manometer

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. An instrument used for measuring the pressure of liquids and gases.
2. n. A sphygmomanometer.

Century Dictionary and Cyclopedia

1. n. An instrument for determining and indicating the elastic pressure of gases or vapors. It measures the weight of a column of liquid or the tension of a spring that exactly balances the elastic pressure of the gas on a unit of area; and, since the relative density of a gas is proportional to its elastic pressure, the measurement of the latter determines also the former. Manometers which measure elastic gaseous pressure by the tension of a spring are used for steam-gages. In some forms the pressure of the gas is on a piston or diaphragm connected with a counterbalancing spring. In others the initial pressure is received on a small primary piston, or diaphragm, and transmitted by a fluid mass acting upon a secondary and much larger piston or diaphragm upon which the pressure per unit of area is reduced inversely as the area of the smaller piston is to that of the larger. Of this kind is Shaw's gage for measuring very high pressures. In the Bourdon steam-gage a curved tubular spring is used, having its interior connected by a tube with the interior of the tank, boiler, cylinder, or gasholder containing the vapor or gas to be tested. In all of these forms the parts moved under varying pressure are connected with an indicator, and the pressure is read on a graduated dial-plate. In the open-air manometer the elastic pressure of a gas is indicated by the height of a column of liquid, usually mercury or water, which it will support. In its simplest form an S-shaped glass tube, open at the upper end, is employed, as shown in the cut. In the compressed-air manometer the tube containing the liquid is closed at the top, and hence the varying elastic pressure of the confined air is added to the weight of the liquid column in balancing the gaseous pressure to be measured. The statical manometer of Boyle has a thin glass bulb counterpoised on a pair of delicate scales, the specific gravity of the bulb and its confined air varying with both pressure and temperature of the surronnding air. The manometer of Ramsden is essentially a compressed-air manometer combined with a scale which indicates temperatures while determining atmospheric density. The ordinary gas-gage is a simple open-air manometer.
2. n. In physiology, an instrument used for determining blood-pressure.

Wiktionary

1. n. An instrument to measure pressure in a fluid, especially a double-legged liquid column gauge used to measure the difference in the pressures of two fluids.

GNU Webster's 1913

1. n. An instrument for measuring the tension or elastic force of gases, steam, etc., constructed usually on the principle of allowing the gas to exert its elastic force in raising a column of mercury in an open tube, or in compressing a portion of air or other gas in a closed tube with mercury or other liquid intervening, or in bending a metallic or other spring so as to set in motion an index; a pressure gauge. See pressure, and Illust. of air pump.

WordNet 3.0

1. n. a pressure gauge for comparing pressures of a gas