The Motion and Distribution of the 8iin spots 



15 



activity of the sun. Stephani, it is true, is of opinion that of the greater sun-spots 

 during 1905 — 1910, only about 8 Vo arise on the side of the sun directed towards the 

 earth. If this were true, we should also have an explanation of the observed spot- 

 excess. The assertion of Stephani, however, is not in the least confirmed by the 

 material of observation treated in the present paper. In another chapter we shall 

 return to this question. 



The two hemispheres also show at times considerable differences as regards 

 the spot-activity. Thus no spots were observed in the northern hemisphere from 

 1672 — 1704. Newcomb draws attention to a growing preponderance of spots in 

 the southern hemisphere in the four cycles 1856—1898 In the above mentioned 

 paper »0n the Distribution of Sun-Spots in Heliographie Latitude» 

 Maunder shows, that the spotted area in the northern hemisphere amounts only to 

 43.6 % of the entire spot area. During the last period, however, the spot-activity 

 of the two hemispheres has been of about equal intensity, as is seen from table VI. 



I here finish the historical summary of the sun-spot research. The present 

 in-vestigation will deal, in the first place, with the motions of the sun-spots. In this 

 connection I borrow the following figurative illustration from Abbot's »The Sun»: 

 »If we imagine an observer on the moon to watch the clouds on the earth's sur- 

 face, they would appear to him on the whole to indicate a mean rotation period 

 of about twenty-four hours for the earth. But he would also discover that many, 

 and perhaps nearly all, of the cloudy areas had proper motions of their own 

 besides, so that no single cloud would give correctly the rotation period of the 

 earth. So it is with the sun-spots, for, after allowing for the sun's average rotation 

 period, nearly every spot has a motion of its own.» 



The purpose of this work is, in the first place, to investigate these proper 

 motions of the sun-spots. In this research I sliall, however, not confine myself only 

 to the computing of means as is the case in the majority of the works on the 

 motions of the sun-spots hitherto published. In order to obtain a complete idea of 

 the distribution of the motions it is also necessary to compute the dispersion, sJce/v- 

 ness and excess. 



The method employed in treating the observations, I have borrowed from 

 Mathematical Statistics, chiefly from the works of Charlier. 



Amongst these works, I especially mention »Re searches into the Theory 

 of Probability* and »Studies in Stellar Statistics I, II» published in the 

 »Meddelanden från Lunds A s tr o n o m i s k a Observatorium». 



Ch. Abbot: The Sun, p. 193. 



