Skip to main content Skip to Search Box

Definition: barometer from Dictionary of Energy

Measurement. an instrument for measuring atmospheric pressure; used in determining height above sea level and predicting changes in the weather.


Summary Article: barometer
from The Columbia Encyclopedia

(bӘrŏm'ӘtӘr), instrument for measuring atmospheric pressure. It was invented in 1643 by the Italian scientist Evangelista Torricelli, who used a column of water in a tube 34 ft (10.4 m) long. This inconvenient water column was soon replaced by mercury, which is denser than water and requires a tube about 3 ft (0.9 m) long. The mercurial barometer consists of a glass tube, sealed at one end and filled with pure mercury. After being heated to expel the air, it is inverted in a small cup of mercury called the cistern. The mercury in the tube sinks slightly, creating above it a vacuum (the Torricellian vacuum). Atmospheric pressure on the surface of the mercury in the cistern supports the column in the tube, which varies in height with variations in atmospheric pressure and hence with changes in elevation, generally decreasing with increases in height above sea level. Standard sea-level pressure is 14.7 lb per sq in. (1,030 grams per sq cm), which is equivalent to a column of mercury 29.92 in. (760 mm) in height; the decrease with elevation is approximately 1 in. (2.5 cm) for every 900 ft (270 m) of ascent. In weather forecasting, barometric readings are usually measured on electronically controlled instruments often tied to computers. The results are plotted on base maps so that analyses of weather-producing pressure systems can be made. At a given location a storm is generally anticipated when the barometer is falling rapidly; when the barometer is rising, fair weather may usually be expected. The aneroid barometer is a metallic box so made that when the air has been partially removed from the box the surface depresses or expands with variation of air pressure on it; this motion is transmitted by a train of levers to a pointer which shows the pressure on a graduated scale. A barograph is a self-recording aneroid barometer; an altimeter is often an aneroid barometer used to calculate altitude.

The Columbia Encyclopedia, © Columbia University Press 2018

Related Articles


Full text Article barometer
The Encyclopedia of Ecology and Environmental Management, Blackwell Science

An instrument for measuring atmospheric pressure . The Fortin barometer consists of a glass tube, closed at one end, filled with mercury ...

Full text Article barometer
Philip's Encyclopedia

Instrument for measuring atmospheric pressure. There are two basic types. A mercury barometer has a vertical column of mercury, whose length...

Full text Article barometer
The Macmillan Encyclopedia

An instrument for measuring atmospheric pressure. There are two main types: the mercury barometer and the aneroid barometer. In the mercury...

See more from Credo