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XVII. On the Propagation of Electric Waves through Wires. 

 ByYvoi. H. Hertz*. 



IF a constant electric current flows in a cylindrical wire, its 

 intensity is the same in all parts of the section of the wire. 

 But if the current is variable, self-induction causes a deviation 

 from this most simple distribution. For, since the inner parts 

 of the wire are in the mean less distant from all the rest than 

 are those on the circumference, induction opposes alterations 

 of the current in the interior of the wire more strongly than at 

 the circumference ; and in consequence of this the flow is con- 

 fined to the exterior of the wire. If the current alters its 

 direction a few hundred times per second the deviation from 

 the normal distribution is no longer imperceptible ; this 

 deviation increases rapidly with the rate of alternation, and 

 when the current alternates many millions of times per second, 

 according to theory almost the whole interior of the wire must 

 appear free from current, and the flow must be confined to 

 the immediate neighbourhood of the circumference. In such 

 very extreme cases the hitherto accepted theory of the pheno- 

 menon is plainly not without physical difficulties ; and pre- 

 ference must be given to another view of the subject, which 

 was indeed first put forward by Messrs. Heaviside f and 

 Poynting % as the true interpretation of the equations of 

 Maxwell as applied to this case. According to this view, the 

 electric force which determines the current is in no wise pro- 

 pagated in the wire itself, but under all circumstances enters 

 the wire from without and spreads itself in the metal compara- 

 tively slowly, and according to similar laws as changes of 

 temperature in a conductor of heat. If the forces in the 

 neighbourhood of the wire are continually altering in direc- 

 tion, the effect of these forces will only enter to a small depth 

 into the metal ; the more slowly the changes take place, so 

 much deeper will the effect penetrate ; and if, finally, the 

 changes follow one another infinitely slowly, the force has time 

 to fill the whole interior of the wire with uniform intensity. 



In whatever way we wish to regard the results of the theory, 

 an important question is, whether it agrees with fact. Since, 

 in the experiments which I carried out on the propagation of 

 electric force, I made use of electric waves in wires which 



* Translated from Wied. Ann. xxxvii. p. 395 (July 1889), by Dr. J. L. 

 Howard, Demonstrator of Physics in University College, Liverpool. 

 t Heaviside, Electrician, Jan. 1885 ; Phil. Mag. [5] xxv. p. 153 (1888). 

 X Poynting, Phil. Trans, ii. p. 277 (1885). 



