ing down, typically by a millionth of a second per year. It has been calculated that pulsars “switch off” after about 10 million years, when their magnetic fields weaken enough.
A pulsar emits two beams of electromagnetic radiation along its magnetic axis. If the magnetic axis is offset from the rotational axis, the beams will sweep out circu¬ lar paths as the star rotates, instead of remaining in one position. An observer in the path of such a beam will thus detect a periodic pulse of radiation as the beam sweeps by.
© MERRIAM-WEBSTER INC.
pulse Pressure wave in the arteries from contraction of the heart. It can be felt where arteries are near the skin’s surface; it is usually read at the carotid artery in the neck or at the wrist. Its rate, strength, and rhythm and the contour of the wave provide valuable information but must be viewed in context (e.g., rapid pulse occurs with serious heart disease, simple fever, or vigorous exercise). The average adult pulse rate is 70-80 beats per minute; the rate decreases with age and is generally faster in women.
puma See cougar
pumice Vpo-mosV Very porous, frothlike volcanic glass that has long been used as an abrasive in cleaning, polishing, and scouring compounds. It is also used in precast masonry units, poured concrete, insulation and acoustic tile, and plaster. Pumice is igneous rock that cooled so rapidly there was no time for it to crystallize. When it solidified, the vapours dis¬ solved in it were suddenly released, and the whole mass swelled up into a froth that immediately consolidated. Any type of lava may become pumiceous under favourable conditions.
pump Machine that uses energy to raise, transport, or compress fluids. Pumps are classified by how they transfer energy to the fluid. The basic methods are volume displacement, addition of kinetic energy, and use of electromagnetic force. Pumps in which displacement is accomplished mechanically are called positive displacement pumps. Kinetic pumps pass kinetic energy to the fluid by means of a rapidly rotating impeller (blade). To use electromagnetic force, the fluid being pumped must be a good electrical conductor. Pumps used to transport or pressurize gases are called compressors, blowers, or fans.
pumpkin Fruit of certain varieties of Cucurbita pepo or C. moschata, of the gourd family. In the U.S., the thick-growing, small-fruited bush, or nontrailing, varieties of C. pepo are called squash, and the long-season, long-trailing, large-fruited varieties are called pumpkin. Pumpkins pro¬ duce very long vines and large (9-18 lb [4-8 kgj), globe-shaped, orange fruits. Giant and miniature varieties are available. The usually lightly fur¬ rowed or ribbed rind is smooth, and the fruit stem is hard and woody. Pumpkins mature in early autumn and can be stored for a few months in
© 2006 Encyclopaedia Britannica, Inc.
1566 I Punch ► puppetry
a dry, warm place. They are commonly grown in North America, Britain, and Europe for human food and livestock feed. In Europe pumpkin is served mainly as a vegetable; in the U.S. and Canada pumpkin pie is a traditional Thanksgiving and Christmas dessert. Pumpkins are used in the U.S. for Halloween decorations.
Punch Hooknosed, humpbacked character in marionette and puppet shows (see puppetry). Adapted from a stock character of the commedia dell'arte, the puppet character was taken to France and England by Ital¬ ian puppeteers in the 1660s. By 1700 every English puppet show featured Punch (from Punchinello) and his wife, Judy. As marionettes became less popular in the 1790s, smaller glove puppets were used in the popular Punch-and-Judy play. The hooked nose and the brutal, vindictive, and deceitful behaviour of the English Punch were established characteristics by the 19th century. In France his popularity declined during the 19th and 20th centuries, and he disappeared there as a comic figure. Puppeteers in England have carried on the tradition of Punch-and-Judy shows.
Punch English illustrated periodical published 1841-1992 and revived in 1996 with a revised format. Initially a weekly radical paper, it became famous for its satiric humour, caricatures, and cartoons. Among its famous early staff members were William Thackeray and John Tenniel. A cover drawing by Richard Doyle was used continuously from 1849 to 1956, when each issue’s cover was made different, though the traditional fig¬ ures of Punch and his dog Toby usually appeared somewhere.
punch press Machine tool that changes the size or shape of a piece of material, usually sheet metal, by applying pressure to a die in which the workpiece is held. The form and construction of the die determine the shape produced on the workpiece. A punch press has two components: the punch, which is attached to the reciprocating (back and forth, or up and down) ram (plunger) of the machine; and the die, which is clamped onto a bed or anvil whose flat surface is perpendicular to the path of the ram. The punch pushes against the workpiece, which is held in the die. Punch presses are usually driven by electric motors. See also hydraulic PRESS.
punctuation Standard set of marks used in written and printed texts to clarify meaning and to separate sentences, words, and parts of words. It often marks discourse features such as intonational contours and pauses. It may also convey information about a word (e.g., hyphens in compound words) unrelated to speech patterns. In English, the period (.) marks the end of a sentence or an abbreviation. The comma (,) usually separates clauses, phrases, or items in a series. The colon (:) often introduces an explanation or series of examples. The semicolon (;) usually separates independent clauses. The em-dash (—) marks an abrupt transition. The exclamation point (!) signals surprise. The question mark (?) signals a question. The apostrophe (’) marks the possessive case or the omission of letters. Quotation marks (“ ”) set off either quoted words or words used _ with special significance. Interpolations in a sentence are marked by
brackets ([ ]) or parentheses ().
Punctation of Olmutz See Olmiitz, Punctation of
Pune Vpii-noV formerly Poona City (pop., 2001 prelim.: city, mm 2,540,069; metro, area, 3,755,525), western India. Called “Queen of the
U Deccan,” it is the cultural capital of the Maratha peoples (see Maratha
confederacy). It first gained importance as the capital of the Bhonsle Mar- athas in the 17th century. Temporarily captured by the Mughals, it again became the Maratha capital from 1714 until 1817, when it fell to the Brit¬ ish. It served as the seasonal capital of the Bombay presidency, and its mild weather has made it a popular tourist resort. It is a major educational centre and headquarters of the Indian army’s southern command; it is ringed by a sprawling complex of industrial suburbs.
Punic Wars Vpyii-nik\ or Carthaginian Wars Three wars (264- 241 bc, 218-201, 149-146) between Rome and Carthage. The first con¬ cerned control of Sicily and of the sea lanes in the western Mediterranean; it ended with Rome victorious but with great loss of ships and men on both sides. In 218 Hannibal attacked Roman territory, starting from Spain and marching overland into Italy with troops and elephants. After an ini¬ tial Carthaginian victory, Fabius Maximus Cunctator harassed him wher¬ ever he went without offering battle. Abandoning this tactic resulted in a major Roman loss at the Battle of Cannae (216); that defeat drew the Romans together and, though worn down, they managed to rally, even¬ tually defeating Hannibal and driving him out of Italy (203). The Third Punic War was essentially the siege of Carthage; it led to the destruction