ETHER, sometimes !ETHER, the name given to the medium which is assumed in astronomy and physics as filling all space. It was shown by Newton, that if light con sisted of material particles projected from luminous bodies, these must move faster in solids and liquids than in air, in order that the laws of refraction might be satisfied .n their motions. Huyghens, on the other hand, showed, that to account for the same laws on the supposition that light consisted in the undulatory motions of an elastic medium, it must move more slowly in solids and fluids than in gases. Fizeau and Foucault have lately, by different methods, measured these velocities relatively, and have found Huyghens's prediction to be correct. Light, then, consists in the vibratory motion of a medium, which musts of course, fill all space. This is called ether As yet, we have no idea as to its ultimate nature; some of our greatest philosophers, even, have supposed that it may be of the class of ordinary gases, and that our atmosphere, for instance, is not finite in extent, but pervades, with greatly reduced density. all inter planetary and interstellar space. Many objections, however, may easily be raised against this supposition. Meanwhile, we may remark, that the mathematical theory of
light, on the hypothesis of undulations, requires that the vibrating medium should pos sess properties more nearly allied to those of an elastic solid than those of a liquid or a gas. The E. being required for the explanation of the existence and the propagation of light, it becomes a matter of importance to inquire how many more of the physical forces may be referred to the same cause or medium. Radiant heat most certainly may, and, in all probability, gravitation, molecular actions, magnetic, electric, and electrodynamic attractions and repulsions, are also to be thus explained. As to sensible and latent heat, electricity and magnetism themselves, the necessity is not so clear; but even these have been of late almost satisfactorily explained by the hypothesis of the all-pervading ether. See FORCE. In the article just referred to, a good deal more will be found with refer ence to this subject, and especially with reference to the impossibility of the E.'s con sisting of air or other gases, which are made up of distinct and separated particles.