10 



H. H. Clayton — Seven Day Weather Period. 



frequency occurred first at higher latitudes and at western 

 stations, indicating that the periodicity was connected with 

 barometric waves which swept from the poles toward the 

 equator and from west to east, or in other words from the 

 northwest. 



Beginning in the arctic region, the results for several suc- 

 cessive stations lying in a general E".W. to S.E. direction are 

 plotted in diagram 1 for both Europe and America. The 

 beginnings of the curves are displaced one day for each suc- 

 cessive difference of about 15° of longitude or latitude so as to 

 show the corresponding points of the curves. The American 

 stations are Pt. Barrow, Cheyenne, Chicago, and Blue Hill, 



