OF EVAPORATION, &C. 1 9 



while it remains in a solid cube or bar ; but when the 

 gold beater has hammered it into thin leaves, it rises 

 and floats m the air. Its great surface gives the air 

 power to support it, and hence the attraction of grav- 

 itation is destroyed. 



It is thus with water. Heat expands the dense 

 particles of water, which becoming lighter ascend to 

 the higher regions. If the atmosphere, which ascends 

 forty miles above the earth, were every where of the 

 same density, the vapour of the earth and sea would 

 rise to the top; but nature designed it otherwise. 

 The density of the air decreases in proportion to the 

 squares of the distances from the earth. Conse- 

 quently, so soon as the vapour rises to a region where 

 the air is equally rarified, it ceases to ascend ; but 

 floats in beautiful white clouds over the earth, or ap- 

 pears in the West in darkness and storm, its bosom 

 occasionally illuminated with the livid lightning. 



As was observed before, the vapours arising from 

 the earth accumulate in the upper regions, where the 

 atmospheric air is of the same specific gravity. 

 Here, by the great accumulations of vapours, clouds 

 are formed; which by coming in contact with a cold 

 current of air, are condensed into water; and which 

 by the law of gravity or weight, falls to the ground. 

 The principle of condensation any one may observe 

 in Winter, by blowing his breath against a cold pane 

 of glass. Every person on a frosty morning must 

 have observed the column of smoke-like breath 

 which issued from his mouth. 



