An important 18th century 15in.(38cm) radius brass sextant, by Jesse Ramsden c. 1773.
Signed on the frame, Ramsden London and numbered 46, bearing the Board of Ordnance mark and Broad Arrow, with rosewood handle. Reading from -5 to 130 degrees on the brass scale, the brass limb with screw vernier to 20 seconds. Horizon mirror with Dollond's patented (1772) lever and clamp adjustment, operated from beneath the telescope. The index glass half-silvered and fitted with a Maskelyne flap. Three red sun shades and a single swivelling horizon shade. In a keystone polished mahogany case, stamped for the Board of Ordnance, and containing a brass sighting tube and a brass inverting telescope with twin cursor lines.