AR´THUR, KING, an ancient British hero of the sixth century, son of Uther Pendragon and the Princess Igerna, wife of Gorlois, Duke of Cornwall. He married Guinevere, or Ginevra; established the famous order of the Round Table; and reigned, surrounded by a splendid Court, twelve years in peace. After this, as the poets relate, he conquered Denmark, Norway, and France, slew the giants of Spain, and went to Rome. From thence he is said to have hastened home on account of the faithlessness of his wife, and Modred, his nephew, who had stirred up his subjects to rebellion. He subdued the rebels, but died in consequence of his wounds, on the Island of Avalon. The story of Arthur is supposed to have some foundation in fact, and has ever been a favourite subject with our romanticists and our poets. It is generally believed that Arthur was one of the last great Celtic chiefs who led his countrymen from the west of England to resist the settlement of the Saxons in the country. But many authorities regard him as a leader of the Cymry of Cumbria and Strath-Clyde against the Saxon invaders of the east coast and the Picts and Scots north of the Forth and the Clyde. See _Grail_, _Merlin_, _Round Table_.--BIBLIOGRAPHY: J. Rhys, _Studies in the Arthurian Legend_; W. Lewis Jones, _King Arthur in History and Legend_.
ARTHUR'S SEAT, a picturesque hill within the King's Park in the immediate vicinity of Edinburgh; has an altitude of 822 feet; descends rollingly to the N. and E. over a base each way of about five furlongs; presents an abrupt shoulder to the S., and breaks down precipitously to the W. It is composed of a diversity of eruptive rocks, with some interposed and up-tilted sedimentary ones; and derives its name somehow from the legendary King Arthur.
AR´TIAD (Gr. _artios_, even-numbered), in chemistry, a name given to an element of even equivalency, as a dyad, tetrad, &c.: opposed to a perissad, an element of uneven equivalency, such as a monad, triad, &c.
ARTICHOKE (_Cyn[)a]ra Scol[)y]mus_), sometimes called 'the Globe Artichoke', a well-known plant of the nat. ord. Compositæ, somewhat resembling a thistle, with large divided prickly leaves. The erect flower-stem terminates in a large round head of numerous imbricated oval spiny scales which surround the flowers. The fleshy bases of the scales with the large receptacle are the parts that are eaten. Artichokes were introduced into England early in the sixteenth century. The Jerusalem artichoke (a corruption of the It. _girasole_, a sunflower), or _Helianthus tuber[=o]sus_, is a species of sunflower, whose roots are used like potatoes; it was introduced into England in the early part of the seventeenth century.