2g2 1,1;. <. rmiKE: SOME PHENOMENA OF SUNSPOTS 



Tl . is .1 faint suggestion of a period of about 13 days, but if it exists its 

 amplitude is very small. 



'I'll,, tirst subsequent pulse is not clearly shown in Table VI. before day 25, while 

 the first previous pulse clearly persists until day 24 if not day 22. Also the previous 

 pulse is not clearly shown until day 30, while the subsequent pulse obviously extends 



until day 32. 



The differences arise undoubtedly in the main from the fact already noticed in 

 connection with the 6-year period, that the first previous and subsequent pulses both 

 follow the primary in having the rise to the maximum more rapid than the subsequent 

 fall. The primary pulse itself in Table VI. is not clearly manifest until the second 

 .lay I M -fore the selected disturbed day, while it clearly persists until the fourth day 

 thereafter. But, in addition to this, there is at least a suggestion that the interval 

 lx-t wen the crests of the primary and the first previous pulse is shorter than that 

 between the crests of the primary and the first subsequent pulse. This result is also 

 suggested by the 6 -year data in Table III. 



Even if we accept the figures as mathematically exact, a real difference in period 

 does not necessarily follow. The phenomenon may be a consequence of the diurnal 

 variation which undoubtedly exists in disturbance. Analysing the list of Greenwich 

 magnetic storms between 1848 and 1903 given by Mr. MAUNDER,* I found that 

 accepting the times of commencement assigned, 60 per cent, of the storms began 

 between noon and 8 p.m., leaving only 40 per cent, for the remaining 16 hours. 

 Again at Potsdam, where individual hours have their disturbance "character" 

 classified, 55^ per cent, of the hours counted as disturbed from 1892 to 1901 fell 

 between 4 p.m. and midnight. The natural inference is that the disturbances which 

 give the "character" to the day at Kew occur in the majority of instances in the 

 afternoon. Thus, supposing the period to be somewhat over 27 days, the occasions 

 when the associated subsequent disturbance falls on the 28th day following would 

 naturally be more numerous than the occasions when the associated previous 

 disturbance fell on the 28th day previous. This marked diurnal variation of 

 disturbance is a difficulty, whatever plan is adopted. It might seem at first sight 

 that the international "character" data would be unaffected. This might be so if 

 the stations were uniformly distributed in longitude, but in reality there are but few 

 stations in the hemisphere whose central meridian is 180 from Greenwich, and 

 European stations largely predominate. 



15. The same mean "character" figure may be arrived at in many ways. For 

 example, in the case of the 1 1 years, when 660 selected days were dealt with, a mean 

 "character" TOO might arise from a 1 on each day. or from a 2 on 330 days and a 

 on the remaining 330 days ; or, more generally, from p cases of 0, p cases of 2, and 

 660 -2p cases of 1, where p may be any positive integer not exceeding 330. It thus 

 appeared desirable to ascertain whether there was an essential difference between the 

 * ' Astron. Soc. Month. Notices,' vol. 65, pp. 2 and 538. 



