284 
chromosphere than is at present the case. It is true, that owing to 
the increased pressure at the surface of the nucleus due to a 
thicker chromosphere, the temperature there may have been a 
little higher ; but Ido not think that difference would make up 
for the increase in absorption of the chromosphere. 
Assuming then that the sun gives out more heat now in a given 
time than he did during the glacial period, and that the earth 
had already so far cooled down that her surface was not sensibly 
more warmed by internal heat than it is in our own epoch, the 
mean temperature of the earth’s climate would have been lower, 
and the sea-level line of perpetual snow nearer the Equator in 
both hemispheres ; and glaciers would have covered vast tracks 
of country which are now denuded of them. 
Again, let us go back some millions of years in the world’s 
history, till we arrive at the carboniferous period. The sun then 
would probably be emitting less heat than even during the glacial 
period ; but the earth would not have cooled down to such an 
extent, and her internal heat would be sensible at the surface. 
The mean climate of the globe would have probably been 
warmer then than it is now, and the temperature more equally 
distributed, depending not so much on solar as on terrestrial 
radiation. This being supposed, the vegetation of England and 
India in those days must have presented less difference than 
what we find at present. Does the flora of our English and 
Indian coal-beds support or upset this conclusion? Can any of 
your correspondents answer this query, or set me right if I am 
wrong in my hypothesis of solar radiation ? 
Hampstead, July 22 J. H. Rours 
P.S.—Is there any good mathematical treatise on heat, Eng- 
lish or French, up to the latest information on the subject? 
Can you or any of your correspondents recommend me such a 
treatise ? 
Telescope Tube for Celestial Photography 
I HAVE not yet seen any satisfactory plan suggested of getting 
over the difficulty experienced in celestial photography by the 
expansion and contraction of telescope tubes, by changes of 
temperature in metal tubes. 
I therefore venture to suggest the following plan, which may 
be so arranged as to keep the object-glass and camera-slide 
exactly the same distance apart, and so keep the true focus when 
once found. The arrangement would have to be modified ac- 
cording to the metal of which the tube is made, but taking a 
brass one (the most common), with the camera attached to the 
eyepiece-slide, the correction will be effected by attaching to the 
main tube, near the eyepiece, two zinc rods the length of the 
main tube, upon which they must rest loosely ; to the free ends 
of these, near the object-glass, attach a rod of iron extending 
to the eye-tube ; let this iron rod be attached to the eye-tube 
when the sensitive-plate is exactly in focus ; any change in tem- 
perature will then have no effect on the focus, for the expansion 
and contraction of the three metals will keep the distance from 
object-glass to sensitive-plate constant, All who have worked 
with a telescope giving sharp definition, will know that this is 
not an unnecessary precaution, as it may seem to some. 
Sydney Observatory, June 14 H. C. RussELL 
Colour of the Emerald, etc, 
T Have to beg “A. H.” to refer again to NATURE (July 24) 
p. 254, col. 1, line 23, where he will find it stated that ‘‘ the 
emeralds employed were canutillos from Santa Fé de Bogota. 
Their specific gravity was 2°69.” It is evident, therefore, that 
they could only be the green silicate of alumina and glucina. 
The green sapphire, known also as the “‘ oriental emerald,” is 
the rarest of all gems; and Mr. Harry Emanuel, in his work, 
‘Diamonds and Precious Stones,” speaking of it says, ‘‘In the 
whole course of my experience I have only met with one speci- 
men.” Its specific gravity would at once distinguish it from the 
true emerald. 
The Beryl A. was colourless, opaque, and had a specific 
gravity of 2°65. GREVILLE WILLIAMS 
INSTINCT, PERCEPTION, AND REASONING 
POWER OF ANIMALS 
HE correctness of the following facts, bearing on the 
above question, 1 can warrant :— 
A beautiful greyhound bitch in my possession 
NATURE 
aa 
Regis Gy cea” ioe eRe tome Wn Ret Se 
| Aug. 7, 1873 
had puppies, and I gave one of them, about a 
month old, to a friend of mine who was also living in 
Montpellier at that time. Some few days subsequently, 
on going to call at my friend’s house, I took the grey- 
hound with me. She appeared delighted at finding her 
puppy again, and expressed her strong feeling by lavish- 
ing on it, in her own way, the most tender marks of affec- 
tion. After a few days I paid a second visit to my friend 
(unaccompanied by the greyhound), when he informed 
me that, in consequence of the earnest request of one of 
his friends, he had been induced to give him the puppy, 
which had thus been removed to a considerable distance. 
I returned home, and on my arrival was struck with the 
peculiar manner in which the animal met me. There was 
nothing of her usual expression of delight—no barking, 
no jumping to and fro—but she met me with a serious and 
thoughtful look, and began slowly to smell my clothes in 
different places, with the most earnest perseverance. 
Nor was she content with a mere cursory effort to dis- 
cover the particular object, whatever it was, which, no 
doubt, she had in view; but she continued the same 
course of proceeding for at least a quarter of an hour, in 
fact, till i found it quite necessary to bring it to a 
close. 
From the above statement of the conduct of the animal, 
the impression on my own mind was that I must have 
carried away from my friend’s house some subtle effluvia, 
which tended to bring back to the mother the recollection 
of her puppy. And this caused me some additional sur- 
prise, inasmuch as greyhounds are possessed of great 
keenness of sight, but are generally considered as rather 
deficient in their power of smelling. The conclusion is 
still more remarkable. During the space of about two 
years I usually paid my friend a visit twice a week, and — 
on every occasion, on my return home, the greyhound 
would invariably go through the same ceremony. At 
length the proceeding became altogether so striking that 
it was quite unnecessary for my wife and family (perhaps 
from a little innocent curiosity) to ask, “‘ Where have you © 
been?” They could save themselves the trouble of a 
question and say “I see that you have been calling on 
your friend.” 
My cousins were residing in a small village about thirty 
kilom. from Montpellier, and on one occasion, when I 
was going to spend some days with them, I took, for the 
first time, my greyhound with me. It so happened that 
not far off there was a hound bitch that belonged to one 
of my cousins’ neighbours, and between these two animals 
(from the beginning of my short stay) there arose the 
deepest hatred and animosity, and conflicts of the most 
ferocious kind were matters of daily, almost hourly, oc- 
currence. Time altogether failed in producing any better 
feeling between them, and to the end of my visit each was" 
ever ready and anxious to try their strength whenever the 
opportunity offered. In the course of the following year 
I paid a second visit to the same place, accompanied by 
my greyhound, and about three-quarters of an hour before 
I reached the village the animal, as if struck with a sudden 
idea, rushed forward at her full speed, and all attempts to 
call her back proved quite ineffectual. On reaching the 
village I found that a terrible encounter had already taken 
place between the two heroines, who were on the point of 
ee the attack after a temporary cessation of hos- 
tilities, 
The following anecdote relating to the same greyhound 
seems to prove that these animals may sometimes exhibit 
a higher standard of reasoning power than according to 
general opinion they possess. 
I was passing some days in the country with my aunt, 
who had a middle-sized spaniel bitch, of a somewhat sul- 
len and treacherous temper. This spaniel observed, with 
an evident feeling of jealousy, that my greyhound was 
making herself quite at home in my aunt’s kitchen, and 
whenever she had a favourable opportunity, without 
