ii 6 Count Rumford's Enquiry concerning the Nature of Heat , 
earthen dish, and replaced it with an equal mass of ice-cold 
water. 
The result of this experiment was, to all appearance, just the 
same as that of the last. The bubble moved towards the cold 
body, and took its station in the same place where it had re- 
mained stationary before. I found reason however to conclude, 
after meditating on the subject, that although the last experiment 
proves, in a most decisive manner, that radiations actually pro- 
ceed from the surface of water , yet the proof of the radiation 
from the surface of ice, afforded by the preceding experiment, 
is not equally conclusive ; for, as the temperature of the air of 
the room in which these experiments were made, was many 
degrees above the freezing point, it is possible, and even pro- 
bable, that the surface of the ice was actually covered with a 
very thin, and consequently invisible, coating of water, during 
the whole of the time the experiment lasted. 
Finding reason to conclude, that frigorific rays are always 
emitted by cold bodies, and that these emanations are very ana- 
logous to the calorific rays which hot bodies emit, I was impa- 
tient to discover, whether all cold bodies, at the same temperature, 
emit the same quantity of rays, or whether (as I had found to 
be the case with respect to the calorific rays emitted by hot 
bodies) some substances emit more of them, and some less. 
With a view to the ascertaining of this important point, I 
made the following experiments. 
Exper. No. 20. Having found that a metallic surface, rendered 
quite black by holding it over the flame of a wax candle, emits 
a much larger quantity of calorific rays, when hot, than the 
same metal, at the same temperature, throws off when naked, I 
was very curious to find out whether blackening the surface of 
