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 to explain circular-polarization. Indeed I regard, in the absence of a theory that explains the phenomenon more deeply, the introduction of the term $$j\ Rot\ \mathfrak{M}$$ as neither better nor worse than the hypotheses of those physicists.

The last term in (68) has a peculiar meaning. Namely a rotation of the polarization plane would correspond to it, that would be caused in a body (that is different from its mirror image) by the motion of earth.