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).
Materiale
Signed on the inlaid ivory plate on the crossbar: "SPENCER & Co. LONDON"
Marked on the inlaid ivory plate: H. Duren New-York.
