54 ELEMENTS OF GENERAL SCIENCE 



region of rising air there is little wind at the surface of the 

 earth, and it is known as the belt of calms. To the north 

 and south of the belt of calms the air is rushing southward 

 (or northward) toward the heat equator, but by the rotation 

 of the earth these winds are turned from the direct course 

 they would otherwise pursue, so that in the northern hemi- 

 sphere they become northeast winds and in the southern 

 hemisphere they blow from the southeast. These winds blow 

 very steadily, and are known as trade winds. 



53. Rainfall in the United States. Rainfall is very un- 

 equally distributed in the United States (fig. 34). It ranges 

 in amount from 100 inches per year in northwestern Wash- 

 ington to 2 inches per year in southeastern California. While 

 there are no very large regions in the United States which 

 deserve to be called deserts, yet much more than a third of 

 the country is arid and cannot be farmed successfully with- 

 out irrigation or other special means. The eastern slope, the 

 lake region, and the Mississippi Valley as far west as the 

 middle of the Dakotas and Nebraska are well watered, but 

 the great plains and mountains of the West have very scanty 

 rainfall excepting on the westward slopes of mountains near 

 the Pacific Ocean. 



The rainfall on the Pacific coast is due mainly to the effect 

 of the mountains upon the prevailing westerly winds. The 

 scantiness of rainfall in the mountains and on the plains 

 directly east of them is due to the same thing. The larger 

 rainfall of the Mississippi Valley occurs principally in con- 

 nection with the cyclones and is condensed from the air 

 which is sweeping northward from the Gulf of Mexico into 

 the cyclones. Farther east the Atlantic Ocean contributes 

 in the same way. 



53. The United States Weather Bureau. The importance 

 of the weather to the people of the country is so great that 

 the government has established a bureau for the purpose 

 of studying the weather and forecasting it as far as possible. 



