Chapter Pemphigus to Penetralia of P by Webster's Dictionary (1913 Edition)

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.

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. — Conicalor 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. — Simpleor 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.

Penelope
(||Pe*nel"o*pe) n. [From. L. Penelope, the wife of Ulysses, the hero of the Odyssey, Gr. Phnelo`ph.] (Zoöl.) A genus of curassows, including the guans.

Penetrability
(Pen`e*tra*bil"i*ty) n. [Cf. F. pénétrabilité.] The quality of being penetrable; susceptibility of being penetrated, entered, or pierced. Cheyne.

Penetrable
(Pen"e*tra*ble) a. [L. penetrabilus: cf. F. pénétrable.] Capable of being penetrated, entered, or pierced. Used also figuratively.

And pierce his only penetrable part.

Dryden.

I am not made of stones,
But penetrable to your kind entreats.

Shak.

— Pen"e*tra*ble*ness, n. — Pen"e*tra*bly, adv.

Penetrail
(Pen"e*trail) n. Penetralia. [Obs.] Harvey.

Penetralia
(||Pen`e*tra"li*a) n. pl. [L., fr. penetralis penetrating, internal. See Penetrate.]

1. The recesses, or innermost parts, of any thing or place, especially of a temple or palace.

2. Hidden things or secrets; privacy; sanctuary; as, the sacred penetralia of the home.