ON THE RADIATION OF HEAT. 
165 
was towards it. On moving the canister still nearer to the mir¬ 
ror, it now began to act as a cold body , and the varnished side, 
as before, showed its superior efficiency. 
The same experiments were also tried (and with the same 
effects), by interposing screens between the balls of the thermo¬ 
meter and the canister, lest the direct radiation to the two balls 
of the thermometer might not have been equal, which would 
have confused the results. 
Experiment 3.—Having covered the bails of the aetherial 
thermometer with cambric, and placed one of the balls in the 
focus of the mirror (of the same temperature as the air = 48° of 
Fahrenheit), I applied water to the focal ball, and the chilling 
effect from the evaporation was equal to 20°. On placing the 
screen before the mirror there was no difference in the effect, 
whether the metallic or the varnished side of the screen faced the 
mirror. 
Experiment 4. I now covered the balls of a common differential 
thermometer with cambric, and having arranged one ball in the 
focus, as in the last experiment, I applied cether with a camel's 
hair pencil to the focal ball; the temperature of the room being 
48°, the evaporation of the aether chilled the ball 102°, as the 
extreme effect, and there w T as still no difference whatever in the 
effect, whether the varnished or the metallic side of the screen 
was opposed to the mirror. In other similar experiments (the 
temperature of the room being higher,) the evaporation of aether 
chilled the ball beyond the extremity of the scale of the instru¬ 
ment ; I therefore altered the zero, making the liquid stand a 
- considerable space below the commencement of the scale. The 
temperature of the room being 51°, I found a common mercurial 
thermometer covered with cambric sunk to 24° from the evapora¬ 
tion of the aether, and, at the same time, the evaporation from the 
ball of the differential thermometer made it stand at 62f° on its 
own scale. There was no difference, as already observed, in the 
effect produced by either side of the screen. I then filled the ca¬ 
nister with a mixture of ice and water, (its temperature was 35°,) 
and on placing the varnished side of the canister opposite to 
the mirror, the evaporation of the aether now cooled the thermo¬ 
meter to 64^°, being 1 j° more than the previous chilling effect, 
so that the canister (though warmer than the focal ball) acted on 
it as if it were a colder body. It is to be observed also that the 
direct chilling effect of the canister must be supposed to be, at 
all events, greater on the non-focal ball from the consideration 
of their respective temperatures, and that, consequently, the 
result ought, on this supposition, to have been precisely the re¬ 
verse of what has been mentioned. 
