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ARC - 8 reference results
arc, in electricity, highly luminous and intensely hot discharge of electricity between two electrodes. The arc was discovered early in the 19th cent. by the English scientist Sir Humphry Davy, who so named it because of its shape. An arc is characterized by a high current, low voltage, and indefinite duration. It is usually started when two electrodes carrying an electric current are drawn apart. At the instant the electrodes are parted, strong electric forces draw electrons from one electrode to the other, initiating the arc. The discharge consists of a current composed of these electrons and charged gas particles, called ions, that form between the electrodes. The first practical electric light, the arc lamp, made use of the arc formed between two carbon rods (see lighting). Today the use of the arc lamp is limited to special purposes, e.g., in searchlights and in research applications. The principle of the electric arc is employed in welding (as in the hydrogen arc, where hydrogen is introduced between tungsten electrodes) and also in generating heat in the electric furnace. A spark, like an arc, is a discharge of electricity between two points, but it has a high voltage and a short duration. Lightning is an example of a spark.
arc, in geometry, a curved line or any part of it; in particular, a portion of the circumference of a circle. The length s of an arc of a circle of radius r and subtending a central angle of θ radians is s=rθ; if θ is measured in degrees, then the arc is given by s=2πrθ/360.
Joan of Arc, Fr. Jeanne D'Arc (zhän därk), 1412?-31, French saint and national heroine, called the Maid of Orléans; daughter of a farmer of Domrémy on the border of Champagne and Lorraine.

Inspiration and Leadership

At a young age she began to hear "voices"—those of St. Michael, St. Catherine, and St. Margaret. When she was about 16, the voices exhorted her to bear aid to the dauphin, later King Charles VII, then kept from the throne by the English in the Hundred Years War. Joan won the aid of Robert de Baudricourt, captain of the dauphin's forces in Vaucouleurs, in obtaining an interview with the dauphin. She made the journey in male attire, with six companions. Meeting the dauphin at Chinon castle, she conquered his skepticism as to her divine mission. She was examined by theologians at Poitiers, and afterward she was furnished with troops by Charles.

Her leadership provided spirit and morale more than military prowess. In May, 1429, she succeeded in raising the siege of Orléans, and in June she took other English posts on the Loire and defeated the English at Patay. After considerable persuasion the dauphin agreed to be crowned at Reims; Joan stood near him at his coronation. This was the pinnacle of her fortunes.

Capture and Martyrdom

In Sept., 1429, Joan unsuccessfully besieged Paris. The following spring she went to relieve Compiègne, but she was captured by the Burgundians and sold to the English, who were eager to destroy her influence by putting her to death. Charles VII made no attempt to secure her freedom. In order to escape responsibility, the English turned her over to the ecclesiastical court at Rouen. She was tried for heresy and witchcraft before Pierre Cauchon and other French clerics who supported the English.

Probably her most serious crime was the claim of direct inspiration from God; in the eyes of the court this refusal to accept the church hierarchy constituted heresy. Throughout the lengthy trial and imprisonment she bravely fought her inquisitors. Only at the end of the trial, when Joan was sentenced to be turned over to a secular court, did she recant. She was condemned to life imprisonment. Shortly afterward, however, she retracted her abjuration, was turned over to the secular court as a relapsed heretic, and was burned at the stake (May 30, 1431) in Rouen. Charles VII made tardy recognition of her services by a rehabilitation trial in 1456 that annulled the proceedings of the original trial.

Joan was beatified in 1909 and canonized in 1920 (feast: May 30). Her career lent itself to numerous legends, and she has been represented in many paintings and statues. In literature and music she appears notably, though not always accurately, in works by many eminent writers and composers.

Bibliography

Among her biographies, the best known is that of J. Michelet (tr. 1957). See also biographies by A. Lang (1908) and V. Sackville-West (1936); translations of the trial records by W. P. Barrett (1932 ed.) and W. S. Scott (1950); R. Pernoud, The Retrial of Joan of Arc (tr. 1955) and Joan of Arc by Herself and Her Witnesses (tr. 1966); C. W. Lightbody, The Judgements of Joan (1961); H. Guillemin, Joan, Maid of Orleans (1973); M. Gordon, Joan of Arc (2000).

Arc de Triomphe de l'Étoile, imposing triumphal arch in Paris standing on an elevation at the end of the Avenue des Champs Élysées and in the center of the Place de l'Étoile, which is formed by the intersection of 12 radiating avenues. It commemorates the victories of Napoleon I, under whose decree it was built. Construction was begun in 1806 by J. F. Chalgrin from his own designs and was carried on after his death by L. Goust, J. N. Huyot, and G. A. Blouet successively, who brought the arch to completion in 1836. It is 164 ft (50 m) high, 148 ft (45 m) wide, and 72 ft (22 m) deep, with colossal symbolic groups flanking the arch. The principal sculpture, La Marseillaise, was executed by François Rude. In 1920 the body of an unknown French soldier of World War I was interred beneath the arch, and a perpetual flame was lighted.

Long, curved chain of oceanic islands associated with intense volcanic and seismic activity and mountain-building processes. Examples include the Aleutian-Alaska Arc and the Kuril-Kamchatka Arc. Most island arcs consist of two parallel rows of islands. The inner row is a string of volcanoes, and the outer row is made up of nonvolcanic islands. In the case of single arcs, many of the islands are volcanically active. An island arc typically has a landmass or a partially enclosed, unusually shallow sea on its concave side. Along the convex side there usually exists a long, narrow deep-sea trench.

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Type of electric furnace in which heat is generated by an arc between carbon electrodes above the surface of the material (commonly a metal) being heated. William Siemens first demonstrated the arc furnace in 1879 at the Paris Exposition by melting iron in crucibles; horizontally placed carbon electrodes produced an electric arc above the container of metal. The first commercial arc furnace in the U.S. (1906) had a capacity of four tons (3.6 metric tons) and was equipped with two electrodes. Modern furnaces range in heat size from a few tons up to 400 tons (360 metric tons), and the arcs strike directly into the metal bath from vertically positioned, graphite electrodes to remelt scrap steel or refine briquettes of direct-reduced iron ore.

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French Jeanne d'Arc

(born circa 1412, Domrémy, Bar, Fr.—died May 30, 1431, Rouen; canonized May 16, 1920; feast day May 30) French military heroine. She was a peasant girl who from an early age believed she heard the voices of Sts. Michael, Catherine, and Margaret. When she was about 16, her voices began urging her to aid France's Dauphin (crown prince) and save France from the English attempt at conquest in the Hundred Years' War. Dressed in men's clothes, she visited the Dauphin and convinced him, his advisers, and the church authorities to support her. With her inspiring conviction, she rallied the French troops and raised the English siege of Orléans in 1429. She soon defeated the English again at Patay. The Dauphin was crowned king at Reims as Charles VII, with Joan beside him. Her siege of Paris was unsuccessful, and in 1430 she was captured by the Burgundians and sold to the English. Abandoned by Charles, she was turned over to the ecclesiastical court at Rouen, controlled by French clerics who supported the English, and tried for witchcraft and heresy (1431). She fiercely defended herself but finally recanted and was sentenced to life imprisonment; when she again asserted that she had been divinely inspired, she was burned at the stake. She was not canonized until 1920.

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