on the Subject of Heat. 193 



tion of knowledge, afforded me during a period of four 

 years abundance of leisure to pursue, almost without 

 interruption, my physical investigations, and I em- 

 ployed this leisure in making a considerable number of 

 experiments on heat. 



In the years 1785 and 1786 I was occupied in re- 

 searches as to the manner in which heat passes through 

 various substances and communicates itself still farther. 

 A detailed description of these experiments is to be 

 found in the two papers which I inserted in the Philo- 

 sophical Transactions of the Royal Society of London. 

 The first is in the seventy-sixth, the other in the eighty- 

 third, volume of this work. For the latter I received 

 the gold medal which this Society is accustomed to con- 

 fer annually.* 



In the summer of 1785 I discovered that heat could 

 be transmitted through, or excited in, a Torricellian 

 vacuum. 



Since this discovery has contributed not a little 

 towards strengthening me in the opinion which I have 

 since adopted with regard to the real character of heat, 

 I do not consider it at all superfluous to give here, with 

 all its details, an account of the experiment by which 

 this fact was established beyond doubt. This experi- 

 ment was conducted as follows. 



After a skilful workman in Mannheim, Artaria by 

 name, had succeeded in fixing firmly the globular bulb 

 of a mercurial thermometer, half an inch in diameter, in 

 the centre of another glass bulb an inch and a half in 

 diameter, the space between the outer surface of the 

 thermometer bulb and the inner surface of the outside 

 ball, or the globe, was filled with mercury by means of a 



* These papers were printed in 1797, in my eighth Essay. Sec Vol. I. p. 401. 

 VOL. II. 13 



