The Motion und Distribution of the Sun-spots 



91 



H. On the Possibility of two Drifts in the Motion of the Sun-spots. 



As mentioned in the introduction, Hirayama, in an exauiination of the table 

 of correlation between latitude and synodic rotation period given by Maündkr, has 

 supposed two apparent drifts of sun-spots as a tentative explanation of the skewness 

 in the distribution of the rotation periods. The metliod employed by Hirayama in 

 dissecting the frequency-curves into two components is exclusively graphical, and 

 thus we cannot attach to it any great accuracy. From the graphical representation 

 given by Hirayama in his paper it seems as if all tlie curves of distribution were 

 attended by a very considerable positive skewness. 



In order to examine the distribution analytically 1 have computed the charac- 

 teristics of these curves. The result of the computations is given in table XL, 

 where designates the mean of the synodic rotation periods. From this it follows 

 that the skewness of the frequency- curves of Hirayama, drawn on an arbitrary 

 scale, is not so large as it appears on a cursory observation. And since the mean 

 errors which are also given in the table are approximately of the same size as 

 the skewness, it seems somewhat ungrounded to make a division into components 

 in such a way as is done by Hirayama. Furthermore, Hirayama does not take 

 the excess, throughout positive, into consideration, an omission which to a eertaiii 

 degree makes this division illusory. 



TABLE XL. 



Characteristics of the Distribution of synodic Rotation Periods. 



Latitude 





To 





S 



E 



-f 25 < ,3 < + 30 



36 



27,578 ± 0.1751 



1.07^ + 0127 



+ 0 050 + 0.33-2 



+ 0,009 + 0.1''2 



4- 20 < < + 25 



115 



27.312 + 0.094 



1.014 + 0.067 



— 0 167 + O.ISO 



+ 0 172 + 0.057 



+ 15 < < + 20 



188 



26 819 + 0.057 



0.782 + 0.040 



+ 0.392 + 0.141 



+ 0.067 + 0.045 



+ 10 < f! < + 15 



290 



26.755 + 0.048 



0.818 + 0.031 



- 0.052 + 0.113 



+ 0 201 + 0.036 



+ 5<ß< + 10 



154 



26.46G ± 0.060 



0.744 + 0.065 



-1- 0.185 + 0 156 



+ 0.014 + 0.049 



- 5<^i<+ 5 



133 



2(3 354 + 0.0G9 



0 800 + 0.049 



+ 0.1G6 + 0.168 



+ 0.022 + 0.053 



- 5 > [rl > - 10 



240 



26.673;+ 0.050 



0.776 + 0.C35 



+ 0.319 + 0 125 



+ 0.088 + 0.040 



- lo>i^>- 15 



204 



26.697 ± 0.051 



0.871 + 0.036 



+ 0.191 + 0.113 



+ 0.177 + 0.036 



- ]5>ß> - 20 



252 



26.944 + 0.060 



0.945 + 0.012 



+ 0.126 + 0.122 



+ 0.138 + 0 039 



— 20 > ß > - 25 



110 



27.136 + 0 080 



0 889 + 0.056 



-f 0.109 + 0.184 



— 0.006 + 0.058 



— 20 > ß > - 30 



44 



27.509 + 0.147 



0.974 + 0.104 



+ 0.259 + 0.291 



+ 0.118 + 0,092 



As seen from the previous investigation, the skewness of the distribution of the 

 motions of the spots is proved to be inconsiderable. It is now obvious that if the 

 distribution of the values of a variable x is normal, the distribution of I : x will 

 be attended by a negathe skewness. We ought thus, upon an average, to expect a 

 negative skewness in the distribution of the rotation periods of the spots instead 

 of a positive, as is the case here. Here, however, we must take into consideration 

 the fact that Maunder has determined the synodic rotation-perioil from spots exi- 



