178 MR. GEORGE W. WALKER ON THE INITIAL ACCELERATED 



A similar argument suggests the interpretation of X, Y, Z as electric force and 

 a distinction between oethereal magnetic force a, /3, y and total magnetic force 



C'K C'K 



The existence of the additional electric force 



o 



' 



C'K > C'K 



is supported by WILSON'S (' Phil. Trans.,' A, vol. 204, p. 121) experiment of rotating 

 an insulating cylinder in a longitudinal magnetic field. It would be equally important 

 to test experimentally the existence of the additional magnetic force 



' 



C'K ' C'K 



by rotating the insulating cylinder in a longitudinal electric field. RONTGEN (' Ann. 

 der Physik,' vol. 35, p. 2G4, 1888) has detected the existence of this force, but the 

 effect was too small to be measured. 



This second system is, I think, intrinsically involved in LORKNTZ' and LARMOR'S 

 equations, although not explicitly put in this symmetrical form, as far as I can find. 



If this system could lie established we could proceed to a higher degree of 

 approximation in the problem of motion of an insulator, and the similarity of the 

 equations to those for the aether shows that no greater analytical difficulty would arise. 



We must still, however, remember the probable fact that K itself will be modified 

 by higher order even powers of the velocity. 



Thus until the accuracy of these equations or modifications of them is established 

 beyond reasonable, possibility of doubt, it would be a little absurd to apply them to 

 the motion of an insulator for velocities comparable with that of radiation, and this 

 consideration prevents me from attempting the solution of a problem which is clearly 

 soluble from an analytical point of view by a method similar to that used for a perfect 

 conductor. 



Although we cannot therefore proceed to the general problem of a moving insulator 

 at high speeds, we may show that if the dielectric ratio K is very large, the electric 

 inertia will be very nearly the same as for a perfect conductor. Since there is 

 continuity of normal flux of disturbed electric force at the surface, the functions 

 which determine the disturbance inside the sphere are of order 1/K as compared with 

 those which determine the outside field. Hence the tangential component of electric 

 force inside, and therefore also outside, is very nearly zero. Thus, since the 

 equations for the aether are not modified by the motion of the sphere, the equation 

 of motion and the surface forces outside differ by terms of order 1/K from those 

 for a perfect conductor. If this argument is valid, the assumption of perfect 

 conduction, or of a high value of K for the charged particle, would equally well 



