From another passage (H . N ., ii. 8) we infer that Sosigenes maintained that Mercury moved in an epicycle about the sun; this doctrine is referred to by his contemporary Cicero, and it was also that of the Egyptians (see Ptolemy). Sosigenes is commonly called an Egyptian and a Peripatetic, but this has arisen from his having been confounded with a Peripatetic philosopher of the same name who lived in the 2d century of the Christian era, and who will be briefly noticed below. It is most probable, however, that he was a Greek of Alexandria, for the following reasons. (1) Caesar had just returned victorious from his Alexandrian expedition, which occupied parts of the years 48 and 47 b.c., when, with the assistance of Sosigenes, he settled the chronological question. (2) We learn from Plutarch (Caes., 59) that “Caesar laid the problem (viz., the correction of the calendar) before the ablest philosophers and mathematicians,” and at. that time the school of Alexandria was world-famous. (3) We know that Caesar was himself a diligent student of astronomy. Lucan, in a passage which refers to his correction of the calendar, represents him as saying that even in the midst of his campaigns he had always found time for astronomical pursuits :—

“media inter praelia semper Stellarum caelique plagis superisque vacavi;

Nec meus Eudoxi vincetur Fastibus annus.”—x. 185-7.

(4) Macrobius says that Caesar wrote a work on the motion of the stars, and expressly states, moreover, that he derived from the Egyptian schools his information on this subject, and also what he required for the correction of the calendar. (5) Caesar’s arrangement was substantially the same as the reform of the Egyptian calendar in the year 238 b.c. under Ptolemy III. Euergetes, a fact which remained unknown until the discovery of the Decree of Canopus by Lepsius at Sanor Tanis in Egypt in the year 1866.

Zeller (Phil. cl. Gr., vol. iii. part 1, 2d ed., p. 705-6, note of p. 703, and p. 694, note 3), and after him, but in a more complete manner, Th. H. Martin (Annales de la Faculté des Lettres de Bordeaux, 2 e fasc., 1879), have shown, in opposition to the prevailing opinion, which had been formerly held by Zeller himself, that the subject of this article has nothing in common but the name with Sosigenes the Peripatetic philosopher, author of a work on restituent spheres (Σωσιγέvης περὶ τωv ἀvελιττoυσωv [ σφαιρωv ]) , which is referred to by Proclus (Hypotyp., p. 111, ed. Halma) and followed by Simplicius in his Commentary on the treatise of Aristotle, De Caelo, author also of some other works, and master of Alexander of Aphrodisias, who lived at the end of the 2d and beginning of the 3d century after Christ, and who was the most celebrated of the commentators on Aristotle.