Estremadura See Extremadura
estrogen Ves-trs-jofo Any of a class of hormones that primarily influ¬ ence the female reproductive system’s development, maturation, and func¬ tion. The three major estrogens—estradiol, estrone, and estriol—are produced mainly by the ovaries and placenta; the adrenal glands and the testes secrete smaller amounts. Estrogens affect the ovaries, vagina, fal¬ lopian tubes, uterus, and mammary glands and play crucial roles in puberty, menstruation, pregnancy, and parturition (labour). They also influence the structural differences between female and male bodies. In experimental animals, loss of estrogens diminishes mating desires and other behavioral patterns.
estrus Period in the sexual cycle of female mammals, except the higher primates, during which they are in heat (ready to accept a male for mat¬ ing). Some animals (e.g., dogs) have only one heat during a breeding sea¬ son; others (e.g., ground squirrels) will come into heat repeatedly during the breeding season until impregnated. During estrus the female secretes pheromones that signal her receptivity to the males; her genital area may become swollen, and she may also give behavioral signals.
estuary Ves-cho-.wer-eX Partly enclosed coastal body of water in which river water is mixed with seawater. An estuary is thus defined by salinity rather than geography. Many coastal features designated by other names are in fact estuaries (e.g., Chesapeake Bay). Some of the oldest continu¬ ous civilizations have flourished in estuarine environments (e.g., the land between the Tigris and Euphrates rivers, the Nile delta, the Ganges delta, and the lower Huang He valley). Cities such as London (River Thames), New York (Hudson River), and Montreal (St. Lawrence River) developed on estuaries and became important commercial centres.
Etana Epic \a-'ta-na\ Ancient Mesopotamian myth concerning dynastic succession. The gods chose Etana as the first king, but his wife, though pregnant, could not give birth, and thus Etana had no heir. The god Sha- mash answered Etana’s prayers by directing him to rescue a maimed eagle, which rewarded Etana by carrying him high up in the sky, near heaven, where Etana could obtain the birth plant to help his wife. Surviving texts are incomplete and divergent: in one version Etana makes it to heaven (but the text then breaks off); in another he falls to earth. A king named Etana ruled Kish in southern Mesopotamia sometime in the 3rd millen¬ nium BC.
etching Method of engraving in which lines or textures are bitten, or etched, into a metal plate, usually copper, with acid. The image produced has a spontaneity of line that comes from drawing on the plate in the same direct way as with pen or pencil on paper. The first etchings date from the early 16th century, but the basic principle had been used earlier for the decoration of armour. Among the pioneers of the medium were Al¬ brecht Altdorfer, Albrecht DOrer, and Parmigianino; the greatest of all etch¬ ers was Rembrandt. In the 20th century, etching was especially popular for book illustration. See also aquatint; engraving.
ethanol \'e-th3-,n6l\ or ethyl alcohol or grain alcohol Organic compound, most important of the alcohols, chemical formula CH 3 CH 2 OH. Produced by fermentation, it is the intoxicating ingredient in alcoholic beverages. Ethanol for industrial purposes is made by either fer¬ mentation or chemical synthesis, then purified by distillation and, to avoid the tax levied on ethyl alcohol for drinking, made unfit to drink (see dena- turation) by mixing it with compounds such as methanol, benzene, or kero¬ sene. Ethanol has many uses as a solvent, a raw material, an extraction medium, an antifreeze, an antiseptic, and a gasoline additive and substi¬ tute. It is toxic, depressing the central nervous system, and addictive to some persons (see alcoholism). Moderate amounts depress the inhibitory activities of the brain and so appear to stimulate the mind, but larger amounts seriously impair coordination and judgment; excessive consump¬ tion can cause coma and death. Taking ethanol in combination with bar¬ biturates or related drugs is especially dangerous.
Ethelbert I or Aethelberht I (d. Feb. 24, 616) King of Kent (560- 616). He married the Christian Bertha, daughter of the king of Paris, and, when St. Augustine of Canterbury and other missionaries arrived in Kent in 597, he welcomed them and gave them a dwelling at Canterbury. Though baptized by Augustine along with thousands of his subjects, he did not try to establish Christianity by decree. He produced the first writ¬ ten laws in Anglo-Saxon (see Anglo-Saxon law).
Ethelred II or Aethelred Unraed known as Ethelred the Unready (b. 968?—d. April 23, 1016, London) King of the English
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(978-1013, 1014-16). He became king after his half brother’s assassina¬ tion and was suspected of involvement in the murder. An ineffectual ruler, he failed to mount an organized defense against the Danish invasions (from 980); his massacre of Danish settlers (1002) provoked further attacks. When Sweyn I was accepted as king in England in 1013, Ethel- red fled to Normandy. He returned to the throne on the death of Sweyn in 1014, but on his death he was succeeded by the Dane Canute the Great. His epithet “Unraed” means “evil counsel” and has been translated incor¬ rectly as “the Unready.”
ether \'e-thor\ Any of a class of organic compounds whose molecular structure has an oxygen atom interposed between two carbon atoms that are part of hydrocarbon molecules. Ethers have the general chemical for¬ mula ROR', in which R and R' represent the hydrocarbons. They resemble alcohols but generally are less dense, less soluble in water, more volatile, and more inert. They are used in chemical processing, for extraction and separation of chemicals, and as solvents. Some are used as insecticides and soil fumigants. They are also used in medicine and pharmacology. Codeine is the methyl ether of morphine. The term ether often refers to ethyl ether (C 2 H 5 OC 2 H 5 ), best known as an anesthetic but also used as a solvent, an extractant, and a reaction medium.
Etherege \'eth-rij\, Sir George (b. c. 1635, Maidenhead, Berkshire, Eng.?—d. c. May 10, 1692) British playwright. He is remembered as the creator of the Restoration comedy of manners. His first comedy. Love in a Tub (1664), was an immediate success and was novel in its lively exploitation of contemporary manners. He also wrote She Wou’d if She Cou’d (1668) and the popular The Man of Mode (1676). Though his own plays ceased to be performed after the 18th century, his style of comedy was adopted by later playwrights and persisted into modern times.
Ethernet Telecommunications networking protocol introduced by Xerox Corp. in 1979. It was developed as an inexpensive way of sending information quickly between office machines connected together in a single room or building, but it rapidly became a standard computer inter¬ connection method. The original data rate of 10 megabits per second has been increased to 100 megabits per second for a new standard known as fast ethemet. The original specification required coaxial cable as the com¬ munications medium, but costs have been reduced through the employ¬ ment of simple paired wires. See also computer network.