120 



FOREST INFLUENCES. 



As tlie interior air of tlie forest; is generally cooler, in the warm sea- 

 son, than the air outside, it must he heavier, and the difference of tem- 

 perature must be often so great that the heavier air will overcome the 



Fig. 58. — Forest circulalioii. 



obstacles to its flow and gradually pour out near the ground. Its place 

 will be taken by the air above which will settle, and thus there may 

 be set up a forest circulation, as represented in the tigure (Fig. 58) 



Fig. 59. — Day circulatiou. 



exactly corresponding to such a system of winds as is found in land or 

 sea breezes, or may be found over a lake at night. 

 During clear nights the forest air is generally warmer than that out- 



*-« *-~«^ '^-^ 



•^-^ 



»—*^ •>— ► iS^^ 



Fir;. GO.— Night circulation. 



side. When this happens a reverse circulation might be set up. This 

 circulation must be slow, and though somewhat enlarged on by writers 

 on tlie subject seems never to have been directly observed. 



