Page:Aether and Matter, 1900.djvu/56

20 doublet, infinite velocities of disturbance of the aether will enter at the very beginning of the motion, so that the steady state cannot be originated.

On the other hand, the abstract theory to be here given may be translated into a concrete scheme which identifies electrodynamic energy with the translatory kinetic energy of the aether considered as possessing inertia: to make the aether remain practically quiescent under all conditions it is then necessary and sufficient to take its inertia to be sufficiently great: in fact if this were not secured, the electrodynamic equations instead of being linear would involve the very great complication of non-linear terms with which we are familiar in theoretical hydrodynamics. In summing up at the end of the above-mentioned essay, Wien formulates three outstanding objections to the hypothesis of a quiescent aether; (i) the observed absence of any magnetic effect of the motion of electrically charged bodies carried along by the Earth, (ii) the absence of any influence of the Earth's motion on the optical rotatory property of quartz, (iii) Fizeau's experiment, in which he found some evidence for changes, arising from the Earth's motion, in the displacement of the plane of polarization of light produced by passage through a pile of glass plates.

As regards these objections, the first appears to be a point in favour of the theory instead of against it (§ 40 infra): the second is based on a theoretical investigation of Lorentz, which appears to be at fault (Ch. XIII.) so that the result is again in favour: while the conclusion in the third case was regarded as doubtful by Fizeau himself on account of the extreme difficulty experienced in excluding disturbing causes (a doubt which has been shared by most authorities who have since examined the matter, including Maxwell and Rayleigh), and the experiment has not been repeated.