AARON, an eminent geographer and hydrographer, born at London in 1750. He published, in 1817, a new General Atlas, 4to, and produced a great number of maps and charts. His map of the world on Mercator's projection is much esteemed. He died in 1823.

ARSAECES VI., otherwise MITHRIDATES, a king of the Parthians, spoken of in the First Book of Maccabees. He considerably enlarged the kingdom of Parthia by his good conduct and valour. There were thirty-one kings of the dynasty of the Arsacidae. See Vaillant, Arsacidarum imperium, sive regum Perthurum historia ad fidem numismatum accommodata. Paris, 1725.

ARENAI (from the Romana arthenal, a citadel), originally denoted exclusively a magazine of naval stores and warlike apparatus, giving probability to the etymology which derives the word from the Latin orx navalis, a naval citadel. Now, however, the term is applied to a repository of warlike stores, whether for land or sea service. The naval arsenals are, however, still the more numerous, and will be found described at length under the article DOCKYARDS.

The great arsenal of Britain (if we except the Tower) is that of Woolwich, where all warlike stores and apparatus are not only preserved, but manufactured in the immense buildings devoted to the purpose. (See WOOLWICH.) Deptford, Chatham, Sheerness, Portsmouth, and Plymouth, are the great naval arsenals. In France, there are military arsenals at Paris, Strasbourg, Metz, Lille, &c., and five great maritime arsenals, the chief of which are those of Brest, Toulon, and Rochefort; next to them L'Orient and Cherbourg. There are also inferior arsenals at Dunkirk, Havre, Saint Servan, Nantes, Bordeaux, and Bayonne. The other principal naval arsenals in Europe are those of Russia, at St Petersburg, Cronstadt, and Sebastopol; of Holland, at Antwerp, Flushing, Helvoetshuyse, and the Texel; of Prussia, at Danzig; of Hamburg; of Denmark, at Copenhagen; of Turkey, at Constantinople; of Italy, at Genoa, Villa-franca, Livorno, Spezzia, Civita Vecchia, Naples, Ancona, Venice, and Trieste; of Spain, at Cadiz, Cartagena, and Barcelona, and the British one at Gibraltar; of Portugal, at Lisbon; of Britain, at Malta and Corfu, &c. The principal naval arsenals of the United States are at New York, Boston, and Baltimore; of Brazil, at Rio Janeiro and Bahia; of La Plata, at Buenos Ayres and Monte Video; of Chili, at Valparaiso; and of Mexico, at Vera Cruz.

ARENIC, a metal, the salts of which are deadly poisons. See MINERALOGY, MEDICAL JURISPRUDENCE, and Index.

ARENIUS, a deacon of the Roman Church, of great learning and piety. He was appointed by the pope to go to the Emperor Theodosius, as tutor to his son Arcadius. Arsenius arrived at Constantinople in the year 383. The emperor happening one day to go into the room where he was instructing Arcadius, his son was seated and the preceptor standing. At this he was exceedingly displeased, took from his son the imperial ornaments, made Arsenius sit in his place, and ordered Arcadius for the future to receive his lessons standing uncovered. Arcadius, however, profited little by his tutor's instructions, for some time after he formed a design of despatching him. The officer to whom Arcadius had applied for this purpose divulged the affair to Arsenius, who retired to the deserts of Scete, where he passed many years in exercises of devotion. He died at Troi, aged 95.