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From The Collaborative International Dictionary of English v.0.48:
Barometer \Ba*rom"e*ter\, n. [Gr. ba`ros weight + -meter: cf. F. barom[`e]tre.] An instrument for determining the weight or pressure of the atmosphere, and hence for judging of the probable changes of weather, or for ascertaining the height of any ascent. [1913 Webster] Note: The barometer was invented by Torricelli at Florence about 1643. It is made in its simplest form by filling a graduated glass tube about 34 inches long with mercury and inverting it in a cup containing mercury. The column of mercury in the tube descends until balanced by the weight of the atmosphere, and its rise or fall under varying conditions is a measure of the change in the atmospheric pressure. At the sea level its ordinary height is about 30 inches (760 millimeters). See Sympiesometer. --Nichol. [1913 Webster] Aneroid barometer. See Aneroid barometer, under Aneroid. Marine barometer, a barometer with tube contracted at bottom to prevent rapid oscillations of the mercury, and suspended in gimbals from an arm or support on shipboard. Mountain barometer, a portable mercurial barometer with tripod support, and long scale, for measuring heights. Siphon barometer, a barometer having a tube bent like a hook with the longer leg closed at the top. The height of the mercury in the longer leg shows the pressure of the atmosphere. Wheel barometer, a barometer with recurved tube, and a float, from which a cord passes over a pulley and moves an index. [1913 Webster] Barometric