in geometry, a quadrilateral figure both equilateral and equiangular. See GEOMETRY.

SQUARE-Root. See ALGEBRA, Part I. Chap. iv. and ARITHMETIC, No. 33. and 34.

Hollow Square, in the military art, a body of foot drawn up with an empty space in the middle, for the colours, drums, and baggage, faced and covered by the pikes every way, to keep off the horse.

Square, among mechanics, an instrument consisting of two rules or branches, fastened perpendicularly at one end of their extremities, so as to form a right angle. It is of great use in the description and mensuration of right angles, and laying down perpendiculars.

SQUARE-Rigged, an epithet applied to a ship whose yards are very long. It is also used in contradistinction to all vessels whose sails are extended by stays or lateen-yards, or by booms and gaffs; the usual situation of which is nearly in the plane of the keel; and hence,

SQUARE-Sail, is a sail extended to a yard which hangs parallel to the horizon, as distinguished from the other sails which are extended by booms and stays placed obliquely. This sail is only used in fair winds, or to fend under a tempest. In the former case, it is furnished with a large additional part called the bonnet, which is then attached to its bottom, and removed when it is necessary to scud. See SCUDDING.