archaeopteryx \ar-ke-'ap-t9-riks\ Oldest known fossil animal that is generally accepted as a bird (classified as genus Archaeopteryx). It flour¬ ished during the Late Jurassic period (159-144 million years ago). Fossil specimens indicate that archaeopteryx ranged in size from as small as a blue jay to as large as a chicken. Archaeopteryx shared anatomical char¬ acteristics with both birds (well-developed wings and birdlike skull) and theropod dinosaurs (well-developed teeth and a long tail).
Archangel See Arkhangelsk
archbishop In Christianity, a bishop who has jurisdiction, but not supe¬ riority, over the other bishops in a province as well as episcopal author¬ ity in his own diocese. Introduced as an honorary title in the Eastern churches in the 4th century, the office did not become common in West¬ ern churches until the 9th century. It is now most widely used in the Roman Catholic and Eastern Orthodox churches. It is more rarely used in Protestant denominations, though the Church of England has archbish¬ ops of Canterbury and York, and the Lutheran churches of both Sweden and Finland have an archbishop.
Archean \ar-'ke-on\ Eon or Archaean Eon or Archeozoic Eon
Older of the two divisions of Precambrian time. The Archean begins with the formation of the Earth’s crust c. 3.8 billion years ago and extends to c. 2.5 billion years ago, up to the start of the Proterozoic Eon, the second division of the Precambrian Period. The earliest and most primitive forms of life (bacteria and cyanobacteria) originated c. 3.5 billion years ago in the middle of the Archean Eon (the Archean’s alternative name, Archeo¬ zoic, means “ancient life”).
archer fish Any of five species (family Toxotidae) of Indo-Pacific fishes noted for their ability to knock their insect prey off overhanging vegetation by shooting it with drops of water expelled from their mouth. Archer fishes are elongated and have a relatively deep body that is almost flat from the dorsal fin forward. The head is pointed, the mouth is large, and the dorsal
crown
trefoil arch ogee arch
The arch supports a vertical load primarily by axial compression of its wedge- shaped voussoirs. As shown on the Roman arch, the first voussoir, or springer, rests on the impost, at the top of the abutment or pier. The haunch, rising from the impost to the crown (highest point), is defined by the inner curve, or intrados, and outer curve, or extrados. The Roman arch, with its semicircular intrados, has a rise exactly half the width of the span. Below it are shown examples of the curved arch (left) and the pointed arch (right). The stilted arch has vertical sides. A Moorish arch widens above the spring points. The trefoil arch's intrados has three indentations, or foils. A Gothic arch is a pointed arch usually having two haunches of equal radii of curvature. A Tudor arch has greater curvature near the springers than near the point. Each haunch of the ogee arch consists of a double curve.
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98 I archery ► Arctic Circle
and anal fins are placed toward the back of the body. Different species are spotted or vertically banded with black. Archer fishes live in both fresh and salt water, usually remaining near the surface. One well-known spe¬ cies (Toxotes jaculator, or jaculatrix ) grows to about 7 in. (18 cm) long.
archery Sport of shooting with bow and arrow. As the bow began to be replaced by the gun as the principal weapon of warfare and the hunt beginning in the 16th century, it increasingly became a sporting device. By the mid-19th century, many archery clubs had sprung up in England and the U.S. Competitions including target-shooting were held at the Olympic Games in the early 20th century, but were then suspended until 1972. Other varieties of archery include field archery, or roving (a simu¬ lation of hunting), and flight shooting (a distance event).
Arches National Park Preserve, eastern Utah, U.S. Located on the Colorado River north of Moab, the preserve was established as a national monument in 1929 and as a national park in 1971. Its area is about 120 sq mi (310 sq km). The park’s sandstone has been eroded into unusual shapes, including Courthouse Towers, Fiery Furnace, and Devils Garden, the site of Landscape Arch, at 306 ft (93 m) the longest freestanding natu¬ ral rock bridge in the world.
archetype \'ar-ki-,tlp\ Primordial image, character, or pattern of cir¬ cumstances that recurs throughout literature and thought consistently enough to be considered universal. Literary critics adopted the term from Carl Gustav Jung’s theory of the collective unconscious. Because arche¬ types originate in pre-logical thought, they are held to evoke startlingly similar feelings in reader and author. Examples of archetypal symbols include the snake, whale, eagle, and vulture. An archetypal theme is the passage from innocence to experience; archetypal characters include the blood brother, rebel, wise grandparent, and prostitute with a heart of gold.
Archimedean screw N.ar-ko-'med-e-sM or Archimedes' screw
Machine for raising water, said to have been invented by Archimedes for removing water from the hold of a large ship. One form consists of a cir¬ cular pipe enclosing a helix and inclined at an angle of about 45°, with its lower end dipped in the water; rotation of the device lifts the water in the pipe. Other forms consist of a helix revolving in a fixed cylinder or a helical tube wound around a shaft.
Archimedes V.ar-ko-'me-.dezX (b. c. 290-280 bc, Syracuse, Sicily—d. 212/211 bc, Syracuse) Legendary Greek inventor and mathematician. His principal discoveries were the Archimedes screw, an ingenious device for raising water, and the hydrostatic principle, or Archimedes' principle. His main interests were optics, mechanics, pure mathematics, and astronomy. Archimedes’ mathematical proofs show both boldly original thought and a rigour meeting the highest standards of contemporary geometry. His approximation of n was not improved on until after the Middle Ages, and translations of his works were important influences on 9th-century Arab and 16th- and 17th-century European mathematicians. In his native city, Syracuse, he was known as a genius at devising siege and countersiege weapons. He was killed by a Roman soldier during the storming of the city.
Archimedes' principle Law of buoyancy, discovered by Archimedes, which states that any object that is completely or partially submerged in a fluid at rest is acted on by an upward, or buoyant, force. The magni¬ tude of this force is equal to the weight of the fluid displaced by the object. The volume of fluid displaced is equal to the volume of the portion of the object submerged.
Archipenko X.ar-ko-'peq-koV Alexander (b. May 30, 1887, Kiev, Ukr.—d. Feb. 25, 1964, New York, N.Y., U.S.) Ukrainian-U.S. sculptor. In 1908 he moved to Paris to study at the Ecole des Beaux-Arts, and he soon became active in radical circles such as the Cubist movement. He began to explore the interplay between interlocking voids and solids and between convex and concave surfaces, forming a sculptural equivalent to Cubist paintings’ overlapping planes and, in the process, revolutionizing modern sculpture. About 1912 he introduced the concept of collage in sculpture, and he went on to further defy tradition in his “sculpto- paintings,” works in which he introduced painted colour to the intersect¬ ing planes of his sculpture. In 1923 he moved to New York City, where he worked and taught for most of his life.
architecture Art and technique of designing and building, as distin¬ guished from the skills associated with construction. The practice of archi¬ tecture emphasizes spatial relationships, orientation, the support of activities to be carried out within a designed environment, and the arrangement and visual rhythm of structural elements, as opposed to the
design of structural systems themselves (see civil engineering). Appropri¬ ateness, uniqueness, a sensitive and innovative response to functional requirements, and a sense of place within its surrounding physical and social context distinguish a built environment as representative of a cul¬ ture’s architecture. See also building construction.