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 18821883,
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, 19021903.
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
4447. The Perturbations of the 22nd March, 1903 127
48. The Perturbations of the 26th December, 1902 137
49- Cyclo-Median Storms 144
5> 5 1 - 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
" 7 2 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
7679. 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 E V = 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".
68208, On the Charts, for "V v ", 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 18991900 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
- I 6
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, 19021903.
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 t 678 &
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, 19021903.
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 6956'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, d 1 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 3C. 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, It 1 , the other end
being held fast by the clamps /, 7 1 , 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
I45o' 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 Vs 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, (5 1 , led into the register-
room. Here were built two solid cement
pillars upon the firm rock. They were pi g . 20 . Observation-huts at Axel0en Station.
of the form shown in the ground-plan
at P and P 1 . 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.
2 8 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 q u ft e 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 9'5C 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 Vs 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 P l , 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. q uite 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 f 1 ).
"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, 19021903.
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, 19021903.
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, F n .
The perturbing force P is the force which, together with /", has F t 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 F Ul , F u , F lv
/' F n h, F n t, F m
P , P h , P d , P,.
We thus obtain
Pk = Ftk-F* =//-// )
Pd = F id ~F, ld = F u ( W
P, = F tv - F,= V t - V n ,
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 O n , and if a deviation of one length-unit on the magnetogram answers to a magnetic
force , then
Ph = tk (Oft Ort) = t h 4
Pa = td (Otd O nd ) d l d
P, = e, (O t , O m ) = e v /,
the differences of the ordinate being denoted by // 4 and /,
According to our definition-equations (i), we shall have P k 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,
e v 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, 19021903.
A simple mechanical reflection then shows that
d = - 8 Ht = aid Hf.
180 . 60 r
If we resolve to reckon P d positive towards the west, we obtain the following rule for the sign of f d .
e d 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 :
H t 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 n d length-units, we obtain
If this is inserted, we obtain, employing the equation for
d rr
ti, = -- . w d rio
, = . 10 d tif,
M c
If we do not here demand greater exactness from s k 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 io d as
constant, x being small in proportion to the unit. We can then generally, instead of H , choose
a mean value, H , 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 R h 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, 19021903. 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
n d
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.
5 1
The table shows that the scale-values for H and V are not constant; in the case of e e 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>dH
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.
5 2
BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 19021903.
TABLE IV.
Scale-values for Dyrafjord.
H = 0.120 0) r d = i734mm. io d H = d = 3-47-
Date
<;
m,
n v
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
;.= 5-5 1 -
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, e v = 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. t v = 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.
H = o.i 1 13
Date
a
X
/.
n d
/,
;,
,
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 e v 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.
8 e = 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 P e 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, 19021903.
58 niRKF.I.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 19021903.
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>dH
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
fi 9 o2= + 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. 3 6
12.
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.
(*) r t 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:
(,,, io d H u 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 8 h 52, and lasts until
14'' 2O m . (The time, when not otherwise stated, is Gr. M. T., o 1 ' = 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.
6 4
RIKKF.LAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 19021903.
TABLE X.
Observatory
i
2
3
4
5
6
8h 5 o.'8
I oil 50.' I
n n ag.'S
12'' 29. '7
I3 h 49'
14!! is.'o
Baldwin (') . . .
8li 5a .' 4
to' 1 53-'5
8h 52/6
Cheltenham (')
8 h 54-'9
ioh 54'
8h 52/6
i oh sa.'p
n h 30/4
i232/3
I3 h 54-'9
14'' i8.'8
Wanting
I2h 29.'8
'3 h 5i-'7
J4 h i5-'7
i
i
III" 27/1
I2h 3 2/5
M h n-'S
Kew
)
i
ijh 32/9
I2h 32/7
i3 h 55-'8
I4 h i9-'5
Wilhelmshaven ....
ill) 30'
I2 1 ' 29. '9
'3 h 53-'6
I 4 h I7.' 3
n
12" 33/2
i3 h 53-'8
14!! i8.'9
8 h 54.'3
i
ii 1 ' 32/5
12!' 33/6
I3 h 54-'5
14^ 19.'!
Tittis
i
iih 31/1
iah 3i.'6
i3 h 5i-'7
14!' 16'
8h 52 .' 7
ioh 51/6
nl'3i.'4
I2'> 32'
I3 h 54-'a
I 4 h i8.'4
8 h 53-'9
io>> 53'
n h 3i-'5
1 2 h 33/3
I 3 h 5 2.'6
I 4 h i 9 .' 7
Zi-ka-wei
i oh 54-'i
" h 33-'S
12" 34/9
I3 h 56'
14!) 20/8
8 h 54-'9
io'i 54.'9
ii"33-'9
i2 h 35/5
I3 h 56'
I4 h I9.'5
8t 54-'8
ioli 53/2
nh 3 3/6
IS* 1 33-'2
'3 h 55-'4
I 4 h 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 (e v = 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
+ 4-5 /
o
+ 5-3 /
IO O
+ 5-9
)
?
+ 4.6
o
+ 5-4
+ 5-o
o
II
-1- 4. i
- 4-1 /
o
+ 4-3
+ 7-2 '
E 1.2 /
+ 5-3
o
12 o
+ 6.2
- 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 )
W 3 .i
7
>
4- 18.0
> 6.7
+ 11.7
14 o
+ 12.9 >
4- 5-i
E 8.0
+ 13-5 '
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
+ 7-3 /
+ 3-7 7
W 2.6 7
5-5 7
7
7
-r 3-6 7
o
10
+ 4-9 '
W 4 -4 Y
o
7
7
7
7
7
-r 4.6
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
+ 7.1
> 3.1
-t- 10.3
4.0 '
+ 5-5 "
bation
+ -J.6 *
3
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
W 4 .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 >
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 '
ceptible
7
?
7
4 4.4
tions of a
duration of
II
+ 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.
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
W 3 . 4 7
?
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 .
?
4- 9.8
deflection.
3
4- 7.8 >
o
I 3 h 45 m
4 9.0
o
4 n.o
W 0.4 7
?
4- 12.6
13 o
4- 16.8
'
0.87
4- 19.0
1.4
4- 22.5
5.2
7
4- 23.6
3
+ 15-5
0.8 '
4- 15.0 >
o
+ 21.6 >
3-3
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.
6 7
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
4- 9.6 y
o
+ 10.6 y
o
10 o
+ 8.2 >
No mea-
No visible
4- 7.8
o
+ 8.2
+ 10.1
o
II
+ 6.7
surable
distur-
+ 8.8
W 1.3 y
No per-
4- 7.6
+ 8.3
12
-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 .
13 o
4- 22.5
small.
+ 24.8
> 2.O >
+ 23.1
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 n h 2o m in many places they have
already become 0. Between g h and I2 h , 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 I2 h , 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 5 h 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 5 1 ' 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 i8 h , 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 6 h o m , and Chart II for g h o m .
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 I2 h 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, i6 h o m and i6 h 45 m . 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.
7 1
stations. At i6 h 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* o m .
The field in southern latitudes has mainly the same character as at i6 h 45 m ; 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 >
+ 2.8
O
+ 2.5
o
+ 3.6
f i-3
o
9 o
+ 7-4
o
4- 4.1 *
1.8
+ 4.6
+ 6.3
o
+ 2.6
o
12 15
+ 6.6
+ 3- "
E 15.8 .
+ 9.2
W 3.8 y
-f 8.1
W 4 .8 7
+ 3-9 "
W 4.1 ;/
15 o
+ 3.8
ii. a
W 9 -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 '
- 1.8
4.8
- 1-5
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
* 15-3 '
o
19.3 >
o
16.0
UIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 19021903.
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
W 12.3
- 17.2
+ 4-5'
W 7.5 y
- IO.2
9
+ 3-8
1.3
- 3-3
7.4
-t 7.1
10.6
2.9
12 15
9
9
7
4- 20.7 Y
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.
9
7
7
4 5.6.
4 7.4 >
2.4 >
o
9 o
4 1.2
> 4.8 >
7
?
9
+ M-3>
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.
o
15
o
. 1.4 *
4 7.77
. 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
- 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
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 3 2 - "
4- 20.4 .
4 22.6
5-5
4 6.0 .
- 14-3
' 9-7
24.2
10.4 >
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
9 o
7
7
7
7
4 9.67
o
O
+ 8.57
W 2.37
+ '4-7 '
12 15
4 9-77
o
4 6.67
7
4 9.6
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
+ u-sy
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 >
+ 7.8
, + 9.6
W 5.27
15
-r 3.0
E 2.97
+ 2.7
+ 1.2 >
+ 3-9
o
o
O
16 o
- 9.2
> 3.7
+ 2.3
IO.3 O
- 7.2
o
- 7.8.
- 8 7 .
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
W 4 . 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 ig h u m , 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 i6 m 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
22 22.5
+ 8.5.
+ 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
+ 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 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 18991900, 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 P v will predominate, athough it is generally comparatively small.
In order to obtain an idea of the conditions for P v , 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 P v 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 o h io m ,
and reaches its maximum at i 1 ' 8 m 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 i h 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 i h 4511 with a perturbing force of only 39.6 y. At Matotchkin Schar it
begins at about o h 5i m . The perturbing force reaches its maximum at about i b 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 3 h 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 o h 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 o 1 ' 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 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
- 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'
- 5-
O
45
- 3-9
o 4.6
- 6-3
o
- 5-3"
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
45
-141.5
W 5 o. 3 y
+ 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
- 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
. 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.
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
Wi 5 .6y
o
+ 7.7 y
Wi6.8y
has been out of
15
- 33-3
15.0
- 2.5 .
> 15-2 "
+ IO.2
. 9.4 .
3
38-1
9-5
order in some other
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 *
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*
1.0
- 0.9
^^
o
TABLE XIV (continued).
(,r. M. T.
Potsdam
San Fernando
Munich Dehra Dun
Pi,
Pd
2
P d
ft
Pd
A
Pd
h m
I
4- 3 .a Y
W 16.87
4- 6.4 y
W 2.0 /
4- 6.0 y
W 7.67
2.8 7
W 4 .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 >
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'
3- '
i-5
| +3.*
4- 1.6
3.0
3-o *
45
2.2
- 1.9
2.3
0.8
o 3.0 s
TABLE XIV (continued).
Gr. M. T.
Ekaterinburg
Ph
Pd
P,
h m
I
-4.07 W 9 .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
4- 5-o i
i.i * | a.o
15
4- 5.0 i
- 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 /'' jo m ,
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 i h 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 2 h .
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 P l is now in accordance
with the two first-named stations, and P c 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 2 h // m .
The distribution of force is the same, but the intensity is less. The turning in Europe is
continued a little.
Chart VII. Time 2 h v/ m .
The force on the whole weaker, except in America, where it seems to be somewhat greater
than it was at 2 h 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 i h 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
9 6
RIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 19021903.
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, 19021903.
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. 4 8.
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 P e 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 P t , 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, P t will increase rapidly; at a certain dis-
tance it will attain a maximum, and then once more decrease.
With regard to P v , 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, 19021903.
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
p u = 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 = -151
sin
cos 6 = cos a cos (>.
sm y
a
R sin
/? sin 9 sin a
I n I R cos sin a
-T - R cos 6
sin a
we obtain
sn
r 1 '
" cos ^ J ==;
,- 2sin Of sin 2 -
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 io 6 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
- 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.
" II V
P + P! j
i
P*
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
P t y + P mv
/v
661.91
+ 48-30
613.61
10
- 26.08
4- 40.36
+ 14.28
3 o
+ 6.15
+ 17.23
-*- 23-38
45
-"- 5-93
+ 9-43
+ 15-36
// = 200 km. ; / = oo
P
10
3
45
p v
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 y 1 - 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, - 75 6 - J 3 an d -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 i 1 ' and i h 15, P t 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 6 m .
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 23 h .
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 2 h 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.
I0 7
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
18
30
27-5'
I
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
* 1 9
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, 19021903.
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
o
o
O
15
- 7 .6.
o
- 9-4 y
o
- 10-57
o
- n-3/
o - 14.77
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
15
- i-3
+ 3.2
o
1.4
o
o
O
o
30
o
o
+ 3.4
o
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
34-
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.
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
15
- 88.0
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 '* 45 m ,
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 "
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
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- 2 7 . 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. 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. " 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
'5
- to.o )' 15.) is directed 6.3"
I.T-6 2.5 J>
i .8 '
7-4
o
3 n
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 2j h ij m .
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 2j h jo m .
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* o m .
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, 19021903.
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 188283 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 2 h 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 3 h , 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 I9 h , 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
23 h i2 m . From 2i h 28 m to 23'', the force remains almost constant both in magnitude and direction. The
perturbing forces are calculated for 22 h , and the corresponding current-arrows are marked upon the chart.
Current-Arrows for the 30th March, 1903, at 22 h .
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 23 h I2 m , 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 o h 24, and concludes almost as suddenly at 2 h i6 m .
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 23 h , the deflections in H begin to increase continuously. At o h 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 o h 36, P v , 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 23 h 50, the effect of the polar perturbation is noticed at all the southern stations
throughout the world. At 2 h io m , 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 o h 12 to i 1 ' i6 m .
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 . . .
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 P t (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 o h 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
+ '3-97
+ 9.07
o
4- 12.07
o
2.42
+ 5-3
W 9.00 7
- 7-3
- 8.5.
W 4.87
- 6.5.
W 1.777
7-5
- 5-33
- 6.5.
1.80
12.2
- 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 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
- 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
P t
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
o
+ 38.3
O O
4- 20.7 >
W 9-07
- 3527
O
- 34-97
15
+ 8.3.
o
+ 45-4
7-5
+ II.O
o
o
- 343"
- 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
7-5
- 515-2
3 1 . 2
4-263.2 t
37-5
- 3 r -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
O O
- 5-5
E 2.3 /
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
5 2 -5
I
+ 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
-(- 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
4 7.97
o
+ 12.6 V
o
+ 13-77
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
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>
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
o
+ 7.67
o
o
4- 9-5 /
o
- 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 >
" 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
4 14.8
O
4- 3-6
4- 6.6 i
> '3-9 >
1.9
I
+ 14-5
F- 4-5
4- II. 2 >
E 1 1. 1
-1- 3-1 '"
+ 11. 1
10.4 >
- 2.8
15
4 6.0
14.2
4- 4.0
13-9 >
4 1.9
+ 10.6
E i.i
- 2.8
3
4- 1.7
* 1 1.3
o
> 9.0
+ 5-3
4.8
- 1.3
45
o
7-9
o
o
4.1
o
4- 2.2
4.1
2
o
5-2 "
3-4 '
+ 0.9
8 3-3
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
+ 4.17
O
12.6
There is
- 5-4
W 2.07
From _ 8 9
E 4-87
- 8.7
7-5
-15.4
only Pi,
for this
- 6.6
5-5
10 a. m. to
2 p.m.,
12.8
> 3-6
10.6 >
: 5
-15-7 "
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
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
4- 2.8
4.9
+ 8-4
o
+ 7.8
Birkeland. The Norwegian Aurora Polaris Expedition, 19021903.
1C.
122 BIRKELAND. THE NORWEGIAN AURORA 1'OLARIS EXPEDITION, 1902 1903.
.Current- Arrows for the 31st March, 1903; Chart I at O h 15 m , and Chart II at O h 30"'.
Fig- 54-
PART I. ON MAGNETIC STORMS. CHAP. II.
Current-Arrows for the 31st March. 19O3; Chart III at O h 45'", and Chart IV at I 1 ' O m .
123
Fig- 55-
124 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903.
Current-Arrows for the 31st March, 1903; Chart V at I 1 ' 15'", and Chart VI at I 1 ' 30 m .
Fig. 56-
PART I. ON MAGNETIC STORMS. CHAP. II. 125
Chart I. Time o 1 ' //'" .
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** I2 m , and which had a current-system
the reverse of that shown on the chart for 22 h o m .
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 o h jo m .
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 P v , 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 P d 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 o h 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 /'' o m .
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 P v = 14 y, and is directed upwards.
At Tiflis and Potsdam, P, is directed upwards, but is rather small. At Wilhelmshaven, P t = 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, P t = 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 P v directed upwards, which also indicates that the axis lies between the two
first-named stations and the latter.
Chart V. Time i h 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 i k jo m .
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 o h 28, and attains a magnitude of 209 y.
PART 1. ON MAGNETIC STORMS. CHAP. II.
I2 7
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 o h 28 m , 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 o h 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 ij h 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 i3 h 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 ia u 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 //* o m and /p* /o m .
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 z l /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'' io m ; in the
United States and at Honolulu it is later about 22 h 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 22 h o m , 22 h 15, 22 h 30,
and 23*" o ln .
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, 19021903. 17
130
BIRKEI.AND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 19021903.
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
3 4 .
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
+ 9.07
W IQ.O y
+ 4.27
?(^) ? ?
?(*)
?< 3 )
15 o
+ 7.1
+ 3-5 '
?( 2 )
? ?
?
7
?
18 10
+ 3-8
o
+ 6.2
E 4-5
9
? | + ii.a y
?
?
19 50
+ 3.2
o
o
W 10.0
?
? -t- 14.0 t
?
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 7.0
W 3 . 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
- 19.7
23.8
- 14.0
1.9 18.9
?
- 14.7
I 1 ) 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
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
(?)
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
+ 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
+ 30.3
o
+ 19.5
o
18 10
+ 15-'
9.2
o 4- 17.8 o
4 12.
o
+ ao.o
o
o
19 50
4- 20.0
. 4.6.
O ! 4- 12.2 O
4- 13.0 >
o
-t- 33.3
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
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 '
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
4- 18.0
o(?)
18 10
4- 16.0
o
4- 15.2
o
4- 9.6
4- 15.0
o
o
19 5
+ 18.6
4- 19.0
o
4- 13.3 o
4 13.0
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
- 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 >
15.0 . !P, = + i.9 7
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
+ 8.9 y
W 3.7 y
- 1.3 V ; 4- 13.4 y
+ lo.oy
15
4- I3.O
o(?)
o
+ 9-5
o(Wi.sy?)
' + I 3 .0
4- II.8
| '|
No curve.
18 10
4- I I.O
o
4- 13.2
O
o ,4- 12.4
4 11.5
'9 5
4- ii. o
o
o
4- 18.8 >
o
- 2.7
+ 17.3
4- 16.0
3i 45
E 25.4
4- 5.0 y
4- 18.8 >
E 9.3
- 3-8
+ 15-7 "
o
33
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
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
33 o
- 4-5
19.2
9.3
o i 0.8
15
- 4-5
" '3-7
I.O
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
15 o
4- I I.o
o
+ IO.O
+ 9.2 i
o
18 10
4- 6.5 >
4- 6.5
+ 10.4
'9 5
+ 8.5 . o
4- 13.5
4- 13.8 .
2' 45
4- 10.2 W 7.0 y
4- 13.2
23
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
o
o
o
Owing to the diffi-
culty in determining
the normal line,
nothing is taken out.
+ 12 y
+ to
+ 5'
W i 7 y
15
8
- 3 7
- 4
- 4.6.
23 o
o
o
o
15
o
o
o
PART I. ON MAGNETIC STORMS. CHAP. II.
Current-Arrows for the 22nd March, 1903; Chart I at 13 h 4 m , and Chart II at 15 h .
133
Fig. 5^
T 34 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.
Current-Arrows for the 22nd March, 1903; Chart III at 19 h 50 m , and Chart IV at 22 h .
Fig- 58.
PART I. ON MAGNETIC STORMS. CHAP. II. 135
Current-Arrows for the 22nd March, 1903; Chart V at 22 h 15 m ,and Chart VI at 22 h 30 m .
Fig. 59-
136
BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.
Current-Arrows for the 22nd March, 1903; Chart VII at 23 h .
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 2o h 45, and
2i h 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 2o h 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 P v . 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, 19021903.
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 23 h o m , 23 h 15, 23'' 30, and 23'' 52.5 m , 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. 5 m , 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 "
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'
5 a -5 - 3-4 *
6.6
o
1.4
1.3
- 0.8
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
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
- 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
- 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
- 38.0 1 - 4.0 .
W 5-5-
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
- 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
+ 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
+ 10.5
3.0
52-5
O
E 6.1
+ 5-o
E 3.0.
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.
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
+ 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
- 4-6/
o
31
+ 3-5
3.9 >
4 3.4 (')
3.0
4 4.2
- 2.8
o
o
23 o
- 1.6
2.9 t
-2.4. (1)
3.0
o
W 12.0 >
- 5-5
4 2.3 7
IS
4.9
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
4 1.9 >
53.5
+ 3.7
o
42.4M 1 )
2.0
- 3-5
18.0
- 2.8
o
+ 3-1
I 1 ) Uncertain value.
PART I. ON MAGNETIC STORMS. CHAP. II.
Ciirrent-Arrows for the 26th December, 1902; Chart I at 20 1 ' 45'", and Chart II at 21 1 '.
142 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQOZ 1903.
Current-Arrows for the 26th December, 1902; Chart III at 23 U , and Chart IV at 23 h 15 m .
Fig. 62.
PART I. ON MAGNETIC STORMS. CHAP. II. 143
Current-Arrows for the 26th December, 1902; Chart V at 23 h 30 m , and Chart VI at 23 U 52.5 m .
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 190203. 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'' i3.5 m 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 I4 h 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 I4 h 22.5 and I4 h 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. 6 4 .
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
-1- 7.1 * j 4.9 >
- '2-3
45
o
0.4
- 1-3 *
O.2 >
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 /
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
3 r -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 >
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
o
TABLE XXII (continued).
Gr. M. T.
Kew
Potsdam
Val Joyeux
Ph
Pd
Ph
Pd
P,
Ph
Pd
P,
li m
14 15
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
- 3-1
3-4
somewhat
37-5
4-4
3.8 > - 1.7
I.O
2.5 2.1
indistinct.
4'-3
- 4.1
2.8 j! i.i
- 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
Wi 5 .oy
+ -4 /
o
1 8.8
4-2.5
* 30.0
4- 1.8.
W 13.1 7
+ '0-4 y
W 27.2 7
22.5
t 1 )
'9-5
+ 3-9
. 22.7
From 14'' 1 6m to
4- 10.3
. 25.9
26.3
3
(>)
+ i.ioM 1 )
11.3
7-5
4- 3.0
4- 0.4
. 15.1
9-3*
I4 h a gm 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
2.2 1 O
2.6
O
3.2
41-3
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, 19021903.
Current-Arrows for the 6th October, 1902; Chart I at 14 h 22.5 m , and Chart II at I4 h 30 m .
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 I 1 ), 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, 19031903.
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 (t o u , 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 io 25
? = [^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 188283.
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 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, 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 i h 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 i6 h 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
224.0 7
E 28.57
- 300 y
- 27.77
E 3.1 y
_ 3
18 52.5
+ 3 .6
o
- 131.0
W 3 6.7
+ 148
21 7.0
136.0
9
20 30
2.2
- 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
+ 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
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
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 5 2 -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.
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
-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
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 6 3
rrent-Arrows for the 29th and 30th October, 1902; Chart I at IS" 52.5 m and 2O 1 ' 30"' on the 29th, and Chart II at I 1 ' on the 30th
Fig. 77-
164 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903.
Chart I shows the conditions at i8 h 52.5'" and 2o h 3O m 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'' 5y m 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 i h , and lasts almost until 5 h . 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 23 h 45 on the 24th, and continuing fairly powerful right
on to 5 h 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 3 h 2i m , 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
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
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
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
- 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
No no-
- 5-6
2.3 >
- 2.8
2.4
A slight
- 3-5 "
1.9
20
10.
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
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
> 4.8
40
- 4-4
7.1
- 2.4
4.2
3 li 30 m.
- I.O
5-3*
o
4
+ 3- a "
" 1-5 "
-1- 3.2
+ 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- 2 7
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
o
- 2.4
- 1.8
o
Current-Arrows for the 25th December, 1902; Chart I at 3 h 15 m and 3 h 20 m .
Fig 78.
PART I. ON MAGNETIC STORMS. CHAP. III.
Current-Arrows for the 25th December, 1902; Chart II at 3 h 30 m and 3 h 40 m .
16?
Fig. ^g.
Chart I; Time j h //"' and j 1 ' 2o m .
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 3 h 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 3 h 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 4 h 40 and 6 1 ', 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 4 h 45 and j h , 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 P d 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 5 h 20, is
very small. In Cheltenham P k and P d 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, 19021903.
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 j h
j h 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.
-I- 4.1
1.2 >
6.6
* 10.4
- 47.2
30
6.9
6.3
o
o
o
1.2
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 >
+ 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
6 o
o
7.8
- 49-2
+ 7-4
+ 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 4 h 45 m and 5 h , and Chart II at 5 h 15 m , 5 h 30 m and 5 h 45
it 1 ^/
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. 3 y
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 P 1 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 i6 h 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 i6 h 15 until I7 h 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 I4 h , and has its maximum at about I4 h 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 I4 h io m to i6 h io m , and the second from i6 h io m
to about i8 h , 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^ 45 m to I5 h 35 m , 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
I 4 h 6m
'5 50 1
15 4
ca. 14 40
J 4 !5
14 15
14 16
14 '5
M 15
14 14
14 14
14 g 1
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'
J 4 r 5
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 a7 m
i 45
16 28
16 33
16 30
16 39
16 42
16 38
i 45
i 37-5
i 45
I5h&i 7 lii 5 m
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.
t 8h 19"!
17 3 o1
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 I5 h 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, 19021903.
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 i5 b .
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 i6 h to
i7 h 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 I4 h to i8 h , 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 i6 h 15,
(2) i6 h I5 m to i7 h i5 m , that is, during the powerful intermediate storm, and
(3) T 7 h I 5 m to its termination.
The conditions during the first section are shown on the Charts I, II, III, and IV for the hours
I4 h 30, 15'' o m , i6 h o m , and i6 h 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
I5 h being either zero or very small.
In the district about Dehra Dun, distinct perturbations do not begin until about I5 h , 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 i6 h o m the force has already changed.
176 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 19021903.
The curve on the whole is much more disturbed; and at i6 h I5 m 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 i6 h 15 to I7 h 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 i6 b 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, P t 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, P t attaining at both places at the
most about 140 y. The direction of P t 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 P v , 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 I7 1 ' 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.
I 79
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
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.
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.
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.
4.4 .
- 8.1
6.0
- 8.6
i.i
TABLE XXVII (continued).
Gr. M. T.
Dyrafjord
Axel0en
Matotchkin Schar
Kaafjord
ft
Pd
P c
A
Pd
P,
Ph
Prf
ft
Pk
Pd
ft
1
li m
14 3
+ 47-6 7
Wi 9 .8v
-1- 28.7 y
- 87.47
W 23.1^
+ 49-57
E 66.6 y
- 12. 0/
+ 4-37
E 8.0 j<
+ 56.57
'5 o
o
?
p
- 73-7
a 56"
+ 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
- 5o,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 /
IO.2 /
o
- 15-27
E 5-87
15 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.
12-7
- M-4
6.3.
16 o - 6.0 18.4
4- 6.0
1 1.2
o
- 14.8
o
16.4
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 '
- 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
- 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.
- 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
10.07
o
15
- 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
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
15
- 14.8
> 10.4 i
+ 1.2
+ 1.57
- '3-3 "
14.8
2.87
3
7.2 i> 6.9
- 9.9
o
'5-9 "
8.5.
16 o
- 16.6
o
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 >
+ 4-4
* 17.4
o
15
- 12-5
ii. I
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
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. 4 7
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
> 2O.O
4 16.0
> I I.O
16 o
-10.75
- 9.8 >
3-
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. 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. 4 1
4 12.5 i
> 2.8 >
45
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
P 1 *
^
P 1 *
Pd
h m
16 o o
o
o
o
E 427
o
o
15
4 12.1 x
W 2.3 7
E n-47
- '-57
E 10.3 7
+ 3-3 ;'
a 16.5
4 6.0 y
E 12.7 /
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 "
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 >
" 2 5-7
4 7.9
22.3
- 2.4
> 22.6
15
6.0
4 1.51
20.0 >
4 2.0
i 15.2 i
- 1.8
14.7
2.2 !>
11.7 i
> 10.0
30 4 2.0
6.0
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
P 1 *
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- r 7
E 6.9 y
o
E 6., y
4 18.1 7
> 2.0 O
i 3.6
3
+ 4-5'
36-5
-f- 6.7
* 25.7
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 >
II. I
4 0.8 i
i.i
+ 4-3'
< 4.9.
4 5-3*
3.4 >
30 o
9.1 ^>
o 7.6
!> IO.7 ' O
o
3.0 o
> 3- *
l82 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903.
Current-Arrows for the 15th February, 1903, Chart I at 14 h 30 m ; and Chart II at 15 h .
Fig. 82.
PART I. ON MAGNETIC STORMS. CHAP. III. jgo
Current-Arrows for the 15th February, 19O3; Chart III at 16 h , and Chart IV at 16 h 15 m .
:
;
T
1^1
Fig. 83.
BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igo2 1903.
Current-Arrows for the 15th February, 1903; Chart V at 16 h 30 m , and Chart VI at 16 h 45 m .
Fig. 84.
PART I. ON MAGNETIC STORMS. CHAP. HI.
Current-Arrows for the 15th February, 1903; Chart VII at 17 h , and Chart VIII at I7 h 15 m .
Fig. 85.
l86 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.
Current-Arrows for the 15th February, 1903; Chart IX at 17 h 30 m , and Chart X at 17 h 45 m .
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 2i h 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 2 h 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 9 h to n h 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 ig h 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 g h to n' 1 ,
(2) a perturbation between 14^ and i8 h , and
(3) the period from i8 b to 23 h .
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 g h to g h 35 m .
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 P t 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
9 h i 5 m -io h o m
9 15 10 o
9 15 10 o
10 8
10 o
IO
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. . . .
t 1 ) 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 8 h 35 m . The maximum is not very distinct, but the time of its
occurence nevertheless does not vary greatly. It terminates simultaneously at about io h 50. As the
force is practically constant for several minutes about the maximum, P t 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, g h 36 and io h .
From 9 h to g h 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 g h 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 g h 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'' o m to i8 h (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 i8 h 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 i5 h 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 74 h 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 j6 h 30 to i8 h .
(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 I4 h 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 I4 h 45,
V at three hours, viz. i6 h io m , i7 h , and 17^ 30"*, and
VI at i8 h o m .
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 i6 h 45 m 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 I4 h to i8 h 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 i6 h io m , T7 h , and I7 h 30 we also find on the whole
the same conditions as at I4 h 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 i8 h o m , 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 i8 h 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 i8 h 33, and is over at 22 h 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 I9 h 8 m and 2o h 14. At about 2o h 37 m 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 ig h 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 22 h 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'' j m . It suddenly increases, and
ten minutes later it is at its height. Right on to 21 u o m , 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 i8 h 37, and in the D-curve at i8 h 58. The perturba-
tion principally affects the //-curve, where it lasts until 22'' 2i m . 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 ig h 18. At 2o h 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 2o h io m . The perturbation then gradually de-
creases, and about 2o h 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. 19021903. 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 I9 h o m , 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 3o m . 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'' o m . 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 22 h 30. In southern latitudes a decomposition of forces has been effected on the charts
from I9 h 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'* I5 m , 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 i9 h 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 2o h , the force is almost as strong at Dyrafjord as at Matotchkin Schar; but
on the next chart, that for ao h i5 m , 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 n h . 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 ig h i5 m and ig 11 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 2o h 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 2o h o m 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
W2 9 . 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
W 3 4-7 ,
- 7-9
. 12.7
-14-4 ,
, 16.3
- 6.3 ,
8.9
16 10
o
- 1 .0
E 14.0
+ 9-7 ,
E 3-7 ,
+ 1.8
+ 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
- 3-6
- 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 , -I 4 .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 .
r 4-6
- 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.
, 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
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.
383.0
3-
- 106.0
226.0 ,
242.0
45
- 175-0
. 163-0 ,
-258.0,
1480.0 ,
116.0,
1-492.0,
292.0
. 8z.o n
- 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-!.
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
- 66.5 ,
. 50.7 .
-199.0,
I IO.O ,
+ 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,
I0 4-o ,
- 48.5,
22 O
+ 36-3.
. 42-3 .
I59-
- 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
+ 145-0,
+ 22.0
20.3
- II.9,,
2-4
19-4 ,
- 54-
PART I. ON MAGNETIC STORMS. CHAP. III.
I 97
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 .
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
- 11.7
O
15-2 .
o
c
3
- 1.5 -
E 9.6
-13-3
E 8.6 .
10.2
E 13.1
1 1.2 B
En.7 ,
I
18 o
- 7-5
O
- 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
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
- 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
3 r -4 u
- 18.8 ,
, 33-6 ,
12.O
n 35-2 .
c o
'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
-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 I 1 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
?
7
?
-17-0
8.2
10 o
3- .
?
?
?
26.4
.. 12.3
14 45
- 41.1 ,,
W 3 o.6
36.0 y
Wi6. 3 y
4-3.67
26.4
21.3
16 10
- 13-' .
I 4' 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 .
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.
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
- 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
24.7 .
, IO -4 .,
o
20.5
11.7
2.1
25.2
o
3<>
32.2
. 19-6
o
-3a.a
, 20.3 ,
-32-5
22
22.9
13.3
o
34.6
12.2
O
-2 5 .8
3
19.6
8.6
22.7
8.1
o
22.3
o
198
BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 19021903.
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
-'i-5 7
o
1
7
-15-7 y
Wn.8 v
36
- ii-5
-18.8
W 0.7 7
?
?
-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 .
+ 1-7 .
14.8
E 4-8 .
+ 1-9 -
n 7-9
3
- 9-5 ,,
E 9.1
- 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
- 7-7
3-3 ,,
t
O
. 4-9 ,,
19 o
- 19-0
W 8.4
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
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
W 3 2.0 /
- 1-5 y
?
7
?
36
~ 19-2
o
-18.1
o
+ 5-9 y
I, 3-7 n
o
?
7
7
IO
26.4
13-2
o
4- 7.6
I7-I
?
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
-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,,
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 ,
+ 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 ,,
E 8.9
.. 7-4
4- 1.2
+ 1-5 n
+ 0.9
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-
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
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
ia.a 7
- 7.27
W 3.07
la. i y
o
3
- "-Si,
o
- 3- n
o
- 30-2
n 5-4
3-5
45
- "-a,,
- 27.2
o
- 2 3- r,
- 28.0
E 7.17
20 o
- "-8 n
o
- 33-0 n
E ia.1 7
~ 27-8
E 27.1
- 2 9.7
n 28.5
15
- 8.9
W 5.07
- 28.2
n 5-7 n
- 19-4 n
i6.8 B
- 23-8
H 14-3 *
3
- 4-1
n 2-5
-18.6,
- 9-9
o
- '3-9 n
n 4-8,
21
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.
- 8.3
W 5-9,
23 O
+ i.o n
* 5-8
"-I
6 -3
- 8.1
n 7-2
- 5-
n 2.9
3
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- 4 i.a B
n 49-7 n
+ 80.3
66.0
+ 34- 2 n
11 52-9 n
45
4- 44.2
o
+ 2 8-5
n 39-4 r
+ 47-5 n
n 39-1 n
+ 32.6 B
n 4I-I n
20 o
+ T3.6,,
n I6.6 B
+ "-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-8 B
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 -8 B
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
P 1 *
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 2 9-5
+ 36-8
n 43-5 i,
-t- 4-5
. 28.2
+ 4-7 n
22.9
20
+ r 4-5
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
+ 2 3-7 .
35-4
3
+ 7-6
n 3-5
o
35- 2
+ 10.0
29.7
4- u. a
a 7- 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,
x 7-5
- 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
P 1 *
I'd
/"*
Pd
Ph
Pt
li la
19 IS
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 ,
2 4-6
+ 42-8
5-2,
+ 32.7
. 9-8,
4- ai.6
, *5-
4- 22.8
6-,
20
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
4-i
4- 20.7
18.6 .
+ i9-3
o
4- 15-6
3-0,
4- 18.8
3-6,
21 O
2.2
+ 7-5,
. 14-9
4- ii.8.
+ 15-6.
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 *
- 0.8
. 13-4 .
+ 3-i,
o
+ 10.8
o
+ 5-7,
-4 >
3
- 8.1
- 2.2
6-7
O
o
+ 3-6.
+ 4-6
2-4
Current-Arrows for the 8th February, 1903; Chart I at 9 h 15 m .
Fig. 87.
PART I. ON MAGNETIC STORMS. CHAP. III. 2OI
Current- Arrows for the 8th February, 1903; Chart II at 9 h 36 m , and Chart III at 10 h .
\
II
"
.
;
.
f
7
'
Fxnpriil
Fig. 88.
1002100^1.
26
2O2 BIRKELANb. THE NORWEGIAN AURORA POLARIS EXPEDITION, I9O2 1903.
Current-Arrows for the 8th February, 1903; Chart IV at 14 h 45 m , and Chart V at 16 h 10 m , 17 h and 17 1 ' 30 m .
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 18 h O m , and Chart VII at 19 1 ' O m .
Fig. go.
204 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903.
Current Arrows for the 8th February, 1903; Chart VIII at 19 h 15 m , and Chart IX at 19 h 30 m .
PART I. ON MAGNETIC STORMS. CHAP. III.
Current-Arrows for 8th February, 1903; Chart X at 19 h 45 m . and Chart XI at 2Oli O m .
205
Fig. 92.
206 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 1903.
Current- Arrows for the 8th February, 1903; Chart XII at 20 h 15 m , and Chart XIII at 2O 1 ' 30 m .
PART I. ON MAGNETIC STORMS. CHAP. III. 207
Current-Arrows for the 8th February, 1903; Chart XIV at 21 h O m , and Chart XV at 21 h 30 m ,
B 3 k Oatltka/l
.,
Zll vj Ii -fci.n
i,
% x
...
.; ,
Br
T 1 '
c?
17
I
Fig- 94-
208 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903.
Current-Arrows for the 8th February, 1903; Chart XVI at 22 h O m , and Chart XVII at 22 h 30 m .
**'/
* 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 i u 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 i6 h 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 I4 h to
2o h 30"", and the second from 2i h 40 until about midnight.
THE DISTRIBUTION OF FORCE.
62. The first section. I4 h 2o h 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 is h 30 and iy b i5 m . This is preceded by
a powerful perturbation lasting from I3 h to I4 h 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, 19027903.
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 I5 h 30'" and i6 h 45. The corresponding storm on the I5th
February lasted from i6 h I5 m to 17'' 45 m .
In the eastern hemisphere a decomposition has been undertaken, the result being shown on
Charts IV, V, and VI, at i6 h , i6' 1 20, and i6 h 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. 2i h 40" -- about midnight.
The polar storm from 2i b 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.
p i 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.
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 4 8
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 22 h and 22'' 20, the point of convergence is in the regions
north of Pawlowsk. P t 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
2-5
- 9-7 .
- 4-
. 14-0 .
,, 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
II.O
,, 26.2
o
21.6
O
n '9-8 n
22
- 7-0
- 7-8 ,
- 5-8 .
. 1-9 .
- 8.1
O
20
- 8.9 .
2.5
10.6
E 0.9
- 8.5
-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
- 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
51-5 n
E 30.2
+ 19-1.0,,
- 195-0 11
n I 8 - tt
I 12.0
2O
28.0
,, 58.0
-f aaa.o
- ca.2i 4 .o n
! 12.0
- 89.1
4
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.O B
- 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
Wi 5 .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 ,,
- 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
n 20.7
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
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.O n
+ 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
-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
2I 4
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
- 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
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
J 3-4
+ 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
22 1 *
20
o
n 9-7 n - 1 + 3-2
IT -7 n
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
- 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
-IS- 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
+ 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
4
+20.9
7-6
4-I3-I n
n J 4-4
+ '5-0
n 8.4
23 o
+ 17.8
n IO -7 n
+ 14.1
n J 7-2
+ I 5- 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
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
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
- 7'9 v
M.8
+ 1-8
- 7-1
8.8
17 o
- 9-9 n
O
-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
- 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
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
- 4-3 n
- ca. 2.3
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'> 20 m
i6> 3om
n
P"d
P 1 *
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 14 h , and Chart JI at 15 h .
;j
K AV
w'."Ah M^AJmSttar
f d>
Fwk
Sib ayW*
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 15 h 30 m , and Chart IV at 16 h .
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 16 h 20 m , and Chart VI at 16 h 30 m .
PART I. ON MAGNETIC STORMS. CHAP. III.
Current-Arrows for the 27th October. 1902; Chart VII at 17 h , and Chart VIII at 22 1 ' .
219
Fig. 99.
22O BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.
Current-Arrows for the 27th October, 1902; Chart IX at 22 h 20 m , and Chart X at 22 h 40 m .
PART I. ON MAGNETIC STORMS. CHAP. III.
Current-Arrows for the 27th October, 1902; Chart XI at 23 1 ', and Chart XII at 23 '' 20 m .
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 i8 h 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 I4 h to ao h 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.
P t
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
a 5-5 n
i7- n
16.5
2 3-5
i5-o r
i6.o n
3-
21.0
I4.o n
3-5
n.o n
10.6
7- n
torms.
h m
19 io(l)
ca. 19 30
n 19 45
19 20
19 26
19 30
19 2 4
I 9 2 4
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.o n
r 5.o n
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 aol 1 )
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 P t 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
- 0.7 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
- 2.7 n
o
- 89.7
* 38.i
+ 258.0
19 o
- 7-8
n 4-1 n
1-7 n
o
o
-153-0 n
r ca.32.3 B
+ 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
- 8.5
n a-5
- 6.8
n 7-2 n
-!66.o
n 1 12.0
+ 352-0
4
- 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
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
- 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 I 5-6 n
22 O
-I 9 I.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
-I3 2 .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 T 4-3 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
I0 9
able
+ 10.3
n 3-1 n
deflec-
21 40
+ I l-3 B
n 4-0
-I-II
o
+ 3- 2
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
4
- 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
4 12.1 7
W 2.8 7
22
+ 21.2
o
+16.9
8.2
+ I6.0
-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
+ r 3-7 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
4
-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 18 h 15 m .
Fig. loa.
Birkeland. The Norwegian Aurora Polaris Expedition. 19021903.
29
226 I3IRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 1903.
Current.Arrows for the 28th October, 1902; Chart II at 18 h 30 m , and Chart III at 18 !l 45 m .
Fig. 103.
PART I. ON MAGNETIC STORMS. CHAP. III.
Current-Arrows for the 28th October, 1902; Chart IV at 19 h , and Chart V at 21 h 40 m .
227
Fig. 104
228 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.
Current-Arrows for the 28th October, 1902; Chart VI at 22 h O m , and Chart VII at 22 h 20 m .
T~
-
7
PART I. ON MAGNETIC STORMS. CHAP. III. 22Q
Current-Arrows for the 28th October, 1902; Chart VIII at 22 h 40 m , and Chart IX at 23 h O m .
-
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 i8 h
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 i6 h . 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 5 h 58.5 m on the 3ist October, and ended at io h 2.3. It was only partial, and the greatest
phase (0.699) occurred at 8 h o.4 m , 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 g h on the 3ist October to 3 h
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 i8 h and i8 h 30. At Matotchkin Schar it changes
in H at about i6 h , in D at i6 h 45", and in V at I9 h 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 22 b . 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 I4 h , the other at about midnight, with maximum about 23 h 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 i3 h i5 m and I4 h , 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 ij h 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 ij h 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 23 h and o h 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 I2 h 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'' I5 m 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 I3 h 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 g h and I2 h 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 I2 h 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 9 h 3o m 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 i 1 ' 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 i7 u 45 (Chart XII).
At i8 h 3o m , 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 i8 h 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, 19031903. 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 i b 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 3 h 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 (a 2 -(- 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
F 1 = 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 P v at the magnetic poles about double the value
of PI, observed near the equator. For greater values of , the proportion P, : P h will increase, and
vice versa.
From about i6 h to i8 h we really find conditions that seem to favour our assumptions, when
we compare the values of P, at Axeleen with the value of P h at Dehra Dun and Batavia. Later on,
however, we find that P 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 I3 h 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 . io 6 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 I3 h 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'' 8 m , 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 i3 h 12, there is a deflection answering to a diminution of H;
at I3 h 24, H has an intermediate minimum, then increases until I3 h 42, then decreases until I4 h 5 m ,
when it again increases, and at I4 h 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 I3 h I2 m and 14'' 30 there is a perturbation of uniform direction, occurring simultaneously
with the perturbation in America. P h and P d 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 i3 h 24"" to I4 b 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 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 I3 h 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 n 1 ' i2 m to o 1 ' 42 m , 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
+ 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 "
> 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
3 6 -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
- 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.
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.
+ 316.0
53-8 .
269.0
17 45
42.2
W 80.0 >
4 119.0 i
-177.0.
> 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
212.
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
- 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
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
- 12.77
W 12.2 7
- 8.9 y
W 15.77
3
12. a
2O.O
- 16.8
> 21.4 >
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
- t9-4 "
18.8
20.5
14.7 >
o
- 15.8
24.8
- 17-4
17.8
3
- 16.3
12.
12. 1
- 9.7
o
- 11.7
14.5
- M-S '
8.6
12 30
II. 2
24-5
18.2 *
34-2
- 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.
- 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
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
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
^ ]> 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
- '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
- 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
- 35-4
17.1
- 3-7 "
15
- 63.5
I.O
6o-5
- 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
- 58.3
" 53.5
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
- 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.
I3 h 3<
>m
I3 h 4
2 m
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
-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
- 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, 19021903.
31
242 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.
Current-Arrows for the 31st October, 1902; Chart I at 9 h O ra , and Chart II at 9 1 ' 30 m .
PART I. ON MAGNETIC STORMS. CHAP. III. 243
Current Arrows for the 31st October. 1902; Chart III at 10 h O m , and Chart IV at 10 h 15 m .
Fig. 108.
2 44 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 1903.
Current-Arrows for the 31st October, 1902; Chart V at 10 1 ' 30 m , and Chart VI at Il h O m .
--
i *
4?
B*k
CWh
Ch Ch
i ' r .
S.l
.,
H Ch Munffirif
\
/
\
\
\
fiWfJ
sfoofrj
pf
itewste
^
r "^sf
TO
2fc.
uH
^
V
^d
y
HOA^-
(fC*
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 Miarti
OiCh OrtttfJuuTh
Dh D Mra AM
Sol saa?
KO
Mr
M&lSch
U ch
Pwsk
FV,1
PU-d
XacjWtf
A>u>
JWfrMw -,V*w
14^,?^"^-
U-An-m^
-v/K
Z
7
1
(7
/
V^
u
r\"
^
QT P
IT 1 '
PART I. ON MAGNETIC STORMS. CHAP. III. 245
Current-Arrows for the 31st October, 1902; Chart VII at ll h 30 m , and Chart VIII at 12 h 30 m .
-
ft. talaeia
S F Sfi.fo
PitJi* Attfl
5th StvyhMTJt
Tulis JWU f
:
II
v
'
>...
Fig. no.
246 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION T.gO2 1903.
Current-Arrows for the 31st October, 1902; Chart IX at 13 h 30 m , and Chart X at 13 h 42 m .
Fig. in.
PART I. ON MAGNETIC STORMS. CHAP. III. 247
Current-Arrows for the 31st October, 1902; Chart XI at 14 h O m , and Chart XII at 17 h 45 m .
;
Cs
9
v7ffT.ii
"
-
2
Ax 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 18 h 30 m , and Chart XIV at 19 h 15 m .
PART I. ON MAGNETIC STORMS. CHAP. III. 249
Current-Arrows for the 31st October, 1902; Chart XV at 20 h 30 m , and Chart XVI at 21 h 45 m .(')
1 1!-.'
si
,
: '
m
7
'
Oilh Outlaid
CfcCh Otmtflu
D)i D Drtra I'
,-** AMd
Si li Slfuhunl
Tuiis nv>
[^ /
s*
;-
Bih 5wb>/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 22 h O m (i), and Chart XVIII at 23 h 45 m .
:,
I'll
5
-nr
"OFT
\
DhD
Dfl
Kolu
teg
7
5F satKr.
Sllka AM*
*> %ff~
?l u
PART I. ON MAGNETIC STORMS. CHAP. III.
Current-Arrows for the 1st November, 1902; Chart XIX at
251
l h O m .
Fig. 1 1 6.
THE PERTURBATIONS OF THE llth & 12th OCTOBER, 1902.
(PI. II).
68. From ii h on the nth October, to about o h 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 n h to I7 h .2o m on the nth October,
The second from iy h 2o m to i8 h 3o m on the nth October, and
The third from i8 h 30"" on the nth October, to o h 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 I7 h o m .
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, 19021903.
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 I2 h 25 and I3 h I5 m , 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 I2 h 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 I3 h i8 m 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 I2 h 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 i7 u 20 to about i8 h 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 i8 h o m . 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 P k . 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 i8 h 30 to o h 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
Ig h 30 m j 20 h gotn^ 2I h I5 m ( 2I h ^o, 2 2 h , 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 ig h 30, when the force at Axeleen and Kaafjord is
almost westerly in direction. At 2o h 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 P h similar to that described at i8 h . 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
r8 h 34 m (see Chart IV), the second between 2o h 45 and 2i h 20 (see Charts VII to X), and the third
between about 23 h io m and o h 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 i8 h 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 i8 h 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 i8 h 34 m .
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 ig h 3O m .
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 ao h 45 to 2i h 2o m .
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 2o h 52.5 m - - 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 P h 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** io m to o h 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 n h i8 h , and the six following polar storms:
(1) The polar storm from I2 h 25 to 13'' 15,
(2) The polar storm from about i7 h 20 to i8 h 30,
(3) The main polar storm from about i8 h 30 to o h 30,
(4) The first intermediate polar storm, maximum at i8 h 34,
(5) The second intermediate polar storm from 2o h 45"" to 21 h 2o m ,
(6) The third intermediate polar storm from 23 h io m to o h 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
W 5 i.77
- -7 /
7
w 5.6 y
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 i8.6 B
- 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 ,
. 81.0,
-25-4 B
8.9
-41.0
B 25.0
- 4 o.o n
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
, 18.1
-io.5 n
B 14-0
21 O
- 8. 4 .
20.8
-27-5 .
. 67.6 .
-31.1 .
9-5 B
-28. 4 B
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 .
-i6.6 n
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
- 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
45
o
o
B "-3B
-12.8
B 2.5
-IS-OB
o
-I5-OB
o
24 o
- 2.6 .
2.2
10.4
9. 1
W 2.6
-10.8 B
W 1.8
-II.2 M
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.o n
+ 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-2 B
+ 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 6 9- 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.o n
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.o n
during the
-i6i.o n
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 I2 9-o
(See PI. II).
-ISO-OB
B 84.4
- 98.0
30
+ S-OB
W 10.7
+ IIO.O,,
- IS 6 - B
B 125-0 B
-IIS-OB
B 6 7 .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 6 5-9 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
W 4.0 y
W 7.0 y
+ 4-4 >'
W 4.2 y
17 o
+ 15-1 ,,
12.4
4- 0.7 ;-
+ -5-3 7
11.4 f,
+ 18.3 ;/
n-7 .
+ 22.4
, 7-5 .
18 o
- 5-
E 44.2
+ 4-9
12.2
o
- i 1-7
- 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
IO.2
- 6. 4( ,
E 0.8
+ 7-5.
20 o
+ 7-6
42.2
-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
- 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
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 -,
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/
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
1 0.0
E 11.4,
30
- 37-3 .
WiS.g
+ 5-0,,
-39-5
W 9.1
26.2
Wi 5 .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
- -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
- 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. ,.
- 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
12. 1
. 21.3
-10.5
. 21.3
-12.8
,, -7-2
- 12.5
24.3
3
- '4-4
12.8
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
+ 13-0 ,
. 15-3
o
n-o
-^ 7-5 ,
16.8,
24 o
+ 9-3,,
a 13-4 -,
4- 8.5
8.9 .
o
ia-7
- 7-5 ,
n 12.2
Birkeland. The Norwegian Aurora Polaris Expedition, 19021903.
2 5 8
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
W 4-8 /
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
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
20 o
- 5-6,
,, 17-4 n
7-8
6.9
- 9-2
4-8
3
- 10.7 ,,
28.5 ,.
+ 1-3 ,i
- 9-1 ,i
,, 12.8
9-2 i,
8.4 ,
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
- 8.0
21
+ 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
- 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
3
- 8.8
I 3.O
- 9-1
6-9 i,
- 7-7 ,,
3-6
o
23 o
- 8.6,,
8.5
- 8.3
. 5-9 .
- 7-9
3.0
45
+ 4-9
ii i-8
- 2.3
o
+ 2.5
o
24 o
+ 2-4,,
ii i- 1 ii
- 1-6
+ 2.8
o
+ 2.6
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,,
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,
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
-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
,, 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
- 13-2
ii 3-6
?
?
7
45
o
- 5-0
W 2.4
7
?
7
94 o
o
- 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
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
- 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
?
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
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
- i7-o n
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
23 45
o
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.
+ 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.S n
o
+ 14.1
, i6-5.
+ 10.2
n 20.0
-1- 13-8
'5-o n
+ 12.4
n 18.4
21
o
W 3.07
+ I5.I n
32-2
- l-2
n 22.8
- 5-i
i6.8 B
+ 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- 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
+ 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
?
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.2 n
B 17-6
+ r 3-o n
B 16.4
21 O
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 2 5-i n
IS
- 4-1 B
22.8
- 6.5
B 21-6
- 10-8
- 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
+ J 5-3B
n 7-3 n
- 8.0
21 O
+ I7-I n
n "- 1 n
4- 2.6,,
+ J 5-7 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
+ 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
F 1 .
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 .
21 O
+ 12.8
B 4-0
4- 8.0
+ 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
For ia n 50"! we have nt
Kaafjoi-d: Very slight and indistinct partial deflections.
Matotchkin Schar: P h = + 43.5 y, P d = o, P v = + 17.5 y.
Axel0en: P t = 35,0 j>.
PART I. ON MAGNETIC STORMS. CHAP. III. 361
Current-Arrows for the llth October, 1902; Chart I Partial values - at 12 h 50 m , and Chart II at 17 U O m .
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 18 h O m , and Chart IV at 18 h 34 m .
PART I. ON MAGNETIC STORMS. CHAP. III. 2 6o
Current-Arrows for the llth October, 1902; Chart V at 19ii 30 m , and Chart VI at 20 h 30 m .
r ool>-
^
?
' /<
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 20 1 ' 45 m , and Chart VIII at 20 1 ' 52.5 m .
tfooO
v
\
*' '
;
Kfi Kaa/int
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 21 h O m , and Chart X at 21 h 7.5 m .
Fig. 121.
266 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903.
Current-Arrows for the llth October, 1902; Chart XI at 21 h 15 m , and Chart XII at 2l h 30 m .
PART I. ON MAGNETIC STORMS. CHAP. III. 267
Current-Arrows for the llth October, 1902; Chart XIII at 22 h O 1 ", and Chart XIV at 23 h O m .
Fig. 123.
268
BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION igO2 1903.
Current.Arrows for the llth October, 1902; Chart XV at 23 h 45 m .
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 I2 h 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 have 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 P k . 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 P h 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 P v , though sometimes zero. We may imagine this
circumstance to be partly caused by the positive polar system of precipitation, which produces positive
values of P e 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 188283, 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 J5 h on the
23rd to 7 h 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 i7 h , 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 I5 h 20 to about i6 h ,
the 2nd section from i6 h to about 22 h , and
the 3rd section from 22 h to 7 h 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 P k 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 i5 h 48 m 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 i6 h , 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 I5 h 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, 19021903.
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 i6 h to about 22 h .
The perturbing forces appearing here are generally small; but from about i7 h 30"" to about 18'' 20
they are comparatively large, especially in southern latitudes.
The conditions at I7 h 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 22 h on the 23rd November, to 7 h on the 24th.
At about 22 h , 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 2i h 30 at Dyrafjord, and an hour later
at about 22 h 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 </> = iotoi/; = 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 23 h 3o m , and at Axeleen from
2 h to about 2 h 2o m . 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 2 h 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 23 b , 24'' and 2 1 ', 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 o h 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 2 h on the 24th. In accordance with this, we here also find positive values of P v .
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 i h 20 and 2 h 40, clearly show, however,
how this area of divergence now rapidly moves westwards, until at 2 h 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
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 /
+ 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
18 20
o
-10.6
B i8.o B
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.o B
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 "- 6 B
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
-45-0 B
W 18.2
-32.8
W 3 8o n
3- n
W 3 i-4B
- 48.5 B
W 20 8
2
o
- 1-3 n
B I8.0 B
-21.0
B 9-5 B
- 20 -5 B
B 2. 4
- 28.0
o
40
-1 1.8
-46.0
B 2 3-5 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 2 5-0
-I8. 3
n IO - 8 B
- 13 5n
B a 4-0 B
- 22.0
n 14-8
6 30
10.4
-28.1
E 28.0
- 2.1 n
B I2 -7
- ".2 B
B !3-o B
- ".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 S 2
>
)
?
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.
- 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.
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
, 6 3-o
247.0
4
- > 800.0
148.0
+ > 85.0
-608.0
150-0
+540.0,,
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.
IOI.O
6 30
244-0 ,
(> 3'
"\<43-o
+ 18.0
- 97-0
61.0
+ 98.0
. 27.0
lor.o
(') The value of f t 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
+ 10.2 y
-t- 10.2 y
o
48
+ 21.0
W 2.0,
+ ia.6
+ 7-6
+ 8.9
W 3.37
16 30
+ 5-o
8.0
o
+ 7-5 .
W 2.3
+ 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
E 7-o
18 20
+ 18.0
29.0
o
- 6-0
9-2 n
O
W 1.7
W 1.9
22
+ 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 47-2 n
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 2 9-0
I 20
224.0
132-0
IOO.O
+ 30.9 *
39-0
- 40-7
- 12.2
68.6
- ii-7
n 6 5-o
2 O
-197-0.
163.0
- 88.0
+ 5-o
20.7
- 30-0,
- 13.8,
25.7
- 17-8,
B 3'-8 n
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.o B
4- 9.1
6-9 .
- 33-5
O
B 25.1 n
- 2.5
B 25.7
5 30
+ 18.0
W 11.0,
- 62.0 r
2-5
13-8 ,
23.1
4-6
17-a
- 8.7
B "-7 11
6 30
30.0
E 22.
- 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
+ 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
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
1 8 20
o
O
o
- 3-3 B
O
6.0 7
O
o
22
4- 2.4
n 4-2
o
- 3-7 B
B 6.1
- 5-o
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
-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
-13-0
6 30
4- ..6
W 7-5 B
- i-9 B
W20.8
- 7-o
1
'*"
Wi 7 .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
+ 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
+ II.2 B
- i.i 7
+ 13-2 B
o
- 3-8 B
16 30
+ 9-6
+ 10.0
B 2.3
+ 7-2 n
o
+ 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 t w
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^' B
B '6.5
O
30
- 7.6
B '9-7 B
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
!O.3 M
B T 3-I B
-16.0
B 16.8 B
-'9-5 B
B 25.0
-"5 B
B "- B
- i-5 B
4
+ 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
Wi 4 . 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
+ 13-0 y
+ 13.1 7
o
+ 11.0 7
+ 5-9 7
o
O
48
+ '3-4 B
+ 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
B 6.6
+ 1.8
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
18 20
+ 3-1 B
B I - 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
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
+ 3-6
<J
O
- 3-o
B I2 '9 B
1
- 2.7 B
B 28.5
' r - 2 n
o 50
-12.6
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
-,,.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
?
1
o
B 9-4 B
?
1
-i 7-8 B
O
o
6 30
? ?
- 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- 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
+ II.O
B 8 -9 B
-'5-0 B
- S-o
B 9-9 B
- 7.0
Birkeland. The Norwegian Aurora Polaris Expedition, 19031903.
282 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903.
Current-Arrows for the 23rd November, 1902; Chart I at 15 h 48 m , and Chart II at 17 h 4O m .
\
<(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 22 h 30"', and Chart IV at 23 h .
Fig. 126.
284 B1RKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, igO2 1903.
Current-Arrows for the 23rd and 24th November, 1902; Chart V at 23 h 20 m and 24 h on the 23rd,
and Chart VI at O h 50 m and l h 20 m on the 24th.
PART I. ON MAGNETIC STORMS. CHAP. III.
Current-Arrows for the 24th November, 1902; Chart VII at 2 h and 2 U 40'", and Chart VIII at 6 h 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 i8 h . At that hour they begin to be
disturbed, especially in the north; and at about I9 h they assume the character of a powerful storm.
From now on, powerful storms alternate with calmer periods, the most powerful being at about 23 h ;
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 i8 h 35 m , and lasts until about 21 h o m . 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 P v is directed downwards.
From Kaafjord we have registerings only for the first part, up to 23^ o m . Here too, a relatively
independent perturbation is observable, which is particularly powerful in V, where a maximum is reached
at I9 h 45 m . Subsequently the storm increases, and is very powerful at about 22 h 30, after which time
it once more diminishes.
At Axeleen, very disturbed conditions commence at about i6 h 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 io m and 2o h 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 22 h 24 m . In D it
begins earlier and more gradually. It is very violent between 22 h 30 and 23'' 30. The storm
decreases until midnight, when another powerful storm commences, reaching a maximum at about o h 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 22 h 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 i9 h 45 is wanting. Even by that
time it is exceedingly violent. It then diminishes for some time, and reaches a distinct minimum at
2i h 6 m , whereupon it once more suddenly increases, and maintains a considerable strength until 2 h . 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 2i h 39, and does not return until 23 h 25. The storm is then
losing strength, and at 23 h 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 o 1 ' 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 i8 h o m on the 26th January to 7 h o m 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 i8 h I5 m 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** o m , the
other at o h 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 22 h I5 m on the 26th, right on to 8 h on the 27th, there is unrest. We here have the same
two maxima as in the eastern hemisphere, namely, at about 22 h 55 and at o h 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 22 h and 23 h , 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
- 3-6
o
-H-5
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
-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
Wi 5 .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
-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
*3
W i8.i n
-no.o,,
- 198.0
B 46.2
+ 344-,,
323.0 7
E 220.0 /
-173.07
3
+ 58.8 B
O
- 7'-
- 22.5
W 6.8
+ 334.0,,
264.0
M5-0
162.0 .,
aa o
-141.0,,
i8.o n
+ 5-3 B
E 22.3
+ 300.0,,
-> 4 o8.o
JOO.O
+ 47-6,
3
Curve almost
Curve diffi-
ca. 281.0
n 102.0 n
+ 643.0 .
-> 4 o8.o
205.0
A violent
23 o
invisible.
cult to dis-
tinguish from
Rather
ca. -519.0
> 166.0
+ 648.0,,
-> 4 o8.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
-> 4 o8.o
357-,,
279-0 .
deflection
of about
o 22.5
3
seen indicate
a negative
deflection of
principally
easterly de-
flections
flections.
2 3 2 - B
-366-0,,
ca. ni.o n
> 166.0
+ 755-0
+ 702.0
-> 4 o8.o n
355-0
3I5-0-
I 82.0
440 /',
after which
the curve
-15
considerable
somewhat
-3I5-0 r,
B 129-0
+ 598.0,,
-> 4 o8.o r
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
- 368.0
B 41-5 B
4-7
o
27.6
- 16.5,
12.2
46-3
- r 5-3B
38.3
30
-577-0,,
B 66.0
-253-0
+ 52.8,,
22.1
- 36.7 B
- '7-8 B
,1 I0 7-o,
+ 10.2
, 82.7
23 o
-276.0
104.0
?
+ 28.7,,
27.6
- 46.4 *
+ M-8,,
I OO.O
*- J 5-3 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
- i8.8 B
+ 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
- 2 4 .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
E 37.67
From i o u 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
- 9-2
B 30.5 B
-15-8,,
3
- 18.0
B 2-9 B
negative de-
- 22.8
B 18.3
- 20 -5 B
B 17-2
- 1 - 2.7
flection with
22 O
- i6B
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 58.4 B
magnetogram
- !5-4 B
B 43-4 B
- !5-o n
- 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 7 2 -8
curve has too
great a value
+ 33-8 B
B 6 9 .I
- i8.o n
+ 28.4
B 49-7 n
~ 22.5
45
- 16.8
B 62.7
before, or too
- I2.I
B 52-0
- SO- 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.
2 9 1
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.i B
22
- 16.3
n tS-6 n
- 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
- 2 9-6
* 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 .
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 I 1 )
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
n.o
Wi 3 .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 ,,
. I 9-
+ 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- ii
+ 6.7,,
,, 8.4
- 7-8 .
., 5-9 .
it is a little
3
+ 12. .
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
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', 19021903.
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
- 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 19 1 ' 30 m (i).,
Fig. 129.
(') By an unfortunate mistake, the arrow for P f 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 20 b 30 m . and Chart HI at 22 h O m (').
Fig. 130.
294 BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, IQO2 1903.
Current-Arrows for the 26th January, 1903; Chart IV at 22 h 30 m , and Chart V at 23 h O m (').
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 23 h 30 m , and Chart VII at O h 22.5 m (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 O h 30 m , and Chart IX at O h 45 m ().
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 66 l /-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-
1 1 ) Archives des Sciences Physiques et Naturelles, Geneva, 4th period, vol. I, 1896.
1 2 ) 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 9 h or io h 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
3 02
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 iSSst 1 ).
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 S a .
(') Expedition Norvcgienne de 18991900, 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 r t ,
the distance from point S 2 to the current, r 2 . The angles these lines
make with the ground-line we will call cp t 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 a l
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 P f
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 -|-a 2 = , (i + d) = D sin (/; = </,
h
- = tan gr>, = p ,
"i
PI = = '-p cos 2 0>, ,
5 rf 5i
Birkeland. The Norwegian Aurora Polaris Expedition, 10031003.
(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 i h 45 and 2 h o m , 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 i h 52-5 m 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(5 2
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
37
(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 an d 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 =
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.
3 o8
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
Pi 1
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'* 45 m 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
23 11 22. 5 m
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.
39
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
23 h 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 P t ' , h and ;'.
TABLE XL VII.
Time
V
d
Pi'
P,' obs.
P,"
P,"
s
h
1
P,' cal.
aah o ni
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
I 4 8
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 i l / 3 million amperes. If we compare the calculated values of P,' with those
observed, we also on this occasion, at 22 h o m , 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*! o m
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 23 b . 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 P v , 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, 23 h 2o m , 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 - g r -
P*
For rays where v = 0.7 X IC)10 > we thus find that
W = -X loi) ' 35 z -44 X iQ 11 ' er g s P e r 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 - * g r - 2 sec -
W = 3.94 X Io12 ' er g s P er 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 io 6 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 io 9 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 18991900", 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 io 13 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 io 13 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 io 9 = 2.7 X io 9 ergs per second.
it 63652 io 10 iog :
If we keep the same designations as before, we thus obtain
Nf.iv* = 2.j X io 9 ,
in which, employing the same ft rays as before, we have the following values:
,U = 1.2 X IO-* 7 (!)
v = 2-. 59 X io 10 .
Hence we find that
N = 6.7 X io 1 ",
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 io 10 ft particles per second, and at the same time gives ofl
100
3600
gramme-calories ( 2
We then obtain
6.7 X io lr ' 100
7.3 X io 10 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
I 1 ) See Sir J. J. Thomson's "Corpuscular Theory of Matter", pp. 16 & 33 London, 1907.
f 2 ) 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 6 th October, 1902
Registerings from 13h 30m to 15h 3Qm, Gr. M. T.
R| &5 bx
tq KI ^
3
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-5
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53
PI. II
The Perturbations of the 11 th October, 1902
Registerings from 12h on the llth to 2h on the 12h, Gr. M. T.
of
w
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o
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PI. Ill
The Perturbation of the 23 rd 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
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DC
PI. IV
The Perturbations of the 27 th & 28 th October, 1902
Registerings from 14h on the 27h ( O lh on the 28th, Gr. M. T.
PL V
The Perturbations of the 28 th & 29 th October, 1902
Registerings from 14h on the 28*h to lh on the 29h, Gr. M. T.
PL VI
The Perturbations of the 29 th and 30 th October, 1902
Registerings from 16 1 ' on the 29 th to 4 1 ' on the 30 th , Gr. M. T.
THE PERTURBATIONS 0]
,ND 30 th OCTOBER, 1902
PI. VII
The Perturbations of the 31 st October and 1 st November, 1902
Registerings from 6 h on the 31 st to 2 h on the 1 st , Gr. M. T.
The Perturbations of the
md 1 st November, 1902.
20 h 22 h 24 fl 2 h
PI. VIII
The Perturbations of the 23 rd and 24 th November, 1902
Registerings from 15 h on the 23 rd to 7 h on the 24 th , Gr. M. T.
f
\
L
*
1
-I
PL IX
The Perturbations of the 9 th December, 1902
Registerings from 5 1 ' to 18 h , Gr. M. T.
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PI. X
The Perturbation of the 15 th December, 1902
Registerings from 23h on the 14th to 5h on the 15th, Gr. M. T.
-I
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PL XI
The Perturbation of the 25 th December, 1902
Registerings from 23 h on the 24* h to 5 h on the 25 th , Gr. M. T.
\
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PI. XII
The Perturbations of the 26 th December, 1902
Registerings from 18 h on the 26 th to 2 h on the 27 h , Gr. M. T.
-
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PI. XIII
The Perturbation of the 28 th December, 1902
Registerings from 3 h to 8 h , Gr. M. T.
THE PERTURBATION OF THE 28 th DECEMBER, 1902.
PI. XIV
The Perturbation of the 26 th January, 1903
Registerings from 7h to 15h, Gr. M. T.
THE PERTURBATIC
T
(Observatory
H,D V
'50
PI. XIV 2 ^I903
IE 6th JANUARY, 1903.
PI. XV
The Perturbations of the 26 th & 27 th January, 1903
Registerings from 18h on the 26th to 7h on the 27th, Gr. M. T.
D
52
U
x
t,
o
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OH
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PI. XVI
The Perturbation of the 8 th February, 1903
Registerings from 8 h to 12 h , Gr. M. T.
PI. XVI f 1903
F.Tuary, 1903.
-75
D &, V
t isfuwcn
D
V
when
v
wet
(WUl
10 h
PI. XVII
The Perturbations of the 8 th February, 1903
Registerings from 13h to 24h, Gr. M. T.
PI. XVIII
The Perturbation of the 10 th February, 1903
Registerings from 2Qh on the 10*h to 3h on the llth, Gr. M. T.
S5
I
I
I
S!
>
X
PI. XIX
The Perturbation of the 15 th February, 1903
Registerings from 13 h to 20 h , Gr. M. T.
PI. XX
The Perturbations of the 22 nd March, 1903
Registerings from 12h on the 22nd to lh on the 23rd, Gr. M. T.
PI. XXI
The Perturbations of the 31 st March, 1903
Registerings from 19h on the 30th ( O 3h on the 31st, Gr. M. T.
8
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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 18821883, by which my earlier results from obser-
vations from 25 stations in medium latitudes in 19021903, 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 18821883.
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 19021903.
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 I 35- 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
J 53- 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
11 XXV.
Tl
11 XXVI.
Tl
11 XXVII.
Tl
11 XXVIII.
Tl
I'I. XXIX.
T
11 XXX.
K;
PI. XXXI.
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.
K;
11 XI. 1.
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 18821883.
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 P d , 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 P h . 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
i5
3
45
60
75
90
Gottingen
i3'
i5i'
S 13'
i56'
i8'
o
60 N. Lat.
o
39'
i8'
II 9 '
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 782o'N., and longitude 6849'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 o h 39 m , 8, or in round numbers to o h 4O m ,
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 io h
and 23 h 2o m Gr. M. T., the latter hour corresponding with 24 h 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 io b to about I4 h 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, 19021903.
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 ia h to I4 h , 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 I2 h to I4 h , 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'' 4o m . 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 //'' 2o m , u 1 ' jo m , I2 k 20, 12*' jo"' and ij h 2o m , 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 I2 h 30 with the two
last times on Chart I. On Chart I I2 h 2o m it is only at Ssagastyr that the positive storm occurs with
considerable violence, in Little Karmakul the perturbating force is still comparatively insignificant. At
I2 h 5o m , 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'* 2o m , 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'' 2o m , 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 P v , 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 20 h or ai h 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'", //'' 2o m and i&> 20 m .
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'' 2o m ; 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 i6 h 5o m 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 I7 h 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 P v . 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 P t . 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 i8 h 25 m they almost entirely neutralise one
another's effect, at I9 h 5 there is a strong effect of the positive system, and at I9 h 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 I9 h 5 to I9 h 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 I9 U 5 m 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 I9 h 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 P t = 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 2i h 5 on Chart VII, there are marked
effects of a system such as this, although at the last hour shown, 2i b 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 2i h 40 and 22 h 4O m , 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
3 a
5 M
- 35
W 67 .
4-2 7
20
1 6 20
- 4i-5 .
IO1
+ 31 .
- 53 .
M 44 n
5 M
-87
84
4-3'
. 18
50
- 80
i9
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
4
- '68
>, 89
+ 61
99
n 5 2 M
-65
- 45 *
. 9 1
4 28 .
3 ,,
18 35
-"4
H5
4 10
+ 3 ,
. is
-65
- 25
109
4-55 .
n 1 .,
'9 5
-i7
'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
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 .
44-5 ,
- 10
n 45 ,.
4
- 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
o
- 67
o
- 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
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-l6 4
+ 27
-60
40 6
W 3 H
-127
4-185
W 3
+ 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-S n
- 7 2 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 8 9
-'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
W 7 4
-I6 7
+ 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 - 3 8
W 3 i ,
-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
+ 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
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
~ I2 9
n 24.5
- 23
+ 361 n iW 41 + ii n
-"3 n
40
I7 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 6 5
9
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 iw 35 . 5
- 3
- 5' n
37
21 5
- 3 57
Wio8
-217
-279 n
21
- 9
- 63
49 n
2O
-135 n
E 10
+ 22 -2I 3
E 50
- 59 n
- 37
w 32
4
-100
W 64.5
- 2 5 n - 7 n
n "2.5 n - 45 n
+ 96
4*
22 2O
38-5
5 n + 74
W II | - 40
+ 21 39 n
23 '5
+ 14
E 6 B
+ 27
+ 38
: '5 n
+ 7 n
- 10
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
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
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
x 57 x
25
4-5 x n 7-5 x
5
E 9 x
4-5 X
o
+ 7-5 X
X 3 8 X
40
- i n
E 5 x
+ 5 x
x 9-5 n
5-5 x
x 8.5
+ 5 x
x 5 *
20
- 3 11 J n 4-5 n
+ 5 x
- 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
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, 19021903.
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PART II. POLAR MAGNETIC PHENOMENA AND TERRELI.A EXPERIMENTS. CHAP. I.
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BIRKKLAND. THE NORWEGIAN AURORA POLARIS KXI'KDITION, ] 902 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 sin 2 cos 6 cos rp ,
where (// has the same meaning as in Art. 53 in Part I.
We will reckon the angle positive towards the west like 'P, 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'' 2o m 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 u 1 ' 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 n 1 ' to i6 h , and a second section from i6 h to 23 h 2o m .
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 u h 3o m . We find the most powerful perturbing forces at about I4 h ; after which the forces
decrease, until about 15*' 3o m , when the conditions are again more or less normal.
At Uglaamie, the conditions are somewhat more complicated. At a little before I2 h , 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 i3 h , 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 I5 b 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 i6 h io m , 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 rj 1 ' 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'", ij k 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 i4 h 20 and on Chart IV at i5 h .
At the latter hour we notice especially strong effects of this system at Ssagastyr. At Cape Thordsen,
on the other hand, we find at I4 h 5 m 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 i8 h 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 i8 h , 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 the 1 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 i8 h , 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>ou f 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. These 1 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 i7 h 4O m ; while Chart VII, for i8 h 2o m ,
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 P w 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 I9 h 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 I9 h 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
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
n i48
+ 74 n
n 3<
4 - 94 n n 93 n + 4 '
- 74 n
n 45-5 n
- J 5 n
- 87
n Ioa
+ 32
n 5-5 n
18 20
~ J 6S n
72
+ 61
- 57 n
n 33 n
- 10
- 65
n I9 n
o
W20
19 20
2O5
48
- 26
- 32 n
o
- 10
- 33 n
82
4 a n
E 4 5
2O 20
"4 ii
n 9
- 43 n
- 4
Wio
- 13 n
n 6 4 I + 8
W 4 o
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
o
+ 7 y
13 20
5B W 3B + 12
o
- 5 7
- 3 7
o
+ 7 B
14 5 +
22 + 18
+ 13 y B s 4- 10
+ 9 n W 5.5 y o
20 4-
24 B + '8
+ 5 B B 20
+ 3 B B '5 n 1
15 o +
35 E 10 4- 35
E 6.5*
4- 19
7 ; E 8 - 15
20 4-
12 6 ' + 22
o
4- 10
4 B o
9 B
16 20 +-
'3B + 34 B
+ 5 B ! o j + 10 B
O
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 I 7
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
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
47
w 26 25
+ 15 E 19
+ 3
+ 225 63.5
20
- 28
n 2 9
- J 9 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 * W 3 o
- 79 B
-544 B
18 20
-378
68.5 n
-32
- 82
E 70.5
- J 74 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
B 2
+ 14 B
20
+ 3-5 B W 7 y
+ 3 B
W 5 B
small devi-
I B
+ '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
B o
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 6 1 ' 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'' io nl and J4 h 2o m ,
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 I5 h , 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 P v 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 i6 h 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
I3 b 2o m 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 i6 h 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 i8 h 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 ig h 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 P v 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
E 18.5;'
- 5= /
E 22.5;-
4- 25 r
E 17 ;
13 20
o
,t 32
-r M ;
- 44 n
i, 22
+ 65 ,,
68
'1 5 - 257 ;
o
4-112
-236
n I0 3 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
->2 5 8
,,217 n
+ 89
-337 n
n '6
+ 55
- 76
'5 '5
"99 n
it l62 it
4- 80
-285
. I02 I,
10
- 55 *
W 57
I 6 20
5 i,
W 37
+ 28
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
- 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 2 9 n
20 -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
26
21 IO
o
n 64
- 23.5
O
n 9 n
^ 25
+ 3 n
n 31 n
22 2O
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
13 20
o
E 25 J' 4- 37
n 8 -5 n
+ 6 r il + 53'
- 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
4 + 20
n 6 5
+ "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
I 7 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
- 64
89
- 85
-168
- a ? n
20 | 5
n IJ
5 r n
64 - 60 ' ! - 83 E 18
- 82
21 10
7 >i
n r 7 It
- 28
n 48.5
+ 23 -123
67
-'77 n
22 2O - 20
it 25
- 77
., 24
o - 86
n 2 5
-'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 \,
3 6o
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 20 h 20 m , 21 1 ' 10 m , and 22 h 20 m .
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' -J l>! " 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 o 1 ' is"', so that after that time we find almost cxclnsivelv positive values of/', until about
2 1 ' ,-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 o 1 ' 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 o 1 ' 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.
Iy 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'" 5o m , 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- I 5J / - -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 o 1 ', 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'' I5 m , 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
45-5
x 32 fl
defined to o
n T r n
"*- 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
* 4
n 27
5 i - 18 I
deduced.
* 3' n
n 4-5
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
~*~ T 4
2 4 n
+ 7
1 7-5 n
-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
3 66
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
W 5 4 5'
-376 3'
E 35-5;'
-i- 103 3'
- 95 r
W2 4 . 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
W 43 -5x
+ 62
-'53 n
2 3 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
+ 51 x
- 83 B
n 46.5 n
-176
20
+ 3
n 33
-I5 n
W 4
+ '5
- 61 *
n 43
-'45 n
5
- 92
n 34 n
- 25 x
n 63 x ! + 35 n
- 38
n J 3'5 n
- 88
I O
- 54
n 84.5
- 59 n
s ' + 5 6
- 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 J 5 n
- 22
2 15 + la
n '4-5 n
- 38
22.5 4- 38
7
23
- 19 n
55 + M ,, 8.5
- 2 3
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
E 44 3-
-139 r
40
- 18
n 4-5 n
+ 88
-'83
M 3 n
+ 96
-i 4 6
n 35-5 n
-129
45
- 16
E 6.5
+ 76
-214
37 j?
-Hi6
- 56
W 4 2. 5n
-"3 n
55
- 21
2 5-5 n
+ 77 n
-203
n 73 n
4-142
-108
42
-124
- 17
32 n
* 58
-168
n 57 r.
+ I 33 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
- 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
E6 4
4- 18
+ 97
li
- 1 n
10
- 6,,
* 6
+ '5
6
r 4 n
- 27
+ 60
8
- 13 *
20
- I 2
x 7-5
+ 5 n
- I n
,, 31
- 38
+ 47 n
O
8 *
40
- '3
n 9 n
- 6
+ 2
+ 23
4- 24
E 3-5
- 17
a 15
+ 3
n J 3 n
7 n
- 6,
80 + 89
+ 39
W 2.5
- m
I 3 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
P d
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
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
B u <4
tfl u o
+ 8
B S 2 B
+ 8 B , B '7 B - I 2 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
B I2 B
20
>> u
"c r ja
+ I B
B J 7'5 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
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
- . 4 B
B 1-5 B
?
E 2.5
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
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
B 2 3
, 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 23 h 25 m .
fig- 152.
368
r,IKKi:l..\M>. Nil NOIUVKC.IAN AlkoKA I'Ol.AUI.i KM'MM'I lt).\, IQO2 1903.
M
re
ro
oo
00
3
u
V
t,
.c
4h
(A
O
C
C.'
O
' .
.
. - ,r
- , V (
PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I.
369
ttt
37
BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1QO2 1903.
S3
00
+4
(fl
o
g
3
U
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 7 h 30"", 8 h 20, and from g h to g h 2o m .
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 [Q 1 ' 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'' there 1 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 I4 h
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 i6 h 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 I7 U 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 2o h , 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 19021903. 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 I5 h 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
I5 h 40 to i5 h 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,
i6 h i5 m , Uglaamie is in its district of precipitation, but the latter does not extend as far west as
Ssagastyr. At i6 h 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 I7 h 2o m (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 i8 h 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 i8 h 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 I9 h 5o m .
Two Charts, XIII and XIV, have been drawn for the last section of the perturbations of the day
under consideration, from about 22 h 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
O
7 3
+ 46
o
+ 10
-202
E 102
o
+ 8
E 22.5;'
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
- 2 3 n
n 9-5 n
10 20
+ 9-5*
o
o
O
- 15
o
n 50
-- 3-5 n
n 2.5
o
o
o
- 52
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
- 8 3
n i8 4
- 22
15 3
'7-5 n
E 9.5
+ 23 n
-MS n
7 n
+ 45
323
Wii S
- 52
40
53 n
.1 2.5
+ 80
-181
83
+ 65
-300
72
5
- 9i
n 53 n
+ 80
-202
n '53 n
+ =8
-205
K MO
- I6 5
16 15
I87-5 B
n 26.5
+ I 37
-325
n 209
+ 220
-285
n 2 33-5 n
- 8 5
40
- 2 9 172
+ 180
-522
280
+ 100
-343 n
it I2 o
- 71 n
17 o
->3 n ' n 20
+ 205
-6l3 n
298
+ I 4
-240
n 62.5
-'25 n
20
-> 3 oo ;Wio8
+ 23
-606
n 4" n
+ 120
-364
86
-126
35 ' ->3 246 + 180
545 n
n 325 n
+ 4 n
-255
n 6 2.5 n
-'36
1
55
->3 ,,609 +135
-338
'28
-200
-216
n '44
-MO
18 20
->3 ; n 2i8 + 80
-134 n
Wn 5
- 55
- =6
E 174 n
- 91 n
55 ' 239
n 205 + 57
+ 3 n
E 47
- 20
+ 24
W2 7 o
101
19 50 i-f 30
W 55 + 10
+ II
W 20
- 20
- 7 n
n I2 4 n
- 63
22 55 48
n 8 n - '5 n
+ 221
E 46
- 4
+ 182
n 191 n
- 21
23 15
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 . 5 y
- '5 P'
E n. 5 y
E 7 /
o
7 3
E 4
o
- 10 y
8 20
o
n 14 n
W 5-5 *
o
o
o
9 5
O
- 9 n
n 3 n
o
o
10 2O
o
o
o
II 50
5
W 8.5.
o
,, 8.5
13 20
+ i
+ 19
7 ,,
o
o
M 35
+ 9
E 83.5
+M3 n
n 4 it
- 2 4 n
+ 73 7
+ 47 7
55
- 3
'53 n
+ 249
E 15-5,
- 37
+ 142 W27
+ J'3
15 3
+ 109
n I2 7 n
+ 220
* 33 ,,
20
+ "3 ,,
E 7
4-130
4
4 24 188.5
+ 2 35
n i5-3,i
35
+ '4
Wl2
+ 118
50 4 103 137
+ 260
W 19
- 61
4 120
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
4 no
55
- 80
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
34 ,,
- 97
+ 55
4 78
33 55
-33 n 235 n
-5
E 138
+ 225
-577
10
-207 ,
23 15
+ 54 n ,,286
-S3 2
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
E 4 y
4 14 y
E 44 y
+ 26}'
4 42 y
o
+ 35 7
7 30
o
o
+ 27
5
o
+ "
o
o
8 20
o
o
o
-"- 15 .
W 4
IS *
o
9 5
o
o
o
5 n
o
- 28
o
IO 2O
o
o
+ 5 ,
10
+ 25
- 13 It
ii 50
o
o
o
4- 5 -
o
13 20
o
o
+ 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 ;'
-^S 2
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 -
+ 2 7
16 15
+ 105
W 4
- 90
-I5
48.5
-225
+ 180 r
, '53
- 26
40
+ 177 .,
25-5
- 60
-I6 5
33-5
248
+ 55 -
> '34
133
17 o
4-149
4i-5
+ 10
-156
i3-5 .
296
4 82
61
3 11
20
+ 253
o
-45
28
-430
+ 150
i 8 .
- 60
35
+ 234
E 6.5
4 81 .
-28 7
178
-476
-212
J 5
-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
+ I 2
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
S-;IL;;IM yr ( 'hriMiania
Pawlowsk
III-. M. 1 .
I 'I, I'.i /'/, I'd I'l, l\l 1\
Ii in
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 ., I3 V 5 45,.
|o 20 .. .. 73.5 ,. -i-O* ,,
1-5 - 4 36 .. 12 .. 4- 5 ..
5o 4 30 .. 37 -,.38 .,
+ 35 - '3-5 11 40,,
IO S 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 ..
" + 5 H 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
20 2 4 1
o o W 15 ..
95+2.. o o
o o .,
1O 2U O O 4 .j
o o K 18 ..
1 1 50 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 ..
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 .. 4 35
417,- i, 8 .. 5 19 .-
20 4 10 ,, o +44 ,,
4 4 ' - K 24 .. 86 1 ..
35 -1- I ., I 1 - 29 .. 451.5 ,.
4 31 11 i, 25 .. ., 684 ..
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.
379
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ro
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PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I.
a
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IHKKKI.AMl. I 111' Ni)U\VK(,IAN Al'KOKA 1'OI.AK!-* KXI'l-'Iin K IN, 1QO2 I 903.
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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.
8
O
a
V
JS
in
S
s
U
e
m
00
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PART II. POLAR MAGNETIC PHENOMENA AXD TERRELLA EXPERIMENTS. CHAP. I.
385
X
a
js
U
u
c
I/I
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3
U
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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 n h , 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 io h 55 m 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 i4 h 3o m and ig h 45, and
(2) the storms from I9 h 45 m 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'' 3O m , 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 i6 h , 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 2o h . 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 I7 h 40 until i8 h 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 i6 u io m , 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 i8 b 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 I5 h 2O m and i6' 1
20, it is distinctly developed only at Kingua Fjord; but at i6 h 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'' ao m 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 i8 h I5 m to i8 h 3o m , 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'' 2o m 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
ig h 45 to the end of the period.
At about i9 h 45 m , 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 i9 h 45;
while the horizontal-intensity curve, which, since about jy 11 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 2i h . 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
2O ii 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 2O h 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 2o h 5o m to 23 h i5 m .
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 22 b 2o m and 23** i5 m 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
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
- 5-5 n
E 20.5
- I0
E 3
14 20
+ 20
2
- I0
+ 20
o
+ a
'9-5
- .0
W 5-5,
15 20
33-5
E i
+ 20.5
- 32.5
a 6.5
- 3'-5,
-'72
W 79.5
+ '5
E 31-5,
16 20
- 23.5
o
- 25
,, 3-5,,
o
-i5
;, 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
' -5,,
+ 81.5
-'55 n
Iaa B
- 82.5,,
-162.5,,
B 87.5,
-'32
Wii 5
18 I 5
->34-5
66.5
+ 214
-255
'80
+ 335
- 92.5,,
I2 9
- '26.5 n
1 18.5.
3
->34-5 ,,
n 32
+ 254
-45
123.5,,
i 268.5
- 91
94
-W-Sn
r, 88. 5n
5
2 76.5
13
+ J 97
-355
73-5
- 90
-121.5,,
94
~*3 l
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 I0 3
- 64
56-5 ,,
- 4
IOO -5
- '5-5
,1 I0 3 r
5
'34
9-5
+ 184
- 85
86.5,,
+ 34-5,,
B ir 5
- 6.5,,
106
21 15
->308
22.5,,
-1-376
- 2 4<>
'42.5
-MO
- -5
Bl82
- 48.5,,
n 179
30
->38
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
W2 5
- 3
+ 46
i 9
4 n
,,214
23 '5
+ 50.5
Wi 4
- 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
+ I4-5/
o
W 7 7
- 0.57
W 17.57
o
12 2O
* 1-5
o
- 5-5.
- I ,,
o
- i
o
9-5 ,
13 20
+ 22.5
W 3 7
+ 6
f i
i-5
+ 3-5 y
12
o
14 20
+ 3
o
o
o
E 1.5,,
- i-5
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
6 3-5
- 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 I0 4-5
- 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
- I0 4
ft 274
+ 42
3
-565
81
+ 3I7.5,,
-"5-5
94
- 47 167-5
22 8
+ 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
+ 2 8
o
13 20
+ 10
IO -5,,
+ I ,,
+ 8,
- '4
+ 3 4
14 2O
5
7
4 n
- 12
n J 5
4
"*" 2 n
15 20
+ 15-5
45
- 2 5 n
o
W 10
+ 3
5
1 6 20
1-5 n
3
- 22
+ 6 n
n I0 11
+ 2
+ 28
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
->76o B
ESIO
- 5
->6 5 5 ,,( l )
2 36.5
3
-295-5
,i "6.5
-120
- 59 11
65
- 4 n
->655 (')
o
5
-156
I02 ,1
- 5
-*- 273
Wi 4 8
12 5
72
E I2 5
19 20
- 50
n 54-5
- 21
4- 82
76
- 36
42
n 8
50
7-5
6 5
25 n
5 n
E '9 11
+ 1 n
7 2
'5
2O 30
- 34 ,
7<>
- 10 647
325
+ 138
60
W 2.5
5
~ I2 n
n I2 5 n
- 27 n 632
,,660
+ '37
->655 (')
I2 -5
21 15 ; 170
95
+ 172 - 636
n34 n
-140
->655 f 1 )
.i '5 a
30 -174
84
+ 219
33 ,1
6 40
- 26 ,
->655 (')
296
4 o
-205
* 49-5
4-270
63 *
n 375 j>
+ 33 n
->655 O
5 2 ..
22 2O
-112
E 66.5 ,. + 188
'45 n
2'4 ,,
+ 2 4 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
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
+ 22
n 7-5 ,'
+ 0.5
,, 76.5
50
+ 23.5
,. 25.5
+ 6
24
+ 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
- 2 9-5
,, 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
2 o
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 - 
