\Hy*drom"e*ter\, n. [Hydro-, 1 + -meter: cf. F.
hydrom[`e]tre.]
1. (Physics) An instrument for determining the specific
   gravities of liquids, and thence the strength spirituous
   liquors, saline solutions, etc.

Note: It is usually made of glass with a graduated stem, and
      indicates the specific gravity of a liquid by the depth
      to which it sinks in it, the zero of the scale marking
      the depth to which it sinks in pure water. Extra
      weights are sometimes used to adapt the scale to
      liquids of different densities.

2. An instrument, variously constructed, used for measuring
   the velocity or discharge of water, as in rivers, from
   reservoirs, etc., and called by various specific names
   according to its construction or use, as {tachometer},
   {rheometer}, {hydrometer}, {pendulum}, etc.; a current
   gauge.