something that relates to the horizon, is taken in the horizon, or on a level with the horizon.—We say, a horizontal plane, horizontal line, &c.

HORIZONTAL Dial, is that drawn on a parallel to the horizon: having its gnomon, or style, elevated according to the altitude of the pole of the place for which it is designed. Horizontal dials are, of all others, the most simple and easy. The manner of describing them, see under the article Dial.

HORIZONTAL Line, in Perspective, is a right line drawn through the principal point, parallel to the horizon: or, it is the intersection of the horizontal and perspective planes. See PERSPECTIVE.

HORIZONTAL Plane, is that which is parallel to the horizon of the place, or nothing inclined thereto.

The business of levelling is to find whether two points be in the horizontal plane; or how much the deviation is. See LEVELLING.

HORIZONTAL Plane, in Perspective, is a plane parallel to the horizon, passing through the eye, and cutting the perspective plane at right angles.

HORIZONTAL Projection. See GEOGRAPHY Index.

HORIZONTAL Range, or Level Range, of a piece of ordnance, is the line it describes, when directed parallel to the horizon or horizontal line. See GUNNERY, passim.

HORIZONTAL Moon. See Moon, ASTRONOMY Index.

HORIZONTAL Speculum. See SPECULUM.