EFFECTS OF FORESTS 



OK THE 



HUMIDITY OF THE CLIMATE. 



INTKODUCTION. 



The following treatise on Meteorological Effects of Forests relates 

 mainly to the effects of these on the humidity of the atmosphere and 

 of the soil. Besides these there are effects produced by forests on the 

 temperature and the salubrity of a country, and all of these are cor- 

 related — each of them affecting the others, and the others, each. 



It is a matter of common observation that houses in the close 

 proximity of trees are often damp ; it is also frequently observed that 

 both in summer and winter the temperature in a wood is different 

 from what it is in the open country ; and it is becoming generally 

 known that vegetation so affects the constitution of the atmosphere 

 as to keep the air fit for the support of man and beast. Phenomena 

 connected with each of these effects, and different phases of these, 

 will incidentally come under our notice ; and their correlation may be 

 attended to ; but the discussion of these does not come within the 

 scope of this treatise. 



No effects are attributed by me to forests which are not produced, 

 or might not be produced, by any and every blade of herbage or of 

 grass according to its measure. The difference is considered to be only 

 a question of degree. As the hue of a single hair, or a thread of spun 

 glass, may be imperceptible to many observers to whom the hue of a 

 mass of the same hair or glass may be apparent at once, so the 

 meteorological effect of a tiny leaf or a tiny moss, scarcely percep- 

 tible by a hurried glance, or those of a single tree, may be inappre- 

 ciable because infinitesimaUy small, but the effects produced by a 

 forest with its countless trees, boughs, and leaves be most manifest ; 

 and then, with these effects known, we may with advantage proceed 



