62 A PEIAIEK (»F r<:)RESTRY = 



powerful inliuence on the--e ditferences. which are also 

 greatly ali'ected by the kind of trees and the density of 

 the forest. 



It niu-t be borne distinctly in mind that the hgiires 

 given above are reliable only for the places in central 

 Europe where they were observed. But the principles 

 on which they depend are just as true in America as 

 they are in Europe. Natural law^ are the same the 

 world over. It is safe to conclude, then, that in the 

 United States the forest modilies the temperature of 

 the air in certain Avays and for certain reasons, both of 

 which we have seen. Ju-t how great this iuflirence is 

 in dilferent part- of thi- continent it is as yet impos- 

 sible to tell But it i- probably greater on the average 

 than these observations indicate, for two reasons: 

 Eirst. the extremes of heat and cold, moisture and 

 drvness. are much greater here than in central Europe. 

 and changes are more sudden: second, in most of the 

 double stations mentioned above the station outside the 

 forest wa- within le-- than a mile of it. and thus likely 

 to be intluenced l)y the cooler air currents Howing from 

 it: that i-. the real effect of the presence or absence of 

 woods over large -tretches of country is probably 

 greater than these observations show. 



A system introduced in Austria is expected to give 

 a clearer idea of the distance to which the forest intin- 

 ence reaches. It con<i-ts of lines of stations beginning 

 in the center of a large forest and extending step by 

 -tep into the open country I)eyond. 



MOI>TUEE IX FOREST ATE. 



The moisture of the air i> greater in the forest than 

 outside. The absolute quantity of water vapor in a 



