216 SCIENCE REMAKING THE WORLD 



that changes which take place in one part of this vast 

 region may exert some influence on the condition of the 

 other? We have seen that in the central states in 

 summer the prevailing westerly and northwesterly 

 winds give way to southerly and southeasterly winds. 

 In other words, in the summer the central states are 

 under the influence of moist winds just at the time when 



PRECIPITATION SHOWN BY 

 -LINL5AND riGURE15 

 WIND SHOWN BY ARROWS 



- WIND DIRECTION AND MCAN PRE.CIPJTATION FOR THE MONTH OF JANUARY 



the evaporation is the greatest and the forest vegetation 

 is especially active. It seems, therefore, that the 

 amount of moisture evaporated within the more moist 

 region of the United States can influence the conditions 

 of humidity, not only in the states close to the ocean, 

 but also in the region into which the prevailing moist 

 winds flow. The more moisture there is evaporated 

 from the ground in the southern and southeastern 





