~~ 

and explained (after Mr. J. W. Flower, Q. J 

Fan. 5, 1871] 
NATURE 
199 

sandpiper, which had been killed by Mr. Petherick himself, on 
the 9th of May last, as near as Cheddar, which would bring it 
quite within range for mention in the paper 
MANCHESTER 
Literary and Philosophical Society, November 29.— 
R. Angus Smith, Ph.D., F.R.S., vice-president, in the 
chair. Mr. R. D. Darbishire, F.G.S., exhibited a series 
of palolithic instruments from the valley of the Little Ouse, 
Geolog. Soz. 
xxv. 449) the general features of the district and the deposit 
of the beds and the implements—Mr. W. Boyd Dawkins, 
F.R.S., indicated the age of these deposits as related to the 
period of the existence of Liephas primigenius in the district of 
the south-east of England and the adjoining portions of the bed 
of the German Ocean and the north-west portions of France.— 
“The Tails of Comets, the Solar Corona, and the Aurora con- 
silered as Electric Phenomena,” by Prof. Osborne Reynolds, 
M.A. Although the tails of comets are usually assumed to be 
material appendages which accompany these bodies in their 
flight through the heavens—and the appearance they present cer- 
tainly warrants such an assumption—yet this is not the only way 
in which these tails may be accounted for. They may be simply 
an effect produced by the comet on the material through which 
it is passing, an effect analogous to that which we sometimes see 
produced by a very small insect on the surface of still water. 
We see a dark spot, and on looking closer we find a small fly or 
moth flapping its wings and creating a disturbance which was 
visible before the insect which produces it. There is nothing 
else that we can conceive their tails to be, so that they must be 
one or other of these two things: either (1) material appendages 
of the nucleus, whether the material be limited to the illuminated 
tail or surround the comet on all sides ; (2) matter which exists 
independently of the comet, and on which the comet exerts such 
a physical influence as to render it visible. There can be no 
doubt that if these tails are matter moving with the comet, this 
matter must be endowed with properties such as we not only 
have no experience of, but of which we can form no conception. 
This alone would seem a sufficient reason for rejecting the first 
hypothesis. | Moreover, on the second hypothesis there is no 
difficulty in the immense velocity with which these tails are pro- 
jected from the head or whirled round when the comet is in 
perihelio. For to take the ‘‘negative shadow” as an illustration, 
here we should have a velocity of projection equal to that of 
light, and the only effect of the whirling would be a slight lag- 
ging in the extremity of the tail, causing curvature similar to that 
which actually exists. And whatever the action may be, if its 
velocity of emission or transmission be sufficiently great, this 
effect will be the same ; but whether this hypothesis is to be re- 
jected because involving assumptions beyond conception or con- 
trary to experience, must depend on the answers to the following 
question : Do we know, or can we conceive, any physical state 
into which any substance which can be conceived to occupy the 
space traversed by comets could possibly be brought so as to 
make it present the appearance exhibited by comets? Now I 
think the answer must be in the affirmative, and that we may 
leave out the terms conceiveand conceivable. For electricity 
is a well-known state, and gases are well-known substances ; and 
when electricity, under certain conditions, as in Dr. Geissler’s 
tubes, is made to traverse exceedingly rare gas, the appearance 
produced is similar to that of the comets’ tails ; the rarer this 
gas is, the more susceptible is it of such a state, and so far as we 
know there is no limit to the extent of gas that may be so illu- 
minated. Hence we may suppose the exciting cause to be 
electricity, and the material on which it acts and which fills space 
to have the same properties as those possessed by gas. What 
is more, we can conceive the sun to be in such a condition as to 
produce that influence on this electricity which should cause the 
tail to occupy the direction it does. For such an electric dis- 
charge will be powerfully repelled by any body charged with 
similar electricity in its neighbourhood. The electricity would 
be discharged by the comets on account of some influence which 
the sun may have on them, such an influence being well within 
the limits of our conception. The appearances of the comet in 
detail, such as the emission of jets of light towards the sun and 
the form of the illuminated envelope, are all such as would 
necessarily accompany such an electrical discharge. In fact, if 
the possibility of such a discharge is admitted, I believe it will 
explain all the phenomena of comets. As to the possibility, or 
even the probability of such a discharge, I think it may be estab- 
| lines correspond to the light from no known substance. 

lished on very good grounds. The tails of comets may or may 
not be one with their heads ; but whichever is the case, it is cer- 
tain that the difference in the appearance of comets and of planets 
indicates some essential difference either in the materials of which 
these bodies are respectively composed, or else in the conditions 
under which their materials exist. Now from the motion of 
comets we know that their heads follow the same laws of motion 
and gravitation as all other matter, and therefore we have good 
evidence, so far as it goes, that comets and planets are similarly 
constituted as regards materials. And since the appearance of a 
comet changes very much as it passes round the sun, any assump- 
tions with regard to the material of comets, in order to account 
for their difference from planets, could not account for 
the variety of appearance the same comet presents at different 
times. On the other hand, the conditions of comets and planets 
must necessarily be very different, from the extreme difference 
in the shapes of the orbits they describe. Each planet remains 
nearly at a constant distance from the sun (whatever that dis- 
tance may be), so that the heat or any physical effect the sun 
may have upon it will also be constant ; on the comets its action 
must change rapidly from time to time, particularly when the 
comet is in certain parts of its orbit. Hence we may say that 
the temperature and general physical condition of planets is 
nearly constant, and that of comets for the most part continually 
varying. From these reasons it seems to me not only possible, but 
probable, that these strange visitors to our system are clothed 
in electrical garments with which the regular inhabitants are un- 
acquainted. The electricity must after all depend on the com- 
position of the comet, for known substances do not all show the 
same electrical properties. Hence by assuming comets to be 
composed of various materials, we have a source to attribute 
the different appearances presented by the different in- 
dividuals. To the same source we may attribute the irregu- 
larity in the direction of their tails and the lateral streamers 
they occasionally send out. Secondly, I think this electrical 
hypothesis is supported by the to me seeming analogy 
between comets, the corona, and the aurora; an analogy 
which suggests that they must all be due to the same cause. They 
may be all described as streams of light or streamers, having their 
starting point more or les$ undefined, and traversing spaces of 
such extent and with such velocities as entirely to preclude the 
possibility of their being material in any sense of that word with 
which we are acquainted. The aurora has long been considered 
as an electric phenomenon, and recently the same effect has been 
produced by the discharge of electricity of very great intensity 
through a very rare gas, there being no limit to the space which 
it will thus traverse. This being so, why should not the tails of 
comets and the corona also be electric phenomena? Their ap- 
pearance and behaviour correspond exactly with those of the 
aurora, and there is surely nothing very difficult in imagining the 
sun which is the source of so much heat being also the source of 
some electricity. Neither will there appear anything wonderful 
in the electricity of comets when we consider that of the earth. 
We must not look on our inability to explain the cause of such 
an electric discharge as fatal to its existence, for we cannot any 
more explain the existence of the electricity which causes the 
aurora. If we cannot explain from whence these electricities 
come, we can at least show that the conditions which are most 
favourable to the development of the aurora exist in much greater 
force on the comets than they do on the earth. The greatest de- 
velopment of the aurora borealis takes place at the equinoxes. 
There is a cessation in summer, and another in winter. Now, 
the equinoxes are the times when the action of the sun on our 
northern hemisphere is changing most rapidly. Hence the con- 
dition favourable for the aurora is change in the action of the sun. 
The same thing is pointed out by the diurnal variation in the 
electricity of the atmosphere. Now, as has been already shown, 
the change in temperature on the comets is incomparably greater 
than it is on the earth, and its variation corresponds with the 
variation in the splendour of the comet. Angstrom has also 
shown that the light from the aurora, the corona, and the zodi- 
acal light, are all of the same character, or all give the same 
bright lines when viewed through the spectroscope, and that these 
This 
indicates that whatever this light may be, the incandescent ma- 
terial is the same in all cases ; or may we not assume that it is 
the medium which fills space that is illuminated by the electric 
discharges? ‘This would be supported by the fact that the light 
from the heads of two small comets indicated carbon, whereas 
that from the tails only gave a faint continuous spectrum, For 

