Summary of the equations.
§ 52. Neglecting the primes over the letters — since was continue to only speak about averages — we summarize the equations of motion now in the following way.
In the interior of any body it is given
,
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,
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,
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,
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and
,
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since, neglecting magnitudes of second order, we may replace, by the relation (53),
by
in equation (54).
At the borderline the conditions apply
,
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If there is no translation, then
falls into
; then the equations (
) and (
) go over into
,
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, etc.
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and the last of the limiting conditions (
) into
.
Thus for this case, the known equations of motion and limiting conditions of the electromagnetic theory of light are given. From formulas
and
we derive (when
are different from each other) the laws of light motion in crystals of two axes, while the assumption
leads back to isotropic bodies. Besides, since
and
depend on the