On closer inspection it appears that the great development of the tail occurs most frequently at a
certain distance from the sun's equator, answering to values of ft of between 15° and 30°.

In this connection, one recalls how the sun-spots also occur most frequently in about 20° helio-
centric latitude.

The comet 1618 III exhibits a peculiar circumstance, the curve for the length of its tail having a
distinct intermediate minimum. This might be due to the comet's having passed through two layi ;
pencils of rays from the sun, one immediately after the other; but it is perhaps just as likely that the
peculiar condition might be due to internal causes in the comet, or to the disturbing influence of moon-
light, or to unfavorable atmospheric conditions.

It would be natural, therefore, to compare the above-mentioned layers that were favorable to the
development of comet's tails with the pencils of the strongest and magnetically stiffest corpuscle-rays
which we imagine to emanate from the region surrounding the sun-spots, and which, when they sweep
past our earth, produce powerful magnetic disturbances. It may be that it is these very rays, with their
abundance of energy, that can charge the comet mass to a high negative tension, and thus occa
sion the secondary electric discharge from the comet into space.

One circumstance that speaks strongly in favour of a hypothesis such as this, is the greater de-
velopment thought to have been found 'in years of sun-spot maxima than in years of sun-spot minima.
This has been demonstrated, for instance, in Encke's comet, by BERBERICH and BOSLER, the latter having
given an exceedingly interesting graphic representation of this condition, which is reproduced here.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELI.A EXPERIMENTS. CHAP. V.

635

The agreement, as will be seen, is so striking that it seems to leave little room for doubt that we here
have phenomena that must be intimately connected with one another.

For the purpose of seeing and studying how a substance containing carbon is discharged as a
cathode in a vacuum-tube, I have made, as already mentioned, numerous experiments with cathodes of
ordinary coal, coke, graphite, and pice'in over a metallic cathode. I have further employed an extremely

1820

1830

1850 1860 1870
Fig. 230.

1880

1890

1900

fine jet of CO.,, which was introduced through a very narrow capillary tube, and flowed out from the
end of a narrow silver tube which served as cathode.

I succeeded several times in making this jet luminous, so that it had the appearance of a fine
needle of light shooting out from the cathode, sometimes as much as 5 cm. in length.

A cathode of coal also sent out similar long needles of light from various points on its surface,
round which the coal even became glowing.

Pice'in emitted long, thin pencils of light, often more than 10 cm. in length, one after another, as
if by violent eruptions. These light-phenomena gave the impression that the electric discharge from

Fig. 231.

both the coal cathode and the cathode with pice'i'n, was accompanied by eruptive outbreaks of gaseous
rays, that were made luminous in the same way as the above-mentioned carbonic acid jet. Fig. 231, i
and 2 show discharges of this kind.

From a cathode of graphite there came long, steady pencils of light, which greatly resembled the
so-called eruptions or jets in comets.

Fig. 231, 3 shows an experiment with graphite.

In these experiments with cathodes containing carbon, the rapid disintegration of the cathode was
especially remarkable. In the course of two or three minutes, large dark patches appeared on the glass
walls just where the long pencils of light had come in contact with them. Fig. i shows an instance of

636

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

Fig. 232.

this in the two dark tongues side by side above on the right. To this phenomenon, which is of pecu-
liar importance to our theory, we shall have frequent occasion to return, for instance in the article on
Saturn's ring, where we assume that material particles are constantly being emitted in the plane of the
ring by electric evaporation (disintegration), analogously to certain experimental observations to be de-
scribed farther on.

In connection with the above-mentioned experiments with carbonaceous cathodes, experiments wen
also made with cathodes of platinum thinly coated with lime. This was for the purpose of finding out

whether rays from a cathode such as this — which, as is known, emit-;
ceedingly soft rays — might be repelled by electric forces, and bent right
round, just as the radiation from the head of a comet appears to be by
apparent repulsion from the sun.

Fig. 231,4 shows how the rays from a coated platinum cathode such as
this, turn away from a large cathode-plate of brass on its right. The ben-
ding of the rays was sufficiently evident, and changed with changes in tin-
tension employed upon the brass cathode; but there was no appearance of any
backward-streaming as in the tail of a comet, as the light ceased at a short
distance from the cathode. It is very possible that better results might be
obtained by an arrangement somewhat different to the one here employed.
In J. J. THOMSON'S "Conduction of Electricity through Gases", Second Kd:
tion, p. 632, the diversion of these rays by electric force is illustrated by a drawing,
reproduced here in fig. 232, which shows how the rays can be turned right back.
It will be of interest for the present question to cite, and reproduce a drawing of, an exprn
described by J. STARK in "Die Elektrizitat in Gasen" published in WI.NKELMANN'S "Handbuch der Physik",
B. 4, p. 582: "If a cathode-ray with a certain initial velocity enters an electric field that is at right angles
to its direction, it will be deflected out of its course from points of lower to points of higher tension.
If its initial velocity is very small, it soon takes exactly the direction of the electric line offeree in which
it lies; if, on the contrary, it is great, it will be deflected more or less in the direction of the line of
force, the less so the greater its velocity, the more so the greater the strength of the field.

"Let us consider the case in which rays from one cathode fall upon a second. In figs. 233 a & 1>,
S is the transverse section of a metal pin that can be connected with the cathode outside the tube.
If, together with the wire-anode beside it, it is connected with the earth,
the primary rays cast a sharp shadow of it (233 a). This immediately
increases when the pin is connected with the cathode; for there is then
formed about it the powerful electric field of the dark space of the
cathode, and through this the approaching cathode-rays are turned aside
(233 b)".

According to this, it might well be imagined that luminous pen-
cils of rays, emitted by electric discharges from a comet, are bent back-
wards by the electric force of cathode-rays from the sun, in such a man-
ner that the discharges pursue their course almost in the direction of
the comet's shadow, forming approximately a cone, possibly on account
of the mutual repulsion of the pencils of rays emitted.

Another circumstance favorable to the assumption of the existence of such negative discharges from
comets, is that of the various envelopes separated by dark interspaces so often observed in the heads
of comets. Fig. 234 shows the head of Donati's comet (1858). For several weeks the coma exhibited
unrivalled perfection the development and structure of concentric envelopes. It is easy to produce, rour

Fig- 333-

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V.

637

Fig. 234.

a globe as cathode in a large vacuum-tube, several concentric luminous envelopes separated by dark
spaces. These different envelopes are more distinctly seen when the globe used as cathode is mag-
netised. In this case the originally spherical envelopes will be flattened so as to form a ring in the
magnetic equator. Fig. 235 gives a representation of such an experiment. Such envelopes, as we know,

contract or expand according as the gas-pressure in the vacuum-tube
becomes greater or less. The very singular phenomenon of the contrac-
tion of the comet's head with the approach of the comet towards the sun
can be reasonably explained by this view. Instead of expanding, as one
would naturally expect it to do under the action of solar heat, the comet's
head contracts when near the sun, just because the gas pressure about
the comet becomes higher there, and the electrically-formed luminous
envelopes therefore contract.

On some occasions comets have been furnished with several tails
in a manner that is not quite easy to explain by the assumption that
an emanation of tail-material from the comet could directly give rise to
all the tails.

Figs. 2363 &b show respectively the famous Donati's comet (1858)
from a drawing by BOND, and the comet of 1744 by M'i? KIRCH at the

Berlin Observatory. It seemed to me it would be worth while examining whether all the luminous
streaks or tails that were seen were perhaps not separate tails, but might possibly be compared with
positive strata in the electric discharge from the negative comet-head such as in the discharge repre-
sented in fig. 231, 2.

I have taken two ways for determining this. First the
angle « was calculated, the angle that a plane through the
centre of the earth and a luminous streak in the tail, formed
with the plane of the comet's orbit. The result for Donati's
comet was

« = 58-99°

I'm- a streak that passed over « and / Coronet Borenlis on Oc-
tober Qth. The calculation is based upon a description by WIN-
NECKE, quoted in Bond's "Account of the Great Comet of 1858"
Ip. 61), Annals of the Astronomical Observatory of Harvard
College, Vol. Ill, Cambridge, 1862.
It was further found that

« = 69-53°

for a streak that issued from the head, and kept separate from
the tail, passing over 6 Scrficntis and ft Herculis, according to
a drawing of the comet on October Qth (1. c.).
For the comet of 1744 it was found that

a = 87.36°

for a streak that, according to a description by LOYS DE CHESEAUX at Lausanne, of the appearance of
the comet on the night of the 7th March (quoted in J^-.GERMANN'S "Mechanischen Untersuchungen iiber
Cometenformen", pp. 397 & 398), passed through the middle of EQUULEUS and ended in a point of which
the longitude was 319° 55', and latitude -f- 34° 35'.

Fig. 235.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903.

81

638

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

In the second place a calculation was also made of the angle between a line from the earth to a
middle-point in the streak, and a perpendicular in the plane of the comet's orbit to the streak at thi«

point. The result was

a = 89.08°

For this a drawing from J^EGERMANN'S above-mentioned work, PI. VII, was employed.

In addition to this streak, which was in the middle, calculations were also made for one
side, No. 3 on the left and No. 3 on the right, according to M. KIRCH'S observation. The results were

« = 74.29° and a = 84,64°.

The idea upon which the investigation was based was that if the streaks of light observed in
the" comet's tail answered to positive strata in a discharge, one would expect these layers to be at

a Fig. 236. b

right angles to the axis of the comet's tail, which, in its turn, would be supposed to lie in the plane
of the comet's orbit.

The calculations for the comet of 1744 harmonised, the angle being nearly 90°, but for Donati'^
comet, for which the calculations were made later, a negative result was obtained.

It is not, moreover, so entirely certain that the projections of possible positive layers that might
be seen from the earth, answer to a plane at right angles to the plane of the comet's orbit. The 1.'
are not always plane in reality (see fig. 231, 2).

The great disintegration of a cathode coated with some carbonaceous substance, by which all the
carbon-particles may be thrown off from the cathode in the course of a few minutes, recalls a ph<
menon observed with regard to comets, namely, that they gradually lose their ability to form tails.
Bredichin says(1) of the comet 1873 V, for instance, that "the emissions appear to be exhausted before
the perihelion"; and of the telescopic comets he says that "as a rule it must be admitted that in the
periodic comets with short period, the force that produces the emissions and the tails is relatively
exhausted".

From what we have seen before, the explanation of the phenomenon of the comet 1873 V, accor-
ding to our view, is that the comet had come out of the main body of cathode-rays from the sun -
active layer -- before reaching its perihelion.

(') See Jaegermann, I. c., p. 229.

PART II. POLAR MAGNETIC PHENOMENA AND TERRF.LLA EXPERIMENTS. CHAP. V. 639

It would be interesting to find out whether the pretty results obtained by Bredichin in his mecha-
nical investigations of comets' tails could be made to harmonise with the theory of electric discharges
through rarefied gases. The formation of several distinct tails from one comet would then possibly have
causes corresponding more or less to those of the formation of the various distinct pencils of cathode-
ravs in an electric or magnetic field (cathode-ray spectrum).

It is now generally assumed that comets belong to our solar system, because no comet has an
undoubted hyperbolic orbit. This also agrees with the fact that the spectra of comets exhibit on the
whole a great similarity.

In a subsequent article we shall see how our theory of an electric radiation of matter from the
sun can give a satisfactory explanation of the comet's formation, even when its orbit carries it to a
distance of 1000 or 10000 astronomical units from the sun.

125. Halley's Comet, May, 1910. An exceptionally favorable opportunity of testing the views
here brought forward regarding comets' tails presented itself in May, 1910, when Halley's comet crossed
the sun's disc at so comparatively short a distance from the earth that there was a possibility of the
earth's passing through the comet's tail. When a magnet as great as the earth came into the comet's
tail, there would surely be magnetic effects to be observed upon and from the tail, if the latter con-
sisted of some kind of electric corpuscle-rays.

It was Herr KROGNESS, who, happening to read in an astronomical journal that Halley's comet
would come so near to the earth, suggested that we should go up to my observatory on Haldde Mt. for
the purpose of studying the possible effects of the passage. This was arranged, when I had succeeded
in getting a friend of mine, Herr SCHIBSTED, to share the expenses equally with me.

In order to secure a more widespread interest in these observations, I sent out, in March, 1910,
the following circular to a number of observatories and a few periodicals (e. g. 'Nature', April 21). The
figures that were reproduced in the circular are here omitted, the reader being referred to the same or
better figures already printed in the present work.

"I beg to direct your attention to the following. —

"It is my intention, at Kaafjord in Finmarken (in the N. of Norway), together with my Assistant
Mr. O. KROGNESS, to take magnetic and atmospheric observations during the period yth May to ist June
lext in connection with the transit of Halley's comet across the sun's disc on the i8th — igth May.

"The thing is, that it is conceivable that the tail of the Comet may chiefly consist of electrical cor-
puscular rays, and, if this be so, we would expect that these rays, owing to Earth magnetism, would
be drawn in, in the Polar regions, in zones analogous with the Aurora zones, assuming the tail of the
comet to be of sufficient length to reach the Earth.

" I hese rays will then, in such case, exercise, amongst other things, magnetic influences and elec-
tric inductionary effects, especially strong in the Polar regions, and it is particularly such effects we are
desirous of tracing. The tail of the Comet, if it should consist, as above assumed, of such radiant
matter, will alter its shape at a very considerable distance from the Earth, and we may expect to see
similar formations of light to those which occur during my experiments with cathode rays around a
magnetic terrella.

"In my work, "The Norwegian Aurora Polaris Expedition 1902 — 1903", descriptions will be found
in several places of these phenomena, but to elucidate the subject here, I append a few new illustra-
tions, which very plainly show the shape of these formations of light.

"Figures i (217) and 2(218), show how the rays are drawn in, in belts around the magnetic poles
ot the terrella, correspondingly, with the Polar-light zones on the Earth. They are taken looking along
and perpendicular to the magnetic axis. Fig. t show the spiral rings of light around a magnetic

6^O niKKKLAM). Mil: MIKWF.I.IAN ATROKA I'UI.ARls K.\ I'KDI'I IO.\ , 1 go2 — 1903.

N. pule, corresponding to the S. pole of Farth magnetism. We find these belts of light sometimes a-;
here, with ;i tolerable, even strength of light like a continuous band, and at oilier times we find tin
ravs eoneeiitrated in three limited streaks, with well definable positions around the magnetic poles of
the terrella.

"Figure 3 1 12081 also shows an equatorial ring. This phenomenon of light is magnificent, but un-
stable; it is difficult to produce; it may suddenly appear and suddenly vanish, as the rays which run
round the terrella at the equator are difficult to get sufficiently concentrated for the rarefied gas to illu-
minatel'l. At the lower part of Fig. 3 and on Fig. 4 (135!, a characteristic pointed tongue of light will
be seen, which is drawn in, and shows the manner in which the rays here come in to the terrella
The magnetic equator is drawn on the terrella with a dark line."

(Fig. 200 tV 219 give a capital picture of these pointed tongues of light. In fig. 219, the two
tongues appear as one, the one being immediately over the other).

"It may now be imagined, that analogous formations of light might be observable, around the Earth,
of the rays from the Comet's tail on the 1 8th — 1 9th of May. The downward rays in the I'olar regions
will, it is true, be difficult to observe in northern parts, owing to the northern declination of the sun,
bill in antarctic regions there could be more hope of being able to do so, and the phenomenon would
then probably appear somewhat similar to the Aurora australis. At night, in low latitudes, one could
conceive the possibility of a ring like the equatorial ring being observable as a sort of zodiacal light.

"About the 2nd of May, the comet will be in the vicinity of Venus (see Bulletin dc la Sociilr
. l^lroiiuinii/iie il/' I~ ranee, l^evner ign>, p. 57), and it is not impossible that indications of an alteration
in those parts of the Comet's tail nearest the Planet might be noticeable.

"We may then possibly expect to find traces of the rays being drawn in towards the Polar
regions of Venus, ill a manner similar to thai demonstrated by the experiment shown in Fig. 4 (135!,
or a more or less distinct bending of the Comet's tail, assuming Venus to be magnetic.

"The probability of such being visible must, however, be admitted to be .small, as the central line
of the tail, if il is directly away from the sun, will be at a considerable height above the Planel; but I
will nevertheless call the attention of Astronomers to these conditions, as Venus, if equally as strongly
magnetised as our Farth, must be expected to exercise a noticeable influence on the tail of the Comet
at a distance of several million kilometres, especially if the rays in the tail are easily deviated by mag-
netic force.

"This phenomenon might, in case it were present, be determined by astronomical observations of
the Comet's tail and Venus in the period from i st to 3rd May and I beg therefore, dear Sir, respect-
fully to ask you, in the interests of science, il you would kindly have the necessary observations made,
il possible, and that yon would favour me with a short account of the results."

1 he matter awakened interest in many quarters, and from Gottingen an expedition similar to mine
was sent to my former station at Oyrafjord in Iceland, under the direction of Dr. G. A.NGENHEISTER.
ISolh tin Norwegian and the German stations were chosen out of regard to the fact that experience had
been gained there from previous observations, especially of magnetic storms.

In addition to magnetic rcgisterings, earth-current registerings were made and measurements taken
ol atmospheric electricity. Meteorological observations were also made.

l>eiore entering upon a description of the experiments that were made, and discussing the results
that may apparently be deduced from the observations at the I laldde Observatory at Kaafjonl, I will
attempt to give an epitome of the astronomical and meteorological observations that I have succeeded
in collecting from various quarters of' the globe; for il is not from observations from one place that

i1) Sec Aitirle- i i [ and i 19.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 64!

decisive conclusions can be drawn, but from united observations from the entire globe, and when looked
upon in this way the result appears in the present case to be of a decided, positive nature.

We will first take the astronomical observations among which those of Mr. INNKS, at the Trans-
vaal Observatory, are the most fully reported — with the definite object in view of discovering whether
the forms observed of some part of the comet's tail can be ascribed to the electro-magnetic influence
the earth.

By the 22iid May, Mr. INNES had already sent the following letter to 'Nature':

The Earth and Comets' Tails.

"In spite of the unreserved predictions of astronomers, the Earth did not pass through the tail of
Ilalley's Comet on the i8th — igth May, nor subsequently. The tail as seen in the morning sky, pre-
vious to the transit of the comet across the Sun's disc, appeared like a long and straight beam of light
stretching from the horizon to Aquila. It was noticed from day to day that the tail was practically
fixed irv position in the sky. We rather expected the tail to get nearer to Venus and Saturn as the
comet approached the ecliptic, but it remained stationary. On the morning of transit, i8th — igth May,
the tail was unchanged, but a second branch to the south was now noticed. It joined the northern
branch to the east ot the Square of Pegasus. Unfortunately this southern branch was near the zodiacal
light and only distinguished from it with difficulty. Both of these tails were seen morning by morning,
including this morning (22nd May, civil day), but they have diminished in brightness and were difficult
,to see. further observation of these will be impossible, because of the Moon remaining above the
horizon until after dawn during the next ten days. The whole eastern horizon where the tails meet,
ami where the zodiacal light is, was suffused with a dim and indefinite glow which was particularly
noticeable on the i8th — igth and 2oth — 2ist. This glow was not so definite in boundary as the
zodiacal light. When the comet was seen on the evening of the 2oth, we were surprised to see it had
the ordinary tail pointing away from the Sun as usual. It had been noticed for several days that in
the neighbourhood of the Sun the sky was not so blue as usual, but this was the case even a week
before the transit and is probably merely a meteorological phenomenon. This brief summary of the facts
will suffice here; the observations in detail will be published elsewhere.

"We have now to explain the reason why the Earth did not pass through the tail of the comet
and why the tail broke up so that some of it was left in the morning sky, where it remains and is
slowly losing its luminosity, and some (or another tail) appeared in the evening sky. It is well known
:hat a comet under the Sun's radiant action (I do not attempt to define it more closely) expels cor-
juscles towards the Sun, which the Sun repels, and these luminous corpuscles form the tail. This pro-
:ess goes on even when (as in the case of Halley's Comet) the distance between the comet and the Sun
xi-ceds the distance of the Earth from the Sun. If the nearer planets do not show tails it is because
.hese corpuscles have been shed by the planets ages ago. In short, a comet and a planet under the
radiant action of the Sun, and the Sun itself, all repel these corpuscles. This being so, it is impossible
for the Earth to go through the tail of a comet; it simply repels the tail, and as a consequence, instead
>l a passage through it, a disruption near the time of passage must occur, one part being left in the
in this case) morning sky, whilst a new one is developed in the evening sky. Here I might remark
hat on the evening of the 2oth the measured length of the new tail was 19°, on the 2ist 32°, and on
:he 22nd it was 40°. Again, the Earth is bombarded with meteorites which are also throwing off cor-
niscles. These will be repelled by both Earth and Sun, so that if we look at the part of the sky
opposite to the Sun we should and do see the faint tail thus formed, which is known as the Gegen-
^chein. This simple theory explains all the facts of observation, and if it is correct, will save nervous
individuals some worry when the next near approach of a comet's tail is imminent.

642 BIRKKI.AM). Till-. M )RW1 ( ,IAN Al'RORA POLARIS KXPI-.MITM IN, 1 QO2 1903.

"I'. S. Mr. II. (.'. RKKVI , of Lorcntxville, under date of 22nd May, lias sent me a letter convevine
the same idea. lie says: 'Whatsoever nature the stress between the Sun and the comet may be which
causes the repulsion of the tail .... the same stress must also exist between the Farlh and tin- count
.... I'nder these circumstances the Earth could not possibly pass through the comet's tail'."

Dr. CIIAS. F. JUKITX. of the Government Analytical Laboratory, Capetown, under date of 2ist Mav
1910, writes:- -

"The last time that I saw the nucleus previous to transit was on the morning of Tuesday, the
1 7th. The nucleus was then not far from the H Arietis, and the tail stretched right awav to the nui»h-
bourhood of the H Afjtiilae.

"(.)n Wednesday, the i8th, the sky was entirely overcast. The comet could therefore not be seen.

"On Thursday, the igtli, at 5 a. m., i. e. while the transit, as originally expected, was supposed, to
be in progress, and the Farth in course of passage through the tail, the tail was longer and wider than
ever .... extending right into the Milky Wav, the northern edge of the tail grazing •/ Pegasi. But this
tune the main tail was Hanked bv two attendant shorter shafts of light. The fainter of these was north
ol the main tail, and inclined more to the north than even the main tail did; the brighter of the two
subsidiary tails stood up almost vertical from the north-eastern horixon, and seemed to extend some 8"
or 9" above Venus, the planet, which was right in the middle of the beam, twinkling through it like a
fixed star. Between this tail and the principal one there was <i distinct circular-pointed wedge of dark
sky. These two fainter tails were apparently between 15" and 20" long. The appearance of the lime
bruins of liiflit produced on me exactly the impression of the mouth ol a great transparent cone into
which the Farth was rushing. Imagine a stupendous glass filter funnel, down the sides of which, from
stem to edge, three streaks of luminous material had been painted; t/n-v convrrgrti toward* the horizon
ami diverged towards tin- :cnilh. The continued bast: of the three beams extended along the north-
eastern horixon some 35".

"On Thursday evening the comet was not yet visible in the west, but on Friday morning, the igth,
the main tail was still practically in its former position, although somewhat fainter. Its northern com-
panion had disappeared, but the southern subsidiary tail was more distinct than before, and also longer,
while the dark wedge separating it from the principal shaft of light was better defined than on the pre-
vious morning."

Father K. (ioi.TX, of the Bulawayo Observatory, writing on the 2ist May, says: -

.... "Might it not be that the tail was more westwards than we expected, and that we passed
it during the day on the igth, and that the taint tail we saw on the 2Oth was a stiranii'r itistinc/ f ruin the
main tail. The slight curvature which was noticeable when the comet passed near Venus makes me think
that the Farth mav also have had some kind of repelling effect on the tail which would have sent it a
little further west than anticipated and account for our delayed passage" ....

Mr. W. II. FINLAY, M. A., writes that he and Professor Rn>(,K, observing at Blocmlbntcin, saw tin-
tail near A(|uila undergo a rupture on the morning of i8th — igth May, and that he considers this was
due to the tail meeting the Farth's atmosphere and being unable to penetrate it.

"It will be remembered (see Circular No. 3! that the eastern or morning tails were actually seen
here on the morning of the 2 1 st Mav, almost exactly three; days after the transit of the comet across
the sun's disk (see sketch fig. 237). At that time the north branch of the morning tail ended in 20 h.
R. A., whilst the head was in 6 h. R. A. and the end of the western tail in 8 h. R. A., or roughly the
angular distance from the end of one tail to the other was 240". But there was then no connection
between the comet and the eastern tails. It is highly probable that a rupture had occurred and this

PART

POLAR MAGNETIC PHENOMENA AND TERRF.U.A EXPERIMENTS. CHAP. V.

643

probably before the i8th May, as on that morning the main or northern tail got thinner as its distance
from the horizon increased (see sketches p. 15 of Transvaal Observatory Circular No. 3).

"As to the actual and unbroken length of the tail, this was measured on the i7th May and found
to be 107°. On the i8th the nucleus was invisible, but the tail ended 140° from the place of the head.
When the whole comet was visible the greatest length seen here was thus 107°. I cannot find any
authentic measure of the angular length of a comet's tail which exceeded or was even as great as this,
but references to authorities are limited at this Observatory. It may be said that it would require much
imagination to desire a more impressive and brilliant spectacle than that presented by Halley's Comet
on the morning of the I5th, i6th, and I7th
Ma)'. It was indeed a «Great Comet», such as
the writer had never seen before and can hardly
expect to see again.

'•The sketch given belove (fig. 238) may be
of use in following the records given in this and
tin previous circular. The tail on the 23rd May
and later dates proved that the comet's emissive
power had not lessened, and it will be remem-
bered that the tail of the 171(1 was still visible
in the morning sky in practically the same
position on the 2ist. From the i7th to the 2oth

t may be assumed that the matter which would

irdinarily go to form the tail accumulated in the

riangle formed by the Earth and the comet's

>'>sitions on the I7th and 2oth May; this matter

>eing visible as the extensive glow involved
vith the Zodiacal Light.

The lengths of the tails shown on the sketch are:

• -ZOMay

• 23 May

Fig. 238.

1910

Ma}- 1 7
» 20
» 23

Units
0.30
0.09

o.i 6

Miles

27 ooo ooo

9 ooo ooo

14 ooo ooo"

The following is an account of a peculiar observation by EGINITIS(') on the evening of the zoth May.

"On the evening of Friday, May 20, 1910, on looking at the head of Halley's comet through our
real equatorial Gautier (0.40 m.), we found it had completely changed its appearance since the last
bservation made in Athens (May 12); it was in the form of a crescent, resembling that of the moon a
ttle before its first quarter. The length of the axis of the head was about 2', almost four times less
lan its breadth; one would have said the comet had been truncated or partly occulted. The outline of
ie head towards the apex appeared very smooth and very bright, and was in the form of a parabolic
re, very luminous, not fringed externally, having its apex tangent interiorly to the nucleus. During the
bservation, this outline became smoother and smoother, while the tail, of which only a few traces,
:arcely more than the beginning, were visible in the concavity of the head, showed no perceptible
rolongation in the direction of the axis, unless it were a little at its margins (fig. 239).

I'l "Ciel et Terre" XXXII, March 1911, p. 94.

644

HIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1003.

"The concave side of the crescent, which was the first to enter the field of the telescope, appear,,] ;,
be turned towards the west. This peculiarity, which has struck us ever since the beginning of tin
observation, has been verified by us on several occasions, on account of its importance, to assure our-
selves of it. We have concluded from it that this evening, as also this morning, the tail, which nii"lit
to be in the concavity of the head, was apparently directed, in consequence of its great am>atinr, towards
the sun(').

'•The same evening, however, but one or two hours later than ourselves, Dr. UARTMANN, observlim
the comet through a sweeper of 8 cm. on Mt. Sonnwendstein in Austria, together with Drs. \\'i
RHEDEN of Vienna, saw the same appearance of a crescent, but with its concavity turned in the o|
direction, namely towards the east (fig. 240) (-).

"How is this difference in the direction of the head of the comet to be explained? Does it an*
from an error of observation? Certainly not! The observations, the one as much as the other, i>o
the elements of guarantee necessary to convince us of their exactness, that of HARTMANN corn

by the data of two other eminent observers, is indisput-
able; our own, that we have verified six or seven times in
succession, by causing the comet to enter the field of the
telescope, and seeing it cross it with its concavity in front
is as certain as the other.

"Is it then possible to make a mistake in such a
simple observation as this? It is not a question of mea-
suring angles of position, or other slightly complicated
observations, where an error might be possible; it is suffi-
cient only to see if the crescent enters and moves in the
field with its convex or its concave side in front.

"The hypothesis of an error being thus inadmissible,
what could be the cause,- of the contradiction of these two
observations?

"We believe that, as in the appearance of the tail, directed in the morning to the east /twin/* I
sun, it is only a question of perspective. In reality, according to the explanation that we have t;iun
of the curious shape presented by the comet at Athens on the evening of the aoth May, the axi>
the head was probably directed at that moment approximately towards the earth; in these comb
the nucleus ought to be projected near the top of the outline, and appear to touch it; the nehiild.-ih
of the tail, which often extends a little in front of the nucleus, became invisible, and the tail ought t"
disappear almost completely in the telescope.

"In this hypothesis, the difference of the two observations might then be explained as the result >
a change in the apparent direction of the convexity of the head in consequence of the rapid rotati,
of its axis, relatively to the earth; and this relative rotation is evidently the result, on the OIK hand, <
the at first very rapid movement of the comet, on the other, of the contrary movement of the earth.'
According to ANTONiADNi(3), the observations of Eginitis must be altogether wrong, as he <
not find them verified by the observations of WOOD and HARTMANN, as seen in the following si
fig. 241 taken from Antoniadni's paper.

We do not think there is sufficient reason in this statement for disqualifying the observation-
Eginitis.

N

Kig. 239

(') Aslr. Nachr., 4414 and 4431 — Comtes rendus t. CL., pp. 1408 and 1578.
(') Drawing by Dr. HARTMANN, published in Astr. Nachr., 4431.
(") "Ciel et Terre", December 1911, p. 435.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V.

645

Photograph by Wood
at 4'' 30"!, G. M. T.

Eginitis at 6'1 40™.
Fig. 241.

Hartmann
at -jh gm.

We will now compare the astronomical observations here quoted, of the forms of the comet's tail,
with the forms that, according to our hypothesis and experiments, it would present if the tail-material
consisted of electrically radiant matter.

In the first place it is obvious that here, as we maintained in our theory of the zodiacal light, we
must allow that the earth's magnetism will try to keep the electric radiant matter away from the earth
except in the polar regions. In the plane of the earth's equator, the negative electric corpuscle-rays
that come out of space straight towards the earth, even when at a distance of millions of kilometres,
arc deflected westwards — as seen from the earth — and this in inverse degree to the stiffness of the
rays. Compare with this the bulk of the rays in the experiment illustrated in fig. 219. The fact that the
material of the comet's tail has to some extent given rise to phenomena that could not be distinguished
from the phenomena of zodiacal light — as a number of accounts state — is therefore in perfect accord-
ance with our theories. In the same way the astonishingly short tail of the 2oth May as compared with
that of the 171)1 and of the 23rd may be explained (see sketch fig. 238).

What should we have ex-
pected to see on the morning
side, when the huge comet's tail
was approaching the earth from
May 17 — 21, if the tail had
(•(insisted of negative* electric
radiation?

We obtain clear informa-
tion on this point by a compa-
rison with fig. 219.

The bulk of the rays must be deflected westwards. This at once explains the fact that the tail of
the romet appeared morning after morning in almost the same position, although the comet had crossed
the sun's disc.

We should further expect two branches from the tail, extending north and south and pointing
towards the poles of the earth. This is seen on a closer inspection of the experiments shown in fig.
;2oo, where the rays strike the floor and roof of the vacuum-box, in fig. 215 — especially Nos. 4 (see
letterpress p. 588) and 14 — and in fig. 219.

1-Yom the position of the earth's axis, one would have expected the in-drawing towards the north
xile of the earth; and INNES' observations seem to indicate this. There appear to have been two such
tranches in the comet's tail, one with a north, the other with a south direction. Dr. JURIT/. says in his
iccount (see above): "These two fainter tails were apparently between //° and 20° long. The apptarattct
if the three ///-trins of liglil produced on me exactly the impression of the mouth of a great transparent cone
nto zi.i/iic/1 the earth was rushing".

We have reproduced here (fig. 237) one of the figures from Innes' account, to which we have added
IK position of the magnetic equator. This, it will be observed, falls just in the dark space between the
wo branches of the tail, which is in itself a very remarkable fact. It is doubtful, however, whether
here is much to be concluded from this circumstance; but it calls to mind the phenomena illustrated
n the above-mentioned figures, where there is a similar division of the cathode-rays in the magnetic
quntor on the morning side of the terrella.

The fact that the main direction of the comet's tail, i. e. of the rays, is oblique in relation to the
•arth's magnetic equator, makes the whole thing a little less clear, as a comparison with the experiments
ihown in figs. 215 & 219 is in this case rather imperfect.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903.

646 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

The tail that at the same time was observed in the evening, pointing away from the sun, is also
in perfect accordance with our theory and experiments.

If, in the experiment shown in fig. 219, the cathode had been bent considerably upwards — an
arrangement that I have carried out several times — a correspondingly strong pencil of rays would have
passed over the terrella, but in such a manner that the nearest rays would have curved themselves
round it.

This condition answers to that of the comet having passed between the earth and the sun, win n
the greater part of the tail will become visible on the evening side, while the retarded or deflected tail
on the morning side will become fainter and finally fade away, as the observations showed. It is not
easy to see what Mr. INNES means when he says that "the angular distance from the end of one tail to
the other was 240°". The distance referred to is perhaps that between the extreme points of the ,
ning and evening tails. Regarding the observations made by EGINITIS and HARTMANN, the most natural
explanation sfeems to be that at the time of observation there has been a narrow, fan shaped tail, with
off-shoots to north and south, which have pointed very nearly towards the earth, the one under KM-
NITIS' observation a little west of the earth, and that observed by HARTMANN having swung over until it
pointed a little east of the earth. This fan-shaped tail with direction towards the earth, calls to mind the
two in-drawn tongues of light in fig. 219, which are just off-shoots from a fan-shaped mass of light
such as this. A calculation of the direction of the terrestrial-magnetic lines of force, looking from the
earth towards the place in which the comet stood at the time of observation, gives a direction ai
due north and south, and thus symmetric in relation to the two crescent-shaped formations observed.

Of some other remarkable observations of the comet's tail about the 2oth May, the folloi
mention may be made.

EVERSHED, in Southern India, saw the comet in the morning sky like a huge search-light. It \v,is
not visible while passing across the sun's disc.

W. VAN BEMMELEN writes from Batavia: "I saw it before dawn on the i8th and igth. The tail
was enormous ; it rose with a high inclination to the north from the eastern horizon, like a search-light,
and reached by its curvature the zenith. I began watching it at 4.30 a. m., but saw no auroral display,
nor could I detect anything of the comet's head passing the sun."

There are similar accounts from Aden, St. Thomas, and Malta.

From more northerly stations, on the other hand, there has been little to relate about the comet's
tail or any luminosity that might have some connection with it. The time of year, the unfavorable
position of the moon, and the atmospheric conditions, have contributed to this result.

Concerning light-phenomena seen in Norway, it may be mentioned that at Fredriksstad, at 10.30
p. m. on the igth May, a luminous band was seen in the northern sky at a height of about 45° above
the horizon, extending from east to west. It was narrowest in the west, and could not be seen quite
down to the horizon, as the sky there was too light; but as far as could be seen, the radiant band
pointed straight to the sun, and extended in a slight curve right across the sky to about 50° above the
horizon in the north-east, where it was broader and very faint. The observer did not think that tin
band was an auroral band, but he was inclined to connect it with the comet's tail.

From the telegraph-office at Tana it was reported that at 3.30 a. m. on the igth May, a light
seen, which resembled aurora, and could not have been a gleam of sunshine. A few strokes on tin
operator's alarm-bell were also noticed once or twice after the light had disappeared.

At Tjarstad, in Sweden, similar auroral arcs were seen at the same hour. Judging from their
position, they were probably the same arcs (see STENQUIST'S "The Light-Phenomena, May, I9io"('), p. n)-

(') Arkiv for Matematik, Astronomi och Fysik. Stockholm, 1912.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V.

647

The probability is that these light-phenomena have been intense auroral arcs that were visible
in spite of the bright sky; but it is not impossible that this unusual aurora had something to do with
the comet.

126. We will now pass on to the meteorological observations that were made at about the time of the
transit, in order to see whether, in those at our disposal, any trace could be found of effects that might
reasonably be ascribed to the
tail-material of the comet.

At the outset we must
state that a number of obser-
vations made at some of the
leading observatories, have
yielded a negative result. As
an instance, a series of bal-
loon-observations, where air-
samples were taken in high
strata, revealed nothing of
interest. On the other hand,
there are other observers,
i who, on the days in question,
noted meteorological pheno-
mena of a peculiar and unu-
sual nature.

In the Transvaal Ob-
servatory's Circular No. 4,
of July ii, 1910, there are
some particulars given by
observers, of phenomena that
they saw, from which it would
appear that a Bishop's ring
was seen. Mr. OTTO MK.N-
/F.I.L, of Pretoria, writes:

.... "At about a quar-
ter to seven I looked at the
Moon, which was then well
up in the sky. I noticed a
haze over it, but when look-
ing through my glasses it Fig. 242.
shone as clear as ever. Some

clouds were gathered round the Moon at that time, as shown in the first sketch fig. 242. A few minutes after-
wards these clouds started moving in a peculiar circular fashion round the Moon (sketch) and continued
doing so for at least five minutes until they formed a broad ring round the Moon, as shown in the third
sketch. I then went home, but returned at about nine o'clock; the ring had narrowed down, as shown
n the fourth sketch. The colours of the ring are described in the sketch. When looking again at the
Moon at one o'clock in the morning of the igth May, the ring had narrowed down a little more, as
seen in the fifth sketch, and it seems to have remained so."

Phenomenon as
seen
6

on A9>*
1310.

Phenomenon 35
seen a 'f about

Phenomenon as
seen at about

6.54. p m.
an l8'hMay
•1310.

1. Yellowish

2. airly ••

3 • Greyish
Reddish

Phenomenon as
seen st about
I. am

Phenomenon

seen it about
9pm on May IS* 1910

648 I5IRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Mr. G. R. HUGHES, of Pretoria, sends the following report: —

.... "The Moon, which was in its second quarter, was surrounded by a ring which had a me-
tallic appearance. It was of considerable diameter and, to my recollection, the inner edge of the ring
(nearest the Moon) was yellowish (the yellow of the Sun), then merging into a dirty brown. The outer
edge was dull grey, like the clouds, that covered the sky. The ring appeared to have walls, if one may
so distinguish from a 'flat' surface. It was exceptionally well-defined. I observed the phenomenon until
nine o'clock, when I ceased to give it attention and am unable to say when it finally disappeared.

"One remarkable phase was an inner ring which manifested nothing metallic. It was faint and
flat in contra-distinction to the outer and larger ring. The inner ring was dull grey in colour.

"The Moon on the night of the igth May was again surrounded by a ring; the latter was much
more clear-cut that on the previous night. There were less clouds in the sky. When I first observed
the Moon between 6.30 and 7 p. m., it was clear of the clouds and had no halo. It, however, appeared
to be less distinct than usual. The features on its surface were not so sharply defined; while no haze
was visible to the eye, I am confident that some influence was present in the atmosphere. I tried a
view with binoculars, but still the features lacked sharpness in definition. As the Moon approached tin
clouds, which previously were scattered, they seemed to break, and I saw the ring evolve. The area
within the ring, unlike the previous night, was clear of cloud. The ring was decidedly metallic in
appearance, but I did not observe so much yellow colour as on the i8th. My note reads: 'Moon sur-
rounded by ring of dark brown material'. I observed the phenomenon for half an hour. The weather
conditions at the time were restful, but later in the evening the wind arose."

Dr. FRANZ LINKE writes in a preliminary statement in "Meteorologische Zeitschrift", June, 1910:

"The Meteorological Geographical Institute of the Physical Association at Frankfurt a. M. had
erected by May I2th a temporary observatory on the Feldberg in the Taunus (880 m.), where arrange-
ments were made for atmospheric-electric and terrestrial-magnetic registerings and observations, the
results of which will be published later. At present, attention will only be drawn to the quite abnormal
phenomena. Since the I2th May, we have had high-pressure weather; an evenly warm, dry current
of air out of the eastern continent continued uninterruptedly, and apart from some thunderstorms, brought
continuous warm, clear, summer weather.

Only on the afternoon of the igth, a few hours, that is to say, after the passage through the
comet's tail, there occurred a remarkable cirrus-overclouding with lunar halo and ring, which, if it
had been observed in an ordinary way, I should have ascribed to the influence of the ions expelled
into the atmosphere. I did not, it is true, even at 2 p. m., at a height of 8500 m. notice anything ol
these ions; on Gerdien's conductivity-instrument, a strong, but for such heights not abnormal conductivit
was observed.

The same evening there first appeared the following abnormal twilight phenomena. In the south-
ern sky a broad, reddish yellow stripe extended southwards from the sun more than 100°.
north there was nothing similar to be observed. On Friday evening, however (May 20), a similar
luminous band, about 10° in width, and of the same horizontal extent, appeared on the northern horiz<
The twilight had also all the characteristics of the disturbance, such as a Bishop's ring, a reddish brown
colour, unusual clearness and duration. In the course of the next few days, from the 2ist to the 24th
May, the clear light in the north constantly spread over the entire sky; not until the 24th was the
twilight symmetrical with the sun.

If we make the cosmic dust of the comet's tail expelled into the earth's atmosphere, responsible
for the twilight anomaly, we must assume that on the day of the transit, Thursday, the igth May,
principally in the equatorial regions, the cosmic dust reached the strata in which the twilight is found
(a height of from 10 to 20 km.). It must however quickly disperse or fall upon the earth. Great quan-

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 649

tities that are more slowly diffused then appear to have streamed into the polar regions, whence they
are slowly distributed over lower latitudes and deeper strata.

A further observation that I believe I have made is in accordance with this, namely, that at the
beginning of the twilight the northern sky is first illuminated, and it is not until later in the evening
that the maximum of clearness occurs in the south. Consequently the light-deflecting and light-reflecting
strata lay deeper in the north than in the south, and have thus sooner, or more rapidly, penetrated
downwards, when they come from without.

I need hardly say that this would prove the electric nature of the comet's tail as a current of
ions deflected by the earth's magnetism, as BIRKELAND has formulated it.

The various phases of the twilight are not so easily recognised after the commencement of the
perturbation, as before. I missed in particular the first and second purple-lights.

MAX WOLF, Konigstuhl-Heidelberg, has sent me a copy of his observation-notes. They are as follows:

From the night of the I7th May, 1910, a cirrus-veil developed, which, up to the afternoon of the
igth, continued to increase in fulness and form.

The veil consisted of quite peculiar forms, nothing similar having ever been seen either before or
since. In addition to the complicated thick and thin, stratified and fan-shaped interpenetrating forms,
there was present an all-penetrating structure of narrow, smoke-like bands, such as previously (and since)
•nave only once been observed, namely, on the 3oth June, 1908.

The colour of these exceedingly high-lying bands was entirely different from that of the tangled
:irrus-covering; and this colour, combined with the apparent, quite unobstructed penetration of the two
•duds of formations, produced the astonishing cloud-picture that reached its maximum on the igth May,
md roused the attention of numerous observers, all of whom were situated in the centre of the area of
ligh pressure that at that time covered certain parts of our land. The direction of the srnoke-like bands
.vas S 20° E to N 20° W.

Late in the afternoon of the igth May, a Bishop's ring was first observable round the sun.

There then developed, after only comparatively unimportant twilight phenomena had for some time
jcen observed, on the evening of the igth May, a twilight of quite unimagined intensity, extent and duration.

Three successive purple lights could be observed— distinctly purple up to 9'' 20™ local time, later
or a long time red in the north-west, with all the colour- phenomena (including the wonderful tur-
|uoise-blue and ruby-red) seen earlier in the eruptions of Krakatoa and Mont Pelee, and occurring on
he ist July, 1908.

Round the moon there appeared a Bishop's ring with an intensity such as we had never seen,
determined the external radius to be 28° at the time of the culmination of the moon (at a height of 37°).

The cirrus cloud-covering then steadily decreased. But in the higher strata there still remained a
cry faint, tangled granulation, which made it possible to see the Bishop's ring, distinct and bright, on
he 2oth May, this being only visible when clearly-illuminated parts of the sky are observed through a shadow.

All the phenomena decreased very rapidly. If we call the ordinary intensity of the twilight i, by
he 1 7th May it had already risen to 3. I estimate the course of the intensity roughly as follows:

May 17, 1=3

18, 6

19, 30

20, 1 6

21, 9

22, 6

23, 4

24, 3

650 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

'

The course of the intensity and extent of the discs round the sun and moon was analogous to
this in this district.

The whole phenomenon was analogous, down to its smallest details, to that of the 3oth June or
ist July, 1908, which I have described in Astr. Nachr. 4266 Bd. 178, 1908.

In a paper by D. STENQUIST (I. c., p. 14), which we only saw after the above was written, a
number of interesting observations have been collected from the period from the lyth to the 2ist Mav.
The author summarises his results as follows:

"From the twilight-phenomena observed, from the abundant occurrence of cirri, in which corona
and halos were produced, and from the existence of aurora borealis, it would seem that the earth, at
the heliocentric passage, was enveloped by not inconsiderable quantities of cosmic dust (probably charged
with negative electricity)".

Concerning the meteorological observations at the Haldde observatory and at Kaafjord during
transit, I will first of all emphasise the fact that many extremely characteristic polar bands were formed
in a striking manner, and in more rapid succession than I ever remember to have seen before. The
significance of such polar bands in connection with the theories here propounded, has been dwelt on in
an article "Sur la Formation des Nuages SupeYieurs", p. 75 of "Expedition Norv£gienne de 1899—1900
pour 1'Etude des Aurores Bor6ales". It is assumed that the polar bands are produced by the in-
drawing, through terrestrial magnetism, of negative corpuscles from space in a manner similar to that
in which the corpuscle-rays that produce auroral arcs are drawn in.

The weather on the i8th and igth May was very unfavorable for observing, as thick mist frequently
prevailed, with snow and ice-spicules in the air. Now and then, however, it was clear for some time,
for instance on the evening of the i8th up on Haldde Mt., and down in Kaafjord on the morning of
the igth, beginning from midnight.

At about 8 p. m. on the i8th, I saw from the mountain at one time 4 parallel, very marked,
polar bands, curving from west to east over the northern sky, with their highest point about 30° above
the horizon. They changed considerably and developed rapidly, but were soon hidden by the mist. On
the morning of the igth, Krogness saw many cloud-formations of the same kind from Kaafjord, concer-
ning which he says:

"Although the cloud-covering was not favorable for the observation of cirrus-clouds on the night
of the i8th May, there were several opportunities at Kaafjord of observing very peculiar cloud-forma
tions. There was a most unusually abundant variety of cirrus-bands. Their shape and mannu
forming showed an unmistakable resemblance to those of aurora. Great drapery-like clouds would fre-
quently appear quite suddenly, or large portions of the sky be covered with clouds in the form of a corona;
and more or less bright polar bands were continually visible. The following are some of the notes made
at the time (Gr. M. T. is employed) :

May 18, 1910, nh 32™ p. m. 6 polar hands in a direction WNW — ESE passing the zenith and
north and south of it.

34 — 35m. Two or three small draperies were formed, which, however, soon disappeared. In the
southernmost band numerous stripes.

39m. A bright band suddenly makes its appearance a little north of the zenith.

40™. A tassel with striped figures appears, and spreads eastwards in the form of a drapery along
the above-mentioned polar band.

Above the mountain in the west several faint, evenly luminous, very characteristic bands. In tl
north brighter bands with from 2 to 3 peculiar, bright, awl-shaped, striped figures pointing downwards
and westwards. These are almost due north.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 65!

45m. In the above-mentioned band in the north, a little lower, occurs a very marked, evenly
nldish light. The highest point of the band is in a direction N 35° E.

48'". Several evenly bright bands in the form of great circles converging towards a point on the

1 rizon in a direction about S 45° E.

To the south many fine, awl-shaped stripes massed more or less in bands.

iih 51"" p. m. Dark cumulo-stratus rising in the west and hiding the cirrus clouds. In the south

II many threadlike bands "

The above extracts are sufficient for our present purpose. The observations were continued
t •niighout the night, with interruptions occasioned by the overclouding of the sky.

The following accounts of exactly similar observations, made at the same hour— 8.30 p. m.— on the i8th May, in the
ti n of Tonsberg, and at Blakjer, about 90 kilometres north-north-east of Tonsberg, read almost like a fairy-tale.

The account from Tonsberg was given by the magistrate of that town, his wife and son, with a statement of their readi-
n!s to confirm by oath what was written. At Blakjer the phenomenon was observed and described by several trustworthy
p ^ants without any knowledge of what had been seen in Tonsberg.

The magistrate's account is as follows: "We were all three walking along the quays. The sun was near the horizon,
a we saw suddenly appear round it a number — I suppose from 50 to 100, possibly more — of dark (blackish grey) circles about
at arge in diameter as the moon, and these then spread out on both sides of the sun".

The people at Blakjer saw at the same hour, in the direction of the sun, bubbles the size of a child's head and smaller
siJenly descending towards the earth, shining in all the colours of the rainbow.

It is not, of course, easy to say what has caused the unusual phenomena here observed, but it can only be supposed
tl there have been certain foreign bodies in front of the sun that have produced the various light-effects.

The magnetic registerings in Kaafjord were begun on the 7th May and continued by us until the

2 1 June, after which date they were carried on more or less completely by Herr L. HEITMANN until
tl middle of July, in order that a general idea might be obtained of the course of the variations through
a .eriod of some length.

In addition to the ordinary slow-run registering-apparatus, we also took with us one for quick-run
re isterings. The latter were begun on the i8th at about 4 a. m. Gr. M. T., and continued until about

3 . m. on the 2oth.

During the same period, magnetic registerings were also undertaken at Teisen near Kristiania, by
HT O. DEVIK.

The special interest of these observations, and our reason for mentioning them here, is the con-
mtion that their results may be supposed to have with the passage of the earth through the
'•I- ict's tail.

With regard to the magnetic curves, this period may be characterised as follows: The period from
th yth May until noon on the i8th was fairly quiet magnetically, the storms that occurred being of
co paratively little strength.

At about i p. m. on the i8th May, an unusually powerful magnetic storm suddenly began, devel-
op ig in the afternoon into a positive polar storm, then changing later, and appearing in the evening
;m night as a negative polar storm.

From about 4 a. m. on the igth, the storm decreased in strength, and at about 6 a. m. the con-
tiitms were once more quiet, and continued so for some days.

On the 24111, at about 9.30 a. m., an unusually powerful magnetic storm occurred once more, with
a mrse similar to that of the storm of the i8th — igth May, but of somewhat longer duration.

As the passage of the comet was to take place on the morning of the igth, it seemed reasonable
at rst sight to suppose the storm of the i8th — igth to be caused by the comet. Just at this time,
li'x-ver, matters were complicated by the appearance of a large group of sun-spots near the sun's cen-
tra meridian. These too, then, might be the cause of the storm, as in its main features the course of
tin perturbation was like that of ordinary perturbations.

652

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

te'V-tt*

Earth currents and magnetic elements 17 — 18 May, 1910.

M ill
II "

iff '**

• i:l. '

Earth currents and magnetic elements 18 — 19 May, 1910.
Fig- 243-

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V.

653

There is one circumstance, it is true, that may seem remarkable in this storm, namely, that it was
not repeated on the following day, as is generally the case with powerful magnetic storms in the polar
regions. On the contrary, calm supervened very quickly, and the next day was very quiet.

At Dyrafjord, however, we find the storm repeated with diminished strength the day after as well,
n the usual manner.

It should be remarked, however, that it was not until two days later that the above-mentioned
sun-spots reached the central meridian of the sun. It is well known that several scientists have thought
hey could show that powerful perturbations do not as a rule occur until from 40 to 50 hours after the
>assage of the corresponding sunspot over the central meridian. If, therefore, we apply this here, it

Earth- currents and magnetic elements, 19-20 May, 1910.
Fig. 244.

ould appear that the magnetic storm came about 4 days too early. On the 23rd May, when, according
> this manner of looking at the question, the influence of the group of sun-spots might be expected,

was very calm magnetically. But on the morning of the 24th, as mentioned above, powerful storms
ice more occurred. It thus appears to be difficult to deduce the magnetic storms from the sun-spots

the usual manner; but on the other hand the above-mentioned difference in time may obviously be
•garded as an average value of a large number of cases, and in reality the connection between sun-
wfe and magnetic storms is not so simple (cf. Art. 98). It is interesting to see that Dr. ANGENHEISTER
is believed he can prove a greater accordance between the appearance of the sun-faculae and the mag-
i;tic storminess on the earth in the month under consideration (l).

The earth-current registerings will be discussed in the next chapter. As the magnetic disturbances
•e exactly repeated in the earth-current curves, the reader is referred, as regards the latter, to what

(') Cf. Angenheister's "Die Island-Expedition im FrOhjahr 1910. Die erdmagnetischen Beobachtungen. Nachrichten der K.
Ges. d. Wiss. zu Giittingen, Math.-phys. Kl. 1911.

Birkeland. The Norwegian Aurora Polaris Expedition, 1002—1903.

83

654 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

has been said above. I here reproduce some of the most characteristic curves from the period between
the i yth and 2oth May.

The atmospheric-electric measurements included measurement of the conductivity by readings, i. e
not registerings. These readings were principally taken at Haldde Observatory.

In these measurements I received capable assistance from Herr FEYLING, telegraph-director at
Bossekop, who kindly accompanied me in order to assist in the observations. Several long series of
5-minute readings were taken, alternately with positive and negative potential. The observations made
on the 2oth May were of special interest. Their results are described in Art. 93 on p. 449.

The above is a comparison of the available observation-material concerning Halley's comet, May,
1910, with our experimental results, and may serve to strengthen the theory that the conn
material consists of electric corpuscles radiated from the comet.

THE SATURNIAN RING.

127. That Saturn's rings cannot be rings of coherent matter, either solid or liquid, has
been well established by theory, which showed that the equilibrium of such an object would neo
be unstable.

The alternative hypothesis that the rings are clouds of minute satellites, or perhaps mere particles,
too small to be individually visible, but so numerous as to look, in our telescope, like a continuous
mass, was investigated by MAXWELL in his Adams prize essay, published in 1859. Although the stability
of such a ring of particles can hardly be said up to the present to have been strictly proved, MAXWELL'S
hypothesis has gained more and more adherents among astronomers, especially since the not>
addition to our knowledge of the rings of Saturn, made by KEELER, that the different parts of the rings
have a rotation in conformity with KEPLER'S third law. The extreme thinness of the rings has been demon-
strated at the times at which the plane of the rings passes through the earth. Even with the 36-inch
telescope of the Lick Observatory, the rings were completely invisible in these circumstances. This shows
that the entire ring must be so thin that its edge is quite invisible, even in the full light of the sun,
at the distance which separates us from the planet. On the other hand, the objects composing it must be
completely opaque, as is shown not only by their disappearance in the circumstances we have mentioned,
but by the darkness of the shadow which they cast upon the planet when the sun illuminates them
obliquely. The cloud of these very small satellites seems to be so dense that a ray of light cannot
penetrate the mass.

At present MAXWELL'S hypothesis seems to be a strong one, although it seems almost incredible
that such a ring of cosmic dust should be able to exist for ever, so to speak, without other governing
forces than gravitation, when the ring is less than 21 kilometres in thickness ('), with an external radius
of 135,100 kilometres.

Some astronomers, however, appear to be beginning to doubt this hypothesis.

HERMAN STROVE, after having proved that their total mass is certainly less than VasTao °f l'iat c
Saturn(2), says that these rings appear to be composed solely of an "immaterial light", mere dust-films
or wreaths of mist.

(') RUSSELL, Astrophys. Journ , vol. XXVII, 1908, p. 233.

(2) Publications de 1'Observatoire Central Nicolas, se>ie II, t. XI, 1898, p. 232; and YOUNG, General Astronomy, p- 3!
Boston, 1900.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 655

Dr. BARNARD, after his examination, in 1907, of the illumination of the dark side of Saturn's rings,
,uggests the explanation(') that the rings are auto-luminous; but he rejects the idea by conjecturing that
mch a hypothesis would not be compatible with the presumed physical composition of the rings.

I think it will be quite possible to satisfy all the results of the observations hitherto made of these
•ings by a hypothesis entirely different from the above-mentioned meteoric theory.

On p. 613 of the present volume, I have described some experiments that have served as a starting-
joint for an explanation of the zodiacal light.

Round a highly magnetic globe, 8 cm. in diameter, in a vacuum-tube with a capacity of 70 litres,
have produced a ring with a diameter of up to 34 cm., and long luminous rays in the polar regions
if the globe, the whole bearing a considerable resemblance to pictures of the sun during an eclipse.

Now if the discharge-current, which in the above experiment was from 10 to 30 milliamperes, be
educed to i milliampere or less, the polar phenomena cease, and the ring becomes exceedingly thin
nd sometimes assumes an appearance almost exactly like that of Saturn's rings.

Round the magnetic equator of the globe, and touching it, a luminous zone appears, then a dark
pace, which, farther from the globe, is gradually formed into a flat, dimly-luminous ring resembling the
rape ring of Saturn. This dimly-luminous ring farther away increases in strength and a light-ring
ippears.

Fig. 245.

Fig. 245, i shows the rings from the side, and fig. 245, 2 a little from above, thus making the
ark space between the globe and the ring distinctly visible. Fig. 245, 3 shows, in addition to a brightly
iminous ring, a fainter ring outside the former, and separated from it by a dark division that might
nswer to CASSINI'S division in Saturn's ring. Fig. 235 shows that by a special arrangement it has
een possible to get as many as 5 rings, one outside another, round the globe. In this case, however,
ic rings are not flat, as the outer ones are in the form of cylinders, which increase in height with
icir distance from the globe. When the magnetisable globe is not magnetic, but is still a cathode, it is
ften seen surrounded by several luminous spherical envelopes. It is perhaps these that, when the globe
; magnetised, become changed in shape and flattened.

How are the phenomena of Saturn's rings to be explained, supposing the rings to be due to
imilar electric radiation from the planet, the latter being considered to be magnetic?

With regard to physical investigations of the power of an electrically luminous gas, and of radiant
latter, to absorb and diffuse solar light, we have mentioned some few known facts on page 623, to
/hich the reader is again referred.

I think there are also here good reasons for admitting that in the radiant matter which we suppose
> have been radiated by Saturn, there is a comparatively very great number of electrons of dispersion,

(') Astrophys. Journ., vol. XVII, 1908, p. 39.

656 B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

which may serve as receivers and resonators of luminous waves coming from the sun, and that here too
it is quite possible that the number of electrons of dispersion is proportional to the intensity of the
electric current emanating from Saturn in the manner admitted by us.

An electric radiation from Saturn such as that here assumed may certainly also be imagined to be
accompanied secondarily by an ejection of tiny material particles resembling what CROOKES has called
electric evaporation or volatilisation from a cathode.

A metallic cathode is so disintegrated during discharges that the material may be deposited in the
form of a reflecting layer upon the neighbouring glass wall.

Different metals disintegrate in very different degrees when they form a cathode, circumstances
being equal.

In arbitrary units, CROOKES (J) gives the loss of weight by disintegration in cold cathodes as follows:

Pd Au Ag Pb Sn Pt Cu Cd Ni Ir Fe Al Mg

108 100 83 75 57 45 40 32 ii 10 6 o o

For incandescent cathodes it is a different matter altogether; the disintegration is then much gr(.
Under the influence of magnetic forces too, there is a great difference in the amount of the disintegration.
I have, for instance, shown that in such a case even a cathode of aluminium can in a short time tl;
off a reflecting deposit upon an adjacent glass wall (C. R., Feb. 21, 1898). The disintegration from
a carbon cathode is very great. From one such, in a large exhausted vacuum-tube, I have seen half a
gramme of matter thrown off in a few minutes and deposited firmly on the glass wall of the tube.

The cause of this cathodic disintegration has not yet been clearly determined. It is possibly to
some extent a kind of evaporation by which the disintegration is brought about, by the high temperature
that the rapid positive ions (channel rays) produce where they strike the surface of the cathode. The
dependence of the disintegration on the strength of the current and of the cathode-fall is in accordance
with this explanation; for with the same duration of current, the cathode's loss of weight by disintegration
is proportional to the product of the strength of the current and the potential-fall from the cathode. But
this product equals the electric work performed upon the positive ions between the negative column <>t
light and the surface of the cathode, that is to say, proportional to the kinetic energy carried by th-
positive ions in the time-unit to the cathode.

This phenomenon of disintegration seems to offer a very important field for future investigation,
for an accurate knowledge of these things is of fundamental importance for the theories here propounded.

HOLBORN and AUSTIN (2) have made some very interesting experiments on the amount of disinte-
gration of cathodes of different metals under similar electrical conditions. When the tube used was
filled with air, they found that y, the loss of weight in 30 minutes from circular cathodes i cm. in
diameter could for platinum, silver (one sample), copper and nickel, be represented by the formula

^
y = 0.0016 —(V— 495)

for silver (another sample), bismuth, palladium, antimony and rhodium, the relation was

y = 0.0018 —(V— 495)

V is the cathode fall of potential in volts, A the atomic weight of the metal, and n its valency. Other
metals such as iron, aluminium and magnesium, do not follow either of these laws. For those metals
which follow the laws (i) or (2) we see that with the same current and cathode fall, the weight of

f1) See WINKELMANN, Handbuch der Physik, 2. Aufl., b. 4, p. 629.

(2) See J. J. THOMSON, Conduction of Electricity through Gases, p. 549.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 657

ithode disintegrated is proportional to the weight of those metals which would be deposited in volta-
eters placed in series with the discharge-tube.

GOLDSTEIN (') has discovered that when channel rays come in contact with a metal, they cause it
disintegrate. If, for instance, channel rays are allowed to fall upon a gold mirror deposit on plate-
ass, the gold disappears from the place where the most intense rays strike, so that in a short time
e sheet of glass becomes transparent again. Silver and nickel also disintegrate very quickly, alumi-
um less so.

According to GOLDSTEIN, cathode-rays also have the power to disintegrate metal plates, but in a
uch smaller degree than channel rays.

The above-mentioned disintegration from a cathode is in all probability closely connected with this
ghly disintegrating effect of channel rays.

It appears that all metals that undergo great disintegration when employed as cathodes, are also
sintegrated in a high degree when under the influence of channel rays. That the velocity of the metal
irticles flying out from the cathode must be considerable has been shown by KAEMPF by means of
otical investigations of double refraction by a metal mirror, produced by electric disintegration. According
i Kaempf, the particles expelled from the cathode are de-formed and brought into tension on striking
te mirror-surface.

Up to the present, the fact of an electric or magnetic deflection of the metal particles expelled from

!cold cathode has not been established. It is interesting, in this connection, to know that it has been
and that a great emission of positive ions from incandescent solid bodies is frequently accompanied by
; distinctly appreciable loss of weight in the emitting bodies.

I have myself of late made some experiments which give promise of throwing light upon the
i cstion of the electric charging of the metal particles thrown off from a cathode.

The difficulty in these experiments is that if a vacuum-tube is introduced into a very strong magnetic
fid (as is here necessary), in such a manner that the direction of the discharge-current is perpendicular
t the lines of force, the character of the discharge is changed, the discharge-current being thrown to
ce side and concentrated in a narrow path.

It is a different matter altogether when the vacuum-tube is placed axially in relation to the
rignetic field.

The character of the discharge- current is then altered, it is true, as the cathode emits the so-called
ngneto-cathode rays; but, as I have already shown, under these circumstances the disintegration of the
chode is very great, and the discharge-current often seems to flow with normal density through the
etire cross-section of the vacuum-tube.

I arranged my experiments in a manner very similar to that in which I first discovered these
ngneto-cathode rays(2).

A cylindrical vacuum-tube had a cathode in the form of a cross 18 mm. from the bottom of the
t >e, which was a plane sheet of plate-glass cemented upon it. The cross was cut out of a thin sheet
c palladium, its surface being parallel with the sheet of glass. The anode was circular, and was placed
snmetrically round the axis of the tube about 10 cm. behind the cathode.

The vacuum-tube was placed axially in front of a powerful cylindrical electro-magnet, in such a
n nner that the sheet of plate-glass at the bottom of the tube was close to the end-surface of the
n gnet.

') See E. GEHRCKE, Die Strahlen der posiliven Elektrizilat, p. 69. Leipzig, 1909.
-) See Archives cles Sciences Phys. et Nat. Geneve, June, 1896, p. 506.

658 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

When the magnet was in operation during the discharge, a luminous column of magneto-cathode
rays, cruciform in section, was sent out towards the sheet of glass, where it formed a reduced represen-
tation of the cross.

The question that interested me here, however, was how the metal corpuscles expelled from the
palladium cross would be deposited.

It appeared that if the cathode were cold, the discharge-current being kept small, a light cross
upon a darker ground was thrown upon the sheet of glass at the bottom of the tube. There was very
little deposit upon the sheet of glass where the column of light with cruciform section had heated the
glass, while beyond this there was the normal deposit of palladium.

The whole thing was different when we employed up to 30 milliamperes and more per square
centimetre of the entire surface of the cathode, which thereby became highly incandescent.

After the experiment, which lasted about one minute, there was an intensely metallic cruciform
deposit where the column of light had struck the glass, a cross of reduced size, opaque and shining
while outside it was a dark, semi-transparent, normal palladium-deposit.

In addition to this normal deposit upon the plane sheet of glass, there was a strongly-marked
ring of evenly dark deposit upon the cylindrical surface of the vacuum-tube, nearest the cathode-cross.

There were thus distinctly two kinds of metal corpuscles ejected by the cathode, first the normal
corpuscles that seem to be expelled from the cathode without being influenced to any great extent,
either by electric or magnetic forces; and secondly a kind of corpuscle that accompanies the magneto-
cathode rays, and these corpuscles are capable of attaching themselves to the glass wall, provided the
velocity with which they reach it is sufficiently great.

This circumstance may possibly favour RIGHI'S idea that these magneto-cathode rays consist of almost
neutral "double stars" of positive and negative ions, expelled in exactly the direction of the magnetic
lines of force, thus possibly a combination of a negative electron with a positive metal ion, which, under
certain circumstances, can be deposited and form a metallic coating upon the glass wall of the vacuum-tube.

I then went on to find out whether I could discover any twisting of this cruciform metallic deposit,
such as I have proved in the case of a cross of cathode-rays under similar circumstances (see the pre-
viously-mentioned paper in Archives des Sciences Phys. et Nat.). These crosses of cathode-rays turn
clockwise when a magnetic north pole is employed and the cross looked at from the pole. We can
thus find out whether the metal corpuscles in the cruciform deposit were negatively or positively charged,
by noting the direction in which the cross was eventually turned.

It soon appeared that the twisting was at any rate too small to be demonstrated directly by these
experiments. The experiment was therefore modified by forming the cathode as a plane, long rectangle
of thin palladium, which .was attached in such a manner that it stood edgewise upon the sheet of glass,
with its long side parallel to it.

The intention with this arrangement was to obtain a sharp linear deposit where the magneto-
cathode rays came in contact with the glass.

The experiment was carried out at first with a south pole in front of the sheet of glass, and then,
at the same distance, a north pole, while the discharge was going on evenly all the time.

Neither was it possible, however, in this way to obtain a double turning-angle of measurable size,
perhaps because the deposit-lines were not particularly sharp.

Photographs of the cruciform and linear deposits are here reproduced, from three experiments in fig. 246.

In the first and second experiments 15 milliamperes was used in the discharge and 10 amperes
the magnet. In the third the discharge-current was the same, but the current to the magnet was first,
22 amperes in one direction, during one minute, and then in the reverse-direction for one minute, sc
that the pole before the cathode changed from S. to N.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 659

In the course of these experiments, however, my attention was directed more and more towards
he normal metal deposit which wcas thrown with special abundance and evenness upon the cylindrical
heet of glass, right in front of, and nearest to, the strip of palladium.

It seems as if it might be worth while to experiment with a mica shade with a slit in it, placed
Imost over the palladium-sheet, to see whether any deflection of the corpuscles could be demonstrated
i this way. The corpuscles moved here almost at right angles to the magnetic lines of force, therefore
chances of a deflection were very much greater than in the above-mentioned investigations. I shall
eturn to these experiments in a subsequent article.

Now even if corpuscle-rays were so stiff that we could only bend them slightly with our strongest
lagnets, a planet with a magnetic moment such as, for instance, that of the earth, would easily compel
uch rays, emitted from equatorial regions, always to move near the plane of the planet's magnetic equator.

It has been shown that the material particles that are thrown off from a magnetised globe that is
athode in a vacuum-tube, are thrown off by preference near the plane of its magnetic equator like the
Icctric rays. This can be seen upon a sheet of glass placed near the globe, the glass being blackened
i such a manner as to make it improbable that any mere evaporation can produce the disintegration.

It is my opinion therefore, that in analogy with this, Saturn throws off tons of matter every day
i the plane of the rings, and that it did so to a still greater extent formerly. The rings are renewed,
o to speak, every moment. I have indeed gone so far in my hypothesis -- as my notes to Comptes
lendus de 1' Academic des Sciences show (J)— as to assume that the moons were originally formed from
uch electrically ejected matter, just as the planets from matter electrically thrown off from the sun.

Whether Saturn's rings consist of radiant matter or of electrically ejected material particles, they
.-ill certainly diffuse and absorb the light of the sun, and thus give rise to light-effects and shadow-
>rmations similar to those now observed. Even if the ring consisted only of electrically luminescent
aseous atoms, there is reason to suppose, as shown above on p. 523, that it would cast a shadow.

I would especially refer the reader to the observations at Kaafjord, where it must be assumed that
ic rapidly-changing cloud-formations were not real, ordinary clouds, but were electrically luminescent
iry masses that had the power of reflecting and absorbing solar light, and thus had the appearance of clouds.

Auroral arcs, observed at night, have been seen after daybreak as arches of cloud ; and it is
ossible that this is a corresponding phenomenon.

My explanation of Saturn's rings may also be looked upon as an extension of MAXWELL'S theory,
n attempt to indicate the manner in which the fine cosmic dust in the ring has formed round Saturn.

By spectroscopic examination of Saturn's ring, KEELER^), as is known, has shown that the various
arts of the rings rotate in accordance with Kepler's third law. These results can be made to agree

I1) Comptes Rendus, 7 aout 1911: Les anneaux de Saturne sont-ils dus a line radiation electrique de la planete?

C. R., 21 aout 1911: Le soleil et ses laches.

C. R., 4 septembre 1911: Sur la constitution electrique du soleil.

C. R., 13 novembre 1911: Phenomenes celestes et analogies experimentales.
('•I Astrophys. Journ., vol. I, 1895, p. 416.

66o

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

with our hypothesis, if the very natural assumption be allowed, that the small particles, molecules
gaseous or vaporous atoms thrown off, separated by comparatively great distances from one another
have come in the course of time to perform their mean rotation about the planet in obedience to Kepler's
law. We return to this question further on.

If, after all, future investigation should confirm BARNARD'S previously-mentioned suggestion that the
rings are auto-luminous, it would probably in a great degree strengthen the electrical theory here brought
forward of the genesis of Saturn's rings.

It appears that of late other scientists have also felt unconvinced of the correctness of MAXWELI'S
purely mechanical view of the nature of Saturn's rings. My colleague, M. GUILLAUME at Meudon, writes
in a letter to me:

"On the subject of Saturn's ring, I draw your attention to an interesting publication by Mr. A;
SCHMIDT, the most distinguished meteorologist of Stuttgart, who, on the basis of the extreme thinness of
the ring, puts forward the idea of a directing force, and he found this force, as a suggestion in a mag-
netic field centred on the axis of the planet, and acting on diamagnetic matter. You will understand
what value there may be in a quotation of this anteriority to which, however, Mr. SCHMIDT attaches
importance only as a preposterous hypothesis".

CHAPTER VI.
ON POSSIBLE ELECTRIC PHENOMENA IN SOLAR SYSTEMS AND NEBULAE.

128. The Sun. The series of experiments that I have made with a magnetic globe as cathode in
a,arge vacuum-box, for the purpose of studying analogies to the zodiacal light and Saturn's ring, have
k to discoveries that appear to be of great importance for the solar theory.

We have already several times had occasion to give various particulars regarding the manner in
\\ ch these experiments were carried out. It is by powerful magnetisation of the magnetisable globe
trt the phenomenon answering to Saturn's rings is produced. During this process, polar radiation and
di'uptive discharges at the equator such as that shown in fig. 2473 (which happens to be a unipolar
di'harge) may also occur, if the current intensity of discharge is great. If the magnetisation of the globe

a Fig. 247. b

be -educed (or the tension of the discharge increased) gradually, the luminous ring round the globe will
be reduced to a minimum size, after which another equatorial ring is developed and expands rapidly
Hi; 247 b). It has been possible for the ring to develope in such a manner that it could easily be de-
incstrated by radiation on the most distant wall of my large vacuum-tube (see fig. 217). The correspond-
in; ring would then have a diameter of 70 cm., while the diameter of the globe was 8 cm.

It is a corresponding primary ring of radiant matter about the sun that in my opinion can give
an efficient explanation of the various zodiacal light-phenomena. In the above-mentioned experiments,
it seen how the rays from the polar regions bend down in a simple curve about the equatorial plane
of ic globe, to continue their course outwards from the globe in the vicinity of this plane. An aureole
is ^reby produced about the magnetic globe, with ray-structure at the poles, the whole thing strongly
resnbling pictures of the sun's corona.

Rarefied gases, rendered luminous by similar discharges from the sun, would first emit a light of
the own, and then diffuse that of the sun.

It is well known that the spectrum of the corona contains above all a brilliant ray of coronium
/. =5304, and besides this there is a faint continuous spectrum, probably due to reflected solar light.

If the sun's corona is of an electric origin such as we have here assumed, we might perhaps
ex] ct to see an enormous ring of light about the sun every time the earth, during an eclipse of the

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903. 84

662

BIKKKLAND. THK NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

b/J
U.

sun, stood very nearly in the plane of the sun's equator. This would
have to be upon the assumption that in the spaces far from the sun
there is a gas that can become electrically luminescent, or, in an electric state
able to reflect sunlight.

It is possible to believe, however, that the sun's chromosphere, which
is a sharply-defined envelope of hydrogen, is again surrounded by an
envelope of coronium, of almost limitless extent.

Analogies from the earth's atmosphere, whose nature has been mail-
clearer through the latest researches of HANN, HUMPHREY (') and WEGKXKK,
seem at any rate to indicate that the above-mentioned assumpti<
probable.

Wegener has recently (2) shown that there must be new fundamental
layer-limits in the earth's atmosphere. Above a covering of hydn
which prevails from a height of 75 to 200 kilometres, a new gas is tn
be found, which he calls geocoronium, extending up to such heights that
the steady auroral arcs, for instance, that are observed as much as 600
kilometres above the earth, would be due to electric luminescence in
this gas.

129. We will now pass on to experiments that in my opinion have
brought about the most important discoveries in the long chain of exp
mental analogies to terrestrial and cosmic phenomena that I have produced.
In the experiments represented in figs. 248 a — e, there are some small
patches on the globe, which are due to a kind of discharge that, under
ordinary circumstances, is disruptive, and which radiates from points on
the cathode. If the globe has a smooth surface and is not magm \
the disruptive discharges come rapidly one after another, and are distril-
more or less uniformly all over the globe (see a). On the other hand,
if the globe is magnetised, even very slightly, the patches from which the
disruptive discharges issue, arrange themselves then in two zones parallel
with the magnetic equator of the globe; and the more powerfully the globe
is magnetised, the nearer do they come to the equator (see b, c, d|. With a
constant magnetisation, the zones of patches will be found near the equator
if the discharge-tension is low, but far from the equator if the tension is high.
Fig. 248 e shows the phenomenon seen from below.
If the pressure of the gas is very small during these discharges,
there issues (fig. 249, globe not magnetised) from each of the patches
narrow pencil of cathode-rays so intense that the gas is illuminated all
along the pencil up to the wall of the tube. This splendid phenomenon
recalls our hypothesis according to which sun-spots sometimes send out
into space long pencils of cathode-rays.

SCHUSTER has recently (3) made some serious objections to the hypo-
thesis that sun-spots emit direct, rather well-defined pencils of cathode-rays, a hypothesis which was put
forward by me in 1899 and 1900, and by MOUNDER in 1904.

(') HUMPHREY, Distribution of Gases in the Atmosphere. Bull, of the Mount Wealher Observatory, II, 2.
(3) WEGENER, Zeitschrift fiir anorganische Chemie, B. 75, p. 107. 1913.
(3) The Origin of Magnetic Storms. Proc. of Roy. Soc., 1911.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 663

Schuster considers that the velocity of such cathode-particles, as they sweep past the earth, is
•duced to about nine kilometres per second, and that the passage between the sun and the earth would
ke about a year, so that the magnetic effects of such rays could not reproduce, even roughly, the
laracteristic features of a magnetic disturbance.

He does, it is true, say at the conclusion of his paper:

"It is otherwise with the more refined form in which the theory has been presented by Prof,
rkeland, who, qualitatively at any rate, has shown that an agreement might be reached, if we can
lagine the particles to be drawn in towards the earth by its magnetic forces, so that for the time being
eir motion is regulated by the position of the earth's magnetic poles. Nevertheless, the argument from
u-rgy and from electrostatic considerations alike, has now been shown to be fatal to the theory in
.iy form".

I do not think, however, that Schuster's objections have any serious bearing on my theory, if we
i nsider the properties which the new sunbeams must be assumed to possess.

1 have shown that cathode-rays from the sun, which are to strike down towards the earth in the
: rora polaris zones, must have a transversal mass about m = 1.83 X io3 X m0. In other words, the

I li^itudinal mass of our particles is 6 milliard times greater than the mass of the particles upon which
.'•huster calculates in his energy-comments. Thus these cathode-rays will pass the earth, not with a
'Incity of 9 kilometres, but with a velocity very little short of that of light.

In his further development, Schuster shows that ordinary cathode-rays that issued from the sun in
Swell-defined, narrow pencil, would instantly be dispersed; for the electrostatic repulsion to which a

I 1 tide near the limits of the pencil would be subjected from the other particles in the pencil of rays,
i mid, according to Schuster's calculation, impart to an electron an acceleration so great that in the very
I st second it would fly over a distance of astronomic magnitude.

If the calculation is applied to our rays, this acceleration would have to be divided by 3.3 millions,
lit even with such an acceleration, an electron would move to a great distance in the 500 seconds that
.'ray with the velocity of light takes in passing from the sun to the earth.

There is still, however, another point of great importance to be considered, and that is that in my
t mry the magnetic storms on the earth are not caused by a great, more or less cylindrical pencil of
i i-s at a great distance from the earth, but generally a small, fine pencil of rays is drawn in in an arc
c wn to a minimum distance of from 200 to 300 km. from the earth in the aurora polaris zones. These
i drawn pencils of rays act partly directly over the earth, partly indirectly by the earth-currents which
t _-\' induce.

Let us return to our experiments. If the globe is

Jghtly magnetised, the patches of eruption are seen to
"ange themselves in zones, with long pencils issuing into
pace, almost as in fig. 249; only these pencils are bent
I the magnetism, which is exactly analogous to what we
1 ve assumed regarding the cathode-rays issuing from
t • sun.

These centres of eruption for the disruptive discharges
more marked by the addition of some Leyden jars
I rallel to the discharge-tube; but care must be taken not
t add too much capacity, as the discharge may then be-
cme oscillatory. I have generally employed about io to

: milliamperes as the discharge-current for the globe of Fig. 349.

(•centimetres diameter.

664

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

If the metallic globe surrounding the electro-magnet is not smooth, but has sharp points on its
surface, for instance near the poles, the disruptive discharges would issue at these points, and it will )>,.
necessary to use a stronger magnetisation to make the patches arrange themselves in zones round the equator
From the results obtained by SWABE, WOLF, CARRINGTON and SPOERER, we know that the sun-spots
arrange themselves just in two zones between 5° and 40° N and S latitude, in such a manner that in
the minimum-period of the spots, they begin to show themselves in high latitudes, and then descend until
at their maximum-period they have reached a latitude of about 16° north and south. If we remember
especially that the spots are the centres of emission of very stiff' cathode-rays (Ho =3 X io"C. G. S.), which

give rise to auroras and magnetic perturbations on our earth, it would appear
as if the sun-spots were the foot-points of disruptive electric discharges from tlv
sun. The possible depressions in the enveloping photosphere by the sun
which many astronomers believe to exist, can be easily explained by rel-
to an experiment with discharges from a quicksilver cathode in a vacuum-tube
(see fig. 201. Winkelmann's Handbuch der Physik, 4, p. 530). The pressure-
that the discharge here exerts upon the surface is probably proportional to the
energy of the discharge, which, as we shall see, must be enormous in tin
of the sun.

If the pressure of the gas increases, the pencils of rays no lon^t T
radially from the globe, as in fig. 249, but the disruptive discharges an

seen to manifest themselves in the shape of a star with four or five arms (see fig. 250), coming from an
eruptive spot, and almost following the surface of the non-magnetic globe, to meet often at a point on
the globe diametrically opposite.

Fig. 250.

Fig. 251.

These discharges from opposite points (this is not clearly seen in fig. 250, however) brought to my
mind a very strange picture of some enormous eruptions on the Sun (see fig. 251), reproduced from
"Marvels of the Universe". On June 26th, 1885, M. TROUVELOT saw two huge prominences, each more
than three hundred and fifty thousand miles in height, rising from the sun. Flames of such dimensions
are exceedingly rare; it is therefore all the more significant that they rose exactly opposite to each othti
from the ends of the same diameter.

It almost always happens too, in the experiment in which the cathode-globe is magnetised, that
there are two or three luminous branches turning in a spiral about the eruptive spot and near the stir-
face of the globe. These vortices move in the opposite direction to that of the hands of a watch on
the hemisphere containing the magnetic north pole, and in the same direction on the opposite hemisphere.

This corresponds exactly with the results recently obtained by HALE, ELLERMAN, and Fox relative
to vortices in the hydrogen filaments and calcium vapour round a sun-spot, provided it is admitted, as 1
have found, that the sun and the earth are inversely magnetised (Comptes Rendus, Jan. 22, 1910).

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 665

These vortices round the spots on the magnetic globe, I have not succeeded in photographing with
he present arrangements. On account of the importance of all these phenomena, however, I have constructed
. vacuum-vessel of 320 litres' capacity, and can employ a magnetic globe with a diameter of 24 centimetres.
.Vith this new apparatus, I have succeeded in obtaining good photographs, which will be mentioned below.

The discharges of the cathode-globe are partly continual discharges all over the surface, and partly
lisruptive at intervals; in the latter case they issue from the eruptive spots.

Fig. 253 shows how a branch of discharge issuing from the spots sometimes follows the magnetic
ines of force in the neighbourhood of the equator, giving rise to a phenomenon which greatly resembles
he black filaments on the sun, studied by HALE, ELLERMAN, Fox, EVERSHED, DESLANDRES and D'AZAMBUJA.

It will be of considerable interest to compare this experiment with some photographs of quiescent
trominences on the sun. Fig. 252 is a reproduction of one of Prof. MALE'S earliest prominence photo-
;raphs taken at KENWOOD'S Observatory. I have unfortunately no data to enable me to decide whether
his prominence follows more or less the lines of magnetic force on the sun.

I have sought by various methods to find
value for the very singular capacity of this globe
in-responding to disruptive discharges, a capacity
/liich seems to vary perceptibly according to the
onditions of the discharge. In the case of this
;lube (8 cm. in diameter), this capacity varies
,bout ,J0 of a microfarad, and if I assume that
he sun has a corresponding capacity C in the
elation of the square of the diameters, I find that
" = 3 X io18 microfarads.

In calculating the tension of the solar dis-
harges according to the value HQ = 3 X io"C.G.S.
u-c M. Abraham, Theorie der Klektrizitat, B. II,
i. 183, equation (120 bis)), I find that £=6.4 X ios

"Its. The energy J/2 £2C =--• 5.9X1 o30 ergs, transformed into heat, will be sufficient to heat to 175° C.
globe of iron the size of the earth.

Sun-spots may be considered as the eruptive centres of similar disruptive discharges, and the
uestion then immediately arises: Where shall we seek for the positive pole of these discharges, in
.•hich the spots, or that which surrounds them, represent the cathode?

There are several possible solutions to this question.

In the first place, it might be imagined that the interior of the sun formed the positive pole for
normous electric currents, while perhaps the faculae, in particular, round the spots, formed the negative
•oles. Or it might be imagined that the positive poles for the discharges were to be found outside the
hotosphere, for instance in the sun's corona, the primary cause of the discharge being the driving away
f negative ions from the outermost layers of the sun's atmosphere in some way or other — for instance,
s ARRHENIUS has assumed, by light-pressure after condensation of matter round them. Finally, it might
>e assumed — and this, according to the experimental analogies, seems the most probable assumption —
iat the sun, in relation to space, has an enormous negative electric tension of about 600 million volts.

The first assumption has the advantage of appearing to give a natural explanation of the move-
lent of the sun-spots in various latitudes, provided that the sun's magnetisation is the opposite to that
'f the earth.

666 BIRKKLAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

In this case the origin of the sun-spots must be that the presumptive more or less insulating
photospheric envelope was sometimes pierced by disruptive discharges, thus forming great electric arcs.
That the tension necessary to pierce the photosphere would be very great would not be surprising
this alone being sufficient to explain the very great rigidity of the cathode-rays emitted.

The temperature of the spots should, upon this hypothesis, be very high. This, it is said, does
not seem to be well confirmed by the measurements; but the temperature of a spot cannot be measured
by STEFAN'S law, because under high degrees of dispersion the spectrum of the spots is not continuous;
it contains nothing but lines.

It may be imagined that under the action of these violent arcs the photosphere tends to
more insulating (thicker?), and that after the maximum of the spots, the discharges cannot penetrate the
photosphere as easily as after a certain cooling by radiation. The discharges then begin again in higl;
latitudes as long as the necessary tension is at its maximum.

We do not know sufficiently how electric arcs move in gases, but it is at any rate not difficult, b
magnetic forces, to attain a transversal velocity of 200 metres per second for an electric arc in air.

In order to be able to some extent to form an estimate of the manner in which the a
electric arcs in the sun would move, we ought to know how the sun's magnetism is distributed, 01
rather its cause. In my opinion it is the pencils of cathode rays appearing at indefinite intervals at tin-
outbreak and in the development of the sun-spots, that give rise to solar magnetism by creating almost
constant currents by induction in the conductive interior of the sun.

I have several times begun the calculations that should serve to verify my hypothesis, but t
not yet completed.

We know that the electric currents circulating in great spheres have a very great persistence (set
LORBERG, Crelles Journal, vol. 71, 1870, and LAMB, Phil. Trans., 1883). Lamb finds that in a copper

sphere of the size of the earth, the time necessary for a current to fall to of its initial value is ten

c

million years.

The induction impulses originating in the cathode-rays emitted at intervals from the sun, seem t<
be able, in the course of time, to create a perceptibly constant current.

In support of my calculations, I am making experiments with a rotating sphere made ot the x
softest magnetisable steel. The diameter of the sphere is 70 cm. The results of these investigations!
be included in the next volume.

If, to obtain a clearer conception, we assume a circular current round the centre of the sun in th
plane of the equator, and with a radius equal to half the solar radius, it becomes easy to calculate
magnetic effects in different latitudes of the photosphere. In assuming spherical currents, we obtain th
same degree of conformity with the currents circulating much nearer the solar surface.

The table gives Fp divided by cos// for each ten degrees of latitude comprised between o° and 50'
where Fp is the component of the magnetic force in an arbitrary unit, the length of the meridian,
purposes of comparison, cos2,:? is given, which, according to FAYE, should be perceptibly proportional
to the variation of the angular diurnal motion of the spots.

/3 o° 10° 20° 30° 40° 50°

Fp sec/? 1.17 1. 10 0.88 0.69 0-54 0.41

Cos2/? i. oo 0.97 0.88 0.75 0.59 0.41

These figures have perhaps a certain interest, although, as we have said, we do not yi
well how electric arcs move in gases, under the action of magnetic forces.

The second assumption may indeed, from a physical point of view, be possible, but it is scared
probable that any process of this nature will play a decisive part in these phenomena. It would imply

PART II. POLAR MAGNETIC PHENOMENA AND TERRKU.A EXPERIMENTS. CHAP. VI.

667

jam

668 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

that the sun's nucleus received a positive charge, of which, it must be imagined, it would to some extent
gradually get rid in the interval between two outbreaks of sun-spots.

There is one circumstance that is perhaps in favour of this assumption, as also of the first, and
that is the peculiar capacity that the sun, in analogy with our magnetic globe, must have. It seems as
if an electric condensation must take place, so that the opposed masses of electricity are found as coatings
lying close to one another.

The third assumption seems the most natural when the matter as a whole, is looked at from the
point of view of the experimental analogies. It is then a question of the manner in which this net;,-1
charge on the surface of the sun has been produced in interaction with space. If to the negative
of electricity on the external surface of the sun, there are to some extent corresponding masses of |
live electricity in the interior of the sun, the first and third assumptions may be combined, which again
would allow of the mysterious movements of the sun spots in the various latitudes being explained
an electromagnetic action.

It must moreover be admitted, even in the third case only, that a magnetic influence on the in
ment of the sun-spots was to be expected, if, as has here been done, the arrangement of the sun-spots in
parallel rows, one on each side of the equator, is assumed to be the effect of the magnetic condii
The question then is whether it is possible, by an estimate, to show the probability of an explan
of the actual motion of the spots — in the third case as well —only as a magnetic influence. This ap[
to be difficult. It is true that the pencils of cathode rays that radiate from sun-spots in higher latitude
curve rapidly down towards the equator, thereby causing the component of the magnetic force at right
angles to the current-element to be comparatively much greater in the third case than assumed ir
first; but whether this can cause the magnetic retrograde motion eventually produced to be more marked
in the case of sun-spots in higher latitudes, than in that of spots in lower latitudes, is doubtful. The distri-
bution of the sun's magnetism may perhaps be rather different from what we assumed in the first
and thus a fairly good explanation could be given. At any rate, the rotation of the sun's body itself must
be greater than the apparent rotation of any sun-spot, and this really agrees with the actual circumstances

SPOERER'S discovery that groups of sun-spots are inclined to be drawn out in length in a din
along a parallel circle on the sun, so that the spots appearing last come to the west of those already
in existence, speaks most in favour of a combination of the first and third assumptions.

The same may be said of SECCHI'S discovery with regard to the characteristic leaps in the normal
rotation of a sun-spot, as the leaps usually take place in the direction of the rotation.

It is at present not easy to see how a negative tension should be continually created by the sun
in relation to space.

It is of course possible to imagine that a surplus of positive ions is always being carried away
from the sun or that negative ions are always being carried towards the sun, and that the negative
tension is produced in this manner; and that the balance is maintained to some extent by distinct dis-
ruptive discharges, as we have presupposed.

It seems a natural thing, however, to connect the creation of this tension with the sun's radiatior
of light and heat. But as MAXWELL'S electro-magnetic light theory at present stands, there is no dired
opportunity of assuming that light-energy is carried over into electric energy, and that for that reasoi
the rays of light are absorbed into space.

It is thought by several that Maxwell's equations require a correcting term. Such a term would
perhaps have influence just when there was question of a disturbance that spread into infinite space.

RIEMANN'S discoveries in the transition from infinitely small to finite amplitudes in sound-waves,
might possibly afford some information.

TAUT II. POLAR MAG.NKIIC PHENOMENA AND TtRKKLLA KXPKRIMKNTS. CHAP. VI.

669

Fig. 255.
Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903.

85

670 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1 QO2 — 1903.

The idea of an unknown transformation, in space, of radiant light and heat from the sun into
another form of energy, seems to have occurred recently to other scientists.

In a paper, just published, by JULIUS, on the results from the "Netherlands Eclipse Expedition
I9i2",(1) the following conclusion is found:

"Less than j~^ of the total (ultra-violet, visible, and infra-red) solar radiation proceeds from thi><r
parts of the celestial body which lie outside the photospheric level.

"This result proves that it is impossible to maintain the theory which considers the photosphere to
be a layer of incandescent clouds, whose decrease of luminosity from the centre toward the limb of the
solar disk would be caused by absorption and diffusion of light in an enveloping atmosphere ("the dusky
veil"). For if this theory were right, then, according to the calculations made by PICKERING, Wn.sn\
SCHUSTER, VOGEL, SEELIGER and other astrophysicists, such an atmosphere should absorb an important
fraction (f to ^) of the sun's radiation. Now, as the fraction emitted appears to be smaller than —
yet the atmosphere must be in a stationary condition, one would be forced to conclude that the main
part of the absorbed energy is continually being dissipated through space in some absolutely un<>;
form. This necessary inference not being acceptable, we must look for another interpretation of the
photosphere."

However this may be, it would be very interesting if the energy of the light and heat
could to some extent return to the sun from space. The electric rays possibly reach as far out a
light rays, or at any rate exceedingly far, and the greater part of the energy in an electric discharge
such as this may gather at the cathode, i. e. on the surface of the sun, where the electric arcs in
turn would create new heat for the radiation of more light.

In this way the age of the sun, which HELMHOLTZ and KELVIN, according to the mechanii
theory, put at not more than 50 million years, may perhaps be put at so many hundred million y
as geologists, after researches on the earth, absolutely require. There are doubtless other sour
reservoirs of energy than those with which we are now acquainted. HELMHOLTZ was not acquainted
with radium, for instance, which has of late been made use of to make the sun old enough.

129. It will be immediately apparent what far-reaching consequences are here built upon our
experimental analogies. There seems to be a constantly increasing appreciation of the fruitfulness of tru
method established by the representation of such analogies for the study of celestial phenomena.

In 1860, HUGGINS made a laboratory, where numerous physical experiments were made for the
interpretation of astronomical observations. The advantage of imitating the celestial phenomena in labora-
tory experiments, a method which forms exactly the base of the present studies, was thus known and
appreciated half a century ago. The method has been followed by many, and has of late yielded marvellous
results, HALE having discovered the existence of powerful magnetic forces in the solar vortices, and
DESLANDRES having in this way made some very interesting experiments on the solar corona.

The important phenomena, which I have discovered, of disruptive discharges from points on a mag-
netic cathode-globe, have especially occupied my attention.

In order to investigate closely the electric analogies to the vortex-formation about the sun-spots,
and to study the wonderful capacity that the globe seems to have in these disruptive discharges, I have
recently resumed the whole of my experimental series with an entirely new arrangement, in which a
magnetic cathode-globe of 24 cm. diameter could be employed.

I will here only give a schematic description of these experiments, of which good photographic
reproductions are found below.

(') Koninklijke Akademie van Wetenschappen te Amsterdam, May 23, 1912.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI.

671

Fig. 254 shows the whole arrangement with the new vacuum-box of 320 litres. Floor and ceiling
re here made of 12 mm. steel plates, the pillars between are of bronze, and the sheets of plate-glass
t the sides are 30 mm. in thickness.

The experiment shows the "zodiacal-light ring". It requires little magnetising of the globe (i 1.3 cm.
i diameter), but a great discharge-current (up to 100 tnilliamperes). Similar experiments are shown in
gures 255, i and 2. In the former the magnetic globe is only 2.5 cm. in diameter; but it was easy,
specially with greatly rarefied hydrogen gas in the box, to obtain a plane of rays about the globe that
nt all four glass walls in brightly phosphorescent, straight stripes from 5 to 10 millimetres wide.

It is easy to prove that the plane of rays is partly formed of rays from the upper hemisphere of
cathode, that are bent down towards the equator, and rays from the lower hemisphere that are bent

Fig. 256.

awards. It will without doubt be possible to produce, with a very small cathode-globe, a ring greater

proportion to the globe than is the real zodiacal-light ring in proportion to the sun, even if the latter

ng be assumed to go right outside the earth's orbit. It is only by careful adjustment of the magneti-

ition of the globe, however, that the ray-masses are made to coincide, so to speak, exactly in one plane.

In general, the ray-masses from above and from below intersect one another in the plane of the

juator; and it is easy to form round the circle of intersection a strongly luminous ring, floating in

>ace round the globe, and resembling a nimbus such as painters in olden times painted round the heads

' saints.

The intersecting groups of rays may often be found upon the glass walls in the form of two se-
irate parallel phosphorescent bands of light that can be moved to and fro by slight variation in
agnetisation. I believe I have seen these groups of rays twice form circles of intersection (node-

672

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

circles), when the magnetising was so arranged that the groups formed only a very small angle with
one another. It would thus appear that the rays move preferably above and below the plane of tin-
equator.

As the magnetisation is made stronger and stronger, the "node-line" in the form of a luminous
circle, will approach the cathode-globe, but suddenly the balance will be disturbed, and the phenomenon
will go over into a secondary ring— "Saturnian ring" — which only developes into full beauty with strong
magnetisation and small discharge-current, as represented in fig. 255, 3, where the cathode-globe is 24
centimetres in diameter. Applied to the sun, our experiments would imply that we must hen
a comparatively low magnetisation, but comparatively high electric radiation.

One can imagine that among the various kinds of cathode-rays that the sun can emit, then
especially a great many that will be brought by solar magnetism to move near the plane of the
magnetic equator, possibly bending alternately above and below it.

Fig. 257.

Fig. 256 shows phenomena with the large 24 cm. cathode-globe — a light that resemble^ the MIM'S
corona. (J)

Applied to Saturn (fig. 257), our experiments must lead us to infer that the quantity of rays emitted
by the planet was comparatively small, while the magnetisation was comparatively greater than that nl
the sun.

Our experiments with the large cathode-globe (see fig. 255, 3) show that if it is desired to ha\ <
ring very thin, it is better to go down to about V10 milliainpere; but in that case the light will also
faint. The ring looks now, however, quite as thick and distinct as with Vj0 milliampere and with one
of the small cathode-globes.

Let us now simply assume that the current issuing from Saturn is as many times greater t
Yio milliampere, as the radius of the planet is greater than that of our globe-cathode. This givi
about 50000 amperes from Saturn. Let us assume the tension to be 100 million volts. We then find

(') As all these figures show, the apparatus has been illuminated beforehand with ordinary light, and the experiments I
made and the electric light-phenomena photographed. In this way various reflexions appear in the figures thai have noth
to do with the phenomena, but they will not give rise to misunderstanding.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI.

673

tit the radiation from Saturn would answer to 5 milliard kilowatts. This is comparatively no great amount
( energy, for the lightning on our earth probably represents on an average from 4 to 5 milliard kilowatts.
This last figure I obtain in the following manner.

AKRHENIUS computes the amount af combined nitrogen falling upon the land-surface of the earth
36 million sq. km.) in the form of nitrate and nitrite of ammonia, at about 400 million tons per annum,
we take for granted that a comparatively similar amount also falls upon the sea, this gives us one
rt out of every three million of the nitrogen of the atmosphere as the amount that is thus combined
ery year, and this, we may say with practical certainty, almost exclusively by electric discharge.

Fig. a58.

Now as we know by experiment that by the most effective electric discharges 600 kg. of nitric
:id is formed by the air per kilowatt-year, we can calculate that the lightning that produces nitric acid
vpour in the atmosphere must at least answer to an average force-supply of 4 milliard kilowatts.

We will return to our experiments with the large cathode-globe in our 32o-litre vacuum-box, as
t- as the previously-mentioned disruptive point-discharges are concerned, these, it will be remembered,
1 ing compared with sun-spots.

It was soon evident that the quite smooth, silver-coated, large globe of 24 centimetres' diameter,
MS not by any means a success when it was a question of getting these negative point-discharges upon
i The smaller globes were much better, but it was apparent that the nature of their surface had much
t say in the matter. These experiments showed that with the smallest globe (2.5 cm. in diameter), it
MS easy to obtain, instead of the brief disruptive point-discharges, lengthy discharges from such points,
i ly provided there was a high vacuum, and that the current-strength of the discharge was great. These
{•ncil-discharges would suddenly change place, and arrange themselves near the equator like the earlier

674

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

spots. This possesses considerable interest, inasmuch as the sun-spots in reality represent phenomen
of long duration, and not brief discharges.

With the large, silver-coated globe, it was thus very difficult to obtain point-discharges when the
globe was cathode; they were pre-eminently continuous discharges from the entire surface or large por-
tions of it.

When, however, the globe is made the anode, and the metal walls of the box, which are compara-
tively rough, unpolished, cast or rolled plates, are the cathode, a perfect firework-display of point-
discharges takes place, in rapid succession, from the inner walls of the box. Not only were the p.,

Fig. 259.

luminous, but long pencils of rays passed from the points (almost like a kind of lightning) in to the
globe. Glowing metal particles were often torn from the points, especially from the steel plates, whence
particles shot inwards along the path of the current.

In fig. 258, only the foot-points are visible, for when the anode-globe was non-magnetic, the flashes
in towards the globe, though fairly powerful, were too brief and of too little intensity too be fixed upon
the photographic plate with the camera used. When, on the other hand, the anode-globe was magnetised,
the flashes became more intense (see fig. 259), and the points of discharge were congregated in the vicinity
of the magnetic poles of the globe. The discharge-rays gathered in two zones about the poles of t
anode-globe, as might be expected; but there also appeared a faint band of light, of which an indicatioi
may be seen, round the magnetic equator of the anode-globe.

In order to obtain point-discharges with my globe-cathode of 24 centimetres' diameter, 1 took 1
hemispherical shells of aluminium, and had them "sand-blasted" outside at a glass factory in the mann<
employed in the production of ground glass.

PART ii. POLAR MAGNETIC: PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. vi.

6?5

As soon as these shells were put on outside the silvered globe, I obtained point-discharges in great
umbers; but they were not so intense as I had expected, not even when a large condenser was placed
i parallel with the vacuum-tube. It was only after having exhausted my discharge-box for a long time
nd filled it with hydrogen, and again and again exhausted it, that these point-discharges began to be
owerful.

Figs. 260 a, b, and c show three photographs of discharges under varied conditions.

The first is of an experiment with a considerable gas-pressure and very slight magnetisation of the
lobe. It shows an interesting radiation from the polar regions, but the point-discharges, which, it is
uc, are most numerous in the equatorial regions, have not separated into two zones as they usually
Id when the surface of the cathode was smooth.

The third photograph is of an experiment in hydrogen gas with a very high vacuum.

The phenomena here were powerful and sometimes of a distinct duration, that is to say not
istantaneous discharges. Another interesting circumstance is that under the above-mentioned experimental

'

a be

Fig. 260

nnditions it was distinctly seen that the patches are not always single spots, but often consist of a group

• spots. For instance, on the original photograph answering to Fig. 260 c, the spot above to the right

distinctly a group of 5 separate spots. We thus have here another analogy to the sun-spot conditions.

As I have frequently mentioned, I have tried in vain to photograph the vortices that sometimes

i-velope into great beauty round the points of light in these point-discharges on the globe-cathode. I

ive said that the motion of these vortices is always counter-clockwise on the upper hemisphere, and

ockwise on the lower, supposing the globe to have been magnetised so as to have a magnetic north

,'lc in the upper hemisphere. In the reverse case, the conditions are of course reversed.

A chance occurrence has now enabled me to produce these vortices with much greater brilliancy
i an before. It was as follows. The vacuum-box was exhausted by a rotary mercury-pump (Gaede
:mp), with a rotary oil-pump in series, both pumps being worked by small electric motors that were
innected with the electric current system of the town. Sometimes, in cases of necessity, I left the pumps
orking while we were absent from the Institute.

On one occasion the tension was broken off, so that the motor stopped; and notwithstanding my
: lf-closing valves, the vaseline-oil from the oil-pump passed through the mercury-pump and into my
irge vacuum-box.

6y6

|;IKKI I. ANIL

>. Mil \OKWI.OIAN ATKOKA POLARIS I- X I'Kl >l I lo\, I 902 1903.

It required considerable labour to put everything into order again, but, after renewed pumpin" it
\vas found tliat a little nil trickled out on to the lloor of the box, thus showing that it had not all hi ,
removed.

After lining the ]>ox with hydrogen and emptying it several times, the point-discharges from th,
glol>e-cath»de were iniieh more marked than helore, being peculiarly intense, even without being coupled
to any external capacitv. The vacuum-box too, now happened to he so air-tight, that alter lettin0' it stand
untouched tor a week, it was impossible to detect the entrance ol anv foreign gas.

The most striking leature, ho\\revcr, of these point-discharges -which, as I have shown, have a
preference tor a hydrogen atmosphere was that the frequently-mentioned branches radiatinrr from tin-
point of light were so intense that thev could easily be photographed by the aid of a cinematographic
lens. It is evident that vapours from the vaseline-oil or decomposition gases here play a part.

\Ylien the cathode-globe was not magnetised, the light-tracery that appeared round the puint-dischariji-
resembled a many-armed starfish (fig. 261 a). On rare occasions it happened that the arms of light could

l-'i,-. 261.

be followed right round the globe, where they met at a point diametrically opposite to the point of discharge.

These meeting-points of the arms of light might also have the appearance of a faint point of discharge.
This calls to mind TKOUVKI.OT'S drawing, which is reproduced in fig. 251.

When the cathode-globe is magnetised with the north pole uppermost, the points of discharge move
near to the magnetic equator. The arms of light about these points still exist, but they have received
a twi-t so that the vortices created have a counter-clockwise motion on the upper hemisphere (fig. 261 l>).
and clockwise on the lower (fig. 261 c|. With a magnetised globe also, the light from a point of discharge
seemed to radiate and as it were meet in a diametrically opposite point on the globe; the light runs at
anv rate- right round the equatorial regions every time a point-discharge occurs. It is understood from
the direction of the twist, that the arms of light radiating from the points of discharge, and sometimes
encompassing the globe, are a iii'^ul'i'i' radiation and thus of the same kind as that which issues almost
perpendicularly from the globe (see fig. 219).

If, therefore, we take for granted that the sun and the earth are oppositely magnetised, as, for other
reasons, I have previously assumed (C. R., |an. 24, 1910), then, if the analogies are correct, negate'
electric radiation will give rise to the vortices round sun-spots, studied by MALI-: and KI.I.KKMAN.

PART II. POLAR MAGNETIC PHKNOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 677

In some spectrographic researches on prominences on the solar disc, Fox makes the following
tatement('): "Examination of all the Hn (hydrogen) plates and the record of earlier observed whirls in
lie calcium vapours results in assigning the direction as counter-clockwise in the northern hemisphere
nd clockwise in the southern. This is in agreement with the demands of FAYK'S theory."

In analogy with our experiments, these whirls should not be due to cyclones or whirlpools, as Faye
upposes, but to negative electric emission from certain centres of electric eruption. It should be remarked
lat as this electric emission is connected with calcium vapours and with hydrogen, it is to be expected
lat its velocity will not be nearly so great as that of light.

Owing to the good experimental results, which already give certain promise of the attainment of a fult
nderstanding of the two above-mentioned important phenomena — the vortex-formation and the apparenl
real capacity of the cathode-globe, — I have begun to construct a vacuum-vessel of 1000 litres' capacity, with
eiling and floor of bronze, and glass sides of 50 mm. thickness. There have proved to be disadvantages
i having the floor and ceiling magnetisable (of steel) and in their not b"eing far enough from the polar
arts of the large cathode-globe. The magnetic cathode-globe is to be 40 centimetres in diameter, for
ischarges of 500 milliamperes at 15000 volts, which is the maximum delivery of my machine (see fig. 67).
: will be easily understood that in addition to the purely scientific reasons for doing this, I have also a
econdary object, which is to give myself the pleasure of seeing all these important experiments in the
lost brilliant form that it is possible for me to give them.

131 The Worlds in the Universe. From the conceptions to which our experimental analogies
;acl us, it is possible to form, in a natural manner, an interesting theory of the origin of the worlds,
"his theory differs from all earlier theories in that it assumes the existence of a universal directing
tree of electro-magnetic origin in addition to the force of gravitation, in order to explain the formation
aund the sun of planets — which have almost circular orbits and are almost in the same plane — of moons
nd rings about the planets, and of spiral and annular nebulae. Even the newly-discovered, most distant
loons of Jupiter and Saturn, with their retrograde revolution, do not place the theory in any doubtful
ght; on the contrary, the discovery would seem to predict that if planets are still discovered round the
in sufficiently far outside Neptune, they might also have a retrograde revolution.

The fundamental assumption with which we shall start will correspond with one of the three above-
icntioned assumptions regarding the sun. For the sake of simplicity, we will assume, in conformity
•ith case 3 above, that all suns in relation to space have an enormous negative electric tension, diffe-
•nt for the different stars, but which, as regards order, might be somewhere about a milliard volts for
:ars of a class similar to our sun.

In this way electric discharges will be produced, among them being disruptive discharges from com-
aratively small areas (spots). One might imagine that radiation from these will give rise to circular
.irrents in the star, parallel with the plane of the equator of the rotating central body, whereby the
intral body becomes magnetic.

We can then begin, for instance, to seek for an explanation of the formation of spiral nebulae.

POINCARK, at the conclusion of the preface to his book, 'Hypotheses Cosmogoniques', says :

"Un fait qui frappe tout le monde, c'est la forme spirale de certaines n6buleuses; elle se rencontre
oaucoup trop souvent pour qu'on puisse penser qu'elle est due au hasard. On comprend combien est
icomplete toute th6orie cosmogonique qui en fait abstraction. Or aucune d'elles n'en rend compte d'une
laniere satisfaisante, et 1'explication que j'ai donn6 moi-meme un jour, par maniere de passe-temps, ne
aux pas mieux que les autres. Nous ne pouvons done terminer que par un point d'interrogation."

(') Astrophys. Journ., November, 1908, p. 257.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903. 8(1

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

:

Now we know that of the 120000 nebulae scattered over the sky, at least half are of a spiral
form. The most remarkable thing about them is that there are very often two spirals issuing symme-
trically from two diametrically opposite parts of the nebula.

We have previously seen how the continuous discharges round the magnetic cathode-globe in our
experiments, could assume a shape that recalled Saturn's ring. These continuous discharges round the
globe may, however, with higher gas-pressure in the almost exhausted vessel, take the form of two
spirals, curved in the plane of the equator, issuing symmetrically from two diametrically opposite point?
on the globe.

The accompanying figure (fig. 262) represents an experiment such as this with two such spirals.
The photograph was obtained by accident, and I have seen still more interesting pictures appear, severa
of which I shall publish at some future time.

In the above-named work of Poincart, a number of older cosmogonic theories, almost all of whir]
are founded upon purely mechanical conceptions, are compared. Those of LAPLACE, LIGONDES and
ARRHENIUS are of special interest. In the last-named, the so-called light-pressure plays a conspiciiou
part side by side with the force of gravitation.

In Poincar^'s work, all theories are in turn subjected to kindly criticism, with demonstration of t

difficulties to which each one leads. It seems to be the celebrated 4
Laplace's nebular theory that is still considered to be the strongest.

Let us now look a little more closely at the idea here put forward
namely, that the sun each day emits by electric evaporation or disintegra
tion considerable quantities of matter in the plane of its equator whicl
forms the part of the electric ring already mentioned, and that in earlie
ages this emission of matter has been still greater.

It is not necessary to admit at first the original nebula extended t'
the orbit of Neptune, as the matter is radiated by electric forces outsidi
the system at its equator. It is very probable, moreover, that the greate
part of the matter thus radiated leaves the system, and in any case take
no part in the formation of the planets.

Our analysis will show that particles from the central body may be so ejected that they afterward
move in approximately circular paths near those in which the centrifugal force due to the revolutioi
movement counterbalances the attraction of gravitation ; and one could naturally believe that it is jus
these globules which condense and form large spheres.

Our explanation will be applicable, not only to the planets round the sun, but also to all satellite>
round the planets. One can imagine Saturn's moons, and Jupiter's, down to the outermost, newly
discovered ones that move round the planet in the opposite direction to the inner, originating in a
natural manner from matter, which, under the action of an electro-magnetic directing force, has been
ejected from the planets in the plane of the equator.

Looked at in this way, Saturn may still be engaged in making moons by electric radiation. Mimas.
almost touching the circumference of the rings, is perhaps the youngest of the satellites.

132. The equations of motion for an electrically charged particle that is in the plane of the equator
of a magnetic globe (.T, y plane), and is moreover influenced by the gravitation of the globe, are

Fig. 262.

(I)

d-y

r8 dt

'tMitx
^ dt

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 679

where A, /« and M (the magnetic moment of the globe) are constants.
From these equations we obtain in the first place

t/x d-x . dy d-y ft ilr

dt ~dP ^"dt ~dP ~ ~r* dt '

whence

in, "•;

In the second place we obtain from (I)

dr
~dt'

whence

dx dy _ iM

>r in polar co-ordinates,

ind

dt
By dividing (II) by (III), we obtain

Js

dtp iAf +

Now, however,

_

T) r/. "

nd thus

nd hence

ar dr

— 2 /ir3 — (ar -f Ji

drp =

Now it is evident that the particle must move in such a manner that the square root in the last

xpression is always real. The radicand must thus be either positive or zero, and hence it follows

lat those values of r which cause the vanishing of the radicand, define limiting circles, which the
article in its motion can never cross.

It will be seen, moreover, from the expression for [3-] , that -j- is always and only then 0 (apart
rom the value r = 0), when

(IV) Cr4 -

68o P.IKKI LAND, nn: NOKU '!•:(. IAN ATKOKA roi..\uis i:xi'i IM IIO.N, 1902 '903.

that is to sav when the particle is on a boundary-circle. Hence it follows that if the- particle at a certain
moment is retri ating fn in the globe, it will continue to do so until it comes to a boundary-circle; but
it will touch this and then turn inwards.

It' we imagine a particle that is expelled from the magnetic equator of the globe, and assume that
after a limited time it comes to the nearest boundary-circle, it will move back to the globe again, aloni?
a path that is symmetrical to the one by which it moved out, i. e. the outward and inward going paths
lie symmetrically about the radius vector to the point on the boundary-circle in which the tangent
takes place.

The correctness, of this is immediately seen when it is remembered that to a given value of r

there are onlv 2 values of , which are equally great with opposite signs.

tiff

If therefore an ejected particle is not to return to the globe, it must move in such a manner as
never to reach the nearest boundary-circle. 'I bus it will move along a spiral with constantly increasing
distance from the globe, approaching the boundary-circle asymptotically.

Let us now consider the integral

'''/..!/ + ai

= (r't.M+ar i/r

•''• '' 1 r,-4 . . o,it-3 J.

- (a i- + IM )t

where i'0 is the radius of the globe, and ifA the value of if for r=r0, and endeavour to find the
condition for the existence of such a spiral curve. If r= >', , indicates the smallest boundary-circle
(provided there are any Mii.li, i. e. that (1Y) has at least i positive root), then the Integral must be
infinite for r =• >\ .

Now it will immediately be seen that if r, is a single root in (IV), the function under the integral
sign may be written in the form

1 /(r},
\r r,

where /(r) remains ordinary in tin: vicinity of r — rt , so that we may put

whereb the function under the integral sign assumes the form

If we multiply by <lr and integrate indefinitely, it will at once be seen that the function of r
resulting from the integration will not be infinite for /•—>',, and we therefore have no spiral curve ol
the kind required.

It, on the other hand, r= ;•, is a double root in equation (IY|, the function under the integral
sign will have a pole of the first order for r — i\ , and then, as is known, the function will be logarith-
mically infinite for the same value. In this case, then, we obtain a curve of the required nature, and
also, as will be easily seen, if r = /•, were a root of higher multiplicity,

The problem is thus reduced to finding the condition for equation (IY) having a double root,
which is ^> r,, .

It we confine ourselves to the consideration of particles that are expelled normally from the globe
in its magnetic equator, with an initial velocity r(l , we obtain

A/A

i>0 = Vc- -•" and ('irr] = " +^ = 0

V ,// / " ,-•- ' ,-3 '

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 68 1

hence

r 2/' i 2 iAf
C = — — -f- vn and a = — .

'"o ro

If these values are introduced into (IV), we obtain

('2V ,

' 0

If = x, - = A-O is introduced, the equation changes to
'' ro

(A) AW*** (* - x,Y + 2« (.v - AO) - »; — 0.

If .v is to be a double root in this equation, the equation

(B) KM*x (x - -vc)- + t?M*x* (x - x0) + /< = 0
uist take place at the same time. The last equation may also be written

ncl as /« is negative, it will at once be seen that the double root must be positive. But we can prove
lat it must also be <^ A-O ; for from (A) and (B) we obtain

KM- (2.i- — .*„) x (x — xg)- ,

As vl is positive, it is evident that this equation cannot take place unless x<^xu. We see then,
lat if there is any double root at all in (A), it is positive and<^A"0, and a double root in equation (IV)
necessarily positive and ^> ra , as it should be.

In order to find the condition for the double root and its value, we must eliminate x from (A)
id (B). This is easily done in the following manner.

By multiplying by x(x — xa) on both sides in (B), we obtain, on substituting the value of A"2 (A- — xa)~
om (A),

(2 * — xa) (vl — 2/i (x — *.)) + /« (x — *„) = 0 ,

;•

(C) — 3 fix (x - or.) -f 2/<A-0 (A- - A-,,) + (2A- - AO) v\ = 0.

If we multiply here by 2x — xa, and substitute the value of A- (A- — x0)(2x — A-O) from (B), we obtain

Alii

(D) 4 (ux0 + vl) x (x - x.) - (2 ft (x - xtt) - vl) xl + . a ^ = 0 .

Then when x(x — A'O) is eliminated from (C) and (D), we obtain

4 (/'*„ + VD (2/"*o (x — xn) + (2 x — A-O) vl) + 3/i (w^2 — (2/« (x — A-O) — vl) xl} = 0,
•hence we obtain

x =

HIKKKI.AM). TI1K .XnKWKI.IA.N Al'KnKA I'OI.AkIS KXI'KI >ITI( ).N, tgO2 1903.

By the substitution of this value in |C), we find the conditional equation, which, after some reduc
lions, assumes the form

If then .v(l = is substituted, and we multiply by ". , we obtain

11 it- ii'' J /. ' M '

If \ve now put

" '-",]- ' = " antl ~ tfM* = ;''
the conditional equation becomes

2 it — n- -f- ->i'(\ + 1 5 it — 24 it- -f H ,r'| -f a 7 ;>- = ( I.

On the other side we may eliminate .v(, from (A) and |B), and then obtain an equation that gives
the connection between the ratlins of the boundary-circle and r(1.
By multiplying (B| by .v and substituting

we obtain

.V — .v.v,

/.-M- L-M- I.-M-

whence

•v-= ^7i-lw^ '

Bv substituting this in (B), we obtain the desired equation

n- luir <--' \n''

~ • 1PM* + )-M^L+ /-M^+ )W " '

or, if we again introduce r instead ol .v ,

We shall now deal with the problem in a general way, that is to say with an arbitrary value «„
of the angle of expulsion or in other words the angle between the ratlins vector and the direction ot
motion at the initial moment.

We then have, as will easily be seen,

arn -\- /.M _ rr0 sin «n

:t '

whence

/..I/
a = ,-„ V0 sin «,, -

' 0

By substituting this value in (IV), we obtain

PART II. POLAR MAGNETIC PHENOMENA AND TKRRELLA EXPERIMENTS. CHAP. VI. 683

If we introduce, as before, r = -- , ra— — , and put

•^o

X

r>0sin aa = t.M(\
he equation takes the form

A double root in this must then also satisfy the equation

(2) .r (kxt + .v) (**„ + 2 .r) + ^ = 0.

If we further put

v = ~°
« '

.'e obtain from (i) and (2)

vl 2(»— \}(kn + \)(kn + 2)-f (kn + I)2 ,

— AT. .

In order that the whole shall have a physical significance, •.,.£>' j~»A<r" an(^ ^° must a" ^e P08'"
ve, and x must be <^ .r0 , and thus

(a) n > i

(b) (k,, H

nd as

sin ftu =
follows that

*

'

The last relation may however be written

— 4)w + 3 ^ 0 ,

(H - !)-((! + ^)-«- + (2
r, as n^> 1 , more simply,

(c) (l+£)2»* + (2 + 4

The 2 conditions (b) and (c) may be simplified by putting

*« — — /.

They thereby assume the form

(b'l (

(c') /- — (2«

684 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

The discriminant for the function of the second order of / in (c'| is

(,t 4. 2)* — W2 _ -2n — 3 = 2« + 1 .

When, in accordance with (a), n ~^> 1 , the discriminant will become > 0 , and consequently there
are real values of /, which satisfy (c'). These values are determined by

Hence it is seen that these values of / are positive. We see moreover that there are always
values of / > 2 which satisfy (c'), and then (b') is also satisfied. Hence it follows that by a sir
choice of the amount of magnetism and gravitation, initial velocity and angle of expulsion, ,vr can //«.«
obtain an annular formation at any desired distance from the globe,

It is further seen that for sufficiently large values of n there are permissible values of /, both<»
and ]> n.

For l<^n, we obtain

that is to say

For / > n , we obtain

that is to say

«0>0.

The particle can therefore approach a boundary-circle both when the direction of expulsion is
positive and when it is negative.

As this applies to negative particles, it of course also applies to positive particles.

It might be interesting to see, however, what direction an expelled negative particle will finally take
when the globe is so magnetised that ).

If we assume that

0,

din .

I 10

the angular velocity —*- is negative at the initial moment, and it will then always continue to be s
for the change from a negative to a positive revolution-direction, or vice versa, can only take place when

that is to say when
or

ar + IM = 0 ,

).M — r>,, sin a'

but as this value of r is <^ ;-„ , no such reversal can take place.

A positive direction of revolution can thus only take place when a0 > 0.

Now we have seen that (c) cannot be satisfied with other than negative values of k, and thus

we have

r>0 sin «0 < IM .

In order that the particle shall not change from a positive to a negative direction of revolution, it
is necessary that the double root r, which is the radius of the boundary-circle, shall be less than

iAfr.

Uf—r*va sin cr/

PART II. POLAR MAGNETIC PHKNOMENA AND TKRRKLLA EXPKRIMENTS. CHAP. VI. 685

It will be seen, however, that this is equivalent to

As we further have, in this case,
e can suitably put

nil then obtain

(d) HI > « .

The condition (c) assumes the form

(in — 1 )2 //- + (2 nft — 4 m) n + 3 m2 ^ 0 .
Hence it follows that

This, in connection with (d) then gives

K24- 2n + n^2n+ 1

wz+2« + 3
,-hence

;/4 + 2«3 + 3«2<0,

•hile at the same time « ]> 1 , which is absurd.

Tin' particle itinsf thus change to negative direction of revolution before it approaches the boundary-circle.

Let us return for a little to the equations

It follows from these that

If

icn

or

lat is to say, a velocity which, if gravitation acted alone, would remove the particle infinitely, thus a
vperbolic velocity. If on the other hand, the initial velocity is hyperbolic, / cannot have other values
lan between 2 and 3 ; for if / ^> 3, then

— — <" l

id consequently

g _ l _ <,-- g

It will further be seen that for these hyperbolic velocities, n cannot be greater than 4; for it
Hows from (c') that

/-I - V2(7^T) <; « ^ /— 1 + V'2(/- 1) ;

Birkcland. The Norwegian Aurora Polaris Expedition, 1902—1903. 87

686

and when

then

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

Thus » is then always less than 4.

Values of n ^> 4 can thus only be obtained for elliptical velocities, i. e. when

Then, moreover, / > 3 , whence it follows that

» . Jl

Hence it will be seen that great values of n can only be obtained for elliptical velocities that ar<
very near the parabolic, i. e. when v'l is only a little less than - - .

133. It might now be interesting to find out whether a negative particle could approach a boundary-
circle with positive direction of revolution, if we were to assume that there was a resistance in the
medium. We have seen that if there were no resistance, such a motion was impossible.

When an electrically charged particle moves in the plane of the magnetic equator of a magnetic
globe, subject to the magnetism and gravitation from the globe, and moreover a resistance in the medium,
we have the following equations of motion :

d2x

f.M dy
~^~ dt

(.1 dx

x ~ m ~

where m is the resistance.
From this we obtain

dzy _ IM dx . ^ dy_

* = ' *> *y' m>

dxd*x . dyd*y ft dr dt((dx\- . fdv\-\

*7P+dtWf**-mdS((lll) +UJ J'

•f * <fs

or, if we put . = v ,

(I)
We obtain moreover

dv /LI dr ds

d2x _ A.M dr m ( dy dx

(II)

d (

- I

dt\

d(D\ 2.M dr m

_Z. I ^ -----

«^- _Z. I ^

dt

dt

m
v

„ dip

2 — '—

dt

Now it is clear that whatever the nature of the resistance may be, it can at any rate be under-
stood as a continually positive function of r (possibly multiform, but if the particle were constantly
retreating from the globe, it would be uniform). If the particle is able to move in such a manner as

dr

to be always retiring from the globe (and approaching a boundary-circle), -. is moreover a continually

(IS

positive function of r. For a path such as this then, it should be allowable to put

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 687

here /(r) is a continually positive function of r. Let us now see what are the consequences to which
u's will lead.

Equation (I) may now be written

vdv = -., dr — f(r) dr ,
hence we obtain

V~ _L I" V« _L <"

2 H- 7 == 2" + r — !' (r) , when F(r) =

Furtlier

., drp „ drr ds

,id

dv fi dr f, , dr

By substitution in equation (II) we then obtain

, drtPr

.ds)

( by multiplying by

—5 —
ds

Here we will put

\icnce we obtain

We then put

\iereby the equation assumes the form

dr d*r dx

= .v and = .v • . ,

ds rfs- dr

m;i i - i - i »

(IV) Z + pi .v + —f + z/^r ^ = 0

688 iiiKKKi.ANn. 'ini: NOK\YI-:<;I.\.N AIKOKA POLARIS KXTI nn IO.N, 1902 1903.

l!v integration of this, we obtain

• „ / ' r i,

+ r'

ilr = i'(/'l , we can write

Since iiioi'<_'ovi.-r

= 1 + ;

t/rf

It no\\- tin: partirk- appi'oaclics a boundary-circle, then necessarily

iv/r

when ;• is the ratlins <>[ the boundary-circle. As ///;/ r = I , and //;// r = r . , then also

= co .

lint as r certainly possesses a continuous 1st ilcrivativc (see (IV)), the necessary and sufficient
condition tor the last integral heini; infinite is that

-,(r. i / -/I ?-0) -

c • \ej "'sin a,

1'AKT II. 1'OI-AK MAGNETIC PI IENOMKN A AND TERRELLA EXPERIMENTS. CHAP. VI. 689

, being a positive root in the equation

Mich is obtained from (IV) by putting v = 1 , and ' • = 0
If (V) is to be possible for real «0 , then of necessity

Let us now look at the function

We obtain

&

dr~

If we put u = - -f- v- -J ., , then it = 0 for r = t\, according to (VI). But further

dn _ _ ,« dv _,_ AM dv '_ 'ivlM _ ft 0 fl^ _j_ IM (p fl^\ _ 2vt.M

dr r- a

imembering that

Consequently « ^> 0 for r<O',, and then also ~ ^> 0 for r<^r^, and consequently

0 for r = r, > s for r = /-„ ,

Mich is at variance with (VII).

It is thus quite generally proved that the partible cannot from within approach a boundary-circle
I a positive orbit-direction.

It might now be imagined that the ejected particle first changed from out-going to in-going motion,
; d approached a boundary-circle from without.

We can here distinguish between two cases.

Case i. The direction of the path of the particle is positive at the moment the change to in-going
ntion takes place.

dy

In this case v must remain positive along the entire in-going path. From the expression for -~

i has been seen that y cannot become 0, unless . '0. If y became negative somewhere along the

i-going path, it must then, owing to the continuity, as its value at the change is 1, also become 0 for
ne or more values of r, and among these there must be a greatest value r1. Then of necessity, how-

< er, for r = >A,

'•J > 0 and i- = 0 ,
dr

Mich is impossible.

690

BIKKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Let us now compare the value of v for a point on the in-going orbit, with the same value of r
as for a point on the out-going.

If there had been no resistance, we should have had

but, owing to the resistance a diminution of the kinetic energy, or of the velocity, has in the mean time-
taken place, so that

Consequently
and then also

If now
then

that is to say,

and as

it follows that

a <^

drl ,„

V'

dy dy
drin drmt '

From this it evidently follows, that the inequality

J'in

in \rV /out

in ==J'out i

must take place for lesser values of r than the one in question. Now for the value of r for which the
change to in-going motion takes place, is of course

and thus the inequality

occurs for all smaller values of r. As, moreover, y-m always remains < 0, this means that the particle
returns to the globe again along a steeper path than the out-going.

This proof holds good, if -j- is always > 0. But we may prove that the result is true even il
dy "ront

were < 0 for certain values of r, at any rate if the outgoing orbit has no point of inflexion. We

will not here, however, go farther in the discussion of this problem.

Case 2. The direction of the path of the particle is negative at the moment when the change ti
in-going motion takes place.

In this case it is certain that the resistance might be of such a nature, that the direction of the
path of the particle during its in-going motion, changed to positive. Let us suppose, for instance, that
for a moment it is suddenly subjected to a very great resistance at the point at which it changes
in-going motion. The path will then at first very nearly coincide with the radius vector inwards, but
then, as the velocity increases, the magnetism will deflect it in a positive direction.

It might therefore possibly happen that the particle in this case would approach a boundary-circle
the positive way.

PART II. I'OI.AR MAG.NKTIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP VI. 69!

The above-found expression for y now holds good, of course, whatever value ra and er0 may have;
other words, we can quite imagine an arbitrary point in the path as the point of commencement. We
uy then write r, instead of rn , and or, instead of a0, and obtain

f t.M

sin o, - ^1 *•*

J *"i

If the particle then approaches, by the positive way, a boundary-circle with radius r,, then of
i cessity

/ F*iM

g- *rj (*•(-,) sin « , — '- ,«M

V J r, If*

> being a positive root in the equation

„='' + ^ + ^1 = 0.
r

If we put

v obtain

z for r = r., <^ s for r =;-, ,

n matter how little greater r, is than ;•., ; but then

(VIII) f>0

dr

(< values of r= ;-., + £, where i is a positive quantity that can be chosen as small as desired.
We found further that

du n

As f(r) along the in-going path is negative, we cannot here, as before, conclude that the value of
must be negative. But if the function f(r] is assumed to be such that

, - <T 0 for r = i\ ,

dr

tl a, as n — 0 for r== t\ ,

it <^ 0 for r = r, -|- e ,

\v -re i has the same signification as before. Then too, however,

-T- < 0 for r = ra -f «,
c/r

ai this is at variance with (VIII).

Hence it follows that the negatively-charged particle cannot approach a boundary-circle from without

ar the positive way, unless

dn

for r = r, .

dr
On the other hand we can prove that if, for r = r2 ,

,t = 0 and dl. ' > 0 .

f/A'

th particle can, from without and the positive way, approach a boundary-circle with rt as radius.

692 BIRKELAN'l). THE NORWKGIAN AURORA POLARIS EXPEDITION, 1902 — IQO3.

We then obtain

dz

0 for ;- = r.2 -j- i ,

and it is thus certain that there are values of r ~> >\_ , for instance rt , such that

dz

(IX)
and thus also
or for an arbitrary r, we have

-, -

0 , when

s for r — t\<~. z for r = r, ,

r**-M ^.1 , r-A^ .„,

(*y\r2l _L_ I — C" (IF ^" f™ l ' — t" I — f9^r'

- 1 1-3 — - 1 *-^ J

Jr '" Jr ^r

If we then put r — r, , we obtain

f
J

« 'i M

We can then, however, find an angle «, such that
(X) ««W>-f f'^jWrfr— <

(//
Jr,

We further put

9n 9i.

(XI)

Since r, may be chosen as little greater than >\ as desired, it may certainly be so chosen that
both sin a, and vt can be found as positive quantities.

It is then clear that if we imagine the negative particle placed at a distance r, from the centre 01
the magnetic globe, and possessing a velocity vs , forming an angle a, with the radius vector (a, mint

be chosen between and re), it will then, from without and the positive way, approach asymptotically

the circle with radius r., . For since v for r = r, has the positive value sin or, , we can prove, as in
Case i, that y must remain positive along the entire in-going path. The particle cannot therefore change
to out-going motion again for a value r3 of r, unless v — -f- 1 for ;• = r3 ; that is to say

sn

but according to (X) we obtain therefrom

z for r = r3 equal to s for ;• = r, ;

and that, on account of (IX), cannot be, if r., > r., .

For the value r = r, , the velocity v will be determined by the fact that

2" 2» „ fr-

v* -.= ,,2 + -J- - 2

r* ri Jr,

f(r}dr;

but if we compare this with (XI) we obtain
;•„ and v^ were so chosen, however, that

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 693

We thus have y = 1 and -r- • = 0 for r=>:2 ; but this means that the particle is asymptoti-

clr

lly approaching the circle with 'radius r. .

In order to obtain the fulfilment of the condition

gr>° for r=rt,

i is only necessary that f(rt) shall satisfy the relation

It this, it is evident, can be done in an endless number of ways, if/\r) is always to be negative.

The only remaining question is, then, whether the particle expelled from the globe can come to
i >ve in this manner. We have not yet succeeded in finding a complete solution of this problem ; but
\; have found that the resistance must be so great that the velocity must be diminished during the
ijoing motion, in spite of gravitation.

134. We will now see whether a negatively-charged particle with positive direction of revolution
en approach a boundary-circle, if we imagine the charge decreasing to 0.

The equations of motion for an electrically-charged particle in the plane of a magnetic globe's
tuator, influenced by gravitation and magnetism, are

dP r3 dt~T~ r3*

d^y _ _ IM dx /(
W ~^*~dt + r*y-

We will now imagine the charge to be variable, in such a manner that it diminishes towards 0,
if the length of path increases infinitely. We can then make A equal a function of r, but this will of
c irse be multiform if the particle should anywhere change from out-going to in-going motion or
v e versa.

We obtain, in the same way as before,

al

By putting

\\ obtain therefrom

G)" = "» + 2'' C0 -7) -? (r°v° sin a» -

a:l by dividing by

\\ obtain

(rtvt sm a, — /'Wj1

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903. Ss

694 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

or

drp __
~dr^

0va sin«0 — F(r)

t"

whence

rp — </)„ -

If the particle is to approach a boundary-circle, then of necessity, when r, is the radius of this circle
(a) (»; + y\ r\ - 2«r, - (rav0 sin or. - />,))* = 0

(b)

, - ft + (r0 »0 sin «„ -

= 0 ,

u 1

where A, is the value A gets for r — ?-, . As the charge is assumed to diminish towards 0 ,

/, = 0,
whence, according to (b),

(c) rt = -- - .

From (a) we then obtain

- /»'i = (^o sin «o — ^K))2 .

or

(d)

= ra v sin

noting that F(rt) — r0va sin «0 must be <^0, if the motion is supposed to take place in
direction.

From (d) we obtain

F(rt) + V^"7, < Vo ,

and as F(ri) is certainly > 0 , we obtain a fortiori

and by the aid of (c),

noting, from (c), that

Then

or

— H1

which is absurd.

Since the particle cannot approach a boundary-circle in a positive direction, it is clear that if
does not change to a negative direction, it must either continue to travel, out indefinitely, or with positi
direction change from an out-going to an in-going motion.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 695

Let us look for a little at the last case. The expression

rava sin aa — F(r]

•

ill then remain positive during the in-going motion; but if we compare 2 points with the same value
f r, one on the out-going, and one on the in-going path, then

(rav0 sin «„ - /»)in <(ravlt sin «„ — /»)ollt ,
id

out»
id consequently

d(f>
~dr

In

dr

out

The particle will thus return to the globe again by a steeper path than that by which it went out
om it.

Setting aside the case in which the particle recedes indefinitely, only those cases are left in which,
ith negative direction of revolution, it either changes to an in-going motion again, or approaches a
jimdary-circle.

We will look at the former of these cases.

If we compare the value of -J- in 2 points with the same value of r, one on the out-going and
ic on the in-going path, it is evident that

dr[> dip

dt in ttt out

It might then happen that - . became positive when the particle came in sufficiently near to the
<>be again; but then ,-- would certainly also be positive for smaller values of r. Then as -/- and

W in dt in

would both be positive for these sufficiently small values of r, we may prove in the same way as

'out

;iove that

/I if
dr

in

dff

it then the particle must return to the globe again. On the other hand, if it does not end in the globe,

en, with negative value of -j. , it will either turn out again, or approach a boundary-circle. It is then

drr
< rtain, however, that -' will continue to be negative for all time. Along an eventual out-going path,

t r

. will certainly remain negative; and if it turns in again, will also, by virtue of the relation

dcp dcp

dt in * dt out '

I: negative along the in-going path, and so on.

In conclusion we will see whether the particle with negative direction of revolution can approach
; boundary-circle from within, when aa > 0. If we call the radius of the circle r, , then

696 HIKKKLANI). T11K N( iRWKCU AN AURORA POLARIS KXPKDIT1ON, igO2 — 1903.

and

(d'l /"(>-,) = >-(,z'0 sin «„ -j- /—/<;', .

The effect of the equation (c'( is that

^ ," < *'f,>'o < — -," -
it r, is to have a positive value ]> ru .

(d'| will certain!}- he satisfied it'

V— ." ''i < " '•' ('',) < W + \ ," '-, = '•„ ;'« -

Moreover r, must he the smallest positive value of r that causes the expression under the square
root sign in the y>-integral to vanish.

The and derivative of the raclicand has for r = r the value

As however

'd I.

., , "C *•' > and '',,''0 sm c'o ~~ ^'"(;'i) <C ^ >

/*/ ^ "/ >• f

the second derivative is negative. The ist derivative then becomes positive for i'<^>\, and conse-
quently the radicand itself negative for values of r <^ rt . But then the particle cannot approach any
boundary-circle.

On the other hand, the orbit can certainly become a conic section at last.

Let us consider the simple case in which the particle retains its charge until it comes very near
the boundary-circle, assuming that it tends towards one, but then suddenly loses its charge.

The changes from in-going to out-going motion, or vice versa, will then take place for those values
of ;• that satisfy the equation

-)- V'0j i" - - 2 ft r — r\ v'\ siir ft, — 0 ,

where r\ is very nearly the radius, r,,, of the boundary-circle, ;', very nearlv the velocity, v(], in the
boundary-circle, and «, very nearly - ~. For the sake of simplicity we may put

•!C

~ ' a < ' ' i == ''v> a i ~ 2 '

whereby we obtain

The discriminant of this equation is

^>'u
and consequently the roots in the equation are always real.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 697

If

ie one root is positive, and the other negative; and at the same time the velocity is hyperbolic, so that
ic particle retires indefinitely.
If, on the contrary,

oth the roots will be positive. Let us call the smallest rv, and the largest ra. Then

-/i — Qtt + rav-} -j" + ( rv

Hence we obtain

__

r

»

at is to say, the particle will move in an ellipse, of which the perihelion is just on the boundary-circle.
The eccentricity will be

0 _2r

e _ r« — r 2" rv "

ru rp

If we substitute as before

e obtain

v*\ r, vl

L' ^ 1 _ „ 2 + -5 1 = 1 — 2?z — «

/" \ H / jtl

We have, however (cf. p. 683),

r d consequently

r kn + 2 ~ kn + 2 / - 2 '
vien we put, as before,

As / may be as great as may be desired, the eccentricity may be as small as may be desired.
. the same time n must have greater values. Thus at a great distance from the globe, the orbit will
b almost circular.

135. We have discussed above the problem of the mouvement of an electrically charged particle
aaut a magnetic and gravitating sphere, when the particle is ejected in the plane of the magnetic
ejator, and thus always remains there. We saw that there were boundary-circles towards which the

698

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

particles, under certain conditions, could draw nearer and nearer, this giving rise to the formation of
planets. It still remains for us to investigate the conditions outside the plane of the equator — whether
the formation of planets is also possible there, when the particles are flung out anywhere on the sphere
or not. This investigation has been carried out as follows.
The equations of motion for the particle are

y

From these it is easily found that

ds if" 2iti „

v = -.-= V C C = constant

at i r

and if the magnetic field originates in a potential V,

(3)

a = constant,

when ip is a certain function of /? = ^x* -\- y* and z.

If we assume that the sphere acts as an elementary magnet, i. e.

then

(4)

-
<P='/.M~

Moreover

3x

rj

whence

dx

dy _ 3Mz ( dy dx\ _ ZMz drp

~ ~ ~ K df

_

ydt~

By substitution in the third equation of motion (i), we obtain

d*z _ 3'j.Ms —^ dtp . z

TIo" " » *^ » '* o

> ' 3

»

eii

'- -~

and by substitution of the value of R'- -~ from (3) and (4) we obtain

As moreover we have

dt- ~ r* r3 '

t-dtf>- -\- dz~ ,

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 699

we obtain by the aid of (2), (3) and (4)

_ r
dt \dt ~^~ \~dt" ' r

We thus have to study the following system of equations:

d*z SL

151

dip _ IMR* -f- ar3
~ dt = ~7" '

If, for the sake of brevity, we put

r _

r RW

.he first equation in (5) may be written in the form

(If- ~2r 3r
From the second equation in (5),

ve obtain by derivation as regards /,

inv t*- iv . uz ct z IVL - 01 \ d t\ 01 z dz
~dl ~dft " ~di~dP~ \3R 9r' r) i/i *~ 9r r dt

d-z
If we introduce the expression just found for -^ , we obtain

O 7T T^~ ~ ' \ ™'J^ 1 ~ I '

dt dt2 \SR ' dr r I dt
md as often as - L ^ 0 , we can from this again conclude that

<f/? =
dft =~2

Owing to the continuity, however, this equation also retains its validity, even if -y- = 0 for certain

pecial values of t.

We can also eliminate t and find a differential equation in only z and R; this determines a surface
>f rotation, upon which the particle will always remain.
We have

dz dz dR , d^z d-z /rf/?V . dz d*R

Tt^ dR' dt ~aJ~dR* \~di~) '^~~dR ~dP

B1RKF.LAND. THE NORWEGIAN AURORA POLARIS EXPKU1TION, 1902-1903.

and as

we obtain

dR _

dt '~'i—

1/1 +

" h

dz

dt

dR

+

h

*

s
and finally by substitution of the expressions found for — , and

P dz

2r

or

•*•

= 0

The coefficients in this equation are irrational functions of R and z. If r is introduced instead of
2 as a dependent variable, we obtain a differential equation in r and R with rational coefficients. Thi-;
differential equation is

It will be seen from the second equation in (5) that the surface P=0 is a boundary-surface through
which the particle can never penetrate during its movement. The line of intersection of this boundary-
surface with the rotation-surface upon which the particle is found, then becomes a boundary-curve, which
the particle can never cross. This boundary-curve is always a circle parallel with the plane of the
equator.

It will be seen that for a given point (z, R) upon the surface of rotation upon which the particle

lies, there are 2 values of —j- which are equally great, but have contrary signs, and similarly for

dt

-

. j

while there is only one value of -J-. From this it will be seen that if the particle moves in such a

manner that, after a limited time, it reaches the boundary-surface, it will thence turn inwards to the
sphere again along a path that is symmetrical with the outward-going path, with reference to the meridian
plane -through the point upon the boundary-surface at which the reversal took place.

We will next see whether the particle could approach this boundary-circle asymptotically. It is
clear that no matter how the particle moves, we may put

and consequently

= /(*)

dz

..V/M'

As / must increase infinitely when z approaches the value that answers to the boundary-circle,
we must have for this value of z

s = 0 and '(z) = 0

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 7OI

iat is to say

(tZ \ .(If (IZ \ " (IZ (l I (tZ \ (t^Z

= 0 and -7— I — =- I = 0 or —=- • -j— I — j- 1 ^ 0 or . ., = < > •

(IZ \(lt / (it (IS \(1tJ (lf-

In the same way we also find that -y-.r = 0 for the boundary-circle. We have, then

Disregarding the plane of the equator s = 0, we have

3P

id of course also

P=0.

If we introduce the actual expressions for P, -— and - , it becomes

a,. _

"" ~~

a ,ft_ =
r' r* ' r' ~

(c) t?M*R* — a-,* = 0.

From (c) we obtain

V = ±
.id from (b)

As of necessity r ^ 0, it must be that

* = + ar3

;id thus

r2 —
From (a) we obtain

•icnce

F~rom this we obtain by substitution of the value found for r-

,r
(Cr —

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903. 89

702

whence

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQOa — 1903.

Cr — 2/i = — - ,

or

r =

3C"

If this is compared with the expressions already found for r2, we obtain

or

or

- 16/j8 =

Let us next consider a value-system R-\-Rlt r-\-r\, R and r indicating the boundary-circle.
According to Taylor's development, we then have

a P 3 P

In an infinitely small region surrounding the point (R, r), in which P—0, -^ ,, = 0, =0,

5/\ c ;•

obtain then

For rj = 0 we obtain in particular

Now

A2 AT2 3a2

2 S^a

Hence it follows that P has negative values as near the point under consideration as might be
desired.

If the discriminant of the quadratic form

a/?2'v'n

is negative, it follows that P must have negative values all over the area surrounding the point under
consideration. Then a particle cannot move towards the circle under consideration. The discriminant
must therefore be positive, that is to say,

or

r5

-"

or, since IMR2 = ar3 ,

..- , 2/« 12aiM 21 1.,,.., ,
T~ (— ^3 ^ 1& >Q

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 703

36«JU/ -f 4 (— 2,1/r2 — 33alM) > 0

0

id, as r=,

But we found above that

Hence it followed that 11 > 0, which however is not the case. It is hereby proved that the particle
iiinot describe a path that asymptotically approaches the boundary-circle.

The question might now arise as to whether the particle could move in such a manner that it did
st reach the boundary-surface, either after a finite or an infinite length of time. This would only be
)ssible if the integral curve we obtain from (6) -- which may be said to be the curve of projection
f circles r = constant in a meridian plane of the path of the particle -- has an infinite length within
e boundary-surface. It would then be an important point to decide whether the path of the particle
•mid approach asymptotically a closed curve.

We have however not yet succeeded in solving this problem quite generally.

Let us now at last try to find out, whether trajectories could exist in the plane

z = kx.
The equations of motion are

dy dx
~~~

By substitution of z = kx we obtain

3iMx t
~ r> \*

dy_
ttt

Here we must assume, that k ^ 0.
From the ist and 3rd equation we obtain

(a)

704 B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

The 2nd equation may be transformed to

d*y

nl ,"„- — -

dt2

From (2) we obtain

dx

dy _ dx _
X ell ~y~dl~

whence

(4)

Further we have

dy
~d~t

dx (Sr2 — 3jy2) • x dy

dt 3(^ — yz) • y ~dt '

dr _ dx . dy . dz . dx . dy

dt dt dt dt dt dt

whence

f dr _ (2r2— 3y2) dy

'~dt= 3y dt^^'dt

^
dt

or

(5)

^ dy_ j^dr
~ydi'~2rdt'

Hence we obtain by integration

(6)
Hence it follows, that

(c = constant).

or

(7)

x =

rye* — r

The 3rd equation in (1) may be written in the form

dy /.ix

~~

~dP ~ (1 + kz) r3 dt
From this equation in connection with (3) we obtain

IM

dfl ' dt* r* \ dt \+kzdt) (1

Hence we obtain by integration

Now, however, we also have

dy dx IM 1

-==-

dy dx
v ^ ..

x ji y^7~^

3y dr

and as

dt J dt 3 ( 1 + £2) x 2r dt 2(1 +
y VT+75 |/r

dt '

— r

PART II. POLAR MAGNETIC PHENOMENA AND TERRE1.LA EXPERIMENTS. CHAP. VI. 705

ve obtain

dy dx r* dr

(9) •»• 7,7 —y -,,- — — —

From (8) and (9) it follows, that

r3 fdrV _ ( AM 1 , \*

4(1 -f P) (<* — r) U J ' U + ** ' r ")

The equation of the kinetic energy gives

According to (5) and (6) we have

dy ^S
f/;-~2
nd from (7) we obtain

/hence

- — 3r)-

( 1 _L A

Consequently

/(2c2— 3r)2 r\ /\2 2

2/t

From (10) and (u) we obtain by elimination of :

By multiplication with 4 ( 1 -|- £2)a (c- — r)r- this equation assumes the form

( 1 + £2) r4 (— 2(i + yr) — (4c2 — 3*-) (A^ + a (1 + £2) r)2 =- 0 .
If r is not constant, this equation must be identically satisfied. Consequently

But, when c = 0 it follows from (6), that r = 0.

Consequently r must be constant in all cases. Then it follows from (4) and (5) that x, y and z
ust be constant, and it is seen from the original system of differential equations that x, y and z
ust be 0.

yo6

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Hereby it is proved, that trajectories do not exist in any plane passing through the centre of the
sphere except in the equatorial plane.

Hence we may conclude, that formation of planets will hardly be possible outside the equatorial
plane. If after all a multitude of trajectories could approach asymptotically a common curve outside the
equatorial plane, this curve as we have shown could not lie in a plane passing through the centre of
the sphere, and as further the particles certainly very soon will lose their charge, they will come to
move in the most different directions. The only possibility for formation of planets must be, that the
particles approached a common curve lying in a plane through the centre of the magnetic sphere, and
this we have proved to be impossible.

136. Our mathematical investigations have shown as their result that if boundary-circles exist for
all the velocities with which material corpuscles are expelled from the central body, the corpuscles will
either return to the central body (this being what will happen in the great majority of cases), or the
particles will continue to approach nearer and nearer to the boundary-circles. Possibly some velocities
may also be sufficiently great to cause the particles in question to leave the system and retire indefinitely.

Concerning the charge of the particles, we may imagine three cases:

I. When the particles are not charged. They will then either retire indefinitely, or fall down again.

II. When the particles are so highly charged that the electrostatic influence dominates that of
gravitation.

III. When the particles carry a charge of medium strength, so that the electrostatic influence plays
an important part side by side with gravitation, which, however, is the dominating force.

If we consider negative particles in case II, we shall easily be able to prove that they can in
approach boundary-circles, but the radius of these circles must be < (1 + V2)r0.

The necessary and sufficient condition for the approach of a particle to a boundary-circle in this
case is that the following relations shall be satisfied:

(a) »>1

(b) (/ — 1) (/ — 2)< 0, or, otherwise expressed, 1 < /< 2

(c) « — ]/2n -\- 1 <^ / —

i i

<0

M"" «(/—»)

(2)

From (b) and (c) we find that

n — «
that is to say, we obtain in connection with (a)

(e) !<

Necessarily, moreover,

, or «2 — 2«

PART II. POLAR MAGNKTIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 707

hence

r n\ ^^

•id consequently
r, if preferred,

3 — 4n
1 — 2«

Thus on the whole / — "1 must satisfy the following inequalities:

n — V^« -f 1 < /— 2 (and / — 2 < « -f |/2« -f- 1 , which is satisfied according to (b))

1

— 2<0 /— 2>

1 — 2w

Now if n satisfies (e), it is evident that /, in an infinite number of ways, can be so determined
i at these last inequalities are satisfied. Then, however, the relations (a), (b), (c) and (d) are also satisfied,
; d we can consequently find positive values of ;•„, va, (.1, i? and M2, which satisfy equations (i) and (2).
hder suitable conditions therefore, the particle can approach an arbitrary circle, of which the radius r
stislies the inequalities

Let us, upon the assumption that gravitation dominates the effect of electric force (case III), see
1 \v the radii of the boundary-circles depend upon the relation between charge and mass, or, in other
\>rds, upon the quantity /.

The necessary and sufficient condition for the approach of a particle to a boundary-circle, is the
snultaneous satisfaction of the following relations:

(a)

«> 1

(b)

(/_!)(/_ 2) >0

(c)

„ _ y2« + i < / — 2 <

» + V2« + 1

(0

0 0 O |

2)

— /< «'«(/ —

rfol

-ftr30 (/—!)(/— 2)

If we confine ourselves to a consideration of those values of n that are i- 1 -f- y 2 , (a) is satisfied,
a i (b) is satisfied, provided (c) is. The three conditions (a), (b) and (c) may therefore be contracted
ii > the equation

/ — 2 = « -f # 1/2*7+7

uere 0- can be given all possible values between -- 1 and -}- 1.
If we substitute this expression for / — 2 in (i), we obtain

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

and by multiplication of (i) by (2), we obtain

The result thus attained is that the necessary and sufficient condition for the approach of a particle
to a boundary-circle with radius n ra , when n > I -j- j/2 , is that the last three equations take place for
a value of 0- between — 1 and -j- 1 .

If we were to imagine ra , va and M maintained, we can find those values of /.t and A which give

ft

T V

the boundary-circles. It is at once seen that for great values of n, - - will keep very near 2. Those

r v
values of — ft that give rise to great values of « will thus approximately be ~-^ . It will be seen,

r v
however, that the greater n is, the nearer to 2 will - - be, and then — u must be a little less than

for smaller values of n. Under otherwise similar circumstances therefore, boundary-circles approach
negative particles will be of greater radius than those approached by positive particles. Moreover it will
be seen from the last equation that for great values of n, A2 will be approximately proportional to w;
i. e. thai particles with small mass in proportion to their charge will give rise to boundary-circles
greater radii than particles with great mass in proportion to their charge.

The particles that approach a boundary-circle may continue to move there for all time. It is con-
ceivable, however, that the number of particles will gradually become so great that they will be capable
of collecting into large globules, which in their turn at last unite to form a planet, as the electric charge
in the original particles may conceivably be supposed to have been lost.

In the case of the sudden loss of the charge, the mathematical investigation has shown that the
particles will afterwards move in ellipses about the central body with perihelion in the boundary-circle

and with eccentricity

1
g / o '

f

where/ - — k.n, »= — , and r~v.. sin or- 1.M (\-\-k).
>'»

That / is great and thus the eccentricity e small, when r is great in relation to the radius ;-„ of the
central body, will be seen from the following relation, which must be satisfied:

n + 2 — V2w+l <; / <: n -f 2 + \/2» + 1.

If the electric charge of the particles is gradually lost, it seems evident that the finite orbit com-
pletely circumscribes the boundary-circle and very nearly becomes a circle, if the boundary-circle of t
particles has a large radius in proportion to ra.

Let us now, on the supposition that the entire mass of particles near a boundary-circle revolvi
directly about the central body (like the .planets), consider the question as to how a planet, originating
in the massing together of the globules here assumed, can acquire a direct rotation about its axis, and
not a retrograde, as at first sight one would imagine.

As regards this question, I subscribe to the explanation given by POINCARE in his "Hypothese
Cosmogoniques" (p. 51), in which he shows how planets, in the event of their having originated
LAPLACE'S ring-formations, can acquire a direct rotation. This explanation is based upon G. H. DARW
important investigations on the effect of tidal reaction between a central mass and a body revolving aboul

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 709

The TROWBRIDGE explanation of the direct axial rotation may perhaps be equally applicable to our
tiory. He shows that if the ring be nearly of the same density throughout, the resulting planet must
1 ve a retrograde rotation like Uranus and Neptune. But if the particles are more closely packed near
.• inner edge of the ring, so that the resulting planet would be formed much within the middle of its
dth, its axial rotation must be direct.

Our results summarised above seem both simple and well fitted to aid in constructing a new and
s .isfactory cosmogonic hypothesis, based on experimental analogies (see experiments represented in fig. 255).

137. We will here take the opportunity of mentioning some more recent experiments that have
ten made with the largest vacuum-box with a capacity of 1000 litres. We have already referred to
t:ir commencement.

Our experiments, as might be expected, prove to be more and more interesting as we increase
t : scale on which they are performed.

Fig. 263 a gives a good idea of the dimensions of the vacuum-box, and the various arrangements
f- the experiments.

The glass walls of the box, each of which supports a pressure of about 7000 kg., are 46 mm. in
t rkness. No firm of makers would supply any thicker, but it was calculated that they should have
I en 50 mm. in order to be safe. The floor and roof of the box are constructed of brass.

The largest cathode-globe employed is 36 cm. in diameter, and the maximal discharge-current has
hen about 400 milliamperes. Fig. 263 b shows how the rays in the magnetic equatorial plane may be
vry pronounced when the magnetism is weak and the discharge-current comparatively strong (150 milli-
a pcres). With a stronger discharge-current, a peculiar electric corona frequently occurs round the
c hode, sometimes with rays out from the polar regions, the whole thing having a striking resemblance
t> photographs of the sun's corona during an eclipse.

If we desire to produce the phenomenon which we think may be regarded as analogous to Saturn's
r g, only i or 2 milliamperes is required, and the magnetisation of the cathode-globe must be some-
v at stronger than in the former experiment.

Fig. 263 c shows powerful and characteristic spot-discharges from the magnetic cathode-globe.

It will be necessary to give some information as to the way in which these disruptive discharges
ny best be brought about.

With a polished metal globe like the cathode, disruptive discharges will not easily be formed. An
a lost continuous discharge with electric corona is then obtained, even if, as previously mentioned, the
s am of vaseline-oil be introduced into the box.

If, on the contrary, the globe is cast and not polished, such disruptive discharges will nearly al-
wys occur; but the difficulty here is that the casting of so large a globe as the one here employed
n.-er yields a homogeneous result, so that the patches keep to certain parts of the globe, even when
tl: latter is not magnetised.

The best way in which to obtain with certainty a continuous discharge, interrupted at definite inter-
s by powerful disruptive discharges, seems to be the following:

The surface of the globe, after polishing, should be sand-blown and then painted over with a thin
ing of vaseline-oil, which is afterwards wiped off again. This painting over, which seems to be
•antageous to the phenomena, is not necessary if the farthest corners of the vacuum-box are greased
h a little vaseline-oil before the box is exhausted.

When a suitable vacuum has been obtained, a short discharge of about 10 minutes with a current-
s'sngth of 200 milliamperes will completely dry up the oil on the cathode. Without discharges the
gbe will remain oily for many days, even in a high vacuum produced by a GAEDE'S molecular pump.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903. 90

yio

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Fig. 263 a b c.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI.

711

is probable that in this case an electric disintegration of the oil on the cathode takes place, possibly
companied by a partial decomposition. This we conclude from the following experiment, which more-

er is important in more respects than the one here mentioned. During our experiments, the floor
.id ceiling of our vacuum-box had received rather too abundant a coating of oil. In order to correct
is, discharges were sent through for several hours with the floor and ceiling as cathode. As these
ent on, the floor and ceiling became practically dry, whereas the glass walls received a powerful
ecipitation of oil or fatty decomposition products in a zone about 3 cm. in width, the edge on one side
•ing somewhat diffuse, but clearly marked towards the cathode, the limit beginning on a level with

Fig. 264.

t: external boundary-surface of CROOKES' dark space. A similar coating also appeared upon the in-
sated tube by which the cathode-globe was suspended, after the corresponding drying of the globe;
ad the same one-sided sharply-defined coating was also found on the glass vessel that contained phos-
poric acid (see figure 264).

It seems from this that just about this boundary-surface all round the cathode there is formed during
tl: discharge an atmosphere of complicated ions, while at the same time a high tension polarisation layer
i: working up and at last gives occasion for a disruptive discharge. This is also shown by the fact that
a ertain time always elapses before the disruptive discharges begin and then attain to a stationary con-
dion of frequency. The author had already put forward this assumption before the above-mentioned
ejeriment was made, and it will be found in a paper previously quoted here (C. R., March 17, 1913).

The experiment seems also to indicate that a great number of the corpuscles ejected in a straight
lie from the cathode by disintegration are stopped again at the end of the dark space.

Next some experiments were made in which the cathode-globe with a diameter of 24 cm. was sur-
Pinded with a well amalgamated zinc shell. The vacuum-box was now cleaned from oil and fat, except
f< a small part of one of the glass walls, where a white coating of fat remained. This patch of fat
gi,-e rise, as we shall soon see, to an important discovery.

712

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

Concerning the experiments themselves and the light-phenomena observed, we shall only state that
the radiation from the polar regions of this cathode were often particularly beautifully developed. It was
further demonstrated that the quicksilver on the surface of the cathode disintegrated greatly, after wlmh
the surface of the globe gave rise to magnificently iridiscent rings of colour, of which we succeeded in
taking several good colour-photographs.

We here reproduce two interesting photographs that were taken during some experiments in which
the globe was no longer the cathode, but acted as a terrella, just as in the experiments described in
Chapter IV.

Fig. 265 a.

Fig. 265 a shows an experiment in which an aluminium plate in one corner of the box acted as
cathode, while the metallic parts of the box were the anode. It will be seen how the rays strike down-
wards all round the auroral zones of the terrella. A glance is sufficient to show the occurrence of phe-
nomena that have previously with much trouble been educed from a long series of experimenls.

By varying the magnetism of the globe, the radius of the light-zone was altered within wide limit;,
diminishing with strong magnetism.

Fig. 265 b shows something similar, but in this case the globe itself was the anode, and the phe-
nomena were even more magnificent; for in the belt in which the rays from the cathode descended
upon the terrella, "positive light" radiated from the latter, giving a remarkably beautiful effect to these
light-zones about the poles.

We will now return to the above-mentioned patch of grease upon the glass wall of the vacuum-
box, as it occasioned the discovery of a phenomenon that is highly worthy of attention.

After the amalgated globe had been acting as cathode for a couple of hours, it appeared that tl
part of the glass wall on which there had originally been a white coating of fat, gradually became grey
and then very dark in colour, without any change taking place in the rest of the clear glass wall.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI.

713

When the box was opened, the passing of the finger over the patch of grease produced an abun-
lance of tiny drops of quicksilver. We thus see that the quicksilver corpuscles from the greatly disinte-
.rating cathode-globe in this large vacuum-box (1000 litres) are thrown against the glass walls, as a rule
nth the result that they are reflected back again. It wax only where the surface of tin- glass was greasy
hnt the corpuscles adhered.

This result made me think of all my former vain attemtps to make the corpuscles thrown off from
palladium cathode produce a shadow upon the glass wall of the vacuum-tube, of an object standing
•tween the cathode and Ihe wall. It seems natural to suppose that corpuscles that are disintegrated

Fig. 265 b.

om a cathode have not generally sufficient velocity to adhere when they strike a wall, but that at first
icy generally rebound, only a few of them adhering immediately. When a coating is once formed, the
.her corpuscles have a better opportunity of adhering, possibly on account of electric attraction.

In order to test the correctness of this assumption, a former experiment was repeated, in which
:> shadow-formation had been obtained. On this occasion all interior surfaces were greased with vase-
ic-oil, whereas before they had been dry and clean. The result, as the accompanying reproduction of
photograph (fig. 266) shows, was in astonishing conformity with the assumption.

The vaseline-oil employed soon stiffens, it is true, under the influence of the cathode-rays, but the
tty substance formed "catches" the corpuscles and prevents them from being reflected back from the
alls. It is thus possible in this way to demonstrate the course of the "metal rays" from the cathode,
ithout having complications introduced into the phenomena by reflected rays.

Exceedingly peculiar conditions would arise in a vessel filled with flying corpuscles, if a patch on one
" its walls had the property of intercepting all particles that had the greatest kinetic energy, while those
ith small velocity rebounded. It is assumed that the walls of the vessel, apart from the patch, throw
ick all corpuscles. Might we perhaps replace the famous little Maxwell's demon with a patch of grease?

7'4

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

On a previous occasion we have in reality shown under somewhat different circumstances that th
rays of corpuscles ejected from the cathode are reflected from the walls. In a paper in C. R., March n
3913, I have said that the long pencils of rays emitted from the cathode and carrying a quantity of dis-
integrated matter from the cathode, are reflected from a wall like rays of light from a mirror.

If, therefore, it is desired to study the course of these bundles of rays, or their ability to pass
through, for instance, thin aluminium-foil, employment should be made of a layer of fat to intercept the
corpuscles after their passage, as the ray-phenomena are then more easily demonstrated.

After the treatment with grease mentioned above, the
cathode is well fitted for patch-experiments, and intensely
powerful disruptive discharges are formed even without
additional external capacity.

In a high vacuum the patches generally consist of
groups, but may also consist of a single patch at each place.
They may often remain in one place for a measurable length
of time. They are surrounded by the previously-mentioned
vortices (see fig. 261), rotating in opposite directions on the
two magnetic hemispheres. Round the single patches more
particularly, these vortices attain a surprising clearness and
regularity.

It appears on comparison of the above with HAL
photographs of sun-spots with vortex-formations, that I have
been guilty of a misunderstanding.

The experimental vortices are in the reverse direction
to HALE'S, supposing the magnetic north pole to be on
the top of the cathode-globe. In my descriptions I have
reckoned the vortex from the centre outwards, contrary to
Hale, who has considered them in the more usual way.

But the consideration of the experimental whirls and the solar vortices as analogous phenomena
does not seem to involve any contradiction.

In my experiment the magnetic power in the spot is determined by the magnetisation of the cathode-
globe. The current-strengths carried by the discharges are too small to produce any marked local field.
In a sun-spot, on the contrary, the local magnetic field predominates, and it may very well be due to
the enormous conditions on the sun. In some way or other with which we are not now acquainted,
vortices may arise from the discharges. The current-strengths are so great that the magnetic forces
formed by them will be able to entirely reverse the original magnetic field which was due to the general
magnetisation of the sun.

Here it should possibly be considered that the current-paths in the photosphere around a spot are
"selected", so to speak, at the first moment, before the current-strength in the discharge has attained to
any magnitude worth mentioning. Later, when it becomes perhaps millions of times greater, the current-
paths retain to some extent their orientation, and produce a corresponding magnetic field.

We have repeatedly pointed out the resemblance that exists between the light-phenomena about a
magnetic cathode-globe and corresponding solar phenomena, such as the corona with the radiating oft-
shoots in the polar-regions, and the sun-spots.

The light-phenomena about a magnetic anode-globe, on the other hand, are quite different, except
that the radiation in the polar regions is sometimes nearly like that from a cat/iodf-globe, and resembles
the polar radiation of the sun.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 715

It might at first sight appear as if this were an indication that perhaps the sun is negative in the
[uatorial regions and positive in the polar. If so, it would suggest the thought whether a difference in
ectric tension might eventually be produced by rotation of the magnetic solar body in space.

It is easy to make an estimate here. MASCART(') has calculated that the rotation of the magnetic
trth must give rise to an aggregate electromotive force of an order ior< volts, acting from the poles
the equator.

If we wanted to make a similar calculation with regard to the sun, we must first of all have a

ilue for the amount of the magnetic force near the sun. This is still unknown. HAI.E(-) is at present

aking attempts to measure it. In the mean time SCHUSTER (3), with certain assumptions, has calculated

a recent paper that the intensity in the sun should be 440 times greater than on the earth. If we

ckon with an even magnetisation of the globes, this would make the sun's magnetic moment 440 X IO23

.•eater than that of the earth.

Now we have shown (see p. 617) that if cathode-rays from the sun with a huge moment such as
lis were to reach the earth, they must have a magnetic stiffness answering to

H • Q > I0«

•lilefrom the situation of the earth's auroral zones we may infer that the helio-cathode rays which pro-
uce aurora and magnetic storms have generally a value of 3 million C. G. S. And to this last result
': are inclined to attach the importance of an experimental fact.

On the other side we have calculated, from the retardation of up to 50 hours of the magnetic
sjrms in relation to a sun-spot's passage of the central meridian, that the magnetic moment of the sun
i from about 100 to 150 times as great as that of the earth, or of the order lo28 C. G. S.

We cannot of course from this conclude anything about the magnitude of the magnetic force near
te sun, for the sun is certainly no evenly magnetised globe. The general magnetisation of the sun is
jobably produced by electric currents in relatively thin layers round the solar equatorial regions inside
< outside the sun's surface. In this way the value of the magnetic force near the sun's surface may be
ilatively great, without any overwhelming magnetic moment for the sun being assumed (4). If we start with

(') MASCART, Traite de Magnetisme Terrestre, p. 74. Paris, 1900

(•3) Mount Wilson Solar Observatory; Annual Report, 1912, p. 179.

(**) SCHUSTER, Proc. Phys. Soc. of London, 1912, p. 127.

(4) The rays emitted from the sun will certainly to some extent serve to increase the sun's magnetism.

We have shown that if the magnetic moment of the sun is of an order lo33 (see p. 617), all rays of which the pro-
duct #b?0<5Xi°5i will return to the sun and fall down again, or must circulate about the sun, the negative rays
clockwise, the positive anti-clockwise, seen from above and assuming that the sun's magnetic north pole is uppermost.

The figures 248 b and c show how such flexible rays are moving in almost cylindrical rings about the magnetic ca-
thode-globe. The radius of such a ring seems never to come up to 2.5 times the radius of the central sphere, as the
theory predicted (p. 617).

Perhaps the "dusky veil" of the sun (see p. 670) is due to such a cylindrical ring of corpuscles moving about the sun.
Under all circumstances (even if the sun's magnetisation is the reverse of that here supposed), a part, and perhaps the
more considerable part, of the rays emitted by the sun will thus serve to magnetise the sun; but there are perhaps also
electric currents in the interior that act in the same way. We may even imagine the sun's magnetism to have originated
in this manner, if we start with the assumption that the initial velocity of the negative rays is greater than that of the
positive.

Suppose that the sun had originally been non-magnetic, but rotated in the same way as it now does. It is evident
that the positive rays, of which the bearers may be assumed to be positive material corpuscles, will then be deflected by
the rotation of the central body, even if the electric forces at first tried to eject the particles normally from the surface of
the sun. Owing to gravitation (and by electric attraction if the sun were negative), the ejected particles now make their
way back to the sun. The total magnetic effect of nil the positive rays must then be that of a positive current circulating
in the same direction as the rotation. The sun would thus be north-magnetic above, that is to say provided no other,
greater forces have been acting in the reverse direction. The negative rays consisting of electrons with great velocities
would probably be deflected by the rotation of the central body in the same direclion as the positive rays; but the deflec-
tion would be less and the electrons would not at first return to the sun. Not until the sun was magnetic would they
be reversed, and then serve, as shown above, to augment the sun's magnetism.

716 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

my assumption of a sun-moment of an order iol0 C.G. S. and opposite to that of the earth, an estimate will
easily show that the induced electromotive force in space about the sun will not be so great as about
the earth, and its direction will be from the equator to the poles. There will then, of course, be no
question of explaining the great discharges from the sun, in which the tension goes up to 600 million
volts p) (see p. 665), as an induction-phenomenon of this kind. The most reasonable hypothesis therefore
seems to be that the sun and the stars are negative all over in relation to surrounding space.

It is otherwise if we calculate with SCHUSTER'S purely hypothetical value for the intensity of 440
times the intensity on the earth. We should then most probably come to an electromotive force of about
2 milliard volts, acting from the poles to the equatorial regions, which would thus have to be regarded
as the cathode in the eventually produced discharges, while the poles were anodes.

138. It is a circumstance in my planet-theory which has given me much trouble, as it looked at
first as though the planets, if formed, would come to revolve the wrong way round the central l>
I considered it at first most probable that the material particles expelled by disintegration from the
negative-electric central body, took with them a negative charge.

It was soon evident, however, that if, for instance, the magnetisation of the sun — as I have had to
assume — is the reverse of that of the earth, the negatively-charged particles would hardly be able to
approach the boundary-circles in the same way as the planets move in their orbits. At any rate they
must first change from out-going to in-going motion, and be subjected to a suitable resistance. For one thing
this resistance must be such that the velocity, in spite of gravitation, would be diminished during the
in-going motion, and it seems physically unreasonable to assume the existence of such a resistance. It
would be far easier for the particles to approach the boundary-circles the opposite way. It therefore
appeared probable from the theory, that we should be compelled to assume that the expelled particles
would, partially at any rate, be positive.

This led me to think that possibly the electric disintegration from a cathode had some poin:
resemblance to the disintegration of radio-active substances, which emit a-particles, even if the emitting
substance is charged negatively.

It occurred to me, moreover, that since it has been decided that the particles in AVrays emitted
by a cathode, are positively charged, it might be well worth finding out whether the material particle
expelled by disintegration also carried a positive charge.

By examining the literature on the subject, I soon saw that there were no definite results that
could decide the question, although our idea of the constitution of matter presupposes that the atoms in a
non-electric piece of metal are positively charged, and that there are corresponding free negative
Irons between the molecules. From a theoretical point of view it might thus be conceivable that the
atoms ejected from a cathode were positively charged.

It was for this reason that I commenced these investigations of the disintegration of cathodes, some
of which have been described in the Article on Saturn's Ring, while others will now be described.

As mentioned on p. 659, my attention, while experimenting on the disintegration of the cathode,
was increasingly drawn to the more or less normally expelled particles which formed an evenly
reflecting deposit of palladium on the cylindrical glass wall of the vacuum-tube, right round the cathode
A number of experiments were therefore made by introducing little, flat screens of mica, with or with
a slit, at various distances from the cathode. The palladium cathode was in the form of a long rectangle
whose long centre line coincided with the axis of the tube. It appeared, however, that notvvithstandin

(') In my experiments with an electric corona I use from o. i to 0.2 milliamperes per sq. cm. of the surface of the globe-ca
If we suppose a similar value of the current from the sun, and the tension to be 600 million volts, this correspon
about too kw. per cm. Such an energy would easily account for all heat and light radiation from the sun.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI.

717

iat the particles expelled from the cathode must now be assumed to move more or less at right angles
> the magnetic lines of force, and that the field-strength was about 1800 lines of force per square centi-
ictre, it was not possible to prove any turning aside of the particles, first of all because the field was
ot strong enough, but also because it was not possible in these preliminary experiments to obtain sharp
mdows of the screen in the metallic deposit upon the glass wall.

On the other hand it appeared that the deposit came not only on the front of the screen, but also
nmdantly on the back of it, especially if it stood near the cathode, a fact which indicated that the par-
ries could acquire a retrograde motion after they had retired from the cathode.

From the appearance of the deposit upon the back of the mica screen farthest removed from the
Lthode, I received the distinct impression that the particles had struck almost parallel with the surface
the screen. I therefore made, on each side of the long side of the mica screen, a raised edge one or
millimetres in height. Both edges turned away from the cathode. It then appeared that there was
) longer any deposit upon the back of the screen, although on the front and on the protecting side
Iges there was an abundant deposit of palladium.

a Fig. 267. b

The next arrangement was as follows. A long, rectangular cathode of palladium was attached to a
tick brass wire that passed through a quartz tube with walls 2 millimetres in thickness. Only the palla-
cam plate reached beyond the quartz tube, which was placed axially in the vacuum-tube. The anode
MS annular in shape, and was placed 10 cm. behind the cathode, which again was only 2 mm. above
t: sheet of plate-glass that was cemented to the end of the vacuum-tube. In order to prevent the
ucking of the sheet of plate glass with the heat from the cathode-rays, a small square of mica was
cmented to the sheet of glass just under the cathode.

There were further cemented to the sheet of glass some half-cylinders at various distances, with
t.'ir convex side towards the cathode.

By these means it was shown that the palladium particles to a very great extent made their way
i o the concave side of the half-cylinder, if it was placed near the cathode, whereas if it was far from
tt cathode, the particles hardly entered it at all, although they abundantly covered the convex side with
flladium. Figs. 267 a and b show how these little half-cylinders were arranged, and also that the most
c.tant half-cylinder has cast an almost straight shadow behind it on the sheet of glass (farthest to the
rht in fig. 267 b), where therefore the palladium has not been deposited. The nearest half-cylinder has
t -own no distinct shadow, or at any rate it is only by careful examination that there is seen to be less
r.lladium deposited just behind it than beside it. It seemed as though some of the expelled palladium
Articles had a tendency to return to the cathode again, just as if they were positively charged.

In a subsequent experiment, the cathode was a fairly thick platinum plate with a surface of a few
saare millimetres, while the anode was a brass plate with a surface measuring a couple of hundred

Birkeland. The Norwegian Aurora Polaris Expedition, 1908 — 1903. 91

7i8

HIKKKLANO. TIIF. NORWEGIAN AURORA POLARIS KXPKniTlON, igO2 — 1903.

square centimetres. A high vacuum was maintained in the vacuum-tube; the tension was over 15,000
volts, ami the temperature of the cathode was kept up by the current near the melting-point of platinum

In three hours the brass anode was completely coated with a shining mirror of platinum. On the
glass wall of the vacuum-case there was a fairly sharp shadow of a screen that stood between the ca-
thode and the wall, so that in this experiment we are fully justified in speaking of "platinum rays".

In the same way, in many and varied experiments, rays of palladium and uranium were produced
with the employment of as much as from 15,000 to 20,000 volts to the cathode (the positive pole was
earthed) and temperatures of from 600° to about 1800° C. The reader is here referred to the remarks
in connection with the above-mentioned experiments, in which the whole of the inner surface of the
vacuum-tube was greased.

The experiments seem to show that these positive rays have several of the most characteristic
properties of «-rays. Both the way in which they arc formed in the firm material of the cathode, and
the way in which they are formed in the firm material of the cathode, and the way in which they spread

T

D— -200

^— o

r\ • CflTHQOe

n nnooe

Fig. 268.

and stop in the surrounding medium indicate this. We also succeeded in sending platinum rays, and
more particularly rays of metallic uranium, right through thin aluminium foil, just as can be done with a-rays.
We will describe two of these experiments more particularly. Rays from a small palladium cathode
were sent through a little hole into an otherwise closed metal capsule (which was earthed) and on be-
tween two parallel brass plates at a short distance from one another, as shown in fig. 268 ('). One oi
the plates had 200 volts, the other was earthed. After the experiment hail been going on for 3 hours,
the coating of palladium showed itself to be quite different upon the two plates. On the - 200 platt,
a long, narrow, more or less well-defined pencil of rays was found, where the precipitation was very
abundant. Hut in addition to this, there was a very thin coating of palladium all oi'cr this plate (which
was 6.5 cm. long and 4.5 cm. wide), even on the back, especially if the plate were smaller. On the
other plate, which was of the same size, there was a short, broad, fan-shaped precipitation of quite another
kind than that on the — 200 plate, and there was no other deposit upon the plate, either on the front

I1) I his vacuum-tube, in several experiments, was placed between the poles of a large electro-magnet, which was just sufti
ciently magnetised to prevent ordinary cathode-rays from forcing their way through the hole into the otherwise closed
metal capsule,

1 he discharge-current from the anode was thereby pressed by the force of the magnet into a thin, luminous cord along
one side of the vacuum-tube.

Kvi-ry time during these experiments, after working for one or two hours, it appeared that palladium corpuscles from
the cathode were driven against the electric current right up towards the anode, the glass under the luminous cord being
thickly coated with a metallic band. This shows that negative palladium ions have moved up against the current. There
arc thus both positive and negative metal ions from the cathode.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 719

the back. This experiment was made in varied forms more than 20 times with in the main the
me result.

My explanation of the thin, diffuse deposit upon the —200 plate is that after the positive rays have
"st their velocity, they are drawn in electrostatically towards the plate, evenly right round it.

A reservation must be made here, however, as there is a possibility that this explanation of the
, c// coating of palladium round the — 200 plate is incorrect.

The cathode rays, as might be expected, were drawn in upon the o — plate. Rays such as these
jukl, as we know, cause an already produced precipitation of palladium to decompose again. It may
( ii tore be imagined that eventually it was the palladium corpuscles detached from the cathode-rays and
i-ed for the second time, that were positive and were thus evenly drawn in towards and all round
le — 200 plate.

The experiments that were made to show that metal rays went through aluminium foil, were car-
•d out in the following manner.

A small cassette of brass had 4 small holes, 0.5 mm. in diameter bored side by side in the lid.
ut of the thinnest aluminium-foil of about one-thousandth part of a millimetre, small entire portions were
arched for with a microscope, and laid in one, two, three or four layers over the four holes. Under
c whole there was a sheet of glass. A little steel magnet was placed behind the cassette, for the pur-
ise of deflecting ordinary cathode-rays from the cathode, which was placed at a distance of 20 mm.
^lit in front of the holes in the cassette.

After the discharge had been going on one or two hours, the cassette was opened and the sheet

glass studied. The precipitation of metal through the foil was not so considerable that it could be

i n without doubt with the naked eye; but by breathing on the glass a sharply-defined, well-marked

ml appeared beneath the hole with one layer of aluminium-foil. Under the hole that was covered with

•o layers there also appeared a distinct spot; under that with three layers the deposit could scarcely

• distinguished; but under the hole that was covered with four layers, not even traces were found in
iv case.

Since cathode-rays as stiff as those in these discharges would easily pass through even four layers

such thin aluminium-foil, and as these rays in most cases were deflected with a steel magnet, it must

obably be assumed that they are metal rays that have penetrated through the foil, but in very different

:grees through the four holes. These experiments, however, will be continued, as also those that have

•en made for the determination of charge and mass of the metal corpuscles.

There is yet another point in these experiments that will be touched upon here. It has been
entioned above that under certain conditions marked oscillations might occur in an oscillatory circuit
>nnected(') in parallel with the anode and cathode in the vacuum-tube as poles.

It appears that the disintegration of the cathode is much greater under these conditions, and that

this case thin, luminous pencils of rays are emitted by the cathode. At the foot-points of these pencils

particular, the cathode-material becomes so greatly disintegrated, that under the microscope the surface

' the cathode gives the impression of having been corroded with a quantity of tiny cavities. It also appears

at it is not necessary to keep the temperature so high as that given above in order to obtain a powerful

:velopment of positive metal rays from the cathode when it is connected with such an external oscillatory circuit.

The rays that have hitherto been called a-rays, consist, as is well known, of positive helium atoms,
ected with enormous velocity from a radio-active substance, e. g. radium.

There seem, from the discoveries here mentioned, to be good grounds for extending the conception
rays to include rays formed of all positive atoms that are ejected with such velocity as to give rise

• the properties of a-rays.

(') I.e., C. R., March 17, 1913.

720

blRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

The processes whereby such rays were formed we might call radio-activity in an extended sens
or electro-radio-activity.

We have not yet succeeded, however, in spite of continual experiments, in producing a proof that
by this extended radio-activity chemical elements might be transformed into one another, or that heat
was developed by the disintegration of a cathode, in the same way as when radium is transformed.
The last question would acquire a fundamental importance in the problem of the heat-store and longe-
vity of the sun and stars.

139. According to our manner of looking at the matter, every star in the universe would be
seat and field of activity of electric forces of a strength that no one could imagine.

We have no certain opinion (') as to how the assumed enormous electric currents with enorrtv
tension are produced, but it is certainly not in accordance with the principles we employ in technics
on the earth at the present time. One may well believe, however, that a knowledge in the future of
electrotechnics of the heavens would be of great practical value to our electrical engineers.

It seems to be a natural consequence of our points of view to assume that the whole of space is
filled with electrons and flying electric ions of all kinds. We have assumed that each stellar system
evolutions throws off electric corpuscles into space. It does not seem unreasonable therefore to think that
the greater part of the material masses in the universe is found, not in the solar systems or nebula?, but
in "empty" space.

Let us see how thickly we should have to imagine iron atoms, for instance, distributed in spa
between the sun and the nearest star, a Centauri, if, in a sphere with the distance 4.4 light-years as
dius we assumed a mass equal to that of our solar system to be evenly distributed.

The mass of our solar system may be estimated at 2 X io33 grammes (see Young, General Astn
nomy, pp. 97 and 603). The distance to a Centauri is 4 X io18 centimetres, and the volume of the said
sphere about the sun would thus be 2.7 X io50 cubic centimetres.

If the mass of our solar system be distributed over this sphere, there will be 7.5 X io -4 grammes
per cubic centimetre.

If the mass of an iron atom be put at 5.6 X io -3 grammes, we find that there will fall i iron atom
upon every 8 cubic centimetres of the sphere in question.

It seems as if no known facts can prevent us from assuming by hypothesis that the average den-
sity of these flying ions and uncharged atoms and molecules might very well be, for instance, 100 times
greater than that found above.

The electron theory assumes that the ponderable atoms are surrounded by some bound electrons
which oscillate about certain positions of equilibrium and with definite periods. These atoms or ions
cannot then, considered optically, have properties that are very different from the optical properties in
a dielectric medium.

Let us therefore imagine that we have on an average io iron atoms per cubic centimetre in empty
space, and try to form some idea as to whether such a density would be at variance with the optical
properties of space, and in the next place whether this density would be irreconcilable with the assump-
tion that the sun sends cathode-rays down to the earth.

The latter question seems the easier to decide when we consider that there must be a row o
^-r- cubic centimetres, one after another, to contain one gramme of iron. A column such as that wouli
be traversed by light in 1900 years. If we assume that the stiff helio-cathode rays of which we are now

(') See "Sur la Source de 1'eleclricite des etoiles", C. R. Dec. 23, 1912.

PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. VI. 721

>eaking would also in this case be absorbed in accordance with the law of traversed masses, we see
once that on this point our hypothesis will scarcely meet with any difficulty.

With regard to the first question, namely how the light in the case supposed would be absorbed

empty space, it is not so easy to say what influence electric atoms, dispersed through space in such

ultitudes, would have upon the light that comes to us from the stars; but it is hardly credible that any

teoretic investigation would show as its result that the stellar heavens would then be darkened in a

anner that is at variance with reality.

Atoms with bound electrons may be imagined to absorb light and heat waves by co-oscillations of
o bound electrons. The absorption conditioned in this way does not attain a noticeable value until the
>riod in the entering waves agrees with that of the oscillations proper of the bound electrons. It may
)w be imagined that the oscillations of these bound electrons may in their turn be transferred to
ther waves, or that one or more electrons may separate and form cathode-rays. We know that cathode-
,ys can be emitted by a metal surface by irradiation with ultra-violet light, and that electrons can be
;t free from a metallic surface when that surface absorbs rays of light.

There is also another question which naturally presents itself for investigation: Will the assumed
;nsity of flying corpuscles in space bring about any appreciable resistance to the motion of the heav-
ily bodies?

Let us look at the case as regards the earth, when it was assumed that there were 10 iron atoms
;r cubic centimetre in space.

We will assume the least favorable case, namely that the earth intercepts all the atoms it meets.
uring a revolution round the sun, the earth encompasses a volume of 1.2 X io32 cubic centimetres. If
e mass of the iron atom be put at 5.6 X io -3 gr. and io atoms be assumed per cubic centimetre,
c earth will intercept 6.7 X io10 gr. in one year.

According to the equation (M + J M}V^ — MV^, the velocity of the earth will then be dimin-
H-d by

If the earth's velocity be put at 3 X 10° cm. per second, its mass at 6.06 X io27 gr., then F0 — Fi
1.7 X io n cm. per second. According to this, the earth, supposed for the sake of simplicity to be
sting in its orbit, would be retarded 5.4 X io~4 cm. per annum, or the length of the year would be
:creased by 1.8X10 10 seconds.

We see from the above that it is not impossible that future investigations will show that without
inning into conflict with experience in any way here mentioned, we may reckon that there are more
lan ten thousand times greater masses gathered as flying corpuscles in "empty" space than the masses
; the stars and nebulae.

And it may be imagined that an average equilibrium exists between disintegration of the heavenly
ies on the one side, and gathering and condensation of flying corpuscles on the other(').

(') In a paper, "De 1'origine des mondes", Archives des Sciences, Geneva, June isth, 1913, the author has made the views
here set forth the subject of detailed consideration.

PART III.
EARTH CURRENTS AND EARTH MAGNETISM.

CHAPTER I.

EARTH-CURRENTS AND THEIR RELATION TO CERTAIN TERRESTRIAL

MAGNETIC PHENOMENA.

INTRODUCTION.

140. As soon as the discovery of OERSTED, in 1819, of the effect produced by galvanic currents
on magnets was made known to the world, attempts were made to explain the earth's magnetism and
its variations by means of currents circulating in the earth.

As early as 1821 DAVY(') suggested that the variation in declination might possibly be due to
such currents, and some years after the same view was taken up and carried further by CHRISTIE (2)
and P. BARLOW(S).

These ideas seem to have met with general acceptance, and soon became the current explanation
for the pulpit.

The theory of magnetism as caused by earth-currents was merely founded on speculation, and years
had passed before the question was put to an actual experimental test.

The first attempts at measuring currents in the earth's crust were made in mines in Cornwall (4).
It seems, however, hardly possible to decide whether the currents measured were real earth-currents
or not.

Experiments of a similar kind were made by BECQUEREL (5) in the salt-mines of Dieuze. He observed
the currents called into play when various layers of the earth were connected by conducting wire.

W. H. BARLOW (°) seems to have been the first to show that currents were almost always circu-
lating in the earth's crust. He used four telegraph lines starting in different directions from the same
central station at Derby. About simultaneously, earth-currents were observed by BAUMGARTNER on the
line between Vienna and Gratz.

It was found that earth-currents ordinarily circulating in the earth were very variable in strength.
The first result of the actual test of earth-currents was that the view put forward by P. Barlow, that
the earth's magnetism was directly caused by currents circulating in the earth, was not confirmed by
experiment. This conclusion, as far as I know, was first positively stated by AIRY.

But there still remained for investigation the question as to whether, or to what extent earth-
currents produce the magnetic variations. As the result of comparison of currents with the variation
of magnetic elements, Barlow finds that simultaneous observations showed no marked similarity in the
path described by the magnetic needle and the galvanometer, LLOYD, however, from the same obser-

(!) Sir H. DAVY: Phil. Trans. 1821 p. 7.

('-) C. H. CHRISTIE: Phil, Trans. 1827 p. 308.

(3) P. BARLOW: Phil. Trans. 1831 p. 99.

(4) R. W. Fox: Phil. Trans. 1830. R. W. Fox, HUNT, PHILLIPS: Annual Report of the Roy. Polytechnic Institution of
Cornwall, 1836, 1841, 1842.

(f>) BECQUEREI. : Comptes Rendus XIX, p. 1052.
I11) Phil. Trans. 1849, p. 61.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903. \\-2

726 B1KKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

vations, but taking the average of several days, found curves for the diurnal variation of earth-currents
which seemed to show some similarity with corresponding magnetic variations. The similarity is not a
striking one, and it is doubtful how a similarity which is not shown in simultaneous observations should
be interpreted ; so it was at last to be considered as rather doubtful whether the diurnal variation of the
earth's magnetism was due to earth-currents.

Thus the actual test of the theory of the electric origin of the earth's magnetism had not given
any trustworthy confirmatory results.

Then an event occurred which should show definitely that a connection of some kind existed
between the variation of the earth's magnetism and earth-currents.

From the 2gth August to the 3rd September, 1859, a great magnetic perturbation took place,
accompanied by aurora borealis, and simultaneously the telegraph-lines were disturbed by currents of an
extraordinary strength, which were observed at the most various parts of the world.

This event gave a great impulse to the study of earth-currents. Earth-current observation
carried on for several years on the English telegraph-lines, and were collected and worked out In
C. V. WALKER^).

About simultaneously earth-current measurements were undertaken by LAMCNT^).

In his first publication, Walker treats the earth-currents observed during magnetic disturb;.)
In spite of the fact that the two phenomena accompany each other, he does .not venture to draw the
conclusion that magnetic storms are entirely caused by earth-currents. His statements are of special
interest when looked upon in the light of recent research. He says(3): "Other influences than those
exerted by electric currents upon magnets may or may not be in play; but one thing is very certain,
that at least a large portion of the motion presented by the magnetometers on storm days is connected
with the then prevalence of earth-currents ; and doubtless some portion of all the more regular and less
violent disturbances may be more or less due to the same causes. At any rate, although we arc
siderably in the dark as to the forms of force in operation to make up the whole of the causes con-
cerned in magnetic disturbances, we are yet quite certain that the current form of force is at least in
part concerned."

In a subsequent work Walker deals with the ordinary currents found on undisturbed days, lie
finds that the currents observed are real earth-currents and are not due to the earth-plates or other
local conditions. They are not equally frequent in all directions, but appear mainly in the two opposite
quadrants N-E and S-W. This result has been confirmed by later observers.

Lament seems to be of the opinion that magnetic storms are produced by earth currents, but he
does not consider it to be proved that all variations in the earth's magnetism are due to earth-am

Up to this time all observations had been. carried out by taking readings at intervals. In this way
it was very difficult to follow the many sudden changes of earth-currents, which accompany the magnetic
disturbances.

Walker has pointed out the importance of having continual photographic records of earth-currents
in connection with magnetic records. The matter was taken up by Airy, Astronomer Royal, and earth-
current registerings were commenced at Greenwich in 1865, and were continued for two years. UK
results are contained in two papers by Airy communicated to the Royal Society in 1868 and 1870;
and the conclusions he has drawn from his observations have to a great extent formed the basis oi
later discussions.

(') C. V. WALKEK: Phil. Trans. 1861, p. 89, and 1862, p. 203.

(2) LAMONT : Der Erdstrom und der Zusammenhang desselben mil dem Magnetismus der Erde, 1862.

(3) loc. eit., p. 114.

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. 1. 727

His results were in short the following:

(1) He thinks that on repeatedly examining the agreements of the two systems of curves it is im-
possible to avoid the conclusions that the magnetic disturbances are produced by terrestrial
galvanic currents below the magnets. There still remain some points to be explained before
we can prove that galvanic currents, as we observe them, will account for all that we observe
in magnetometer records^).

(2) Regarding the total magnetism he says:

"On one point we can speak with confidence; they do not explain the existence of the
principal part of terrestrial magnetism" (2).

(3) The general agreement of curves, especially in the bold inequalities, is very striking particularly
in the curves relating to northerly force (3).

(4) The small irregularities in the curves of galvanic origin are more numerous than those in the
curves of magnetic origin (3).

(5) The irregularities in the curves of galvanic origin usually precede, in time, those of magnetic
origin, especially as regards westerly force (3).

(6) The proportions of the magnitudes of rise and fall in the curves often differ sensibly, especially
as regards westerly force (4).

(7) The northerly force appears, on these days of magnetic storms, to be increased, whereas
general experience leads us to expect that it would be diminished(4).

(8) In agreement with Walker he finds that the earth-currents observed on calm days are real earth-
currents, and finds that they show a well-marked diurnal period; but he says that neither in
magnitude nor in law are these inequalities, consequent on galvanic currents, competent to
explain the ordinary diurnal inequalities of magnetism (5).

(9) At present we are unable to say whether the records of the galvanic currents throw any light
on the origin of the diurnal variations of the magnetic elements (''').

The next great step in earth-current research was inaugurated by the Electrical Congress at Paris
i 1881. It was decided that earth-current observations ought to be carried out simultaneously in as
lany countries as possible. Partly as a result of the work of the committee, partly in connection with
ie international polar expeditions of 1882 — 83, a great amount of work was next done to investigate
ie laws of terrestrial currents.

In France registerings were undertaken by BLAViER(7), in England at the Greenwich Observatory (8),
i Russia by H. WILD("), in Finland by LEMSTROM)10), in Italy by BATELLif11), in Bulgaria by BACHMETJEW(I:!),
t Kingua Fjord near the auroral zone by GIESE(IS), and in India by E. O. WALKER (14).

(') loc. cit , 1868, p. 471.

(-> „ „ 1868, p. 472.

(:ll „ „ 1870, p. ai6.

(4) „ a 1870, p. 216.

(J) „ „ 1870, p. 226.

(°) „ „ 1868, p. 472.

(") E. BLAVIER: Etudes des Courants Telluriques, 1884.

(8) Greenwich Magnetical and Meteorological Observations, 1882 and 1883.

l") H. WILD: Beobachtungen der elektrischen StrGme der Erde in kilrzern Linien. Mem. Acad. Imp. Sci. St. Petersburg,

1883.

(10) Expedition Polaire Finlandaise: 1882—83 et 1883—84.

(n) A. BATELLI : Sulli correnti telluriche. Atti R. Acad. Lincei 1888.

(12) BACHMETJEW: Der gegenwartige Stand der Frage fiber elektrische ErdstrOme. Mem. Acad. Imp. Sci. St. Petersburg.

f'-l» Beobachtungsergebnisse der deutschen Stationen, 1882 — 83, I, p. 411.

(14) F.. O. WALKER: Earth-currents in India, Journal Soc. Tel. Eng. Xll, 1883; XVII, 1888; XXII, 1893.

728 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

An extensive series of registerings were undertaken in Germany on two long lines, one from
Berlin to Dresden, 120 km. and the other from Berlin to Thorn, 262 km., and are treated by B. WEIX-
STEIN ('). Continual photographic records were kept from 1893 — 97 at Pare Saint Maur, and in recent
years earth-current registerings have been made in Java by W. VAN BEMMELEN^).

STRENGTH AND DISTRIBUTION OF EARTH-CURRENTS.

141. In spite of the great amount of work done on the subject, the earth-current problem is still in a
somewhat unsatisfactory state. We are still very far from having attained a full comprehension of the
various causes producing the galvanometer deflections.

The deflections observed are only to be considered as the algebraic sum of deflections due to a
great variety of causes, some of which are due to experimental arrangements, and even the true earth-
currents may be summed up from a very different origin.

Wild, Blavier and Weinstein found that on an average the electromotive force between two
points in a certain direction is proportional to their distance, and Wild estimates that on undisturbed
days the electromotive force per kilometre is of the order Viooo v°lt- Batelli finds 0.00068 volts per
kilometre along the magnetic meridian, and 0.00081 normal to it.

During perturbations we shall find much greater values, Wild has found values up to 0.05 volts
per km., and at certain moments during the disturbance of September, 1859, the electromotive force in
telegraph-lines in France obtained values of about i volt pr. km. In 1881, PREECE found, in English
telegraph-lines, 0.3 volts per km.

Some attempts at comparing simultaneous observations at various places were made by Lemstrom,
who coordinated his own observations for Sodankyla with those of Wild from Pawlowsk.

He found that in the greater number of cases the conditions at the two stations were similar,
that great disturbances at the one station were accompanied by great disturbances at the other; but
there were also cases where no similarity was found, and LemstrOm concludes that besides the more
universal currents there are a number of quite local ones which are strong at the place but soon die off.

He also makes an interesting comparison of the absolute magnitude of earth-currents at the two
places and finds as the average of 24 term-days that the amplitude at Pawlowsk is 0.0008 v°l'/krn. and
for Sodankyla 0.06 volt/km., or corresponding amplitudes are 75 times as large at Sodankyla. From
this rapid increase in the earth-currents towards the arctic regions Lemstrom was led to the suggestion
that probably there is a maximum zone of earth-currents similar to the auroral zone.

One point on which most authorities seem to agree is that the earth-currents at a certain place
mostly run along a certain line of direction, either in the one direction or in the opposite. To this
circumstance it is to some extent, at any rate, due that the earth-currents will run along the lines in
which the earth's conductivity is greatest. In addition to this there are other reasons, e. g. an eventual
marked direction of the electromotive force, which causes certain marked directions to be found in
various districts.

C. V. Walker has thought he could show that this constancy of direction was not due to local
causes, as he found the direction to be about the same for various places in England, viz: NE— SW.

Wild in Russia, Blavier in France, Batelli and Palmieri in Italy, and Bachmetjew in Bulgaria, also
found more or less the same direction — NE — SW; but Weinstein in Germany found it NNW— SSE
and Lament almost E — W in the neighbourhood of Munich.

(!) B. WEINSTEIN: Die ErdstrOme im Deutschen Reichstelegraphengebiet und ihr Zusammenhang mil erdmagnetischen Er

scheinungen. Braunschweig, 1900.
(2) W. VAN BEMMELEN: Koninklijke Akademie van Wetenschappen te Amsterdam, 1908.

PART III. KARTH CURRENTS AND EARTH MAGNETISM. CHAP. I.

As Lament and Bachmetjevv employed only short lines, and Palmier! made his observations on the
ope of Vesuvius, their determinations in this respect must be treated with great reservation. If we
ut them on one side, we may draw from the above the conclusion that the earth-currents as a whole
ill be inclined to flow in a direction N— S in Europe; but local circumstances at the various places
•ill often cause the currents to deviate considerably from this main direction.

In the United States of America it has been found that during magnetic storms it is the lines
inning E — W, or NE — SW which are most strongly affected.

In India the directions of the earth-currents, from a number of observations on telegraph-lines,
as found to be N — S.

DIURNAL VARIATION OF EARTH-CURRENTS.

142. As first shown by Barlow and later by Airy, the earth-currents recorded on calm days show a
;ry marked diurnal period. On this point all authorities who have entered into the question seem to
jree. The result is confirmed by Wild. Tromholdt, observing on telegraph-lines in Norway, found a
incipal maximum at about 7 — 9 p.m.

The most extensive and complete treatment of the diurnal variation is that of B. Weinstein. He
und the average diurnal variation for the five years from 1884 — 1888, and also the variation for the
air seasons of the year, and finally the diurnal variation for each month. The type of variation is
-•ry similar all through the year, but the amplitude is greatest in the summer and smallest in the winter
•ason The diurnal period, whatever may be its cause, appears to be a very definite thing, showing
jite definite properties. In accordance with Walker and Airy, Weinstein says:

"After this I think that we already by looking at these curves can draw no other conclusion than
lat the phenomenon with which we here have to deal is a real one, and that its origin is due to a
rocess of a more general character(')".

From the comparison made with the diurnal period of terrestrial magnetism, it appears, as the
isult of all the efforts made to find a connection, that no simple relation is found between the two
nenomena.

Weinstein finds a similarity as regards variation of earth-currents and that of the total intensity,
lit such a similarity seems very difficult to interpret physically, for the effect of a surface-current
^tending over a large area should distinctly be felt in a similar manner in the horizontal elements, i. e.
edination and horizontal intensity. Weinstein, however, is of the opinion "that nearly all the total move-
lent observed on the magnetometers generally named terrestrial magnetic variations, are only caused
1; variations of the earth-current, which affect the magnetometers in the same way as galvano-
ieters"(2). But this result of Weinstein's does not seem very convincing while he takes for granted
lat "when the current-sheet has a horizontal position, there should not exist any horizontal magnetic
irces worth mentioning(3)". Lately van Bemmelen (4), from records observed in Java determined
te diurnal variation and found by comparison with magnetometer records "that the direction
( the earth-current is such that it can be regarded as causing the variations of the magnetic com-
pnent and that the vibrations for them correspond"; but he finds "that the magnetic component is
itarded with respect to the earth-current", and finally "that the ratio of the amplitudes of corresponding
'brations decreases with the duration of that vibration, so that those of the earth-current are relatively
Irger with a shorter duration".

(') loc. cit. p. 18.

<?\ loc. cit. p. 78.

(3) loc. cit. p. 69.

|J) v\.\ BKMMKI.KN • loc. cit. p. 513.

730 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

The difference in phase as well as the change in the relative magnitude of the amplitudes of the
two phenomena with variation in length of period of vibration, is against the view that the diurnal
variation of terrestrial magnetism is entirely due to earth-currents. In fact most authorities— Barlow
Airy, Wild, Lemstrom, Ellis— consider it very doubtful whether the earth-currents can explain the diurnal
variation of terrestrial magnetism.

We are not at present going to discuss fully the problem of the diurnal variation of terrestrial
magnetism, which will be reserved for a subsequent chapter; but I think we may say that in spite of
of the most elaborate researches into the laws of terrestrial galvanic currents, no one has been able to
show that these currents form the principal cause of the diurnal variation of terrestrial magnetism.
Moreover recent investigation on magnetic diurnal variations, especially by A. SCHUSTER(I), von BEZOLD|'-|
and SCHMIDT has led to the result that the currents causing the diurnal variation must have their seat
above the surface of the earth.

EARTH-CURRENTS AND MAGNETIC DISTURBANCES.

143. Most investigators in the field of earth-currents since 1880, have confirmed the result of
Airy with regard to the connection between these currents and magnetic disturbances. It is in particular
Blavier who has got results essentially different from those of Airy. Lemstrom, Wild and Bachmetjew,
however, all agree with Airy, who considers the earth-currents to be the cause of magnetic disturb;]
Most investigators, however, consider that there are certain exceptions yet to be explained.

Blavier, on the other hand, found that the earth-currents and magnetic disturbances are not related
in such a way that the earth-currents have produced the magnetic variations; but he takes rather the
opposite view that earth-currents are produced by the changes of magnetism. According to him the
magnetic disturbances were mainly due to extraterrestrial currents above the place, while the earth-
currents are produced by induction due to changes in the extraterrestrial currents.

This assumption is based on the fact that from his records he found the amplitudes of the accidental
earth-current to be proportional to the rate of change which at the time considered is found for the
corresponding magnetic elements.

Although Blavier, in a way, is certainly on the right track, I should consider it probable, in view
of the results of the other investigators, that he is giving his conclusions too great generality. It might
even be possible, as Blavier himself admits, that his induced currents are not altogether real earth
currents, but are partly currents induced in the cable system. Such currents, indeed, may have been
present and may have influenced the results so as to give the impression that the induction-relation
holds more general than it actually does. In order to find out whether the induction in the cable-system
exerted any real influence, Blavier made simultaneous observations over the same areas in underground
cables and in aerial lines. As the two curves thus obtained were identical, he thought himself justified
in concluding that the currents observed were due to actual earth-currents.

Quite recently the question regarding the connection between earth-currents and magnetic distur-
bances has been treated by J. BOSLER (3), who has examined a number of disturbances recorded at Pare
Saint-Maur. He finds for the cases considered that the relation is such as would be expected if the
perturbing forces were directly due to the earth-currents flowing underneath the magnets.

(') A. SCHUSTER: Phil. Trans, of the Roy. Soc. Vol. 180, p. 467, 1889.

(*) W. VON BEZOLD: Sitzungsberichte der Kgl. Akad. d. Wissenschaften zu Berlin, 1897.

(3) J. BOSLER: Comptes Rendus, p. 342, 1911.

PART III. EARTH CURRENTS AND KARTH MAGNETISM. CHAP. I. 731

The opinion expressed by Wild, Weinstein and others on the one side, and Blavier on the other,
cpresent the two extremes. We think that the right explanation will be one which unites the two
xtreme cases into one theory.

In fact we think that recent investigations on terrestrial magnetism have already made it possible
look into the complexity of earth currents with a keener eye than it was possible for those who
/ere working some years ago.

Through the works of A. SCHUSTER('), von BEZOLD and AD. SCHMIDT, we are already familiar with
K- idea of extraterrestrial currents. The existence of such currents is a necessary consequence of the
ypothesis that magnetic disturbances are the effects of electric radiation from the sun.

My previous research (2) as to the cause of various disturbances has shown that at any rate at places
car the poles, most magnetic disturbances are due to peculiar current-systems above the surface of the earth.

The view we take as regards the cause of magnetic disturbances will necessarily influence the view
•e take as regards their connection with earth-currents. If our hypothesis is right, we shall certainly
et currents induced in the earth on account of changes in the external currents.

Recently van Bemmelen in his paper, "Registrations of the earth-currents at Batavia for the investi-
ation of the connection between earth-current and force of earth-magnetism", treats the earth-currents
om the point of view, that they may be considered as currents induced by external currents.

He finds the ratio of the amplitudes in the earth-current registerings to the corresponding magneto-
ieter-records to increase as the time of oscillation diminishes and usually finds a difference in phase
etween the earth -current oscillations and those of the magnetometer.

ARTH-CURRENT REGISTERINGS AT KAAFJORD AND BOSSEKOP, 1902—1903.

144. At our stations Kaafjord and Bossekop, the earth-currents were recorded in cables, 400 metres
•ng and resistance 1.55,?.?, one directed along the magnetic meridian and another perpendicular to it.
he cable-system formed a cross with equal branches, in the centre of which the instruments were
troduced.

The galvanometers employed were of the type Deprez-d'Arsonval, and were placed as a shunt on
>e principal line, as indicated in the accompanying figure.

The current measured in this manner on the galvanometer, will be a standard for the component

the earth-current which goes in the direction of the connecting line between the two earthplates,

•, if preferred, for the component of the electromotive

rce occurring in this district.

The earth-current conditions will be to some extent
mnged when the cable is introduced. This might be
;sumed to have special influence if the resistance in the <<
ible is small in comparison with the earth-resistance. If,

i the contrary, a great resistance is introduced into the

^ 'fOO"1

rmer, it will not have any appreciable influence.

Fig. 269.

How important a part this may play it is not easy
say; but in any case it will not exert any essential influence in the main phenomena.

The influence of the polarisation of the earth-plates will be very considerable where the lines, as
this case, are short. Here, therefore, it is only the brief variations that are suitable for investigation

7

Earth

(') A. SCHUSTER: Phil. Trans, of R. S. 180, p. 467, 1889.

I3) Expedition Norvegienne 1899—1900. Parti of the present work.

732

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

by this arrangement, and it is also these that are of special interest to us. They will be only slightly
influenced by the plate currents, as the changes that might take place in the polarisation conditions must
be assumed, as a rule, to take place comparatively slowly.

Possibly occurring thermo-electric forces will as a rule also undergo only slow, gradual changes.

Finally, we have left the effect of the direct induction in the cable-system, produced by the mag-
netic variations. This is made as small as possible by placing the cables on the ground.

In order to obtain an idea of its amount, we may make the following estimate. We will assume
that we have a surface of flow of 400 sq. metres. Further we will assume that the component of the
magnetic field at right angles to this surface varies with a velocity of 100 y per minute. In the system
there will than be induced an electromotive force with magnitude

io

„ o.ooi X 400 X
~8

60

6.7 X io~7 volts.

- volts

Now the earth-resistance between the plates has been measured and found to vary between 150 i>
and 1500 i?. If we employ a mean value of 670 Q we find the strength of the current to be

. _ 6.7 X io~7
670

io~9 amp.

This current is divided between the galvanometer and the shunt, generally in the proportion i
Thus through the galvanometer there will pass

Tr,— 9

= 3 X io~12 amp.,

300

and a current of this size will produce a deflection on the photographic paper of about

3X

3 X

= o.ooi mm.

Thus, even for so powerful a variation in the magnetic field, there will if our assumptions hold good
be only an imperceptible deflection, whereas in reality very considerable deflections are found with
variations of such magnitude. The surface of flow must therefore be of an altogether different order of
magnitude, if this kind of induction is to have any disturbing influence.

It appears from this estimate that what we observe must be produced by actually existing earth-
currents.

As regards the nature of the soil, the following may be said.

It will be seen from the maps on p. 15 of Section I, that the observation-place in Kaafjord is situa-
ted in a region that is inclosed on all sides by high, steep mountains.

Alien Fjord, moreover, sends a narrow branch, Kaa-Fjord, up into this mountain mass; and the
earth-current cables were laid upon the terraces above this branch-fjord, just at the foot of the excee-
dingly steep slope of Grytbotten Mountain.

These mountains are probably very rich in well-conducting veins of copper ore.

At Bossekop, the region surrounding the observation-place is flatter, and it would appear that th
the local conditions play a less important part.

The reader is further referred to the description on p. 14, Part I.

Records were kept at Kaafjord from the middle of November, 1902, to the end of February, 1903,
then the registerings were continued at Bossekop until April 2.

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I. 733

It is beyond our power to give the complete series of records of the earth-currents during this period ;
jut we shall attempt to give, as far as possible, a true representation of the typical cases of earth-
.-urrent phenomena by selecting a number of disturbed days for which we have successful records.

We are of course aware that a complete representation would have been preferable ; but such a
Drocedure in our case is excluded from the very fact that owing to difficulties with the galvanometers
iiiccessful earth-current registerings are wanting during considerable intervals, and unfortunately records
>{ earth-currents are wanting for a number of the very greatest disturbances. Being unable to give a
omplete representation, I think our procedure will be the best one, because very little would be gained
y giving curves for intervals during which nothing of particular interest has happened.

The curves treated will be represented at the end of this volume in a series of plates giving a
lirect reproduction of the curves recorded photographically. In addition to the earth-current curves, the
nagnetometer registerings will be given for the same interval. The curves were copied partly photo-
graphically, partly by drawing on transparent paper directly from the photograms.

On each of the earth-current curves an arrow is drawn giving the direction of the galvanic current
vhich produces a deflection in the direction of the arrow.

The plates are divided into three series.

The first series contains, in chronological order, a number of 24-hourly records representing mode-
•ate variations.

The second scries contains 24-hourly records of a number of comparatively great storms, in fact
he series contains all the great storms for which earth-currents have been successfully recorded.

Thr third series contains a number of two-hourly records.

Although we are unable to find absolute values of the earth-currents, it may still be of interest to
hid relative numbers for the current-changes which accompany the magnetic variations In this way
ve may for instance be able to form vector diagrams for the currents, and compare them with the
orresponding ones for the magnetic elements.

The determination of the somewhat rapid changes of earth-currents only lasting for a few hours
an be done in a similar way as for the determination of the perturbing force, by placing on the photo-
;ram a normal line harmoniously connecting the quiet parts of the curve.
The change of current Jim the cable is given by the equation

G + s
Jl = £ - - Jn

s

is the shunt-resistance, G is the galvanometer-resistance, J n is the deflection measured on the photo-
;ram, e is the scale-value for the photogram, and gives the current through the galvanometer coil which
orresponds to a deflection of i mm.

The corresponding electromotive force J e between the cable terminals will be approximately

jc = (Q + s) Jl,

,-here Q is the resistance of the cable, and is equal to 1.55.1?, as throughout s is small compared with

/, or with sufficient accuracy

/~*

4e — — (p -H .s) . £ • Jn.

s

The quantity J r is probably not equal to the electromotive force J E between the same points in
ase the cable was removed. We may put

Birkelarul. The Norwegian Eurora Polaris Expedition, 1902 — 1903.

734

lilRKKI.AN'I). THE NORWEGIAN Al'RORA POLARIS EXPEDITION, I QO2 — 1903.

where c/ 1 and q> are quantities which depend on the resistance of the cable and the soil and on the way
in \vhich the cables are connected with the ground. These quantities, </\ and </> may easily be verv
large numbers.

During the stay at Kaafjord and Bossekop the resistance of the soil between the earth plates was
rvpcutcdlv measured by using a Wheatstone bridge arrangement with alternating current and telephone

The results of measurements are here given in tabular lorni.

TABLK CIX.

Date

Resistance

N~S E-W

Date

Rusistanrr
N-S K-\V

Nov. 15 .

,, 26 .

Dec. 4 .

6 .

I OOO

700

700

I 1 50

850

400
1 400
I 500
I 600

500

1 500

1 200

Jan.

;• '5
17

„ 3 r
Feb. . i

700

I OOO

75°

.(OO
'J OOO ,, 27

i 500 Mnri'li 7

i 7°° „ -'3
500 April i

i 500

i 250
Hoo

'5°

600
600
•150
650

400

-i 30
400

1 1OO

800

'5°
500
600
400
600
35°
13°
400

We notice that the resistance of the soil undergoes great variations, but always in such a way that
the resistance is about equal in both circuits.

As the earth-connections for the two cables were made as equal as possible, we should probably
at any moment be able to put

Thus I think when we take J >• as a relative measure of the earth-current, we ought to get approxi-
mately the right direction of the current. Values of J c found at different times with different conditions
of the soil however need not be exactly comparable.

CONSTANTS FOR THE EXPERIMENTAL ARRANGEMENTS.

145. The three galvanometers used we shall call si, 1> and />'.

The sensitiveness of the galvanometers was measured by disconnecting them from the cables and
exposing the instruments to a current of known strength. The deflections were indicated by marks
made by the spot of light on the photogram. The scale-values for the instruments were observed at
intervals and were found to keep constant within the limits of experimental error.

The scale value and inner resistance of the galvanometers are given in the following table:

TABLK CX.

Instrument

Resistance Scale- value

A

540 il 5.5 X 10 •' amp. mm.

B

735 „ '2.1

A1

|

57 .. 2.2

PART 111. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I.

735

The scale-values give the current in amperes corresponding to a deflection of i mm. on the origi-
nal magnetogram.

In order to calculate J e from the copies of curves given in the plates we must further know the
iint-resistance used in each case, and the galvanometer used in the two directions. These data are
given in the following table for the various plates.

TABLE CXI.

N-S

E-W

Plate Number

Galv.

5,

Galv.

•S,

ohm

ohm

I

A

i

B

j

I

a-8

2

B1

O.I

1

I

A

I

B

0.8

2- 7

n

2

„

2

8—io

„

a

B1

O.I

II

11-13

»

2

„

0.2

M-15

n

2

„

O.I

16

n

2

B

I

n

„

4

*

4

Date

Nov. 14 ....

A

I

B

I

III

„ 24 ....

'

2

m

2

25 ....

»

2

n

2

March 31 . . . .

»

4

«

4

The shunts will also be put up on each plate, where

-St is the shunt in E — W circuit
S3 » » » N— S

With the exception of the two-hourly records of November, the direction can be found from the
bllowing rules:

For the N — S curve a deflection upwards corresponds to a current from north to south, and for
he E — W curve a deflection upwards corresponds to a current from east to west.

The perturbing forces can be calculated from the curves in the usual way by using the scale-
values given in Table II, Part I, p. 50. The direction can be found from Table VIII, p. 59, or from
.he rule that on the plates a deflection upwards corresponds to increasing H. I., increasing westerly
declination and increasing numerical value of V. I.

The sensitiveness given in the tables corresponds to the curves on the original photogram. The
;ensitiveness to be employed in each case can easily be found by measuring on the base-line of the
ilate the length ([) which corresponds to one hour. Then we obtain for the scale-value to be employed

/

24
/

for 24-hourly records

£ is the scale-value corresponding to the original photogram; / is to be measured in cm.

736 BIRKELAND. THK NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

In calculating the scale-values we can with sufficient accuracy put the length of one hour on tin-
original photogram equal to 2 cm. for all twenty-four-hourly records and equal to 24 cm. for all two-
hourly records.

These values are true for the magnetograms within the limits of error of determination. For the
earth-current photograms the hour-length is a little greater, for 24-hourly records it is about 2.015 CIT>,
for 2-hourly records about 24.18 cm.

In copying the curves we have decided not to make reductions for the small differences in hour-
length. The curves have been copied directly partly photographically partly on transparent paper, and
then the whole plate is reduced to its proper size.

The time-marks given are as a rule first determined on the magnetic curves, as there the deter-
mination of time is easist and surest. In the next place, the time-marks are transferred to the earth-
current curves, by the aid of synchronous serrations in them and in the declination-curve. This, as «•<•
shall show later, is permissible, and is the surest method when there are not simultaneous time-marks
on both sets of curves.

In the rapid registerings on the contrary, we have by an electric arrangement exactly simultaneous
time-marks on both sets of curves. These are marked on the plates, and the time is given below for the
first and last break.

THE MAGNETIC EFFECT OF EARTH-CURRENTS.

,e effti :

146. Regardless of the way in which the earth-currents are produced, they must have some
the magnetometer, and thus in a way it may be said that magnetic disturbances are due to earth-
currents.

In fact looking at the records we find, especially for the fairly moderate perturbations, that there
is often an almost exact correspondence between the earth-current and the magnetometer curves, which
shows that in these cases a considerable or rather the greater part of the magnetometer deflections are
directly due to earth-currents.

Unfortunately this circumstance is not so distinctly shown on the copies as it appears in the
original curves.

It is principally in the very small jags that the resemblance is most striking, and it has been found
difficult to make an exact reproduction of these by drawing them on tracing paper.

Some of the curves have been copied photographically, these being both sets of curves for January
26 and February 10, and the earth-current curves for March 30 — 31.

In these it is easy to see the great similarity between earth-current and magnetism in their small,
rapid oscillations.

In the curve for the loth February especially, given as No. 13 in Series II, the characteristic
oscillations at about 2oh are noticeable, these being apparently identical in the earth-currents and the
horizontal magnetic elements, only shown in different scales.

There seems, therefore, in this case to be no doubt that the oscillations in the magnetic curves are
to be understood in the main as the direct magnetic effect of the earth-currents.

If the time for the various jags be determined, it is also found that they are simultaneous within
the limit of error to be taken into account here.

If we compare the amplitude of the deflections by these jags, we have a means of finding
the effect of the earth-current. As, further, the total effect of the earth-current should be approximately
proportional to the deflections measured on our galvanometers, we can, with this to aid us, eliminate
the effect of the earth-current on the magnetograms.

TART. III. KARTH CURRKNTS AND KARTH MAGNETISM. CHAP.

737

Now forces of other origin will always be asserting themselves, but if we take into consideration
only those in which the similarity is greatest, and employ a large number of jags, the mean of all these
will give a more or less correct result, provided that an approximate proportion is always found to
exist between the deflections in respect of amplitude.

For this purpose we have measured about 400 jags for Kaafjord, and about 100 for Bossekop.

We give here some of these determinations, as also the calculated mean values.

TABLE CXII.

Date

Ph

Ph

PA

Pd

JeKW

Date

Ph

Plt

1

p*

Pd

JeEW

J<MW

*ty

^W

^'v.s-

Jfxs

*<MV

''IS

«»MW

*S8

*»8

30-31

19 — 20

Oct. 0.22

0-35

0.40

0.60

'•53

Dec.

0.24

0-34

0.40

0.56

1.40

0.35

0.78

2.25

0.2O

o-35

0.28

0.48

1.72

0.19

0.32

1.68

0.34

o-37

0.46

0.70

1-5'

0.23

0.41

1. 80

0.30

o.37

0.38

0.47

'•25

0.32

0.48

1.50

o-54

0.88

1.61

0.28

0.48

1.74

o-39

0.49

0.64

0.80

'.25

0.43

0.66

1.56

0.36

0.61

1.68

24-25

o-45

0.66

1.50

Dec.

0.26

0.15

0-59

o-35

o-59

0.58

0.92

1.62

0-39

0.26

034

0.31

0.64

0.29

0.48

1.68

O.23

0.18

0.43

0.36

0.84

0.50

0.96

1.92

0.46

0.34

o-39

O.29

o.73

0.18

0.43

3.40

o-35

0-33

0.36

°-34

0.92

0.49

I.IO

3.28

0.46

0.32

0-34

0.33

0.69

0-39

0.68

'•74

o-33

0.25

0.74

0-55

0.74

0.38

0.62

1.68

0-54

0.36

0-55

0.36

0.67

0.42

0.68

1.65

0.44

O.2O

0.46

0-45

0.83

1.86

0.98

0.43

o.43

0.36

°-55

1-56

'

0.52
°-57

0.72
0.96

'.38

1.74

29-30
Jan.

'•39

0.78

1.67

o-93

0-57

0-23

0.42

0.48
0.36

°-35
0.31
0.41

0.69
0.65
o.59
045
0.69

1.46
1.83
I.7I

1.50
1.68

'•39

1. 00

"•95
0.72

0.27
0.36
°-39
035
0.23

2.23
2.60
1.83
1.50
i-33

°-43
0.38
0.70
0.56
0.42

o. 19
0.14
0.38
0.38
0.32

0.40
0.39

o-59
0.60

1.50

0.72

0-39

o-93
1.76

0.50
0-93

0-55
0-53

0.26

0.43

1.68

0.50

0.15 i. 80

0-53

0.29 •

o-39

O.Og 2.OO

0.53

0.26

0.12

0.42

0.20 0.45

o-73
0.72

'•74
1.62

0.6 1

O.2I

1.67

o-57

o.34

0.30
O.I2

0.5I
O.2O

0.66
o-55

0.94
0.84

'•59
i 56

' 5°
1.50

0-35
0.23

1.83
3-43

0.42
o-37

0.23
o.'5

0.36
0.36
0.23
0.32

0.41
0.51

0.61
o-54
0-35
0.67

0-75
0.82

'•74
'•50
1-56
2.07
1.83
1.62

2.12
2.23

3.5'

,.67
0.39

O.2I

0.26

1.17

0.44
0.13

2.50

t-33
2.96
2.76
2.66
1.67

0.25
0.15
1.40
0.70
0.70
o-55

O. IO
0. 12

0.47
0.25
O.26

o-33

0.36

0.56

'.56

1.50
3.13

0.44
0.74

1.50
2.83

0.44
0.96

0.29

19 — 20

1.84

0.66

'•33

0.47

o-35

Dec.

0.15 O.2O

0.48

0.64

1.30

3-83

1.32

°-34

°35

0.44

'•35

1.67

0.88

o-53

0.31

0.62

3.03

2.66

1.40

o-53

°-34

0.30 0.88

2.76

0.88

0.32

0.28

0.70 2.44

2.03

0.60

0.29

0.38

0.70

1.87

2.36

'.05

0.44

738

BIRKELAND. THK NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.

TABLE CXII (continued).

Date

Ph

P.

Pd

Pd

JeSH.

Date

P,

Ph

Pd

"• i

'J*W

*»S

^W

**m_

**

*>MW

<*<m

-**..•

4*KS

7— 8 Febr.

I.OO

0.64

1-73

i. 08

0.63

10— II

Febr.

1.66

1.06

o-59

'•57

0.88

0.57

I.OO

0.42

0.42

i-45

0.63

i-73

0.76

0.44

I.IO

0.52

0.48

i-45

0.74

2.26

1.13

0.50

1.22

0.40

1.70

Q-57

o-33

0.56

0.26

'•93

0.90

0.46

i-34

0.28

1.36

0.29

O.2 1

0-95

0.49

1. 60

0.82

0.50

I.OO

0.29

1.83

0.52

0.29

0.72

0.42

1.76

i. 08

0.61

1-33

0.70

0.52

i-34

I.OI

J-33

I.OO

0.76

1.17

0.49

0.42

I. II

0.47

2.16

0.91

0.42

1.67

0.91

0-54

1-43

"•93

0.65

I.OO

0.60

0.6 1

i-34

0.67

i-37

0.70

0.50

1.27

0.70

0.56

I.OO

0.50

i-37

0.70

0.50

1.87

1.05

0.56

2.OO

0.84

0.42

I.IO

0.70

0.65

2.OO

0.58

0.29

1.96

0.98

0.50

J-33

0.62

0.46

0.73

0.42

0.58

1.57

°-55

0.36

I.IO

0.52

0.48

1.67

0.8 1

0.48

r-43

0.70

0.48

1.40

0.62

0.44

i-43

0.70

0.48

i -58

0.76

0.48

i-33

0.70

0-5=

1.67

0.70

0.42

r-33

0.77

0.58

1.27

0.42

°'33

1-33

0.70

0.52

9 — i o

Febr.

2.50

1.05

0.42

2.13

0.62

0.29

1.83

0.84

0.46

2.86

1.05

Q-37

2.66

°-93

0.36

0.72 0.47

•i.oo

0.70

0.63

12 — 13

i-39 °-59

2.16

0.91

0.42

Febr.

0.36

0.18

1.05

0-54

0.51

r -39 °-39

1.83

0.60

0.32

0.80

0.41

1.03

0.52

o-5'

3-5°

0.97

1.67

0.47

0.27

0.74

°43

0.82

0.48

0-59

0-33

0.26

0.60

0.44

0.71

0.62

0.49

o-S9

0.47

0.78

Q-33

0-45

0.25

0-39

0.29

0.94

0.70

0.74

i-39

0.36

0.83

O.22

o 26

0.68

o-35

0.96

0.49

0.51

2.OO

0.42

3'°3

0.64

O.2I

0.92

0.65

0.89

0.62

0.70

1.72

1.02

2.OO

I.I7

°-59

0.71

°-53

0.84

0.62

o-74

I.I I

0.42

1. 80 0.67

0.38

0.92

0.58

0-55

°-35

0.62

o.6r

O.22

i-53 °-53

0.36

0.42

0.23

0.77

0.42

o-55

0.56

0.21

t-93

°-73

0.38

0.89

0.70

o-53

0.42

0.78

0.30

O.2O

Q-53

°-35

0.66

10— I I

1.22

0.68

o-73

0.41

o.55

Febr.

0.84 0.35 1.37 0.57

0.42

1.10

0.49

0.66

0.40

0.62

1. 1 1

0.46 i.io 0.45

0.42

0.89

0-55

°53

0-37

0.70

0-95

0.67 I.O3 O.7O

0.69

I.O7

0.58

0.64

0-35

0.55

0.89

0.42

1.46 0.70

0.48

0-39

0.29

o-59

0.44

0.74

0-95

0.42

i.io 0.51

0.46

0.50

0.28

1.09

o-59

0-55

1.17

0.58

0.97 0.49

0.50

0.74

I.OO

0-73

o-39

1.13 0.61

0.52

0.50

1.19

0.89 °-44

1.07 0.52

0.50

0-59

0.44

1. 12

0.83

0.74

i.oo 0.58

1.07 0.63

°-59

0.56

0-37

0.98

0.65

0.66

0.89 0.42

0-73 0.35

0.48

0.72 0.27

1.46 054

0.38

0.84

0.46

i.oo 0.54

0.52

14-15
Febr.

0.50

0.23

1.43 0.65

0.46

0-75

0.61

0.26

0-93 0.39

0.42

0.68

0.78

0-34

i. 60 0.70

0.44

1.16

'•27 0.55

0.44

1.05

I.IO

"•S3

0.84

—

PART III. EARTH CURRKNTS AND EARTH MAGNETISM. CHAP.

739

TABLE CX1I (continued).

l\

Pt

Pd

pd

JeEW

/»

Ph

Pj,

Pd

JeSH.

Date

*>MW

<t<M

*>MW

*n

**n

Date

~^*w

-^Y.V

*MW

^n

*M

14 — '5
Febr.

0.50

0.47

16— 17

Febr.

0.84

0.55

0.66

0.50

0.30

0.64

o-54

0.86

0.27

0.96

o.77

0.64

0.86

1.30

0.66

0-49

0.74

0-33

1.07

!.48

0.47

0.78

0.84

0.82

0.98

1-33

1.48

0.70

o.47

0.44

0.78

1.37

0.82

0.59

0.50

1. 01

0.77

0-53

0.68

0.78

0-53

0.52

0.98

0.71

0.89

0.58

0.66

1-25

0.77

o-53

0.68

0.77

0.70

0.90

0-77

0.60

0.78

1-25

0.70

0-55

ID — 1 6

Febr.

2-37
0.62

0.94
0.80

1.19

1. 21

0.76
0.90

0.62
0.74

0.77

0.77

0.65

1.40

1.11

0.82

I.OO

1.03

0.85

0.82

0.66

o-93

0.80

0.86

0.62

0.68

0.50

0.96

0.70

0-73

1.16

0.45

o-35

1.16

0.91

0.78

0.82

0.45
0.56

0.32
0-39

1.42
0.86

I.OI

0.61

0.70
0.70

0.98
0.89

1.07

0.70

0.66

1.48

088

o.59

0.50

0.74
0.80

0.54
0.58
0.70

0.77
0.77
0.80
0.69

0.53
0.80
0.63
0.61

0.70
i 05
0.78
0.86

o-59

2. IO
0.89
1.26

030
..30
0.50
0.8 1

0-59
0.63

0.55
0.62

0.92

0.85

0.77

0.70

0.90

0.45

028

0.62

0.68

0.57

0.82

1.65

1.03

0.62

0.87
0.87

0.80
0.70

0.92
0.82

0.25
0.73

0.23
0.52

0.47
°-7P

1.07

0.73

0.66

0.52

0.41

0.78

0.98

1. 10

I-I3

0.96

o.49

0.51

0.27

0.15

0.89

o-53

0-59

^37

0.70

0.51

0.91

0.67

0.70

1 OO

0.58

o.59

0-33

0.28

[-05

0.92

0.86

0-33

0.26

0-93

0.73

0.78

0.94

0.76

0.78

17—18

0.77

0.60

0.78

Febr.

0.65

0.47

1.28

0.91

o 70

I.OO

0.88

0.88

0.44

023

1. 12

0.60

0-53

0.73

0.64

0.86

0.43

o. [6

1.78

0.70

0.70

0.52

0.41

0.78

0.59

0.29

1.42

0.70

0.49

0.96

0.92

0.94

1. 12

0.86

0.85

0.69

0.70

0.97

0.74

'•51
1.43

j

1.05
1.25
0.89
0.80

0.98
0.84
0.79

0.78
0.94
0.98

I.48

0.36
1.07
2.24

0.55
0.15
0.58

O.ID

1.91
1.26
1.41
1.96

0.70
0.56
0.77
0.62

0.36
0-43
0.55
0.62

I.OO

0.78

0.78

080

0.56

0.70

1.07
0.78

0-97

0.77

0.90
0.98

1.42
0.89

0-93

I. 12

0.65
'•25

I.OI

0.93

0.90

1.28

0.80

0.79

0.97

•

740

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION. 1902 1903.

TABLE CXIII.
Mean Values for Kaafjord.

Pi,

Pi,

Pd

Pd

**gw

Date

A<?£1|.

TV

*»m

&eKW

N

Aexs

N

&em

-Si S>

1

30—31 Oct. . . .

O.3I

5

°-35

5

0.38

47

0.65

45

1.69

0.8

I

2—3 Nov. . . .

0.49

13

0.70

13

i-39

08

1

19 — 20 Dec . . . 0.27

6

0.36

6

0.40

12

o.6r

12

I.5I 2

3

24-25 „ ...

0.38

8

0.28

8

0.51

IO

°-33

10

0.64

2

2

4-5 Jan

0.80

7

2

2

29 — 30 „ ....

1. 16

15

°-37

'5

2

22

0.71

24

0.36

0.2

2

7- 8 Feb. . . .

1.05

12

0.52

1 1

1.64

27

0.80

24

0.49

0.2

a

9-10 ,

1.28

8

o-37

10

I.9I

15

0.71

16

0.38 0.2

a

10—11 „ ....

I

22

0.38

22

'•37

51

o.59

49

0.43 0.2

2

11-12 „ . . . . 0.53

22

0.41

22

°-75

36

0.67

38

0.89

O I

2

12 — 13 „ .... 0.68

22

°-43

20

0.82

22

0.50

20

0.61

O.I

a

14-15 „ ....

0.44

8

0.89

'7

O.I

a

15 — 16 „ . . . . 0.59

14

0.49

'3

0.91

39

0.77

37

0.84

O.I

2

16— 17 „ ....

0.96

38

0.64

29

0.66

O.I

2

17-18

0.77

9

0-33

8

1.32

14

0.74

1 1

0.56

O.I

2

Weighted Mean

o 74

o 40

1. 02

0.66

0.82

The number of jags used in the calculations are indicated in the columns "N". The numbt
Pfjc are expressed in the units y/microvolt; de corresponds to a distance of 400 metres

In the calculation of the above, a number of the jags that agreed ill were left out of consideratio

The table also gives the relations P^I^CEW and PhjJcss-

These quantities only acquire physical importance if we assume that the currents within the area i
which they influence the magnetometers, are of so local a character that the observed Je^ and Jo
cannot be said to represent the corresponding earth current components, or in other words, if the eartl
currents here flow along comparatively very sinuous current-lines. We have here included tin -i
they can be employed for the purpose of eliminating the effect of the earth-current in cases in whic
we have only successful records of one earth-current component.

These figures show how great accuracy we attain by this method.

Among similar synchronous oscillations may be noted those occurring in the interval betwet-
2ib and 22'' on February 10.

Here too, however, there are evidently considerable direct effects of the extra-terrestrial curren
systems; but they do not appear to have so rapidly changing a character as the variations that are du
to the earth-currents.

An examination of the remaining curves will show similar synchronous oscillations throughou
I will here draw attention to a few of the more characteristic in Series I.

January 13, time about i6h

18, » » I5b — IS1/-/1

20, »
February 1 3, »

I9h—

23,

» 19'' — 21"

» 4h — 6h and

2Ib— 221/,1'

i6h— 24h,
especially about I7h.

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I. 74 l

In Series II we have collected a number of powerful storms. Here the external perturbing forces
terfere largely, so that the effects of the earth-currents only appear, as a rule, as secondary waves on
main dellections. Here too, however, they are generally very distinct.
We will indicate a few.

Dec. 26, time about 2o3/4h

Jan. 23, » I?2/;

l/8h

Feb. 7, » I7h— 18''

and 2ih — 22''
9, » about 18''
10 & IT, » 23'' — i1'.

The last two sets of curves in Series II are from Bossekop. We will examine them a little more
isely later on.

On looking at the reproduced curves from Kaafjord, and especially the intervals mentioned above,
\- notice in the first place that the two earth-circuits exactly correspond in every detail; and as the
ble CXII shows, the relation between the deflections in the two components for one and the same day
• very nearly constant, whereas it varies somewhat from day to day.

In the next place, the resemblance between the earth-current curves and the declination curves is

considerably greater than between the former and the horizontal intensity.

These facts are, I think, accounted for by the small sentiveness of the H, /.-magnetometer com-
•ed with that of the declinometer, and further by the fact that the direct effect of extra-terrestrial
•rent-systems is much more pronounced in H than in D.

Owing to the smallness of the oscillations and the difficulty of identification Ph is only found in
i ntively few cases.

If we could put (/! = q.,, we should expect to find that the relation Phjje EVi. would equal PdjjeNS
II we compare the mean figures, we also find that such is the case; but while the relation
/ _A'VS. remains nearly constant all the time, relation Ph/Jcf.w varies very considerably. As long as
tH shunt is kept unaltered, however, the relation is fairly constant.

Before January 12, in the NS line, galvanometer B was employed, after that date galvanometer
h With the change, a very distinct leap in the values of the relation Pijde Kg is observable. A simi-
la leap is observable at the change from shunt-resistance 0.2 Q to o.i J2.

In the last case the relations are reduced to very nearly half the value, which probably indicates
th: contact-resistances have here played a decisive part, and they must be assumed to occur in the
slint-circuit itself. An explanation may also be found for the discontinuity here found in the conditions
c.i i changing the galvanometers on January 12, merely by assuming that an influence is exerted by
cc tact-resistances. In such case it must be assumed to occur at the points where the cable is connected
w i the galvanometer and shunt circuits. Its effect will be the same as if the resistance of the cable
increased by a corresponding amount.

It is therefore doubtful whether any great importance can be attached to the agreement between
th mean figures.

ON THE CONNECTION BETWEEN POLAR STORMS AND EARTH CURRENTS.

147. As above mentioned the second series of plates, PI. XXI — XXIII, contains a number of
sii iltaneous records of earth-currents and the magnetic elements during a number of comparatively
-nt storms. The conditions during polar storms are also given in greater detail in some of the rapid
: • MI\!S contained in the third series of plates, e.g. PI. XXXIV and XXXV.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903. 94

-_|2 I'.IKKKI.A.M). [UK Me >R WFe ,1 A.\ ATKoRA I'UI.ARiS KXI'l-'lHTle >N, I gO2 1903.

I he first important conclusion which we can draw from the curves is tin.1 following:

Tin' ini'lli i'iirn:i//s us inanifrsletl l>v tin' galvanometer ilrflcctinns if/trim; point- star/us <v//;t7i IMI;-
t/n'/r Cfii/ri's in ////' I'irinilv <>/ llif station, cannot explain the main part <>/ the perturbing force.

The justilioatioii of this conclusion will he immediately apparent on looking at the curves; fi,'r
while the magnetometers can maintain a largo deflection in a certain direction lor hours, the galvano-
meters will change direction of deflection relative to the normal line usually a great many times duriii"
the same period. Indeed the galvanometer curves have often the appearance of oscillations round tin-
normal line (see I. i. the curves tor Nov. 2 and Fe.br. 12).

Now we saw in the previous article that the earth-currents produce- magnetic variations according
to rules given in tahle CX11I.

In consequence we. always find that, superposed on the main wave of the magnetometer curve, which
is probably due to extra-terrestrial currents, there arc a number of waves and oscillations which, as regards
occurrence and form, coincide with the galvanometer oscillations, a phenomenon, that is well illustrated in
Series 1 and II, Plates XXX XXXIII, and even better in Series 111, Plates XXXIX' and XXXV, giving the
copies ot a number of rapicl-registerings. hrom the coincidence in form and phase I think we may safely
conclude that these; synchronous and similar rapid magnetic changes are direct effects of earth-currents flowing
underneath the magnets. 'I his conclusion is also confirmed by the fact that the curves of vertical intensity
run more smoothly than those' of the horizontal elements; for if the rapid changes are mainly due to
earth-currents spread over a considerable area, such currents would produce verv little effect in the
vertical din ction.

The rapid synchronous oscillations in the two sets of curves will always occur with greatest strength
simultaneous with the strongest magnetic disturbances, and from this it is evident, that these briefer
variations must be due to the same primary cause as the magnetic storms themselves, i. e. according to
our assumption to an extra-terrestrial corpuscular current-svstem. The most natural way of explaining the
connection between the outer current system and the earth-currents is that the latter are induced by
variations in the former. From this, however, we cannot draw the conclusion that we always must find
such a simple connection between the two sets of curves as that expressed bv the rule of Blavier. On
regarding the curves one would also see, that such a connection in far the most cases does not exist.

From the relations given in Table (.'XIII we should be able; to subtract from the magnetometer-records
the effect of the earth-currents. But even this corrected curve would hardly be competent to explain from
the rule of Blavie-r the manv oscillations of the earth-current curve. Looking at the curves for Kaafjord
we shall often find that the corrected curve for this place will apparently run rather smoothly compared
with that of the earth-currents.

This circumstance is easily explained when we consider how the perturbation-conditions develope
in the polar regions.

\Ye have become acquainted with the typical arrangement of the polar svstems. On the afternoon
side in latitudes that are not too high, we me-e't with the positive' polar storms, on the night side with
the negative. Wo have- seen that the positive system answers to the effect of ravs that descend towards
the earth, arc ele-llected westwards, and again leave the earth; the negative: to rays that are deflected
eastwards. Both these current-systems presumably lie at a comparatively great height above the auroral
/one, and their smaller and more rapid changes will therefore be' less evident, and the curves in consequence
are- characterised bv comparative smoothness. Among these svstems, however, rays are met with, which
descenel dire-ctly earthwards te> within e'omparativelv small heights above the surface of the earth. Here
the.- magnetic e'tirves are- exceedingly serrated. 1 hero are verv rapiel and comparatively strong variations,
some of wlue'h are due- to displacement of the districts of positive' and negative precipitation, and some

PART III. KARTH CURRENTS AND EARTH MAGNKTISM. CHAP. I. 743

i) the fact that every change occurring here will be felt comparatively powerfully in places where the
•ays come very near to the earth.

Kven if, as the observations seem to show, the magnetic forces, in absolute value, are only
•omparatively small, or at any rate are more restricted in their effect as compared with the forces at
vork in the great perturbation-systems, these rapid changes will now be assumed to generate particularly
jowerful induced currents, as the strength of these currents approximately is only proportional to the
apidity with which the change takes place, and not to the strength of the external current.

The apparently more rapid decrease outwards in the effect of these rays than in the other systems,
nay also be explained by the fact that here the rays will leave the earth in paths lying very near
hose by which they came in, whereas in the other systems the contrary is the case.

It may therefore reasonably be assumed that the rapidly alternating currents observed in the earth-
urrent curves, accompanied by synchronous oscillations in the magnetic curves in which it is difficult
>r impossible to trace the influence of external forces that might be assumed to generate these currents,
ire mainly created by induction of the above-mentioned systems of rays which descend towards the
•arth between the positive and negative polar systems of precipitation, and far from the place of
rgisierings.

In more northerly latitudes too, there are possibly local storm-centres, which will have a power-
ul inductive effect. In fact the curves for Axeleen are disturbed almost at any time.

There is moreover another most important point, namely, that the relation between the magnetic
•ffect of an extra terrestrial system of the form we find during polar storms, and the effect of the in-
luced current-system, decreases with increasing distance from the inducing current-system, and t/uts
lie farther we get from the external current-system, the more strongly would the induced current be Jclt.
»Ve shall prove this relation more fully later on. In other words the earth-currents are able to bring to
ower latitudes a message of a great many distant perturbations with their centres in the vicinity of the
>oles in cases where the external systems are too weak to cause any appreciable direct effect on our
nagnetometers.

In this way we may understand that in lower latitudes most observers in a great number of cases
lave found the magnetometer variations to be such as would be produced by the earth-currents flowing
inderneath the magnets, and still external currents may be the primary cause of the magnetic distur-
)ances.

From what has been said it will be evident that we cannot usually expect to be able to trace out
he cause of the earth-currents at a certain station from a comparison with magnetometer-records from
he same station.

Very often the galvanometers during polar storms merely perform rapid oscillations about the normal
ine (see Series II, Nos. t, 3 & 14, PL XXXI and XXXII); but in some cases of somewhat small and regular
>olar storms with their centres in the vicinity of the stations, earth-currents were observed varying in
i regular way, and in accordance with the view that earth-currents are induced from changes in the
irimary external systems.

The most typical instance of such a regular curve is the perturbation of the loth of February, but
he same type of correspondence between earth-current variations and polar storms is very well brought
>ut in a number of other storms. I will direct attention to a few of these. In Series I, January 13,
ibout i8h— 18'' 30m, February 13, about i9u — 2oh; in Series II, December 26, about 23''— 24'', January 24,
ibout i8h, February 9, about 18''.

In all these cases the following typical correspondence is found.

744

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

VECTOR DIAGRAMS.

Kua/jtrrd

Fig. 270.

I'AUT III. KARTII CfRRENTS AND EARTH MAGNETISM. CHAP. I.

745

During the time of the most rapid increase of the perturbation the earth-currents obtain a maximum.
When the disturbance is at its maximum the galvanometer has nearly its normal position, and when
the disturbance diminishes at the greatest rate we get another maximum of galvanometer deflection, but
now to the opposite side of the normal line. The storms which show this type of variation are
.specially those which we called polar elementary storms.

A number of elementary storms showing a correspondence of this type are graphically represented
n vector diagrams (fig. 270).

Fig. 271.

If we look at these vector diagrams we notice that the current vector when passing from one
lirection to the opposite is not turned round quite gradually, but the vector is kept in the same line of
lirection. This peculiarity with regard to direction will be seen from the plates (PI. XXX — XXXIII),
ml is even better illustrated by some of the rapid records, e.g. PI. XXXIV and XXXV.

Even the rapid oscillations seem to pass along the same direction which is seen from Table CXII,
,'hich shows that the ratio between corresponding amplitudes in the two directions is about constant.

If we try to deduce the direction of the earth-currents from the variation of the magnetic force at

laafjord by applying Lenz's law, we find a current-direction nearly opposite to that actually observed.

liis circumstance may seem remarkable. In order to prove that there was not some error in the deter-

lination of sensitiveness, I again, in May, 1910, made earth-current measurements with earth connec-

ons in exactly the same places as before, and found the condition confirmed.

It is to some extent doubtful where the cause of this peculiar circumstance is to be sought; but it
reasonable to assume that the local conditions in the ground have a very essential part to play.

746 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

A consideration of the country in which the earth-current measurements were made, confirms thi*
assumption.

We have previously described this 'country (p. 732), and from the description it is evident that
local conditions would probably exert a great influence on the earth-current conditions, taking into
account that the earth-current lines are only 400 metres long.

If we compare the current-directions found in Kaafjord with the sketch-map on p. 15 and with fig. 271
we see that the direction of the earth-current is parallel with that in which the mountain-ridge and tlu
branch-fjord run. Now in inductions of this kind, the main direction of the earth-current should be
E — W; but if we look at the shape of the fjord and of the mountain mass on the maps, we see that if
on the whole the earth-currents are influenced by local conditions of this kind, it would be by no means
unlikely that in the regions surrounding Kaafjord, a peculiar deflection of the current-lines such
have here observed might take place. In order, therefore, to come to a clear understanding of this
question, it would be better to observe the earth-currents with considerably longer earth-conn
and in more level country.

It was chiefly for this reason indeed that at the beginning of March we moved our station to
Bossekop, where the ground is less rough.

There proved to be a considerable difference in the earth-current conditions We no longer find
such a marked constancy in the current-directions. As the vector diagram for March 31 shows, the
currents may here flow under various azimuths. From the same diagram it appears moreover that when
the magnetic force varies in strength, the directions are throughout in accordance with those we
expect to find according to Lenz's law, especially as regards the currents with direction NW— SE.

Unfortunately, however, we have only very few successful records of typical perturbations from
Bossekop.

EARTH-CURRENTS AND POSITIVE EQUATORIAL PERTURBATIONS

148. The characteristic properties of the positive equatorial perturbations are given in the first pan
of this work :

Discussing the various systems which might produce these perturbations, we found it very diffinil:
to explain their properties by supposing that earth-currents were the primary cause of these distur-
bances.

In lower latitudes the perturbing force is directed towards the north nearly along the magnetic
meridian, and it can maintain a considerable value for a great many hours.

At Kaafjord successful earth-current records have been obtained for the E — W circuit during tin
most typical equatorial perturbation observed by us, namely, that of January 26. The galvanonn i< i
the N — S line being in some way out of order no oscillations were recorded in this line.

Looking at the curves in No. 10, PI. XXXII, we notice that the H and D curves show small, hut
still quite noticeable deflections lasting for several hours In the earth-current curve there is absolute!)
no deflection of long duration to be noticed, but merely sudden oscillations about the normal line.

ON THE SIMULTANEITY OF EARTH-CURRENTS AND MAGNETIC DISTURBANCES

149. The question regarding the simultaneity of the occurrence of earth-currents and magnetk
storms was first discussed by Airy and since then it has been subject to considerable attention ti
most authorities.

PART III. EARTH CURRFXTS AND KARTH MAGNKTISM. CHAP.

747

We know that in a number of cases the magnetometer oscillations are direct effects from earth-
currents underneath the magnets, and for these oscillations, at any rate when their beginning is abrupt
rind well marked, we should expect to find simultaneity within the limits of experimental errors, because
the delay caused by the periods of the apparatuses can only be a question of seconds.

To be clear of this question, we must have recourse to our rapid registerings. Of these we have
i gvi -at number, but as, for this purpose, the occurrence of especially characteristic serrations is required,
.here are not very many that are of use to us. We find a number of these reproduced in Series III.
We have taken a number of the most characteristic notches on these curves, and the time-differences
"mind between deflections in the earth-currents and the declination are given in the following table.

TABLE CX1V.

^/IM1' — 6l>pm.

25/ll 5h-7h P.m.

*/H 7h-9'' p.m. -43h55m— 5>'47ma.m.

2/4 51' 5am — 7>'46m a.m.

Point

Dill' in sec.

Did', in sec.

Did', in sec.

Diff. in sec.

Diff. in sec.

A-D

A-B

B-D

A-D

A— B

B—D

A-D

A-B

B-H

A—H

A— B

B—H

A—H

i

- 0.9

0

— 10.6

— 10.6

+ a.o

4- 2.7

+ 4-7

- 4-2

+ 5-6

4- 1.4

- 7-6

+ I.O

- 6-7

2

-1- 1.8

0

— 18.4

-i 8.4

- 34

O

- 3-4

- 4.2

- i-4

- 56

- 57

4- 19

- 38

3

- 2.7

o

-f 6.6

4- 6.6

4- 4.1

- 0.7

+ 3-4

o

- i-4

- 1.4

- 3-8

+ 1.9

- '-9

4

- 63

o

+ 59

+ 5-9

0

- 5-4

- 5-4

0

- 8.8

- 8.8

- 38

- 38

- 7-6

5

— O.O 0

+ 0.7

+ 0.7 4- 2.7

— 2.0

+ 0.7

- 3-2

- 6.4

- 9-6

— I.O

- 4.8

- 5-7

6

- 4-5 o

- 66

- 6.6

- 1.6

->• 3-9

+ 2.4

- 6.0

4- 4.4

- 1.6

o

- 4.8

- 4.8

7

- 8.1 o

- 1-4

- 1-4

- 55

4- 6.3

4- 0.8

- i-4

- 4.2

- 5-6

— I.O

- 4-8

- 5-7

8

-16.2 o

— 10.3

-10.3

•+ 4-7

4- 3.2

4- 7.9

- 2.8

- i-4

- 42

— I.O

- 5-7

- 6-7

9

— 16 2 o o

o

+ 7-1

- 45

4- 2.6

- 4-2

o

- 42

- 5-7

- 2.9

- 8.6

10

-1- 2.1

+ 3-5 - 4-6

- 1.2

- i-9

+ 3-9

4- 1.9

0

- 7-o

- 7.0

0

- 36

- 36

1 1

4- 2.1

4- 1.2

- 5-8

- 46

o

- 3-9

- 3-9

— I I.I

4- 5.6

- 5-6

- 3-6

- 5-i

- 8.7

12 — I.O

+ 1.2

4- 1.2

4- 2.3

- i-3

4- 1.9

4- 0.6

o

- i-4

- 1.4

0

— 10.9

— 10.9

"3

— 2. 1

o

- 4.6

- 4.6

4- 0.7

- 0.7 o

o

o

o

- i-5

- 6.5

- 8.0

M

- 4-3

4-2.3

- 7-5

- 5-2

+ 3-2

o

4- 32

- 5.6

4- 4.2

- i-4

+ 1-5

- 5-i

- 3-6

'5

- 6.9

o

- 1.2

- 1.2

+ 5-2

f 0.7

4- 5.8

- 2-3

— 1.2

- 3-5

—

_

—

16 - 0.8

4-4.0

- 5-2

— 1.2

4- 3.2

- 3-9

- 0.7

- 7.0

+ 3-5

- 3-5

—

—

—

'7 +3-5

o - 4.0

- 4°

+ 0.6

o

4- 0.6

0

- 35

- 3-5

—

—

— -

18 —10.6

0

0

O — I.I

4- 4.6

* 3-4

- 5-9

- 2.3

- 8.2

—

-

—

19 -1- 2.6

+4.5

4- 7.0

-+-II-5

- 0.6

4- 2.9

4- 3.3

-•3

4- 12

•— 1.2

—

—

-

20

— 1.8 o

— 6.2

— 6.2

4- 2.9

0

+ a-9

- 2.3

- 4-7

- 7-0

—

—

—

21

- 3 -o

0

+ 06

+ 0.6

- 0.6

4- 1.7

+ LI

- 2.3

- 2.3

- 4-7

—

-

—

22

- 1.4

0

4- i.i

4- i.i

+ i.i

- 5-7

- 4-5

0

-12.8

— 12.8

—

—

—

23

4- 8.3 -1.2

- 1.8

- 3-0

4- i.i

- i-7

- 06

- 3-5

-11.7

-15.2

-

—

—

24

- 2.O 4-4.1

- 4-i

o

+ 3-4

- 5-i

- i-7

o

- 4-7

- 4-7

-

—

—

25

4- 4.8 o

4- 1.8

+ 1.8

+ i-7

- 8.5

- 6.8

—

—

—

-

—

—

26 o o

- 9.6

- 9.6

+ 5-i

- 4-0

4- i.i

—

—

—

—

-

—

27 4- 7.7 o

- 7-°

- 7.0

4- 2.8

- 6.2

- 3-4

—

—

—

—

—

—

28 4- 2.8

+ 5-1

4- 4.0

4- 9.1

- 2.8

- 4-5

- 7-3

—

—

—

-

—

29

- 3-5

o

- 5-7

- 5'7

—

—

—

—

—

—

3°

0

- 2-4

- 2.4

—

—

—

—

—

—

Mean

- 2.05

4-0.82; — 2.94

— 3.12

4- 1. 17

- 0.89

4- 0.28

- 3.85

— 2. II

- 4 97

- 2.37

- 3-8o

- 6.16

748 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

We will look at the accuracy that we can here count upon. Both the earth-current curves and tin-
magnetic elements are registered with a rapidity of 4 mm., a minute. On both curves, at suitablt
intervals, exactly simultaneous time-breaks are produced by an electric contact. Now the curves an
hardly be measured with greater accuracy than o.i — 0.2 mm., nor the serrations fixed more sharply
than at about 0.2 mm. When therefore the time-breaks are clear, the limit of error should be
0.3 — 0.4 mm. or 5 — 6 seconds; but as we have the difference between two such measurements, the i
may amount to twice that figure under otherwise favorable circumstances. Add to this the possible
indistinctness of the time-break, and the difficulty of fixing the point upon the curve, and it will
appear that we cannot reckon upon a greater accuracy than of about 10 sec. in the measurement of
the difference. When, with this in view, we look at the figures we have obtained for the time-ditfen
we notice at once that of the 125 measured differences, only 10 have gone above 10 seconds, tin
remainder being all considerably less.

For November 24, about 4'' — 6'1, only the N — S curve has been drawn, as galvanometer /,
some reason would not work. Here there is therefore only one series of differences.

How much may we venture to conclude from these comparisons? The difference generally si
to keep below 5 seconds. The differences between the serrations in the various earth-current ci<
nents are as a rule less than the difference between the latter and the magnetic elements; but a
personal equation evidently plays an important part, as we can see when we compare the nsu::
'""'/n 7l1 — 9h P-m- with the others, the former having been determined by one person, the remaindt
another. While in the named interval there are practically no differences worth mentioning, and tin
difference A — B between the earth-current components themselves is the greatest, the reverse i-
case throughout with the others, and the negative differences, which answer to those in which tlv
earth-current deflections come first, predominate there.

As the number of differences of more than 10 seconds is so few, and the personal equation s<
considerable, there seems to be little doubt that in reality the deflections are practically exactly simulta-
nous, and that the greater time-differences that occur are only due to the chance accumulation <>l en

We thus venture to say that it is not impossible that a time-difference does exist between the
variations in the earth-current and the corresponding variations in the magnetic elements; but if so, it
is so small that we cannot prove it in our registerings with 4 mm. to the minute.

We learn something from this however, for we see that in our ordinary registerings (i'1
we may consider brief variations as absolutely simultaneous on the earth-current curve and the magneto
gram, so exactly, indeed, that we can quite well check the time-determination by a comparison ol
characteristic small serrations (5 seconds here answering to 0.028 mm.). Thus our previously-advance
assumptions (p. 736) are justified.

EARTH-CURRENTS AT BOSSEKOP.

150. It may be mentioned as characteristic of the earth-current conditions in Kaafjord, that t
currents which occurred there ran backwards and forwards in the same direction in the earth, this !
very nearly the direction of the adjacent coast-line.

The consequence of this is that the curves of the two earth-currents exhibit a very great resemblana
in all their details. All simultaneous brief deflections are approximately proportional in the two curve

The details in the declination, moreover, show a striking resemblance to the earth-current curve

If, however, we look at the earth-current curves from Bossekop, we find the resemblance i
nearly so great. The deflections in the two earth-current components are not always synchronoui
which again indicates that the direction of the current may vary.

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I. 749

This, as already pointed out, is also apparent from the vector-diagram for the 3ist March (fig. 270).

It we endeavour to find corresponding serrations in the earth-current curves and the magnetic
arves, we can, as regards the declination, show a number in which the correspondence is quite
Uisfactory.

In the curves for March 30 — 31, in Series II, f. i., we find a number of serrations in which the
irrespondence is comparatively good.

The resemblance here is striking if D and the N — S curve are compared during the time from
:)out 2h onwards.

The serrations in the E— W curve, on the other hand, have no distinct counterparts in the mag-
nic ; but unfortunately we have no observations of H at this time.

As regards D, we have compared with the earth-currents, in all, 107 serrations, which showed the
•ratest similarity; and in this way we found more or less constant values for the relation P^jJeSN
> that here an elimination of the effect of the earth-currents could be made.

With regard to //, we have only succeeded, during the same period of time, in identifying to
rrations with an}' certainty.

THE INFLUENCE OF THE EARTH-CURRENT UPON THE VERTICAL INTENSITY.

151. We have hitherto only considered the connection between the earth-currents and the varia-
ms of the horizontal magnetic elements.

On looking at the vertical curves, however, we also frequently find very characteristic points of
-H mblance between them and the earth-current curves.

In the case of Kaafjord, where the direction of the current is constant, it is easy to form there-
1 mi an idea as to the quarter in which the main mass of the current is to be found.

Identification is very much more difficult here than in the horizontal elements, but if we look at
te curves for the I5th February in Series II, a close examination will reveal a number of small simul-
tieous deflections in the P-curve and the earth-current curves. An upward deflection in the K-curve
; swers in every case to a downward deflection in the earth-current curves, and vice versa.

As the sensitiveness for the vertical intensity is comparatively small, the resemblance in the small
(flections will be difficult to demonstrate, especially in the copied curves. In the original photographs
tt- identification is easier.

In the stronger deflections the resemblance is more striking; and if we compare the course of the
i rtical curve at the times when the earth-current curves show considerable deflections, very characteristic
1'ints of resemblance will as a rule be found between the two systems of curves.

In these powerful deflections, however, external current-systems will always exert a considerable
cect influence, so that the phenomenon becomes less perfect. We may here point to a number of the
i >re powerful deflections, which give a distinct impression of this resemblance.

From Series I

Jan. 13, time about 18'' — 18'' 30'".

— 18, » 15'' 30™— i6h 3om.

Feb. n, » i8h20m.

From Series II.

Dec. 24, time about 15'' 45™ & i8h 30™.
Jan. 5, » i6l'3om— 17'' 30™.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903. 95

750 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Jan. 23, time about I7h3om — i8h 30™, and

jgh ^om — 20h gOm

24, » I7h3om— i8''3om. (Note especially the secondary deflection

at about 17'' 57m.)
Feb. 7, » i7h25m

» i8h.

» I7h4om — i8h 2om.

At all the places mentioned, the same condition is found as has been pointed out in the small
serrations, namely, an upward deflection in the F-curve answering to a downward deflection in the .•
and Z?-curves.

The resemblance is throughout so great that there seems no doubt that to a considerable e:
the deflections are due to the direct influence of earth-currents.

We have endeavoured to determine on the original curves the relation P,fjc for some small
oscillations.

We have found that the numbers oscillate in such a way that the mean values of two consecutive
numbers attain a satisfactory constancy. The reason of this is to be found in the fact that during the
period of observation the external force changes considerably. Bv taking the mean this external
will be more or less eliminated. By the aid of these numbers, we can then approximately eliminate
the influence of the earth-current upon the vertical curve.

We have effected an elimination such as this for March 30 — 31, 1903. Unfortunately \ve have no
earth-current registerings for the time about the commencement of the perturbation. It may perhaps
seem that little that is of interest has been gained; but one fact at any rate is very apparent, namely,
that the effect of the earth-currents on the vertical intensity curve is very small compared with that of
the extraterrestrial currents.

In order to find out where the main body of the current is to be sought for, we may first con-
sider one of the smaller deflections, e.g. the serrations at about 17'' 5m and 17'* 13'" on the 15*
February, Series II.

At I7u5'n we find a current that flows from SW to1 NE. It seems to occasion an upward deflec-
tion in the vertical curve, which answers to a magnetic force directed vertically downwards

A horizontal current that would produce such an effect and have the the direction observed, must
now be looked for in NW, i. e. in the direction of the mountain-ridge.

At 17'' 13™ both the earth-current and the corresponding deflection in the vertical curve have
changed their direction. The current is therefore still to be looked for in the same direction, i. e. NW
of the place.

This seems to agree with the assumption that the current follows the well-conducting veins of
copper in Grytbotten Mountain.

At Bossekop, on the other hand, the vertical intensity is apparently more strongly affected by the
earth-currents than in Kaafjord. This is easily seen by comparing the part of the vertical curve about
oh— 2h for the 23rd March with the corresponding part of the N— S curve for the earth-currents; and
the resemblance between the curves for March 30 — 31 is still more distinct.

It is principally in the N — S curve that we find agreement with the magnetic curves at Bossekop.
If we here, in the same way, try to determine where the main body of the earth-current is situated, wt
meet at the outset with the difficulty that the current may flow under various azimuths, which may
possibly indicate that the current-line in the neighbourhood of the place of observation is much curved.

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I. 751

It would appear from the general survey map that the geographical conditions would favour such
. view.

It will be seen that Bossekop is situated on a peninsula bounded partly by Alien Fjord with its
co arms, Kaafjord and Rafsbotten, partly by the comparatively broad mouth of the Alien River.

The soil itself does not seem to contain any metal strata which would be more favorable to one
. rrent-direction than to another.

On the border-line between land and sea, however, there will always, on account of the difference
the electric conductivity, be an unsymmetrical distribution of the earth-current density.

If we look at the serrations at about 2h im and 2h 8m on the 313! March, we see that the direction

• the current at the first hour mentioned is more or less from N to S. At the same time there is a
i.i-rosponding force westwards in D, and in V a force vertically upwards. This last might indicate

at the main body of the current was situated to the west of the place, i. e. out in the fjord; but it
ight also be imagined to be produced by currents in the east that had a contrary direction, a

• indition of things that would not be impossible. To decide this question, simultaneous observations
ith short cable-lengths at various places is required.

If we assume that the first alternative is correct — which the greater conductivity of sea-water as
"iiipared with soil perhaps makes probable — it might seem remarkable that in Kaafjord the main body
' the current is found in the land and not in the sea.

In reality, however, this is easily explained, as the upper branch of the Kaafjord, which lies near

• ir observing-place, is connected with the lower fjord only by a very narrow channel, while the Bossekop
•ninsula is surrounded by the great, wide Alten Fjord.

In the case of the second deflection at about 2'' 8m, the deflections in the magnetic curves are
versed, as also in the N — S curve. We find, moreover, a distinct current-component in a direction W — E.
The direction of the current is thus now more or less SW — NE.

The same two alternatives may also be employed for the explanation of this phenomenon. It is
oubtful which of the two is to be preferred; perhaps they act in concert.

OBSERVATIONS OF EARTH-CURRENTS AT KAAFJORD, MAY 1910.

152. During the expedition which I, accompanied by Mr. KROGNESS, made to Kaafjord at the time
passage of Halley's comet across the sun's disc in May, 1910, we also, as has been stated, took
jservations of earth-currents with earth connections, as far as possible in exactly the same places as
1902 — 03.

The arrangement was the same as at that time, but for reasons already touched upon, we inserted
each of the earth-connections a great resistance.

As the galvanometers previously employed had proved to be rather too sensitive, and, more parti-
ilarly, to have no constant zero-point, we used, in their stead, two new school-instruments from

DELMANN.

In the N — S line, the resistance added was 55 300 Q, and the galvanometer employed — which I
ill call a - had an internal resistance equal to 152 Q.

In the E — W line, the resistance added was 53000 2, and the galvanometer b had an internal
-•sistance equal to 187 SJ.

The galvanometers a and b were set up at respective distances of 172 cm. and 115 cm. from the
?gistrator-cylinder.

752

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

The two galvanometers were introduced as a shunt upon a circuit with a resistance of o- "
this arrangemement was employed the whole time.

The earth-resistance was determined from time to time, and the following values were found'

TABLE CXV.
Earth-resistances.

Dale

N-S

E-W

May 9

q8so ii

— 13

— 25 .. ...

The sensitiveness was determined in the manner previously employed, and the results v
follows :

TABLE CXVI.
Scale-values for one millimetre deflection; unit volt per 400 m.

Date N-S

E— W

May 9

a-3 X 10— 3

4.2 X io-;i

'3

2.2

3-9

- 25

2.O

36

- 31

• 3

3-5

The new instruments, it appeared, maintained a very constant zero-point, but, as the determinations
of sensitiveness show, the temperature-coefficient was comparatively high.

The curves otherwise exhibit the same characteristic peculiarities as those previously found.

We have here, too, determined the relation between a number of synchronous serrations.
will be seen from the following table, the conditions are very constant, especially as regards the first
three days.

The numbers - - are given in units — ~ — — .
zle millivolt

The numbers for June 1—2 are perhaps not so valuable as for the other days; the small value
for the sensitivenes seems to indicate that contact-resistances have played a considerable part.

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I.

753

TABLE CXVII.

/' p

p

p

Je

p p //>

Date

'i

'/

A'W

Date

a

a Mw

<"**

^

^MW

Jexs

<"»

<",w

<"XS -^.v.s

May 9—10

1.74

2.13

1.23

May 16—17

'•75

2.47

1.43

1.04

'59

1-52

0.66

0.74

'•'5

1.04

!.46

1.41

0.8 1

1.16

1.42

3 .10

2.65

0.86

0.70

0-89

1.26

2.03

2.42

1.19

0.70

0.84

1.22

1.24

1.77

1.42

0.88

1. 06

1. 2O

'•25

3°5

2-43

o.55

0.74

1 35

2.03

2.23

1.09

0.94

i 30

1.42

1-38

1.72

1.24

o 91

i.i i

1.24

0.63

0.92

1.48

i 02

'•43

1.40

o 29

0-33

0.70

0.83

i '7

0.62

0.84

1.38

' 53

1.86

158

1.91

1. 20

'.15

i-53

'•35

1.17

1.46

1.16

1.49

1.30

0.50

0.64

'3'

049

054

I. ii

0.98

1.36

1.40

1.19 1.45

1.22

1.40

1.97

1.42

o-55

0.67

083

i. 06

1.26

0.76

I.OI

'•35

0.40

0.60

0.67

1. 00

1.50

0.50

0.67

'35

1.28

1.40

0.47

0-51

1.09

'•75

2.29

'•3'

1.72

1-93

0.90

1.03

'•'5

0.87

1.16

1-35

0.70

0.97

'•37

'•33

2. 02

'•52

0.81

1.14

1.42

0.69

0.96

I 44

°5'

0.67

0-83

I 02

1.22

0.94

1.30

I 40

1.28

1-53

°-95

i 16

1.22

1.09

'•SO

1.38

0.67

1.14

1.70

0.83

'. '3

1.40

0.87

'•3°

I.50

o 42

052

1 .22

1.32

3.17

1.62

0.62

0.81

I.36

1. 12

1.62

1.44

056

0.71

1.26

o 92

' 35

1.48

0.70 0.89

1.28

o-93

1.06

'•35

0.74

0.98

'•33

0.78

1.02

1.30

°-73

I.OI

1.42

0.82

o 91

1.09

°-59

0.8 r

1.40

0.98

1.08

i. ii

0.83

t.lfl

I 43

May 16—17

0.74

0.98

1-35

0.83

1.06

i .29

°95

'•55

163

May 27 — 28

°-95

1.3°

' 37

0.70

0.89

1.26

0.89

1.09

1. 21

1.40

1.77

I. s8

0.92

1.27

' 37

060

086

'•45

0.89

1.30

i 45

0.87

i 23

1.44

0.63

0.91

1.41

0.53

0.71

1.40

1.24

1.69

'•37

1.27

1.90

'•5'

0-59

0.82

'•39

'•°5

1.26

1.33

0.79

1.09

1-39

0.80

1.03

1-3'

0.67

0.79

1.21

0.83

'•'3

1.40

068

0.83

1.21

I.OI

'•53

1.52

0.44

0.01

i 39

0.77

o 96

1.33

I.OI

I 27

' 25

0.99

1.30

«-3«

0.85

1.18

'•37

o 70

086

1.22

0.86

l.OO

'•'5

094

1.23

'•33

0.67

094

'•37

754

BIRKELAND. THE NORWEGIAN AURORA POLARIS. EXPEDITION, 1902 — 1903.

TABLE CXVII
(continued).

Date

Pd

P.

i

JeKVr

Date

Pi

Pd JeKVf

***

<"m

Jesw

*M

<"n

May 27 — 28

1. 01

I.a<7

1-25

May 27 — 28

0.91

1.09

1. 21

0.76

0.97

1.29

0.54

0.79

1-39

0-73

0.88

1.19

079

1.03

'•3'

°95

1.24

1-3'

0.88

1.09

1.23

0.70

0.97

1-39

o 92

1.24

'•33

0.56

0.76

i-39

«-»s

'•57

1 35

0.76

I.OO

'•33

0.98

1.18

1. 21

0.68

1.36

I-5I

0.69

0.88

1.23

1.36

1.36

0.99

0.92

1.24

'•35

0.80

I.OO

1.25

0.35

0-45

1.39

0.56

0.79

i 39

1. 12

1.72

'•53

0.92

I 24

'•35

0.80

1.27

'•57

°53

o 70

'•3'

1.24

1.69

'•37

0-57

0.79

1-37

i-35

184

'•37

0.62

082

1.29

0.44

0.64

1.47

0.74

I 00

'•35

June 1—2

'•43

2.68

1.86

o 92

1.30

J'39

'•15

2.09

1.83

1.03

'•45

1.41

1-34

2-43

1.83

0.88

1. 21

i-35

0.78

1.38

I 80

0.94

'33

1-43

TABLE CXVI1I.
Mean values.

Date

P*

P*

p*

Pi

JeKW

JeBW

Jexs

JeEW

J'm

JeffS

May 9 — 10

0.98

M3

1.09

1-43

i-37

May 16 — 17

0.87

1.16

'•33

May 27 — 28

0.82

1.18

'•33

June i — 2

1.17

2.13 1.83

As regards absolute magnitude, however, the figures we have here determined are very different
form those previously found. We see here that Je has throughout values about 400 times greater than
before, which indicates that q\ and qt in the previous instances have really had an order of magnitude
of several hundreds, as mentioned on p. 734.

In the period of about one month, during which we made observations, there is no case in which
induction-phenomena are so conspicuous as in the storm of the loth February, 1903; but it is quiti
distinct in a number of storms.

We have previously reproduced some of the registered curves (see p. 652 — 653).

The induction-phenomenon appears perhaps most clearly in the vector diagrams that we have drawn
and which are represented here.

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I.

755

We have also determined the relation between the maximal effect of the earth-currents and of the
external current-system upon the magnetic elements.
We found the following figures:

May 1 6

Storm I; duration 1.5"' Storm II; duration 18'"

o.i 8 0.09

VECTOR DIAGRAMS.

Kaaljord.

1910

25 V,

May 27

Duration of storm 2h ,
0.15

» Pert, force

Fig. 272.

We have previously determined this relation for some of the storms from 1902—1903 and found
alues varying between 0.12 and 0.52.

This last investigation therefore serves to show that the small cable-resistance that we employed
Deviously did not occasion any essential change in the phenomena. This should therefore justify us in
he conclusions that we drew from that material.

Finally, in this connection, I would touch upon a phenomenon that we observed during this ex-
pedition, and which may be of special interest.

756

B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.

In my earlier work, "Expedition Norvegienne 1899 — 1900" (p. 7), I drew attention to a number o
very regular sinusoidal oscillations that were observed at the Haldde Observatory on March 19 and 20
1900. I here reproduce on an enlarged scale the previously published curves showing this condition (fig. 2-^1
On the i8th May, 1910, we had the opportunity of observing exactly similar rapid, regular oscil-
lations simultaneously in two sets of magnetic apparatus, which were placed at a distance of about 300
metres from one another. They proved to be accompanied by exactly similar oscillations in the earth-
currents, and the two appear to be exactly synchronous, although an eventual small phase-alteration
could scarcely be demonstrated. I here reproduce those curves in which these oscillations are notio

It will be seen that the oscillations occur in two epoch

At the end of these epochs there is also rapid registerin

with one set of magnetometers. It is here therefo

that the period of oscillation can best be determine

For this we find the following values:

119 sec. n8 sec.

122 » 113 »

1 28 » 121

I 24 » I 09

Mean value: 119.3 sec-
With regard to the cause of these oscillatii
we will only refer the reader to Art. 122. What wt
would especially call attention to here is that tli> -
oscillations occur simultaneously and probably t :
273. synchronously in earth-current and magnetism.

//-

hyfij"**™~»>^^\/<f\f~ — — -vwwv/v*"^^^ ' ""**'*'*

f 1

r •

Earth currents and magnetic elements 17 — 18 May, 1910.
Fig. 374.

PART III. KARTH CURRENTS AM) KAKTH MACNKTISM. CHAP. I.

757

There will hereafter be more frequent opportunities of studying these phenomena, as the Norwegian
ate, at my request, has conceded means to keep the Haldde Observatory in continual activity. Figure 276
lows the observatory as it looked in 1912; but at the present time large new buildings are being added,
id it is very well equipped with up-to-date instruments.

IB May

Fig. 275.

THEORETICAL INVESTIGATION OF THE CURRENTS
HAT ARE INDUCED IN A SPHERE BY VARIATION OF EXTERNAL CURRENT-SYSTEMS.

153. In the foregoing Article, we have had occasion to draw attention to conditions which indicate
ie existence of earth-currents that are induced by variations in the outer polar current-system, which
p have assumed as the cause of the polar magnetic storms.

In the next place these currents exerted a considerable influence upon the magnetic apparatus, so
<at especially the smaller details in the phenomena had mainly to be regarded as the effect of the
i rth-currents.

In order to arrive at greater clearness, it may be interesting to make some calculations as to how
sch currents on the whole will flow in the earth, and what magnetic effects they will produce.

A comparison of the results that can be obtained by the aid of the theory and the actual obser-
•tions, will of course only hold good of the main features of the phenomena, as in the calculations we
1 ve to make a number of simplifying assumptions, which in reality are by no means exact.

Fig. 276. Haldde Observatory.
Hirkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903.

96

758

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

What we shall thus have to do is to study the currents that are induced in a sphere by variatic
in an external magnetic field.

This problem has been studied by a number of scientists, some of whom have looked at it nu
from a general, others more from a special, point of view.

The investigations of LORBERG ('), NIVEN (-), and LAMB (3) are of great interest. If we start with t
assumption that the specific resistance of the earth is constant and equals y., we may directly empluv t
formulae previously developed by them.

We assume that we can write the magnetic potential of the inductive current-system in the U

V — 2S 2H£HSea™ '?* '

where n may run through all whole positive values from o to oo , and the summation with ret;.
extends over a series of ps, which in the special cases are to be determined.

£HS is a solid harmonic of positive degree n, t is the time, * = \ — i, and />s is a constan:
employ LAMB'S formulae, and the same system of coordinates as before (cf. fig. 177, p. 424!,
then express the currents induced in the following manner. (LAMB has employed the symmetrical

k°- i

r.

h

where u, v, w, are the components of the electric current. Further,

i

r)

and

- ... = ( — !)" 3- 5- ...(2«+l)

By these formulae the induction-currents can always be determined, but the above form is not particular!}
well adapted to practical calculation.
As, however,

xu + yv -\- zw = o ,

the currents will run in concentric spherical shells, and these may be more simply expressed by the
of a current-function, «/>. This current-function we will define in the following manner: If, in the spherical
shell with radius Q, we move a little way ds, and y>, on this piece, increases from (// to ifi + <
then the component of the current at right angles to the direction of this element from left to rig
when the observer is imagined to be standing on the spherical shell at the point in quest:
looking in the direction of the motion, equals

dif>
4s '

(1) Crelle, Vol. 71, p. 53.
(3) Phil. Trans. 1881, p 307.
(3) Phi!. Trans. 1883, p. 519.

PART 111. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. i. 759

ir the current-components /^ and i,,, along respectively meridians (w = constant) and parallels
= constant), we then obtain the following expression, changing to polar coordinates by the aid of
uations (6) on p. 425:

)W

/« = it cos 0 cos to -j- v cos 0 sin u — w sin 6

fra = — M Sl'n It) -\- V COS W

o = ii sin 0 cos lit -J- i> sin 0 sin ti» -f- 01 cos 6* ,

icnce we find

• "' =_J__v^ (P

9 sin 9 si~ ° * - -

osinfl 3# "

' ic expression for the current-function will therefore be

The numerical calculation according to the above formula will be rather troublesome for an ordi-
itry case in which the serial developments are not particularly simple, more especially if the series
en verge only slowly. This will be the case with the field of the polar storms, as the acting current-
sstems come comparatively near to the earth.

The formulae can, however, be simplified and put into a better form in the two extreme cases,

(1) where | k \ . R is very small, and

(2) where k \ . R is very great,
e will especially consider these two extreme cases.

(i) k . R is assumed to be very small.
We may then put, cf. (4)

we may also assume that this equation holds good for « = o . We then obtain

It now we can write

/ 2 T 3

4«^ "IT ' a7

d thus

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 — 1903.

. ir 2 - f s *>*
* ***}

«/>s/ J

?

We have hereby succeeded, in this case, in making all serial development superfluous.

(2) k | . R is very great.

If we look at the conditions near the surface, we find that there, too, k ' . Q is 'very great. But
from the last expression for %n in equation (4) it appears that for great values of the argument we
may put approximately

r\
J

= (— I)" I . 3 . 5 . . . (2 »

1+1

From this we find, since

k = + 27t(l —

when ps is positive, and

- / p

k = + 2/r(i + /) r * when /»A. is negative,

after some reduction, that

~\ e

•//•«' - \l ?—(R - ?)

v r *

when /„ is positive, and

« I 2 7. \ (»

when ^, is negative.

The expressions may also be written in the following form, as

(91

2«

— i, l ~ i**fij(y*V.J — _ Ju, i,' ^-**-/

r j r^ ^ l /--(A^I/^ ./?-?)+;)

-in "J'

where the upper signs are to be employed when p, is positive, and the lower when ps is negative.
this case therefore, in order to find the currents at the surface, we need, only make a single serial
development of the potential.

PART III. KARTII CURRENTS AND EARTH MAGNETISM. CHAP. I. 761

It appears from equation (9) that tp, and with it the strength of the current, diminishes very rapidly
as one moves inwards into the sphere. The currents are thus concentrated in the outermost layers ot
Lhe sphere, and in this case we may imagine, as LAMB has already shown ('), that all the currents are
replaced by the currents in a spherical shell with radius R. If i//! stands for the current-function for
:he currents in this spherical shell, we shall have

R

= J if>de ,

A

vvhere p0 's a value of Q, where the strength of the current is insignificant.
Now

271(1 + i)"\l£L(f-R)

X

-*(v* }

Rl )

(II)

27C(I +

ind thus

y v 2 n ~t~ I •*•*'"' (ffi anip,t _ 1
n -\- i 4 7C 4 n

Thus no serial development is necessary for the determination of this current-system.

Our next important task is to determine the magnetic effect of the induction-currents. From LAMB'S
•xpression for the magnetic components in space, we can easily omit the expression for the potential
>f the induced currents. We find, if we call this Vit that

*•

/»» '

f k . R is very small, we may write

ind if k ! . R is very great, we may put

Special interest attaches to the value of the potential at the surface. There, too, we can condense, so
is to avoid serial developments.

In the first extreme case then, we have, for p = R ,

,« — - r-T
»-f-i (a»-f i)(a»

n+ i (zn + i) (2« -f 3)
Jut now

(13)

(!) loc. cit. p. 537.

762

I5IRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION. 1902 — 1903.

_,.

-JL- Vn = Vn f VndQ

n + i <> )

0

n V* _ i Cdgf i C \

, — I — r— I "» I ' n n o i

„+!«+£ VeJVeV <?J /

Here the summation with regard to « can be made direct, and we can therefore in this case write

o o

In the second extreme case, where j k j . R is very large, Q = R is simpler,

n

= H*) - ^ f v

If we now look at the conditions on the earth during the magnetic storms, we can assume
earth-current conditions as a whole exhibit a greater or less resemblance to the idealised case that \\x
have here studied. Whether the conditions followed either of the two extreme cases, and if so, \\huh
of them, would mainly depend upon the specific resistance and the length of period. If they agreed
with neither case, it might still be assumed that they will answer to something intermediate betuvm
the two.

If we assume the length of period to be 2 hours, i. e. p = -^^ , then

87r2/>/?2 = 4.5 X io15 .

For sea- water we may put x = about io10,

for rain-water about 6 X io13,

and for purest distilled water about iolr> .

The corresponding values of k | . R are

7 X io2, 9,

The specific resistance in the outermost strata of the earth may probably now be assumed to have an
order of magnitude corresponding to these figures. It should therefore be assumed that the earth-current
conditions answer to something between the two extreme cases.

In order to obtain a general view of the course of the earth-currents during a polar elementary
storm, we will determine the course of the induction-currents at the surface for the current-system pre-
viously employed in Art. 91, answering to the first and second extreme cases, assuming that the positimi
of the system is fixed in relation to the earth, and that the strength of the current, i , varies. We have
previously found for the potential of this system [see equation (28), p. 428],

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP.

II.,

-f

(cos 9 — cos £ cos ft) [0 - (A '/) cos
sin- ft . d

«\
fi) \k\. R is very small.

In accordance with equation (7), we then have

P ."2

= -'/ if
* <*'} }

[cos 0 — cos £ cos ft] [g — (L — d) cos ft]
"

"2

sn

0 ."1

hat is,

i dif

*-Trf*J

cos 6 — cos 'C cos ft r

__± !_ I « /»r

(16)

The integration could be carried further, but the above form is the most practical for the numerical
•alculation.

For the current-components /^ and im , we find

infl 3/.<

hat is

nd

psinfl x

i 3(/< i

- --

cos 0 — cos £ cos ft
sin2 ft

ft = //-j

. [g cos ft -f rf — L]

» cos ft + rf — Z.

— L

"1

vhere we have put

3 cos 0 — cos £ cos ft _ sin2 8 + (cos 6 cos ft — cos £) cos £

36 sin2 ft

sin 0 sin2 ft

2 (cos 0 — cos £ cos ft) (cos 6 cos ft — cos £) cos ft
sin 8 sin4 ft

nd

cos 6 — cos L cos ft 3 cos ft (cos 6 — cos £ cos ft) (cos 9 cos ft — cos C)

sin- ft 30~ sin2 /? sin fi

sin2 ft sinfl

'or the magnetic potential Vt , we have, according to equation (14),

(I?)

(20)

o o

Ve now have

764

B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.

. f cos 8 — cos £ cos /J
sin2//

m

ip \ Q — L

[am?** -j

— L cos ft d — L
cos p

_ . . f cos 6 — cos t cos jff Q cos jj -\- d — L

2

sin

,"1

Further we have

Now

therefore

as

Thus we find that

f

J

Q.d

f / f e cos /? + d - L . \ \ Q cos H + d - L ,

-tyr1 - dQ \ dQ = Q \ -—— - dQ -

J\J Q\ Q . d I J (>}Q.d

rt \ it * n

cos /? + d L ,

2 d

0 = 0

.. d—L Z(Q - L cosfi}

Iim0 = 0 -- = Imi0 = 0 -

V? rf

ail

a o

w

Q cos ft -\~ d — Z,

e

if ;/?

J VP-

We therefore put

and obtain

_ fa

ir , TD\ JC V^ d i I cos 0 —co
F,(/?)= - -j- ^-

'- ft i j sin*'

Z. COS (S -f- Q

~Z

—cos £cos 8
-^

n

i-j

(22!

where </w is </'s value for Q = R .

Here /i and Jt are elliptic integrals. If, in the numerical calculation, the employment of LEGENI
tables is desired, they must be put into LEGENDRE'S normal form. If this is done by known method!
we find, if cp is introduced as a new variable determined by the equation

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP.

cos^

cos2 m — —

ifter some reduction, that

-/'te, pi)

~

cos-

"T .; ,

1/Z cos2 £
4

s2-^- (F(£, 9%) — F(k, r/),)) — 4cos4-^ (£(£, I/),) — £(£, r/>i)
2 4

- 2 cos- J— cos —
4 2

765

(25)

(26 a)

R-v^RLcos

(26 b)

ihcre /'(/t, 1/1) and E(k , cp) are defined as before [see equations (17) and (18), p. 427].
Further,

it &

- -

2 4

()/L - i) cot £-

4

.nd finally

Vom this we can deduce by derivation the corresponding expressions for the force-components
hemselves.

By equation (24) we find directly

di

cos 6 — cos £ cos /J

f =

sin2 ? sin 9

CQS

., . -i

/J+ L)^ —(Lcosfi + K)J.,\ . (27)

f = /'i

"or the determination of Pg,- we may start from equations (14) and (21), whence we easily deduce

R o o

-ii

>y employing the abbreviations we introduced into equations (19) and (20), we obtain

3 /cos 8 — cos £ cos ft Q cos p -\- d — L\ o cos ft -|- d — L Q(Q — L cos ft)

j0 I „:_« a I V ~ rtl I T^" I" rt-

Vr \\ill then determine the integral

R
— Lcosft) , „ [ lj Q(Q — L cos /

A

[ , f y? IP — •£ '

p

- R

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903.

766
but as

I I.A.N'D. 1111 NORWEGIAN AURORA POLARIS KXl'F.niTJOX, K)O2 1903.

V0I" Lcosft) i

* r

h {,/,.. 2 A) I'A' -+ A (A' cos /; -|- L\ /, (/. Cos ^ + A')./, |

"i

• ; A I A./, - 3 ./,!<,/,„ .

I' we desire t' i determine /';,,, \ve must go back to equation (12), from which it is easy to deduce

/•-A'- A^'H ,

(281

, '/0
xVA'S/ J

c /'

1 o d i
So

(cos 0 cos _ cos ,j) r/a

eVe

= A + 2 A

A-

j \ a >/:' L- sin- ,j

t/i- "".A.

•• ./ 1 ~ ./-^ ~r i A' cos /;

2 A A . (/;,.

(291

(30)

\ve obtain, alter some ix-chiction,

PART III. KARTH CURRENTS AND EARTH MAGNETISM. CHAP. I.

767

n di ( cos 8 — cos

cos

~ 3 L}

- (R - L cos ft}J, + 2 da

'2) k\ . R is very great.
If we here put

V = i£ = i0 Q Es a, sin 2 nps t ,

can then write

n

f cosj? -

-5

- cos £ cos /? Q — (L — d) cos /?

/?

md we have

(32)

_.± f ijrf. - f
^ J "

sin2/?

-'«/,, .

(33)

t this is inserted in equation (10) or (n), we have the current-function's expression for this extreme case,

*

_ f cos 8 — cos g cos /? Z?2 -

A e . \ •

f

•]

+ L)

(34)

i'here

^1

,"•2

»' _ f c
4^ J

cos 0 — cos £ cos /? /e2 - Z2 + dK(Rcosp + Z.)
sin3/? 7? . a?B

T, = i0 . ^s«s

"or the current-components we find

. sn 2

Qsind

cos 0 — cos £ cos /? R* — L* + dK (R cos /

f = ,

(35)

(36)

(37)

«i

?2j -Z24-rffl(^cos/? + L)

R.<*R

(38)

.'here a\ and «2 have the same significance as before [see equations (19) and (20)].

In order to obtain the expressions for i\m and i\Q, we need only put - in the place of Ts in

he last two lines. The expression for the value of the potential at the surface is given by equations
15) and (21), and we find, for Pmi(R) and Pf)i(R) ,

7o8

. COS t) COS ." COS ft L{R COS ft -{- ffjl - /.)

sin fi sin-/; A- . </,; (39I

// = //]
and

f | A cos,-; -f ,/,. i. A /. cos^^
1 '• "' /,. / 4 "- ,, ''." • (401

A - (in tin )

A

In this ruse llu-n, tin: magnetic effect along the radius vector is equal, and in the reverse direction
to the din et eilcet ot the external system, which is a fact well known from tin: theory of electro-
magnetic screens.

154. In accordance with the- above formula', we have calculated the current-field at the earth's
surlare lor a system like the previously employed 1' = 20° and // = 400 km. — 0.063 '^-

It appears tnmi the lormuke that liu'c too we may calculate o- functions similar to those in Art. 91,
that is to say, functions by the aid of which we can find by .subtraction the various quantities answering
to the external current-system with an arbitrary Ju .

In the tables below, a series of such quantities are given The index o has the same significance
as in Art. 91. ]• urther the value of the current-function and the current-components are calculated for
the. same three values of Jit as before, namely, 75°, J 80°, and aye>°.

On the charts (lii^s. 277 — 282!, the current-lines are drawn for equidistant values of ip answering
to the two extreme cases in these systems.

1' or the magnetic effect (if the earth-currents, the components /'/, and /',, are calculated for 3 lati-
tudes, H = 20°, 40° and 90° (see Table CXXY).

TAI'.LK CXIX.
Values of ip in the first extreme case.

-If = 75C

i8or

".315 --0.315 -0.315 — °-3'5 - o-^i.S,— o-3'5 —0.315 —0.315 -0.315 --°'3'5 —0-315 — °-3 ! 5 —°3'5 -0-3'J

--o.;->8:." -0.28-' - o._8o —0.^77 —0.274-0.275 —0.278 --0.283 —0.288 -0.293 —0.297 ~°-301 — °-3°3 -~0-3°3

— O.O|O — 0.013 0.058 — O.OQO — 0.127 —0.162 -0.103 ~ O.2l8 -O.2(O —0257 — 0.269 —0.277 —0.282 —0.202

1-0.252 ---0.247 — o.:'ii ^ o. i |8 -+0.072 — o.ooi — 0.065 —0.117 — ° 1 5^ — O.JQO —0.213 — 0.227 ~°-235 ~°-23"

* 0.250 - O.2|t) -4-O.22O ^0.173, 4 O.I I.} -O.O5I — O.OO9 - O.O6I — O.1O5 — 0.130 —0.165 — O.l8l —O.190 —0.191
*O.2OI 4-0.199 -^0.183, -^0.153 ^O.115 -+ O.O7 I ^O.O26 — O.O15 — 0.05: -O.o8l —O.1O.) -O.II9 -O.I^7 —0.120

- o.ioo 4o.log ^0.103, -t-o.of)~' ^0.078 -*- o.oo i ^0.042 4 0.1123 -^-0.006 0.009 — 0.021 i — 0.029 ~ °-°33 ~°-°33

PART III. EARTH CURRENTS AND EAKTH MAGNETISM. CHAP. I.

769

TABLE CXIX (continued).

Ju = 1 80°

e

o

(it = o

'5°

30°

45°

60°

75°

90°

.05°

120°

135°

.50°

'65°

1 80°

0

-0-755

-0.755

-0-755

-0-755

-0.755

-0-755

-0.755

-0-755

-0-755

-0-755

-0.755

-0-755

-0-755

IO

-0.664

— 0.665

-0.668

- 0.673

-0.678

— 0.683

— 0.686

— 0.690

-0.694

- 0.699

-0.704

—0.708

-0.709

20

-0.258

- 0.263

— 0.278

— 0.304

— 0.340

-0.387

-0.442

-0.498

-0.545

-0.581

— 0.607

— 0.632

— 0.627

40

+ 0.266

+ 0.256

+ 0.226

+ 0.174

+ 0.099

+ 0.004

— o. 1 05

— 0.014

-0.309

—0.384

-0.436

-0.467

-0-477

60

+ 0.340

+ 0.330

+ 0.298

-1-0.245

+ 0.174

+ 0.087

— 0.009

— 0.104

— 0.191

— 0.263

-0.315

-0-347

-0.358

go +0.317

+ 0.308

+ 0.282

+ 0.24 1

+ 0.186

+ O.I2O

+ 0.050

— o.oao

-0.085

— o. 1 4 1

—0.182

—0.208

— 0.217

140 +0.202

+ 0.198

+ 0.187

+ 0.168

+ 0.144

+ O.II5

+ 0.085

+ 0.055

+ 0.026

+ O.O02

— 0.016

— 0.028

— 0.032

1 80

-1- 0.09 1 -1-0.091

+ 0.091

+ 0.091

+ 0.091

+ 0.091

+ 0.09 1

+0.091

+ 0.091

+ 0.09 1

+ 0.091

+ 0.091

+ 0.091

Jfl = 270°

e

,„ = o°

•5°

30°

45°

60°

75°

90°

105°

130°

•35°

•50°

165°

1 80°

0

— 1.132

— 1.132

— 1.132

— 1.132

— 1.132

- 1-132

— 1.132

— I.I32

— 1.132

— 1.132

— 1.132

— 1.132

— 1.132

10

— I. Oil

— I.OI2

— 1.015

— 1. 020

— 1.025

— 1.032

— 1.038

— I.O42

-1.043

— 1.042

— 1.040

-1.038

-1.037

20

— 0.550

-0.552

— 0.560

-0.572

—0.590

— 0.613

— 0.641 ' —0.675

-0.714

-0.757

-0.794

—0.818

-0.835

40

+ 0.067

+ 0.063

+ 0.049

+ 0.027

— 0.006

— 0.050

— 0.107 — 0-177

-0.259

-"•345

— 0.421

-0.471

-0.489

60

+0.205

+ O.20I

+ 0.186

+ o. 1 60

+ 0.124

+ 0.077

+ O.020

— 0.047

— o. 1 1 9

— 0.189

—0.248

— 0.288

—0.302

9°

+ 0.249

+ 0.244 +0.230

+ 0.208

+ 0.176

+ 0.137

+ O.09I

+ 0.040

— 0.0 1 I

-0.059

— 0.098

—0.123

— 0.132

140

+ 0.207

+ O.2O5 +0.198

+ 0.186

+ 0.170

+ 0.151

+ 0.130

+ 0.108

+ 0.087

+ o 069

+ 0.054

+ 0.045

+ 0.042

1 80

+ 0.137

+ 0.137 +0.137

+ 0.137

+ 0.137

+ 0.137

+ 0.137

+ 0.137

+ 0.137

+ 0.137

+ 0.137

+ 0.137

+ 0.137

TABLE CXX.
Values of i/( in the second extreme case.

•Jf = 75°

H <•> = o°

7°-5

o
22 .5

37°-5

52°.5

67°-5

82°.5

97°.5

II2°.5

I27°.5

I42°.5

i57°-5

I72.°5

1 80°

-2.154

-2-154

-2-154

-2.154

-2.154

-2.154

-2.154

— 2.154

-2-154

-2.154

-2.154

-a. 154

-2.154

-a-154

i -3.148

— 3.126

-2-957

— 2.664

-3.342

— 2.070

-1-875

-1.742

-1.648

-'•595

-'•558

- 1-533

— 1.522

-1-521

2 —0.561

-0.567

— 0.626

—0.80 1

-0959

- 1.038

-1.079

— 1.104

— I.I2O

— 1.131

-1.138

— 1.142

-1.144

-1.144

4 + 1.614

+ 1-583

+ 1-340

+ 0.919

+ 0.456

+ 0.067

— 0.213

— 0.404

-0533

— 0.618

-0.675

-0.709

— 0.726

—0.728

6 + 0.974

+ 0.959

+ 0.848

+ 0-655

+ 0.421

+ o. 1 9 1

— 0.008

-0.168

— 0.290

-0.378

— 0.440

-0-479

-0.497

—0.500

9 +0.556

+ 0.550

+ 0.503

+ 0.418

+ 0.308

+ 0.188

+ 0.072

— 0.032

— O.II9

— 0.188

-0.339

— 0.272

— 0.288

— 0.290

14 +0.239

+ 0.237

+ 0.225

+ O.20I

+ 0.168

+ 0.130

+ 0.090

+ 0.050

+ 0.013

—0.018

— 0.042

-0.059

— 0.067

— 0.069

18 +0.078

+ 0.078

+ 0.078

+ 0.078

+ 0.078

+ 0.078

+ 0.078

+ 0.078

+ 0.078

+ 0.078

+ 0.078

+ 0.078

+ 0.078

+ 0.078

Jl, = 1 80°

e

,„ = 0°

•5°

3°°

45°

60°

75°

90°

105°

120°

135°

150°

165°

1 80°

o -5.169

-5.169

-5-169 -5-169

-5.169

-5.169

-5.169

-5.169

— 5.169

-5.169

—5.169

-5-169

-5.169

10 —6.062

— 6.040

-5.969 -5.837

— 5-624

-5.3I3 -4-927

— 4-54° '• —4-229

— 4.016

-3-884

-3-8i3

-3-79'

2O — 2.OOO

— 2.004

— 2.017 —2.041 —2.083

— 3.167 —2.360

-2.553 -2.637

-2.679

-2.703

— 2.716

— 2.720

40

+ 1.728

+ 1.696

+ 1-594

+ 1-405

+ 1.099

+ 0.651 +0.094

— 0.462

— O.giO

— 1.216

— 1.405

-1.508

— 1-540

60

+ 1.292

+ 1.262

+ 1.168

+ 1.008

+ 0-779

+ 0.490

+ o. 1 64

— o. 1 62

-0.451

— 0.680

— 0.840

-0-934

-0.964

90

+ 0.860 +0.839 +O-775

+ 0.671

+ 0-531

+ 0.364

+ 0.182

— O.OOI

-0.168

— 0.308

— 0.412

-0.476

-0-497

140

+ 0.437 +0.429

+ 0.404 + 0.364

+ 0.312

+ 0.251

+0.186

+ O.I2O

+ 0.059

+ 0.007

-0.033

—0.058 —0.066

1 80

+ 0.186

+ 0.186 +0.186 ' +0.186

+ o. 186 +0.186

i

+ 0.186

+ O.I86

+ 0.186

+ 0.186

+ 0.186

+ 0.186 +0.186

770

BIRKEI.AND. THK NORWEGIAN AURORA POLARIS EXPKDIT1ON, igO2 — 1903.

TABLE CXX (continued).

du = 270°

(9

,„ = 0°

15°

3o°

45°

60°

75°

90°

0 ! 0

105 i mo

'35°

i5o°

165°

•^— — ^
180°

o

-7-753

-7-753

-7-753

-7-753

-7-753

-7-753

-7-W3

-7-753

-7-753

-7-753

-7-753

-7-753

-1-153

10

— 8.026

— 8.019

-7.998

-7.961

-7-901

-7.809

-7.671

-7.464

-7-173

-6.825

— 6.502

-6.287

-6.213

20

-3-365

-3-367

-3-371

-3-377

-3-388

-3405

-3-430

-3-47'

-3-553

-3-737

-3-896

-3-965

-3-984

40

+ 1-045

+ 1-035

+ 1.005

+ 0.949

+ 0.862

+ 0.729

+ 0.529

+ 0.233

—0.184

-0.686

— 1.149

-1-457

-1.562

60

+ 0.916

+ 0.905

+ 0.870

+ 0.808

+ 0.716

+ 0.587

+ 0.416

+ 0.198

—0.056

— 0.320

-0.554

-0.713

-0.768

90

+ 0.701

4-0.691

+ 0.661

+ 0.610

+ 0.538

+ 0.4-14

+ 0.330

+ 0.2OO

+ 0.062

—0.069

-0.179

— 0.252

-0.277

I4O

+0-449

+0-443

+ 0.428

+ 0.404

+ 0.371

+ 0.331

+ 0.286

+ 0.239

+ 0.193

+ 0.152

+ O. I2O

+ 0.099 +0.092

1 80

+ 0.280

+ 0.280

+ 0280

+ 0.280

+ 0.280 +0.280

+ 0.280

+ 0.280

+0.280

+ 0.280

+ 0.280

+ 0.280 4-0.280

|

TABLE CXXI.
Values of iai.o in the first extreme case.

e

o

(i) = o

15°

3°°

45°

60°

75°

9°°

105°

o
120

135°

•50°

165°

1 80°

o

o

+ O.OOI

+ O.OOI

+ O.O02

+ O.OO2

+ 0 OO2

+ OOO2

+ O.O02

+ O.O02

+ O.O02

+ O.OOI

+ O.OOI

O

IO

-1-0.781

+0.703

+0.616

+ 0.503

+ 0.388

+ 0.291 +0.209

+ 0.148

+ 0. 1 O I

+ 0.068

+ 0.041

4 O.O20

O

2O +2.IO9 + I.22O

+ 0.863

+ O.622

+ 0.451

+ 0.327 +0.237

+ 0.171

+ O. I2O

+ 0.08 I

+ 0.050

+ O.O24

o

40

+ 0436 1 f 0.429

+0.398

+ 0.348

+ 0.292

+ 0.239 +0.191

+0.149

+ O.II3

+ 0.08 I

4 0.052

+ 0.026

o

60

+ 0.177 i + ° 19^

+ O.2IO

+ 0.209

+ O.I97|+0.[77 +0.153

+ 0.127

+ 0. 1 0 1

+ 0.075

+ 0.050

4-O.O25

0

90

+ 0.071

4- 0.095

+ 0.115

+ o.ia8

+ 0.133

+ 0.130

+ 0. 1 2O

+ 0. 106

+ 0.088

+ 0.068

+ 0.046

+ 0023

o

140

-f 0.019

+ 0.042

+ O.O62

+ 0.079

+ 0.090

+ 0.095

+ 0.094

+ 0.088

+ 0.076

+ O.O6 I

+ 0.042

+ O.O22

0

l8o

O +O-O22

+ 0.042

+ 0.059

+ O.O72

+ 0.08 1

+ 0.083

+ 0.08 1

+ 0.072

+ 0.059

+ 0.042

+ 0.022

0

Values of ig 0 in the first extreme case.

6

l» = 0°

•5°

3°°

45°

60°

75°

90°

105°

120°

•35°

150°

l65°

1 80

o

— O.OO2

— O.OO2

— O.002

— O.OO2

— O.OOI

— O.OOI

0

+ O.OOI

+ O.OOI

+ 0.002

+ O.O02

+ O.OO2

4- O.O02

IO

+ 4-138

+ 4.158

+ 4.196

+ 4.221

+4.223

+ 4.209

+ 4-185

+ 4.156

+4.128

+ 4.104

+ 4.086

+ 4.074

-"-4.070

20

+ 2.747

+ 2.686

+ 2.589

+ 2.496

+ 2.413

+2.339

+ 2.277

+ 2.224

+ 2. 1 82

+ 2.149

+ 2.126

+ 2.1 12

-r2.1o8

40

+ 1.836

+ 1-794

+ 1.696

+ 1.586

+ 1.487

+ 1.404

+ 1-337

+ 1.284

+ 1.242

+ 1. 211

+ 1 . 1 90

+ I.I77

60

+ 1.338

+ 1.321

+ 1.276

+ 1.217

+ '-'54

+ 1.095

+ 1.044

+ I.OO2

40.068

+ 0.942

+ 0.924

+ 0.913

+ 0.910

90

+ 1.108

+ I.IOI

+ 1.079

+ 1.048

+ I.OI2

+ 0.975

+ 0.940

+ 0.909

+ 0.883

+ 0.862

+ 0.848

+ 0.839

4-0.836

140

+ 1-599

+ 1.596

+ I-585

+ 1.568

+ 1-547

+ 1.524

+ 1.500

+ 1-477

+ 1.456

+ 1.440

4-1.427

+ I.4I9

+ 1.417

180

+ 0.083

+ 0.08 1

+ O.O72

+ 0.059

+ 0.042

+ O.O22

0

— O.O22

— 0.042

-0.059

— O.O72

+ 0.08 1

-0.083

TABLE CXXII.

Values of im,0 in the second extreme case.

(9

I,, = 0°

15°

30°

45°

60°

75°

90°

^05°

120°

135°

150° 165° 180°

0

0

+ 1.004

+ 1-939

+ 2.743

+ 3-359

+ 3-747

+ 3-879

+ 3-747

+ 3-359

+ 2.743

+ 1-939

+ 1.004 o

10

+ 3.623

+ 5-596

+ 6.313

+ 6.004

+ 5-266

+ 4-447

+ 3.657

+ 2.930

+ 2.269

+ 1-655

+ 1.080

+ 0.534 o

20

+ 32-325

+ 14.887

+ 8.616

+ 5-831

+ 4.261

+ 3-233

+ 2.492

+ 1.921

+ 1-444

+ 1.036

+ 0.673

+ 0.338 o

40 f 0.509

+ 1.402

+ 1-799

+ 1.784

+ 1.591

+ 1-352

+ 1.116

+ 0.897

+ 0.695

+ 0.508

+ 0.333

+ 0.165 o

60

+ 0.077

+ 0.388

+ 0.612

+ 0.721

+ 0.734

+ 0.689

+ 0.610

4-0.515

+ 0.413

+ 0.309

+ 0.206

+ 0.103 o

90

+ 0.014

+ 0.137

+ 0.241

+ 0.312

+ 0.347

+ 0.35I

+ 0.331

+ 0.294

+ 0.245

+ 0.189

+ 0.128

+ 0.064 °

140

+ O.OO2

+ 0.059

+ O. I 1 1

+ 0.153

+ 0.181

+ 0.195

+ o. 1 96

+ 0.183

+ 0.159

+ 0.126

+ 0.088

4- 0.045 °

1 80

O

+ 0.045

+ 0.087

+ 0.123

4-0.150

+ 0.167

-f 0.173

+ 0.167

+ 0.150

+ 0.123

4-0.087

+ 0.0-15 o

PART III. EARTH CURRKNTS AND EARTH MAGNETISM. CHAP. I.

771

i /\ni_E, v^-^wu (toiumueuj.
Values of i^ 0 in the second extreme case.

0

til = O°

•5°

30°

45°

60°

75°

90°

•05°

120°

135°

150°

165°

1 80°

0

- 3-879

-3-747

-3-359

-2-743

- 1-939

— 1.004

o

+ 1.004

+ 1-939

+ a.743

+ 3-359

+ 3-747

+ 3.879

IO

— 10.087

-9.072

-7-o'S

-5-135

-3.788

-2.885

- 2.286

-1.884

— 1.614

-1-434

-t-3'9

-1-355

-1.235

20

+ 2.748

-t-i-5'7

+ 0.844

+ 0.567

+ 0.425

+ 0.340

+ 0.285

+ 0.249

+ 0.224

+ 0.207

+ 0.196

+ 0.190

+ 0.188

4°

+ 4.021

+ 3.626

+ 2.822

+ 2.096

+ 1-577

+ 1.228

+ 0.995

+ 0.837

+ 0.731

+ 0.659

+ 0.613

+ 0.587

+ 0.577

60

4- 2096

+ 2.014

+ 1.808

+ 1-555

+ 1.317

+ 1.118

+ 0.963

+ 0.846

+ 0.760

+ 0.699

+ 0.659

+ 0.636

+ 0.638

90

-f 1.411

+ 1.387

+ 1.322

+ 1.230

+ 1.128

+ 1.028

+ 0.940

+ 0.865

+ 0.806

+ 0.761

+ 0.730

+ 0.711

+0.705

140

4 1.763

+ 1-755

+ 1.73°

+ 1.692

+ 1.645

+ '-593

+ 1.542

+ 1-493

+ 1.450

+ 1.416

+ 1.390

+ '•375

+ 1.370

180

+ 0-173

+ 0.167

+ 0.150

+ o. 123

+ 0.087

+ 0.045

0

-0.045

— 0.087

— 0.123

— 0.150

—0.167

-0.173

TABLE CXXIII.

Values of in, in the first extreme case.

Jp = 75°

6

'" = 7°-5

22°.5

37°-5

52° 5

67°-5

82°.5

97°-5

o
112 .5

I27°5

I43°5

>57°5

I73°.5

0

— 0.003

— O.O02

— O.O02

— O.OO2

— o.oo r

— o.ooo

+ o.ooo

+ 0.001

+ O.OO2

+ O.OO2

1

-I-O.OO2 , +O.003

10

+ 0.443

+ 0.470

+ 0.490

+ 0.494

+ 0.468

+ 0.401

+ 0.320

+ 0.250

+0.189

+0.148

+ 0.122

+ 0.109

20

+ 2-733

+ 2-547

+ 1.782

+ 0.983

+ 0.692

+ 0.502

+0.370

+ 0.277

+ 0.214

+0.171

+ 0.144

+ 0.131

40

+ 0.126

+ 0.151

+ 0.197

+ 0.238

+ 0.249

+0.235

+ 0.2 r i

+ 0.186

+ 0.165

+0.149

+0.139

+0.133

60

— 6.066

— 0.041

— o.ooo

+ 0.045

+ 0.083

+0.108

+ O.I2I

+ 0.127

+0.128

+ 0.127

+ 0.126

+0.125

90

— O.I02

—0.087

-0.059

— 0.025

+ 0.009

+ 0.040

+ 0.065

+ 0.084

+ 0.097

+ 0.106

+ 0. 1 1 2

+ 0.114

140

— O.I02

-0.093

— 0.076

— 0.052

— 0.026

+ O.OO2

+ 0.029

+0.053

+0.073

+0.088

+ 0.098

+ 0.103

180

— O.IOI

-0.094

—0.081

— O.o62

— 0.039

— 0.013

+ 0.013

+ 0.039

+ 0.062

+ 0.08 1 1 + 0.094

+ O.IOI

Jfl = 180°

e

,„ = o°

15°

30°

45°

60°

75°

90°

105°

o
1 20

•35°

I5°°

•65°

1 80°

o — 0.004

— 0.004

— 0.004

— 0.003

— O.OO2

— O.OO I

o

+ O.OO I

+ O.OO2

+ 0.003

+ 0.004

+ O.O04

+ 0.004

[0 +1.143

+ 1.123

+ 1.073

+ 0.991 +0.904

+0.838

+ 0.781

+ 0.724

+ 0.658

+ 0.571

+ 0.489

+ 0.439

+ 0.419

20 +3743 +3-720

+ 3-647

+ 3.515 +3-3°5

+ 3.974

+ 2.109

+ 1.244

+ 0.913

4-0.703

+ 0.571

+ 0.498

+ 0.475

40 +0.490

+ 0.484

+ 0.467

+ 0.443 +0.421

+ 0.417

+ 0.436

+0.455

+ 0.451

+ 0.429

+ 0.405

+ 0.388

4 0.382

60 +0.048

+ 0.050

+ 0.056

+ 0.069 + 0.093

+ 0.131

4-0.177

+0.223

+ O.260

+ 0.285

+ 0.298

+ 0.304

+ 0.306

go — 0.099

-0.095

— 0.080

-0.055

— O.O2O

+ 0.023

+ 0.07 1

+0.119

+ o. 161

+ 0.196

+ O.22I

+ 0.236

+ 0.241

140

— 0.150

—0.144

— 0.128

— O. IOI

— O.066

—0.025

+ 0.019

+ 0.063

+ 0.104

+ 0.140

+ O.I66

+ 0.183

+ 0.188

1 80

— 0.167

— 0.161 —0.144

— 0.118

— 0.083

—0.043

0

+ 0.043

+ 0.083

+ o.r 18

+ 0.144

+ o. 161

+ 0.167

= 270

H

fit = o°

15*

30°

45°

60°

75°

90°

105°

o
1 20

•35°

150°

I65°

1 80°

o

—0.003

— 0.003

— 0.003

— O.OO2

— O.OO2

— o.oot

o

+ O.OO I

+ O.OO2

+ O.OO2

+ 0.003

+ O.OO3

+ 0.003

10

+ 1.426

+ 1.420

+ 1-394

+ 1-353

+ 1.292

+ 1.215

+ 1.127

+ 1.047

+ I.OO7

+ 0.990

+ 0.994

+ 1.005

+ 1.005

20

+ 4.056

+ 4.048

+ 4.024

+ 3.980

+ 3-9M

+3.817

+3.677

+ 3-475

+ 3.168

+ 2.346

+ 1.548

+ I.3I4

+ 1.243

40

+ 0.710

+ 0.706

+ 0.697

+ 0.681

+ 0.659

+ 0.632

+0.605 1 +0.587

+ 0.592

+ O.627

+ 0.668

+ 0.690

+ 0.696

60

+ 0.203

+ 0.203

+ O.2O2

+ O.2OI

+ 0.202

+ 0.207

+ 0.220

+ 0.245

+ 0283

+ 0.330

+ 0.375

+ 0.407

+ 0.418

90

+ 0.006

+ 0.007

+ O.OI2

+ O.021

+ 0.035

+0.055

+ 0.08 r

+ 0.114

+ 0.152

+ O.I9I

+ 0.225

+ 0.248

+ 0.256

140

—0.084

— 0.080

— 0.071

— 0.056

-0.035

— 0.009

+ 0.02 I

+ 0.053

+ 0.084 +o-rI3

+ 0.137

+ 0.152

+ 0.157

I 80

—0.118

— o. 1 1 4

— O. IO2

— 0.083

-0.059

- 0.03 1

o

+ 0.031

+ 0.059

+ 0.083

+ O. IO2

+ O.II4

+ o. 1 1 8

1

772

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

TABLE CXXIII (continued).

Values of IQ in the first extreme case.

4« = 75°

0

»-7'.S

22°.5

37°5

52°.5

67°-5

82°.5

97°-5

, 12°.5

I27°.5

I42°.5

•57°5

'72.°5

o

— o.ooo

— O.OOI

— O.OO2

— O.OO2

- O.OO2

— 0.003

—0.003

- O.OO2

— O.OO2

— O.002

— O.OOI

- o.ooo

10

—0.025

— 0.065! — 0.071 — 0.026

+ 0.039

+0.092

+0.119

+ 0.123

+ O.IIO

+ 0.086

-1-0.054

+ 0.018

20

+0.093

+0.274

+ 0.408

+ 0.409

+ 0.305

+0-314

+0.263

+ 0.213

+ 0.164

+ 0.116

+ 0.069

+ 0.023

40

+0.109

+0.306

+ 0.431

+ 0.456

+ O.1I2

+0.344

+0.376

+ 0215

+ 0.160

+ O.III

+0.065

+ 0.021

60

+0.059

+0.167

+ O.242

+ 0.277

+0.275

+0.249

+ O.2I2

+ 0.172

+0.131

+ 0.092

+0.055

+ 0.018

90

+0.031

+0.089

+ 0.134

+ 0.161

+ 0.171

+0.166

+ 0.150

+ O.I27

+ O.IOI

+0.073

+0.044

+0.015

140

+0.017

+o.o.|9

+ 0.076

+0.096

+ O.I08

+ O.II2

+ O.IO7

+ 0.097

+0.080

+ 0.060

+0.037

+ 0.013

1 80

+0.013

+0.039

+ O.O62

+ 0.08 1

+ 0.094

+ O.IOI

+ O.IOI

+ 0.094

+0.08 1

+ 0.062

+0.039

+ 0.013

= 180°

e

f» = 0°

15°

30°

45°

60°

75° 90°

-05°

120°

135°

'50°

.65°

.80°!

0

0

— O.OOI

— O.OO2 — O.OO3

— 0.004

— 0.004

— 0.004

— 0.004

-0.004

—0.003

— O.OO2

— O.OOI

O

IO

o

+0.053

+ 0.095 +O.II6

+ O.IIO

+ 0.084 +0.068

+ 0.084

+ O.IIO

+0.116

+ 0.095

+ 0.053 o

20

o + o. 1 1 5

+ 0.231

+ 0.347

+ 0.463

+ 0.574 +0.640

+ 0-574 • +0.463

+ 0.347

+ O.23I

+ 0.115 °

40

0 + 0. 1 2 1

+ 0.245

+ 0-375

+0.506

+ 0.616

+ 0.663

+ 0.616 +0.506

+ 0.375

+ 0.245

+ O.I2I

o

60

o +0.094

+ 0.187

+ 0.275

+0.353

+ 0.408

+ 0.428

+ 0.408 +0.353

+ 0.275

+ 0.187

+ 0.094

o

90

o +0.066

+ O.I29

+ 0.186

+ 0.232

+ 0.262

+ 0.273

+ 0.262 +0.232

+ 0.186

+ o. 1 29

+ 0.066

o

140

o +0.047

+ O.O9I

+ 0.129

+0.158

+ 0.176

+ 0.183

+ 0.176

+0.158

+ 0.129

+0.091

+ 0.047

0

I 80

0

+ 0.043

+ 0.083

+ 0.118

+ 0.144

+ 0.161

+ 0.167

+ 0.161

+ 0.144

+ 0.118

+ 0.083

+ 0.043

o

270

e

o

ft) = 0

•5°

30°

45°

60°

75°

9°°

105°

120°

'35°

150°

•65°

180°

o

0 — O.OO I

— 0.002

— O.OO2

—0.003

— 0.003

— 0.003

—0.003

— 0.003

— O.O02

— O.OO2

— O.OOI

0

10

o

+ 0.043

+ 0.082

+0.114

+ 0.135

+ 0.138

+ o.n6

+ 0.067

+ O.OO2

— 0.046

— 0.051

—0.028

0

20

o

+ 0.056

+ O.II2

+0.169

+ 0.227

+ 0.286

+ 0-347

+ 0.407

+ 0.462

+ 0.471

+ 0.347

+0.177

o

40

0

+ 0.052

+ 0.106

+ 0.164

+ 0.227

+ 0.297

+ 0-375

+ 0.453

+ 0.510

+ 0.499

+ 0.389

+ 0.208

0

60

o

+ 0.044

+ 0.089

+0-135

+0.182

+ 0.230

+ 0.275

+0.309

+ 0.319

+ 0.293

+ 0.225

+ 0.122

o

90

o

+0.035

+ 0.070

+ 0.104

4-0.136

+ 0.165

+ 0.186

+ 0.197

+ 0.192

+ 0.169

4/O.I26

•+ 0.067

o

140

o -(-0.029

+ 0.058

+0.083

+ 0.104

+ O.I20

+ o. 1 29

+ 0.128

+ O.II9

+ 0. IOO

+ 0.072

+ 0.038

o

1 80

o +0.031

+ 0.059

+0.083

+ O. IO2

+ O.II4

+ 0.1 18

+ O.II4 +O.I02

+ 0.083

+ 0.059

+ 0.031

o

TABLE CXXIV.
Values of in, in the second extreme case.

4« = 75°

e

"' = 7°-5

22°.5

37°.5

52°.5

67°-5

82°.S

97°-5

ir2°.s

I27°.5

r42°-5

I57°.5

I73°5

o

- 4.682

- 4.363

- 3-747

- 2.875

— 1.807

— 0.6 16

+ 0.616

+ 1.807

+2.875

+ 3-747

+4.363

+4.682

10

- 5-071

- 3.6l6

- 0.824

+ 1-938

+ 3-383

+ 3-735

+ 3.612

+ 3-367

+3.123

+ 2.930

+2.804

+ 2-734

20

+ 50.202

+ 45-502

+ 29.091

+ 12.395

+ 6.696

+ 4.986

+ 3-224

+2.560

+2.154

+ 1.921

+ 1.782

+ 1.709

40

- 2.565

- I-976

- 0.843

+ 0.286

+ 0.902

+ 1.089

+ 1.082

+ 1.019

+0.951

+ 0.897

+ 0.860

+0.841

60

- 1.179

- 0.967

— 0.612

- 0.222

+ 0.098

+0.309

+0.424

+0.484

+0.507

+ 0.515

+ 0.515

+ °5'5

90

- 0.524

- 0.456

- 0.337

- 0.194

-0.053

+ 0.067

+ 0.159

+0.224

+ 0.267

+ 0.294

+ 0.309

+ 0.316

140

- 0.259

- 0.236

- 0-193

- 0.136

— 0.072

— 0.006

+ 0-055

+0.107

+0.151

+ 0.183

+0.204

+0.214

1 80

- 0.209

- 0.195

- 0.167

- 0.128

— 0.081

— 0.028

+ 0.028 +0.081

+ 0.129

+ 0.167

+O.I95

+0.209

PART III. KARTH CUKRKNTS AND KARTH MAGNKTISM. CHAP. I.

TABLE CXXIV (continued).

Ju = 180°

773

1

o
tn = O

15°

30°

45°

60° 75°

90°

ro5°

1 2O°

'35°

•50°

•65°

180° .

0

- 7.758

- 7.494 - 6.719

- 5.486

- 3879

- 2.008

0

+ 2.008

+ 3.879

+ 5-486

+ 6.719

+ 7-494

+ 7-758

o

- 0.069

— 0.131 — 0.289

- 0.412

- o.r47

+ 1.116

+ 3-623

+ 6-130

+ 7-393

+ 7.658

+ 7-535

+ 7-377

+ 7-3I5

o

+5966

+59.50 +58.94

+57.78

+ 55.36

+ 49.42

+32-32

+ I5-a2

+ 9-289

+ 6.866

+ 5-705

+ 5-154

+4-985

o

- 1.215

- 1.231 — 1.268

- 1.274

- J.ti4

- 0.550

- 0.509 + 1.567

+ 2.132

+ 2.292

+ 2.286

+ 2.249

+ 2.232

(1

- 1.065

- 1.049 — 0.992

- 0.876

- 0.663

- 0.336

+ 0.077

+ 0.491

+ 0.818

+ 1.031

+ 1-146

+ 1.204

+ I.32O

0

- 0.634

- 0.617

- 0564

- 0.472

- 0.340

- 0.174

+ 0.014

+ 0.202

+ 0.369

+ 0.500

+0.592

+ 0.645

+ 0.663

0

- 0387

- 0374

- 0.336

- 0.275

- 0.195

— 0. IOO + O.O02

+ 0.104

+ 0.199

+ 0.279 +0-340

+ 0.378

+ 0.391

0

- 0.347 — 0.335 — 0.300

- 0.245

- 0.173

— O.O90

0

-f- 0.09O

-1- 0.173

+0.245 j +0.300

+ 0.335

+ 0.347

= 270

in = 0°

15° 30°

45°

60°

75°

90°

•05°

120°

'35°

150°

165°

180°

1

o - 5.486

- 5-299 - 4-751

- 3-879

- 2-743

- 1.420

O

+ 1.420

+ 2-743

+ 3.879

+ 4 751

+ 5.299

+ 5.486

o + 3-937

+ 3.897 + 3-781

+ 3-589

+ 3-334

+ 3.059

+ 2.897

+ 3-202

+ 4.580

+ 7.280

+ 10.04

+11.58

+ I2.OI

0

+ 62.58

+ 62.53 +62.39

+ 62.16 i +61.75

+ 61.06

+ 59-86

+ 5748

+ 51.68

+ 34.82

+ 18.12

+ 12.88

+ 11.66

o + o.oo i — o.o ro — 0.044

— 0.099

— 0.170

— 0.240

- 0258

- 0.086

+ 0.512

+ 1-625

+ 2.754

+ 3-390

+ 3-567

o — 0.464 — 0.464 — 0.463

- 0.455

- 0.432

- 0.373

- 0.258

- 0.045

+ 0.28l

+ 0.687

+ 1-077

+ 1.346

+ 1-443

0

- 0.349

- 0.344 - 0.330

— °-3°3 — °-259 — 0.191

- 0.095

+ 0.033

•+ 0.185

+ 0.345

+ 0.489

+ 0.588

+ 0.624

3

— 0.248

- 0.243 - 0.223

— 0.191

- 0.146

— 0.089

— O.O2O

+ 0.052

+ 0.128

+ 0.198

+ 0255

+ 0.292

+ 0.305

r

— 0.245 — °-237 — 0.212

- 0.173 — °. I23; — 0.063 o

+ 0.063

+ 0.123

+ o.ns

+ 0.212

+ 0.237

+ 0.245

Values of ig in the second extreme case.

dp = 75°

e

'" = 7°5

23°.5

37°-5

52°-5

67.°5

82°.5

97°-5

II3°.5

i27°-5

M2°-5

i57°-5

'72°-5

0

— 0.616

— 1.807

-3.875

-3-747

-4-363

— 4.682

-4.682

-4-363

-3747

-2.875

— 1.807

-0.616

ro

-1.878

-5-a83

-7.192

-6.786

-5-129

-S-S22

-2.355

-1.566

— i .030

— 0.649

-0.358

— 0.115

20

+ 0.277

+ 1.093

2.409

1.232

0.596

0.344

0.218

0.144

0.096

0.06 1

0.034

+ O.OII

40

0.726

2.049

2-794

2.631

1.984

1-365

0.918

0.615

0.407

o 260

o.i43

0.046

60

0-253

0.698

0.978

1.051

0.962 j 0.795

0.617

0-459

0.327

0.217

0.124

0.040

90

0.092

0.260

o.383

0.448

0-457

0.424

0.367

0.299

0.228

O.I 60

0.094

0.031

140

0.038

O. I IO

0.170

0.213

0.237

0.241

0.229

0.303

0.167

0.123

0.076

0.025

1 80

0.028

0.081

0.129

0.167

0-195

0.209

0.209

0.195

0.167

0.129

0.081

0.028

Jfl = 1 80°

0

la = o°

•5°

30°

45°

00°

75°

90°

105°

120°

135°

r5o°

I65°

1 80°

0

0

— 2.008

-3879

-5.486

-6.719

-7-494

-7.758

— 7-494

-6.719

-5-486

-3.879

— 2.008

0

IO

0

— I.OOI

-3.175

-3-703

-5-694

-7.816

— 8.842

-7.816

-5.694

-3.702

-2.175

— I.OOI

0

20

O

+0.091

+ 0 201

+0.361

+0.649

+ I-327

+ 2.561

+ 1-327

+ 0.649

+0.361

+ 0.2OI

+0.091

o

40

0

+0.390

+0.846

+ 1-437

+ 2.209

+ 3-039

+ 3-444

+ 3.039

+ 2.209

+ 1-437

+ 0.846

+0.390

0

60

o

+ 0.272

4 0.556

+ 0.856

+ 1.149 +1-378

+ 1.468

+ 1-378

+ I.I49

+0.856

+ 0-557

+0.372

0

90

o

+ o 163

+ 0.322

+ 0.469

+0.592

+ 0.676

+ 0.706

+ 0.676

+ 0.592

+0.469

+ 0.322

+0.163

o

140

o

+ O.IOI

+0.194

+0.276

+0.339

+ 0.380

+0-394

+ 0.380

+ 0-339

+ 0.376

+ 0.194

+ O.IOO

0

I 80

o +0.090

+0.173

+0.245

+0.300

+ 0-335

+0-347

+ 0.335

+ 0.300

+0-245

+ 0-173

+ 0.090

o

Birkeland. The Norwegian Aurora Polaris Expedition, 1902 — 1903.

774

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 — 1903.

TABLE CXXIV (continued).
dp = 270°

e

m = o°

15°

30°

45°

60°

75° 90°

•05°

o
120

135°

150°

165° ,80°

o

0

— 1.420

-2-743

-3.879

-4-751

-5299

-5.486

-5.299

-4-751

-3-879

-2-7-13

— 1.420

=====

0

IO

0

-0.295

— 0.628

— 1.050

— 1.630

- 2.469

-3.702

-5-399

-7.188

-7.792

-6.186

-3-225

0

20

0

-(-0.028

+0-059

+0.098

+0.150

+ 0.229

+ 0.361

+ 0.621

+ 1.268

+ 2.463

+ 1.177

+ 0.420

0

40

o

+ 0.118

+ 0.250

+ 0.417

+ 0.641

+0.964

+ 1-437

+ 2.091

+ 2.789

+ 3027

+ 2.398

+ '•245

0

60

0

+ O.IOI

+ 0.2IO

+0-334

+0.482

+ 0.658

+0.856

+ 1.048

+ I.I68

+ I-I33

+ 0.896

+0.491

0

9°

0

+ 0.076

+ 0-I54

+0.234

+ 0-3I7

+0.398

+ 0.469

+ 0.516

+ 0.522

+ 0.471

+ 0-359

+0.194

o

140

o

+0.060

+o 118

+0.172

+0.218 +0.255

+ 0.276

+ 0.279

+ 0.262

+ O.222

+ o. i6[

+ 0.085

0

1 80

0

+ 0.063

+0.123

+0.173

+ O.2I2 +0.237

+ 0-245

+0.237

+ 0.212

+ o.t73

+ 0.123

+ 0.063

0

TABLE CXXV.

Values of Pg e and Pme due to the external current-system,
and of PQ^ and /* • due to the induced current.

4« = 15°

e

» = 7.°5

22°.5

37°-5

52°-5

67°-5

82°.5

97°-5 H2°.5

"I'*

<42°.5

i57°-5

P6e

+26.47

+ 24.O2

+ 15-44

+ 6.689

+ 3-694

+ 2.444

+ 1-797

+ 1-419

+ 1-184

+ i .046

+ 0.963

+ 0-920

po,<

+ 0.245

+ 0.225

+ 0.187

+ 0.144

+ o. 1 06

+ 0.076

+ 0.054

+ 0.037

+ 9-024

+ 0.015

+ O.OIO

+ 0.00?

20°

6,e

82 6

38 8

68 6

IQA 8

P9,i

P6,e

— 1.220

- 0-9I3

- 0.323

+ 0.262

+0.576

+ 0.662

+ 0.647

+ 0.603

+ 0.558

+ 0.523

+ 0.499

+ 0.487

P9,i

+ O.O6 1

+ 0.06 r

+ 0.06 1

+ 0.058

+0-054

+ 0.047

+ 0.041

+ 0.035

+ 0.030

+ 0.026

+ 0.024

+ 0.023

40°

!L*±

D

-19.9

-14.9

- 5-34

+ 4-48

+ 10.7

+ 14.0

+ 15-9

+ 17-4

+ 18.7

+ 2O.O

+ 21. 1

+ 21 7

D

- 0.313

— 0.272

— 0.198

— o. no

— O O22

+ 0.053

+ 0. 112

+ 0.154

+ 0.182

+ 0.200

+ O.2II

+ 0.215

P9,i

— O.O2O

— 0.017

— O.OII

— 0.004

+ O.OO4

+ 6.010

+ 0.016

+ O.O2O

+ 0.024

+ O.O26

+ O.O27

+ 0.028

90

p

H,f

+ 15-8

+ 16.3

+ 18.2

+29-3

- 5-97

+ 5-12

+ 6.99

+ 7-54

+ 7-73

+ 7-77

+ 7-78

+ 7-79

pe,i

P*,<

- 0.185

- 0.683

- 1.408

- 0.821

— 0.480

- 0.329

— 0.240

— 0.178

— 0.130

— 0.089

— OO52

-0.017

P .

+ 0.018

4- 0.052

+ 0.077

+ 0.085

+ 0.084

+ 0.078

+ 0.068

+ 0.056

+ 0.045

+ 0.032

+ O.OI9

+ 0.006

20°

ftf,t

P

co,e

D

— IO.2

-I3-I

-18.4

— 9.60

- 5-71

- 4.24

-3.54

-3.16

-2.91

-2.74

— 2.70

-2.73

r>

- 0.417

- 1.178

- 1.612

- 1-544

- 1.198

- 0.855

-0.597

-0.415

— 0.284

-0.185

— O.IO4

-0.034

r>

+ O.OI9

+ 0.054

+ 0.078

•f 0.087

+ 0.084

+ 0.075

+ 0.063

+ 0.051

+ 0.039

+ 0.028

+ 0.016

+ 0.006

40°

'

P

A f>,e

-21.7

-21.8

— 20.7

-17.9

-'4-3

-1 1.4

-9.46

-8.10

-7-25

-6.74

— 6.40

—6.07

<», 1

—

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I.

TABLE CXXV (continued).

775

H

«=7°.5

a2°-5

37°.S

5"°.5

67.°5

82°.5

97°o

II2°5

.a7°.5

.4.'.S

'57°-5

.73°.5

Pm f

- 0.062

- 0.174

- 0.258

- 0.304

- 0314

- 0.295

—0.358

— 0.213

—0.165

— 0.116

— 0.069

—0.023

P..','

-t- 0.007

4 o.oa i

4- 0.033

4 0.039

4 0.04 1

4- 0.040

40.037

40.031

+0.025

+ 0.018

4o.ori

4 0.004

90"

P

01, e

- 8.39

- 8.30

-8.il

- 7.89

- 7.61

-7-03

6.78

-6.57

— 6.42

— 6.33

-6.25

P,.,,i

7-3°

As regards form, the current-charts exhibit, as might be expected, a great resemblance to the
harts for the equipotential curves on the earth's surface and the curves for constant values of P?. It
vill further be seen that the current-lines in the second extreme case draw closer together about the
.torm-centre than in the first extreme case. The form, however, in its main features, is very similar,
during a polar storm, therefore, we should suppose, if the conduction-conditions in the earth were as
deal as we have assumed, that a current-system would be formed, of which the form at the surface
vould be something between these two extreme cases.

For large values of Ju, we see that the current-lines from the neighbourhood of the stormcentre
ollow more closely the parallel-circles than for small values of J/t. In a latitude of about 40° in
>articular, we notice that it is often in a N — S direction that the comparatively powerful earth-
•urrents occur.

This may possibly have some significance in explaining the peculiar fact that in Germany, for
nstance, the direction of the earth-currents is so markedly N — S. It may even be remarked that the
nain direction for the earth-currents in Germany is approximately perpendicular to the auroral zone.

Another peculiarity in the occurrence of the active systems of precipitation, which also certainly
>lays a part in this respect, is the ease with which the systems of precipitation appear to form at the
Norwegian stations at about midnight, Greenwich time, a circumstance which we have frequently pointed
>ut before.

If the current-strength in the outer system varies sinusoidally, there is in the first extreme case a
>hase-difference of 90° between the strength of the current in the outer system and that in the inner
ystem.

In the second extreme case there is a phase-displacement of 45° at the surface, and changing
•ery rapidly inwards. The whole current-system might approximately be imagined replaced by a system
hat was concentrated in an infinitely thin globular cup, and the current-strength in this imaginary
•urrent-system must be assumed to oscillate in time with the current-strength in the outer system.
The direction of this current will be the reverse of that in an outer current-sheet, which we may
magine replacing the outer system.

If phase-displacement can be observed, there should be a means of forming a conception of the
.•arth's conductivity. The observations in the north seem to show that the conditions follow the first
•ather than the second extreme case; but I think that here one ought to be very careful in drawing
my conclusions whatever concerning this circumstance, especially as x must be supposed to vary within
/ery wide limits. In the next place, as regards the magnetic effect of the induction currents, we can

Pe

especially point out how the relation 7,- varies when one retires from the current-system. In the first

-* i

:ase, it decreases greatly as one retires from the storm-centre ; in the second extreme case, this is not so.

776

KKKI.AMi. I HI-. MlK\Vi,(,l.\\ ATKUKA I'oI.AKIS K.\ I'KI >] I IU.V I 902- — I 90'-$.

3
(J

.A » i

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I.

777

778

BIRKKLAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I. 779

In the first extreme case therefore, the effect of the earth-current will be relatively greatest at
some distance from the storm-centre; in the second extreme case, on the other hand, this distance will
have less significance in this respect.

At Kaafjord we found that the greatest effect of the earth-currents amounted to about '/0 of the
greatest effect of the outer system in the horizontal components for storms of about 2 hours' duration.

As we shall see in the next chapter, we can make a similar estimate for southern latitudes,
whereby it will be possible to draw a comparison between observation and calculation, and also, by
this relation, to obtain certain information concerning the earth's conductivity, although here too the
uncertainty will be very great. We shall return to this later.

Finally, the condition of the vertical intensity also gives information that might afford indications
of the conductivity, but here the uncertainty will be still greater.

Upon the basis of the figures that might be determined in this way, the most suitable value of y.
might be sought. In the first place, however, such a calculation will be rather complicated, especially
as one would have to include comparatively many terms of the series developments, as the systems in
operation come very near to the earth. In the second place, the result of such a calculation would be
a priori very uncertain.

It may however be mentioned in this connection that the requirement for having conditions answer-
ing to the first extreme case in the terms of higher order will be fulfilled for greater values of \k\.R
than in the lower terms, the requirement being that

kz R*

i \ on

shall be a small quantity. The importance of the higher terms will thus cause the approach of the
conditions to the first extreme case. Vice versa, in the higher terms | k \ R must be comparatively
greater, in order to satisfy the conditions for the second extreme case, than in the lower, as we have
here set aside terms of the order

J2L

\k\.q

The condition of the vertical intensity might also be employed to separate inner and outer mag-
netic forces during the perturbations, but I think the result of such an investigation would not be nearly
so certain as the method here employed of comparing synchronous serrations, as all deflections occurring
in this component are very slight, and the earth's permeability certainly has a great influence here.

CURRENTS THAT ARE INDUCED BY ROTATION OR REMOVAL OF THE SYSTEMS.

155. In the preceding pages we have frequently pointed out that the systems of perturbation
may be moved, especially along the auroral zone. A removal such as this will also induce currents
in the earth, and it will be interesting to study the course of these currents.

As the movement takes place approximately along a small circle, the same currents will be in-
duced as would be, supposing the system were fixed in space and the sphere rotated in relation to it
about an axis perpendicular to the plane of the small circle. For this case HERTZ has deduced special
formulae ('), but these are already contained in the expression given in the preceding article.

We can choose the Z-axis perpendicular to the plane of the small circle. If we then designate
the angular velocity with which the system moves, or the corresponding rotation-velocity, as w, and

(') Cf. HERTZ, Gesammelte Werke, Vol. I, p. 37.

78o

HIKKKI.AM). TIIK \< >l( WKC.l A X ATKORA POLARIS I XT'KDI'I IO\, I G.O2 K)"'-j.

reckon it positive it the inoveineiit of the system takes place in the direction of increasing M, or the
rotation ot the sphere takes place in the direction of decreasing o, if we imagine the outer current-
svstem fixed in space. \\'e need then only put

-if' ^ i •

SI. . c I

, instead ot

cci cl

i we confine ourselves to the first extreme case, we therefore have, according to equation (7),

</' =

31'

do

(421

l''or inir polar current-system we found let. eq. i6|

H — cos _~ cos fi

Thus we find

I'"'

o cos,? 4- (I - I.\ <ln

I') . COS ti COS _" COS fi

i I ..,-." ' \o cos .i 4- d — /. )

and nccordins;' to equation (24)

sin- ,j

.C')S- C°S'' |
sin- j

1431

/x) /,]

Here too we have calculated the value of the current-function for systems answering to Jit =75°,
180°, 270', and sjiven similar o-functions which \ve have previously defined, and we have also repre-
sented the induced current-system on four charts.

FABLE CXXYI.

« —-

15

30°

45°

60°

•

75°

00°

1 °5°

1 20'

'35

.50

,65°

1 80°

0 0.000

o.6gq

0.690

0.699

O.6qq

o.6qq

0.600

0.699

o 6oq

0.699

O.6QO

0.699

0.699

10 o. 7 i o

0.722

o. 720

0-733

°-733

0.731

0.727

0.722

0.7 i 7

0.7 13

O.7IO

0.707

0.707

2O 0.0)0

o.q i q

0.886

0.854

0.825

0.800

0.779

0.761

0.746

0 735

0.727

0.723

O.J2I

.|0 I.I 8(>

J-'53

i .ogo

i .020

0.056

0.003

0.859

o 825

0.708

°'779

0.765

0.757

0-754

60 1 . 1 58

1.144

i . i 05

i .054

i .000

0.040

o.OO)

0867

0.838

0.8 i 6

C.8OO

0.791

0.788

go 1.1 ofi

1 . 1 0 1

1.079

1.048

1 .O I 2

0 975

0.04°

0.909

0.883

0.862

0.8,8

0.839

0.836

I JO 1 .028

1 .026

1 .0 I O

r .008

0.094 '

0.979

0.064

0.940

0.936

0.925

0.017

0.012

0.0 II

i Mo o.ooo

0,969

o o6u

O.Q'»O

o.q6o

o.q6q

0.969

0.069

0.069

0.060

0.060

0.969

0.069

PART in. EARTH CURRKNTS AND EAR in MA«;NKTISM. CHAP. i.

78i

TABLE CXXVI (continued).

Values of ty, due to rotation.

->.« = 75°

i

,„ = 0°

7°-5

22°.5

37°-5

5*°.5

67.°5

82°.5

97°-5

II2°5

i»7.°s

I4a°5 | <57°-5

i73°-5

1 80°

o

o

o

O

0

0

0

o

o

o

o

0

o

0

o

10

0

— 0.004

— O.OII

— O.OI 2

— 0.005

0.007

o.o 1 6

O.O2I

0.021

0.019

0.015

0.009

0.003

o

20

o

0.032

0.094

0.140

0.140

0.125 0-107

0.090

0.073

0.056

0.040

0.024

0.008

0

40

0

0.070

0.197

0.277

0.293 0.265 o.aai I 0.177

0.138

0.103

0.071

0.042

0.014

0

60

0

0.051

0.144

O.21O 0.240 0.238

0.216 0.184

0.149

0.113

0.080

0.047

0.016

o

QO

0

0.031

o 089

0 134

0.161

0.171

0.166

0.150

O.I27

O.IOI

0.073

0.044

0.015

0

|0

o

0.0 I I

0.031

0.049

0.062

0.069

0.072

0.069

0.062

0.052

0.039

0.024

0.008

o

Ko

0 0

o

O

0000

O

0

0

0

0

o

Ju = 1 80

e

o
tit -= o

•5°

3°°

45°

60°

75°

90°

105°

o
1 20

'35°

.50°

.65°

180°

0

o

1

O 0

o

0

0

o

o

o

0

o

o

0

10

0

0.009 0.017

O.020

0.019

0.015

O.O 1 2

0.015

0.019

O.O2O

0.017

0.009

o

20

0

0039 0.079

O.II9

0.158

0.196

o 219

0.196

0.158

o.i 19

0.079

0.039

o

40

o

o.o ;8

0.158

0.24 I

0-325

0.396

0.426

0.396

0-3=5

0.241

0.158

0.078

0

60

o

0.081

0.162

0.238

0-305

0-353

0.371

0-353

0-305

0.238

0.162

0.08 1

o

90

0

0.066

0.129

0.186

0.232

0.262

0.373

0.262

0.232

o.i 86

o. 129

0.066

o

140

0

0.030

0.058

0.083

O.IOI

0.113

O.II7

0.113

O.IOI

0.083

0.058

0.030

o

1 80

0

0

o

0

0

0

0

o

0

o

0

o

0

Jfl = 270°

0

o
tit = O

15°

30°

45°

60°

75°

90°

•05°

120°

135°

150°

165°

1 86°

o

0

0

0

0

o

0

o

o

0

0

o

0

0

10

o

0.007

0.014

O.02O

0.023

o 024

O.O2O

O.OI 2

O.OOO

—0.008

— 0.009

— 0.005

o

20

0

0.019

0.038

0.058

0.078

0.098

O.II9

0.139

0.158

0.161

0.119

0.060

o

40

o

0.034

0.068

0.105

0.146

0.191

0.241

O.29I

0.328

0.320

0.250

0.134

0

60

o

0.038

0.077

O.II7

0.158

0.200

0.238

0.267

0.276

0.254

0-195

o. 106

o

00

o

0035

0.070 0.104

0.136

0.165

o. 186

0.197

O.I92

0.169

0.126

0.067

0

140

0

0.019

0.037

0-053

0.067

0.077

0.083

0.083

0.076

0.064

0.046

0.024

0

1 80

0

0

0

O

0

0

o

O

O

o

o

o

0

In fig. 283 the current-system answering to a simple inductive system is given, in fig. 284 the
impound effect of two simultaneously occurring systems, situated on the same meridian, each at the
ime distance from its pole, i. e. £j = 20°, £% = 160°.

The current-fields given on the charts will have, during the rotation, or displacements, a fixed
osition in relation to the outer current-system. We may remark in particular that here in mean
.titudes, the direction principally found for the induced currents is N — S. These systems will pro-
ably have something to say in the explanation of the diurnal variation of the earth-currents, to
hich we shall return later.

The values of t// placed upon the charts answer to a current-system of which the horizontal
ortion has a direction W— E, and moves from E to W.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903. 99

782

BIRKE1.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902—1903.
'" t* » » » » i i i i i i'

PART III. KAKTH CURRENTS AND EARTH MAGNETISM. CHAP. I.

783

-84 lilKKKI.AND. I' I IK NnKWKI.IAN Al'KnKA 1'oI.AKIS KXI'I :l)ll ION, I gOl> [903.

EARTH-CURRENTS IN LOWER LATITUDES.

15(5. In the preceding pages, \ve have tried to obtain by theoretical considerations a general
idea of the \vay in which the earth-current conditions develope in the vicinity ot the auroral /one.

In order to conic to a better understanding, however, it will be necessary also to consider the
conditions in lower latitudes somewhat more closely.

This seems to be all the more neccssarv from the tact, already mentioned, that the views on the
subject of earth-current phenomena in these regions, held by those scientists who have studied them,
are verv conflicting.

For the purpose of undertaking an investigation such as this, Mr. Krogness. with the aid of a
grant from the University, went to Germany in the summer of 1910, in order to study the original
curves from Professor VVeinstein's material, and compare them with simultaneous magnetic curves from
\Vilhelmshaven or Potsdam. An investigation such as this, based upon the points of view maintained
above, would be of peculiar importance, especially as Professor Weinstein himself, after similar studies,
had arrived at a result that appeared to be at variance with our view of the phenomena, A great part
of this material proved to be accessible, but unfortunately, there were only a few days on which there
were simultaneous observations ot the two earth-current components. The one component, however, as
we shall presently see, seems to be sufficient tor our investigation.

Through the kindness of Professor IS. \Ycinstein and Professor Ad. Schmidt in Potsdam, where
this material is at present preserved, Mr. Krogness obtained the loan of a number of original curves
with copies of simultaneous magnetic curves trom Wilhelmshaven.

In the spring of 1911, Krogness and I, as already mentioned, made an expedition to Egypt and
the Soudan for the purpose of studying the xodiacal light. On the way home, we spent a few days at
Pare St. Maur and Greenwich, in order to go through some of the original earth-current registerings
made at these observatories. Krogness had the opportunity of making photographic copies from
a series of characteristic perturbations. The observatories further had the kindness to send us copies
of a number of other selected storms.

Finally, we have had sent us from Pawlowsk a couple of photographic copies of the earth-current
registerings made at that station.

As the working up of this material is inseparably connected with the investigations of the earth-
current conditions in the polar regions described in the preceding articles, Krogness has kindly handed
over the material he collected, so that the whole can be studied together.

In order to obtain as comprehensive a view as possible of the connection between earth-current
and magnetism, we will here produce a number of copies, principally photographic. The magnetic
curves from Wilhelmshaven are the only one's for which drawing on transparent paper has been em-
ployed. For the sake of the reproduction, however, we have had to darken with Indian ink those parts
of the curves that were faintly reproduced; but this has been done as little as possible, and always
on the photographic copy itself. We thought that in this way the curves would best preserve their
character, which is here of importance, as it is often in the small details that the greatest resemblance
is found.

EARTH-CURRENTS IN GERMANY.

157. \Ye will first consider the curves from Germany.

Two earth-circuits were employed here, namely, Berlin to Thorn (V. \\'|, and Berlin to Dresden
(X — S), and the scale-value was determined daily by the interpolation of known electromotive forces, as
more fully described by Weinstein in his treatise (I.e., p. IT).

PART 111. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I. 785

If we compare the curves for the two earth-current components for November i — 2, we find
:hroughout the most striking resemblance between the two curves. Every single jag and deflection in
:he one curve is accompanied by so exactly corresponding a deflection in the other curve, that by
altering the sensitiveness we should be able to get all the briefer deflections to become very nearly
dentical. [The pait of the curves just after 20'' (Gr. M. T.) answers to a time-mark, the earth-current
icre being interrupted for about 5 minutes in both lines (not exactly simultaneous)].

In other words we here find again the same peculiarity in the earth-currents that we found
U Kaafjord.

We shall also find the same thing on looking at the perturbation on the 5th November, 1883;
)ut in this case the curves are not photographically reproduced, but are drawn with Indian ink, as
he originals were too faint and rubbed out.

If we look at the remaining curves from which we have simultaneous registerings in the two
>arth-current components -- which we have not reproduced here --we make everywhere the same
ibservation.

From this we may conclude, as at Kaafjord, that the earth-currents in the district here observed,
ollow very nearly the same direction in the earth. As a consequence, however, the one component in
lie brief variations -- with which we are principally concerned -- will be sufficient to characterise the
•nurse of the earth-currents. The want of the second component is therefore not of great importance.

We have at the end of the present volume reproduced a number of examples of various typical
Magnetic storms with their attendant earth-currents, from 1883.

On looking at these, several things are at once apparent. In the first place there is always a great
esemblance between the course of the earth-current curve and the Z>-curve in nearly all details, which
eems to indicate that the latter component is strongly influenced by earth-currents; but on the other
land we very often meet with conditions that indicate induction-currents. This is most noticeable in the
implest polar storms. The following are some examples where the conditions are especially distinct:

1883, Nov. 5, Dec. 9, March i, Oct. u, Nov. 28 — 29.

While in these cases the deflections in the D-curve as a whole increase comparatively evenly to
maximum, only to decrease once more to o, a change takes place in the earth-current.

At the beginning of these perturbations the current flows in one direction, then turns, and during
he last half we find the direction to be the reverse.

If, however, we examine the time of the change in the earth-current curves, we find, that it does
>ot as a rule coincide with the time of the maximum of :he deflection in D.

The reason of this, however, is easy to demonstrate. We need only look at the curves for the
torm of the 5th November.

It is easy to prove the presence of a number of small serrations both on that day and on other
ays on which we see without doubt the effects of almost exclusively earth-currents. With their assi-
tance we can now, as before, eliminate the effect of the earth-currents, leaving only the direct effect of
ic outer system.

In the case of the D-curve the agreement is so distinct that it presents no special difficulties. It
; often difficult, however, to measure the small serrations in the magnetic curves, as we have only
lue copies, in which, as a rule, the small details are not at all sharp. We have determined the rela-
on between the deflections in the D-curve and the two earth-current curves.

In one day the figures found exhibit a (fairly) satisfactory constancy; but from one day to another
ic conditions vary somewhat. In this way we found the following figures:

786

BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1 QO2 — 1903.

TABLE CXXVII.

Date

»/,

»/,

30/?

18,' 1 22 -23;'

/» ,'n

Weighted mean

~2t

1.46

1.29

2.44

0-95

a.i3

1-39

2 13

Number of
serrations

ii

12

15

35

3°

.
73

30

Line used

B-D

B-D

B-D B-D

B-T

B-D

B-T

If by the aid of these numbers, we eliminate the effect of the earth-currents for instance, on tin
Z?-curve the 28 — 29th November, we find that the change in the earth-current takes place very nearlv ai
the time when the perturbing force attains its maximum.

The same thing will be found in a number of other simple storms when we operate in the same
manner, e. g. in those of

Dec. 8—9, Nov. 5, March i, Oct. n.

From this it appears that the effect of the earth-current in the declination is considerable, so con-
siderable in fact, that the first distinct maximum in the earth-currents seems to produce the principal
maximum of the Z>-curve.

In that time-interval the curve corresponding to the direct effect of the outer system vario
slightly as it approaches a maximum, whereas the variation in the earth-current curve is very marked.

As the effect of the earth-current in this district brings about an increase of the deflection, i:
be easily understood that the two maxima may be very nearly simultaneous, a result at which Professor
Weinstein has long since arrived; but it does not follow, as he seems inclined to suppose, that tht
induction-phenomenon is out of the question. It is our opinion, on the contrary, that in these storms it
comes out very clearly and distinctly.

I can also here point out a peculiarity about the deflection in D after the distinct maximum, which,
though it may seem unimportant, is yet very characteristic as regards both this storm and a number of
others. I refer to the slight bulging exhibited by the descending branch of the curve.

This occurs at the times when the change takes place in the earth-current curves. Here their
effect is only slight, and the reason for the somewhat altered character that the curve has here acquired
is evidently that in this region the curve will mainly represent the variation in the outer current-system,
while before it was also influenced to a great extent by the earth-currents. This little peculiarity w
find again in most similar storms, the phenomenon being in some of them more distinct than here, in
others less so. 1 will only refer the reader to those storms mentioned above.

A number of examples of this kind can also be shown in the material from 1902 — 03, as for
instance, on PI. XVIII, the course of the //-curve from about 23h 2om to 24'' at the western Central
European stations in connection with the simultaneous maximum at about 23'' 40™; on PI. XIX,
course of the //-curve at Tiflis just before iyh in connection with the intermediate maximum at Matotcl
kin Schar, etc.

On a comparison of the variations in the horizontal intensity with the earth-currents, we may t(
some extent make remarks similar to those we have just made regarding the declination.

The agreement here, however, is not nearly so great; indeed, in the less powerful storms i
often impossible to demonstrate distinct synchronous serrations. In more powerful storms, the agreemi
is often somewhat better. Thus an elimination of the effect of the earth-current in the //-curve is attendee
with considerable difficulty, and probably cannot invariably be performed with the material at <
disposal.

TART 111. EARTH CLJKRK.NTS AND KARTH MAGNETISM. CHAP.

787

As the main direction of the earth-currents very nearly coincides with the direction of the mag-
etic meridian, it will be easily understood that the effect of the earth-current is more distinct in D
mn in //.

We have also in the case of H attempted to determine the relation between synchronous deflec-
:jns in the earth-current curves and the //-curve and found the following:

TABLE CXXV11I.

Date

»/7

ao/7

18/9

~ --'u

Weighted mean

Pk
ile

1-39

0.94

I. O2

1.46

1. 10

1.46

Number of
serrations

6

3

16

20

25

2O

Line used I B — D

B-D

B-D

B-T

B-D

B-T

It is doubtful, however, whether any special significance should be attached to these figures, parti-
ilarly as the deflections have not always themselves the same direction.

Sometimes distinct induction-phenomena may also be found in //, e. g. on

Nov. 28 — 29, Sept. 4, March i.

In these storms we also find a peculiarity similar to that in the D-curve, namely a more or less
iirked bending-out of the curve simultaneous with the reversal of the earth-current curves. In such
<ses we can distinctly see the effect of the earth-current also in the //-curve; and the amplitude of the
i flection harmonises well with the figures found in Table CXXV.

Finally I may here draw attention to the fact that in cases where this bending-out is distinct, we
m infer directly from the course of the curve the effect of the earth current, without at the same time
1 ving registerings of the earth-current. This is immediately apparent from what has just been said.

In the storm of the loth February, we found that the greatest effect of the earth-currents at Kaa-
f rd amounted to about V6 of the greatest effect of the outer current-system. By the aid of the out-
\ird bends shown by the magnetic curves in southern latitudes, it is now easy, in accordance with the
iovc, to estimate the greatest effect of the earth-current. If we compare this with the greatest effect
c the outer system answering to the magnetic force at the time about the characteristic bending-out,
c rather perhaps at the beginning of the latter, we find

H ma*

p

Hi max

Potsdam 0.53

Wilhelmshaven .... 0.52

Pawlowsk 1. 1 2

Tiflis 0.64

•* H ronx
"at max

Kew 0.50

Stonyhurst 0.54

Val Joyeux 0.44

Munich 0.40

If we compare this with the values we found in the theoretical argument in Art. 154, we see that

ft the first extreme case the relation -=-- ' varies when one moves away from the storm-centre to a

f if.- ~.

dtance of about 20° from it, on an average from 100 to 20, or if preferred from 5 to i, that is to
the effect of the earth-current at the last place should be comparatively about 5 times as strong as
a the first place.

-8,H I1IKKKI.AM). TIIK M iKWF.I.IAN AKKOKA 1'OI.A KIS KXI'KI )l'l ION , [902 -1903.

Ill {\^c second extreme case, however, the conditions are more or less constant.

\Ye now find that when one moves from Kaatjord to Wilhelmshaven, the relation varies from about
1 ,; to ' .., that is to say, the effect of the earth-currents is relatively about 3 times as strong at the
latter place as at the former. 1'or this reason, therefore, the conditions during these storms seem to
resemble extreme case Xo. i more than extreme case No. 2, which also seems to agree with the phase-
displacement between earth-current and the outer inducing system, this apparently being nearly 90°.

This is most easily shown by the curves in the north; at Wilhelmshaven such a determination
becomes more uncertain on account of the relatively greater importance of the earth-currents.

We may remark that the current here, in all cases, flows in such a manner that it is in harmony
with the general law of induction. 1 his should therefore be a confirmation of our view that at Kaa-
fjord, for instance, there is really a kind of eddy in the earth-currents.

In conclusion I would point out a condition that might possibly sometimes give rise to mistakes
In Part 1 we have often shown that while, during a polar elementary storm, the one horizontal mag-
netic curve has a single bend, the other, owing to the moving of the systems of precipitation, may have
a double bend.

During a simple storm of this kind, the earth-current curve will also take the form of a double
undulation, owing to the induction. It may then be that these two double undulations, which of course
are essentially different from one another, may yet exhibit so great a similarity that one might be
tempted to assume incorrectly that the double undulation in the magnetic curve was an effect of
the earth-currents. We appear to have such a case, tor instance, on the 5th Nov., where a closer
inspection shows that the double bend in // certainly cannot be an effect of the earth-current. In such
cases therefore, one should be careful in drawing conclusions.

EARTH-CURRENTS IN FRANCE.

!.)}{. In France there are two sources in particular from which important material is obtained,
namely, Hlavier's work, and the earth-current registerings at Pare St. Maur. From the first of these a
number of curves have been published in sICtudes des Courants Telluriques« (Paris, 1884); from the
second a number of curves have been published in --Annales du Bureau Central Meteorologique de
France . All the curves published have been reproduced from drawn copies. As this method of repro-
duction may easily, as we have already said, destroy a number of small details which are here of con-
siderable interest, this may, in certain respects, perhaps be a somewhat uncertain foundation for con-
clusions of the kind with which we are occupied. This will especially be the case when we have to
compare and determine very small, synchronous serrations, and calculate the relation between the ampli-
tudes. It is moreover comparatively only a tew days that are reproduced in these reports, and it was
therefore not impossible that a number of perturbations might exist which were not reproduced, and
which might be of greater interest in our investigations.

It was in order to procure the best possible basis for our study therefore, that Krogness went
through the original curves, and selected a number of characteristic storms, of which we have obtained
photographic copies. These copies are reproduced in PI. XXXVIII to XL1I.

The earth-wires at Pare St. Maur were in a straight line, both 14.8 kilometres in length, the one
placed exactly in the direction 1C-— W, the other exactly in the direction N — S.

lly automatic disconnection there were further, except for the first couple of months of 1893,
introduced exactly simultaneous time-marks on the earth-current curves and the magnetic curves. The
galvanometers were shunted out, by which means the apparatus went back to its zero position, while
at the same time an electric current produced oscillations in the magnetic curves.

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I. 789

We have here, therefore, a capital means of making exact comparisons of the points of time of
the deflections in the two sets of curves.

The reader is further referred to MOUREAUX'S description in "Annales du Bureau Central Met6oro-
logique de France", 1893, P- B. 25.

If we here compare the two earth-current curves, we at once discover that they do not, as at
Wilhelmshaven, go together in every detail. As a rule, however, the resemblance is very close in the
principal features, but it is frequently found, especially in the smaller details, that the character of the
deflections differs a good deal in the two curves.

Nor, in accordance with this, is the relation between corresponding deflections in the two curves
constant

From this it would appear, in the first place, that the direction of the current in these regions is
,iot so constant as at Kaafjord or in those parts of Germany in which Weinstein made his obser-
vations. The conditions, indeed, are more in accordance with those at Bossekop. The cause of the
greater constancy in the direction in east Germany than in France, is probably to be found mainly in
:he different natural character. It may possibly be assumed that the considerably shorter length of the
:ircuits at Pare St. Maur may play a decisive part; but such an explanation is certainly not sufficient,
is in the curves published in Blavier's previously cited work, we find a similar disagreement between
;he circuits that make different angles with the meridian. We here too, however, in more powerful
storms, find a marked principal direction for the earth-currents (cf. Bosler, Comptes Rendus, 6 fevrier,
1911, or his Dissertation, Paris 1912, p. 67).

In the next place we find throughout a very striking resemblance between the E — W curve and
he H curve. This condition is thus in accordance with what we found in Germany, and, as in the
•ase of that country, we may conclude from this that the influence of the earth-current upon the hori-
zontal intensity is comparatively great, although possibly other conditions during certain storms may act.
refer here to the changes that are caused by displacements of the systems of precipitation along the
uiroral zone.

Another circumstance that may also possibly cause the earth-current conditions in these two districts
o be somewhat different is that — as we have often pointed out -- the polar districts of precipitation
requently have quite a definite geographical position, e. g. at about midnight (Greenwich), when the
.torm-centre is situated, as a rule, between the four Norwegian stations.

In relation to this storm-centre or to the corresponding area of convergence, the two districts here
inder discussion will have a somewhat different position, and it might be imagined that this had some-
hing to do with the matter. Possibly too, the distribution of land and water has some significance, and
his should then be more evident in France than in Germany.

A comparison between the D and N — S curves reveals throughout conditions that clearly point
o induction-phenomena, for in the great majority of cases there exists, as a closer investigation shows,
. more or less approximate proportion between the rate of change in the Z>-curve and the deflections
n the N — S curve. The direction of the current is reversed as the Z?-curve attains its maximum or
ninimum; and the current-curve reaches its extremes at the time when the Z>-curve varies most. This
ondition is here very clearly marked. In the smallest serrations, however, we think we again find an
mdoubted synchronism. At the same time we may remark that if we imagine the N — S curve, for
nstance, moved a little to the right, its resemblance to the D-curve will in many cases be striking.

I need here only refer the reader to the perturbation of March 30 — 31, 1894, where there are
pecially-marked variations in both curves, or to November 24, 1894, where the perturbation-conditions
re simpler. We also meet with similar examples, of which we can easily convince ourselves, in a
lumber of the other storms given.

Birkeland. The Norwegian Aurora Polaris Expedition, 1902—1903. 100

ygo H1KKKI.AND. THF. NORWEGIAN AURORA 1'OLARIS EXPEDITION, 1 902 — 1903.

I'"roni this it will not be difficult to understand how a number of scientists, such as AIRY, WILD
and others, have thought they could demonstrate a difference in time between the deflections in earth-
current and magnetism, the former being in advance of the latter. It is at any rate by no means im-
possible that without their knowing it their conclusions have really been based upon induction-phenomena
similar to those here Ipointed out. If we measure the difference in time between various maxima in
/> and X S curves of the same set -- for instance, of April 30—31, 1894 -- we find for the most
part time-differences that vary between about 5 minutes and 20 minutes, or an average of about
12 minutes, and thus of an order of magnitude just such as the above-mentioned scientists have found.

It mav perhaps be unnecessary to point to special cases of induction-phenomena, as the curves
exhibit such a multiplicity of them ; but 1 may mention a few of the simplest and most distinct.

October

2,

1893,

about 22''

\i ivember

2,

- ,

]8h

—

3.

- ,

16''

January

5'

1894,

4"

March

i ,

- ,

23''

May

28,

- ,

22 23''

September

19,

- ,

ig — 20h

October

16,

- ,

2O — 21h

—

27*

- ,

•2O 2 11'

November

24.

- ,

19 — 2Oh

&c.

&c.

Here too, we find that the direction of the current is what we should expect to find it according
to the general law of induction. Such examples can be multiplied considerably. These same con-
ditions are, however, not found in all perturbations. For instance, in the storm of the 28th January,
1893, o — 3'', the I) and N -S curves appear to keep more or less together, while the change in the
earth-current curves, which is here very nearly simultaneous, occurs at about the time of the maximum
in the //-curve.

The induction-phenomenon is therefore here seen by comparing the earth-currents with the //-curve.

In the preceding article we pointed out that from our calculated fields of perturbation for the polar
storms, we should sometimes expect to find such a condition, but that it must only be regarded as
exceptional.

Unfortunately we have no time-marks on the earth-current curves, so the time cannot be deter-
mined so accurately as in the later perturbations; but \)\ the aid of the short interruptions in the curve
we have determined it as accurately as possible, and it seems to show that the conditions here indi-
cated an exceptional case of this kind. No certain opinion can be expressed until more is known of
the details of the field of perturbation. Something similar may possibly assert itself, for instance in the
storms of the 6th March and 8th November, 1893, where the change in the N— S curve does not occur
so exactly simultaneously with the maximum of the deflection in I).

\Ve thus find here too the same chief peculiarities in the earth-current conditions as in Germany —
conditions that agree exactly with those which, according to our theory, we should expect to find.

It is only in certain unimportant details that the conditions in Germany and France differ from
one another.

1 lere too, we have endeavoured to determine the extent of the magnetic effect of the earth-
currents; but the conditions are more difficult to deal with from the fact that the earth-currents may
How under different azimuths.

PART HI. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I. 791

We here give the results of the comparisons of synchronous serrations.

P P

^KW 2'59 millivolt IFeyg '' 4'32 millivolt

p* Pd

:o.58 :o.87

Jes\\-' Je.\s

EARTH-CURRENTS IN ENGLAND.

159. We have also received from Greenwich photographic copies of registerings of earth-currents
md the horizontal magnetic elements for a number of selected days. They are given in PI. XXXVI to
XXXVIII, XLI and XLII.

We also give a series of examples of storms taken from curves of 1883, published in the Green-
wich Observatory Reports. The curves selected are taken from various periods, but principally from
he more recent years, from which there are also observations from other stations. One example in-
:luded is from AIRY'S observations, namely, a storm on the aist September, 1866.

In the more recent years the earth-current curves are so greatly perturbed by wandering currents,
hat in the majority of cases only the night registerings are of importance to our investigations.

If we now look at these registerings from the same points of view as before, we see in the first
>lace that it is chiefly only one of the earth-current curves, the ^4-curve, that has powerful deflections.

It further appears that the deflections in the two components very nearly go together. It is, how-
•ver, difficult to follow the details, partly on account of the apparently slight sensitiveness, and partly
>ecause of the strong, disturbing influence of local causes.

It therefore seems as if the direction of the current here once more remains fairly constant, and
hus in accordance with the conditions at Kaafjord and in East Germany.

Here too, as at Pare St. Maur, an automatic arrangement introduces exactly synchronous time-
larks into all the curves.

If we now attempt to compare the earth-current curves with the magnetic curves, we find that
ic conditions here appear to be more variable than those of the two sets of registerings previously
escribed. If we first look at the storm of the 2ist September, 1866, we there find the induction phe-
omenon extremely distinct when we compare the earth-current curve Greenwich-Croydon with the D-
urve; while in the //-curve there is evidently a very marked effect of the earth-currents, the deflections
i the two curves appearing very nearly to go together.

The other earth-current component, Greenwich to Dartford, exhibits only very small deflections.

In the next storm, however, on July 21 and 22, 1889, the D and H curves seem to have changed
lies. The deflections in earth-current and declination seem to be very nearly synchronous, while on
omparing the earth-current curves with the //-curve, we find displacements which indicate induction-
henomena.

Conditions such as those in the first of these two are found strongly marked in a number of

ases, e. g. the storms of

March 26 — 27, 1883,

October 5, 1883,

October 16, 1883,

November i — 2, 1893,

January n — 12, 1894,

November 24 — 25, 1894,

November 7—8, 1893.

792 B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

Examples of the other type, besides those already mentioned, are found in the storms of

February 26 — 27, 1893,
January 27 — 28, 1893, an^
August 25—26, 1895.

In several of these, however, the phenomena seem to be of a very mixed character, and still
more so in a number of other storms, e. g. of

November 3 — 4, 1889,
March 5 — 6, 1893,

January 7 — 8. 1895.
We thus see that the earth-current conditions in these districts exhibit throughout exactly the same
chief peculiarities as in Germany and France; but at the same time the cases that we have characterised
as exceptional may possibly occur somewhat more frequently here.

This, however, only agrees with what, according to the above, we should consider probable.
The districts in which the observations were made here, have of course a somewhat more northerly
position magnetically than the two corresponding districts in Germany and France, and a removal in a
direction N— S in relation to the points of convergence of the perturbation-systems, the respective
vortex-centres of the earth-current systems, must be assumed to bring about just such deviations as we
have here observed.

In reality, these earth-current conditions at Greenwich may be regarded as an indication of a
change from the conditions in Germany to the current-conditions in the auroral zone. In these last
districts we have seen that the conditions are practically always as in the above-mentioned excep-
tional cases.

EARTH-CURRENTS AT PAWLOWSK.

160. Some examples of earth-current registerings and simultaneous magnetic registerings of tun
magnetic storms were also sent us, as already mentioned, from Pawlowsk; but as we have had no
opportunity of going through the greater number of these, we have been unable to form any well-
grounded opinion as to the nature of the conditions here. Two of the sets of curves that have been
sent us show conditions during rather powerful storms, and the curves are of so jagged and disturbed
a character that it is very difficult to follow them. Local disturbances also seem to exert a great in-
fluence. It was our intention, however, to give a reproduction of the third storm sent, namely, that of
March 17 18, 1889. Here too there are great local disturbances, but nevertheless the principal course
of the curves can be clearly followed. Unfortunately it appears at the last moment that the original
curves are missing.

If these curves are considered from the same points of view as before, it will be easily discovered,
on looking at the course of the curve as a whole, that there exists an approximate proportion between
the N — S and E — W curves, and the rate of change in the D and H magnetic curves respectively.
Changes in the direction of the brief deflections in the earth-current curves correspond in time with tin-
extremes of the magnetic curves; and the most powerful deflections in the earth-current curves take
place simultaneously with the greatest variations in the magnetic curves. Thus the induction-phenomenon
comes out clearly on consideration of both components.

The two components of the earth-current exhibit a fairly strong resemblance; but the direction
appears to be a little more variable than in Germany.

Here too, the same- remark may be made as before, namely, that the resemblance between the
two sets of curves becomes quite striking if the earth-current curve is moved slightly along the time-

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I. 793

'axis in the same direction as before. The direct effect of the earth-currents upon the magnetic appa-
ratus is here more difficult to trace, but seems to be noticeable especially on comparison of the H and
E — W curves, where the induction-phenomenon is not quite so distinct as in the other components.

As far as can be concluded from the observations at our disposal, it would appear that the same
chief peculiarities are to be found in the earth-current conditions at Pawlowsk as at the stations pre-
viously studied.

The distinctness of the induction-phenomenon in both components here, may be partly due to the
rather more northerly situation of this station, partly to the probably homogeneous nature of the soil there.

We cannot, as we have said, have any well-founded opinion as to whether the circumstances here
pointed out are the usual ones, as we have so few curves to refer to.

COMPARISON OF SIMULTANEOUS EARTH-CURRENT OBSERVATIONS.

161. In selecting the storms given here, we have, in a number of instances, paid especial regard
to those cases in which we have simultaneous observations from several places. In this way we can
obtain some idea of the course of the earth-currents within a somewhat larger district. A number of
such cases are shown in the Plates.

Of two days we have simultaneous observations from Germany, France and England, these days
being November i — 2, 1883, and November 5 — 6, 1883. The observations from France are Blavier's
and are published in his previously-mentioned work. As, however, his curves for the first of these
^torms are exceedingly jagged and their course in consequence not very clear, we have here given
:opies only of the second perturbation. It will be seen that there is a very great resemblance between
:he earth-current curves in Germany and the one earth-current component in France, namely, the curve
ror the line Paris to Dijon. We here find a very striking resemblance both in the principal course of
;he strong deflection that, as we have seen in Germany, indicates the effect of induction from the outer
system, and in a number of details.

As regards the details, I can only point to a number of undoubtedly synchronous serrations, which
ire numbered on the various curves with figures from i to 10.

The change in the principal deflection of this current-component takes place at any rate almost
simultaneously with the change in Germany.

The effect of the earth-current upon the horizontal magnetic elements cannot unfortunately, as in
jermany, be eliminated, as the point of light at the time of the maximum had passed out of the field;
)ut it seems probable, from the course of the curves, that if such elimination had been effected, the
•esult arrived at would have been the same as in Germany, as all the characteristics of Weinstein's,
curves are also found here. The change in the earth-current component takes place a little while after
he Z)-curve has reached its maximum, and just at a place where the descending branch of the curve
las an outward bend exactly similar to that found on the curve at Wilhelmshaven, and which we con-
sidered to be probably produced by the more marked direct effect from the outer systems where the
.•fleet of the earth-current was only slight.

It will be seen that in the line Paris to Dijon a shunt of ]/40 of the galvanometer's resistance is
;mployed, while in the others a shunt of J/20 >s employed.

As the resistance in the lines is very nearly equal, and the distance between the earth-connections
ilso approximately equal, we see from this that if the deflections in the various curves were to be
•ompared, those in the line Paris to Dijon would have to be imagined increased to twice the number.
vVe then see that it is the currents in this line that greatly predominate in stength.

794 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903.

Thus the earth-current moves principally in the direction given by this earth-circuit, i. e. from N'VV
to SE and vice versa, that is to say, on the whole as in Germany.

The deflections that occur in the other two curves Paris— Nancy and Paris— Bar-le-Duc, and
that show a somewhat different course, seem therefore to have to do only with details in the
phenomenon.

As it is very difficult, if indeed possible at all, to find sufficiently distinct points of agreement
between these last curves and those from Germany, it would seem probable that the variations here
observed might be contingent in a comparatively greater degree upon the local geographical conditions
in this country.

But in all essential phenomena we find a satisfactory agreement between the conditions in Germany
and those in France.

In England too, in the various curves, we can to some extent find the same peculiarities as those
here pointed out. The principal deflection in the earth-current here, however, is not nearly such a good
example as in the material previously dealt with, but seems to be of a similar character. The deflec-
tions, however, are considerably smaller, and comparative!}' strong effects of wandering currents evi-
dently break in and efface many of the smaller deflections with their characteristic peculiarities.

The first and most powerful deflection, simultaneous with an increase in the deflections in D, is
here too, exceedingly distinct in both components, while the last, most marked bend during the time
when Pd is diminishing, is extremely inconspicuous.

As regards the details, there can be seen, especially in the magnetic curves, a number of the same
small, characteristic jags as in the two previously-considered regions; and they are also exceedingly
typical here.

They can also be observed in the earth-current curves, but only sometimes distinctly, on account
of the small degree of sensitiveness and the great local disturbances.

In all the other cases here brought together, in which we have simultaneous registerings from two
of the three districts, exactly the same conclusions may be drawn as here, namely, that the earth-
currents behave in all cases, in the main, uniformly throughout the district. Characteristic deflections-
both large and small, are followed, as a rule, synchronously, and the magnetic influence of the earth-
currents upon the magnetic elements has its outcome in the exact uniformity in all the details, especially
of the course of the horizontal intensity curve, at the various stations within the district under con-
sideration.

The fact that the course of the declination-curve is so strikingly similar at the various stations
should be accounted for, according to what has been said, by the almost identical effect of the com-
bined extraterrestrial and intraterrestrial current-systems upon this magnetic element at the various places
within the district. Concerning this, I need only refer the reader to the various comparisons of curves
given in the plates.

162. In the preceding pages, we have principally considered the conditions during polar storms,
and throughout have found our former precisely-defined view of the phenomena confirmed.

We have, however, also included a number of examples of positive equatorial storms.

The chief peculiarity of these storms consisted, it will be remembered, in the rather sudden ir
crease in the horizontal intensity all over the earth, the deflection thus obtained remaining more c
less constant for a period of varying length, until, as a rule, other forces of a more polar nature
interfered.

At first, also, a deflection in the //-curve to the opposite side was very frequently found.

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I. 795

% '

The currents that will be induced at the beginning of such a storm will of course, everywhere in
rather lower latitudes, have a direction E — W, as will instantly be seen from the formulae for ifa I'Q,
which, according to equations (5) and (6) on p. 759 may be written in the form

>f) === 2s — n Ans Pains = O

im = - S, En Ans P9ns

where Ans is a certain function of n, ps, s, Q and t, of which the analytical expression is easily found
by equation (6). At the beginning of the perturbation, therefore, one would expect to find a deflection
in the E — W curve — which is uniform in direction — that quickly increases to a maximum, and again
quickly decreases towards 0.

If the E — W and N — S curves answered to the earth-current components in the magnetic E — W
and N — S, the latter of these two should not exhibit a similar condition.

We have seen however, that simultaneously with the commencement of such a perturbation, one
or more rather locally circumscribed polar systems of precipitation are formed.

A system such as this, however — as we remember in medium latitudes — will act throughout most
strongly in the N — S component. As* the polar systems of precipitation, which we have ordinarily seen
to be of a briefer nature, so that the deflections in the magnetic curves increase to a maximum only to
decrease again immediately afterwards, the earth-current curves answering to them will as a rule be in
the form of twofold undulations.

We should expect, therefore, that at the beginning of the perturbation deflections of such a nature
might sometimes be found, especially in the comparatively high latitudes here under consideration.

If we now look at the examples of such storms given in our material from the three southern
stations, we see, for instance at Pare St. Maur, on the nth January, 1894, a very characteristic example
of a case of this kind.

In the E — W curve we find at first a uniformly-directed deflection, while in the N — S curve the
deflection has the character of twofold waves. We see that the first earth-current impulse in this latter
component must undoubtedly, at any rate to a very great extent, produce the "starting impulse" that
appears so distinctly in the Z)-curve.

For the rest, fairly strong polar systems of precipitation are acting here all through the further
course.

We thus see here that the character of the deflections at first in the E — W and N — S curves is
rather different.

As it will very often be difficult or impossible to separate the deflections that are due to equa-
:orial perturbations from those that are due to simultaneous polar systems of precipitation, when con-
sidering the magnetic curves, it will of course be so to a still greater extent if we were to try to
separate the deflections in the earth-current curves that were due to the variations in these two systems.

As, however, we have seen a distinct example of the great difference between the character of
he deflections in the N — S and the E — W curves, where two such systems are acting, it seems likely
hat this might frequently have something to say; in other words, the difference in the two earth-current
:urves, that we have before pointed out and ascribed chiefly to local causes, might to some extent,
jossibly a very great extent, be caused by the different induction-effect of simultaneously occurring
)olar and equatorial perturbation-systems.

If we look at the other examples that we have of equatorial storms, we find everywhere these
;ame conditions confirmed.

From Germany and England we have two examples of such storms, on the i6th and 2oth
Dctober, 1883.

d

'

796 B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 — 1903.

In Germany there is only the one component, Berlin to Dresden; and this very nearly coincides
with the direction of the magnetic meridian.

In both cases, at the beginning of the perturbation, there is a double oscillation, which should
indicate the influence of polar systems.

The "starting impulse" observed in the magnetic curves at the beginning of the perturbation,
southwards in H, and eastwards in D, seems to be caused by the magnetic effect produced by the.se
induction-currents.

The direct effect of this polar precipitation must be assumed to decrease very rapidly at rather
great distances, as the strength of the current in these systems of precipitation can only be compara-
tively small, but the changes take place with comparatively great rapidity.

If, on the other hand, we look at Greenwich for these days, we see here too an indication of a
double wave; but the principal phenomenon at the beginning of the perturbation is a uniformly-directed
deflection in the current-component EI , that is to say, conditions that must have been produced by the
induction-effect of the equatorial system.

The deflection in E^ answers to a current-direction from NE to SW, and is thus fairly what
we should expect, as the current-direction in the outer equatorial System is from W to E.

The deflection in the E — W curve for Pare St. Maur, on the nth January, 1894, answers to a
current direction from E to W also in accordance with what we should expect.

We further find in all cases that the maximal deflection in the earth-currents occurs at the time
when the deflection in the //-curve increases most, that is to say quite in accordance with what we
should expect to find from our former experience.

These examples may easily be multiplied, but in this connection I need only refer the reader to
the curves published from Pare St. Maur and Greenwich.

I will, however, draw attention to a difficulty that might possibly sometimes lead to misunder-
standing. In certain cases the variation will be exceedingly strong, and both the magnetic and the
earth-current curves may then be very faintly reproduced upon the photographic papers, often so faintly
indeed, that it may be impossible to follow the curve in its sudden and most rapid movements. It will
therefore sometimes be very easy to overlook certain small serrations.

At the beginning of the storm of the nth January, 1894, we have a case in which the photo-
graphic curves were very faint and difficult to follow; and here, in order to indicate the uncertainty
arising therefrom, we have represented these parts of the curves with dotted lines. If, therefore, in
certain cases, a disagreement may be found in this respect, this uncertainty should be kept in mind.

During the positive equatorial storms also, we thus find confirmation of our previously expressed
view of the connection between the magnetic perturbations and the earth-current phenomena.

THE DIURNAL VARIATION OF THE EARTH-CURRENTS.

163. In the previous articles, we have studied the connection between the earth-currents and t
magnetic storms. In addition to these, however, there are certain other, more regular variations, one
of which in particular, the diurnal variation, has been carefully studied. As regards earth-current
Weinstein has made a very thorough investigation of the phenomenon, based upon his observations i
Germany. The principal result at which he has arrived is given in a series of curves and vector dia-
grams in his previously-mentioned work.

In England too, similar investigations have been carried out (see Airy, Phil. Trans. 1870, p. 2
and PI. XXIV).

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP I. 797

Although we will not here enter upon a detailed treatment of this phenomenon, but will reserve
it for a subsequent chapter, in which the diurnal variation of magnetism at our four Norwegian stations
will be discussed, it will yet be natural, in connection with what has been said, even now to point to a
few circumstances regarding the diurnal variation of earth-currents, particularly as Dr. L. STEINER(I),
upon the basis of Weinstein's curves, has drawn some very interesting conclusions. He finds that while
the diurnal variations in the magnetic X-component — i. e. the force-component in the direction N — S -
very closely follow the E — W curve, so that the variations in the former may be supposed to be the
direct effect of the corresponding earth-current component, the deflections in the N— S curve are approxi-
mately proportional to the rate of change of the component Y (in the direction E — W).

It will be seen that this is in the main the result at which we have here arrived by a conside-
ration of the earth-current conditions in Germany during the magnetic perturbations; and it would be
natural to look for an explanation of the diurnal variation similar to that of magnetic storms. In these
more slowly passing variations, however, other forces will exert an influence to a much greater extent
than in the briefer variations. The thermo-electric forces in the earth's surface may perhaps play a
very important part; and as STEINER suggests it may possibly be these currents that are mainly the
cause of X so closely following the E — W curves. Of the other phenomenon, however, he gives no
satisfactory explanation, but remarks that "these connections — as far as they are not due merely to
chance - - still await explanation". Our points of view naturally lead us to explain these conditions
in the following manner.

Both ou,r observations and our experiments have shown us that broadly speaking a purely geo-
metric connection must always exist between the position of the sun and the situation of the systems
of perturbation. In other words, what has been said seems with undoubted certainty to show that the
earth will as a rule rotate in relation to an external corpuscular current-system with a more or less
fixed position in space. The strength of the current, especially during magnetic storms, may vary
within very wide limits; but its form has always proved to be approximately constant. I further assume,
as already stated, that from the entire surface of the sun, a comparatively regular radiation of corpuscle-
rays goes on, similar to the stronger and more irregular pencil-radiation of probably stiffer rays
from the regions of the sun-spots.

This corpuscular field of radiation from the entire surface of the sun will now constantly surround
the earth, and it is obvious that its shape will in the main be the same as that which we have found
to be characteristic of the magnetic storms. When the earth now rotates in relation to this system of
rays with its approximately fixed position in space, earth-currents will be induced.

The formulae necessary for the calculation of these are given in Article 155, equations 42 — 44.

In this chapter we have also calculated the earth-current system that is induced by a polar system
of precipitation of the previously-described form (see Table CXXVI).

Fig. 283 is a chart of the current-lines on the surface, answering to this; and we may here once
more draw attention to the peculiarity already pointed out, namely, that the direction of the current-
lines in medium latitudes such as those regions of Germany in which Weinstein made his observations,
is practically only N — S.

It further appears very distinctly from the experiments that the rays in the equatorial regions are
concentrated in such a manner that the main body of the ray-system swings round in front of the earth
and passes nearest just before noon (see fig. 219). As the greater number of the rays run here, this
system will in all probability also play an important part in this connection. .

(>) Terr. Magn. XIII, p. 57.

Birkcland. The Norwegian Aurora Polaris Expedition, 1902—1903. 101

798

BIRKELAND. THE NORWEGIAN AURORA POLARIS KXPEDIT1ON, IQO2 — 1903.

In order to obtain a general idea of the course of the earth-currents induced by the rotation of
the earth in relation to a system such as this, we have made a calculation of this current-system upon
the assumption that the equatorial system can be replaced by an infinitely long, rectilinear current
situated outside the earth in the plane of the equator.

For the potential of a current such as this, that flows at right angles to the XZ-plane, and inter-
sects it in the points x = x\, z = zi, we have, as is well known, the following expression:

-i a — 3j _ i o cos 6 — z\

V = — i . tan - = — i . tan

x — #i o sin 6 cos w — ,

(45)

where the direction of the current is reckoned positive when it coincides with the direction of increasing y.
If we say that the rotation-velocity equals w, and further, for the sake of brevity, that

a ^ i — sinft) sin

b = Xi sin 6 cos w

c = cos 6

d = sin w sin B

cos 6

(46

we find, after some reductions, that

3V

and

W .c.d( ,

->T-'V{? +

zac

log nat

L*

ay* - 2bQ + L*

(47!

L-

+

2^-c — abzi — acL2 _i Q\aL* -

tan

:2 — 06 )

If we here put z\ = o, we obtain the expression for the current-function answering to the equa-
torial position of the current.

We have calculated the current-system answering to an extra-terrestrial current such as this, the
result being given in the table below.

TABLE CXXVII.

Values of the current- function ifj answering to an extra-terrestrial current
situated in the plane of the equator.

x\ is here put — 20. The multiplicator o — is left out.

v. 10

e

0°

10°

30°

50°

70°

9°°

110°

o

130

15°°

o

170

1 80°

20°

o

0.052

0.145

O.2II

O.24I

0.237

0.207

0.158

0.099

0.033

0

40°

o

0.107

0.288

0.392

0.414

0.378

0.307

0.222

0.134

0.045

o

60°

0

O.I 28

0.33°

0.419

0.410

0-344

0.274

O.I 86

o. 109

0.036

o

80°

o

0.064

0.158

O.igo

0.1 76

0.144

o. 106

O.O72

0.041

0.014

0

For 6 == 90° we have ip = o. Further ip (n — 6) = — t/; (6).

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I.

799

8oo

r.IKKFI AM). Till! XOK\VK(,IAN AL'KORA POLARIS KXPKIHTIO.N, I QO2 — 1903.

In fig. 287 \vr have also drawn a chart of the course of the current-lines at the surface.

Then.- is to he noticed here a striking agreement with the main features of Schuster's chart of
tin potential lines for the diurnal variation (cf. his admirable memoir in Phil. Trans., 1889, p. 508).

In addition to this equatorial system, there are polar systems also at work, and we ought therefore
bv rights to bring such together il we want to represent the earth-current system that is induced bv

IMC;. 288.

Fig. 289.

rotation in relation to the entire external system. In this wav it would be easy, bv a suitable choice,
to find current-fields that in their details too, exhibited a more perfect agreement with Schuster's chart.

A composition such as this, however, will in the first place always be rather arbitrary, and in
the second place it will only answer to a part of the earth-current system that characterises the diurnal
variation of these currents; while in the third place a chart of the earth-current lines and the magnetic
potential lines are only comparable in certain respects.

As there is, moreover, no chart of the diurnal variation of the earth-currents all over the earth,
we will not here undertake any such composition as regards the entire earth. All that exist are the
determinations of the diurnal variation in Germany and England.

PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I. 8oi

To enable a comparison to be made with these, we have put together, for 0 = 40°, which about
answers to the position of Berlin, the current-components for two systems of this kind.

One of them answers to an external inducing current at the equator, where L — 2/?, and which
ies nearest to the earth at a place answering to Noon; the second answers to a rectilinear current
jarallel with the plane of the equator, lying at a least height, // = 0.25 R, above a point in a small
:ircle round the pole with a spherical radius of 20°, where the time is 2h a. m., a night-system corres-
aonding to a negative polar storm.

The strength of the current in the equatorial system is put at 20 times greater than the strength
it the current in the polar system.

The vector diagram that has been drawn (fig. 288) shows us the suggestive agreement that exists
n the main between this and the vector diagrams that Weinstein has calculated from observations, one
t" which we here reproduce (fig. 289).

\Ve must emphasise the fact that in this first experiment we have not taken into consideration the
rays that at about 6h— 7'' p. m. must penetrate into the polar regions just where we have been
ed to assume that the rays which produce the positive polar storms descend towards the earth.

This group of rays will be included in our future calculations, as a preliminary investigation seems
o show that in this way a surprisingly close agreement may be obtained between calculated and observed
diagrams.

It may further be noticed that in the equatorial system in a latitude of about 50°, i. e. ft -= 40°,
he currents are as a rule only in a direction N — S.

llnse currents will now approximately be proportional to , i. e. to or, in other words

am ?« 3(j

ar

o , in accordance with what Dr. Steiner has found.

\Ve can therefore, from our points of view, find a natural explanation of all the hitherto known
>rincipal features of the diurnal variation of earth-currents.

\Ve will not at present, however, go more thoroughly into the matter of the diurnal variation of
errestrial magnetism, but will reserve it for a subsequent chapter.

Reprint of fig. 204.

Earth-currents and magnetic elements from Pawlowsk, 17 — 18 March 1889.

Local Mean Time.

nh I

NS

The Pawlowsk-curves, which were missing, as mentioned in Article 160 (p. 792),
were found just before publication and are here reproduced.

PI. XXII

The Perturbations of the 15th October, 1882

Term-day observations from 231' 20"' on the 14th to 23h 20m on the 15th, Gr. M. T.

PL XXIII

The Perturbations of the 1st November, 1882

Term-day observations from 10'1 to 23" 20m, Gr. M. T.

oo
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—

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PI. XXIV

The Perturbations of the 15th December, 1882

Term-day observations from 8h to 23h 20m, Gr. M. T.

oo

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K

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s

u
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u
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£

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1— I

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PI. XXV

The Perturbations of the 2nd January, 1883

Term-day observations from llh to 23h 20m, Gr. M. T.

CO
00

oo

55

CM

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ffi

55

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pq

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PI. XXVI

The Perturbations of the 15th January, 1883

Term-day observations from 10h to 23h 20™, Gr. M. T.

CO

00

oo

12

u

H

P3

K
D

H

OS

U
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PI. XXVII

The Perturbations of the 1st February, 1883

Term-day observations from 10h to 23h 20m, Gr. M. T.

PI. XXVIII

The Perturbations of the 14th and isth February, 1883

Term-day observations from 23h 20nl on the 14"' to 6h 20m on the 15th, Gr. M. T.

n

00

oo

3

OS

m
w

m
Q

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£

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OU

PI. XXIX

The Perturbations of the 15th juiy} 1883

Term-day observations from 6h to 23h 20m, Gr. M. T.

PI. XXX

Earth currents and magnetic elements. Series I.

Kaafjord.

•3- -

0%

f

,

-

s

-LT

-w

•0 3~

£

s

3"

LI ~9f

PI. XXXI

Earth currents and magnetic elements. Series II.

Kaafjord.

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PI. XXXII

Earth currents and magnetic elements. Series II continued.

Kaafjord and Bossekop.

"31 '

3-

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—

71'

3 IV

v; -3:

Cf

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E

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PI. XXXIII

Earth currents and magnetic elements. Series II continued.

Bossekop.

PI. XXXIV

Earth currents and magnetic elements. Series III.

Kaafjord.

PI. XXXV

Earth currents and magnetic elements. Series III continued.

Bossekop.

PL XXXVI

Earth currents and magnetic elements from Germany.

(For Nov. 5 — 6 also curves from France and England.)

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u v

•£ -

>

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I

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PL XXXVII

Earth currents and magnetic elements from Greenwich.

Greenwich.

Greenwich.

1

-I T

^7- -™

=0 *l\

PI. XXXVIII

Earth currents and magnetic elements from Pare St. Maur

and Greenwich.

Pare St. Maur.

P d r c .Sf/ M a u r

27-2S.hw.18DS Paris M.T. . 7<S'7' 2lh MN

J. '

D

JVA M

F.W

15h

18''

21''

^Sj\ •

MN

A A.

Greenwich.

It W L C,h

(!nvrui>i<-Jt Mmn

|W^pP|r*Ty*|' T"

PI. XXXIX

Earth currents and magnetic elements from Pare St. Maur.

a

,1

e«

1

iL. • i " ^5 1m:.

i N

K tt; ^
**

^ 5 ' 1 *

PI. XL

Earth currents and magnetic elements from Pare St. Maur.

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gLL f •]

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PI. XLI

Earth currents and magnetic elements from Pare St. Maur

and Greenwich.

Simultaneous r, _

21-25

1)

l.r>h Paris MT lSh

21

h

MN

26-27 Feb.lS93

MNParisM.1

tf*

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JEW

t. \Taur and Greenwich.
~\2*t-25 Nov. 189k ~Gr.MT

— 1~~*

/2 /fA

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u

PL XLII

Earth currents and magnetic elements from Greenwich and

Pare St. Maur.

Greenwich.

Simultaneous registerings from Pare St };•
and Greenwich.

Greenwich Mean Time

7-8Jan.l895 Paris M.T.

i L . I . l. . I

21-22 Jtdy 1SS9

25-2GAuyl$95 Paris M.T. gi,.

"

Pare St. Main:

30-31

m -. i.;
A'.yLrf^E^J ^/V^V

V ;••--$

^v^— .

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VvV

>,

Series 247'

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