166 
FIFTH REPORT- 1835. 
The evaporation of the aether was so rapid that I found these 
experiments very troublesome, and in order to obtain the maxi¬ 
mum effect I found it necessary to have the aether previously 
cooled considerably; thus, in the last experiment, even when 
the aether was cooled to 34° of Fahrenheit, on dropping some of 
it on the ball, the immediate effect was to heat the focal ball 
from 3 to 8 or 10 degrees, according to the quantity of aether 
dropped on it at the same time. 
Being desirous to try the “diathermancy"" (to use Melloni’s 
term) of rock salt, I had a plate sawed out of the largest block 
of it I could procure at the time: its dimensions were 8 inches 
by 6, and four tenths of an inch thick. I placed a screen with 
an opening in it (which the plate of salt just filled up) at 2 feet 
9 inches from the mirror, having one ball of the aetherial ther¬ 
mometer in the focus, and placed the 10-inch canister contain¬ 
ing hot water with its varnished side 2 feet behind the screen. 
While the rock salt remained in the opening the thermometer 
continued at zero, but on removing it the thermometer imme¬ 
diately began to rise, and in less than ten minutes had risen 14°. 
On replacing the rock salt the thermometer fell again, and in a 
few minutes sunk to zero. 
The plate of salt was certainly not a favourable specimen, and 
therefore I should not lay much stress on the present experi¬ 
ment if Meiloni’s expressions had not led me to expect a diffe¬ 
rent result from even the worst specimens of this substance. 
It is unnecessary to point out how completely the experi¬ 
ments I have mentioned are at variance with the received doc¬ 
trine of the radiation of heat, as, on such a theory, the radiation 
of cold appears to be equally established. If the mirror be heated 
or cooled, and the thermometer so placed that both balls are 
equally heated or cooled by the mirror, there is no reason why 
any heating or cooling radiation towards the mirror should af¬ 
fect the focal ball; if we suppose such radiation to heat or cool 
the mirror, both balls (from their position) should be equally af¬ 
fected. Now we might suppose heat to be merely radiated to 
and reflected by the mirror, but we cannot admit the same with 
regard to cold. Why then does this appear to be the case, both 
balls being equally affected by the temperature of the mirror; 
why does the focal ball appear to radiate more heat towards the 
mirror than the non-focal ball when a (comparatively) cold body 
is placed opposite to the mirror? 
On the other hand, these experiments appear to be in no re¬ 
spect incompatible with the views of the late Professor Leslie, 
whose ingenious theory (whether true or false) has not, in my 
mind, ever received the attention to which I think it is entitled. 
