222 Mr. J. Larmor. A Dynamical Theory [June 20, 



plan of the magnetic rock causing the disturbance has been made, 

 and, together with the complete set of observations, the following 

 results have been deduced. 



The cause of the disturbance is a ridge of rock permanently magne- 

 tized, repelling the north-seeking end of the needle. In the trans- 

 verse section this ridge is steeper on the south-east side where the 

 disturbances are at a maximum than on the north-west side. Longi- 

 tudinally the ridere rises rather abruptly to a principal peak (as 

 determined by the point of maximum disturbance of the vertical 

 force), followed by a depression, and a second peak, finally falling 

 abruptly to the level. 



The principal values of the disturbances caused by this ridge are 



Declination 56 E. on S.E. side, 26 W. on N.W. side. 



Inclination 29. 



Horizontal force. . T92 on S.E. side ; + 1'04 on N.W. side. 



Vertical force . . . 4'44 metric units. 



A geological survey of the coast at the Red Cliff (see map), where 

 the greatest disturbances of the magnetic elements were observed, was 

 made, and specimens of rock and sand were obtained which have 

 since been tested for susceptibility. The evidence from these does 

 not give any direct information tending to show the exact nature of 

 the rock causing the remarkable disturbances over the magnetic 

 shoal, but the character of the disturbances caused by the visible and 

 invisible land are of a similar character. 



Five diagrams are appended showing the data from which the 

 foregoing results have been deduced, with a map showing the position 

 of the " magnetic shoal " relative to the neighbouring land. Also a 

 geological map of the Red Cliff and neighbourhood. 



II. " A Dynamical Theory of the Electric and Luminiferous 

 Medium. Part II ; Theory of Electrons." By JOSEPH 

 LARMOR, F.R.S., Fellow of St. John's College, Cambridge. 

 Received May 16, 1895. 



(Abstract.) 



In a previous paper on this subject,* it has been shown that by 

 means of a rotationally elastic aether, which otherwise behaves as a 

 perfect fluid, a concrete realization of MacCullagh's optical theory can 

 be 'obtained, and that the same medium affords a complete repre- 

 sentation of electromotive phenomena in the theory of electricity. 

 The ponderomotive electric forcives were, on the other hand, deduced 



* ' Roy. Soc. Proc.,' November, 1893; ' Phil. Trans.,' 1894, A, pp. 719822. 



