Pocket brass framed sextant

Pocket brass framed sextant, with mahogany keystone box, made by Jesse Ramsden, Piccadilly, London, England, 1785-1795. Polished brass frame and limb, no handle. Signed on the crossbar: ‘Ramsden London’. Brass scale from -2° to 145° every 30', measuring to 125° (digits read from the pivot). Brass vernier to 1', zero at the left. The tangent screw is on the front of the index arm; the clamping screw is on the back. Two shades (both red); no horizon shades. Index-glass adjustment by screw; adjustment of the horizon glass by fixed milled screw and by Dollond's extended lever and clamp, operated from beneath the telescope bracket. Detached telescope bracket, to be fit to the frame by a dovetail mount; perpendicular adjustment by rising-piece and a milled screw. Detached magnifier on a 35-mm swivelling arm. Telescope (62 mm) erect image. Shaded eyepiece (red).

Sextants like this one ( 120mm high) signed by Ramsden were used by army personnel and road builders for making military maps and surveying land for roads and railways. Jesse Ramsden (1735-1800) was one of the top ten specialist instrument makers in 18th century England, supplying large-scale astronomical and surveying instruments both at home and abroad.