and the Mode of its Communication. 65 



were used than when the experiments were made with 

 the cold bodies ; and it is evident, that the distance to 

 which the bubble is driven out of its place must neces- 

 sarily be greater or less in proportion as that difference 

 is greater or less. 



In those experiments in which the horizontal cylin- 

 drical vessels were filled with hot water, and then pre- 

 sented to the balls of the instrument, the temperature 

 of the circular flat surfaces was that of 180, while the 

 temperature of the air of the room in which those ex- 

 periments were made, and consequently that of the 

 balls, was about 60; the difference amounts to no less 

 than 1 20 degrees of Fahrenheit's scale; but, in these 

 experiments with cold, the difference of the tempera- 

 tures at the moment when the cold bodies were first 

 presented to the instrument did not probably amount 

 to more than 40, or at the most 50 degrees; and in a 

 very few seconds it must have been reduced to less 

 than 30 degrees, in consequence of the freezing of 

 the water precipitated by the air of the atmosphere 

 on the surface of the vessel containing the cold mixt- 

 ure. 



This precipitation of water by the surrounding air 

 was so copious that the brilliancy of the polish of the 

 metallic surface was almost instantly obscured by it, 

 and the vessels were very soon covered with a thick 

 coat of ice. These accidents, which were not to be 

 prevented, affected in a very sensible manner the results 

 of the experiment. The bubble, instead of remaining 

 stationary for some time after it had reached the point 

 of its greatest elongation, as it had done in the experi- 

 ments with hot bodies, had no sooner reached that 

 point than it began to return back towards the place 

 VOL. ii. 5 



