-THE PATH OF A CURRENT. 159 



Other as shown in Fig. 19, where the two blocks are seen to be 

 withdrawing from each other with the speed of light. They again 

 rush to the termini of the line, where they undergo reflection with 

 reversal of electric flux and persistence of magnetic flux. This 

 condition of reflection and collision would continue forever, under 

 the conditions assumed. 



We have hitherto assumed that the insulator insulated perfectly 

 and the conductor conducted perfectly. Neither of these two con- 

 ditions is attained in practice. We will first assume that there is 

 imperfect insulation in the insulator, with perfect conduction in 

 the wires. For convenience, we may change the type of circuit to 

 the second ; namely, a cable composed of a central wire and annu- 

 lar external conducting sheath. This is represented in Fig. 20 





u^ K ^^ "^i ^ 



Figs. 20-22. — Movement of Electric Flux in Cable of Imperfect Insulation and 

 Perfect Conduction. 



where AB, is the central conductor and CD, CD, the external con- 

 ducting sheath. Let us suppose that a metre block of flux, at 1000 

 volts, is, as before, called into existence, and released from the 

 centre of the line. The flux block immediately starts with the vel- 

 ocity of light in the ether of that particular insulator, which may 

 be, perhaps, 200,000 kilometers per second, instead of 300,000 kilo- 

 meters per second, as in free ether. The block, as before, subdi- 



