Double-frame brass sextant. Science Museum Group Collection

Anodized brass sextant, double-frame bridge (18 straight-bars) type, with polished brass limb, wooden handle and threaded hole for stand, in mahogany keystone shaped fitted case, by Charles Augustus Schmalcalder, 82 Strand, City of Westminster, London, England 1810-1826. Consists of inlaid 123° silver scale (-5° to 140°) with 10' divisions, silver vernier scale (10") two sets of filter shades (4 & 3, red & green) and reading magnifier with reflector on a swivel arm (65mm). Fitted with threaded telescope bracket with collimation correction for two telescopes, 90mm and 176mm (erect & inverted image) and extra draw tube (47mm). Case contains repair label for Henry Porter, 181 Strand, London, dated April 1885. Case and sextant marked, ‘Da 18 [and] H O [broad anchor] 18’, the property sign of the Hydrographic Office of the British Admiralty (adopted in Feb.1828, D indicates sextant)

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