EXCENTRIC, or EXCENTRIC CIRCLE, in the ancient Ptolomaic astronomy, was the very orbit of the planet itſelf, which it was ſuppoſed to deſcribe about the earth, and which was conceived excentric with it; called alſo the deſerent.
Inſtead of theſe excentric circles round the earth, the moderns make the planets deſcribe elliptic orbits about the ſun; which accounts for all the irregularities of their motions, and their various diſtances from the earth, &c. more juſtly and naturally.