Ebony frame with brass index arm and fittings. Tangent screw on the front of the index arm; clamping screw is on the back. Three index shades (red, red, green); one horizon shade (green). Index glass adjustment by screw; horizon glass by screw, square-headed screw and detached key, and worm gear. The sight vane has two pinholes and a swiveling shutter. Ivory cap for (missing) pencil; detached adjusting key. Fitted keystone mahogany box with trade labels for H. Duren, 20 Burling Slip, New York and Samuel Emery, Water Street, Salem (before 1864).
Inscription/Sig.
Signed on the inlaid ivory plate on the crossbar: "SPENCER & Co. LONDON"
Marked on the inlaid ivory plate: H. Duren New-York.
