in Navigation and Astronomy, an instrument made use of for taking an altitude of the sun, &c. It is commonly of brass, about nine inches in diameter, suspended by a small swivel, at the distance of 45°, from the point of which there is a perforation, being the centre of a quadrant of 90° divided in the inner concave surface. It is to be held up by the swivel when used, and turned round to the sun, till his rays, falling through the hole, form a spot among the degrees, by which the required altitude is pointed out. This instrument is deemed preferable to the astrolabe, because the divisions are larger than on that instrument.