RAINFALL 



399 



receives little heat it has winter ; because the southern hemi- 

 sphere receives the heat rays straight on its surface it has 

 summer. In June the northern hemisphere is turned toward 

 the sun and the southern is turned away; summer therefore 

 extends over the northern hemisphere and winter over the 

 southern hemisphere. 



At the equator the sun is always high in the sky whatever 

 the position of the earth in its orbit, and therefore brings fierce 

 heat to the land ; summer exists all the year round. The polar 



regions are always cold, t i 



because the sun's rays 

 always strike them at a 

 very acute angle, and 

 what little heat the rays 

 contribute is absorbed 

 in melting huge masses 

 of ice formed during 

 the long arctic night 

 (Fig. 267). In temper- 

 ate regions, winter with 

 its short days and long 

 nights changes gradually into spring with equal days and 

 nights ; spring in turn changes into summer with long days and 

 short nights ; then summer days wane into autumn with days 

 and nights of equal length. 



Rainfall. Heat and rainfall, including both snow and 

 rain, are the most important factors in climate. In certain 

 parts of the state of Washington the rainfall is so heavy that it 

 amounts to over 60 inches or 2 yards a year; in certain parts of 

 Nevada, California, and Arizona the rainfall is so scant that it 

 amounts to less than 10 inches in a year (Fig. 268). We get 

 the exact quantity of rain that falls in a region by placing a 

 straight-sided bucket, or rain gauge, out of doors during rains 



FIG. 267. An iceberg. 



