aneroid barometer

A barometer that measures variations in atmospheric pressure from the deformations those changes cause in the elastic, thin walls of a hermetically sealed metal capsule, in which a partial vacuum has been created. The small contractions or expansions of the so-called aneroid capsule drive a mechanical lever that amplifies those movements and transmits them to a needle, which indicates the pressure value on a graduated dial. Barometers of this type usually include a second needle, moved manually, intended to mark the pressure value recorded at a nearby observatory. By comparing that reference value with those the moving needle indicates over time, one can know at all times whether atmospheric pressure is rising or falling. This barometer was invented by the French physicist Lucien Vidie (1805-1866) in 1844.