GB675335A - Improvements in or relating to magnetic compasses - Google Patents

Abstract

675,335. Magnetic compasses. HANSSEN, H. A. Sept. 1, 1950, No. 21682/50. Classes 97 (ii) and 97 (iii). A magnetic compass, e.g. for determining heading direction or bearing comprises a magnetic needle 14 swinging over a graduated compass dial 7, Fig. 2, provided on a transparent bottom plate 2 and a domed transparent cover 1, Fig. 3, adapted to contain a light refracting liquid so as to form a lens attached to the plate 2 to enclose the needle 14 and dial 7 and mounted concentrically with the dial, a rotatable disc 9, Fig. 3, having graduations 13, Fig. 2, encircled by those of the dial. The disc 9 is mounted to turn on a guide-ring 8 centrally disposed with respect to the dial and is retained by a housing 10 and ring 11. A screw 16 carries a steel point needle 15 on which the needle 14 is journalled. By removal of the screw 16, a clear, light refracting liquid may be introduced into the domed cover 1. The side of housing 10 has a cut-out portion 12, Fig. 3, to permit rotation of disc 9. The cover 1 has an engraved ring at the top portion thereof and an air bubble 19 of about the same diameter as the ring is formed in the liquid to form a box level. The graduations on the plate 2 may be provided on a thin exchangeable plate 17, Fig. 3, located between the plate 2 and the housing 10. The plate 2 may be square or bevelled and, as shown in Fig. 2, preferably provided with distance graduations for maps. The upper surface of the plate is provided with a line 2a extending through the middle point of the compass dial and with lines 2b, 2e forming, with the sides of the plate, right-angled triangles of 30, 60 and of 45 degrees respectively.