3. The third section enters on more speculative ground. It developes the exact consequences, as regards the influence of convection through the aether, which flow from the hypothesis that the atom of matter is constituted of an orbital system of equal primary electric point-charges (or electrons) and of nothing else: or, what comes in certain respects to the same thing in a mode of statement that may possibly be preferred, it assumes that the mass of each sub-atom is proportional to the absolute number of electrons, positive and negative, that it carries, and that the effective interatomic forces are entirely or mainly electric. From this basis a complete formal correlation is established between the molecular configurations of a material system at rest and the same system in uniform translatory motion, which holds good as far as the square of the ratio of the velocity of the system to the velocity of radiation. This correspondence carries with it as a consequence the null result, up to the second order, of the very refined experiments of Michelson and Morley on the influence of the Earth's motion on optical interference fringes. The correlation presupposes that the material atoms are independent systems that maintain their relative positions: thus in the simplest case, with which alone we are actually concerned, the material bodies are supposed to be solid, and the influence of the distantly wandering ions, if there are such, that convey electric currents, is left out of consideration as relatively negligible on account of the smallness of their number. In an appendix the mechanism of electrolytic conduction is scrutinized, primarily with a view to drawing conclusions by analogy as to the extent and character of the migrations of the ions in solid conductors: this discussion has however grown altogether out of proportion to its connexion with the present subject, and forms to some extent a connected theoretical account of electrolysis and the voltaic phenomena associated with it, such as the concentration of the electrolyte investigated by Hittorf, the electromotive forces of concentration investigated by von Helmholtz and Nernst, the electric osmosis of Quincke, and the nature of contact differences of potential.
4. It is generally held, chiefly on the ground of Lorentz's
