32 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



vot.. 82 



Pressure curves are plotted for five widely separated stations. These 

 plots show distinctly an oscillation in the atmosphere of the length of 

 7.5 years and a progress southward from high latitudes. 



1860 1870 1880 1890 1900 19 10 1920 



Fig. 22. — 7.54-year period in sun spots and pressure means of 3 periods. 



VI. SOLAR CYCLES AND WEATHER CYCLES 

 From the preceding investigation it is evident that atmospheric 

 and solar conditions show wavelike changes of a periodic nature. 

 The question has long been a challenge to investigators, as to whether 

 there are fixed and regular cycles in weather and in solar changes. 

 If such regular cycles could be found, it would greatly assist in 

 unraveling the complexities of the weather and in forecasting future 

 occurrences. There is a dominating period of about 11 years in sun- 

 spot numbers, and many efforts have been made to find this same 



