Posidonius
(
Ποσειδώνιος).
1.
A Stoic philosopher, a native of Apamea in Syria, and the last of the Stoics who belongs to
the history of the Greek philosophy. He taught at Rhodes with such great success that Pompey
came there, on his return from Syria, after the close of the Mithridatic
War, for the purpose of attending his lectures. When the Roman commander arrived at his
house, he forbade his lictor to knock, as was usual, at the door; the hero, who had subdued
the Eastern and Western world, paid homage to philosophy by lowering the fasces at the gate
of Posidonius (
Cic. Tusc. ii. 25; Pliny ,
Epist. vi. 30). Posidonius studied natural as well as moral science; and, in
order to represent the celestial phenomena, he constructed a kind of
planetarium, by means of which he exhibited the apparent motions of the sun, moon,
and planets round the earth (
Cic. N. D. ii.
34). Cicero says that he himself attended upon this philosopher (
N. D. i. 3). Posidonius was also known as an historical writer, having
composed a supplement to the history of Polybius (
Ἱστορία τῶν μετὰ
Πολύβιον). It appears to have extended to B.C. 63, or the close of the
Mithridatic War. This work is lost, but was one of Plutarch's sources. The fragments are
edited by Bake
(Leyden, 1810).
2.
An astronomer and mathematician of Alexandria. He was the disciple of Zeno, and
contemporary with, or else a short time posterior to, Eratosthenes. He probably flourished
about B.C. 260. He is particularly celebrated on account of his having employed himself in
endeavouring to ascertain the measure of the circumference of the earth by means of the
altitude of a fixed star.