and the Mode of its Communication. 69 



I knew, from the results of former experiments, that 

 this ball would, at the same time, be heated by the calo- 

 rific rays from the hot body and cooled by the frigo- 

 rific rays from the cold body ; and I concluded that if 

 its mean temperature should remain unchanged under 

 the influence of these two opposite actions, that event 

 would be a decisive proof of the equality of the inten- 

 sities of those actions. 



The result of the experiment showed that the inten- 

 sities of those opposite actions were in fact equal ; the 

 bubble of spirit of wine, which, by its motion, would 

 have indicated the smallest change of temperature in 

 the ball of the thermoscope to which the hot and 

 the cold bodies were presented, remained at rest. 



On removing the cold body a little farther from the 

 ball, to the distance of 3} inches, for instance, the 

 hot body remaining in its former station, at the distance 

 of 3 inches, the bubble began immediately to move to- 

 wards the opposite ball of the thermoscope, indicating 

 an increase of heat in the ball exposed to the actions of 

 the hot and the cold bodies ; but, when the hot body 

 was removed to a greater distance, the cold body re- 

 maining in its place, the bubble indicated an increase of 

 cold. 



The celerity with which the ball of the thermoscope 

 acquired heat or cold might be estimated by the ve- 

 locity with which the bubble of spirit of wine advanced 

 or retired in its tube ; but, on the most careful and 

 attentive observation, I could not perceive that it 

 moved faster when the ball was acquiring heat than 

 when it was acquiring cold, provided that the hot and 

 the cold bodies from which the calorific and frigorific 

 rays proceeded were at the same relative distances. 



