Compasses
a mathematical instrument used by describing circles, measuring lines, etc. They consist simply of two pointed legs movable on a point or pivot. For describing circles the lower end of one of the legs is removed and its place supplied by a holder for a pencil or pen. Hair Compasses are compasses having a spring tending to keep the legs apart, and a finely-threaded screw by which the spring can be compressed or relaxed with the utmost nicety, and the distance of the legs regulated to a hair's breadth. Bow Compasses are compasses having the two legs united by a bow passing through one of them, the distance between the legs being adjusted by means of a screw and nut. - Proportional Compasses are compasses used for reducing or enlarging drawings, having the legs crossing so as to present a pair on each side of a common pivot. By means of a slit in the legs, and the movable pivot, the relative distinces between the points at the respective ends may be adjusted at pleasure in the required proportion. COMPASS PLANT (Silphium laciniatum), a plant of the order Compositæ, It is called compass-plant because it is said that it presents the edges of its leaves N. and S., while their faces are turned E. and W. It grows freely on our western prairies.