Barometer

Barometer An Intruments that measures atmospheric pressure. Italian physicist Evangelista Torricelli discovered the principle of the barometer in 1643 and made a mercury barometer. This is basically a glass tube full of mercury up-ended in a bowl of mercury.

The pressure of the atmosphere balances a column of mercury about 760 mm (30 in) high. Domestic barometers are of the aneroid ( without liquid) type. The pressure sensor in the aneroid barometer is a partly evacuated box, which expands or contracts as the pressure changes. This movement is magnified by levers and moves a pointer over a graduated scale.