Compasses

Compasses are very useful instruments for drawing circles, marking off distances, or for other similar purposes in geometrical and mechanical drawing, architectural drawing, and workshop practice. Essentially, they consist of two points that can be kept at the same distance apart. The ordinary compass satisfies this condition by having two equal arms of brass, German-silver, or other suitable metal pivoted together at one end and pointed at the other. There is generally an arrangement for replacing one of the metal points by a pencil or pen, so that curves, etc., may be drawn in pencil or in ink as required. Beam-compasses admit of much greater distances between the points; the two pointers are separate, and slide along a batten or lath of hard wood. There are numerous other varieties of such instruments, designed for special geometrical purposes.