Arretium took the part of Marius against Sulla, and the latter settled some of his veterans there as colonists. Caesar, or Octavian, added others, so that there are three classes, _Arretini veteres, Fidentiores_, and _Iulienses_. A considerable contingent from Arretium joined Catiline and in 49 B.C. Caesar occupied it. C. Maecenas[1] was perhaps a native of Arretium. Its fertility was famous in ancient times, and still more the red pottery made of the local clay, with its imitation of chased silver. The reliefs upon it are sometimes of considerable beauty, and large quantities of it, and the sites of several of the kilns, have been discovered in and near Arretium. It was also considerably exported. See _Corp. Inscrip. Lat._ xi. (Berlin, 1901) p. 1081, and _Notizie degli scavi, passim_ (especially, 1884, 369, for the discovery of a fine group of the moulds from which these vases were made). The museum contains a very fine collection of these and a good collection of medieval majolica. (T. As.) FOOTNOTE: [1] The name Cilnius was apparently never borne by Maecenas himself, though he is so described, e.g. by Tacitus, _Ann_. vi. II, cf. Macrob. ii. 4, 12. The Cilnii with whom Maecenas was connected were a noble Etruscan family. ARRHENIUS, SVANTE AUGUST (1859- ), Swedish physicist and chemist, was born on the 19th of February 1859, at Schloss Wijk, near Upsala. He studied at Upsala from 1876 to 1881 and at Stockholm from 1881 to 1884, then returning to Upsala as privat-docent in physical chemistry. He spent two years from 1886 to 1888 in travelling, and visited Riga Polytechnic and the universities of Wurzburg, Graz, Amsterdam and Leipzig. In 1891 he was appointed lecturer in physics at Stockholm and four years later became full professor. Arrhenius is specially associated with the development of the theory of electrolytic dissociation, and his great paper on the subject, _Recherches sur la conductibilite galvanique des electrolytes_--(1) _conductibilite galvanique des solutions aqueuses extremement diluees_, (2) _theorie chimique des electrolytes_, was presented to the Stockholm Academy of Sciences in 1883. He was subsequently continuously engaged in extending the applications of the doctrine of electrolytic conduction in relation not only to the problems of chemical action but also, on the supposition that in certain conditions the air conducts electrolytically, to the phenomena of atmospheric electricity. In 1900 he published a _Larobok i teoretik elektrokemi_, which was translated into German and English, and his _Lehrbuch der kosmischen Physik_ appeared in 1903. In 1904 he delivered at the university of California a course of lectures, the object of which was to illustrate the application of the methods of physical chemistry to the study of the theory of toxins and antitoxins, and which were published in 1907 under the title _Immunochemistry_. In his _Worlds in the Making_ (1908), an English translation of _Das Werden