Marine navigation aids. The radio direction-finder and the gyro-compass

A radio direction-finder equipped with a gyro-compass repeater motor to set automatically the bearing scale is briefly described; a detailed elementary exposition of the gyroscope and gyro-compass follows. Reasons for precession and the rules governing it are explained. Gyro-compasses combine inertia and precession with the earth's rotation and the force of gravity to provide a bearing on the true geographic north. The addition of mercury ballistic tubes to the simple gyroscope controls precession; a "phantom" element or driven outer frame is employed to secure the action of the mercury ballistic about both the horizontal and vertical axes and as a friction-free suspension for the gyro. Damping of oscillation, compensation for unsymmetrical distribution of weight in the swinging compass, latitude correction and correction for ship's speed and course, are provided for in the design.