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.