XII. A dynamical theory of the electric and luminiferous medium

Abstract

1. The object of this paper is to attempt to develope a method of evolving the dynamical properties of the aether from a single analytical basis. One advantage of such a procedure is that by building up everything ab initio from a consistent and definite foundation, we are certain of the congruity of the different parts of the structure, and are not liable to arrive at mutually contradictory conclusions. The data for such a treatment lie of course in the properties of the mathematical function which represents the distribution of energy in the medium, when it is disturbed. The consequences which should result from the disturbance are all deducible by dynamical analysis from the expression for this function; and it is the province of physical interpretation to endeavour to identify in them the various actual phenomena, and in so far to establish or disprove the explanation offered. A method of this kind has been employed by Clerk Maxwell with most brilliant results in the discovery and elucidation of the laws of electricity; he has also been led by its development into the domain of optics, and has thus arrived at the electric theory of light. His expression for the energy of the active medium has been constructed from reasoning on the phenomena of electrification and electric currents; this procedure offers perhaps difficulties greater than might be, owing to the intangible character of the electric co-ordinates, and their totally undefined connexion with the co-ordinates of the material system which is the seat of the electric manifestations. In the following discussion, the order of development began with the optical problem, and was found to lead on naturally to the electric one. We shall show that an energy-function can be assigned for the aether which will give a complete account of what the aether has to do in order to satisfy the ordinary demands of Physical Optics; and it will then be our aim to examine how far the phenomena of electricity can be explained as non­ vibrational manifestations of the activity of the same medium. The credit of applying with success the pure analytical method of energy to the elucidation of optical phenomena belongs to MacCullagh; he was however unable to discover a mechanical illustration such as would bring home to the mind by analogy the properties of his medium, and so his theory has fallen rather into neglect from supposed incompatibility with the ordinary manifestations of energy as exemplified in material structures. We shall find that such difficulties are now removed by aid of the mechanical example of a gyratory sether, which has been imagined by Lord Kelvin to illustrate the properties of the luminiferous and electric medium. The sether whose properties are here to be examined is not a simple gyrostatic one it is rather the analogue of A medium filled with magnetic molecules which are under the action, from a distance, of a magnetic system. But the same peculiarities that were supposed to fatally beset MacCullagh’s medium and render it inconceivable, are present in an actual mechanical medium dominated by gyrostatic momentum.