[ 245 ] 



VI. Some Phenomena of Sunspots and of Terrestrial Magnetism. Part II. 



liy C. CHREE, Sc.D., LL.D., F.R.S., Superintendent of Kew Observatory. 



Received June 10, Read June 26, 1913. 



CONTENTS. 

 



1. Introductory 245 



2. International magnetic " character " figures 246 



3-6. 27-day period in international " character " figures 247 



7-8. Subsequent and previous associated " pulses " 250 



9-11. Estimates of length of period 255 



12-13. Relations between primary and associated pulses 258 



14-15. Comparison of previous and subsequent associated days in 1890 to 1900 261 



16. Annual variation in 27-day period 263 



17-18. Relation of magnetic " character " figures to sunspot areas 267 



19. Sunspot areas, projected and corrected, faculse and WOI.FER'S sunspot frequencies . . 271 



2Q. Amplitude of 27-28-day period in projected sunspot areas 274 



21-22. Concluding remarks 275 



1. IN a previous paper, described here for brevity as S.M.,* whicb referred to 

 sunspots and terrestrial magnetism, I had occasion to enquire into the existence of 

 any relation between the magnetic character of individual days and that of days 

 separated from them by a given interval of time. References to previous work 

 bearing on the subject will be found in S.M., p. 97. 



The material of which I made principal use consisted of magnetic " character " 

 figures on the international scale (quiet), 1 (moderately disturbed), and 2 (highly 

 disturbed) assigned by myself to all the days of the eleven years 1890 to 1900, from 

 consideration of the Kew magnetic curves. 



In each of the 132 months of the eleven years the five days were taken which gave 

 the largest daily range to the magnetic horizontal force. In default of any more 

 satisfactory means of selection, the 660 days thus obtained were taken as representative 

 of disturbed conditions. Regarding any one of the selected days as day n, the 

 " character" figures for the 41 successive days n 5ton + 35 were written down in a 

 row. This was done for each of the 660 selected days in succession, so that there 

 were in all 41 columns of figures, each containing 660 entries. 



* 'Phil. Trans.,' A, vol. 212, p. 75. 

 VOL. CCXIII. A 502. Publiihed epartelj, Augurt 8, 1913. 



