Page:The New International Encyclopædia 1st ed. v. 07.djvu/265

* ETHER. 283 ETHER. would be possible with any matter of properties comparable with ordinary matter. The ether has inertia, because time is required for the propagation of waves; but there is no evidence that it lias weight. In fact, the passage of radiation through all bodies, t>> a greater or less degree, proves that the ether is a medium per- meating all space, and that portions "i ordinary matter, i.e. molecules and atoms, are immersed in it, as particles of dust float in the air, or small .-olid particles exist in water. The lengths of ether-waves may be measured by suitable means (see Light); and those that appeal to physical instruments are found to vary from many miles to less than two-millionths of a milli- meter. If waves as short as these last are prop- agated in a medium, it shows that the structure of that medium must be extremely minute, its portions — if there are any — being much smaller than the smallest wave-length known; otherwise waves as short as these could not be produced. Nothing of the actual structure of the ether is known; but from analogy with matter its 'elas- ticity* and 'density' are spoken of, simply mean- ing those properties of restitution and inertia by virtue of which waves may be transmitted. These waves are transverse, meaning that, what- ever the disturbance is, it is perpendicular to the direction of propagation. This shows that the ether must have properties analogous to the material properties of an elastic jelly, be- cause the only form of matter which can carry transverse waves is one with rigidity. It should be observed that some forms of matter behave like solids for sudden forces, but like fluids for slow ones : thus shoemaker's wax is brittle for quick blows, but a piece of lead put on top of the wax will in the course of time pass through, the wax flowing around it. Waves in the ether are produced by electric os- cillations, and they are emitted also by all forms and conditions of matter (see Radiation) ; and the statement that these waves have identical properties — except as to wave-number — is the so-called "electro-magnetic theory' of light. The phenomena of radiation and absorption prove that if a minute portion of matter — an 'atom' — is vibrating extremely rapidly, it produces waves in the ether. This establishes the fact that there is some connection between ether and ordinary matter in this case. Whether a large piece of matter moving with motion of translation drags the ether with it, or simply allows the ether to pass through it — like wind through a tree — is still to a certain extent an open question. There is. however, no decisive experimental fact in favor of the idea that the ether is dragged along, I xcept in the experiments of Michelson and Morley to be referred to later. It lias been shown by Fizeau and by Michelson and Morley that a beam of light is accelerated by its passage through a current of water moving in the direction of the beam, and retarded by an opposing current. This can be explained on the hypothesis of Fresnel that, in addition to the free ether which exists equally everywhere, there is in any transparent body an amount of ether n* — 1 times that of the free ether occupying the same volume, n being the index of refraction, and that this extra amount of ether is attached to the body and moves with it. On this hypothesis the density of the ether in the body is therefore ir times that of the ether in free space, meaning by density thai property oi : urn which measures its inerl ia. The phenomena of Btellar aberration (q.v.) ■ 'in to prove thai the ether near the earth must be independenl of i he eai i h's mol ion, or al l< i hal i here should nol be pi odui i d in it what i called in hydrodynamics 'rotational' motion. On the oilier hand, Michelson and Morl.y have shown thai the ether near the surface of the earth moves with at least very nearly the velocity of the earth, assuming thai their ap- paratus is not affected by the motion. Lodge, however, has performed most careful experiments from which he conclude thai the velocity of light between tWO steel plate-, moving toL'etlier in their own plane- an inch apart i- nol altered by an appreciable quantity. It is extre ly difficult to reconcile these experimental results; and there are many others, equally confusing. II ma_ be that, in order to explain them, it will be neces- sary to assume that the dimensions of solids change as they move through the el her. Bibliography. The subject of the ether is one that presents many difficulties: and, while much has been written in Ibis connection, it, is not al- ways in a shape to be of assistance to the aver- age reader. The following references, however, may be consulted by the physicist: Larmor, .i:ihir and Matter (London, 11101 ) ; Lodge, "Aber ration Problems," in Philosophical Transactions (London, 1892-93) ; id., in Philosophical Trans- actions (London, 1897); Larmor, "Dynamical Theory of the Electric and Luminiferous Ether," in Philosophical Transactions (London, 1894, 1898) ; Michelson and Morley, in Philosophical Magazine, vol. xxiv. (London. 1SS7I: Lorenz, Yersuch i iner Thcoria drr elektrischen und opti- srli, n Erschei/nungen in bewegten Korpern ( Ley- den, 1873): Wien. Referat, 70. Versammlung deutscher Naturforscher und Aerzte in DiisseT dorf (Diisseldorf, 1898). ETHER, or more properly Di-Ethtl-Etheb, (C,H 5 ) a O, otherwise called 'sulphuric ether.' A substance composed of carbon, hydrogen, and oxygen. At ordinary temperatures it is liquid; if chemically pure, it boils at 35° C, and its specific gravity at 0° C. is 0.736. It is sparingly soluble in water, but mixes in all proportions with alcohol, chloroform, acetone, carbon di- sulphide, and other organic liquids. It is an ex- cellent solvent for fats, oils, resins, many alka- loids, and certain inorganic salts, including mer- curic chloride (corrosive sublimate) and the chlorides of iron and copper. The collodion used in photography is a solution of certain nitrates of cellulose in a mixture of alcohol and ether. Ether is also used in the preparation of fats and in determining the amount of fat in samples sub- mitted for analysis (see Fats I : it is likewise employed for removing grease-spots. Its vapors are extremely inflammable, and therefore it should under no circumstances be used in the neighborhood of artificial lights. It is very vola- tile and has a characteristic pleasant odor and a burning sweetish taste. Ether is made on a large scale by the action of strong sulphuric acid on ordinary alcohol. The chemical transforma- tion takes place in two steps: first an ethyl group replaces one of the hydrogen atoms of sul- phuric acid, with formation of ethyl-hydrogen sulphate, CJfl.IISO,, the following reaction tak- ing place: