Nov. 17, 1881] 
region of facts to that of laws,” are no less applicable to physio- 
logy than to physics ; although Whewell himself (in his ‘‘ History 
of the Inductive Sciences ”) had maintained the contrary. The 
full acceptance of the doctrine of evolution as our highest ex- 
pression of the order of creation seems to me to lead to a much 
nobler conception of the Intelligent Cause of that order than any 
accumulation of such individual adap'ations as might be made 
by the “‘mechanic-god” of Paley. 
WILLIAM B. CARPENTER 
56, Regent’s Park Road, N.W., November 14 
The Aurora and its Spectrum 
You have already illustrated in NATURE the aurora and e’ec- 
tric storm of January 31. Though somewhat tardily, another 
drawing with a description of this fine display has found its way 
into my hands, of sufficient interest, I think, to be added to 
those already published. It comes from Mr. C. L. Prince, the 
well-known meteorologist of Crowborough Beacon, Tunbridge 
Wells, who says, “‘I inclose a photo of my sketch ona slate. 
I had a splendid sight of the aurora at about 9h. 15m. It soon 
became very hazy, but I saw it again at 11h. 15m., when I made 
the sketch (see drawing). The arch was exceedingly well de- 
fined, and extended about 80° along the horizon. At 11h. 20m. 
some more brilliant streamers shot up along the whole convexity 
of the arch, and the two fatches of /ight became very tremulous, 
almo-t shifting a little from right to left; but I particularly 
noticed that they did not vibrate simz/taneously, z.e. if one indi- 
cated motion the other was quiescent z¢i/ the first had ceased 
to show excitement, and this action was alternating for nearly 
anhour. At 1rh. 40m. the arch had much contracted, and by 
midnight had nearly faded away. The whole phenomenon was 
free from colour. 
I noticed a few small meteors. 
Was quite calm ; wind south-west.” 
This account seems to me interesting in connection with an 
obseryation made by my friend Dr. Vogel of Potsdam, that 
during the aurora of April 9, 1871, certain lines in thespectrum | 
The night 
alternated in intensity with the character of 
some brightening as others faded. 
Mr. Prince does not mention any spectroscopic observations, 
and while noting this will you permit me to make a few remarks 
on the ‘spectrum of the aurora,” an old hobby of mine. I 
notice that Dr. Spottiswoode, P.R.S., in his lecture delivered 
before the British Association at York on September 5 last 
(NATURE, vol. xxiv. pp. 572, 3, ‘‘Onthe Electric Discharge, its 
Forms and Functions,”) has referred to the aurora in connection 
with experiments showing that the discharge in rarefied gases 
differs from that at higher pressures, and that the difference 
corresponds to that observed between the flickering play of the 
aurora and the crashing spark of the lightning-flash. After 
then referring to the questions of height and colour of the 
auroral discharge, Prof. Stokes’ theoretic view of the connection 
of earth-currents, disturbances of the magnetic needle, and solar 
radiation is dwelt upon. In Nature, vol. xxiv. pp. 613-18 
(lecture by Prof. Stokes, Sec.R.S., in the South Kensington 
Theatre, on ‘‘ Solar Physics”), this theoretic view is set forth, 
1 I commend this method of sketching to other observers, the slate pencil 
showing white cn the dark slate being readily photographed with good 
effect, displaying the aurora light7on a dark ground.—J. R. C. 
the discharge, 
NATURE 
53 
and the aurora is described as a flash of lightning passing 
through the higher regions of the atmosphere where the air is 
rarefied. There are, I think, some objections to this theory 
founded upon certain circumstances of the aurora itself, such, 
for instance, as the well-authenticated cases of aurorz seen close 
upon the surface of the earth. ; 
The passage, however, in Prof. Stokes’ lecture which particu- 
larly struck me is this: ‘‘ But what of the aurorze? It has long 
been recognised that the aurora is an electrical phenomenon. It 
has been supposed to be imitated, and there can be no doubt that 
the supposition ts a correct one [the italics are mine] by sending an 
ordinary electric discharge through a highly exhausted tube.” 
Now it may be true that the aurora is thus imitated so far as 
external appearance is concerned, and it has long been a favourite 
idea that this imitation in some way extended to the aurora’s 
actual composition ; but what does that Ithuriel spear, the spec- 
troscope, say upon that point—a point which gains the more im- 
portance from the fact that such an instrument is mentioned by 
Prof, Stokes (p. 614) as the true touchstone for the aurora? It 
says positively that Prof. Piazzi Smyth’s citron. line, the one 
trne test of the aurora, has never yet been seen in any electric 
discharge whatever which we have yet produced, whether in air 
at ordinary pressure, or rarefied ; that thered line (its companion 
in some aurorz) is equally noticeable for its absence therefrom ; 
and that of the remaining faint and less marked lines one or two 
only have with doubt and uncertainty been by some referred to 
the air spectrum as excited by the electric spark or glow. The 
late Prof. Angstrom endeavoured to place some of these fainter 
lines in accord with the spectrum bands of the violet pole in 
Geissler air-tubes, but the comparison failed on critical examina- 
tion. Prof. Vogel has also considered the aurora might probably 
be an air-spectrum modified by conditions of temperature and 
pressure. The Professor’s actual line comparisons, however, 
quite failed as to the citron and red lines, and could hardly be 
called a success as to the fainter ones. In fact any analogy 
between the aurora spectrum and the spectrum of the electric 
discharge in air is all but hypothetical, and the aurora still main- 
tains that mysterious quality which distinguishes it from electric 
discharges of all sorts, and indeed everything else, viz. its 
peculiar spectrum. 
I therefore again plead the necessity for spectrum observations 
in connection with the aurora, a point from which Prof. Stokes’ 
lecture, I am afraid, owing to its absence of any remarks on the 
subject (save that before referred to) is somewhat calculated to 
draw them away. It is certainly fossié/e that some special gas 
may exist in the upper regions of the atmosphere giving rise to 
the citron, perhaps the red, lines; but then (as Prof. Smyth 
remarks) if so, why, being an emission spectrum in the aurora, 
does it not, according to the theory of exchanges, appear as an 
absorption spectrum or dark lines in the solar spectrum? Even, 
too, could this be shown, it would still remain an unexplained 
fact that such a gas has hitherto failed to be recognised in any 
other body, celestial or terrestial. 
| To sum the matter up, the electric discharges in vacuum- 
tubes, as tested by Prof. Stokes’ prism and slit, no more repre- 
sent the aurora than did the cirrus cloud illuminated by the light 
| of the moon, mentioned by him, which also simulated it. 
Upon reliable authority the spectrum of lightning may be con- 
sidered that ordinarily given by a spark in air; but when we 
| come to rarefied discharges and the aurora, the same comparison 
does not hold good ; and where the electrician has to leave the 
matter, the spectroscopist has yet to take it up. 
To aid in solving the aurora’s mystery I would invite all 
spectroscopists, armed with suitable instruments, persistently to 
aim at accurate micrometer readings of the aurora spectrum. 
The approximate places of the lines are pretty well established, 
but their actual wave-length positions are much wanted, for so 
only may we hope to master one of the remaining riddles of 
science. J. RAND CAPRON 
Guildown, November I 
So 
Arctic Research 
“‘ProGREss of Arctic Research since the Foundation of the 
British Association,” by C. R. Markham, C.B,, F.R.S. Such 
is the title of a very able and instructive paper read before the 
Geographical Section of the British Association at York on 
September 6 last, and published # exfenso in the November 
number of the Proceedings of the Royal Geographical Society. 
The casual reader of this history may suppose it to be a fair and 
| correct record of half a century of Arctic exploration, and that 
