Aneroid barometer

Antiguo barómetro aneroide. Moderno barómetro aneroide.

The aneroid barometer is an accurate and practical barometer where atmospheric pressure deforms the elastic wall of a cylinder in which a partial vacuum has been made, which in turn moves a needle.

It was invented in 1843 by scientist Lucien Vidie. It uses a small flexible metal box called an aneroid cell (capsule), which is made from an alloy of beryllium and copper.

The evacuation capsule (or usually more capsules) prevents collapse by a strong spring. Small changes in external air pressure cause the cell to expand or contract. This expansion or contraction drives a mechanical lever, such that small movements of the capsule are amplified and are shown on the face of the aneroid barometer. Many models include a manual action needle that is used to mark the current measurement, so a change can be easily seen. In addition, the mechanism is deliberately made "hard", so that touching the barometer reveals whether the pressure is increasing or decreasing as the pointer moves.

wiki