ARCTOWSKl, VOLCANIC DUST VEILS 171 



In the case of rainfall, Charles Meldrmn'^^ long ago noticed the double 

 oscillation. For the weather conditions in the United States, Frank H. 

 Bigelow^^ found that "the occurrence of four subordinate crests in the 

 11-year periods suggests strongly that a 2%-yea.r period is superposed 

 upon the long sweep of that periodic curve." Later, Bigelow'^ discovered 

 a correlation between this short period variation and the frequency 

 changes of solar prominences. 



One may conclude that Ivoeppen's calculations give only a first ap- 

 proximation, and that in reality the phenomenon of the 11 years' varia- 

 tion is complicated by a variation of a shorter periodicit}^, perhaps also 

 m connection with the changes of sun-spot frequency. 



A strong argument in favor of this supposition is the circumstance 

 that the commonly known 11 years' variation is not the only sun-spot 

 cycle. The relative numbers of AVolf and AVolfer have been analyzed 

 by Arthur Schuster,'^ who found the folloAving periods : 13.5, 11.125, 

 8.36, 5.56, 4.79, 3.71. Hisashi Kimura,^^ on the other hand, found 

 periods of 16.59, 13.53, 11.114, 9.99, 8.25, 5.95, 5.49, 4.85 and 3.63 years. 

 According to the most recent investigations^^ it may be, however, that, 

 ^'while these various periods are apparent, yet many are illusory." 



All these researches show very plainly that the frequency variation of 

 sun-spots is a most complicated phenomenon. So are also the tempera- 

 ture variations. It is certain that the pleionian variation of the Arequipa 

 or equatorial type has apparently nothing in common with the 11-year 

 cycle; but some correlations exist. In 1893 the antipleions were pre- 

 dominant. The year 1900 was a j)leionian year. One may presume, 

 therefore, that the solar cycle of 11 years has a direct influence on the 

 long range or macropleionian variations and that the shorter pleionian 

 and antipleionian oscillations of terrestrial temperature are the product 

 of some minor sun-spot C3Tle, or perhaps of some other solar cycle which 

 does manifest itself with the same evidence as the sun-spot frequency 

 variations. 



As soon as the particulars of the pleionian variations are better known, 



«8 Charles Meldrum : "Report on Sun-spots and Rainfall," Rep. 48tli meeting Brit. 

 Assoc, p. 257. 1879. 



^ Frank H. Bigelow : "Abstract of a Report on Solar and Terrestrial Magnetism in 

 their Relations to Meteorology," Bull, no. 21, U. S. Weather Bur., p. 125. 1898. 



■^0 Frank H. Bigelow : "The Relations Between the Meteorological Elements of the 

 United States and the Solar Radiation," Amer. Jour. Sci., ser. 4, vol. 25, p. 423. 1908. 



■^1 Arthur Schuster: "On the Periodicities of Sun-spots," Phil. Trans. Roy. Soc. 

 London, vol. 206 A., p. 69. 1906. 



''- Hisashi Kimura : "On the Harmonic Analysis of Sun-spot Relative Numbers,'* 

 Monthly notices Roy. Astr. Soc, vol. 73, p. 543. 1913. 



'^ A. E. Douglass: "A Photographic Periodogram of the Suti-spot Numbers," Astroph. 

 Jour., vol. 40, p. 326. 1914. 



