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Visconti \ves-'kon-te\, Gian Galeazzo known as Count of Valor
(b. 1351, Milan—d. Sept. 3, 1402, Melegnano, near Milan) Leader of Milan who brought the Visconti dynasty to its height. The son of Gale¬ azzo II Visconti, who shared the rule of Milan with his brother, Gian Galeazzo united all the Visconti lands, added the march of Treviso (1387), and became a prince of the Holy Roman Empire through bribery. By 1402 he held Pisa, Siena, Umbria, and Bologna. He was close to becoming ruler of all of northern Italy and was planning an attack on Florence when he died of the plague.
Visconti, Luchino orig. Don Luchino Visconti, count di Modrone (b. Nov. 2, 1906, Milan—d. March 17, 1976, Rome) Italian film and theatre director. Born into the nobility, he became an assistant to Jean Renoir in 1935. He directed his first film, Ossessione (1942), in a style foreshadowing the Neorealism of Roberto Rossellini and Vittorio De Sica. His later films include the documentary-style drama La terra trema
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viscosity ► vitamin C I 2011
(1948), Senso (1954), Rocco and His Brothers (1960), The Leopard (1963, Golden Palm), The Damned (1969), and Death in Venice (1971). As a stage director, he introduced to Italy works by Jean Cocteau, Arthur Miller, and Tennessee Williams, and he staged operas starring Maria Callas that combined realism and spectacle.
viscosity \vis-'ka-s3-te\ Resistance of a fluid to a change in shape, or movement of neighbouring portions relative to one another. Viscosity denotes opposition to flow. It may also be thought of as internal friction between the molecules. Viscosity is a major factor in determining the forces that must be overcome when fluids are used in lubrication or trans¬ ported in pipelines. It also determines the liquid flow in spraying, injec¬ tion molding, and surface coating. The viscosity of liquids decreases rapidly with an increase in temperature, while that of gases increases with an increase in temperature. The SI unit for viscosity is the newton-second per square metre (N-s/m 2 ).
viscount \'vl-,kaunt\ European title of nobility, ranking immediately below a count, or earl. The wife of a viscount is a viscountess. In the Carolingian period, the vicecomes were deputies or lieutenants of the counts {comes), whose official powers they exercised by delegation. In the 11th century most of Normandy was divided into vicomtes, but the viscountcy was not introduced into the English peerage until nearly 400 years after the Norman conquest.
Viscount Melville \'vl- 1 kaunt- , mel- 1 vil\ Sound formerly Melville Sound Body of water, northern Canada. Located in the Arctic Archi¬ pelago, between Melville and Victoria islands, the sound is 250 mi (400 km) long and 100 mi (160 km) wide. Its discovery, when reached from the east (1819-20) by William E. Parry and from the west (1850-54) by Robert McClure, proved the existence of the Northwest Passage. The sound is navigable only under favourable weather conditions.
vise Device consisting of two parallel jaws for holding a workpiece. One of the jaws is fixed, and the other can be moved by a screw, lever, or cam. Vises used for holding a workpiece during hand operations (such as fil¬ ing, hammering, or sawing) are usually permanently bolted to a bench. In vises designed to hold metallic workpieces, the faces of the jaws are hardened steel plates, often removable, with teeth that grip the workpiece. Woodworking vises have smooth jaws, often of wood, and rely on fric¬ tion alone rather than on teeth.
Vishnu \'vish-nu\ Principal Hindu deity worshiped as the protector and preserver of the world and restorer of dharma. He is known chiefly through his avatars, particularly Rama and Krishna. In theory, he manifests him¬ self anytime he is needed to fight evil, and his appearances are innumer¬ able, but in practice 10 are most common. His various names, numbering about 1,000, are repeated as acts of devotion by his worshipers.
Visigoth Vvi-z3-,gath\ Western division of the Goths. Separated from the Ostrogoths (Eastern Goths) in the 4th century ad, the Visigoths were driven from Dacia by the Huns (376) and crossed the Danube into the Roman empire. Oppressed by Roman taxation, they revolted and plun¬ dered the Balkan provinces, defeating Valens and his army at the Battle of Adrianople (378). Theodosius I settled them in Moesia (382) to defend the frontier. Converted to Arian Christianity, they left Moesia in 395 under Alaric and invaded Greece and Italy, sacking Rome (410) and settling in southern Gaul and Spain (415). Recalled from Spain by Constantius III, they lost their first king, Theodoric I, in a battle against Attila (451). They were federates of Rome until King Euric declared independence (475). He extended their kingdom from the Loire to the Pyrenees and the lower Rhone, including most of Spain. In 507 they were defeated by the Franks under Clovis; retaining only Septimania (a strip from the Pyrenees to the Rhone), they held it and much of Spain until defeated by the Muslims in
vision See photoreception
vision, computer See computer vision
vision quest Essential rite of passage for adolescent boys of the East¬ ern Woodlands and Plains Indian peoples. The youth was sent out from the camp on a solitary vigil involving fasting and prayer in order that he might gain some sign, often through a dream, of the presence and nature of his guardian spirit. Upon receiving these visions, he returned home and communicated them to a shaman or elder, who helped interpret them.
Visistadvaita \vi-'shish-tad-'vi-t3\ Principal school of Vedanta. Its seminal figure was Ramanuja, the first Vedanta thinker to establish as the
cornerstone of his system the identification of a personal God with the Brahman of the Upanishads. For him, soul and matter depended on God for their existence. Exclusive devotion to God can elicit his grace, assist¬ ing the devotee in gaining release from the cycle of rebirth. After Ramanuja, a schism developed over the role of grace, giving rise to dif¬ ferent schools. The spread of Visistadvaita was important in the devotional renaissance of Vaishnavism. In southern India the philosophy remains a major intellectual influence.
Vistula Vvis-cho-loN River Polish Wista \'ve-swa\ River, Poland. It rises on the northern slope of the Carpathian Mountains in southwestern Poland, flows in a curve through Warsaw and Torun, then empties into the Baltic Sea at Gdansk. Most of its 651 mi (1,047 km) are navigable. Poland’s largest river, its tributaries include the Bug and Dunajec rivers.
visual-field defect Blind spot (scotoma) or area in the normal field of vision. It may be persistent or temporary and shifting, as in a migraine aura. The field may narrow, as in glaucoma. The normally small blind spot corresponding to the point where the optic nerve enters the eye can enlarge if fluid accumulates at that point (papilledema). Methanol or qui¬ nine poisoning, diseases of the nerve sheaths, deficiency diseases, and atherosclerosis can also cause blind spots. Tumours pressing on the optic nerves in different locations can cause loss of different halves or quarters of the visual field of each eye. See also macular degeneration.
visual purple See rhodopsin
visualization, scientific See scientific visualization
vitamin Organic compound required in small amounts in the diet to maintain normal metabolic functions. The term vitamine (1911) was changed to vitamin when it was realized that not all vitamins are amines (i.e., not all contain nitrogen). Many vitamins act as or are converted to coenzymes. They neither provide energy nor are incorporated into tissues. Water-soluble vitamins (vitamin B complex, vitamin C) are excreted quickly. Fat-soluble vitamins (vitamin A, vitamin D, vitamin E, and vitamin K) require bile salts for absorption and are stored in the body. The normal functions of many vitamins are known. Deficiency of specific vitamins can lead to diseases (including beriberi, neural tube defect, pernicious anemia, rickets, and scurvy). Excess amounts, especially of fat-soluble vitamins, can also be dangerous: e.g., too much vitamin A causes liver damage, an effect not seen with beta-carotene, which the body converts into vitamin A. Several vitamins are now known to support the immune system. Most vitamins are adequately supplied by a balanced diet, but people with higher require¬ ments may need supplements.