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oscillation period, also the explanation of the dispersion of light is contained in the formulas.

Also the case of the pure aether is not excluded. Since no electric moments ${\mathfrak {M}}$ exist in it, then we have to set by (64) $\sigma _{1.1}=\sigma _{2.2}=\sigma _{3.3}=\infty$ and thus $\varkappa _{1}=\varkappa _{2}=\varkappa _{3}=1$. The equations $V_{c}$) and ($V'_{c}$) thereby are transformed into

${\mathfrak {E}}=4\pi V^{2}{\mathfrak {D}}+[{\mathfrak {p.H}}]$, ${\mathfrak {E}}=4\pi V^{2}{\mathfrak {D}}$.

We can easily see, that the equations which we obtain in this way for the aether, are in agreement with formulas (I)-(V) or ($I_{b}$)-($VII_{b}$)

It is self-evident, as regards the interior of the pure aether, that the connection between the various magnitudes is always the same, the ponderable matter may be in motion or not.

Circular polarizing media.

§ 53. Bodies, which turn the polarization plane, were excluded above. It's not feasible to form a thorough theory for them until now; nevertheless some general consideration, as required by our purpose, may find their place here.

Since the rotation of the polarization plane is connected with the fact, that the medium is not in accordance in all its properties with its mirror image, then the things said in § 51 are not applicable anymore. Nevertheless, everything becomes quite easy when we restrict ourselves to isotropic media.

If we assume, in the relation between ${\overline {\mathfrak {E}}}$ and ${\mathfrak {M}}$, that no derivatives with respect to x, y, z are present, then we have to understand under $F_{1}({\mathfrak {M}})$ of equation (62), a vector that is completely determined even by ${\mathfrak {M}}$, namely the isotropy requires that the figure consisting of ${\mathfrak {M}}$ and $F_{1}({\mathfrak {M}})$ can be rotated in an arbitrary manner, without that $F_{1}({\mathfrak {M}})$ ceases to fit to ${\mathfrak {M}}$. If we now choose the direction of ${\mathfrak {M}}$ itself as the rotation axis, then ${\mathfrak {M}}$