DICTIONARY OF

Pennant 250 Periscope
Pennant. Four-sided flag with a head deeper than the fly, the upper and lower sides sloping
towards the middle line. Usually spelt 'pendant", but this is open to criticism.
Pentad. Period of 5 days. Used in meteorology as being an aliquot part (1/73) of a year.
Pentekontor. Ancient Greek vessel of about 700 B.C. propelled with 50 oars.
Penumbra. Modification of an eclipse by the formation of a partly-illuminated area, or
penumbra, between the lighted and eclipsed areas. In eclipse of Moon, it is due to sunlight
being refracted by Earth's atmosphere and falling on some of Moon's eclipsed part.
People. Old name for a ship's company.
Perch. Vertical pole erected as a navigational aid and carrying a distinctive topmark.
Periplus, Peripli. Voyage or voyages, or sailing directions, of the ancient Greeks.
Performance Monitor. A device for testing the performance of a radar set and indicating
the result.
Perforst Men. Seamen taken out of a merchant ship for service in the Royal Navy.
Corruption of 'per force'.
Perigee. That point, in orbit of a solar system body, particularly Moon, at which it comes
nearest to Earth.
Perihelion. That point, in orbit of a solar system body, at which it comes nearest to Sun.
Perils of the Sea. In policies of insurance and in bills of lading it denotes fortuitous
accidents and casualties due to the sea. Does not include ordinary action of winds and
waves.
Periodical Comet. Comet whose orbit is around Sun, and so reappears at intervals.
Periodical Meteors. Meteor showers, that occur at more or less constant intervals. More
precisely, interstellar debris lying in Earth's orbit and becoming incandescent when
subjected to friction of Earth's atmosphere.
Periodical Stars. Variable stars whose magnitudes change during a certain period.
Periodical Survey. Survey of a ship every four years in accordance with international
regulations.
Periodic Month. 'Tropical Month.'
Periodic Wind. 'Monsoon.'
Period of Encounter. Time interval between successive wave crests passing a given point in
a vessel.
Period of Roll. Time, in seconds, taken by a vessel to roll from extreme angle on one side to
extreme angle on opposite side.
Period of Wave. Time interval, in seconds, between passage of two wave crests past a
stationary point.' With ocean waves, this interval, in seconds, is about 2/7 speed of wave in
knots.
Periscope. Long, slender prismatic telescope fitted in submarines for observing surface
vessels while submarine is submerged.