372 GREAT MEN OF SCIENCE 



in motion a delay occurs - in the case of the electric current 

 as a consequence of the opposing electromotive force, in the 

 case of the water on account of mechanical inertia; and when 

 the current is interrupted we perceive a striving for it to 

 flow on - again on account of the electromotive force of 

 induction in the wire and on account of inertia in the water. 



This phenomenon of inertia in the case of electric current 

 must not be interpreted, at any rate not for the most part, as 

 inertia of electricity in the wire. For the magnitude of the 

 inertia - the self-induction - is very different in the same 

 wire according to the manner of its winding, and to its sur- 

 roundings; it is for example much larger in a coil of wire, 

 than when the same wire is stretched out straight - and it 

 becomes very much greater still if iron is introduced into 

 the coil. If self-induction is to be regarded as a phenomenon 

 of inertia, it would be necessary to look for the inertial mass, 

 not in the current carrying conductor, but in the lines of 

 force belonging to the current; for it is these that determine 

 the self-induction. 



This view remained unlikely, as long as Faraday's idea of 

 lines of force still appeared as of minor importance; but it 

 suddenly became very obvious, when Hertz's result had 

 shown these lines of force to be without any doubt repre- 

 sentative of states of space or ether, which make up the 

 most essential feature of all electrical and magnetic phe- 

 nomena. From that time on, an increasing number of 

 attempts were made to connect inertia or mass with self- 

 induction, that is with the states or processes in the ether 

 represented by Faraday's lines of force; the idea being that 

 perhaps all inertia - all mass - even that of ordinary material 

 bodies, might be shown to be simply the mass of the accom- 

 panying ether.i 



^ In an analogous way Hertz developed his mechanics (1894) by taking 

 account of mass in the ether, though in another way; the object was not to 

 refer tangible mass, but all forces of nature, to hidden ether masses. 



