Nautical instruments are the tools used aboard ship for navigation, timekeeping, signalling and the measurement of weather and depth. The category includes octants and sextants, marine chronometers, ship's compasses in gimballed binnacles, telescopes, ship's clocks, barometers, sounding leads, logs for measuring speed and parallel rules and dividers for chart work.
The great age of British instrument making ran from the mid eighteenth century to the early twentieth, when London makers supplied the Royal Navy and merchant fleets across the world. The development of the octant and sextant, followed by John Harrison's work on the marine chronometer, transformed the ability to fix a ship's position. Good examples are made of brass, often lacquered or silvered, with fine engraved scales and fitted mahogany or oak boxes bearing the maker's or retailer's trade label. Collectors look for complete instruments with original mirrors, filters and accessories, legible scales and well-preserved cases, and value provenance linking a piece to a named vessel or officer. Displayed on a library table or desk, a brass sextant or telescope brings a strong maritime character to a room.
