extrasolar planets See planets of other stars extrovert See introvert and extravert
Extremadura or Estremadura \es-,tra-m3- , thu-ra,\ Portuguese \ l ish-tri-m9-'dur-9\ Historical region and autonomous community (pop., 2001: 1,058,503), west-central Spain. Covering an area of 16,075 sq mi (41,634 sq km), it encompasses the southwestern provinces of Caceres and Badajoz. Its capital is Merida. During the Christian reconquest of the Iberian Peninsula, the name Extremadura was used to refer to the zones outside of Moorish territory. From the late Middle Ages the term was applied to an area approximating the modern region. The countryside remains partitioned into latifundios (large estates); wheat, grapes, and olives are important crops.
extreme sports Sports events characterized by high speed or high risk. Such sports include aggressive inline skating, wakeboarding, street luge, skateboarding, and freestyle bicycle events (wherein tricks such as back flips are performed on a bicycle). Many of the events—snowboarding, skateboarding, and freestyle biking are examples—are performed on ramps and inclines or in a halfpipe, some with walls as high as 50 feet, which allows the athletes to get air, or achieve the height necessary to, for example, rotate on a bicycle. Many of these sports were made popu¬ lar’ by the X Games (championship competitions sponsored by the cable- television network ESPN). The 1998 and 2002 Olympic Games featured extreme snowboarding events in a halfpipe, in which boarders performed jumps, rotations, and mid-air maneuvers.
extrusion Process in which metal or other material is forced through a series of dies to create desired shapes. Many ceramics are manufactured by extrusion, because the process allows efficient, continuous production. In a commercial screw-type extruder, a screw auger continuously forces the plastic feed material through an orifice or die, resulting in simple shapes such as cylindrical rods and pipes, rectangular solid and hollow bars, and long plates. In metalworking, extrusion converts a billet of metal into a length of uniform cross-section by forcing the billet through the orifice of a die; aluminum is easily extruded. Formed sheet aluminum is used for opaque curtain-wall panels and window frames.
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extrusive rock ► Ezra I 651
extrusive rock Any igneous rock derived from magma that is poured out or ejected at the Earth’s surface. Extrusive rocks are usually distin¬ guished from intrusive rocks on the basis of their texture and mineral com¬ position. Lava flows and pyroclastic debris (fragmented volcanic material) are extrusive; they are commonly glassy (e.g., obsidian) or finely crystal¬ line (e.g., basalts and felsites).
Exupery, Antoine de Saint- See Antoine de Saint-Exupery
Exxon Mobil Corporation U.S.-based oil and gas company formed in 1999 through the merger of Exxon Corp. and Mobil Corp. It has invest¬ ments and operations in petroleum and natural gas, coal, nuclear fuels, chemicals, and ores. It also operates pipelines and one of the world’s largest fleets of tankers. Exxon Mobil engages in every phase of the petroleum industry from oil fields to service stations. Both Exxon and Mobil had their origins in Standard Oil (see Standard Oil Co. and Trust) and were founded in the late 1800s. In 1926 the New Jersey subsidiary of Standard Oil, Exxon’s predecessor, introduced the Esso brand name. The name was changed to Exxon in 1972. As of 2002 Exxon Mobil was the world’s largest integrated oil company.
Eyasi \a-'ya-se. Lake Lake, northern Tanzania. At an elevation of about 3,400 ft (1,040 m), the lake covers an area of about 400 sq mi (1,050 sq km) and occupies the bottom of a bowl-like depression. Its walls are purple lava, enclosing a broad expanse of white alkaline shallows. Flamingos inhabit the lakeshore in vast flocks. Hominid fossils were found nearby.
Eybeschutz \1-ba- I shffits\ # Jonathan (b. c. 1690, Krakow, Pol.—d. 1764, Altona, Den.) Polish rabbi and Talmudic scholar. He served as rabbi in a number of European towns, and his scholarship gained him a loyal following. He was reputed to have mystic powers; when the women of his congregation asked him to give them protection from death in child¬ birth, he offered them amulets that contained a prayer to the false mes- siah Shabbetai Tzevi. A prominent German rabbi, Jacob Emden (1697- 1776), denounced the amulets. The dispute that ensued between Emden and Eybeschutz divided the European Jewish community.
Eyck \'ik\, Jan van (b. before 1395, Maaseik, Bishopric of Liege, Holy Roman Empire—d. before July 9, 1441, Bruges) Flemish painter. He is recorded in 1422 as a master painter working for John of Bavaria, count of Holland, and later was employed by Philip III the Good, duke of Burgundy. Securely attributed paintings survive only from the last decade of his career; 10 are signed and dated, an unusually large number for the period. He produced portraits and religious subjects that are unmatched for their technical brilliance, their intellectual complexity, and the richness of their symbolism; he perfected the newly developed technique of oil painting. His masterpiece is the Adoration of the Lamb (1432), known as the Ghent Altarpiece, which he painted with his brother Hubert (c. 1370-1426). He is commonly regarded as the greatest northern European artist of the 15th century. His works were widely copied and avidly collected.
eye Organ that receives light and visual images. Non-image forming, or direction, eyes are found among worms, mollusks, cnidarians, echino- derms, and other invertebrates; image-forming eyes are found in certain mollusks, most arthropods, and nearly all vertebrates. Arthropods are unique in possessing a compound eye, which results in their seeing a multiple image that is partially integrated in the brain. Lower vertebrates such as fish have eyes on either side of the head, allowing a maximum view of the surroundings but producing two separate fields of vision. In predatory birds and mammals, binocular vision became more important. Evolutionary changes in the placement of the eyes permitted a larger overlap of the two visual fields, resulting in the higher mammals in a par¬ allel line of direct sight. The human eye is roughly spherical. Light passes through its transparent front and stimulates receptor cells on the retina (cones for colour vision, rods for black-and-white vision in faint light), which in turn send impulses through the optic nerve to the brain. Vision disorders include near- and farsightedness and astigmatism (correctable with eyeglasses or CONTACT LENSes), colour blindness, and night blindness. Other eye disorders (including detached retina and glaucoma) can cause VISUAL-FIELD DEFECTS Or BLINDNESS. See also OPHTHALMOLOGY; PHOTORECEPTION. See illustration opposite.
eyeglasses Lenses set in frames to wear in front of the eyes to aid vision or correct vision defects (see ophthalmology, optometry). Their use for far¬ sightedness and nearsightedness has been known since the late Middle Ages. In 1784 Benjamin Franklin invented bifocals, with divided lenses for
distant and near vision. Eyeglasses can also correct astigmatism. Most lenses are made of glass or plastic (lighter and more shatterproof than glass but easily scratched). Sunglass lenses are tinted to reduce glare and often treated to reduce ultraviolet light exposure. See also contact lens.
Eyre Peninsula Large promontory, South Australia. Projecting into the Indian Ocean, the peninsula is about 200 mi (320 km) long and lies between the Great Australian Bight and Spencer Gulf. Wheat, sheep, and barley are raised there; iron is extracted in the Middleback Ranges to the northeast. There are numerous resort and fishing towns along the coasts.