CHAPTER II. 



EyPBCTs OP Forests os the HmiroiTT op ths Gbouns. 



Il may be considered a departure from the professed subject of thi« 

 treatise to speak liere of the effects of forests on the humidity of the 

 ground ; but the subjects are correlatel. Practically it is huLuidity of 

 soil which is what is desired, and the conservation of at )isture in the 

 soil has a direct iuflueace, in different ways, on the moisture in the 

 atmosphere, so important as to justify, if not to require, some 

 attention, being given to it in treating of the meteorological effects of 

 forests. 



The subjects coming under consideration here are the following : 

 The wetness of roads when overshadowed by trees ; the shelter afforded 

 by trees against drying winds j and the attraction and retention of 

 moisture by vegetable mould ; and to this might be added the effect 

 of trees in arresting the flow and escape of the rainfall-^but a better 

 opportunity for bringing these under consideration will afterwards 

 present itself. 



Seot. I. — On, the Wetness of Rotis where these are Overshadovied 



hy Trees. 



We have had under consideration the dampness of houses over- 

 shadowed by trees, or situated in close proximity to woods. Not less 

 noticeable than this is the wetness of roads where these are over- 

 shadowed by trees. This may frequently be observed while elsewhere 

 the road is dry, and it may be supposed that in this we have only an 

 exaggerated effect of what occasions the dampness of such houses ; 

 but there is more in the phenomenon than this would imply. 



While much of the rain which falls upon the earth, and much that 

 falls in the form of snow and hail, flows away to the sea — the tiniest 

 streamlet and the mi;^'htiest river or flood being alike the product 

 of such flow — and while a portion is absorbed by the earth, a great deal 

 is evaporated and absorbed by the air. The higher the temperature of 



