160 



At a distance it began with slight quivering, gradually attained a 

 maximum, and then suddenly ceased. Now if the disturbance oc- 

 curred along a large fissure, perhaps several miles in length, and of 

 unknown depth, the waves from different portions would reach any 

 given point in succession, and at intervals the combined effect of 

 many waves would be felt, producing a result analogous to the rolling 

 of thunder due to the varying distance of the source of sound, while 

 the sudden concussion at a nearer point is like the detonation heard 

 when the lightning is near the auditor. 



The shocks were less severe in the mountains than in the valleys. 

 As far as the wave progressing horizontally is concerned, it would, 

 on entering a mountain, at first be nearly bounded by a horizontal 

 plane continuous with that of the valley, just as light is propagated 

 in straight lines ; but there would also be a diversion of a part (ana- 

 logous to the diffraction of light at a screen) into the mountain, so 

 that where the wave passed for some distance into a range it would 

 finally be felt at the summit. It is observable that the shock on the 

 25th was less severe on the Riffelberg than at Zermatt, yet it travelled 

 through the mountain and was felt at Turin. 



The period of elevation of the Alps seems about contemporaneous 

 with the older Pliocene of Sir C. Lyell. The country is broken up 

 with faults, which probably there, as elsewhere, follow the lines of 

 valleys. The valley of Visp lies in the axis of two ranges which 

 have all the appearance of a mighty valley of elevation. The shock 

 may have arisen from a shifting of the beds on this line of ancient 

 disturbance, and very probably the somewhat rectangular corner 

 between the valleys at Visp suffered the principal displacement. 

 Earthquakes in non-volcanic regions probably arise from a failure of 

 support. At the period of the elevation of the Alps, the more heated 

 lower parts of the earth's crust must have come nearer to the surface 

 than their normal position, and contractions and failure of support 

 must occur while cooling, and the comparatively recent elevation of 

 the Alps may give reason for thinking this to be still going on. 



December 10, 1855. 



A paper was read by Mr. Maxwell on Faraday's Lines of Force. 



The method pursued in this paper is a modification of that mode 

 of viewing electrical phenomena in relation to the theory of the uni- 

 form conduction of heat, which was first pointed out by Professor W. 

 Thomson in the Cambridge and Dublin Mathematical Journal, vol. iii. 

 Instead of using the analogy of heat, a fluid, the properties of which 

 are entirely at our disposal, is assumed as the vehicle of mathematical 

 reasoning. A method is given by which two series of surfaces may 

 be drawn in the fluid so as to define its motion completely. The 

 uniform motion of an imponderable and incompressible fluid permea- 

 ting a medium, whose resistance is directly as the velocity, is then 

 discussed, and it is shown how a system of surfaces of equal pressure 



