Angle of declination, the angle made by a descending line, or plane, with a horizontal plane. -- Circle of declination, a circle parallel to the celestial equator. -- Declination compass (Physics), a compass arranged for finding the declination of the magnetic needle. -- Declination of the compass or needle, the horizontal angle which the magnetic needle makes with the true north-and-south line.
Dec"li*na`tor (?), n. [Cf. F. déclinateur. See Decline.] 1. An instrument for taking the declination or angle which a plane makes with the horizontal plane.