Page:Aether and Matter, 1900.djvu/38

2 references to the earlier historical data Ketteler's treatise has proved most useful: the principal writings among these, and all the later ones, have also been examined directly.

To this review is appended a general account of wave and ray propagation in moving media, which though originally written independently, necessarily follows very much the same course as the one given in Lorentz's memoir of 1887.

2. The second section developes the general theory of the relations between matter and aether, which is to form the basis of the treatment of moving material media. In it the electric and optical activity of the matter are assigned to the presence of electric charges associated with the material atoms: the complete scheme of electrodynamic and optical equations is then derived as a whole, on this basis, from the single foundation of the Principle of Least Action. The modifications which arise in the scheme owing to motion of the matter are on this hypothesis directly and definitely ascertainable, on the supposition that the motion of the matter does not affect the quiescent aether except through the motion of the atomic electric charges carried along with it. It appears that the law of the phenomenon of astronomical aberration is fully verified, as are also all the other first order effects — mostly of a null character — of the motion of material systems, which experiment has established. This portion of the subject has been already profoundly treated by Lorentz , by an analysis very different from the present one, but with ideas and results that are in the main in agreement with those here arrived at. In the treatment here given, the essential distinction between molecular theory and mechanical theory, and the principles involved in effecting the transition from the former to the latter, are carefully traced.