July 18, 1913] 



SCIENCE 



67 



PREVAILDIO DIEECII0N3 OT THE SUHJAOB WIUBS AMD THE UEAK PEEOIPITATIOH 

 IH THK UMITED STAIRS UnRHIQ JOT.Y 



even into eastern New Mexico, and as far 

 east as New England, the precipitation 

 over the entire eastern half of the United 

 States is very heavy. In winter the pic- 

 ture of both wind direction and precipita- 

 tion is radically changed. The northerly 

 and northwesterly winds have not the same 

 pronounced persistence as the summer 

 winds. Tet through the entire south — 

 Texas, Louisiana and Mississippi — as well 

 as the Atlantic states, the lake states and 

 the central states, the prevailing winds are 

 northerly and northwesterly winds. At 

 the same time there is a perceptible de- 

 crease in precipitation through the entire 

 eastern half of the United States, and 

 where in July there fell as much as three 

 inches of rain, in January there is less 



than one inch, and where in July there fell 

 as much as five inches there is in January 

 less than two inches. 



This increase and decrease in precipita- 

 tion over the eastern half of the United 

 States, with change in the direction of the 

 wind, points to the fact that the eastern 

 half of the United States depends for its 

 moisture upon the prevailing southerly 

 winds, which originate in the Gulf of Mex- 

 ico and the Atlantic Ocean. 



Professor "Willis Moore, therefore, is en- 

 tirely right, it seems to me, when he claims 

 that the Pacific Ocean has little influence 

 upon the precipitation of the eastern half 

 of the United States, as Mr. Gannett and 

 Mr. Bailey "Willis have tried to prove. It 

 is possible that some of the vapor that orig- 



