344 The Followers of Maxwell. 



It may, however, be remarked that this view of th>rigin of 

 mass is not altogether consistent with the principle^that the 

 electron is an indivisible entity. For the so-called self-induction 

 of the spherical electron is really the mutual induction of the 

 convection-currents produced by the elements of electric charge 

 which are distributed over its surface ; and the calculation of 

 this quantity presupposes the divisibility of the total charge into 

 elements capable of acting severally in all respects as ordinary 

 electric charges ; a property which appears scarcely consistent 

 with the supposed fundamental nature of the electron. 



After the first attempt of J. J. Thomson to determine the 

 field produced by a moving electrified sphere, the mathematical 

 development of Maxwell's theory proceeded rapidly. The 

 problems which admit of solution in terms of known functions 

 are naturally those in which the conducting surfaces involved 

 have simple geometrical forms planes, spheres, and cylinders.* 



A result which was obtained by Horace Lamb,f when 

 investigating electrical motions in a spherical conductor, led 

 to interesting consequences. Lamb found that if a spherical 

 conductor is placed in a rapidly alternating field, the induced 

 currents are almost entirely confined to a superficial layer ; and 

 his result was shortly afterwards generalized by Oliver Heavi- 

 side,| who showed that whatever be the form of a conductor 

 rapidly alternating currents do not penetrate far into its sub- 

 stance. The reason for this may be readily understood : it is 

 virtually an application of the principle|| that a perfect conductor 

 is impenetrable to magnetic lines of force. No perfect conductor 

 is known to exist ; butU if the alternations of magnetic force to 

 which a good conductor such as copper is exposed are very 



* Cf., e.g., C. Niven, Phil. Trans, clxxii (1881), p. 307 ; H. Lamb, Phil. Trans, 

 clxxiv (1883), p. 519 ; J. J. Thomson, Proc. Lond. Math. Soc. xv (1884), p. 197 : 

 H. A. Rowland, Phil. Mag. xvii (1884), p. 413 ; J. J. Thomson, Proc. Lond. Math. 

 Soc. xvii (1886), p. 310; xix (1888), p. 520; and many investigations of Oliver 

 Heaviside, collected in his Electrical Papers. 



t Loc. cit. % Electrician, Jan. 1885. 



The mathematical theory was given hy Lord Rayleigh, Phil. Mag. xxi. (18S6), 

 p. 381. Cf. Maxwell's Treatise, 689. || Cf. p. 313. 



H As was first remarked by Lord Rayleigh, Phil. Mag. xiii (1882), p. 344. 



