156 DR. R. ANGUS SMITH ON A 



He also says (in XL.), "The specific weights of water 

 and air are as 900 to 1. A vesicle of water must there- 

 fore be a thousand times as large as the drop of water of 

 which it is composed. The vapours, therefore, cannot be 

 so dilated as to rise by being specifically lighter than air." 



But how are these vesicles elevated ? 



"According to Mr. Halley's observations, air which 

 touches boiling water is dilated one quarter, and the air 

 heated by the sun is dilated by a seventh. Therefore the 

 air becomes lighter than the colder air which surrounds it ; 

 it ought, therefore, to rise with an accelerated movement, 

 and to employ a quarter of its weight as force." "The 

 bubbles are not able to overcome by their weight the cohe- 

 sion of the air, but remain suspended." — LX. 4. 



" The vapour will rise with the air when it preserves its 

 heat ; the air would lose its heat very slowly, because the 

 cold air which surrounds it has a very small specific 

 gravity." — LX. 6. 



" The motion of the air ceasing, the molecules of the air 

 remain adhering to the vapours ; and because the vapours, 

 being so small, are unable by their weight to overcome 

 this adherence, they become supported in the air even 

 when it is calm." — LX. 7. 



I think I have shown enough from M. Kratzenstein to 

 prove that he has given in reality no argument for the 

 vesicularity of vapours. He has, in fact, shown quite 

 clearly that the vesicularity does not do away with the 

 difficulty of floating water in the air; and he has taken 

 refuge in heated and expanded air. Not knowing that 

 the cold produced by expansion allows the vapours to be 

 seen, he is far misled, and ends at last in the cohesion of 

 the air and smallness of the particles, forgetting appa- 

 rently the importance at first given to his vesicles. The 

 whole is like the work of a clever youth, as the author 

 seems to have been. By diminishing the size of the par- 



