\Ba*rom"e*ter\, n. [Gr. ? 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.
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.
{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.