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.