Brass sextant with straight-bar-pattern pillar frame, wooden handle threaded for use on stand in fitted keystone mahogany case, by Edward Troughton and William Simms, London,1824-51. Consists of polished inlaid silver scale with silver vernier (10”), four index-filter shades, three horizon filters and magnifier on a swivelling arm. Fitted with threaded bracket for sighting telescope (75mm – erect image & 87mm – inverted image), plus extra draw tube and sighting tube (131mm). Other accessories include leather-capped adjusting key and magnifying glass. On the lid of the storage case is a certificate of examination of the National Physical Laboratory, dated May 1907, a printed instruction on how to store the instrument in the box, and a MS note dated 1902 on the index error.