From WordNet (r) 2.0 (August 2003) [wn]:
barometer
n : an instrument that measures atmospheric pressure
From The Collaborative International Dictionary of English v.0.48 [gcide]:
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