252 ADVANCED ELECTRICITY AND MAGNETISM. 



of the wave causes a continual building up of the electric field 

 in that part of the wave, the tapering electric field in the back 

 part of the wave causes a continual decrease or letting down 

 of the magnetic field in that part of the wave, and the tapering 

 magnetic field in the back part of the wave causes a continual 

 letting down of the electric field in that part of the wave. Thus 

 the wave is being continually let down in the rear and built up 

 in front and energy is continually streaming from the back part 

 of the wave where the wave is being let down to the front part 

 where the wave is being built up. 



133. The electric current. Consider a wire* AB, Fig. 195, 

 along which an electric current is flowing steadily from B 

 towards A . The magnetic field on opposite sides of A B is in 

 opposite directions, so that the positive ether cells at p and p f 

 are rotating in opposite directions as indicated. A steady 



electric current may be main- 

 tained for an indefinite length 

 of time, but the opposite rota- 

 tions of positive ether cells on 

 ^^^ -B the two sides of AB, Fig. 195, 

 cannot be accommodated by 

 an ever-increasing ether dis- 

 tortion (distortion of the rub- 

 Fig 195 ber-like teeth of the ether 



cells as shown in Fig. 189), 



there must be a slip between adjacent cells somewhere between 

 p and p f . This slip between adjacent ether cells takes place 

 in the material of the wire and constitutes the electric current. 



Steady electric currents flow in closed circuits. Maxwell's 

 conception of the ether shows that this must be true as follows: 

 Consider the opposite rotations of like ether cells at p and p', 

 Fig. 195, and consider a chain of geared cells passing from p 



* Strictly, a broad metal sheet. Maxwell's conceptions apply to two dimensions 

 only. 



