PRIMER OF PRIMERS. 197 



the rivers receiving such drainage are apt to over- 

 flow their banks during the wet season. 



Any disturbance in the natural drainage of a 

 country may cause damage from the too rapid 

 drainage of its surface : 



1. By insuring too much water in its rivers 

 during inundations. 



2. By insuring too little water in its rivers 

 during drought. 



The preservation of forests on mountain-slopes, 

 where the drainage is more rapid than elsewhere, 

 insures a proper drainage of its surface, and con- 

 sequently the proper flow of its rivers. 



The condition of the air of a country as regards 

 its heat or cold moisture or dryness, healthfulness 

 or unhealthfulness, is called its climate. 



The atmosphere receives its heat from the sun : 



1. Directly, by absorption. 



2. Indirectly, from the heated earth. 



The atmosphere receives its heat indirectly from 

 the heated earth : 



(a) By contact with the heated earth. 



(b) By radiation from the heated earth. 



(c) By reflection from the heated earth. 



All parts of the earth in the same latitude do 

 not possess the same temperature, because the 



17* 



