1^97.] HOUSTON, KENNELLY — THE PATH OF A CURRENT. 157 



Fig. 13, represents this condition of affairs. Here the two blocks 

 have passed completely through each other and once more rush out 

 with the velocity of light towards the ends of the conductors, 

 which they will reach in the yo^ott^^^ ^^ ^ second. This process of 

 meeting in the centre, separating, reaching the ends, and being 

 reflected therefrom, will repeat itself indefinitely in cycles which 

 take y-^^th of a second to complete, the current direction reversing 

 at each reflection from the ends. In this case of perpetual motion, 

 we have assumed that there is no dissipation of electromagnetic 

 energy, there being no leakage between the two conductors, and 

 perfect conduction in the two wires. 



We have hitherto assumed that the two wires AB and CD, were 

 open-circuited, that is insulated from each other at their termini. 

 We now suppose that they are short-circuited; that is directly con- 

 nected at the termini. Let the metre block of flux be started from 

 E, the centre of the line, as in Fig. 5. Then, in y^Vo^^"^ ^^ ^ ^^^" 

 ond, the two metre blocks, into which the original block divides, 

 will rush over the intervening 300 kilometres, and will reach the 

 ends of the line as shown in Fig, 14, the arrows v and v^ indicating 

 the direction in which the blocks have arrived, and the curved arrows 

 representing the direction of accompanying magnetic flux. In this 

 case, instead of the electric density being doubled, the electric flux 

 vanishes completely as soon as the magnetic flux is compressed into 

 half a metre of length. The magnetic flux is, however, doubled in 

 density, as represented by the doubled curved arrows of Fig. 15. 

 Here the energy is all magnetic, and each half- metre block of mag- 

 netic flux at the ends of the line contains 500 ergs of energy. 



hy.x-* ^ 



4- 



jjium'^T — ^ * \mii, 



fi^lS nit m'l 



A 



C 





m, 



Rg 16 



A 



m. 



m. 



f— : Z^ 





^1 



m. 



Figs. 14-16. — Reflected Movement of Electric Flux in Circuit of Perfect Conduc- 

 tion and Insulation, Short-Circuited at Termini. 



PEOC. AMER. PHILOS. 800. XXXVI. 155. L. PRINTED JUNE 15, 1897. 



