222 Historical Review of Experiments 



of air by the cooling influence of cold bodies. It now 

 happened that for the first time my opinion on the 

 subject of heat was publicly announced. 



Two metallic mirrors fifteen inches in diameter, with 

 a focal distance of fifteen inches, were placed opposite 

 each other, sixteen feet apart. When a cold body (for 

 example, a glass bulb filled with water, and pounded 

 ice) as was the case on this occasion, was placed in the 

 focus of one of the mirrors, and a very sensitive air- 

 thermometer was placed in the focus of the other mir- 

 ror, the latter thermometer began immediately to fall. 

 If, instead of being placed directly in the focus, the 

 thermometer was removed a short distance from it to 

 one side, the cooling power which in the former case the 

 cold body had exerted upon it was no longer perceptible. 



The matter was, however, not allowed to rest with 

 merely repeating the experiment of Pictet just as he 

 describes it, but I was allowed, in addition, to make 

 various changes, that I might lay aside every doubt, and 

 elucidate in the most convincing manner the fact in 

 question. 



I expressed my opinion on the results of these ex- 

 periments in the following words : 



" It is not possible that caloric has an actual exist- 

 ence. The communication of heat and the communi- 

 cation of sound seem to be completely analogous. The 

 cold body in one focus compels the warm body (the 

 thermometer) in the other focus to change its note." 



It is owing to a peculiar circumstance, the further 

 discussion of which would be neither appropriate nor 

 useful in this place, that I here introduce word for word 

 the expression which I used on this occasion. 



A considerable time before, I had already projected 



