8 ELEMENTS OF SYLVICULTUEE. 



there more frequently, and perhaps in greater 

 abundance. Finally, forests, by presenting a barrier 

 to the wind, break its force. They certainly act in 

 other ways on the climate, but this action is not yet 

 sufficiently understood, and it would be premature 

 to go into the question here. 



The elevation of plains chiefly affects the temper- 

 ature ; thus, in France, 330 feet of elevation have 

 the same influence as one additional degree of 

 latitude ; that is, the effect is to lower the tem- 

 perature by half a degree centigrade. 



The nature of the soil is not without its influence 

 on the temperature and humidity of the atmosphere. 

 A free soil, by permitting the infiltration of water, 

 gives off less watery vapour and thus increases the 

 temperature; a stiff soil, produces the contrary 

 effects. The darker the colour of the soil, the 

 higher will be the temperature. 



The proximity of the sea tends to equalize the 

 annual temperature, increases the amount of 

 moisture in the air, and allows fall play to the 

 violence of the winds. 



Lastly, mountain chains, according to their 

 direction, exert an influence on the temperature and 

 the humidity of the atmosphere, and break the force 

 of aerial currents. 



CLIMATE OF MOUNTAINS. The climate of moun- 

 tains varies chiefly with elevation and aspect, result 

 of the configuration of the surface, while still re- 

 maining subject to the same modifying causes as the- 

 climate of plains. 



As one gets higher and higher, the air becomes 



