226 DISTORTION [APR K 



and to a certain extent it must be considered experimentally 

 verified by Kaufmann's results. The function 0(0) has 

 the value unity when u = 0, or even when u/v is small. 



APPENDIX L. 

 Distortion due to High-speed Motion through the Ether. 



Mr. Searle, in the Philosophical Magazine, October, 1897, 

 points out that the simplest charged body when in motion 

 is not a sphere, but an oblate spheroid, oblate in the direc- 

 tion of motion, with its axes in the ratio ^(l A 1> 1 > 



and that this produces on all points outside itself exactly 

 the same effect as a point charge at its centre: where- 

 fore such a spheroid in motion at the speed u takes 

 the place of the sphere in electrostatics. He calls this a 

 Heaviside ellipsoid, because Mr. Heaviside first indicated 

 its importance in the theory of moving charges. 



But it is well known that a spheroid of this kind is 

 exactly what a sphere in rapid motion would auto- 

 matically become, on the FitzGerald-Lorentz theory ; viz., 

 that hypothesis which was started in order to account 

 for the negative result in Michelson's experiment, by postu- 

 lating a change of dimensions in solid bodies according to 

 their direction of motion through the ether. This hypo- 

 thesis, shown to be plausible by Lorentz, became a definite 

 theory when Larmor proved (^Jther and Matter, ch. xi.) 

 that on the electric theory of matter that is, assuming 

 that the whole inertia of matter was electric not only 

 was such a change of dimensions reasonably likely, as 

 FitzGerald had perceived, and likely also to be of the 

 right amount to give a compensating effect, and pre- 



