GB424285A - Improvements in or connected with magnetic compasses - Google Patents

Abstract

424,285. Magnetic compasses. BAIRD, N. C., 14, Marfield Street, Carntyne, and STUART, J., 65, West Regent Street, both in Glasgow. Aug. 19, 1933, No. 23164. [Class 97 (ii)] Two magnetic systems are coaxially mounted to turn independently of each other and are so arranged that their mutual magnetic attraction is exerted in a horizontal plane and serves to damp azimuthal oscillations. In the form shown in Fig. 1, a primary magnetic system comprising magnets N', S<1> mounted on a support 12 is pivoted on a pin 13 within a vessel 18. The secondary magnetic system 2, comprises magnets N<2>, S<2> secured to yokes 19, 20 depending from the compass card 3, which is pivoted on a pin 15 secured to the top of the vessel 18 vertically above the pin 13. The vessel 18 is mounted on the bottom of a glass-topped fluid-tight bowl 4, which pivots by knife edges on a gimbal ring pivoting in turn on bearings 8 supported by springs 9 in a casing 11. The latter is preferably filled with liquid so that the bowl 4 is supported on its bearings in a critical condition between floating and sinking. A flexible tube 25 containing air and sealed at both ends is provided to accommodate expansion or contraction of the liquid. In a modification the vessel 18 may be filled with liquid and, as shown in Fig. 6, may be pivotally supported on a pin 21 secured to a bowl 4. Preferably a liquid filled chamber 23 surrounds the vessel 18 so that the latter has its weight neutralized by buoyancy. According to the Provisional Specification an optical image of a reference mark may be arranged to appear on the compass card or the secondary magnetic system may carry a reflector arranged to reflect a vertical beam of light radially in opposite directions to a graduated ring of ground glass.