a celebrated mathematician, flourished in the times of Cicero and Pompey; but the time and place of his death are unknown. This Theo- do-sius, the Tripolite, as mentioned by Suidas, is probably the same with Theodosius the philosopher of Byzantium, who, Strabo says, excelled in the mathematical sciences, as also his sons; for the same person might have travelled from the one of those places to the other, and spent part of his life in each of them; like as Hipparchus was called by Strabo the Byzantine, but by Ptolemy and others the Rhodian.

Theodosius chiefly cultivated that part of geometry which relates to the doctrine of the sphere, concerning which he published three books. The first of these contains 22 propositions; the second, 23; and the third, 14; all demonstrated in the pure geometrical manner of the ancients. Ptolemy made great use of these propositions, as well as all succeeding writers. These books were translated by the Arabians, out of the original Greek, into their own language. From the Arabic the work was again translated into Latin, and printed at Venice. But the Arabic version being very defective, a more complete edition was published, in Greek and Latin, at Paris 1558, by John Pena, Regius Professor of astronomy. And Vitello acquired reputation by translating Theodosius into Latin. This author's works were also commented on and illustrated by Clavius, Helleganius, and Garinhus, and lastly by De Chales, in his Curius Mathematicus. But that edition of Theodosius's Spherics, which is now most in use, was translated and published by our countryman the learned Dr. Barrow. row, in the year 1675, illustrated and demonstrated in a new and concise method. By this author's account, Theodosius appears, not only to be a great master in this more difficult part of geometry, but the first considerable author of antiquity who has written on that subject.

Theodosius, too, wrote concerning the Celestial Houses; also of Days and Nights; copies of which, in Greek, were in the King's library at Paris. Of which there was a Latin edition, published by Peter Dalypody, in the year 1572.