121 
and the Mode of its Communication . 
the middle of a large quiet room, at the temperature of 72 0 F. 
I presented to one of its balls, at the distance of 3 inches, the 
flat circular end of one of the horizontal cylindrical vessels (A) 
above described, with an oblique cylindrical neck, this vessel 
being filled with pounded ice and water; and, at the same mo- 
ment, an assistant presented to the opposite side of the same ball 
of the thermoscope, at the same distance, (3 inches,) the flat 
end of the other similar and equal cylindrical vessel, (B,) filled 
with warm water at the temperature of 1 12 0 F. the opposite ball 
of the thermoscope being hid and defended, by means of screens, * 
from the actions of the bodies presented to the other ball, as also 
from the calorific rays which proceeded from the bodies of the 
persons present. 
From this description it appears, that while one of the balls 
of the thefmoscope was so defended by screens that it could not 
be sensibly affected by the radiations of the neighbouring bodies, 
the other ball was exposed to the simultaneous action of two 
equal bodies, at equal distances; (two vertical metallic disks, 3 
inches in diameter, placed on opposite sides of the ball, at the dis- 
tance of 3 inches;) one of these bodies being at the temperature 
of 32 0 F. or 40 degrees below that of the ball, while the other 
was at 112 0 F. or 40 degrees above the temperature of the ball. 
I knew, from the results of former experiments, that this ball 
would, at the same time, be heated by the calorific rays from 
the hot body, and cooled by the frigorific rays from the cold 
body; and I concluded, that if its mean temperature should 
remain unchanged under the influence of these two opposite 
actions, that event would be a decisive proof of the equality of 
the intensities of those actions. 
The result of the experiment showed, that the intensities of 
mdccciv. R 
