GB1001076A - Improvements in or relating to optical instruments - Google Patents

Abstract

1,001,076. Angle measuring instruments. W. R. MACLEAN. June 26, 1962 [June 26, 1961], No. 24569/62. Heading G1F. [Also in Divisions A3, B4 and B6] An optical coincidence instrument for measuring angles of sight, particularly from small dinghies in estuaries, lakes of adjacent the coast, comprises a pair of small optically plane substantially opaque, highly reflecting mirrors mounted in edge-to-edge abutting relationship at a precisely designated angle between 0 degrees and 90 degrees with their reflecting surfaces facing outward and intersecting in a sharp unobstructed dihedral edge so as to permit simultaneous viewing of two distant scenes. As shown, Fig. 6, the instrument is in the form of a finger ring 45 provided with a faceted gem having surfaces 47, 48, 49 at angles of 60 degrees, 75 degrees, 45 degrees to one another and a top facet 46 at right angles to facet 48 so that any pair may be used in taking an angle of sight. In a modification the finger ring has two gems each of which provides one pair of specular sides intersecting at a sharp edge. In a further form, Fig. 10, a hollow tube 91 has a sector removed and has secured thereto a rod 92 one end of which is cut away to form a thin sector with a specular side 93 coming to a sharp edge at the cylindrical centreline. This co-operates with a similar specular side 95 on a sector of a second rod 94 rotatably received in tube 91, the angle between faces 93, 95 being determined from scale 97. The device may be provided on a pencil, penknife, cuff links, watch charms or other small objects.