1891.] Comparison of Simultaneous Magnetic Disturbances. 129 



Still the matter is left indeterminate from the statical standpoint. 

 From the dynamical standpoint, however, we are led to a certain 

 definite stress distribution, which is also, fortunately, free from the 

 above objection, and is harmonised with the flux of energy. A pecu- 

 liarity is the way the force on an intrinsic magnet is represented. It 

 is not by force on its poles, nor on its interior, but on its sides, refer- 

 ring to a simple case of uniform longitudinal magnetisation ; i.e., it 

 is done by a gwasi-electromagnetic force on the fictitious electric 

 current which would produce the same distribution of induction as 

 the magnet does. There is also a force where the inductivity varies. 

 This force on fictitious current harmonises with the conclusion pre- 

 viously arrived at by the author that, when impressed forces set up 

 disturbances, such disturbances are determined by the curl of the 

 impressed forces, and proceed from their localities. 



In conclusion it is pointed out that the determinateness of the 

 stress rests upon the assumed localisation of the energy and the 

 two laws of circulation, so that with other distributions of the 

 energy (of the same proper total amounts) other results would follow ; 

 but the author has been unable to produce full harmony in any other 

 way than that followed. 



VI. "Comparison of Simultaneous Magnetic Disturbances at 

 several Observatories, and Determination of the Value of 

 the Gaussian Functions for those Observatories." By 

 W. GRYLLS ADAMS, D.Sc., F.R.S., Professor of Natural 

 Philosophy in King's College, London. Received June 11, 

 . 1891. 



(Abstract.) 



After drawing attention to previous investigations on this subject, 

 and pointing out the importance of adopting the same scale values for 

 similar instruments at different Observatories, especially at new 

 Observatories which have been recently established, the discussion 

 of special magnetic disturbances is undertaken, especially the dis- 

 turbances of a great magnetic storm which occurred on June 24 and 

 25, 1885, for which photographic records have been obtained from 17 

 different Observatories : 11 in Europe, 1 in Canada, 1 in India, 1 in 

 China, 1 in Java, 1 at Mauritius, and 1 at Melbourne. 



The records are discussed and compared, tables are formed of the 

 simultaneous disturbances, and the traces are reduced to Greenwich 

 mean time and brought together on the same plates arranged on the 

 same time-scale. Plates I and II show the remarkable agreement 

 between the disturbances at the different Observatories, and the 



VOL. L. K 



