Diamond- pattern frame sextant.

Sextant made by Edward Troughton and William Simms, London, about 1840. Polished brass diamond-pattern frame and polished brass limb, a wooden handle with a threaded brass hole for fitting it on a stand. Signed on the limb: Troughton & Simms, London. Marked on the index arm: V & A . Mus. Inlaid silver scale from -45° to 135° every 10', measuring to 129°. Silver vernier to 10", zero at the right. The tangent screw and clamping screw are on the back of the index arm. Four shades (three red, one green); three horizon shades (two red, one green). Index-glass adjustment by screw; adjustment of the horizon glass by a screw and a capstan screw. Magnifier on a 70-mm swivelling arm; the magnifier is fitted in a brass disc that is painted white on the back for reflection. Threaded telescope bracket in two parts, fitted for correcting collimation error; perpendicular adjustment by rising-piece and a milled knob. Telescope (73 mm) erect image; telescope (180 mm) inverted image, two parallel cross-wires; extra draw tube (70 mm) inverted image, two parallel cross-wires. Shaded eyepiece (red), an adjusting pin; the magnifying glass is missing.