Page:Elektrische und Optische Erscheinungen (Lorentz) 096.jpg

 to for an investigation on the interference fringes that appear at calcite plates in polarized light.

The entrainment of light waves by ponderable matter.
§ 68. In a stationary, isotropic or anisotropic body a bundle of plane light waves propagate, as to which the components of $$\mathfrak{D}$$ and $$\mathfrak{H}$$ can be expressed by expressions of the form

thus W is the velocity of propagation. This magnitude can depend on $$b_{x}, b_{y}, b_{z}$$, and T. After we have given to the body the velocity $$\mathfrak{p}$$, a state of motion can occur in it, for which expressions like

or

apply. The direction constants $$b'_{x}, b'_{y}, b'_{z}$$ of the wave normal are now proportional to the magnitudes

If we consequently put

then (80) becomes

for which we can see, that $$W'$$ is the velocity by which the waves of relative oscillation period T are propagating