Compass, Mariner's.
A compass distinguished by the card being attached to and rotating with
the needle. A mark, the "lubber's mark" of the sailors is made upon the
case. This is placed so that the line connecting it, and the axis of
rotation of the card is exactly in a plane, passing through the keel of
the ship. Thus however the ship may be going, the point of the card
under or in line with the "lubber's mark," shows how the ship is
pointing. The case of the mariner's compass is often bowl-shaped and
mounted in gimbals, a species of universal joint, so as to bc always
horizontal. (See Compass, Spirit-Gimbals.)