i 
FIFTH REPORT- 1835. 
about 12 to 1 : and 3rd, If the canister alone be cooled, the focal 
ball is more chilled by the varnished than by the metallic side in 
the same proportion of about 12 to 1. 
I now proceed to give a few examples of such experiments as 
have been sufficiently frequently repeated to remove all doubt, 
from my own mind, of their having been produced by occasional 
or accidental causes. 
Experiment 1.—In a close room (temperature 62° Fahrenheit) 
I placed a large tin screen, 4 feet 6 inches by 2 feet 9 inches, 
in front of the mirror, at a distance of about 6 feet; and having 
ascertained the position of the focus, I filled the hollow back 
of the mirror with water at 200° of Fahrenheit, and arranged 
the aetherial thermometer so that one of the balls being in the 
focus the other was equally heated by the mirror, the instrument 
marking zero. I now placed a smaller tin screen, 24 inches by 
17 , varnished on one side, about a foot in front of the large 
screen, with its metallic surface facing the mirror : on so doing 
the focal ball was chilled above one fourth of a degree; and on 
turning the varnished side towards the mirror the focal ball was 
cooled 3^ degrees below zero. On moving the small screen 
nearer to the mirror, the chilling effects of both sides increased, 
and more rapidly than they should have done in reference to the 
mere diminution of the distance; a fact indeed which maybe in¬ 
ferred from the effect of the metallic side of the small screen in 
its primary position. I also remarked that when either side of 
the screen was left facing the mirror for any considerable time, 
its effect began to diminish, evidently from that surface be¬ 
coming warmer. But the other side being then turned pro¬ 
duced its peculiar effect; and the former side also being again 
(after the lapse of a few minutes) put fronting the mirror was 
found to produce its full effect as at first. 
Experiment 2.—The large screen and the thermometer being 
arranged as before, and the mirror heated to 173°, I substituted 
for the smaller screen a ten-inch canister filled with water at 59°, 
the temperature of the room being 55° only ; and on repeating 
the trials, as in the previous experiment, 1 found that this also 
acted as a cold body, and the varnished side produced the greater 
effect: just in front of the large screen, however, its effects be¬ 
came very small, the black side only producing a chilling effect 
of about three fourths of a degree. I then filled the canister with 
water at 67°, and (in this same position) it now acted as a warm 
body, and the varnished side most efficaciously. On moving it 
gradually nearer to the mirror, the effects diminished, and at 
length altogether ceased, so that the thermometer remained at 
zero, whether the metallic or the varnished side of the mirror 
