ARROWSMITH, Aaron, a distinguished English chartographer, born 1750, died 1823; he raised the execution of maps to a perfection it had never before attained.--His nephew, John, born 1790, died 1873, was no less distinguished in the same field; his _London Atlas of Universal Geography_ may be specially mentioned.
ARROYO ([.a]r-r[=o]´yo), the name of two towns of Spain, in Estremadura, the one, called Arroyo del Puerco (pop. 5727), about 10 miles west of Caceres; the other, called Arroyo Molinos de Montanches, about 27 miles south-east of Caceres, memorable from the victory gained by Lord Hill over a French force under General Gerard, 28th Oct., 1811.
AR´RU (or AROO) ISLANDS, a group belonging to the Dutch, south of western New Guinea, and extending from north to south about 127 miles. They are composed of coralline limestone, nowhere exceeding 200 feet above the sea, and are well wooded and tolerably fertile. The natives belong to the Papuan race, and some of them are Christians. The chief exports are trepang, tortoise-shell, pearls, mother-of-pearl, and edible birds'-nests. Pop. of group about 20,000.
ARSA´CES, the founder of a dynasty of Parthian kings (256 B.C.), who, taking their name from him, are called Arsacidæ. There were thirty-one in all. See _Parthia_.
AR´SAMAS, a manufacturing town in the Russian government of Nijni-Novgorod, on the Tesha, 250 miles east of Moscow, with a cathedral and large convent. Pop. 12,000.
AR´SENAL, a royal or public magazine or place appointed for the making, repairing, keeping, and issuing of military stores. An arsenal of the first class should include factories for guns and gun-carriages, small-arms, small-arms ammunition, harness, saddlery, tents, and powder; a laboratory and large store-houses. In arsenals of the second class workshops take the place of the factories. The Royal Arsenal, Woolwich, which manufactures warlike implements and stores for the army and navy, was formed about 1720, and comprises factories, laboratories, &c., for the manufacture and final fitting up of almost every kind of arms and ammunition. Great quantities of military and naval stores are kept at the dockyards of Chatham, Portsmouth, Plymouth, and Pembroke. In France there are various arsenals or depots of war-material, which is manufactured at Mézières, Toulouse, Besançon, &c.; the great naval arsenals are Brest and Toulon. Until 1919 the chief German arsenals were at Spandau, Strassburg, and Dantzig. The chief Austrian arsenal was the immense establishment at Vienna, which included gun-factory, laboratory, small-arms and carriage factories, &c. Russia had her principal arsenal at Petrograd, with supplementary factories of arms and ammunition at Briansk, Kiev, and elsewhere. In Italy Turin is the centre of the military factories. There are a number of arsenals in the United States, but individually they are of little importance.