2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 87 



periodic terms of 7- and 8-month periods. In what follows, all the 

 modern results are derived from data thus smoothed. In the use of 

 precipitation observations the absolute values are first converted into 

 percentages of the monthly mean values as these are given in bold 

 face type in " World Weather Records." Temperature departures 

 are computed from the appropriate monthly means printed in bold 

 face type in the same source book. 



In our early work we found that the seven periodicities discovered 

 by the writer in solar variation ' and a few others have their counter- 

 parts in temperature departures. Figure i shows, for instance, a study 

 of the departures from normal monthly temperatures for Clanton, 

 Alabama, for the years 1918-1930. It is apparent that the residual 

 remaining after removing periodic terms is small. 



B. THE SUN-SPOT INFLUENCE 



When we expanded our research to embrace records extending 

 from 1875 to 1925, we were embarrassed like other investigators by 

 changes of phase and amplitude in the periodic terms. It occurred 

 to me that since the periodicities employed were nearly related to the 

 sun-spot period of 1 1 years, it might well be that they would be altered 

 with the number of sun spots prevailing. This proved to be true. 

 Figure 2 shows, for instance, the 11 -month periodicity in the depar- 

 tures from normal temperature at Bismarck, North Dakota. The 

 results are as computed from four groups of data between 1875 and 

 1925, segregated with reference to the sun-spot numbers correspond- 

 ing. It will be seen that the phases remain unchanged throughout this 

 50-year interval when obtained for homogeneous groups chosen from 

 sun-spot considerations, but alter steadily from group to group as the 

 sun-spot activity increases. 



Thus it is apparent that the sun-spot activity produces an important 

 influence on weather not heretofore recognized. This unperceived 

 influence has no doubt disappointed many meteorologists in their 

 studies of periodicities. 



C. THE 23-YEAR CYCLE 



In the year 1908 Dr. George E. Hale at Mount Wilson Observatory 

 discovered magnetism in sun spots. He soon found that magnetic 

 polarities are opposite in adjacent spots. Following up the investiga- 

 tion it was disclosed that the order of the two polarities is opposite in 



' Abbot, C. G., Weather dominated by solar changes. Smithsonian Misc. Coll., 

 vol. 85, no. I, 1931 ; also, Forecasts of solar variation, ibid., vol. 89, no. 5, 1933. 



