METEOROLOGY. 133 



INFLUENCE OF AGRICULTURE ON THE CLIMATE AND THE ANNUAL 

 FALL OF RAIN, 



The question, wlietlier the clearing away of forests and the 

 labors of the agriculturalist have had any influence in lessening 

 the annual quantity of rain and the quantity of water in streams, 

 as well as in modifying the climate, is one of considerable 

 interest and importance. The clearing away of forests, so as 

 to allow^of free evaporation of water from marshes, and per- 

 mit the access of the sun's rays to the soil, most certainly has 

 a tendency to equalize the distribution of heat, if it does not 

 actually raise the mean annual temperature. The mean tem- 

 perature of the whole earth, however, was much higher 

 formerly than at present. The tillage of the soil, by rendering- 

 it loose, and exposing a greater surface to the action of heat 

 and air, favors evaporation, and in this way makes a cold, wet 

 soil, dry and warm. It also increases the capacity of the soil 

 for heat, and favors nocturnal radiation and the formation of 

 dew : but perhaps this fact goes about as far to sustain one 

 side of the question as the other. 



It is a fact universally admitted by geologists, that the level 

 of the waters of the earth have every where undergone a 

 change. The instances are numerous, in which rivers, lakes, 

 seas and marshes, have been greatly diminished or totally 

 dried up; this may be one of those phenomena which is 

 evident to all, but which is nevertheless difficult clearly to 

 explain. Islands have risen out of the sea, coasts have been 

 left dry by the receding of the waters, and the beds of large 

 rivers have become dry arable soil. This has of course been 

 in some instances owing to the actual elevation of portions of 

 land by some subterranean force: and it is also true that 

 portions have been submerged by similar causes. But these 

 causes are insufficient to account for the general drying of 

 streams and diminution of rains in cleared agricultural dis- 

 tricts. " In felling the trees which covered the crowns and 

 slopes of mountains, men in all climates seem to be bringing 



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