Page:Elektrische und Optische Erscheinungen (Lorentz) 129.jpg

 moving plate certainly not behaves like a stationary one of somewhat different refractive index.

§ 96. We consider two isotropic media (separated from each other by a plane) whose ponderable parts are either at rest, or move with a common velocity $$\mathfrak{p}$$ in a direction perpendicular to the marginal surface. If one part of this surface, whose dimensions are considerably larger than the wavelength, is hit by plane waves, which are laterally limited by a cylinder that shares the translation, then the reflection and refraction give rise to two similar light beams. Any theory of aberration has to assume now that, independent of translation, the describing lines of the cylindrical marginal-surfaces, the relative light rays, are subject to the ordinary laws of reflection and refraction.

Accordingly, we can once and for all imagine four cylinder: 1, 2, 3, 4, as those mentioned above, — we want to say "four paths of light" —, of which 1 and 2 are in the first, 3 and 4 in the second medium, and which belong together in the following way. From an incident motion in 1, a reflected one shall emerge in 2, and a transmitted one in 4, while also an incident beam in 3 gives rise to motions in 2 and 4. In reverse, incident oscillations in 2 or 4 will excite motions in paths 1 and 3.

For simplicity, we also assume that the part of the marginal surface that was hit by light, has two symmetry axes that are mutually perpendicular, one of which lies in the plane of incidence of the rays. The figure consisting of four light paths, thus has two symmetry planes which go through one of these axes and the normal to the marginal surface. That one, which coincides with the plane of incidence, may be called the first, the other one be called the second symmetry plane.

§ 97. Of the deviations from equilibrium that constitutes light, it shall be assumed that they