Octant made by Edward Troughton, London, about 1780. Mahogany frame and limb with lacquered brass index arm and fittings; inlaid ivory plates on the crossbar and the back of the frame. Signed at the bottom of the index arm: Troughton London. Inlaid ivory scale from -2° to 98° every 20', measuring to 91°. Ivory vernier to 1', zero at the right. There is no tangent screw; the clamping screw (missing) is on the back of the index arm. Three socket shades (two red, one green). Index-glass (glass missing) adjustment by screw; adjustment of the horizon glasses by screws, and by levers, wing nuts and milled clamping screws. The sight vane has one pinhole, the back sight vane is missing. A pencil or screwdriver is missing from the crossbar. No box.