64 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. jy 



of solar radiation. This latter influence probably results from or is 

 aided by absorption and radiation of heat from the earth's surface, 

 as well as by direct absorption and radiation of heat by the atmos- 

 phere. The independence of these two variables should be kept 

 clearly in mind. The first remains more or less constant throughout 

 the year, while the second reverses between winter and summer. 



A third variable is the atmospheric drift, carrying with it the air 

 circulations around high and low pressure areas. In part, this varia- 

 tion in drift results from variations in the general atmospheric cir- 

 culation and in part from variable contrasts of air temperature over 

 large areas of the earth's surface. 



A fourth variable is perhaps a readjustment of the pressure and 

 temperature due to the movements of ocean currents set up by the 

 winds attending the distribution of pressure determined by the causes 

 enumerated above. The study of Helland-Hansen and Nansen proves 

 that the movement of ocean currents cannot be the primary cause 

 of pressure changes, but they may produce a modifying efifect. 



The longitudinal shifts, that is, the east to west shifts of the centers 

 of action attending solar heat changes are not yet fully understood, 

 and there may be other variables in the solar action not yet disclosed. 



A clearer idea of the theory here outlined may be gained by study- 

 ing the diagrams in " World Weather," ^ more especially figures 58, 

 62, loi, 102, 107, and 109. 



^ " World Weather," by Henr}^ Helm Clayton. Cloth, 393 pages, 265 figures 

 and illustration, 16 plates. For sale by Eliot C. French, Canton, Massachusetts, 

 U. S. A., $4.00 postpaid. 



