Sailing Glossary - Term Marine barometer

A mercury barometer designed for use aboard ship. The instrument is of the fixed-cistern type (see Kew barometer). The mercury tube is constructed with a wide bore for its upper portion and with a capillary bore for its lower portion. This is done to increase the time constant of the instrument and thus prevent the motion of the ship from affecting the reading. The instrument is suspended in gimbals to reduce the effects of pitch and roll of the ship.