Anodised brass three-circle pattern frame, wooden handle. Signed on the limb 'Dennis's Lunar Sextant. London.', and marked on the frame 'Register N° 1287 June 6, 1842'. Bronzed limb with inlaid silver scale from -5° to 150° by 10', measuring to 128°. Silver vernier to 10'', zero at right. Index glass adjustment by screw, horizon glass by detached key. Four shades (mauve, mauve, yellow, mauve), three horizon shades (all mauve). Tangent screw and clamp screw on the back of the index arm. Magnifier on 89 mm swivelling arm, and frosted glass shade. Telescope bracket in two parts, fitted for correcting collimation error, perpendicular adjustment by rising piece and milled knob. Telescope (181 mm) inverted image, with two cross wires, focus manually or by milled screw and work gear, spare draw tube (74 mm) two cross wires, telescope (83 mm) erect image. Sight-tube (80 mm), shaded eyepiece (red), magnifying glass, horizon glass adjustment key, piece of chamois leather (not found). Radius 7.25'' (184 mm).
The artificial horizon consists of a rectangular cast iron tray and a brass roof-shaped cover both black-lacquered. Two sides of the cover have clear glass panels, at an angle of 90°. Boxwood jar for storing the mercury (present) when not in use. In fitted square wooden box lined with green cloth, and on the lid an ivory plate inscribed 'J.C. Dennis.s [coat of arms] Patent Sextant London' and containing in the lid a trade label for J.C. Dennis, 122 Bishopsgate Street, London.
Dennis's patent was not found in the list of patents 1636-1866.