HOW THE SUN WABMS THE BAKTH — ABBOT 173 



of low with intervals of hi<j^h sun spots. To reinforce this observa- 

 tion, I shall give one other instance from Cape Town, South Africa, 

 10,000 miles from Bismarck. Again in figure 16, observing the 11- 

 month solar period as reflected in Cape Town temperature depar- 

 tures, and confining ourselves to intervals of time when Wolf's sun- 

 spot numbers did not exceed 30, we find that the 11-month period is 

 so definite and so accurately in the same phase from 1865 to 1925 

 that we are able to correct the length of the period and detect that it 

 lacks 3 days of a full 11 months. It is in fact 331 days. 



I need not detain you to discuss others of the numerous solar 

 periodicities which I have found reflected at numerous stations all 

 over the world, both in temperature and precipitation. I will only 

 state that the cumulative evidence that the solar variations largely 

 control the weather is overwhelming. The regular periodicities that 

 comprise solar variation are all important in governing weather, but 

 their weather effects shift in phase according to the sun-spot numbers 

 prevailing. 



THE 23-yEAR PERIOD IN WEATHER 



It happens that 7 solar periodicities above specified all come 

 very close to finding their least common multiple in the double sun- 

 spot period of 276 months, or 23 years. It may be very significant 

 that this interval, within the error of observation, is equal to Hale's 

 magnetic cycle in sun spots. Since all of the solar periodicities of 

 which it is the least common multiple are influential in governing 

 weather, we need not be surprised to find that the weather tends to 

 repeat itself, detail after detail, at intervals of 23 years. 



As an illustration, figure 17 shows the smoothed percentages of 

 normal monthly precipitation found at Nagpur in south-central India 

 from 1856 to 1930. The values are arranged in 23-year cycles, so 

 chosen that the year 1875 begins a cycle so as to fit with most of the 

 lists in World Weather Records.- Lines have been drawn to guide 

 the reader's eye to what seem to me to be homologous features in 

 the four cycles illustrated. I would like to call special attention to 

 the regions 1865-70, 1888-93, 1912-17. In 1865, 1868, and 1870 we 

 find 3 pillarlike features of high-percentage precipitation bound- 

 ing 2 features of subnormal precipitation. Thus there stand out 

 two intervals of 3 and 2 years, respectively, as if guarded by these 

 sentinel features, but embracing nearly a score of subordinate fea- 

 tures. The reader's attention is now invited to similar features, 

 1888-93 and 1912-17, in which nearly all the details seem to be 

 recojrnizable. 



» Smitlisouiau Misc. Coll., vol. 79, 1927 ; vol. 90, 1934. 



