(Διονυσόδωρος), a geometer of Cydnus, whose mode of cutting a sphere by a plane in a given ratio is preserved by Eutocius, in his comment on book ii. prop. 5, of the sphere and cylinder of Archimedes. A species of conical sun-dial is attributed to him, and Pliny (H. N. 2.109) says, that He had an inscription placed on his tomb, addressed to the world above, stating that he had been to the centre of the earth and found it 42 thousand stadia distant. Pliny calls this a striking instance of Greek vanity; but, as Weidler remarks, it is as near a guess as any that was made for a long time afterwards. (Weidler, Hist. Astron. p. 133; Heilbronner, in verb.)