FORMATION OF CLOUDS. 65 



lakes and rivers would be perpetually frozen, as has been 

 said ; and on the other hand, without those rivers of solid ice, 

 which we call glaciers, there would in time be neither lakes 

 nor rivers, nor even seas and oceans. 



The hot air of the tropics is constantly drinking up many 

 millions of tons of water, and if none were restored to it 



Fig. 14. SNOW CRYSTALS. 



again, the whole surface of the ocean would be lowered 

 about eight or ten feet every year, and in time must be 

 utterly exhausted. But the water thus taken up and trans- 

 ported thousands of miles by the currents of the air con- 

 denses into rain clouds or snow clouds, according as the tem- 

 perature which it encounters is above or below freezing point, 

 and after a longer or shorter journey, is poured back into 

 the ocean by the rivers. 



Snow consists of crystals of ice (Fig. 14), which look 

 F 



