Abstract
1. The nature of the connexion between ether and gross matter is one of the most striking physical problems which now appear ripe for solution, and as a preliminary to the undertaking of fresh experiments I propose to review the subject in order to realize our present position in connexion with it. The subject may be attacked either optically or electrically. It first prominently presented itself historically in connexion with the earth’s motion through space and the finite velocity of light; and it will be convenient to consider the matter first on this side, and to realize precisely what ought to be expected to happen on any simple hypothesis concerning the ether; working it out, however, in most cases with accuracy, and by no means ignoring as negligible small quantities of the second order (hundred-millionths), which Michelson has practically shown to be nowadays within the limits of highly-refined observation.