Barometer

A major disadvantage of the mercury barometer is its bulkiness and fragility. The long glass tube can break easily, and mercury levels may be difficult to read under unsteady conditions, as on board a ship at sea. To resolve these difficulties, the French physicist Lucien Vidie invented the aneroid ("without liquid") barometer in 1843.

An aneroid barometer can be compared to a coffee can whose sides are flexible, like the bellows on an accordion. Attached to one end of the coffee can (aneroid barometer) is a pointer. As atmospheric pressure increases or decreases, the barometer contracts or expands. The movement of the barometer is reflected in the motion of the pointer, which rides up and down with changes in atmospheric pressure.

One way to observe the motion of the pointer is to attach it to the hand on a dial that moves around a circular scale, from low pressure to high pressure. The simple clock-like aneroid barometer hanging on the wall of many homes operates on this basis. Another way to observe the movement of the pointer is to have it rest on the side of a rotating cylinder wrapped with graph paper. As the cylinder rotates on its own axis, the pen makes a tracing on the paper that reflects increases and decreases in pressure. A recording barometer of this design is known as a barograph.