270 THE CHEMISTRY OF CREATION. 



in a gaseous form in the air. On putting a lew 

 lumps of ice into a tumbler, the surface of 

 which is carefully wiped clean, and carrying 

 the glass into a sitting-room, it will be imme- 

 diately found to be covered with a dense cloud 

 of dew, which will form again and again, even 

 after the first deposit has been wiped off. The 

 amount present in the air varies greatly, but a 

 certain portion is never absent, and the amount 

 is usually greater in warm than in cold air. It 

 arises from the evaporation of water on the 

 earth. The atmosphere on the summit of lofty 

 mountains is occasionally remarkable for the 

 absence of watery vapour. On the lofty passes 

 of the Cordilleras this degree of dryness pro- 

 duces some curious effects. Articles of food 

 become perfectly dry and hard, wood-work 

 shrinks ; and if a mule dies it is preserved from 

 putrefaction, as this process does not take place 

 in the absence of water for a length of time. 

 The atmosphere in such a condition is remark- 

 ably clear and transparent. Electricity also is 

 developed on the slightest friction ; articles of 

 flannel clothing, when rubbed in the dark, glisten 

 with the electric fire, and the hairy coats of ani- 

 mals crackle and emit sparks. 



The state in which watery vapour exists in 

 the air is closely analogous to that of the other 

 gases, and it is influenced equally with them, 



