18 



O. A. Åkesson 



Here 1 only want to define the meaning of the longitude and latitude of a 

 spot. These co-ordinates are referred to a system with the origin in the centre of the 

 sun. The fundamental plan coincides with the equator determined hy Carrington, 

 the inclination of which to the ecliptic is 7 "15'. The longitude of the ascending 

 node is 73"40'. This system of co-ordinates is assumed to rotate with the mean 

 angular velocity of the sun as determined by Carrington, corresponding to a rotation 

 period of 25.38 days. As zero-meridian in this system that meridian is assumed 

 which passed through the ascending node of the sun's equator on the ecliptic at 

 Greenwich Mean Noon January 1 1854. 



As regards the computation of the heliographic longitude and latitude of the 

 spots, I refer to the Greenwich Observations, where complete formules are given. 



The following investiga- 

 tion comprises the observa- 

 tions from 1886—1909. 

 These 24 years I have 

 divided into two periods, 

 1886-1897 and 1898-1909. 

 The reasons why I began 

 the investigation with the 

 year 1886 are rather arbi- 

 trary. It seemed convenient 

 to include as many years 

 as would make it possible to 

 divide the material into two 

 periods in treating it. Thus 

 one might compare the 

 results from the two periods 

 and be prevented from draw- 

 ing conclusions from any 

 regularities that are indicated 

 in one of the periods but not found in the other. Another reason why I 

 began with the year 188() was that at the beginning of the work I had not the 

 Ledgers of the preceding years at hand. Further, from the year 1886 (or 1885) 

 there are photographs of the sun for almost every day. And lastly, the two periods 

 1886 — 1897 and 1898 — 1909 correspond to about two cycles in the spot-activity of 

 the sun, as is seen from table VII, where the daily mean areas denote the mean 

 of the areas of the spots, corrected for foreshortening and expressed in millionths 

 of the sun's visible hemisphere. From this table we also see a considerable difference 

 between the spot-activity of the northern and southern hemispheres. 



As the principal object of the present paper is to examine whether any physical 

 drifts exist in the motions of the sun-spots, it seems convenient to treat the observations 

 in a different way -from that of other authors who have dealt with the motions of 



TABLE VII. 

 Daily Mean Areas of Sun-spots 



Northern 



Southern 

 s^ihere 



1874 

 1875 

 1876 

 1877 

 1878 

 1879 

 1880 

 1881 

 1882 

 1883 

 1884 

 1885 

 188G 

 1887 

 1888 

 1889 

 1890 

 1891 

 1892 



1897 

 1898 

 1899 

 1900 

 1901 

 1902 

 1903 

 1904 

 1905 

 1906 

 1907 

 1908 

 1909 

 1910 



