Note: The time of oscillation of a pendulum is independent of
the arc of vibration, provided this arc be small.
{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 rodsof
different metals.
{Compound pendulum}, an ordinary pendulum; -- so called, as
being made up of different parts, and contrasted with
simple pendulum.
{Conical} or {Revolving}, {pendulum}, a weight connected by a
rod with a fixed point; and revolving in a horizontal
cyrcle 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} 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.
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.