THE ATMOsrilKKK. 47 



which the wind reaches first in its ciistomarv course 

 receives mure rain tlian the opposite side, since the cur- 

 rents of air h)se moisture in ]»assin^- over it. The aljsence 

 of rain on some parts of the coast of South America is 

 due to the fact that the wind, which l)lows constantly 

 from the east in those rej^ions, causes tlie atmosphere to 

 deposit rain, and become comparativ.ely dry in passing 

 the Andes Mountains. 



3. By the 3Iixture of Warm and Cool Currents of 

 Air. — In the changing courses of variable winds, warm 

 currents of air often meet and mingle with cooler cur- 

 rents. When the air is saturated, this is liable at any 

 time to cause rain. 



Snow and Hail. — Snow^ and hail are frozen forms of 

 atmospheric mi^isture. In the case of snow, the minute 

 ])articles of moisture are frozen as they form, and arrange 

 themselves about each other in beautiful crystals, pro- 

 ducing the snowflake. 



Hailstones are often formed by whirling currents of 

 wind, which carry raindrops or minute snowballs first 

 into the iii)per, cold regions, where they are frozen, 

 then downward through a warmer section, where more 

 water is added, and then upward again. The size of the 

 stones is thus gradually increased until they become too 

 heavy to be carried upward again, and are flung to the 

 eai'th. 



Fogs, Mists, and Clouds. — These are all of the same 

 nature. They are simply particles of water or ice which 

 have formed at points where currents of air of different 

 temi)eraturcs meet each other, but not in sufficient quan- 

 tity to produce raindrops. 



Clouds are formed wherever the air, in rising, is cooled 

 enough to condense vapors, When the air is quite dry, 



