150 METEOEOLOGICAL INFLUElSrCE OF THE FOEEST. 



ecarcely any green thing except the bitter colocjnth and the 

 poisonous foxglove is ever seen.* 



General Meteorological Injhience of the Forest. 



The physico-geographical influence of forests may be divided 

 into two great classes, each having an important influence on 

 vegetable and on animal life in all their manifestations, as well as 

 on every branch of rural economy and productive industry, and, 

 therefore, on all the material interests of man. The first respects 

 the meteorology of the countries exposed to the action of these 

 influences ; the second, their superficial geography, or, in other 

 words, the configuration, consistence and clothing of their sur- 

 face. 



For reasons assigned in the first chapter, and for others that 

 will appear hereafter, the meteorological or climatic branch of 

 the subject is the most obscure, and the conclusions of physicists 

 respecting it are, in a great degree, inferential only, not founded 

 on experiment or direct observation. They are, as might be ex- 

 pected, somewhat discordant, though one general result is almost 

 universally accepted, and seems indeed too well supported to 

 admit of serious question, and it may be considered as estabhshed 

 that forests tend to mitigate, at least within their own precincts, 

 extremes of temperature, humidity and drought. By what pre- 

 cise agencies the meteorological effects of the forest are produced 

 we can not say, because elements of totally unknown value enter 

 into its action, and because the relative intensity of better under- 

 stood causes can not be measured or compared. I shall not occupy 

 much space in discussing questions which at present admit of no 

 solution, but I propose to notice most of the known forces whose 

 concurrent or conflicting energies contribute to the general result, 

 and to point out, in some detail, the value of those influences 

 whose mode of action has been ascertained. 



* The French traveller, Largeau, believes the Sahara to have been anciently 

 well watered and well wooded, and to have been reduced to its present con- 

 dition by the folly and improvidence of man. He thinks, too, that much of 

 it might easily be restored to fertility. — Le Pays de BirTui, Paris, 1879, chap, 

 -viii., ix., xvii., et alibi. 



