æther

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Century Dictionary definition:

In astronomy and physics, a hypothetical medium of extreme tenuity and elasticity supposed to be diffused throughout all space (as well as among the molecules of which solid bodies are composed), and to be the medium of the transmission of light and heat. See the extract. The phenomena of Light are best explained as those of undulations; but undulations, even in the most extensive use of the term, as signifying any periodic motion or condition whose periodicity obeys the laws of wave motion, must be propagated through some medium. Heat, while passing through space, presents exactly the same undulatory character, and requires a medium for its propagation. Electrical attraction and repulsion are explained in far the most satisfactory way by considering them as due to local stresses in such a medium. Current electricity seems due to a throb or series of throbs in such a medium, when released from stress. Magnetic phenomena seem due to local whirlpools, set up in such a medium. … We are led to infer, therefore, that there is such a medium, which we call the Luminiferous Ether, or simply the Ether; that it can convey energy; that it can present it at any instant, partly in the form of kinetic, partly in that of potential energy; that it is therefore capable of displacement and of tension; and that it must have rigidity and elasticity. Calculation leads us to infer that its density is (Clerk Maxwell) that of water, or equal to that of our atmosphere at a height of about 210 miles, a density vastly greater than that of the same atmosphere in the interstellar spaces, and that its rigidity is about that of steel; hence, that it is easily displaceable by a moving mass, that it is not discontinuous or granular, and hence that as a whole it may be compared to an impalpable and all pervading jelly through which Light and Heat waves are constantly throbbing, which is constantly being set in local strains and released from them, and being whirled in local vortices, thus producing the various phenomena of Electricity and Magnetism, and through which the particles of ordinary matter move freely, encountering but little retardation, if any, for its elasticity, as it closes up behind each moving particle, is approximately perfect. A. Daniell, Prin. of Physics, p. 208.

October 17, 2010