Epicycle
Webster's Dictionary [1]
(1): ( n.) A circle, whose center moves round in the circumference of a greater circle; or a small circle, whose center, being fixed in the deferent of a planet, is carried along with the deferent, and yet, by its own peculiar motion, carries the body of the planet fastened to it round its proper center.
(2): ( n.) A circle which rolls on the circumference of another circle, either externally or internally.
The Nuttall Encyclopedia [2]
An expression 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 less, but that all these centres themselves moved in procession round the earth, a theory which fell to pieces before the investigations of Kepler and Newton.
