§ 87. If we replace in equation (113), by , and by , it follows
.
Since the terms with and are in any case very small, the value of m following from it, can be represented by a row that progresses with respect to the powers of and . The first term independent of these magnitudes, has the value
,
and then we also find
,
where we didn't calculated the three latter terms more closely, and we have neglected all higher powers of and , as well as all terms that include . To these latter ones, also the terms with and do belong, since .
Now, we obtain , or , depending on whether we put , or . The sought rotation of the polarization consequently becomes
,
or, when we denote the propagation velocity by W,
.
The natural rotation of the polarization plane in stationary bodies would consequently be
;
(116)
if we were allowed to consider as constant and j, then it would be, as it follows from the meaning of , proportional to the square of the oscillation time. It's known that all bodies deviate