Arrhenius \ar-'a-ne-9s\, Svante (August) (b. Feb. 19, 1859, Vik, Swed.—d. Oct. 2, 1927, Stockholm) Swedish physical chemist. His theo¬ ries on dissociation of substances in solution into electrolytes or ions, first published in 1884 as his Ph.D. thesis, were initially met with skepticism, but increasing recognition abroad gradually won over the opposition in Sweden. He also did important work on reaction rates; the equation describing the dependence of reaction rates on temperature is often called the Arrhenius law, and he was the first to recognize the greenhouse effect. After receiving the Royal Society of London’s Davy Medal (1902), he
became in 1903 the third recipient of the Nobel Prize for Chemistry. He is regarded as one of the founders of the field of physical chemistry.
arrhythmia \a-'rith-me-3\ Varia¬ tion from the heartbeat’s normal rate or rhythm, caused by problems in the heart’s pacemaker or in nerves con¬ ducting its signals. Occasional arrhythmias are normal. Tachycardia is a fast regular rhythm; bradycardia is a slow rhythm. Premature atrial or ventricular beats are extra contrac¬ tions in normal rhythm. Ongoing arrhythmia in some heart diseases can reduce the heart’s ability to sup¬ ply the body with blood and can lead to heart failure. Severe arrhythmias can trigger atrial fibrillation or ven¬ tricular fibrillation. Arrhythmias are detected by electrocardiography and treated by electric shock (often with an implanted pacemaker) or by drugs such as quinidine and digitalis.
arrow See bow and arrow
Arrow, Kenneth J(oseph) (b. Aug. 23, 1921, New York, N.Y., U.S.) U.S. economist. He received his Ph.D. from Columbia University and taught principally at Stanford and Harvard. Arrow’s books include Social Choices and Individual Values (1951). His most striking claim was that, under certain conditions of rationality and equality, a ranking of societal preferences will not necessarily correspond to the rankings of individual preferences, given more than two individuals and alternative choices. In 1972 he shared the Nobel Prize with John R. Hicks.
Arrow War See Opium Wars
arrowroot Any of several plant species of the genus Maranta (family Marantaceae), whose rhizomes yield an edible starch. Chief among these is the herbaceous perennial M. arundinacea, the source of genuine, or West Indies, arrowroot. The powder obtained from the harvested roots is almost pure starch; it is used in cookery as a thickener. Arrowroot is eas¬ ily digested and is used in diets requiring bland, low-salt, and low-protein foods. Its name is sometimes applied to starches obtained from other plants and used as substitutes for true arrowroot. Brazilian arrowroot, from the cassava plant, is the source of tapioca.
Ars Antiqua Vars-an-'te-kw3\ Latin "Ancient Art" Musical style of 13th-century France. The term was derived retrospectively to distinguish 13th-century music from that of the 14th century (Ars Nova). It is partly characterized by use of the six rhythmic modes, each being a rhythmic pat¬ tern that would recur throughout a piece, such as long-short (first mode) or short-long (second). Akin to the “feet” of poetry (see prosody), the relative lengths of long and short depended on the mode. The system broke down as composers began to use subdivisions of the short note. The musical genres of the Ars Antiqua included organum and the early motet.
Ars Nova \'ars-'no-v9\ Latin "New Art" Musical style of 14th- century Europe, particularly France. As composers began to use ever shorter notes in their music, the old system of rhythmic modes (see Ars Antiqua) ceased to be adequate to describe it. In his treatise Ars nova (1323), Philippe de Vitry (1291-1361) proposed a way of relating longer and shorter notes by a metrical scheme—the ancestor of time signatures— whereby each note value could be subdivided into either two or three of the next-shorter note. Though seemingly abstract, this innovation had a marked effect on the sound of music because composers were better able to control the relative motion of several voices, and 14th-century music consequently sounds much less “medieval” to modern ears. De Vitry and Guillaume de Machaut are the principal composers of the Ars Nova. The term is sometimes extended to describe all 14th-century music, including that of Italy. See also formes fixes.
Arsacid \ar-'sas-id\ dynasty (247 bc-ad 224) Persian dynasty. It was founded by Arsaces (r. c. 250-211? bc) of the Parni tribe, which origi¬ nally dwelt east of the Caspian Sea and entered Parthia after the death of Alexander the Great (323 bc), gradually extending control southward. Arsacid power reached its peak under Mithradates I (r. 171-138 bc). The
Svante Arrhenius, 1918.
BY COURTESY OF THE KUNGLIGA BIBLIOTEKET, STOCKHOLM
© 2006 Encyclopaedia Britannica, Inc.
arsenic ► Art Ensemble I 109
government was influenced by that of the Seleucid dynasty and tolerated the formation of vassal kingdoms. The dynasty legitimized its rule over former Achaemenian territories by claiming descent from the Achaeme- nian king Artaxerxes II. It controlled trade routes between Asia and the Greco-Roman world and used its resultant wealth to erect many build¬ ings. The dynasty was overthrown in 224 by the Sasanian dynasty.
arsenic poisoning Harmful
effects of arsenic compounds (in pesticides, chemotherapy drugs, paints, etc.), most often from insecticide exposure. Susceptibility varies. Arsenic is believed to combine with certain enzymes, interfering with cellular metabolism. Symptoms of acute arsenic poisoning include nausea and abdominal pain followed by circulatory collapse. Acute exposure to the gas arsine causes destruction of red blood cells and kidney damage; chronic exposure causes weakness, skin disorders, anemia, and nervous- system disorders. Arsenic in urine and hair or nails is the key to diagno¬ sis. Treatment involves washing out the stomach and promptly administering the antidote dimercaprol.
arson Crime commonly defined by statute as the unlawful damage or destruction of property by means of fire or explosion. In nearly all coun¬ tries (except Great Britain) an arsonist is guilty of murder if someone dies as a result of his action, even if he did not intend to kill. Germany and some U.S. states also impose serious penalties for arson when it is com¬ mitted to conceal or destroy evidence of another crime. Although fire caused by accident or ordinary carelessness is not arson, a person may be guilty of arson if he causes a fire in reckless disregard of the consequences of his actions.
art also called visual art A visual object or experience consciously created through an expression of skill or imagination. The term art encom¬ passes diverse media such as painting, sculpture, printmaking, drawing, decorative arts, photography, and installation. The various visual arts exist within a continuum that ranges from purely aesthetic purposes at one end to purely utilitarian purposes at the other. This should by no means be
taken as a rigid scheme, however, particularly in cultures in which every¬ day objects are painstakingly constructed and imbued with meaning. Par¬ ticularly in the 20th century, debates arose over the definition of art. Figures such as Dada artist Marcel Duchamp implied that it is enough for an artist to deem something “art” and put it in a publicly accepted venue. Such intellectual experimentation continued throughout the 20th century in movements such as conceptual art and Minimalism. By the turn of the 21st century, a variety of new media (e.g., video art) further challenged traditional definitions of art. See aesthetics; art conservation and restora¬ tion; drawing; painting; printmaking; sculpture; photography; decorative arts.
art brut V.art-'briit, ar-'brCet\ French "raw art" Art produced by people outside the established art world, particularly crude, inexperienced, or obscene works created by the untrained or the mentally ill. The term was coined by Jean Dubuffet, who regarded such works as the purest form of expression. See also naive art.