314 



FIRST YEAR SCIENCE 



mountains near their borders it happens that most conti- 

 nental interiors are comparatively dry. 



Regions over which the prevailing winds blow from a 

 colder to a warmer latitude have little rainfall, as the 

 air is continually having its capacity to hold moisture in- 

 creased by its rise in temperature. This is well illustrated 

 in the Sahara region. Accordingly, the amount of rainfall 

 in different parts of the earth varies greatly. In eastern 

 India south of the Khasi Hills a "record" fall of over 

 50 feet was recorded in one year, while in desert regions a 

 year may go by without any fall of rain. 



In the United States the greatest rainfall, over 80 inches, 



Fig. 111. 



is found along the northwest coast and the least in the Basin 

 Region of Utah, Arizona and Nevada. Whether rain falls 

 in large or small quantities, its effect is always marked. 

 Without it the surface of the ground is a parched and 

 barren waste of dust and rock, with it, a green and varied 

 expanse of never failing beauty. 



150. The Sphere of Activity of Rain. When rain falls 

 upon the ground, it may do one of three things. It may 

 evaporate immediately from the surface and return to the 

 air ; or it may run rapidly off the surface and quickly join 

 the streams and rivers which bear it to its final goal, the 

 sea; or it may sink into the ground. In this last case 

 part of it returns gradually through capillary action to the 

 surface where it is again evaporated; part finds its way 



