192 THEORY OF RADIATION. 



caloric, or that it was even modified by their 

 attraction for it. 



It was supposed by Prevost, whose opinion 

 has been adopted by a majority of writers on 

 Chemistry and Natural Philosophy, that the 

 tendency of all bodies to an equilibrium of tem- 

 perature, is owing to a perpetual exchange of 

 caloric from one to the other by radiation : but 

 it is evident from the foregoing facts, that the 

 motions of caloric by which it passes out of one 

 body into another, are owing to its attraction 

 for ponderable matter, as well as to its self- 

 repulsive or radiating power. When a hot body 

 is placed in vacuo, and at a distance from other 

 bodies, it parts with caloric by radiation alone, 

 with a rapidity proportional to temperature. 

 When placed in atmospheric air, it loses the 

 same quantity of caloric by radiation, while an 

 additional portion is abstracted by the contiguous 

 particles of air. 



It is generally stated, that bodies cool about 

 twice as fast in air as in vacuo. Count Rumford 

 found that a thermometer cooled from 212 F. 

 to 32, in vacuo, in .... 10m. 5 sec. 

 in air 7 3 



water 1 5 

 mercury 36 



But if it be true that all bodies attract and absorb 

 caloric, with a force and rapidity in proportion 

 as they are deprived of it, it is obvious that in 



