..,; 4 DR. C. CHREE: SOME PHENOMENA OF SUNSPOTS 



to the selected disturbed days of the 11 years; columns 9 to 14 do the same for the 

 6 years. The largest " character" figure found in days n + 25 to n + 30 is in heavy 

 type, and the ratio borne by this maximum to the character figure on day n (i.e., the 

 ratio' of the maximum for the first subsequent pulse to that of the primary pulse) is 

 given for the two periods separately in columns 15 and 16. Column 17 gives the 

 arithmetic mean of the ratios in the two previous columns. 



Investigations by Mr. W. ELLIS and Mr. E. W. MAUNDER, covering a very long 

 series of years, showed that whether one considers magnetic storms averaging about 



13 a year or days of large and moderate disturbance averaging about 77 a year 



the frequency of occurrence of disturbance at Greenwich is above the average in the 

 4 equinoctial months, and below it in the 4 summer months, May to August ; the 

 numbers in the equinoctial months standing to those in the summer months roughly 

 in the ratio of 8 to 5. 



A preponderance of disturbances in the equinoctial months has been noticed at 

 many other stations, but there is reason to doubt whether it is universal. 

 Dr. W. VAN BEMMELEN'S lists of disturbances at Batavia, averaging about 60 a year, 

 showed but a very slight excess in the equinoctial months, and the records of Captain 

 SCOTT'S expedition in the Antarctic during 1902 to 1904 indicated a marked maximum 

 of disturbance at midsummer. Still the equinoctial months are undoubtedly the 

 most disturbed at Kew, or at the average station on which the international figures 

 depend. 



In both periods of years the order in which the months come as regards disturbance 

 is not quite the same when one takes the mean character figure of the selected 

 disturbed days, given in Table VIII., as when one takes the mean character figure of 

 all days of the month, or when one takes the number of days of character " 2." 



In the 6-year period the months of March, September, February, and October 

 appear to have been distinctly the most disturbed. In the 11 -year period, March 

 and February were clearly the most disturbed, and judging by the number of days 

 of " character " " 2," October came next. Thus both periods manifested the usual 

 tendency to an increase of disturbance towards the equinoxes, but that season was 

 less prominent than in ELLIS and MAUNDER'S lists. Also the want of smoothness in 

 the sequence of the figures in the first two columns of Table VIII. suggests that 

 a considerably longer series of years would be required for the elimination of 

 " accidental " features. 



All months in Table VIII. show the first subsequent pulse clearly, the. crest 

 generally falling on the 27th day itself. The maximum in the subsequent pulse is 

 considerably larger in some months than others, but the months in which it is 

 largest, or smallest, are not the same for the two periods. In both, the maximum 

 figure is above its average in January, February, March, August, and September ; 

 but these months represent Winter, Summer, and Equinox. 



Judging by the differences between the two periods, and between successive 



