HOI 



agreement is not imaginary, and hence that the 89-year period has 

 a real existence. 



On the nature of this 89-year periodicity I will not say much, 

 now that analysis has yielded nothing definite. It is evident that 

 'we have no simple curve here. It should be mentioned that Prof. 

 Turner, after his elaborate investigation of the fluctuations of the 

 sun's activity^), obtained as chief periodic terms: {a) 8.3, ib) 10.2, 

 (c) J1.4, and {d) 14.7 years, and that a x 11 = Ö1.3, 6x9 = 9i-8, 

 c X 8 = 91.2, (/ X 6 = 88.2, on the average about 90 or 91 years. 

 The deviation /from our &9-year period (the aveiage length ofwdiich 

 appears not to be very elastic) would however be large enough to 

 disturb the agreement in the long run, if Turner's investigations did 

 not extend over a much shorter time than our climatological 

 series. The phenomenon of sun-spots (and only this element of solar 

 activity has been studied for a long time) has only been observed for 

 three centuries, and so incompletely before 1820 that Wolfer assigns to 

 the earlier observations an average weight of only 0.4 as compared 

 with the later ones. The analysis of a much longer series of solar 

 observations would perhaps have yielded periodic tei-ms of a some- 

 what longer or shorter duration. It should also be noticed that the 

 approximately 11-year period, with the largest amplitude, has by all 

 other observers been found shorter than l\y Turner (Newcomb, Wolfer 

 and Schuster 11 1/8, R. Wolf and Hirayama 11 1/3, Kimura 11 

 19). — Now 11 1/8 X 8 = 89. 



Moreover it followed already from my former investigation — 

 and this conclusion is confirmed by the new material — that very 

 likely neither the length nor the amplitude of the periods that may 

 lie hidden in the 89-year climatic periodicity, remain constant. 

 Turner vsays of the solar periods found by him: "that their coeffi- 

 cients do nol remain constant", only the 11,4 years period being 

 sensible at the present lime. 



1) tVom the extensive literature on the periodicity of the soliir activity we here 

 only note : 



R. Wolf and Spöreb [Mem. d. Soc d. spettrosc. ital, X), R. Wolf (Astr. 

 Nachrichten 2563), Newcomb {Astrophy.-^. Journal XllI), A. Wolfer {Astron. 

 Mitteihmgen XClll seq.), Kimura {Monthly Notices E A.S. 73), Hirayama 

 (cit. Kimura), Schuster (Phil. Trans. 206, 1906), Turner (Monthly Not. 78, 

 74j, MicHELSON {Aph. J. XXXVIll), Douglass {Ai}h. J. XLI). 



The conclusion of Michelson's investigation with the "harmonic analyser" is 

 interesting: "indeed it would seem that with the exception of the 11 y.-period 

 and possibly a very long period of the order of 100 years, the many periods 

 found by previous investigators are illusory". 



