analysis, that the absence of any dependence between the optical rotatory power of quartz and the direction in which the light travels with regard to the Earth's motion, is in discrepancy with theoretical schemes like the present one which considers the Earth to move through the aether without carrying the medium along with it. In the fourth section this question is treated, with results however that prove to be in accord with the facts. As there seems to exist a feeling, — put in evidence by Lorentz's conclusion above mentioned, which asserts a convective influence on rotatory power although he had shown that there was none such on ordinary optical phenomena — that these rotatory phenomena are intrinsically of a class by themselves, a view which may derive strength from their relatively slight or residual character, a discussion of the general nature of the structural and the magnetic rotatory optical properties is given. An attempt to connect rotatory power with density fails, for reasons that are tentatively suggested. It is pointed out that the absence of any convective influence on the rotation affords some independent evidence, in addition to Michelson's result above stated, in favour of the effective validity of the view as to molecular constitution that is considered in the third section.
5. The fifth section treats of the subject of the radiation of material systems, the difficulties of which are not peculiar to any special theory of the connexion between aether and matter. The present theory, which attributes radiation to the oscillatory motions of electrons in the molecule, must give some account, of why it is that molecules radiate only when they are violently disturbed; and in particular, which concerns more closely our special subject, why it is that motion of bodies through the aether does not affect the amount or quality of their radiation, except after the merely kinematic manner of the Doppler effect. To carry out this purpose, an expression is found for the train of radiation and of general aethereal disturbance emanating from a single electron moving in any manner.
As connected with the molecular theory, and in fact demanded by it, a discussion is also given of the principles on which optical resolving apparatus is able to decompose the
