66 ECONOMICS OF FORESTRY. 



rate, yet, nevertheless, more or less closely related, 

 directions, namely : 



1. Upon the climatic conditions within its own 

 limits and beyond. 



2. Upon the distribution and character of the 

 waterflow. 



3. Upon the mechanical condition and erosion 

 of the soil under its cover. 



4. Upon the health conditions. 



5. Upon the ethics of a people. 



This last influence is one which we cannot measure 

 or even argue with any determinable force, but 

 which we ourselves may feel more or less strongly, 

 according to the degree to which our emotions in 

 general are susceptible. In either of the other 

 directions in which an influence of forest cover 

 is asserted, the mechanical obstruction which it 

 represents is the principal effective element; the 

 physiological functions of the living plant playing, 

 to be sure, a part, but of much less importance, 

 probably, than has been often supposed. 



It requires no instrument to find out that the 

 effective temperature is higher when the sun has 

 full sway upon our skulls than if we interpose the 

 shade of a densely foliaged tree to obstruct the 

 sun's rays ; on the other hand, the cooling breeze, 

 which may pass over the open field, is also ob- 

 structed by the forest growth, and its absence may 

 make the air temperature appear higher, even in 

 spite of the shade. Again, it stands to reason 



