RAINFALL AND ITS MEASUREMENT 



233 



and this must be properly distributed throughout the 

 year. 



On examining a map of the mean annual rainfall (page 

 235), we see that there are large areas where it is not sufficient 

 for agriculture with- 

 out irrigation. Such 

 areas are within the 

 belts of dry winds 

 or in continental in- 

 teriors far from large 

 bodies of water. The 

 rain-bearing winds 

 coming from the wa- 

 ter are forced to rise 

 and cool so that their 

 moisture is deposited 

 before reaching these 

 interior regions. 



The rainfall of a 

 place depend s 

 largely : (1) upon its 

 elevation, since most 

 of the rain-bearing 

 clouds lie at low alti- 

 tudes; (2) upon the 

 direction and kind of 



winds that blow over it ; and (3) upon the elevation of the 

 land about it. The sides of mountains toward the direction 

 from which the rain-bearing winds approach will be well 

 watered, while the opposite side may be a barren desert. 



A cylindrical vessel having vertical sides, called a rain 

 gauge, is used to determine the amount of rain. It is placed 



WATERSPOUT SEEN OFF THE COAST OF 

 NEW ENGLAND 



