MATTER, SPACE, AND TIME 229 



front, and at right angles to each other in that 

 plane. But such an arrangement is precisely 

 that required to explain the phenomena of light. 



In the simple case we have taken, the electron 

 oscillates backwards and forwards in a straight 

 path : the vibrations travel as tremors along the 

 tubes of force in one plane only ; the resultant 

 light is plane polarized. In the more general 

 case, we must suppose that the electron oscillates 

 in a circular, or elliptical orbit, and the tubes of 

 force will be displaced in corresponding motions ; 

 the tremors running along them will no longer be 

 simple to and fro movements, but points on the 

 tubes will describe curved paths. These paths 

 continually change as the orbit of the electron 

 changes, and we get a more complete model of 

 the propagation of common, non-polarized light. 



Faraday's tubes, it is clear, give a very 

 powerful and convenient method of studying the 

 phenomena of the electro-magnetic field, and 

 Thomson has used them in such ways as that 

 just suggested to elucidate modern problems. 

 Indeed it is almost possible that electric tubes 

 of force may represent something more than a 

 useful mathematical fiction. If the structure of 

 the electric field be discontinuous in reality, as our 

 tube-picture of it indicates ; if the electric and 

 magnetic effects of a charge of electricity are in 

 reality exerted throughout the surrounding space 

 by means of discrete tubes of force — vortex fila- 

 ments in the aether, or whatever they may actually 

 be — an advancing wave of light must be discon- 

 tinuous also. Could we look at such a wave from 

 the front, and magnify it millions of millions of 

 times, we should see, not a uniform field of 



