Aneroids

Aneroids are instruments that measure atmospheric pressure without the use of liquids, most commonly referring to aneroid barometers and related altitude-sensing devices. They are used in meteorology, aviation, and navigation, and appear in handheld instruments, aircraft gauges, and some compact altimeters.

The basic mechanism relies on a sealed, flexible metal chamber that contracts or expands as external air pressure changes. The chamber’s motion is transmitted through a system of levers and linkages to a pointer on a dial, providing a reading of pressure or, when calibrated for altitude, an indication of altitude. Because the metal capsule can drift with temperature and aging, many designs incorporate temperature compensation and periodic calibration. Some configurations employ multiple capsules to increase sensitivity and stability.

Historically, aneriods date to the 19th century. The French instrument maker Lucien Vidie patented an improved aneroid barometer in 1844, coining the term “aneroid” from the Greek for “without air.” The technology was quickly adopted for altimetry by early aerial explorers and later became standard in aircraft instrumentation. Over time, aneriods evolved into a range of formats—from compact handheld barometers to mechanical altimeters used in aviation and outdoor activities.

Variants and applications include barometric measurements that help predict weather and track pressure changes, and altimeters that translate pressure readings into altitude for navigation. In modern practice, many devices have been supplanted or complemented by electronic pressure sensors and digital altimeters, but mechanical aneriods remain in use as backups, in legacy equipment, and in hobbyist and educational contexts.