The Motion and Distribution of the Sun-spots O 



a planet interior to Mercury». As is well known, Schwabe did not succeed in disco- 

 vering a planet interior to Mercury. That lie valued the discovery of the perio- 

 dicity of the sun-spots is shown in the above mentioned letter, where he compares 

 himself with Saul, »who went out to seek his father's 

 asses, and found a kingdom*. 



Induced by the discovery of Schwabii;, Wolf 

 of Zürich made his well-known researches. Up to that 

 time, they had employed the number of spots, or groups 

 of spots, as a measure of the frequency of sun-spots. 

 For well-known reasons, Wolf, in the year 1851, in- 

 troduces his relative mimhers r, defined by the relation 



TABLE III. 

 The Relative Numbers and 

 Spot-areas 1874 1910. 



= ^■(10,7+/) 



where 



g = the number of spot groups and individual 

 spots, 



f = the sum of individual spots and spots be- 

 longing to the different groups, 



^ = a constant, dependiiig on Ihe power of the 

 instrument. 



For the observations made by Wolf with his refractor 

 of 3 inches, he put 



Though these relative numbers are arbitrarily 

 chosen, they are, nevertheless, a much better measure 

 of the spot-activity tiian the preceding spot-numbers. 

 In general one assumes the relative numbers to be 

 proportional to the spot area. »One hundred as a 

 sun-spot number corresponds to about of the sun's 

 visible disk covered by spots, including botli umbras 

 and penumbras. » ' 



In order to examine the relation between relative 

 numbers and spot-areas, I have used the values of 

 the daily mean area for every year, corrected for for- 

 shortening, which values are obtained from photographs 

 of thesun published in the Green wich Observations^. 

 This examination comprises the time from 1874 to 

 1910. The daily mean area, expressed in millionths 

 uf the sun's visible disk, I designate by ^. The relative numbers of Wolf are, 

 as above, designated by r. In Table III, r and A are given from 1874—1910. 



1880 

 1881 

 1882 

 1883 

 1884 



1885 

 188G 

 1887 

 1888 

 1889 



1890 

 1891 

 1892 

 1893 

 1894 



1895 

 1896 

 1897 

 1898 

 1899 



1900 

 1901 

 1902 

 1903 



190« 

 1907 

 1908 

 1909 



32.3 

 543 

 59.7 

 63.7 



26.7 



62.0 

 48.5 

 43.9 



1191 

 778 



1082 

 697 

 692 



Abbot: The Sun p. 184. 

 ' A more complete account of tliese pliotog 



•aphs 



iven in Chapter I. 



