TRANSACTIONS OF SECTION A. 523' 



tlip strict concordance between the curves of sunspot frequency and those of the • 

 diurnal ran^e of the decliuation and horizontal force magnets as to period and 

 intensity. Lord Kelvin has proved theoretically that such concordance is not the 

 outcome of efficient cause and eflect. Father Sidgreaves has proved the same ■ 

 observationally IVcim a detailed study of the greater solar and magnetic storms for 

 tlie period l8ril-18i)0, and advances a theory according to which the two phenomena 

 are eflects, and not necessarily conjoined, of one common cause. Professor Young 

 contends that 'solar disturbances are not the cause of our magnetic storms, but 

 only the cause of some of them,' meaning by ' a cause ' an instrumental cause which 

 releases the potential energy that directly atl'ects the magnets. To examine this 

 position a detailed study of the spots and faculse on the sun and the diurnal range 

 of the declination magnet has been made for the years 1899-1901, covering the 

 minimum period of sunspots and magnetic storms, as the unravelling of the various 

 storms and the perception of the concurrence of the two phenomena, if any, is 

 rendered easier during such a period. The table prepared gives tlie mean daily 

 disc-area for spots and faculiE for the thirty -eight solar rotations covered by the 

 period under review, taken from the Greenwich records, and in parallel columns 

 are also set out the mean daily diurnal ranges of the declination magnet and the 

 greatest swing for each rotation. This table shows the existence of great anomalies 

 between the sunspot and magnetic records. A detailed comparison ot the greater 

 spots on the sun and the greater magnetic movements only serves to confirm the 

 existence of these departures from exact accord. The greatest spot of 1901, tliat 

 of May 19-June 1^6, which was coincident with an unusual disturbance noticed 

 in the solar corona on May 18, and was responsible for 74 per cent, of the total 

 spotted area for the year, had no concordant greater m.agnetic movements ; and, ou 

 the other hand, a greater magnetic movement of April 10, 1902, took place at 

 a time of absolute solar calm. It is yet possible that solar spots are one of the 

 instrumental causes of magnetic storms, but it is more likely that the two 

 phenomena are correlated as connected, though sometimes independent, efl'ects of 

 one common cause. 



SATURDAY, SEPTEMBER 13, 

 The Section did not meet, 



MONDAY, SEPTEMBER 15, 



Department I. — Mathematics. 

 The following Report and Papers were read : — 



1. Bqwrt on the Present State of the Theory of Point G'roiips,. 

 See Reports, p. 81. 



2. On the Partial Differential Equations of Mathematical Physics, 

 By E. T. Whittaker, il/.yl. 



The principal results contained in this paper were the following : — 

 1. The general solution of Laplace's equation 



