A reflecting instrument used to take the altitude above the horizon of the sun, moon, or stars at sea, and thereby to determine the latitude and longitude of the place, &c. &c. It was invented by Hadley. Also, in speaking of double stars, or of two objects near each other, the position of one component in reference to the other is indicated by the terms, north following, north preceding, south following, or south preceding, the word quadrant being understood.
♦ A gunner's quadrant, for determining the gun's angle of elevation. The long arm is inserted into the bore, while the short one remains outside, with a graduated arc and plummet, showing the inclination. For depression, on the contrary, the long arm must be applied to the face of the piece. Also, a graduated arc on the carriage showing, by an index on the trunnion, the gun's elevation above the plane of its platform; first applied by the gallant Captain Broke.
The mural quadrant, was framed and fitted with telescope, divisions, and plumb-line, firmly attached to the side of a wall built in the plane of the meridian; only used in large observatories.
♦ Senical quadrant, consists of several concentric quadratic arcs, divided into eight equal parts by radii, with parallel right lines crossing each other at right angles. It was made of brass, or wood, with lines drawn from each side intersecting one another, and an index divided by sines also, with 90° on the limb, and two sights on the edge, to take the altitude of the sun. Sometimes, instead of sines, they were divided into equal parts. It was in great use among the French navigators, from its solving the problems of plane sailing.