AGRICULTURE ON CLIMATE. 181 



a region absolutely rainless. I have ventured to refer to 

 this somewhat hackneyed explanation of some of the phe- 

 nomena connected with rain-fall, because it so well illustrates 

 some points hereafter referred to in connection with forests. 



Evaporation is a cooling process, and by this means for- 

 ests cool the air for quite a distance above and around them, 

 and thus have the same effect in condensing the moisture of 

 the air blowing over them, as the coldness of the atmosphere 

 incident to increased elevation. The moisture-laden air com- 

 ing over an extensive forest is cooled below the dew-point, 

 deposits its moisture thereon and becomes comparatively* 

 dry, and passing thence into the warmer air over the mossy 

 pastures and scanty growth of exhausted fields far above the 

 dew-point, not only does not give out any of its own scanty 

 moisture to the parched earth, but carries off also the small 

 amount evaporated therefrom. Thus though nature is no 

 respect(?r of moral qualities, but sendeth her rain on the just 

 and on the unjust, she hath regard for the faithful tiller of 

 the soil, and sendeth her refreshing showers on his luxuriant 

 fields and forests, while she withholdeth it from the soil of 

 the unfaithful, who hath robbed it of all its fertility, again 

 illustrating that principle in nature already referred to, that 

 to him that hath shall be given and he shall have abundance, 

 and from him that hath not shall be taken away that which 

 he hath. 



I quote a few reported facts in regard to the effect of for- 

 ests on climate. In Italy the clearing of the Apennines is 

 believed to have seriously changed the climate of the Po val- 

 ley, and now the African sirocco, formerly unknown to this 

 region, reaches the right bank of the river in the territory 

 of Parma. 



The removal of the pine forests near Ravenna induced 

 the same desolating wind, and the same destruction of the 

 old forests of Vosges and of the Cevennes has had a like 

 deteriorating influence upon their climate. 



In Egypt, where, during the French occupation in 1798, 

 not a drop of rain fell for sixteen months, and where from 

 time immemorial the country had been a rainless bed of 

 sand, Mohamed Ali, by planting his millions of fig and 

 orange trees, has seen his country blessed with au annual 

 ram-fall of several inches. 



