56 Inquiry concerning the -Nature of Heat, 



the ball to which it was presented, it was drawn back- 

 ward to a greater distance from it, the action of its calo- 

 rific rays on the ball was diminished by this increase of 

 distance ; and, being overcome by the action of the rays 

 from the hot body presented to the opposite ball (at a 

 smaller distance), the bubble was forced out of its 

 place, and obliged to move towards the ball which had 

 been drawn backward. 



When one of the hot bodies only was presented to 

 one of the balls, the bubble was immediately put in 

 motion, and by bringing the hot body nearer to the 

 ball, it might be driven quite out of the tube into the 

 opposite ball ; this, however, should never be done, be- 

 cause it totally deranges the instrument, as it is easy to 

 perceive it must do. 



Having, by these trials, ascertained the sensibility 

 and the accuracy of my instrument, I now proceeded to 

 make the following decisive experiment. 



Experiment No. 13. Having blackened the flat cir- 

 cular bottom of one of the cylindrical vessels by hold- 

 ing it over the flame of a wax candle, I now rilled both 

 vessels again with water at the temperature of i8oF., 

 and presented them, as before, to the two opposite balls 

 of the instrument at equal distances. 



The bubble was instantly driven out of its place by 

 the superior action of the blackened surface, and did 

 not return to its former station till after the vessel 

 which was blackened had been removed to more than 8 

 inches from the ball to which it was presented ; the 

 other vessel, which had not been blackened, remaining 

 in its former situation, at the distance of 2 inches from 

 its ball. 



The result of this experiment appeared to me to 



