460 Of the Propagation of Heat 



when not actually in contact with the glass, and a propor- 

 tional part of its water being let fall at the same time, 

 and in the same place, would necessarily descend in the 

 form of rain ; and, though this rain might be too fine 

 to be visible in its descent, yet I was sure I should find 

 it at the bottom of the bottle, if not in visible drops of 

 water, yet in that kind of cloudy covering which cold 

 glass acquires from a contact with hot steam or watery 

 vapour. 



But if the particles of air, instead of communicating 

 their Heat from one to another, from the center to the 

 surface of the bottle, each in its turn, and for itself, 

 came to the surface of the bottle, and there deposited its 

 Heat and its water, I concluded that the cloudiness oc- 

 casioned by this deposit of water would appear all over 

 the bottle, or, at least, not more of it at the bottom 

 than at the sides, but rather less ; and this I found to 

 be the case in fact. 



The cloudiness first made its appearance upon the 

 sides of the bottle, near the top of it ; and from thence 

 it gradually spread itself downwards, till, growing fainter 

 as it descended lower, it was hardly visible at the distance 

 of half an inch from the bottom of the bottle; and 

 upon the bottom itself, which was nearly flat, there was 

 scarcely the smallest appearance of cloudiness. 



These appearances, I think, are easy to be accounted 

 for. The air immediately in contact with the glass 

 being cooled, and having deposited a part of its water 

 upon the surface of the glass, at the same time that it 

 communicates to it its Heat, slides downwards by the 

 sides of the bottle in consequence of its increased specific 

 gravity, and, taking its place at the bottom of the bottle, 

 forces the whole mass of hot air upwards ; which, in its 



