PECULIAR FOG IN ICELAND. 157 



tides be may, it is true, diminish to an indefinite extent 

 the resistance of the air ; but the heat, which he wishes 

 to retain, cannot be allowed to him. 



In the same year, and at the same Academy of Bor- 

 deaux, a prize was adjudged to M. Hamberger, Professor 

 of Physics and Medicine in the Academy of Jena. Both 

 he and Kratzenstein were Germans, and from Saxony. 

 Hamberger shows that the weight of water cannot be 

 reduced by increasing the size of the vesicles or, indeed, 

 by making vesicles. He says, "the force which raises 

 bodies into the air diminishes with the size of the bodies ; 

 but as the elevating forces act only on the surface, and 

 these diminish as the squares of their diameters, whilst 

 the bodies (and consequently their weight) diminish as 

 the cubes, it is easy to see that a force insufficient to raise 

 a body may raise the small portions." In other words, 

 the smaller the body the less can it resist the air. It is 

 somewhat wearisome to go over the eighty-four para- 

 graphs, some considerably divided; so I need only add 

 one or two. 



" 7 1 . Nothing but the motion of the air is the ultimate 

 cause of the rise of vapours. We must now therefore 

 explain what is the cause which, during the time of 

 evaporation, produces the motion of the air." 



" 72. The movement of the air and its direction upwards 

 are produced by the vapours themselves, which are heated 

 when raised into the air by causes explained in par. 63, 

 no. 2, letter B, and no. 3, letters A and B, because the 

 heat passes from the vapours warmed into the air which 

 touches the vapours, whence it arises that this air is heated 

 and expanded ; consequently it becomes specifically lighter 

 than the surrounding air, by which it is pressed upwards. 

 This air follows the dilated air, which yields its place and, 

 being put in motion upwards, carries with it the vapours 

 attached to it." 



