RAIN. 451 



precipitated in different parts of the globe, and its distribu- 

 tions among the different seasons, has an important bearing 

 on many departments of physical science. The life of plants 

 and animals depends as much on moisture as on tempera- 

 ture, and their development is greatly modified by the dry- 

 ness or humidity of the atmosphere. Rain is very unequally 

 distributed over the different regions of the globe. It is 

 generally most abundant in those latitudes where evapora- 

 tion takes place most rapidly; yet there are exceptions to 

 this rule. In many parts of the earth it almost never rains, 

 because, as Kamtz remarks, the greatly heated atmosphere 

 does not contain sufficient moisture to admit of precipitation 

 even during the greatest decrement of temperature. The 

 temperate zone of the New World gives an annual amount 

 of thirty-seven inches in the United States, according to 

 Johnston, and forty inches according to Butler and Blodget. 

 Rain is most abundant at the equator, and decreases to- 

 ward the poles, in some lines of observation, from 150 to 

 13 inches. The amount of rain decreases, ascending from 

 low plains to elevated table-lands ; on the contrary, increases 

 from plains and slopes of mountains, if those are steep and 

 rugged, as shown by the annual fall at Paris being twenty 

 inches, while at great St. Bernard it is 36*13 inches. Steep 

 and rugged mountains promote, through partial currents of 

 air, the formation and increase of clouds, such mountains 

 being more cloudy than those with uniform summits and 

 smooth slopes. The quantity of rain decreases, receding 

 from coasts to the interior of continents, from the greater 

 amount of evaporation on sea than land, and because of 

 greater interchange of heat between land and sea, conse- 

 quently greater movement of arial currents than between 

 different parts of a continent. This rule is apparent in the 

 interior of the United States of North America, in the cen- 

 tre of the plains of Orinoco, in the Steppes of Siberia, and 

 in the interior of Australia. There are exceptions to this 

 rule from the geographic position of countries in relation to 

 regions of winds, and the direction of mountain chains, 



