400 



CLIMATE 



and snows, and by measuring the depth of water or melted 

 snow which the vessel catches. The total of all these depths 

 for the year gives the annual rainfall, or precipitation as it is 

 usually called. We know by observation that the states bor- 

 dering on the Atlantic Ocean and the Gulf of Mexico have 

 abundant rainfall and that most of Nevada, Utah, Arizona, 

 New Mexico, and Wyoming are dry and parched, and have 



FIG. 268. Map showing annual rainfall. 



acanty rainfall. The rain gauge gives an accurate measure 

 of rainfall and shows that the rainfall of the first region is 50 

 inches a year, while that of the second is less than 10 inches a 

 year. The rainfall in the great Mississippi Valley is less than 

 that of the coasts, but is sufficient to support vegetation. A 

 farm or garden needs about 30 inches of rainfall yearly ; if it 

 gets this, it yields good crops and is profitable. 



Rainfall is usually more abundant along the borders of con- 

 tinents than in their interiors, because border lands are nearer 

 the supply of water. But this is not always true ; some lands 



