barometer
    n 1: an instrument that measures atmospheric pressure

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

BAROMETER, n.  An ingenious instrument which indicates what kind of
weather we are having.