and the Mode of its Communication. 63 



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 remained 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 proceed 

 from the surface of water^ yet the proof of the radiation 

 from the surface of ice, afforded by the preceding ex- 

 periment, is not equally conclusive ; for, as the tem- 

 perature of the air of the room in which these experi- 

 ments were made was many degrees above the freezing 

 point, it is possible, and even probable, 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 emana- 

 tions are very analogous to the calorific rays which hot 

 bodies emit, I was impatient 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. 



Experiment 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 



