120 Mr. 0. Heaviside on the 



Attention has recently been forcibly directed towards the 

 phenomenon above described of the inward transmission of 

 current into wires by Professor Hughes's Inaugural Address 

 to the Society of Telegraph Engineers and Electricians, 

 January 1886. This paper was, for many reasons, perhaps 

 the most remarkable one ever written. It was remarkable for 

 the extraordinary ignoration of well-known facts, thoroughly 

 worked out already ; it was remarkable for a quite phenomenal 

 mixing up of the effects due to induction and to resistance, 

 and the author's apparent inability to separate them, or to see 

 the real meaning of his results ; one might indeed imagine 

 that an entirely new science of induction was in its earliest 

 stages. It was remarkable that the great experimental skill 

 of the author should have led him to employ a method which 

 was in itself highly objectionable, being capable of giving, in 

 general, neither a true resistance nor a true induction-balance 

 (as may be very easily seen by simple experiments with coils, 

 without any mathematical examination of the theory) — a 

 method which does not therefore admit of any exact interpre- 

 tation of results without the fullest particulars being given 

 and subjected to laborious calculations ; and finally, it was 

 remarkable as containing, so far as could be safely guessed at, 

 many verifications of the approximation towards mere surface- 

 conduction in wires. This is, after all, the really important 

 matter, against which all the rest is insignificant. 



As regards the method employed, I have shown its inaccu- 

 racy in a paper " On the Use of the Bridge as an Induction- 

 balance/' in ' The Electrician/ April 30, 1886, wherein I also 

 described correct methods, including the simple bridge with- 

 out mutual induction, and also methods in which mutual 

 induction is employed to get balance, giving the requisite 

 formulae, which are of the simplest character. 



As regards the interpretation of Prof. Hughes's thick-wire 

 results, showing departure from the linear theory, by which I 

 mean the theory that ignores differences in the current-density 

 in wires, I made the following remarks in the ' Electrician/ 

 April 23, 1886. After commenting upon the difficulty of 

 exact interpretation, I proceed : — 



" The most interesting of the experiments are those relating 

 to the effect of increased diameter on what Prof. Hughes 

 terms the inductive capacity of wires. My own interpretation 

 is roughly this. That the time-constant of a wire first in- 

 creases with the diameter " [this is of course what the linear 

 theory shows], " and then, later, decreases rapidly ; and that 

 the decrease sets in the sooner the higher the conductivity and 

 the higher the inductivity (or magnetic permeability) of the 



