RAIN. 101 



1. The moist air may blow along the earth's 

 surface towards colder regions. 



2. The moist air may rise directly from the 

 earth's surface into the higher and colder regions 

 of the air. 



As a rule, the moist air which blows along the 

 earth's surface towards the poles becomes chilled 

 and deposits its moisture as rain or snow. On the 

 contrary, the moist air which blows along the 

 earth's surface towards the equator becomes, for 

 the greater part, warmer and, thus, becoming 

 drier takes rather than gives moisture, and pro- 

 duces drought. 



Therefore, as a rule, only the surface winds 

 which blow towards the colder regions of the 

 earth can be expected to bring rain. 



In the tropical regions, however, any wind, 

 whether from the equator or from the poles, which 

 has crossed the ocean or any other large body of 

 water, and has thereby become saturated with 

 moisture, will deposit some of its moisture as rain 

 when it strikes the cooler coasts of a continent or 

 island. Even in such cases, however, the equa- 

 torial winds are more apt to cause heavy rainfalls 

 than those from the poles. 



A warm, moist air, when sufficiently chilled, will 

 9* 



