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CAUSERIE generally well known, its style is convenient where readers are interested in the author as well as in what he says. It is less formal than the generally accepted style of essay.

CAUSERIES DU LUNDI, du lex'de (Mon- day Chats). The modest title of collections of eritiques by Sainte-Beuve, beginning with 1851. They are distinguished by brilliancy and keen analysis, and are concerned not only with French authors. but also with prominent writers of other nations.

CAUSSES, kôs, Plateaux des. A name ap- plied to a barren plateau region of cretaceous formation in south central France, lying chielly in the departments of Lozère, Aveyron, Hérault, and Gard. It is crossed by mountains and ravines, resembling cañons, which add to its for- bidding aspect, and is very sparsely inhabited.

CAUSSIN DE PERCEVAL, ko'sax' de par's val', ARMAND PIERRE (1795-1871). A French Orientalist, born in Paris. He was appointed professor of the Arabic language and literature at the Collège de France, and in 1849 was elected to a seat in the French Academy. His Essai sur l'histoire des Arabes avant l'Islamisme (3 vols., 1847-49) is a noteworthy study, in which the author was greatly assisted by the large manu- script collection of the Imperial Library.

CAUSTIC (Lat. causticus, Gk., kaustikos, from , kaustos, burned, from , kaicin, to burn). A term used in medi- cine and chemistry in connection with substances that have a corroding or burning action on the skin and flesh, Lunar caustic is silver nitrate fused and east into the form of small pointed sticks of the thickness of a lead-pencil. Caustic potash is, chemically, potassium hydroxide; caustic soda is sodium hydroxide; caustic lime is calcium hydroxide.

CAUSTIC. In mathematics, an envelope of rays radiating from a point and reflected or refracted by a given curve. One form of the caustic may be readily observed by letting sun- light fall on milk, in a glass or cup not quite filled with it. Caustics are distinguished catacausties (caustics by reflection) and dia- caustics (caustics by refraction). The names 'catoptric caustixs' and 'dioptrix caustics' have also been applied to the two classes. The figure represents both branches of the catacaustic of a

circle. The curve four cusps C$1$, C$2$, C$3$ C$4$, and the lines PP, QQ, are asymptotes to its two branches. The cardioid (q.v.) is a catacaustic of a circle for luminous rays proceeding from a point on the circumference. Consult: Cayley, "Memoir on Caustixs," Phil. Trans., Vol. CXLVII. (London, 1857: 273-312. See also Vol. CLVII.). For further bibliography, consult the Intermediaire des mathématiciens (Paris, 1894- 95). See also Aberatiob, Spherical; and Light (section, Geometrical Optics).

CAUTERETS, ko't'-ra (formerly Cauldres, from its hot springs, Fr. chaud, Lat. caldus, cali- dus, hot, from calere, to be hot). A watering- place in the Department of Hautes-Pyrénées, France, 26 miles southwest of Tarbes (Map: France, F 9). It is in a basin 3254 feet above the sea and is visited yearly, between May and October, by about 20,000 people, for its twenty- four hot sulphur springs, which range from 103° to 104° F., and are the most abundant in the Pyrenees. There are nine establishments for drinking, inhaling, and taking plunge and douche baths. Population, in 1901, of town, 1132; of communes, 1547.

CAUTERY. See Bleeding.

CAUTIN, kou'ten. A province of Chile, bounded by the Pacific on the west, Argentina on the east, and the Chilean provinces of Malleco and Valdivia on the north and south respectively (Map: Chile, C 11). It has mountains of con- siderable elevation in the western part, including the active volcano Llaimas, nearly 9800 feet. The chief river is the Cautin. The Cautin basin has a productive soil yielding grain and fruit in abundance. The chief export is wheat. The province has developed rapidly, many immi- grants settling in that quarter. Its population increased during 1885-95 from 33.291 to 78,221. Capital. Temuco (q.v.), and chief port Tolten.

CAUTIO, ka'shi-ü (from cavere, to safeguard, to assure). In Roman law cautio meant: (1) A formal undertaking to fulfill a legal obligation, especially an obligation imposed by the court upon a party to a suit. Such a judicial cautio was usually established in the form of stipula- tion, i.e. by question and answer (see Stiplua- tion), with security in the form of an identical undertaking by a surety (fidejussor). Of such undertakings a memorandum was usually made in writing: and thus cautio came to mean: (2) a written acknowledgment that a promise had been made upon oral stipulation. By further acknowledgment in general, and in particular extension, cautio came to mean: (3) a written an acknowledgment of the receipt of money, whether as a loan or as payment of a debt.

Cautio damni infecti. Literally, assurance against damage not yet done. At Roman law, when land or a building was threatened with injury in consequence of the defective condition of a neighbor's land or building, the person whose interests were imperiled could demand. from the neighbor an undertaking (cautio, in the sense first noted above) to make good any damages that might ensue. If the neighbor re- fused to give the cautio, the party imperiled was put in possession, and, in case of continued con- tumacy on the neighbor's part, was made owner of the neighboring premises. A similar cuutio. could be demanded when new work.' e.g. exca- vation or construction, had been begun: and if the cautio was refused, the work was arrested by injunction (interdictum).

CAUVERY, ka'vēr-ĭ.

CAVA, kä'và. An episcopal city in south Italy, 21 miles from the gulf, and 6 miles