Self-induction of Wires. 119 



dary conditions are made similar, which is easily to be realized. 

 Similarly we may compare the circular electric current in the 

 core to the circular magnetic current in the wire. 



I also found the transfer of energy to be similar in both 

 cases, viz. radially inward or outward to or from the axis of 

 the core or the wire. It was therefore necessary to consider 

 the dielectric, in order to complete the course of the transfer 

 of energy from its source, say a voltaic cell, to its sink, the 

 wire or the core where it is finally dissipated in the' form of 

 heat, and its temporary storage as electric and magnetic 

 energy in the field generally, including the conductors* ' 



Terminating the paper above referred to, having so much 

 other matter, I started a fresh one under the title of " Electro- 

 magnetic Induction and its Propagation/'' commencing in 

 the i Electrician,' January 3, 1885. Having, according to 

 my sketched plan, to get rid of general matter first, before 

 proceeding to special solutions, I took occasion near the com- 

 mencement of the paper to give a general account of some of 

 my results regarding the propagation of current, in which the 

 following occurs, describing the way the current rises in a 

 wire, and the consequent approximation, under certain cir- 

 cumstances, to mere surface-conduction. It was meant to 

 illustrate the previously-mentioned stoppage of current-con- 

 duction by high conductivity. After an account of the 

 transfer of energy through the dielectric (concerning which I 

 shall say a few words later) 1 continue ('Electrician/ January 

 10, 1885):— 



" Since, on starting a current, the energy reaches the wire 

 from the medium without, it may be expected that the electric 

 current is first set up in the outer part, and takes time to 

 penetrate to the middle. This I have verified by investigating 

 some special cases. 



" Increase the conductivity enormously, still keeping it 

 finite, however. Let it, for instance, take minutes to set up 

 a current fct the axis. Then ordinary rapid signalling 'through 

 the wire' would be accompanied by a surface- current only, 

 penetrating to but a small depth. The disturbance is thus 

 propagated parallel to the wire in the manner of waves, with 

 reflection at the end, and hardly any tailing off. With infi- 

 nite conductivity thefe can be no current set up in the wire 

 at all. There is no dissipativity ; wave-propagation is perfect. 

 The wire-current is wholly superficial, an abstraction, yet it is 

 "nearly the same with very high conductivity. This illustrates 

 the impenetrability of a perfect conductor to magnetic induc- 

 tion (and similarly to electric currents) applied by Maxwell to 

 the molecular theory of magnetism." 



