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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^[1].

1. The following consideration might be sufficient, to make the existence of the electric force $k[{\mathfrak {{\dot {M}}.p}}]$ somewhat probably, for which only the possibility was shown in the text. Since a molecule of a circular-polarizing substance must have a so-called "helical" structure, then the particles from which it consists may be mutually connected, so that the displacement of one of them produces a circular motion of one or many others. Let, for example, a positive ion A be in motion along the line G, and by that the moment ${\mathfrak {M}}$ shall be produced, so that the velocity is proportional to ${\dot {\mathfrak {M}}}$, and this motion may be accompanied by the rotation (in a circle with G as its axis) of some other ions B that are also positive. Between the velocities of A and B there is a constant relation. The motion of particle B then forms a circular electric current, proportional to ${\dot {\mathfrak {M}}}$, and this produces in the molecule and in its vicinity a local magnetic force, which in A falls into line G and thus also into ${\dot {\mathfrak {M}}}$, and which is proportional to ${\dot {\mathfrak {M}}}$. If we combine, in accordance with the last term of fundamental equation (V), this magnetic force with the velocity ${\mathfrak {p}}$, then we obtain an electric force like $k[{\mathfrak {{\dot {M}}.p}}]$.