CLIMATE AS INFLUENCED BY THE FOREST. 129 



earth from losing heat. The frost will, therefore, 

 he prevented from entering the ground to any great 

 depth. In the temperate regions of the Northern 

 Hemisphere, in districts covered by forests, the 

 early snows of winter are, for the greater part, apt 

 to fall before the ground is frozen to any con- 

 siderable depth. In the early spring, when the 

 thaws come, the water derived from the melting 

 of the ice and snow can then drain quietly into the 

 ground and fill the reservoirs of the springs. 



If, however, the forests are removed, the ease 

 with which the ground loses its heat generally per- 

 mits it to freeze before the first snow falls, and the 

 non-conducting power of the layer of snow causes 

 the ground to remain frozen until long after the 

 spring thaws have melted the snow. Under such 

 circumstances, the water derived from the melting 

 snow rapidly drains almost entirely off the sur- 

 face, and is apt to produce disastrous floods. 



Tyndall has shown that the ability of air to be- 

 come heated, by absorbing heat directly from the 

 sun's rays as they pass through it, depends almost 

 entirely on the presence of water vapor. The air 

 over a forest district is necessarily more moist, and 

 consequently better able to absorb heat and become 

 heated than the air over a dry, barren tract. 

 i 



