220 SCIENCE REMAKING THE WORLD 



The vapour brought by the prevailing winds from the 

 ocean is many times turned over or reinvested before it 

 is returned again to the ocean through the rivers. If 

 we could reduce the surface run-off, and at its expense 

 increase the evaporation from the land, we would 

 thereby increase the moisture in the passing air currents 

 and in this way contribute to the precipitation of that 

 region into which the prevailing winds blow. This 

 conclusion is almost axiomatic. 



If the southerly and southeasterly winds in their 

 passage toward the north, northwest, and northeast, in 

 the spring and summer, did not encounter the vast 

 forest areas bordering the shores of the Gulf of Mexico 

 and the Atlantic Coast and those of the Southern 

 Appalachian region and, therefore, were not enriched 

 with enormous quantities of moisture given off by 

 them, the precipitation in the central states and the 

 prairie region would undoubtedly be much smaller 

 than it is now. 



If the present area occupied by forest in the Atlantic 

 plain and the Appalachian region were instead occupied 

 by a large body of water, no meteorologist would hesi- 

 tate for a moment to admit that this water surface 

 would have a perceptible influence upon the humidity 

 of the central states and prairie region. Should not, 

 therefore, the forests which give off into the atmosphere 

 much larger quantities of moisture than free water sur- 

 face have at least a similar influence upon the regions 

 into which the prevailing air currents flow? 



Direct proof of this climatic influence quantitatively 

 expressed is still lacking. It will take many decades 



