- A device for measuring atmospheric pressure. It measures the weight of the column of air that extends from the instrument to the top of the atmosphere. There are two types of barometers commonly used today:
- Mercury Barometer
- Consists of a closed tube filled with mercury inverted in a mercury reservoir. The height of the mercury column indicates atmospheric pressure (with 1 atm = 760 mm of mercury). Invented by the Italian physicist Evangelista Torricelli (1608 - 1647), a pupil of Galileo, in 1643.
- Aneroid Barometer
- Consists of an evacuated container with a flexible wall. When atmospheric pressure changes, the wall flexes and moves a pointer which indicates the changing pressure on a scale. Invented by the French scientist Lucien Vidie in 1843.
- Early barometers from the 17th Century used water, also known as storm glasses.