pendulum Body suspended from a fixed point so that it can swing back and forth under the influence of gravity. A simple pendulum consists of a bob (weight) suspended at the end of a string. The periodic motion of a pendulum is constant, but can be made longer or shorter by increasing or decreasing the length of the string. A change in the mass of the bob alone does not affect the period. Because of their constancy, pendulums were long used to regulate the movement of clocks. Other, special kinds of pendulums are used to measure the value of g, the acceleration due to gravity, and to show that the earth rotates on its axis (see Foucault pen¬ dulum).
peneplain Vpe-n3-,plan\ Gently undulating, almost featureless plain near sea level. This would form, theoretically, by various erosional pro¬ cesses that reduce areas of initially high relief produced by active uplift to areas of virtually no relief. The lack of present-day peneplains tends to discredit the theory, but some geomorphologists propose that large areas of low relief at high altitude in some mountains are evidence of uplifted peneplains. Others question whether the dynamic relationship between erosion and rock type would ever allow the development of a peneplain, even over very long timespans.
Peneus River See Pinios River
penguin Any of 17 species (order Sphenisciformes) of flightless sea¬ birds that breed mainly on islands in subantarctic waters and on cool coasts of Africa, Australia, New Zealand, and South America. A few spe¬ cies inhabit temperate regions, and the Galapagos penguin (Spheniscus mendiculus) lives in the equatorial tropics off South America. Species dif¬ fer mainly in size and head pattern; all have a dark back and a white belly. The smallest species, the little blue penguin {Eudyptula minor), is about 14 in. (35 cm) tall; the largest, the emperor penguin (Aptenodytes for- steri), is almost 4 ft (120 cm) tall. At sea for weeks at a time, flocks feed on fish, squid, and crustaceans.
penicillin Antibiotic derived from the Penicillium mold. It was discovered in 1928 by Alexander Fleming; by 1940, Howard Walter Florey, Ernst Boris Chain, and others had produced commercial quantities that proved vital to the treatment of war casualties, making penicillin the first successful antibiotic for human bacterial infections. Many natural and semisynthetic (ampicillin, amoxicillin) variants have since been produced. All work by inhibiting the enzymes responsible for bacterial cell wall synthesis (and therefore do not work against microorganisms without cell walls or with certain variant cell walls; e.g., the tuberculosis bacillus). Among the bac¬ teria susceptible to penicillin are those causing strep throat, spinal men¬ ingitis, gas gangrene, and syphilis. Overuse has led to drug resistance in some strains. Penicillin’s chief side effect is allergy, which can be life- W threatening.
wm Penicillium V.pe-ns-'si-le-omV Any blue or green mold in the genus Pen-
!■ icillium (kingdom Fungi; see fungus). Common on foodstuffs, leather, and
fabrics, they are economically important in producing antibiotics (see peni- wm cillin), organic acids, and cheeses such as English Stilton, Italian Gor-
J gonzola, and French Roquefort.
Peninsular War (1808-14) Part of the Napoleonic Wars, fought on the Iberian Peninsula. After French forces occupied Portugal (1807) and Napoleon installed his brother Joseph Bonaparte as king of Spain (1808), a rebellion in Madrid began what was called in Spain “the War of Inde¬ pendence,” and insurrections soon erupted in other cities. By 1810 the French overcame the Spanish rebels in Madrid and elsewhere in Spain. Meanwhile, the British under the future duke of Wellington landed in Portugal (1808), where they fought the French in inconclusive campaigns until 1812. After Napoleon withdrew French forces to bolster his invasion of Russia, Wellington began his gradual advance into Spain. The British victory at the Battle of Vitoria (1813) and their march into southwestern France forced the French to withdraw from Spain and to reinstall Ferdi¬ nand VII as king (1814).
penis Male sex organ, which also provides the channel for urine to leave the body. Three long columns of tissue extend through its length, covered by elastic tissue and a thin layer of skin. One expands at the tip into a mushroom-shaped structure (glans penis) and contains the urethra (see urinary system), which ends in a slitlike opening. In sexual arousal, blood fills spaces in the tissue, and blood vessels constrict to hold it there,
enlarging and hardening the penis in an erection. The foreskin, a circular fold of skin covering the glans, is often removed (see circumcision). See also REPRODUCTIVE SYSTEM.
Penn, Irving (b. June 16, 1917, Plainfield, N.J., U.S.) U.S. photogra¬ pher. He aspired to be a painter but at 26 took a job designing photo¬ graphic covers for Vogue and soon was established as a fashion photographer. His austere fashion images communicated elegance and luxury through compositional refinement and clarity of line rather than through the use of elaborate props and backdrops. He branched out into portraiture after World War II and became much admired as a portraitist of celebrities. In his portraits the subject is usually posed before a bare backdrop and photographed in natural northern light. The resulting images combine simplicity and directness with great formal sophistication.
Penn, William (b. Oct. 14, 1644, London, Eng.—d. July 30, 1718, Buckinghamshire) English Quaker leader and founder of Pennsylvania. Expelled from Oxford for his Puritan beliefs, he was sent to manage the family estates in Ireland, where he joined the Society of Friends in 1667. He was imprisoned four times for stating his Quaker beliefs in print and in speech; one of his trials resulted in the precedent-setting Bushell’s Case, which established the independence of juries. In The Great Case of Liberty of Conscience (1670), Penn advocated religious toleration and envisioned a colony based on religious and political freedom. On his father’s death, he inherited his estates and his influence with Charles II, who granted him a vast province on the Delaware River in payment for debts owed his father. In 1682 he drafted a Frame of Government that established freedom of worship in the settlement. Upon his arrival later that year, he negotiated a series of treaties with the local Indians. In 1684 he traveled to England to defend his interests against claims by neigh¬ bouring Maryland. With the accession of his friend the duke of York as James II, he secured the release of imprisoned Quakers. He returned to Pennsylvania in 1699, where he wrote the Charter of Privileges, which allowed the assembly greater autonomy. The years after his return to England in 1701 were clouded by debt and illness.
Penney, J(ames) C(ash) (b. Sept. 16, 1875, Hamilton, Mo., U.S.—d. Feb. 12, 1971, New York, N.Y.) U.S. merchant. He became a partner in a dry-goods store in Wyoming in 1902 and five years later bought out his partners’ shares to launch what became the J.C. Penney Co. His stores offered a wide variety of inexpensive merchandise, and he offered profit- sharing plans, first to managers and later to all employees. By 1929 the company had 1,392 stores across the U.S., and at the time of Penney’s death it was the second largest merchandiser in the country, behind Sears, Roebuck and Co.
Pen nines Vpe-.nlnzX Upland mass, northern England. The Pennines extend south from Northumberland to Derbyshire; the highest point is Cross Fell, at 2,930 ft (893 m). Water action has developed underground cav¬ erns in the uplands’ limestone, which is extensively quarried. Sheep farm¬ ing is also important. Archaeological remains in the area include the ancient Roman Hadrian's Wall.
Pennsylvania officially Commonwealth of Pennsylvania
State (pop., 2000: 12,281,054), middle Atlantic region, U.S. It covers 45,333 sq mi (117,412 sq km); its capital is Harrisburg. The state is bounded on the north by Lake Erie and New York; on the east by New York and New Jersey; on the south by Delaware, Maryland, and West Virginia; and on the west by the panhandle of West Virginia and by Ohio; the Delaware River forms part of the eastern boundary. The Monongahela River unites with the Allegheny River at Pittsburgh to form the Ohio River. The area was inhabited by Indian peoples, including the Shawnee and Delaware, when Europeans arrived in the 17th century. In 1664 the English seized control of the region, and in 1681 the English king granted a char¬ ter to William Penn, who established a Quaker colony based on religious tolerance in 1682. Much of the fighting of the French and Indian War took place there. The first and second Continental Congresses met in Philadel¬ phia, and the Declaration of Independence was signed there in 1776. One of the original states of the Union, it was the second state to ratify the U.S. Constitution in 1787. During the American Civil War it was a centre of military activity (see Battle of Gettysburg). The postwar period brought great economic, industrial, and population growth, consolidating the state’s position as a major commercial power. It is one of the most pros¬ perous states, with an economy based on farming, mining, manufactur¬ ing, and high technology. The state continues to produce much of the