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The Collaborative International Dictionary of English v.0.48 (gcide)

Hydrometer \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.
[1913 Webster]

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.
[1913 Webster]

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. Hydrometric


Pendulum \Pen"du*lum\, n.; pl. {Pendulums}. [NL., fr. L.
pendulus hanging, swinging. See {Pendulous}.]
A body so suspended from a fixed point as to swing freely to
and fro by the alternate action of gravity and momentum. It
is used to regulate the movements of clockwork and other
machinery.
[1913 Webster]

Note: The time of oscillation of a pendulum is independent of
the arc of vibration, provided this arc be small.
[1913 Webster]

{Ballistic pendulum}. See under {Ballistic}.

{Compensation pendulum}, a clock pendulum in which the effect
of changes of temperature of the length of the rod is so
counteracted, usually by the opposite expansion of
differene metals, that the distance of the center of
oscillation from the center of suspension remains
invariable; as, the {mercurial compensation pendulum}, in
which the expansion of the rod is compensated by the
opposite expansion of mercury in a jar constituting the
bob; the {gridiron pendulum}, in which compensation is
effected by the opposite expansion of sets of rods of
different metals.

{Compound pendulum}, an ordinary pendulum; -- so called, as
being made up of different parts, and contrasted with
{simple pendulum}.

{Conical pendulum} or {Revolving pendulum}, a weight
connected by a rod with a fixed point; and revolving in a
horizontal circle about the vertical from that point.

{Pendulum bob}, the weight at the lower end of a pendulum.

{Pendulum level}, a plumb level. See under {Level}.

{Pendulum wheel}, the balance of a watch.

{Simple pendulum} or {Theoretical pendulum}, an imaginary
pendulum having no dimensions except length, and no weight
except at the center of oscillation; in other words, a
material point suspended by an ideal line.
[1913 Webster]