8 



O. A. Åkesson 



were introduced in 1851. As the observations of different observers after the year 

 1749 partially covered each other, it was possible for Wolf to get the observa- 

 tions from this year converted into homogeneous relative numbers ^. 



The material collected by WoLr has been employed by different authors in 

 order to determine the period of the sun-spot activity. Wolpee, by a critical exami- 

 nation of the observations from 1749 — 1901, found the following values: ^ 

 Period from sun-spot minima = 11.141 ± 0.036 years (weight 2) 

 » » » maxima = 11.091 ± 0.053 » ( » 1) 



Mean = 11.124 ± 0.030 

 Time from min. to max. = 5.16 years. 



» » max. » min. = 5.96 » 

 From the material of Wolf and the photographical observations after 1874, 

 Newcomb ^ got a period of 



11.13 ± 0.02 years. 



The interval from minimum to the following maximum he found to be 4.62 years 

 and from max. to min. 6.51 years, values that considerably differ from those found 



by WOLFER. 



An interesting contribution to the question of the periodicity of the spot- 

 activity is given by Schuster \ though many distinguished investigators doubt the 

 results of his researches. As is well known, Schuster makes use of Harmonic 

 Analysis. He has shown that the spot-frequency may be represented by a series 

 of sine-curves. For the most prominent of these he has also determined the periods 

 and found them to be as follows : 



l:o. 11.126 years, 



2:o. 8.36 » , 



3:o. 4.8 » . 

 Very remarkable is the fact that we have 



i . 33.375 = 11.125, 

 i . 33.376 = 8.344, 

 1. . 33.375 = 4.768. 



We might therefore consider these three waves as harmonics of a wave, the period 

 of which is somewhat longer than 33 years. 



A method similar to that of Schuster is also employed by the Japanese 

 Astronomer Hisashi Kimura ^. His investigations of the relative numbers of Wolf 



^ R. Wolf: Astronomische Mitteilungen 50. 1880. 



A. Wolfee: Astronomische Mitteilungen 93. 1902. 

 ' S. Newcomb: On the period of the solar spots. Astrophysical Journal 1901. Vol. XIIl. 

 * A. Schuster: Proceedings of Royal Society 77. 136—140. 1905. Phil. Transactions A 

 206. 69-100. 190G. 



^ H. Kimura : On the Harmonic Analysis of Sun-Spot Relative Numbers. Monthly Notices. 

 May 1913. 



