Barometer

A barometer is an instrument that measures atmospheric pressure. Its readings help track weather changes and determine altitude.

Mercury barometer: A barometer that measures pressure from the height of a mercury column in a sealed glass tube. Its column rises or falls as atmospheric pressure changes.
Atmospheric pressure: The force per unit area exerted by the weight of the atmosphere. This is the physical quantity every barometer measures.
Evangelista Torricelli: An Italian physicist and mathematician who invented the mercury barometer in the seventeenth century. His mercury-tube experiment produced the first practical pressure-measuring instrument.
Water barometer: A liquid-column barometer that uses water instead of mercury to indicate atmospheric pressure. Its much taller column makes the mercury design more compact.
Aneroid barometer: A barometer that uses a sealed, flexible metal chamber to respond to pressure changes. The chamber expands or contracts, moving a pointer without liquid.
Weather forecasting: The use of observations and models to predict future atmospheric conditions. Changes in pressure help indicate approaching weather systems.
Blaise Pascal: A French mathematician and physicist whose experiments helped establish the role of atmospheric pressure. His mountain measurements tested how pressure changes with altitude.
Fortin barometer: A mercury barometer with an adjustable cistern designed for precise readings. Its adjustable mercury level improves the reference point for measurement.
Barometric pressure sensor: An electronic device that detects atmospheric pressure and converts it into an electrical signal. Digital barometers use these sensors to produce pressure readings.
Isobar: A line on a weather map connecting locations with equal atmospheric pressure. Barometer readings provide the observations used to draw isobars.

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