i6 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



Fig. 11. — Thirty-nine-month period in solar variation cleared of shorter 

 harmonics. 



computed, using all the solar constant measures from the years 1923, 

 January, through 1943, June. Periods 273/14, 273/21, 273/28, 

 273/35, 273/91 (and 273/24 doubtful) are shown successively re- 

 moved by computation and are exhibited as graphs B', C, D', E', F', 

 leaving curves B, C, D, E, F. This leaves 273/7 almost fully cleared 

 of irregularities. It is a very pretty sine curve v^ith amplitude 0.28 

 percent of the solar constant. 



5. ANOTHER TYPE OF PERIODIC VARIATION DUE TO 

 SOLAR ROTATION 



The late Dr. H. Arctowski published (Proc. Nat. Acad. Sci., 

 vol. 26, pp. 406-411, 1940) graphs (here fig. 12) which show vari- 

 able differences in brightness over the sun's rotating surface asso- 

 ciated with corresponding variation of the solar constant. Figure 13 

 shows solar-constant results, March to April 1920. A huge sunspot 

 group passed centrally over the sun's disk March 20-24 (see fig. 13). 

 It produced a large depression of the sun's radiation. L. B. Aldrich 

 gave extensive evidence (Smithsonian Report for 1952) proving the 

 increase of solar radiation with increased sunspot activity (see fig. 14). 



