12 6 Count Rumford’s Enquiry concerning the Nature of Heat, 
I knew, from the results of former experiments, that the 
intensity of the calorific radiations from the hot disk, would be 
very much increased, in consequence of its surface being black- 
ened ; and I was certain, that if the intensity of the frigorific 
radiations of the cold disk should not be increased in exactly the 
same degree , the ball of the thermoscope, exposed to the simul- 
taneous actions of these two disks, could not possibly remain at 
the same constant temperature, that of 72 0 . 
The result of the experiment was very decisive : the bubble 
of spirit of wine remained at rest ; which proved, that the in- 
tensities of the rays emitted by the two disks, still continued to 
be equal at the surface of the ball of the thermoscope, which, at 
equal distances, was exposed to their simultaneous action. 
Hence we may conclude, that those circumstances which are 
favourable to the copious emission of calorific rays from the 
surfaces of hot bodies, are equally favourable to a copious emis- 
sion of frigorific rays from similar bodies, when they are cold. 
But it is time to consider these emanations in a new point of 
view. What difference can there be between calorific rays, and 
frigorific rays ? Are not the same rays either calorific, or fri- 
gorific, according as the body at whose surface they arrive is 
hotter, or colder, than that from which they proceed ? 
Let us suppose three equal bodies, A, B, and C, (the globular 
bulbs of three mercurial thermometers, for instance,) to be 
placed, at equal distances, (3 inches,) in the same horizontal 
line ; and let A be at the temperature of freezing water, B at 
the temperature of 72 0 F. and C at that of 102° F. The rays 
emitted by B will be calorific , in regard to the colder body A ; 
but, in respect to the hotter body C, they will be frigorific ; and, 
