(fl. Alexandria, second half of the third century b.c.)
He was a friend or pupil of Conon, and on the latter’s death, Archimedes, who had been in the habit of sending his mathematical works from Syracuse to Conon for discussion in the scientific circles of Alexandria, chose Dositheus as the recipient of several treatises, including On the Quadrature of the Parabola, On Spirals, On the Sphere and the Cylinder (two books), and On Conoids and Spheroids. At the beginning of the first of these Archimedes says, “Having heard that Conon has died, who was a very dear friend of mine, and that you have been an acquaintance of his and are a student of geometry... I determined to write and send you some geometrical theorems, as I have been accustomed to write to Conon” (Heiberg, ed., II, 262). The preambles to the other works make it clear that Dositheus on his side often wrote to Archimedes requesting the proofs of particular theorems. Nothing is known about Dositheus’ own mathematical work.
His astronomical work seems to have been concerned mainly with the calendar. He is cited four times in the calendar attached to Geminus’ Isagoge (Manitius, ed., p. 210 ff.) and some forty times in Ptolemy’s Phaseis for weather prognostications (ἐπισημασίαι) such as formed part of a parapegma, a type of almanac, originally engraved on stone or wood and later transmitted in manuscript form—like the two mentioned above—giving astronomical and meteorological phenomena for the days of each month (cf. A. Rehm, “Parapegmastudien,” in Abhandlungen der Bayerischen Akademie der Wissenschaften, phil.- hist. Abt., n.s., vol. 19 ). Dositheus may have made observations in the island of Cos (Phaseis, p. 67. 4, Heiberg, ed.—but the text here is insecure; cf. proleg. cliii note 1) as well as in Alexandria.
According to Censorinus (De die natali, 18, 5), Dositheus wrote on the octaëteris (an eight-year intercalation cycle) of Eudoxus, and he may be the Dositheus Pelusiotes (Pelusium, at the northeastern extremity of the Egyptian delta) mentioned as providing information about the life of Aratus (Theonis Alexandrini vita Arati, §2, Maas, ed.—but spelled here Δωσίθεος).
In addition to the works cited in the text, see F. Hultsch, “Dositheos 9,” in Pauly-Wissowa, Real-Encyclopädie, X (1905), cols. 1607–1608.
D. R. Dicks