QC
76
UC-NRLF
J REESE LIBRARY
\\J * * . * . OF THE
UNIVERSITY OF -CALIFORNIA
Received
Accessions No..-3A&6.3.-' Shelf No.
THE RAINBAND IN SPECTROSCOPE
OF MODERATE DISPERSION.
A aB C
!! I
E b
StanfardJs Geogl- Estab*.
A PLEA FOR THE RAINBAND,
AND
THE RAINBAND VINDICATED,
BY
J. RAND CAPRON, F.R.A.S., F.RMET.Soc.
'UNIVERSITY
LONDON :
EDWARD STANFORD, CHARING CROSS, S.W
LIST OF ILLUSTRATIONS.
The Rainband in Spectroscope of moderate dispersion.. Frontispiece.
Rain and Rainband Diagrams, 1880 aud 1881 ...... Plate I. to face page 8.
Monthly Rainfall and Rainband, 1882-3 ...... II. 20.
Rainfall and Rainband at Guildown for four consecu-
tive months of 1881 .............. ,, III. 21.
Ozone and Rainband at Guildown for four months of
1882 .................... IV. 22.
Pocket Spectroscope ... ... .. ... ... Fig. 1, page 15-
The Standard Spectroscope (exterior) ......... ,, 2 ,, 17.
,, ,, (interior) ......... 3 17.
Double Slit Plate ................... 4 ,, 18.
Double Spectrum ... ... ... ... ... ... ,, 5 ,, 18.
Kinkerfues Weather Compass ............ ,, 6 23.
Electrometer and Battery (plan) ............ ,, 7 ,, 26.
,, ,, (elevation) ... ..... ,, 8 ,, 26.
Collecting Apparatus .. ... ... .. ... ,, 9 ., 28.
PKEFACE.
" A PLEA FOR THE EAINBAND " was originally published in Symons's
Monthly Meteorological Magazine for December, 1881.
It subsequently, as a separate pamphlet, attained a considerable
circulation, and though by no means the earliest treatise in which
the subject is dealt with, was probably the first to bring it in a mono-
graph form before the general public. It has, however, lately been
out of print. Four years since its appearance, that is to say in the
October and November numbers of the present year, it has been
followed by a second article in Symons's Magazine, entitled " The
Rainband Vindicated." As " The Plea 5 ' is still frequently asked for,
and the second article is really a continuation of the first, it has been
determined to publish the two together, so that those who wish for
information may have the subject before them as a whole.
" The Plea " (Part I.) is reprinted, except that it has been slightly
condensed. The original lithographic plate of " The Rainband as
seen in a Spectroscope of moderate dispersion,'' has been revised and
redrawn. " The Rainband Vindicated " (Part II.) is a reprint of the
article as it appears in the Magazine, with the same plates and wood-
cuts. Since its publication, it has received corroboration in the
shape of "Tables of the Climate at Falmouth for the years 1883 and
1884," kindly sent to me by Mr. Wilson Lloyd Fox, F.R.Met.8.
Mr. Fox, in these tables gives the sums of his daily rainband observa-
tions when compared with rainfall as follows :
Means of last four months of year 1883
Rainband, 49. Rainfall, 5'170 inches.
Means of twelve months of year 1884
Rainband, 37. Rainfall, 3'141 inches.
His scale runs from to 4. Two letters on "Atmospheric Elec-
tricity at Guildown," were also published in S-ymms's Magazine for
August and October, 1 885. A reprint of these has been added by
way of Appendix, for the use of those who desire to take up the
subject more fully.
IV. PREFACE.
In them are described and figured the necessary apparatus for col-
lecting and testing atmospheric electricity, and the methods of using
them. Those who are disposed to make further research into the
subject of Ozone are advised to consult Dr. Cornelius B. Fox's
" Ozone and Antozone " (Churchill, 1873), which contains a full de-
scription of its properties, and the tests by which its presence and
quantity in the air may be recognised. The Klinkerfues Weather
Compass (with instructtons for its use) can be obtained from Messrs.
Biernatzki and Co., Hamburg, the patentees, and from Mr. John
Browning, 63, Strand, London. A short index of principal matters
has been added.
The Eainband, Atmospheric Electricity, and Ozone are, it appears
to me, all subjects legitimately and closely connected with Meteor-
ology ; and yet for various reasons they hardly seem to have hitherto
received from observers their fair share of attention. My object in
writing these articles will have been accomplished if I succeed in
drawing to them more of this attention, and in exciting in them such
an interest as will stimulate their more extended investigation.
J. R. C.
Guildown,
January, 1886.
PART I.
A PLEA FOR THE RAINBAND,
WHAT is the rainband 1 I will describe the rainband as a dark band
or shading (or rather, under sufficient amplifying power, set of fine
lines) seen on the less refrangible (red) side of the double line D in
the atmospheric spectrum ; and the presence or absence of which is
indicative of the presence, or otherwise, of moisture (more strictly
speaking) excess of moisture in the atmosphere Its history may be
said to date from the time when Angstrom's maps of the solar lines
were found to present different aspects according to the condition of
moisture of the atmosphere at the time of observation, and when
that early spectroscopist proved the presence and absence of certain
lines forming bands in the spectrum, more especially a set near D,
to depend on that condition. No practical meteorological result fol-
lowed, however, until, as Prof. Piazzi Smyth tells us, the subject was
first presented to him as a marked feature in sky spectrum at
Palermo before and after a sirocco in 1872. Next, when in July,
1875, destructive floods in both France and England (not predicted by
the barometer) were noticed by him in connection with a peculiar band
in the spectrum under dates July 19th and 26th, 1875. Prof. Smyth
vividly describes in Nature (vol. xii., pp. 231, 252) the phenomena
then observed, how the dark band near D was found the forecast of
a drenching afternoon following the fine opening of a Scotch holiday
in Edinburgh ; and how, on another occasion, it became the " spec-
troscopic provision of rain with a high barometer." Then followed
observations in May, 1876, to the same effect in France, especially at
Marseilles, where the rainband was seen in the spectrum, and fol-
lowed by rain to the surprise of the natives, who consulted only the
public barometer and thermometers, and found none predicted. In
February, 1878, appeared the fourteenth volume of the Edinburgh
Astronomical Observations, 1870-1877, and here, under the head of
" Meteorological Spectroscopy in the small and rough," we have the
subject treated in a most complete and elaborate manner, and illus-
trated by a set of engravings of spectra. The Scottish Meteorological
Society's Journal, N.S., Nos. li., lii., also contain contributions by
Prof. Smyth on the subject. Again, in Nature, of July 1st, 1880,
vol. xxii., pp. 194, 5, the subject of "rainband spectroscopy " is dealt
with in a condensed and epitomized form very acceptable to the
reader, who, doubtless will recognise the identity of the " Edinburgh
experimenter " in this useful contribution on the subject.
For rainband observation a spectroscope is necessary.
A large one with several prisms is desirable, if the ultimate com-
position of the band or bands is to be examined ; but for ordinary
meteorological purposes, and to observe the general character of the
band near D, a pocket or miniature instrument is quite sufficient,
indeed best adapted. This may be obtained from any scientific
optician, and will cost, according to construction, from one to three
guineas. The more expensive ones have an adjustable slit and
achromatic lenses ; but these are not necessities, and the cheaper
form is nearly as useful.
I employ for my own observing a McClean's star spectroscope with
a slit arrangement adapted, which makes also an efficient instrument
with rather a larger spectrum than the pocket spectroscope.
Having obtained the instrument, nearly close the slit and adjust
the focus till the lines in the solar spectrum are sharp and clear.
This should be done on a bright part of the sky. Then point the
instrument to the quarter of the heavens which it is desired to
examine, and note results as to, especially, lines D and their neigh-
bourhood.
I generally observe thus at 9 a.m. daily from my laboratory
window (looking towards the south), but if time and opportunity
allow three observations, at 9 a.m., 1 p.m. and 5 p.m. would be
better, varying the parts of the sky tested ; and I examine with the
spectroscope elevated about 13 degrees. Prof. Smyth recommends
to point as low as you can to the horizon provided you get trans-
mitted light, and to observe when the sun is neither high nor low.
I find in practice 9 a.m. (the same hour when my other instruments
are observed) a good time to make the observation when only a
single one is taken daily, and also that if I get too low on the hori-
zon I am apt to have always a " rainband," or rather a false band
due to earth moisture. In observing you will soon remark changes in
the characters of some of the spectrum lines, as compared with these
when seen on a blue sky with an elevated spectroscope, and, more-
over, bands of varying intensity are found added to the low spectrum
not seen in the higher one. The lines and bands that change their
character, or are variable in their appearing, are telluric ; either rain-
bands or lines, called by Prof. Smyth a " function of moisture and
temperature," or low sun bands and lines distinguished by him as "a
function of dry air and low sun." The true solar lines remain un-
changed. Prof. Smyth, in the Edinburgh volume before referred to,
fully describes, both in type and by illustrated drawings, all these bands
and lines and their changes, and points out that there are several
smaller rainbands besides that near D. In practice it will, however,
generally be found sufficient to examine the principal one on the
red, or if you have the spectrum as I do (with the red end of the
spectrum to my left hand), left side of D. An examination of the
other lines, though desirable for special purposes, will only tend to
confuse the general observer. Prof. Smyth recommends, and has
used a dry air band on the right hand side of D as a standard of
comparison with the rainband ; but I have not often myself made
use of it, judging independently by the rainband itself.
In enumeration of the darkness of the band, for the purpose of
record, I use from No. 1 to 5, as under :
1 means faint.
2 faint to moderate.
3 moderate.
4 moderate to strong.
5 strong.
1 to 10 is the enumeration recommended and employed by Prof.
Smyth. I found, however, the dividing into so many degrees was
difficult, especially when the intensity is slightly changing by passing
clouds. Simultaneous observations should if practicable be made
and recorded, of barometer, wet and dry bulbs, and wind (force and
direction) ; and the circumstances of sun, sky and cloud at the time
should be shortly noted.
Ozone test papers may also be usefully referred to, as cold winds
alike affect them and rainband readings. The D lines are generally
more or less involved in the rainband shading.
To enable the observer to judge of the general appearance and in-
tensity of the larger rainband near D, I have given (see frontispiece)
some drawings of spectra as seen in the McClean spectroscope, of
which the following is a description :
(1) Spectrum as seen upon a pure high sky, showing principal
solar and telluric lines in their proper positions, and with their de-
signations, but not showing the finer lines between, nor any bands.
(2) Spectrum observed January 17th, 1881, 8 a.m. Morning dull;
red sunrise ; low sunbands and lines (note especially band to right of
D) strong. No rainband.
(3). Spectrum observed 24th August, 1881, 8 a.m., showing
moderate low sunbands and lines, and a, faint rainband with rain
lines showing through.
(4) Spectrum seen November 16th, 1880, 1 p.m. Eain and wind,
but clearing in some parts of the sky. Low sunbands and lines
weak. Rainband moderate.
(5) Spectrum seen December 9th, 1880, 8 a.m.^,Sun shining
through watery clouds ; low sun lines strong. Rainband strong.
(6) Spectrum seen July 6th, 1881. Rainband everywhere, and
exceptionally strong, stretching nearly half way between C and D.
Whole spectrum darkened and obscured.
The above-described drawings do not give, except in a rough way,
the details of the lines and bands other than the rainband, which is
situated to the left of the double line D, and has its place marked by a R.
Spectra 2, 3, 4, and 5 are meant for observing by, as representing :
2, none ; 3, faint ; 4, moderate ; and 5, strong. Rainband faint to
moderate, and moderate to strong (the intermediate intensities) can
be estimated, and in practice the eye and judgment will soon be
found to accommodate themselves to the graduations 1 to 5.
8
Before proceeding to the questions affecting the rainband's value
to forecast rain, it may be desirable at once to say that it does not
claim absolute infallibility as to time and quantity of rain to follow,
though Prof. Piazzi Smyth believes "it is never really absent when
rain is imminent."
How its appearance and indications may be modified will be re-
ferred to later.
Its action is hygrometric, and involves the general principle that
according to the amount of suspended moisture in the air, so are its
appearance and strength. A faint, or faint to moderate, rainband,
may in some cases only show an amount of moisture which will
remain suspended for some time. A moderately strong or strong
rainband, represents an excess of suspended moisture, which before
long is sure to descend. Prof. Smyth mentions instances, and I have
met with them myself, where an apparently perfectly transparent sky
showing rainband has, on a change of temperature, condensed, as it
were into clouds, which have poured.
A little while since (August, 1881) I observed only a faint, or at
most faint to moderate, rainband in the morning at 9 a.m., on a
beautiful blue sky, studded with white cauliflower innocent-looking
cumuli. I predicted wet, and at the mid-day meal was twitted with
the sunshine and the brightness, but sure enough in the afternoon
down came the rain. On the other hand it will sometimes be raining,
and yet only a slight rainband shows, an effect generally connected
with a cold wind N. or E. No rainband is also sometimes observed
when the wet and dry bulb readings only slightly differ, but the ex-
planation of this may be that low earth moisture affects the bulbs,
which is not recognised in the sky-directed instrument looking through
a thin stratum of it.
In order to illustrate the practical working of the rainband, I have
prepared the diagrams on Plate I, which show graphically by
line lengths the rainband and rainfall during two periods of 1880 and
two of 1881. The rainfall is represented by vertical lines, in which
each one-tenth inch is one-tenth inch rainfall ; the rainband by similar
lines, in which each one-tenth inch is one of the scale 1 to 5. The
rainband was observed daily at 8 a.m. in 1880, and 9 a.m. in 1881.
The rain represents the fall during the 24 houi's following the rain-
band observations, so that where the lines correspond the rain
follows the rainband within that period.
The general result of these diagrams is to show that the rainband
predicts and also accompanies the rain, and to a certain extent cor-
responds in strength with the predicted rainfall. There are discre-
pancies and irregularities in most of the diagrams, it is true, some of
which are to be explained and accounted for by incidental circum-
stances, the particulars of which I take from notes made at the time,
and others (such as cases of rain at night after faint rainbands in the
morning) by the interval of time elapsing between the spectroscopic
observation and the rainfall, it sometimes happening that the rain-
band will much change its intensity during three daily observations
On the other hand, occasionally the rainband will precede the rain
by a day or two.
Diagram 1 July 21st to August 2nd, 1880. This diagram repre-
sents a set of rainbands, of which moderate to strong is the highest
figure, leading up to a moderate rainfall. July 25th appears as ex-
ceptional in the absence of the band. The day was fine and hot, and
the rain fell during the night with a change of wind from W. to S.
This fall ('35) was, however, shown to be in prospect by the bands
on the 22nd, 23rd, and 24th, gradually increasing in intensity from
faint to moderate.
Diagram 2 September 16th to October 13th, 1880. The first and
last sets of lines agree fairly. The heavy rainfall of the 18th (nearly
an inch) was forecasted by a strong rainband the day before, which
was reduced to moderate during the fall itself, and as the rain passed
away so did the rainband diminish in intensity, dropping to faint on
the 19th, for -20 of rain. On the 10th of October a strong rainband
was only followed by a small rainfall, but the wet and dry bulbs
were but 2 apart, so that much suspended moisture must have been
in the lower atmosphere, and in fact on the 13th some more rain
fell. In the centre of the diagram we have six rainbands (five faint
and one moderate) with only a slight rainfall. The following figures,
however, show for the five days on which these rainbands appeared
the differences in the wet and dry bulbs.
1880. Sept. 21. -2
22. 4
At 8a.m.
26 2 -5
27. 3 )
The following passages also appear in my journal at this time :
" The main feature of the week has been the persistent heavy morn-
ing and evening mists," and again (after quoting the above figures)
" so that the air has been kept in a chronic state of saturation," a
condition quite sufficient to account for a faint rainband. While on
the subject of this diagram it may be mentioned that space would
not allow, otherwise I should have given in a graphic form the rain-
band and rain lines from 8th to 15th September, 1880, as they well
illustrate how a strong rainband (on the 9th) came before very heavy
rain on the llth, while pending the actual rainfall the band was
moderate, and at last even faint. I insert instead the following
tabular particulars :
Rainband.
None.
Strong.
Faint.
Moderate.
Moderate.
Faint.
Faint.
Faint.
Date. Rain.
1880. Sept. 8th .
... -oo
9th .
... '04
10th -.
00
llth .
.. 1-58
12th .
54
13th .
... 1-19
14th .
... 1-48
15th .
... 113
10
We thus see that the rainband indicated the finely-divided trans-
parent moisture ready to collect and fall as rain, and also showed
itself upon the saturated air and warm morning mists (wind mostly
S. and S.W.) above referred to, while it only moderately or faintly
appeared during the heavy rain itself.
One explanation of this peculiar phenomenon of a low number
rain-band on falling rain may be that, pending heavy rainfall, the
whole spectrum is more or less obscured, and thus the rainband
shading near D, for want of contrast is less observed. We shall see
later that it does appear strong on a light misty rain.
In connection with this diagram it may be further pointed out
how a distinction lies between warm mists and cold fogs in the rain-
band's behaviour. The mists before spoken of were warm ones, and
a rainband, though faint, appeared almost without exception upon
them, but at a later period (in October) partly shown in the same
diagram, there were cold foggy mornings with N. wind, during which
the band was absolutely and persistently nil.
It results from these observations that the rainband is less reliable
in winter than in summer for indicating a rapid following of rain,
and we can understand this in the fact that watery particles may
remain without precipitation in a cold and comparatively even
temperature in winter, while they will quickly descend from a warm
air in summer, as the result of a fall of temperature.
We now pass to diagram 3, representing rain, and rainband
from May 16th to June 8th, 1881, and to Diagram 4, which gives a
two months' comparison of rainband and rain viz., from 20th
January to 20th March, 1881. The relative periods of rainfall and
rainband agree fairly well in these two diagrams, and in some
instances (June 5th, 6th, and 7th, and January 27th, 28th, and 29th)
the intensities agree, but the peculiar feature about the diagrams
is a certain number of strong, or moderate to strong rainbands,
coinciding with a very disproportionate amount of rainfall (see
especially dates February 4th and 14th and March 9th, when rainfall
was only -02, '05, and -02).
To be also noted is March 10th, when rainband 4 had no rain to
follow, and where the observation is marked, " Sunshine through
Clouds," and January 26th, rain -40 with no rainband. On this last
occasion there must have been more snow and sleet than rain (with
wind N., and temperature 29 for maximum) which melted in the
gauge. By the 27th the wind had changed to S. and a faint rain-
band appeared with rain !!.
The strong rainbands before mentioned as accompanied by so little
rain, being exceptional to the general rainband rules, I have tabu-
lated, for comparison, all the cases (7) of No. 5 (strong) rainband
between 1st January and 1st July, 1881, as under :
11
Table shewing circumstances of all strong Eainbands (No. 5), between
January 1st and July 1st, 1881.
W.&D.
No.
Date.
Bar.
Ther.
Bulbs.
Diff.
Wind.
Rain.
band.
Ozone
Notes, 9 a.m.
1
Feb. 4th
29-33
46 -0
o
8.
02
5
4
Clouds 10. Rain.
2
10th
29-00
49 -5
5
S.W.
16
5
8
Clouds 10. Rain.
3
,, 14th
29-60
38 -0
2 -5
s.
05
5
6
Clouds 10. Dull.
4
,, 15th
29-64
38 -0
5
S.W.
25
5
5
Clouds 10. Rain.
5
Mar. 9th
29-83
48 -0
o
w.
02
5
7
Dull heavy rain.
6
May llth
29 "06
53 '3
3
w.
08
5
8
Raining.
7
26th
2976
61'0
3'0
w.
12
5
4
Overcast, slight
mist, no rain.
These records present as peculiar features, barometer generally low,
difference in wet and dry bulbs slight, wind S. and W., rain minute
in quantity (except the 15th with J of an inch), and ozone mostly
strong, while in five cases out of the seven rain was falling at the time
of observation. One can understand moderate rainbands accompany-
ing the really moderate rainfalls of the half-year in question, but the
above seem anomalous. A possible explanation is afforded by the
strong air saturation at low level, indicated by the slight differences
in the wet and dry bulbs, and the probability that the rain so small
in quantity, was in quality of the misty drizzling character containing
minutely divided particles, which is favorable to the strong enforce-
ment of the moisture bands in the spectrum.
I add a few general instructions and hints which may be useful to
observers.
(1). Occasionally look to your instrument and see that the prisms
and lens are clean, and remove any dust from the slit. This last
should be done with a camel's hair pencil.
(2). Distrust observations and reports made by assistants or friends
who are not practised in spectroscopic work. I have known dust
accumulated on the face of the prism give a false obscurity to the
spectrum ;* persons (scientific and otherwise) who never could see a
rainband at all ; others who insisted on the horizontal dust lines as
rainbands, and even well-practised observers differ very widely in
strength estimates (a matter which may possibly affect my own
diagrams).
(3). Observe generally at the altitude which you may have selected
as a standard, but do not altogether confine yourself to this, and
note :
* To guard against this I cement a plate of microscopic glass over the eye- hole
of the spectroscope.
12
(a) If the rainband is strong on the horizon and weakens
towards disappearance (or nearly this) at 15 or 20 degrees
above, distrust it as a prognostic of rain.
(b) If strong on the horizon, and still strong at the height
above mentioned, trust it as a prognostic.
(c) If strong on the horizon, above, and also to the zenith, or
nearly so, then, as Professor Smyth says, "Beware!"
He had only known two such instances (at the time he
was writing) and deluges followed.
(4). A rainband will sometimes shew at the same time, of varying
intensities on sky, clouds, and breaks in clouds. The respective
intensities should be considered and valued in relation to the
character of the various objects examined, e.g., I observed, on an
occasion this summer (1881), at 9 a.m., a faint (No. 1) rainband on
an apparently perfectly pure blue sky, and a stronger one (moderate
No. 3) on some by no means dangerous looking clouds floating in it.
Rain soon came, and I have no doubt both sky and clouds were
nearly equally charged with moisture, though under different con-
ditions.
(5). The solar lines in the spectrum may be brought in aid in ob
serving. When these are bright, clear, and sharp, rainband is usually
absent ; when they are obscure and seen faintly, rainband is generally
present. A lady, who assisted me in observing, used to judge with
success by the appearance of these lines when she felt in doubt about
the rainband itself.
(6). The general rules of conduct of the rainband may be summed
up as follows :
(a) It indicates an excess of moisture in the air (often in-
visible) and presages according to its intensity, sometimes
upon a clear, and sometimes on an opaque sky, the coming
of rain and its quantity. "It is strong when the air is
saturated with moisture ready to fall." (Piazzi Smyth).
(b) When the actual rain comes, the band frequently drops
in intensity, sometimes becoming even quite faint during
heavy rainfall. In summer, during a warm wind, a pro-
nounced rainband will accompany rain. If the two last
are not found together, it is during the prevalence of
cold winds. In winter, a moderate rainband may be
observed for some time, and yet rain does not fall. This
is found during the presence of a warm wind, which
holds the air moisture in suspension. Upon change to a
cold wind, rain follows.
(c) A long continued faint, or faint to moderate rainband is
pretty sure to be followed by rain, generally in quantity.
(d) A faint, or perhaps faint to moderate rainband may be
often seen upon fog or mist. It does not necessarily
presage rain, unless it increases to strong, which it
seldom does. If the sky above fog or mist be clear, the
spectroscope should be elevated to examine this as the
test for the rainband true.
(7). Ozone and rainband are usually in accord with one another,
both weak during cold winds and cold fogs, and both strong during
warm winds and warm mists. Observations on the electric condition
of the atmosphere might be usefully combined.
Lastly. Observers should not be discouraged if the rainband pre-
dictions are not always immediately and exactly fulfilled. If there
were but one form of rainband, and one condition of moisture in the
air, we might get the formula : Rainband =r rain ; no rainband =
no rain, in all cases ; but this is far from the fact. The spectroscope
is a delicate instrument of research, and the intensity of the rainband
admits of degrees which maybe considerably modified by, (1) cir-
cumstances of observing, such as width of slit, altitude of spectro-
scope, time of day, and part of the sky examined ; (2) conditions of
the matter examined in its graduations of transparent vapour, mist,
cloud, and rain (the size and proportion of the aqueous particles
varying in each) ; and (3) by other meteorological conditions and
especially that of temperature, as largely affecting the quantity of
moisture held in suspension.
If the character of the band is liable to be thus modified, the judg-
ment to be formed as the result of its examination must be neces-
sarily applied with caution, and with due regard to the probable
effect of these modifications.
J. RAND CAPRON, F.R.A.S.
Guildown, Nov. 1881
14
PART II.
THE RAINBAND VINDICATED,
IT is now some four years since that in the pages of the Meteorological
Magazine I essayed to give a popular character to a comparatively
unknown branch of science in my " Plea for the Rainband."
Has this plea been successful, and has the rainband vindicated its
position as a weather prognostic 1 I venture to think that both
these questions may be answered in the affirmative. Soon after the
publication of the article, I was requested by a well-known optician
to permit a reprint of it as a companion to the spectroscope, and
before long many copies of it were distributed amongst meteorologists
and others. This brought the matter before the public, and not
long after rainband spectroscopes, pamphlets, and discussions showed
that a keen interest was felt in the subject.
Of course, as in the case of all other new objects, the first rush for
information and possession by and by passed, and the interest in
it to a certain extent subsided. I have recently found, however,
from enquiries and correspondence addressed to me, that this, though
diminished, has by no means died out. I propose, therefore, to
justify what the "Plea" advanced by shortly stating the subsequent
progress of rainband spectroscopy to the present time.
The impetus given to the enquiry may be recognized in three
ways: by (1) its recent literature; (2) the increased use of the
spectroscope as a meteorological adjunct ; and (3) recorded observa-
tions and their results.
THE RECENT LITERATURE.
In taking up the first subject, the recent literature of the rain-
band, I propose to deviate somewhat for the purpose of introducing
an interesting early notice of it which escaped my attention when
writing my " Plea," and which it would be unjust now to omit. It
dates back as far as 1869, and will be found in the Meteorological
Magazine for July and October of that year, vol. iv. Nos. xlii. and
xlv., " The indications of the sky." The first part of this article
describes and figures Saussure's cyanometer and its mode of use, and
then after quoting Kaemtz on the blue colour of the air comes the
following passage : " In spite of ourselves the above extract has led
from the original subject of this article, the cyanometer, to what
must, we presume, be held to be its legitimate successor, the spectro-
scope." The second part of the article treats of the spectroscope and
its advantages to meteorologists, and by an extract from the British
15
Association Report for 1868, "Observations on the atmospheric
lines of the solar spectrum in high latitudes, by George Gladstone,
F.C.S., F.R.G.S.," it points out the distinction between " atmospheric"
and " solar " lines, and shows how these former are always most pro-
minent with a low sun, while scarcely visible with a high one. Also
that the red end of the spectrum varies under similar circumstances
in length and brilliancy. Prof. Roscoe's " Spectrum Analysis " is
quoted, a figure of a pocket spectroscope (reproduced here, Fig. 1) is
Fig. 1.
given, and the article ends thus : " No one can tell what secrets lie
hid in these atmospheric lines, but to us it seems that by their careful
and systematic observation the ' Message from the Stars ' which has
taught us so much may be rivalled in practical importance by a
'Message from the Sky.' "
This prediction may not have caught the full import and meaning
of the atmospheric bands and lines, but at least it forecasts the value
they subsequently attained in meteorology.
Passing from this, we will refer to a correspondence in the Times,
which took place in the latter part of 1882, and in which both sides
of the question were jealously advocated. Prof. C. Piazzi Smyth
here pens a series of letters in favour of the rainband. In one of
these he states he saw a spectroscopic rainband, " the blackest and
most intense of the season," and " destructive floods followed." As
the rainband cleared away, " magnificent harvest days followed. '
Mr. Ralph Abercrombie sees no value in the rainband, and pins his
faith upon " isobaric lines," and the forecasts of the Meteorological
Office derived therefrom. The Duke of Argyle in a yachting cruise
could not see that the rainband had any predictive value, and thinks
Prof. Smyth's case was a " good shot." Per contra, Mr. Cory, F.M.S.,
contends for the value of the rainband, and gives reports of a series
of observations proving his case. Agricultor (in the English
Mechanic) " has been much struck by the accuracy with which the
rainband appearance predicts coming rain."
Mr. Abercrombie's isobars are most amusingly discounted by Sir
Edmund Beckett in a letter containing a long list of official weather
prophecies and their want of fulfilment, and recommending " a return
to Zadkiel." In June, 1883, my weekly weather report to the
Surrey Advertiser contained the following : " Of these rainfalls, the
only indication was the rainband, the barometer throughout standing
fairly high (between 29-84 in. and 29-99 in.)" Thus the public prints
not only took an interest in, but on the whole supported the rainband
theory.
16
As observers and observations increased, more solid literature was
developed, including : Nature, vol. xxvi., pp. 552-4, " Spectroscopic
Weather Discussions," by Prof. C. Piazzi Smyth, in which the whole
subject is reviewed in a condensed form with instructions to observers,
and illustrated by two diagrams of the D part of the solar spectrum
under considerable dispersion, the one taken in August, 1882, under
moist air conditions, and the other on September 4th, 1882, after
a whole week of very dry weather. In this article it is shown
that, apart from the spectroscope, the wet bulb difference only
slightly indicated the sweeping away which took place in September
of the water vapour details shown in the August spectrum. On
another occasion Prof. Smyth defended the rainband, Nature, vol.
xxix., p. 525, " Rainband spectroscopy attacked again." In an essay
read before the Phil. Society of Washington, and printed in the
American Journal of Science, the writer of it referred to the " unsatis-
factory evidence " of the rainband, because " if the spectroscope is first
turned to the sky in any direction, and afterwards to a white wall
fifty feet distant, it will be found impossible to distinguish between
the appearance of the rainband, as shown by the whole atmosphere,
and by the layer fifty feet thick/'
The Professor disposes of the objection by promptly pointing out
that " the white wall reflects the light and sky spectrum solar lines,
and telluric lines and all ! "
Of the books and articles published, the following were kindly
sent me by the authors :
" The Science Monthly," illustrated, for December, 1883. " The
Hygro- Spectroscope (or Rainband Spectroscope)," by F. W. Cory,
F.R.Met.S., with illustrations of a spectroscope and a rainband
spectrum.
" How to foretell the weather with the pocket spectroscope," F. W.
Cory (Chatto and Wiridus, 1884) ; 86 pages, and 10 illustrations of
instruments, charts, &c. The Appendix contains the September,
1882, Times correspondence in full.
" Observations of the Rainband from June, 1882, to January
1883," by Hugh Robert Mill, B.Sc., communicated by Prof. Tait to
the Proceedings of the Royal Society of Edinburgh, with a chart.
" The Rainband : How to observe it, and what to expect from it,"
by Hugh Robert Mill. Hilger, 1883. With four figures and a
chart.
In the above papers and volumes are contained much useful in-
struction in the use of the spectroscope, and valuable tables and
statistics of rainband results, some of which are referred to later on.
THE INCREASED USE OF THE SPECTROSCOPE.
The increased use of the spectroscope quickly followed the publi-
cation of the " Plea."
Mr. Browning, at my suggestion, prepared a " standard " instru-
17
ment (Figs. 2 and 3), in which was represented a spectrum, as nearly
like as possible that represented in the frontispiece to the " Plea."
In this instrument was introduced what I considered for the
special purpose an improvement, viz., a fixed slit. This showed ^the
lines about as wide as in the plate, and in a series of observations
secured their correspondence.
THE STANDARD SPECTROSCOPE.
Fig.
Of course many other opticians soon began to supply "rainband
spectroscopes," but these varied considerably in power and disper-
sion, and thus did not realize what was my idea of uniformity of
observation. I do not wish to specially recommend any maker, but
I think it really would be of great advantage if the Royal Meteoro-
logical Society or some other competent tribunal would define the
width of slit, dispersion of prisms, and the magnifying power to be
used. Every observer who has tried several spectroscopes knows
how the appearance of the rainband varies according to these
incidents.
One important requirement not yet fulfilled is a gauge or micro-
meter to estimate the tint and width of the rainband or bands. The
width may be measured (though with difficulty in small instruments)
by some form of moving web or point, but a comparison spectrum
for tint is far more difficult to obtain. Mr. Mill made to me a very
ingenious suggestion of the use of didymium for this purpose. This
gives as a salt in solution, or as a component of glass, an absorption
band, varying in tint with the thickness of the quantity of the solution
or of the glass, and he proposed to use a sliding wedge-shaped cell or
plate, and to adjust this till it accorded with the rainband.
Unfortunately the didymium band falls exactly in the place of a
rather strong low sun band, on the more refrangible side of D, and
is complicated by it. I propose to avoid this inconvenience by means
of a reflecting prism so arranged that the light to pass through the
didymium solution or glass shall come from the zenith. For micro-
18
metric measurement of the band width, and for comparing the didy-
mium or any other selected band with the rainband, I know of no
better arrangement than one illustrated below (fig. 4). In this case
the slit plate is divided horizontally in two, and the upper half with
its spectrum is made by means of a micrometer screw to traverse the
lower half as shown in the diagram (fig. 5).
By this means measurements and comparisons may be easily made,
e.g., the D lines in the upper spectrum may be used to measure the
width of the rainband in the lower, or the didymium band in the upper
may be brought into direct comparison with the rainband. The D
line or any other may also be brought over and compared with F or
other of the solar lines. All these comparisons are thus rendered
less difficult than when the bands and lines are a distance apart.
It has been proposed to place a " condensing lens " in front of the
slit, but I do not for ordinary use see any advantage in it. The sky
light cannot be condensed, and I doubt whether in any picture
Fig. 4
formed on the slit of a small spectroscope it would be possible to dis-
tinguish a cloud spectrum from that of the sky.
In the case of larger spectroscopes, with considerable slit length,
the device might perhaps be more useful.
OBSERVATIONS AND THEIR RESULTS.
As the number of observers, evidenced by the sale of instruments
has increased, so also have the methods, quantity, and quality of
the observations.
With regard to the methods, the more simple form of observation
recommended by me in the ' ; Plea " has been by some extended, and
19
the lesser rainbands, the dry air bands, and the atmospheric linos
other than D have all been enlisted into service. By the varying
thickness and appearance of these, the judgment obtained from the
larger rainband near D has been reinformed and strengthened.
Much information on this head will be found in Mr. Cory's " How
to foretell."
That observer, too, has extended his scale from Prof. Piazzi
Smyth's 10 to 20. After much experience, I still think the scale
given in the " Plea," to 5, is the more useful for general observers,
except that I have introduced 0--1 as indicating a very faint band.
Mr. Cory says " the rainband is never absent." This may be strictly
true, but it is more convenient in practice to begin with as indi-
cating all that is seen in dry fine weather.
Mr. J. A. Bramley Moore in a letter to Knowledge, No. 60, p. 485,
remarks : " (2) If the sun lines in the green instead of appearing
clear and distinct are thick and muddy, heavy rain (like thunder
rain) will follow, and this whether there is any " rainband " in the
red or not.
" (3). If on moving the spectroscope slightly to the left the "blue "
appears very light, and the dark line down is clearly seen, then wind
may be expected." He adds that this " never fails."
"(4) On one occasion on moving the spectroscope as above, the
green instead of giving way to the blue, seemed to fight with it, and
pass over it. A thunderstorm followed."
Twice since he found the same thing to occur. Mr. Cory, p. 30,
corroborates this form of thunderstorm prediction.
Mr. Cory also notices that the rainband decreases before snow, and
the diagram on his Plate III. illustrates this.
He also recommends pointing the spectroscope to the direction
from which the wind comes ; a useful suggestion.
Coming now to the question of how far the spectroscope makes
good its predictions, we have :
(1) General evidence as afforded by the statements of Prof. Piazzi
Smyth, Mr. Cory, Mr. Mill, Mr. Clapham, and others, who have
borne testimony in favour of its value for forecasting.
(2). Recorded sets of observations, either daily or as averages for
longer periods ; and either in figures, or as lines and curves, express-
ing the result in a graphical form.
In a letter to the Times of September, 23, 1882, Prof. Piazzi
Smyth gives a fortnight's notes, September 1st to 15th, 1882, in three
columns (1) Temperature, (2) Rainband intensity, (3) Rainfall at
the Royal Observatory, Edinburgh. A glance at these will show how
rain fell as the rainband increased, and how some small successive
rainbands led up to a fall of rain.
Mr. Cory has not given statistics in his book, but in a letter to the
Times, February 1st, 1881, he gives a list of observations taken at
9.15 a.m. daily for the month of January of that year. The results
are as follows :
20
1 case of 70% raiiiband was followed by heavy rain.
2 cases of 60% rain in both.
8 50% rain every time.
7 40% rain in 5, overcast in 2
cases.
9 30% 6 of rain.
1 case of 40% decreasing to 30% was followed by nimbus.
1 30% increasing to 40% rain.
1 20% 30% slight rain and
heavy snowfall.
1 20% was followed by very fine weather.
31 days.
These figures seem to be conclusive as to the rainband's predictive
value.
To Mr. Cory I am also indebted for the graphical chart, a copy of
which I give on Plate II., showing the mean per-centage of rainband
in dotted curves, and the amount of rainfall in vertical lines for each
month during the year 1882 and a part of 1883, at Buckhurst Hill,
Essex. The observations were taken in the N. direction, three times
a day, and at an angle of from 10 to 20 degrees above the horizon.
As Mr. Cory remarks in his accompanying letter to me, " there is a
decided connection between the two." The high per-centage of rain-
band in June and July, with a not excessive fall, is due to the
rainband being stronger in summer. The heavy fall in the later half
of October was preceded by a very high mean rainband during the
first half of the month. Of the fall in March, with a low rainband,
half was snow, and the actual amount of rain was very small.
These apparent discrepancies are consistent with the rainband laAvs.
Mr. Mill, in his u The Rainband," gives a graphical chart and some
tabular statements showing how his rainband predictions were ful-
filled.
Tables II., III. and IV. in that work give the results when the
rainband was compared in intensity with the Fraunhofer lines,
b and F, during seven months of 1882.
These tables show there was 8 per cent, of cases when the rain did
not, and 92 per cent, of cases when the rain did, follow maximum
rainband; and 21 per cent, of cases when the rain did, and. 79 per
cent, of cases when the rain did not follow a minimum rainband.
Table V. gives the result of observations made in Callander for
the months June to December, 1882 :
Rain predicted ... ... ... ... ... 125
Rain followed 97
Per-centage of fulfilled predictions .. 78
PLATE II.
MONTHLY RAINFALL AND RAINBAND, 1882-3.
X.
21
No rain predicted... ... ... ... ... 80
No rain followed 51
Per-centage of fulfilled prediction
64
Total predictions 205
Total fulfilments 148
Per-centage of total fulfilled predictions ... = 72
Table VI., for January to September, 1883, gives the total of ful-
filled predictions at 209, and of unfulfilled 64. Per-centage of ful-
filled predictions = 76 - 5.
With respect to the Guildown observations, these have been taken
since the 1st of July, 1880, at 9 a.m. daily, with the spectroscope,
and in the manner mentioned in the " Plea." All the barometric
and other meteorological observations for a half year are from time
to time reduced to curves upon a chart, in which, in tenths of inches,
the days of the year form the abcissce, while the readings of each
instrument form the ordinates. In these the rain is shown in tenths
of inches of fall, and the rainband in degrees of strength 1 to 5.
The rainfall and rainband portion of the chart for four consecutive
months of 1881 is shown in Plate III.
These charts if put together would extend to a length of 12 feet
2 inches, and comprise over 1,800 observations. I have not tabu-
lated the results except for yearly values, but a glance at the curves
ought to convince the most sceptical that the connection between
the rainband and rainfall is, as a general rule, well established.
The yearly values run out thus :
Table of Yearly Values of Rain and Rainband.
YEAU.
Rainfall in
inches.
Rainband in
numbers.
1881
25-68
353-5
1882
28-10
392-5
1 of Rainband
1883...
24 '35
404-5
- -Q6 of Rain
1884
18-70
314-0
It is obvious that if such a method of long-period comparison as
this shows an approximate reciprocal rise and fall in the total values
of rain and rainband it is as much as can be expected from it. If
special circumstances prevail, such as fogs and mists, which give a
low rainband without rain, we may expect to find (as in 1883 and
1884) an advance of total rainband over rain for that year.
Other observers doubtless have preserved records which have not
come under my notice ; but taking Mr. Cory's, Mr. Mill's, and the
Guildown ones alone, I think the fact is established that the little
dark " bar " in the yellow of the spectrum can well hold its own in
forecast with any other " bars," and that its character has been
amply vindicated.
It now only remains to refer to one or two meteorological subjects
allied to the rainband, but not generally finding a place with the
observations of pressure, temperature, wind, &c. These are ozone,
atmospheric electricity, and the weather compass for forecasting
invented by the late Prof. Klinkerfues.
THE RAINBAND AND OZONE.
Mr. Cory, in his " How to Foretell," (p. 32) remarks that the blue
and yellow colours in the spectrum are useful guides to the presence
or absence of ozone. If the air is very pure, the blue will be clear,
and F will stand out distinctly, while the yellow will show itself as a
true colour or have an orange tint. If the reverse, the yellow will
have a greenish hue, and the blue will be deep and dark, with an
indistinct r.
I have not particularly observed these colour changes, but the
meteorological charts above mentioned contain ozone curves on the
same principle as those of the rainband, and for similar periods. The
scale for rainband is, as before, 0-1 to 5 ; that for ozone 1 to 10 of
Negretti and Zambra's scale for their iodide of starch papers. A por-
tion of one of the charts comprising four months (the first of each
quarter of 1882) is given in Plate IV. An examination of this will
show that generally the curves of rainband and ozone agree in rising
and falling together. It does not of ten occur that ozone is nil; but when
it is, rainband also is found absent. This is indeed what might have
been expected, for with warm winds, W. and S., the rainband is re-
inforced ; with cold winds, N. and E., it is depressed. A similar
effect, but even more regular in its action, is found with the ozone
tests. Thus a S. W. wind gives the strongest tinted papers ; a N.E. wind
the lightest. We know so very little of ozone and its properties
that it would not be safe to connect its quantity in the air with con-
ditions of moisture, though such a connection may be fairly suspected.
Guildown is remarkable for exceeding in average quantity of
ozone places situate much nearer the sea. This is probably due to
its altitude of 225 feet, and to an open valley to the W. from which
there is a prevalent air current.
ATMOSPHERIC ELECTRICITY.
In the "Plea" I suggested that observations of atmospheric elec-
tricity might usefully accompany those of rainband. The rela-
tion of these to each other becomes more apparent when the influ-
ence of electricity upon aqueous particles is considered, and how the
size of these latter determine the strength of the rainband.
When these are minute in the form of transparent water vapour,
evidenced only by the hygrometer, the rainband is strong. When
the particles are larger in the shape of visible fog or mist, the rain-
band considerably weakens. Lastly, when the gross particles fall as
heavy rain-drops or snow-flakes, there is frequently no rainband, or
23
hardly any. Now, the property of atmospheric electricity (as shewn
in the familiar experiment of a sponge suspended from the prime
conductor of an electrical machine) is, when developed, to cause the
finer cloud particles, by mutual repulsion in the first instance, to
coalesce and descend as rain. Electric action is always strongly
marked when rain suddenly falls, even to the extent of yielding
sparks from a properly insulated conducting wire, and it has evidently
much to do with the breaking up of clouds. I have not traced, as
Mr. Moore and Mr. Cory have, a forecast of storms by the aspect of
the rainband, or the colours of the spectrum, but I have noticed a
sudden increase of atmospheric electricity, and a weakening of the
rainband frequently to accompany a clearing shower.
Those who desire to combine observations of atmospheric electri-
city with those of the rainband, will find the mode and the apparatus
used fully described and illustrated in the Metewological Magazine for
August and October 1885.
The collecting is effected by means of elevated points, or a water
stream, and the examination by a Bohnenberger suspended gold leaf
electrometer ; or by a Thomson's quadrant electrometer, excited by
a chloride of silver battery.
KLINKERFUES' WEATHER COMPASS.
Lastly, I have to notice an instrument invented by the late Prof.
Klinkerfues, of Gottingen, for the purpose of weather forecast. It is
an ingenious combination of an aneroid barometer, a string hygro-
meter, and a wind scale, jointly affording indications of the effects of
pressure, moisture and wind. A general idea of its construction will
be obtained from the annexed wood cut (Fi; 6).
Fig. 6.
24
In this drawing a is the aneroid vacuum box; b, moveable
weather scale ; s, moveable wind scale ; c, hygrometric hair string ;
d, segment actuating index; e, lever connecting barometric with
hygrometric effects; / and g, arms to which the hair string is
attached ; h, lower end of index, the upper end of which projects on
to the weather scale.
The working arrangement is such that in dry air conditions the
hygrometer string acts with the barometer for a rise ; and in moist
weather against it ; and the two instruments thus comjbine in a joint
reading, depending on the variation of each. When fine weather is
approaching, the hygrometer will give the barometer an extra " pull
up," and in moist assist it in "a fall," while at times the two may
balance one another.
In this way more variation is obtained than with the ordinary
barometer, and the concurrent effects of pressure and moisture are
read off.
To forecast, the method is this
At any definite time, say 9 a.m., set the outer dial with the words
describing the weather, " Rain," &c., with the inner wind dial, so that
the word denoting the prevailing weather will stand against the wind
direction at the time, e.g., set the centre of the larger dial " Change "
against the centre of the wind dial " North ; " then turn both dials
together, until the index covers the words "Change " and " North."
Twelve hours after, we will suppose the index to have risen to
" Fair/' and the wind to have changed to the " West." We must now
move the outer dial only in the wind direction, so as to correspond with
the pointer " West."
This will bring " Change " again under the index, and indicate that
the prospect of fair weather shown by the index rise has been
neutralized by the wind change, and changeable weather may conse-
quently be predicted. Had the wind gone Eastward with the index
rise, the words " Set Fair " would have taken the place of " Fair," and
continuous fine weather would have been foretold. Of course no
meteorological instrument is infallible ; but I may fairly say that
with proper care in setting, much may be made of the " Klinkerfues "
for weather forecasting. A friend of mine, a large farmer, has used
one for years ; and to quote his own words, " I always set my farm
work by it."
To prevent disappointment in its use, it is necessary to remember :
1. That its movements are relative, and are not intended to com-
pare with those of the barometer, being on nearly twice the scale,
and acted upon hygrometrically.
2. It must be set each time as before described for a forecast. If
left alone with " Change " at top, the index will sometimes run right
off the marked part of the dial, in consequence of the greater range.
When sent from abroad by the patentees (Messrs. Biernatzki & Co.,
of Hamburg), the index is secured to ensure safe travelling. This
has to be released, and then set by a screw at the back of the case,
either by a barometer, or to the prevailing weather sign. This
25
setting should not afterwards be altered, the dials being in future
adjusted to the index, and not it to them.
How sensitive the hygrometric action is, may be seen by breathing
on the back of the case, when the index will at once be in movement.
The instrument, although now introduced some years, has not been
so well received as it deserves, owing, as correspondents have told
me, to the setting arrangement not being properly understood. It
is, however, after a little practice, very simple. Though not in
strictness an instrument fully adapted to scientific research (a divided
scale would add to its value), it certainly merits attention, if it will
only succeed in saving a hay crop, or telling the farmer how long his
stacks may remain out, matters as to which his mercurial barometer
sometimes misleads him. Probably a better acquaintance with it by
meteorologists would more fully develope its qualities as an adjunct
to the rainband spectroscope, for which it seems well adapted.
26
APPENDIX.
ATMOSPHERIC ELECTRICITY.
To the Editor of the Meteorological Magazine.
SIR, Noticing a reference in your current number to the subject
of atmospheric electricity, it occurred to me that you might be
interested to know of some experiments in that regard which have
been tried here. The collecting sources are two
(1) A long cane carrying a brass ferule armed with three fine
platinum points, elevated some 30 feet above the ground,
on a building situated near the Observatory.
(2) A tower situated on a rounded eminence, 620 ft. to the N.
of the Observatory, its base being 55 ft. above it.
The conducting wires are of copper, gutta percha covered, and are
led into the Observatory. The cane on the building is insulated, by
being divided by a vulcanite stem protected by a copper funnel, the
wire passing inside the upper half.
The pole on the tower terminates in a corona of 25 platinum
points, and this is insulated by being placed on a glass rod, which
runs through a Mascart bottle filled with sulphuric acid. The corona
I is about 30 ft. above the base of the tower.
The receiving apparatus is of three sorts
Fig. 7.
27
(a) A Bohnenberger electrometer composed of a single gold leaf
suspended between the opposite poles of two Zamboni's
piles.
(b) A pith ball electrometer, consisting of two gilded pith balls
suspended in contact by fine platinum wires.
(c) A Thomson quadrant electrometer of simple form, in which
the ordinary arrangement is reversed, the needle being
used to test the wire, while the opposite pairs of quadrants
are kept permanently charged by two of De La Rue's
chloride of silver batteries of 30 cells each, connected at
centre to earth (Figs. 7 and 8).
The needle carries a mirror, and the deflections are read off on a
scale in the usual way. The instruments are usually examined at
9 a.m. , and specially as occasion offers.
The Bohnenberger is the most sensitive, and is affected by small
currents. The pith balls are used as these are found stronger. The
quadrant is employed for measurement of quantity and duration of
current. Generally the lower points are found to give stronger
indications than those on the Tower, which I attribute to the greater
resistance in the longer length of wire.
In calm weather the electricity is usually feeble and Positive. In
broken weather Negative electricity is oftener developed ; but some-
times the sign changes rapidly. On one occasion at least I have
found the upper and lower points of opposite signs simultaneously.
As a shower of rain or hail comes on, the current strengthens, and
sparks now and then fly from the wires. Once my assistant obtained
long ones from the wire, and rapid discharges from a pint Leyden
jar, coupled up to it. The quadrant arrangement seems a useful
one, as avoiding the need of a " replenisher," and as affording a con-
stant charge ; and I have every reason to be satisfied with it.
I have not at present examined and arranged the results obtained
since the apparatus has been at work, but I hope to do this shortly
in connection with the general meteorological observations taken at
the same time. We seldom get heavy storms, as they are apparently
broken up by the Hogs' Back and opposite hills ; and cases of light-
ning injury are rare. I have not yet tried a small captive balloon,
but probably valuable results might be had by thus extending the
exploring height. The observatory (51 13' 39 "'2 N. ; 028'47"W.)
faces south on the spur of the Hogs' Back, and is 150 feet above
Guildford town, and 250 feet super mare. Booker's Tower is marked
on Ordnance Map, B M. 305 ft. 5 in.
J. RAND C APRON.
Guildown Observatory, July 18th, 1885.
28
ATMOSPHERIC ELECTRICITY.
To the Editor of the Meteorological Magazine.
SIR, In continuation of my former letter, and before stating the
" results," I wish to describe another way of collecting electricity
from the air which has been adopted. This consists of a copper can
about six inches across and eighteen inches high, and containing
about two gallons of water. This is furnished with a long tube or
spout, ending in a brass tap with a small aperture. It is placed on a
Mascart insulating stand, and connected with the electrometers by a
copper wire. As soon as the tap is turned on, and the water issues
from it, the can at once becomes charged with electricity of the same
sign as the surrounding air. The effect is greatest when the stream is
broken into drops in its fall. This apparatus (Fig. 9) was found to
give, at 15 ft. above ground, deflections of 5 and 10 with the quad-
rant electrometer, when both sets of points gave no signs of charge
whatever. At another time, and when only 4 ft. from the ground, it
afforded results, the air being so damp that it was difficult to excite
the electrophorus, with which the quadrants were at that time
charged. It is thus very sensitive, and at the same time portable.
The general observations have been hardly numerous enough to
warrant the assertion of fixed laws, but they seem to establish the
following facts pretty satisfactorily :
29
(1) The wind is evidently a strong excitant of electricity. One
bright morning, as gusts of wind swept across an outside
insulated brass plate, each gust was accurately repeated
by a beat of the gold leaf suspended in the Bohnenberger
electrometer.
(2) As a rule, though not without exception, the mornings
marked " blue sky " showed feeble positive electricity.
The exceptions seemed to have occurred lately, when
much morning mist has prevailed, and the hygrometer
has stood high.
(3) Clouded and damp mornings, though also with exceptions,
have yielded the negative sign.
(4) Storms (with one exception) have always given a strong
negative sign as they approached the "points." As
snow or rain fell, this changed to positive, and in
several instances there was a change back to negative
before the indications ceased. The exception was a
storm on the 24th of July, 1884, at 8.30 p.m., after a
fine day, when the sign was first positive, then negative,
and ultimately positive again. On rain or snow falling,
the electrical conditions in these cases, became very
marked, sparks flying from the ends of the conducting
wires, the pith balls diverging widely, the mirror deflec-
tions amounting to 80, and the gold leaf being torn
away or broken up.
(5). Probably strata opposite in sign may co-exist at different
elevations above the earth's surface. Thus on December
6th, 1883, at 10 a.m., a snow-storm coming on, the
tower points were strongly negative, but the points near
the observatory were charged positively, and this per-
sisted for a quarter of an hour.
(6). The observations do not show with any certainty whether
the quantity of electricity varies with the height of the
points above the observatory. Five instances are, how-
ever, marked "from the tower only," and two "from the
lower points only." The tower current has at times
been the stronger. Generally it is the weakest, but this
I attribute to the resistance of 300 feet of wire, which
complete its connection with the receiving apparatus.
From what I have described, it will be seen that periodic observa-
tions of atmospheric electricity are possible with simple and inexpen-
sive apparatus. Where expense is not an object, it would be easy to
convert these into self-recording forms (as at Greenwich), and thus
obtain a continuous and more valuable series of observations.
J. BAND CAPRON.
Quildown Observatory, August 9th, 1885,
30
INDEX.
PAGE
Abercrombie, R., Rainband and
Isobars 15
Agricultor on Rainband 15
Angstrom, Prof , Solar Spectroscopy 5
Argyll, Duke of, on Rainband 15
Atmospheric Electricity (appendix).. 26
,, Apparatus for Collecting and
Testing 26
and Rainband 13, 22
Results at Guildown 29
,, and Rainband Spectra de-
scribed 7
Beckett, Sir E., on Official Forecasts 15
Collecting Apparatus of Atmospheric
Electricity described 8
Cory, F. W. , " How to Foretell "... 16
Monthly Rainfall and Rainband 20
,, Percentage Result of Predic-
tions 20
Diagrams, Rainfall and Rainband,
described 9, 21
Diagram, Rainbaud and Ozone, de-
scribed 22
Electrometer and Battery for observ-
ing Atmospheric Electricity, de-
scribed 27
Fogs and Mists, Effect of on Spec-
trum 10, 13
Gladstone, G., Research on Atmo-
spheric Spectrum 15
Guildown, Result of Observations at:
for Atmospheric Electricity 29
,, for Ozone 22
,, for Rainband 21
Klinkerfues Weather Compass de-
scribed 23
,, Forecast by 24
Micrometer Slit Plate described 18
Mill, H. R., Per-centage result of
Predictions 20
"The Rainband" 16
,, Use of Didymium Wedge 17
Moore, Bramley, J. A. , Observations
on Spectrum 19
PAGE
Ozone, Effect of Cold Winds on ...7, 22
Effect on Spectrum 22
And Rainband 13, 22
,, And Rainband Compared 22
Predictions by^Rainband 8,
12
Rain, effect on Spectrum 8, 12
Rainband and Atmospheric Elec-
tricity 22
Description of 5
,, History of 5
,, Literature (recent) of 14
,, Mode of observing 6, 11
Monthly, and Rainfall (Cory).. 20
,, Observations and their Re-
sults 12, 18
and Ozone 13, 22
Predictions by 8, 12
and Rainfall, Guildown, 1880
and 1881 9, 11
and Rainfall, Guildown, 1881 11 , 21
,, Rules of conduct of 12
,, Scale of Degrees 7, 19
,, Spectra (see Frontispiece) de-
scribed 7
,, Spectroscope for Observing re-
quired 6, 17
,, Strong, instances of 5,11, 12
,, Yearly Results at Guildown ... 21
Smyth, Prof. Piazzi, Researches in
Rainband Spectroscopy ...5,12, 14
Snow, Effect on Rainband 10, 19
Spectra Atmospheric and Rainband
described 7
Spectrum, double, described 18
Spectroscope, Early Application of... 5
Early Figure of 15
,, Increased use of 16
,, Micrometer slit plate described 18
,, Rainband described 6
Standard 17
Thunderstorm, Predictions of 19
Weather, Forecast by Klinkerfues
Compass 24
Winds, Cold, Effect of on Spectrum..
7, 13
G. SHIELD, PRINTER, SLOANE SQUARE, S,W.
UNIVERSITY OF CALIFORNIA LIBRARY
