concerning Heat. 137 



I have shown, by direct and conclusive experiments, 

 that bodies cool and are heated, and that with consider- 

 able celerity, when placed in a space void of air ; * 

 and by experiments made last year, with the intention 

 of clearing up this point, I found reasons to conclude 

 that when a hot body cools in tranquil air, not agitated 

 by winds, one twenty-seventh only of the heat lost by 

 this body (or, to speak more correctly, which it excites 

 in surrounding bodies) is communicated to the air, 

 all the rest being carried to a distance through the air 

 and communicated by radiation to the surrounding solid 

 bodies. 



SECTION II. Experiments on cooling Bodies. 



It is only by careful observation of the phenomena 

 which accompany the heating and cooling of bodies, 

 that we can hope to acquire exact notions of the nature 

 of heat and its manner of acting. 



Many experiments have been made by different per- 

 sons, at different times, with a view to determine what 

 has been called the conducting quality of different sub- 

 stances with regard to heat. I have myself made a con- 

 siderable number ; and it is from their results, often no 

 less unexpected than interesting, that I have been gradu- 

 ally led to adopt the opinions on the nature of heat which 

 I have presumed to submit to the judgment of this 

 illustrious assembly. The flattering attention with 

 which the Class has honoured the three Memoirs I 

 have lately presented encourages me to communicate the 

 continuation of my researches. 



All philosophers are agreed in considering glass as 

 one of the worst conductors of heat which exists ; and 



* In my Essay on the Propagation of Heat in various Substances. See Vol. I. 

 p. 401. 



