172 
NATURE 
[Fune 25, 1885 
For some years past a system of more or less careful watering 
has been practised in some of the largest and driest of the steam 
coal collieries in South Wales as a precaution against explosions 
—and the recent occurrences at Usworth, Lievin, Camphausen, 
and Pendlebury seem to show that similar measures are greatly 
wanted elsewhere. 
Should watering the dust (locally in the neighbourhood of 
blasting-shots, or generally in the workings) ultimately prove to 
be the panacea for great colliery explosions, then it is obvious 
that the responsibility for the holocausts that are now occurring 
lies almost as heavily upon those who, haying the power, fail to 
hasten its adoption, as upon those who continue to offer it a 
selfish or factious opposition. W. GALLOWAY 
The Colours of Arctic and Alpine Animals 
I MucH regret that I have been too busy to reply to my friend, 
Mr. A. R. Wallace (NATURE, April 16, p. 552), till the present 
moment, but this delay, unavoidable on my part, is the less to 
be regretted, since it has given an opportunity for the interesting 
facts recently adduced by Sig. Lorenzo Camerano (NATURE, 
May 28, p. 77) to be taken into consideration. As Mr. Wallace, 
with that keen penetration so familiar to all who know him and 
his writings, goes to the root of the matter under discussion and 
raises a distinct issue, I will now beg permission to offer a few 
words in reply to both these gentlemen. 
First, with respect to the physical side of the question, Mr. 
Wallace is perfectly correct in supposing that colour er se has 
no influence upon the radiating or absorbing powers of bodies 
as far as regards obscure radiation. But I would point out that 
in the present case we are not concerned with colour alone ; we 
have not merely to consider whether black or white is the best 
radiator, but we have for comparison two surfaces, hair or 
feathers, as the case may be, having, as far as we know at 
present, the same structure, and differing only in colour, The 
question before us is whether this colour-difference zz the same 
substance is associated with any difference in radiating or absorb- 
ing power, and the final answer can only be given by carefully 
conducted experiments, I may add that I have long been 
waiting for an opportunity of conducting the necessary investi- 
gation, and with aid that has been kindly offered from several 
quarters I hope before long to be in a position to arrive at some 
satisfactory conclusion. The form of experiment suggested by 
Mr. Wallace, although decidedly worth the trial, does not appear 
to me to be very safe, inasmuch as the natural structure and 
arrangement of the fur would be lost in the [process of weaving 
into cloth. Mr. Wallace’s strictures as to the use of artificial 
dyes are, however, quite sound, and in these I fully concur. I 
may further state that when this question was raised some years 
ago, I searched literature (although by no means exhaustively) 
to see whether any experiments had been recorded, and although 
many hundreds of observations upon the radiative and absorp- 
tive powers of different bodies have been made by various 
physicists from the time of Franklin downwards, I have not 
been able to find any experiment bearing directly upon the 
question under consideration. 
The point to be decided is, not only whether dark hair or 
feathers are better radiators than white hair or feathers, but 
whether the radiative power of these white coverings is less for 
that particular kind of radiation which is most greedily absorbed 
by the substance (snow) 2mong which the animals have to pass 
their winter existence. Till this problem is solved physically 
we have, as it seems to me, only the purely biological considera- 
tions to fall back upon. 
Before passing on to the more strictly zoological side of the 
subject I should like to disclaim the notion to which Sig. Came- 
rano’s letter may give rise, that the radiative (as distinguished 
from the protective) theory of Arctic colouring is original as far 
as concerns myself. With respect to the white covering of the 
warm-blooded animals, this theory was, as far as I knew at the 
time, original when first broached in 1880; but Lord Walsing- 
ham afterwards showed that the same conclusion had been 
arrived at in 1846 by Craven, with whose name it should be 
more fairly associated. The application of this theory (in a 
reversed sense) to explain the melanism of Arctic insects is 
entirely due to Lord Walsingham, and as my friend Mr. Wallace 
is disposed to give the weight of his authority to this extension 
of the theory, there is no occasion to discuss this point further 
on the present occasion. 
It now remains to point out some of the considerations which 
have led me to the belief that the protective theory of white 
colouring is not wholly sufficient. Thus, among birds there seems 
to be a tendency among the falcons (7. candicans, F. islandus, 
&c.) to become white in high latitudes—a mode of coloration 
which does not appear to me to be of much use in such species. 
These birds, as far as I know, swoop down on their prey from 
above, under which circumstances the lighter colouring would 
be of no advantage in enabling them to approach their prey un- 
detected ; on the other hand, it can hardly be maintained that 
these birds are subject to any persecution which would cause 
their lighter plumage to be of protective value. When on the 
wing the back only would be seen by another bird hovering over 
the falcon, and it is noteworthy that this part of the falcons in 
question is darker than the under side. The same considerations 
apply to the snowy owl (WVyctea scandiaca). In many other 
birds, again, such as the plovers (Charadrius pluvialts, Sguata- 
rola cinerea, &C.) and various species of Scolopacide (Tringa 
variabilis, T. subarguata, &c.), the under side only changes to 
white in winter—a change which it is impossible to associate either 
with protection from foes or with predatory advantage. On the 
other hand, it seems not unreasonable to suppose (on the radiation 
theory) that the under side of the bird, being nearest to the snow- 
covered surface of the ground, would require the most protec- 
tion. It is of interest also to bear in mind from the present 
point of view that many mammals are known to become white 
on the under side during winter. Thus, Surgeon-Major Leith 
Adams, F.R.S., states in his observations on the natural history of 
Eastern Canada? that ‘‘there is, moreover, a seemingly strong dis- 
position for the lower parts of animals to become white in winter 
—i.e. the parts in closest contact with the snow ; thus the under 
surfaces of the deer tribe are {always whitest. And, as if from 
its habit of constantly digging among the snow with its snout in 
quest of food, we find the cariboo with a white patch on its lips 
and around the hoof, &c.” Such facts as these cannot, as it 
appears to me, be explained on the protection theory ; but if any 
connection exists between the mode of colouring of an animal and 
its external conditions of life, the theory of preventive radiation 
or even the direct action of low temperature on the formation of 
the pigment seems to be more applicable. 
The objections raised by Signor Camerano, although supported 
by some interesting observations, are, I venture to think, some- 
what wide of the mark. The writer, indeed, endeavours to 
bring within the scope of the radiation theory classes of facts which 
I for one should certainly never dream of attributing to this cause, 
even if it had been demonstrated on a sound experimental basis. 
There can be no question as to the truth of his concluding state- 
ment that the causes tending to modify the colours are of an 
extremely complex character. It is this very complexity, indeed, 
which renders it so highly important to thoroughly investigate 
any explanation which bears the stamp of truth, though per- 
haps applicable to but a very limited group of facts. In view of 
these difficulties, and bearing in mind the inexhaustible re- 
sources of nature in adapting organisms to their environment by 
apparently opposite means, it is not at all surprising that cases 
should exist which stand apparently opposed to the particular 
class of cases here dealt with. There are many conceivable 
ways of enabling an animal to struggle against a severe climate 
besides that of lightening the colour of its fur, and natural 
selection would take advantage of any and every means pre- 
sented for securing this end. To say, therefore, that some 
animals become darker in winter (Cervus mandarinus), or that 
others do not change colour at all (Rupicapra europea, Capra 
zex), is no real objection to the radiation theory, but simply an 
illustration of the principle that there are many ways of securing 
the same result. Thus, in the case of the two last-named 
species, Sig. Camerano himself states that there is a great differ- 
ence in the thickness of the winter covering. Then, again, the 
statement that a more or less distinct seasonal change of colour 
is observable in many animals appears to me to have no precise 
bearing on the question—all that can be said from the point of 
view either of adaptation or climatic protection is that in such 
slight mutations we have given to us a hint as to the method by 
which the more striking seasonal changes have been brought 
about. We must regard such changes either as the incipient 
stages of a seasonal variation which could, if necessary, be 
worked up into a more perfect adaptation (protective or climatic), 
or as the vanishing remnants of a seasonal variation formerly 
important, but now useless. The facts that some animals 
which are not polar or alpine are Zeranently white, that the 
tHe t ‘* Field and Forest Rambles,” 1873, p. 124. 
