346 HUMPHREYS: AMERICAN TEMPERATURES 



One of the most interesting of the inter-relations between cli- 

 matological factors so far shown by this study is the close relation 

 between the annual average temperature of the eastern United 

 States and the total annual precipitation over a large portion of 

 northern Europe. Since the prevailing winds across the North 

 Atlantic are from America to Europe it would seem that when the 

 annual average temperature of the eastern United States is high 

 these winds should reach Europe relatively heavily laden with 

 moisture (evaporation increases rapidly with increase of tempera- 

 ture) and give to it a correspondingly large annual total precipi- 

 tation. On the other hand, when the annual average tempera- 

 ture of the eastern United States is below normal one might 

 reasonably expect the corresponding annual precipitation of 

 Europe also to be below its normal. 



This argument is exactly the same as that which would lead 

 us to anticipate an increase of world-wide precipitation following 

 a universal, or practically universal, increase in the average 

 temperature; but as it applies to well known and restricted regions 

 it is far more easily tested statistically. To this end the averages 

 were taken for each year from 1874 to 1913, inclusive, of the 

 annual average temperatures of 30 rather evenly scattered United 

 States Weather Bureau stations east of the 90th meridian, and the 

 results compared with the average of the annual precipitations 

 at 21 stations widely scattered over Germany. The temperature 

 data were furnished by the Climatological Division of the U. S. 

 Weather Bureau, Mr. P. C. Day in charge; and the rainfall data 

 from 1874 to 1900, inclusive, were obtained from Hellmann's 

 Die Niederschlage in den Norddeutschen Stromgebieten, volume 

 1, pages 336 and 337. The subsequent precipitation data were 

 derived from official meteorological publications relative to the 

 same stations in the library of the U. S. Weather Bureau. Both 

 sets of data, the temperature and the rainfall, were ''smoothed" 

 according to the equation, commonly used for this purpose, 



,, _ q + 26 + c 

 4 



in which b' is the "smoothed" value for the year in question, 



