230 SCIENCE AND METHOD. 



a rectilineal and uniform motion. At least it is gener- 

 ally agreed to admit it, though Lindemann has raised 

 objections to the assumption. I do not wish to take 

 sides in the discussion, which 1 cannot set out here 

 on account of its extremely difficult nature. In any 

 case, the theory would only require slight modifications 

 to escape Lindemann's objections. 



We know that a body immersed in a fluid meets 

 with considerable resistance when it is in motion ; but 

 that is because our fluids are viscous. In an ideal 

 fluid, absolutely devoid of viscidity, the body would 

 excite behind it a liquid stern-wave, a kind of wake. 

 At the start, it would require a great effort to set it 

 in motion, since it would be necessary to disturb not 

 only the body itself but the liquid of its wake. But 

 once the motion was acquired, it would continue 

 without resistance, since the body, as it advanced, 

 would simply carry with it the disturbance of the 

 liquid, without any increase in the total vis viva of 

 the liquid. Everything would take place, therefore, 

 as if its inertia had been increased. An electron 

 advancing through the ether will behave in the same 

 way. About it the ether will be disturbed, but this 

 disturbance will accompany the body in its motion, so 

 that, to an observer moving with the electron, the 

 electric and magnetic fields which accompany the 

 electron would appear invariable, and could only 

 change if the velocity of the electron happened to 

 vary. An effort is therefore required to set the 

 electron in motion, since it is necessary to create the 

 energy of these fields. On the other hand, once the 

 motion is acquired, no effort is necessary to maintain 

 it, since the energy created has only to follow the 



