COURTESY OF THE STAATSBIBUOTHEK, WEST BERUN
clavichord Early keyboard instrument, an important forerunner of the piano. It flourished c. 1400-1800, especially in Germany. It is usually rectangular, with the keyboard inset. The strings are struck by metal tan¬ gents, rather than plucked as on the harpsichord. The tangent becomes the endpoint of the vibrating string; thus the point where it strikes determines the pitch. So-called fretted clavichords permit more than one tangent to strike a single pair of strings (which somewhat limits the notes that can be sounded simultaneously); unfretted clavichords use only one tangent per pair of strings. The player’s touch can produce dynamic variation; variation in finger pressure can even produce vibrato. Its tone is silvery and soft, best suited for intimate music.
clay Soil particles with diameters less than 0.005 mm; also a material composed essentially of clay particles (see clay mineral). In soils, clays provide the environment for almost all plant growth. The use of clay in pottery making predates recorded human history. As building materials, clay bricks (baked and as adobe) have been used in construction since ear¬ liest times. Kaolin, or china clay, is required for the finer grades of ceramic materials; used for paper coating and filler, it gives the paper a gloss, per¬ mitting high-quality reproduction, and increases paper opacity. Clay mate¬ rials have many uses in engineering; earth dams are made impermeable
Clay, Lucius D(uBignon) (b. April 23, 1897, Marietta, Ga., U.S.—d. April 16, 1978, Cape Cod, Mass.) U.S. army officer. After graduating from West Point, he served in various military engineering assignments. In World War II he directed the U.S. Army procurement program (1942—44). In 1945 he was appointed deputy military governor of the U.S. zone of occupation in defeated Germany. Two years later he was elevated to com¬ mander in chief of U.S. forces in Europe and military governor of the U.S. zone. In 1948-49 he organized the successful Allied airlift of food and supplies into Berlin during the Soviet blockade of that city (see Ber¬ lin blockade and airlift). After retiring in 1949, he entered private business and became an unofficial adviser to Pres. Dwight D. Eisenhower.
clay mineral Any of a group of important hydrous aluminum silicates with a layered structure and very small (less than 0.005 mm or micro¬ scopic) particle size. They are usually the products of weathering. Clay minerals occur widely in such sedimentary rocks as mudstones and shales, in marine sediments, and in soils. Different geologic environments pro¬ duce different clay minerals from the same parent rock. They are used in the petroleum industry (as drilling muds and as catalysts in refining) and in the processing of vegetable and mineral oils (as decolorizing agents).
Clayton, John Middleton (b. July 24, 1796, Dagsboro, Del., U.S.—d. Nov. 9, 1856, Dover, Del.) U.S. politician. He served as Dela¬ ware’s secretary of state (1826-28) and chief justice (1837). He also rep¬ resented Delaware in the U.S. Senate (1829-36, 1845-49). As U.S. secretary of state (1849-50) under Pres. Zachary Taylor, he negotiated the Clayton-Bulwer Treaty.
Clayton-Bulwer Treaty (1850) Compromise agreement designed to harmonize contending British and U.S. interests in Central America. The treaty provided that the two countries jointly control and protect what was to become the Panama Canal. The Clayton-Bulwer treaty was superseded
to water by a core of clay, and water loss in canals may be reduced by lining the bottom with clay (called puddling). The essential raw materi¬ als of Portland cement include clays.
Clay, Cassius See Muhammad Au
Clay, Cassius Marcellus (b. Oct. 19, 1810, Madison county, Ky., U.S.—d. July 22, 1903, Whitehall, Ky.) U.S. abolitionist and politician. The son of a slaveholder and a relative of Henry Clay, he was strongly influenced by the abolitionist ideas of William Lloyd Garrison. In 1845 he founded the antislavery publication True American in Lexington, Ky., but he was forced by opponents to move it to Cincinnati, Ohio, and then to Louisville, Ky., where it was renamed The Examiner. He helped found the Republican Party in 1854. As U.S. minister to Russia (1861-62, 1863— 69), he helped negotiate the Alaska Purchase.
Clay, Henry (b. April 12, 1777, Hanover county, Va., U.S.—d. June 29, 1852, Washington, D.C.) U.S. politician. He practiced law from 1797 in Virginia and then in Ken¬ tucky, where he served in the state legislature (1803-09). He was elected to the U.S. House of Repre¬ sentatives (1811-14, 1815-21,
1823-25); as House speaker (1811—
14), he was among those who pro¬ pelled the U.S. into the War of 1812. He supported a national eco¬ nomic policy of protective tariffs, known as the American System, a national bank, and improvements to internal transportation. His support of the Missouri Compromise earned him the nicknames “The Great Pacificator” and “The Great Com¬ promiser.” After his bid for the presi¬ dency in 1824 fell short, Clay threw
his support to John Quincy Adams, _
who made him his secretary of state
(1825-29). He served in the U.S. Senate (1806-07, 1810-11, and 1831- 42), where he supported the compromise tariff of 1833. He was the National Republican Party candidate for president in 1832 and the Whig Party candidate in 1844. In his last Senate term (1849-52) he argued strongly for passage of the Compromise of 1850.
Henry Clay, by Frederick and William Langenheim, 1850.
LIBRARY OF CONGRESS, WASHINGTON, D.C.
© 2006 Encyclopaedia Britannica, Inc.
416 I Clazomenae ► Clement V
in 1901 by the Hay-Pauncefote Treaty, under which the British govern¬ ment agreed to allow the U.S. to construct and control the canal.
Clazomenae Mdo-'za-mo-.neV Ancient Ionian Greek city, Anatolia. Founded on the mainland, the city was subsequently moved to a nearby island. Part of the Ionian Dodecapolis, it was known for its painted terra¬ cotta sarcophagi (6th century bc). During the 5th century bc it was con¬ trolled by Athens, during which time the philosopher Anaxagoras was bom there. It became subject to the Persian Achaemenian dynasty in 387 bc. A half century or so later Alexander the Great built a causeway con¬ necting the city to the mainland. Under the Romans (see Roman Republic and Empire) it became part of the province of Asia.
Clear Grits Political movement in Canada West (now Ontario). It devel¬ oped in 1849 within the Reform Party in opposition to the province’s pre¬ mier, Robert Baldwin, who advocated reforms that included the use of crown lands to support the Protestant churches. It allegedly took its name from the motto “All sand and no dirt, clear grit all the way through.” Its early leader was Peter Perry; after his death in 1851, control gradually passed to George Brown. It eventually joined other groups to form the Liberal Party of Canada; the term “Grit” denotes a member of that party.
clearinghouse Institution established by firms engaged in similar activities to enable them to offset transactions with one another in order to limit payment settlements to net balances. Clearinghouses play an important role in settling international payments and the transactions of banks, railroads, and stock and commodity exchanges. Bank clearing¬ houses are usually voluntary associations of local banks set up to simplify the exchange of checks, drafts, and notes, as well as to settle balances. Increasingly, the automated clearinghouse (ACH) is used to transfer funds electronically. The clearinghouse idea was applied to various forms of trade from an early time. The Amsterdam Exchange Bank, founded in 1609, became Europe’s largest clearinghouse and made the city an inter¬ national financial centre. The first modern bank clearinghouse was estab¬ lished in London in 1773. The first bank clearinghouse in the U.S. was established in 1853.
cleavage Tendency of a crystalline substance to split into fragments bounded by plane surfaces. Cleavage surfaces are seldom as flat as crys¬ tal faces, but the angles between them are highly characteristic and valu¬ able in identifying a crystalline material. Cleavage occurs on planes where the atomic bonding forces are weakest; for example, galena cleaves par¬ allel to all faces of a cube. Cleavage is described by its direction (as cubic, prismatic, basal) and by the ease with which it is produced. A perfect cleavage produces smooth, lustrous surfaces. Other degrees include dis¬ tinct, imperfect, and difficult. See also fracture.