Epicycle

an expre ion used in the Ptolemaic ( q. v .) system of astronomy; the old belief that the celestial bodies moved in perfect circles round the earth was found to be inadequate to explain the varying position of the planets, a difficulty which led Ptolemy to invent his theory of epicycles, which was to the effect that each planet revolved round a centre of its own, greater or le , but that all these centres themselves moved in proce ion round the earth, a theory which fell to pieces before the investigations of Kepler and Newton.