A barometer is a device that measures atmospheric pressure. It is commonly used in meteorology to forecast short-term changes in the weather, as changes in atmospheric pressure can be an indication of approaching weather systems.
Barometers can be divided into two main types: mercury barometers and aneroid barometers. A mercury barometer consists of a glass tube filled with mercury that is inverted in a container of mercury. The pressure of the atmosphere is transmitted through the mercury in the tube and creates a vacuum above the mercury column. The height of the column is measured in millimeters or inches and indicates the atmospheric pressure.
An aneroid barometer, on the other hand, does not use mercury but instead relies on a flexible metal box that is sensitive to changes in air pressure. As the air pressure changes, the metal box expands or contracts, which causes a mechanical movement that is translated into reading on a dial.
Barometers are used in a variety of applications, including weather forecasting, aviation, and navigation. They are also used in many industrial applications where precise atmospheric pressure measurements are needed, such as in vacuum systems, gas analysis, and chemical manufacturing.