188 CONFLICTESTG INFLUEISTCES. 



remainder descending into the sub soil and percolating through 

 earth and rock until it issues in the form of springs. He found 

 an evaporation of one and one-tenth millimetres per day to be the 

 maximum from a forest of firs, and this, too, under the excep- 

 tionally favorable conditions of a fertile and humid soil and 

 abundance of sunlight. 



Balcmce of Conflicting Inflmences of Forest on Atmosjpheric 

 Heat cmd Sumidity. 



We have shown that the forest, considered as dead matter, 

 tends to diminish the moisture of the air, by preventing the 

 sun's rays from reaching the ground and evaporating the water 

 that falls upon the surface, and also by spreading over the earth 

 a spongy mantle which sucks up and retains the humidity it re- 

 ceives from the atmosphere, while, at the same time, this covering 

 acts in the contrary direction by accumulating, in a reservoir not 

 wholly inaccessible to vaporizing influences, the water of precipi- 

 tation which might otherwise suddenly sink deep into the bowels 

 of the earth, or flow by superficial channels to other climatic re- 

 gions. We now see that, as a hving organism, it tends, on the 

 one hand, to diminish the humidity of the air by sometimes ab- 

 sorbing moisture from it, and, on the other, to increase that hu- 

 midity by pouring out into the atmosphere, in a vaporous form, 

 the water it draws up through its roots. This last operation, at 

 the same time, lowers the temperature of the air in contact with 

 or proximity to the wood, by the same law as in other cases of 

 the conversion of water into vapor. 



As I have repeatedly said, we can not measure the value of any 

 one of these elements of chmatic disturbance, raising or lowering 

 of temperature, increase or diminution of humidity, nor can we 

 say that in any one season, any one year, or any one fixed cycle, 

 however long or short, they balance and compensate each other. 

 They are sometimes, but certainly not always, contemporaneous 

 in their action, whether their tendency is in the same or in oppo- 

 site directions, and, therefore, their influence is sometimes cumu- 

 lative, sometimes conflicting ; but, upon the whole, their general 

 effect is to mitigate extremes of atmospheric heat and cold, moist- 

 ure and drought. They serve as equalizers of temperature and 



