ETHER

also spelled aether, also called luminiferous ether, in physics, a theoretical, universal substance believed during the 19th century to act as the medium for transmission of electromagnetic waves (e.g., light and X rays) much as sound waves are transmitted by elastic media such as air. The ether was assumed to be weightless, transparent, frictionless, undetectable chemically or physically, and literally permeating all matter and space. The theory met with increasing difficulties as the nature of light and the structure of matter became better understood; it was seriously weakened (1881) by the Michelson-Morley experiment (q.v.), which was designed specifically to detect the motion of the Earth through the ether and which showed that there was no such effect. With the formulation of the special theory of relativity by Albert Einstein in 1905 and its acceptance by scientists generally, the ether hypothesis was abandoned as being unnecessary in terms of Einstein's assumption that the speed of light, or any electromagnetic wave, is a universal constant. by James Clerk Maxwell In the First Edition (1768-71) of the Encyclopdia Britannica, the article on "ther," began thus: "the name of an imaginary fluid, supposed by several authors, both ancient and modern, to be the cause of gravity, heat, light, muscular motion, sensation, and, in a word, of every phenomenon in nature." The article then proceeded to quote various of those authors, at length. By the time the Ninth Edition was published (1875-89), the ether was understood to be a medium that transmitted electromagnetic waves, its qualities were explained with mathematical precision, and Britannica turned to James Clerk Maxwell, the creator of modern electromagnetic theory, to describe it. His essay's blend of science and speculative philosophy is characteristic of Victorian scientific writing. It is also the concept's swan song; in a few short years the discoveries of Albert Michelson and Alfred Morley, Heinrich Hertz, and, finally, Albert Einstein, would completely destroy the centuries-old concept. ether any of a class of organic compounds characterized by an oxygen atom attached to two carbon atoms that are part of a hydrocarbon. Ethers are similar to alcohols but are generally less dense, less soluble in water, and have lower boiling points. They are relatively inert. At room temperature, ethers are pleasant smelling, colourless liquids. In nature, ethers are found as part of substances such as sugar, starch, and cellulose. Ethers may be manufactured by dehydrating alcohols, but catalytic hydration (addition of water) of olefins (forms of hydrocarbons) is the major method of production. While often regarded as derivatives of alcohol, ethers exhibit properties that are more likely to resemble those of their parent hydrocarbons. They form salts called oxonium compounds when they are reacted with strong inorganic acids and Lewis acids (compounds capable of accepting electron pairs). When strong acids break one of the carbonoxygen linkages, alcohols are formed. Other organic derivatives are produced if both linkages are broken. Heat decomposes ethers into olefins. In the presence of oxygen, ethers slowly oxidize to unstable peroxides; this reaction can result in an explosion. Ethers will form azeotropes (constant-distillation mixtures) with a large number of organic compounds. As a result, they are used extensively for extraction and separation of organic chemicals. Ethers are also employed as solvents for fats, oils, waxes, perfumes, resins, dyes, gums, and hydrocarbons. Vapours of certain ethers are used as insecticides, miticides, and fumigants for soil. Ethers are also very important in medicine and pharmacology, especially for use as anesthetics. Codeine, for example, is the methyl ether of morphine. Ethyl ether is best known as an anesthetic. A highly volatile liquid, it is also used as a solvent, an extractant, and a reaction medium. Methyl ether is used as a spray propellant and refrigerant. The ethers of ethylene glycol are used as solvents and plasticizers.