1897.] HOUSTOX, KEXXELLY — THE TATII OF A CURREXT. 171 



they have accounted for the conditions which exist in the space sur- 

 7'oiinding the condticior in the phenomenon called electric current. 

 In fact I could not attempt to add anything to this very clear ex- 

 position. I have therefore collected the objections that can be 

 raised against some of the views and conclusions of the authors. 



We first encounter a difficulty as long as we do not bear in mind 

 the dual nature of the electric flux considered in relation to elec- 

 trostatic conditions. The flux is to be taken, respecting one of its 

 manifestations, as a measure of electric quantity inasmuch as, when 

 rushing, each unit will produce the same magnetic flux, but this 

 effect is independent of the difference of electric potential. The 

 energy transferred is, however, proportional to this difference. 



In the case represented by Fig. 39 of a perfectly insulated closed 

 circuit, the quantity of flux, owing to the perfect insulation, must 

 remain unchanged as it rushes along the line, but the other factor 

 in the transfer of energy, due to the rush of flux, the difference of 

 potential, decreases as the energy is transformed into heat in the 

 conductor. If I understand the authors correctly, they consider 

 the process as entailing a diminution of the first factor (quantity) 

 by partial reflexions constituting the imperfect conduction, while 

 the second factor remains unaltered. It is difficult to see how, with 

 perfect insulation, at any point of the line, where such reflexions 

 occur (the reflected fractions of flux returning towards the origin), 

 energy will cease to be electric and become thermic, since the re- 

 flected fractions will carry their energy away undiminished from 

 that point, while the unreflected part of the flux will carry its share 

 away in the primary direction of main rush. 



As to the view held by the authors that the electric current runs 

 through the insulator, or, more broadly, through the space outside 

 the conductor, and is merely guided or localized by the latter, it 

 seems to me open to some grave objections. It is true that the old 

 view, which considered the conductor as the only real seat of the 

 phenomenon, is not tenable. But there is another intermediate 

 position, which has been expounded by Poynting, Lodge, J. J. 

 Thomson and others, which is : that while the current flows through 

 the conductor, the energy, which is generally transferred simul- 

 taneously, travels through the space surrounding the conductor. 



As stated by Lodge : '' We must learn then to distinguish be- 

 tween the flow of electricity and the flow of electric energy ; they 

 do not occur along the same paths Electric energy is not 



