Schematic drawing of a simple mercury barometer with vertical mercury column and reservoir at base
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A barometer is an instrument used to measure atmospheric pressure. It can measure the pressure exerted by the atmosphere by using water, air, or mercury. Pressure tendency can forecast short term changes in the weather. Numerous measurements of air pressure are used within surface weather analysis to help find surface troughs, high pressure systems, and frontal boundaries.
History
The first barometer is thought to have been built unintentionally by Gasparo Berti, sometime between 1640 and 1643.[1] Evangelista Torricelli is generally credited with inventing the barometer.
Barometers- an instrument used to measure atmospheric pressure.<science><science>
Barographs may be calibrated for altitude and this type is often used to preserve a record of balloon and glider flights.
Applications
- See also: Surface weather analysis
- See also: Weather forecasting
Barograph using five stacked aneroid barometer cells.
A barometer is commonly used for weather prediction, as high air pressure in a region indicates fair weather while low pressure indicates that storms are more likely. When used in combination with wind observations, reasonably accurate short term forecasts can be made.[2] Simultaneous barometric readings from across a network of weather stations allow maps of air pressure to be produced, which were the first form of the modern weather map when created in the 19th century. Isobars, lines of equal pressure, when drawn on such a map, gives a contour map showing areas of high and low pressure. Localized high atmospheric pressure acts as a barrier to approaching weather systems, diverting their course. Low atmospheric pressure, on the other hand, represents the path of least resistance for a weather system, making it more likely that low pressure will be associated with increased storm activities. If the barometer is falling then deteriorating weather or some form of precipitation will fall, however if the barometer is rising then there will be nice weather or no precipitation.
Compensations
Temperature
The density of mercury will change with temperature, so a reading must be adjusted for the temperature of the instrument. For this purpose a mercury thermometer is usually mounted on the instrument. Temperature compensation of an aneroid barometer is accomplished by including a bi-metal element in the mechanical linkages. Aneroid barometers sold for domestic use seldom go to the trouble.
Altitude
As the air pressure will be decreased at altitudes above sea level (and increased below sea level) the actual reading of the instrument will be dependent upon its location. This pressure is then converted to an equivalent sea-level pressure for purposes of reporting and for adjusting aircraft altimeters (as aircraft may fly between regions of varying normalized atmospheric pressure owing to the presence of weather systems). Aneroid barometers have a mechanical adjustment for altitude that allows the equivalent sea level pressure to be read directly and without further adjustment if the instrument is not moved to a different altitude.
Patents
Table of Pneumaticks, 1728 Cyclopaedia
- US patent 2194624, "Diaphragm pressure gauge having temperature compensating means", granted 1940-03-26, assigned to Bendix Aviat Corp
- U.S. Patent 2,472,735 : C. J. Ulrich : "Barometric instrument"
- U.S. Patent 2,691,305 : H. J. Frank : Barometric altimeter"
- U.S. Patent 3,273,398 : D. C. W. T. Sharp : "Aneroid barometer"
- U.S. Patent 3,397,578 : H. A. Klumb : "Motion amplifying mechanism for pressure responsive instrument movement"
- U.S. Patent 3,643,510 : F. Lissau : "Fluid displacement pressure gauges"
- U.S. Patent 4,106,342 : O. S. Sormunen : "Pressure measuring instrument"
- U.S. Patent 4,238,958 : H. Dostmann : "Barometer"
- U.S. Patent 4,327,583 : T. Fijimoto : "Weather forecasting device"
References
Further reading
- Middleton, W.E. Knowles. (1964). The history of the barometer. Baltimore: Johns Hopkins Press. New edition (2002), ISBN 0801871549.
See also
External links
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Earth-based meteorological equipment and instrumentation |
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