Marine instruments are the navigational, timekeeping and measuring devices used aboard ships to determine position, direction, speed, depth and weather. The category includes octants and sextants, ship's compasses and binnacles, marine chronometers, telescopes, barometers, ship's clocks, logs for measuring speed, sounding leads and the charting tools used by navigators.
The great age of the English marine instrument maker ran from the eighteenth to the early twentieth century, when London in particular supplied the Royal Navy and merchant fleets of the world. The development of the octant and sextant made it possible to measure the angle of the sun or stars above the horizon, while the marine chronometer, pioneered by John Harrison, allowed longitude to be calculated accurately at sea. Instruments were usually made of brass, often in fitted mahogany boxes with makers' or retailers' labels. Collectors value original cases, clear engraved signatures, complete accessories such as spare mirrors and shades, and unpolished surfaces with old lacquer intact. Over-cleaning and later replacement parts reduce value. Beyond their historical interest, these finely engineered objects make handsome display pieces in studies, libraries and coastal homes.
