by H. A. Lorentz; and it involves the general electrodynamic considerations, including the discrete distribution of electricity among the molecules of matter, on which the present essay is based. Shortly after Lorentz the subject was taken up from a similar point of view by von Helmholtz, primarily in relation to the theory of optical dispersion: but his equations, derived from a difficult abstract procedure in connexion with attempted generalizations of the principle of Least Action, were soon found to be at fault in the matter of moving media just as much as was the original scheme of Maxwell. Possibly thereby incited, von Helmholtz considers directly the question of motion of the aether in his last published memoir: he finds, as Hertz had done some years before, that the mechanical force as given by the equations of Maxwell cannot by itself keep the aether in equilibrium if we suppose this force to act on it as well as on matter: and on the assumption that the aether is fluid as regards movements arising from extended disturbance, and of very small density, he obtains differential equations for the determination of the steady state of aethereal motion that must on that hypothesis exist in an electrodynamic field. The existence of any finite motion of this sort, unless it is very minute, has been negatived by the elaborate experiments of Lodge, and also by more recent observations on the same plan by Henry and Henderson which were inspired from von Helmholtz's theory.
14. Quite recently a general summary of the state of the question of the mutual relations of aether and moving matter has been published by W. Wien[1], as a guide to a discussion of the subject at the annual meeting of the German Scientific Association. He there works out some special cases of von Helmholtz's theory just mentioned, arriving at the result that of the density of the aether is absolutely null there can exist a steady translational motion of electric charge through the aether which will not involve any disturbance of that medium, while if the density is very small the disturbance thus involved will be very slight: but in motions not steady, for example the uniform separation of the components of a stationary electric
- ↑ Wied. Annalen lxv., July 1898.
