Pergolesi V.par-go-'la-zeV Giovanni Battista (b. Jan. 4, 1710, Jesi, Italy—d. March 16, 1736, Pozzuoli) Italian composer. In 1732 he was appointed chapel master to a Neapolitan prince. His comic opera Lofrate ’nnamorato (1732) was followed in 1733 by an opera seria, which had a comic intermezzo that became his best-known work, La serva padrona. His health failing, he moved into a Franciscan monastery (1736), where he wrote his famous Stabat Mater and Salve Regina before dying at age 26. Traveling opera troupes took up La serva padrona, and in 1752 the success of a Paris production set off the controversy known as the guerre des bouf- fons (“war of the buffoons”), with musical forgers vying to produce spu¬ rious works of Pergolesi, leaving some uncertainty about the authenticity of works attributed to him.
Periander \,per-e-'an-d9r\ (d. c.
587 bc) Second tyrant of Corinth (c.
627-587). He was the son of Cypse- lus, founder of the Cypselid dynasty.
One of the most violent of the early Greek tyrants, he killed his wife and avenged the death of his son in Cor- cyra by sending 300 Corcyran boys to be castrated (they managed to escape). He treated the nobility harshly but built a strong, prosperous Corinthian economy. His extensive building program included construc¬ tion of the Diolkos, a portage used to transport ships across the Isthmus of Corinth.
Pericles \'per-9-,klez\ (b. c. 495,
Athens—d. 429 bc, Athens) Athenian general and statesman largely responsible for the full development
of Athenian democracy and the Athe¬ nian empire. Related to the influential Alcmaeonid family, he was elected to power sometime after 461, and he quickly helped adopt essential demo¬ cratic reforms. He asserted Athenian control over the Delian League and used the league’s treasury to rebuild the Acropolis, which had been sacked by the Persians. His influential con¬ sort Aspasia bore him a son, who was legitimated when his legitimate sons died. In 447—446 Athens lost Megara, giving Sparta direct access to Attica.
Though Athens and Sparta agreed on a Thirty Years’ Peace (446-445), Per¬ icles had the Long Walls from Athens to the port at Piraeus strengthened for protection. When war broke out in 431, he relied on the navy to keep the city supplied. Attica’s population was brought inside the Long Walls, leaving the countryside open to Spartan pillaging. When plague broke out, killing one-fourth of the population, he was deposed and fined. He was reelected, but he too died of the plague. His great funeral oration (c. 430) remains one of the greatest defenses of democracy, and his era is remem¬ bered as the Golden Age of Athens.
peridot \'per-9-.dat, 'per-9-,do\ or precious olivine Va-l9-,ven\ Gem- quality, transparent green olivine. Very large crystals are found in Myan¬ mar; peridots from the U.S. are seldom larger than two carats. Yellow- green peridot has been called chrysolite (Greek for “golden stone”); this term, used for various unrelated minerals, is now less common for the gemstone.
peridotite Vps-'ri-ds-.tltV Coarse-grained, heavy, igneous rock that con¬ tains at least 10% olivine, other iron- and magnesium-rich minerals (gen¬ erally pyroxenes), and not more than 10% feldspar. Peridotite is the ultimate source of all chromium ore and naturally occurring diamonds, and of nearly all chrysotile asbestos. Nearly all peridotite is more or less altered to ser¬ pentine; in warm, humid climates peridotite and serpentine have weath¬ ered to soils and related deposits that, though now worked on a relatively small scale, are potential sources of iron, nickel, cobalt, and chromium.
Perier \par-'ya\, Casimir (-Pierre) (b. Oct. 21, 1777, Grenoble, France—d. May 16, 1832, Paris) French statesman. Son of a financier, he cofounded a bank in 1801 and by 1814 was a leading banker in Paris. He was elected to the French Chamber of Deputies (1817), where he opposed Charles X. After the July Revolution of 1830 made Louis- Philippe king, Perier became premier (1831) and quickly restored civic order in France. Active in foreign affairs, he sent an army to defend Belgium against the Dutch (1831) and ordered the occupation of Ancona to check Austrian predomi¬ nance in the Papal States (1832). His authoritarian approach brought attacks from both left and right and sometimes alienated the king.
Perigord \,pa-re-'g6r\ Historic and cultural region, southern France. The counts of Perigord played a part in the troubled affairs of Aquitaine, and control of Perigord was disputed by the French and the English from 1259. The area was transferred to the house of Albret in 1470. After it was inherited by the crown of Navarra, Henry IV united it with the French crown in 1607.
period In geology, the basic unit of the geologic time scale. During these spans of time, specific systems of rocks were formed. Originally, the method for defining the sequence of periods was relative; it was based on stratigraphy and paleontology. Carbon- 14 dating and similar methods are now used to determine absolute ages for various periods.
periodic motion Motion that is repeated in equal intervals of time. The time of each interval is the period. Examples of periodic motion include a rocking chair, a bouncing ball, a vibrating guitar string, a swing¬ ing pendulum, and a water wave. See also simple harmonic motion.
periodic table Organized array of all the chemical elements in approxi¬ mately increasing order of their atomic weight. The elements show a peri¬ odic recurrence of certain properties, first discovered in 1869 by Dmitry I. Mendeleyev. Those in the same column (group) of the table as usually
Periander, marble bust in the Vatican Museum, Rome
THE MANSELL COLLECTION
Pericles, detail of a marble herm; in the Vatican Museum
ANDERSON-AUNARI FROM ART RESOURCE/EB INC.
© 2006 Encyclopaedia Britannica, Inc.
1474 I periodical ► Perl
arranged have similar properties. In the 20th century, when the structure of atoms was understood, the table was seen to precisely reflect increas¬ ing order of atomic number. Members of the same group in the table have the same number of electrons in the outermost shells of their atoms and form bonds of the same type, usually with the same valence; the noble GAS es, with full outer shells, generally do not form bonds. The periodic table has thus greatly deepened understanding of bonding and chemical behaviour. It also allowed the prediction of new elements, many of which were later discovered or synthesized. For an illustration of the periodic table, see chemical element.
periodical Publication whose issues appear at fixed or regular inter¬ vals. Periodicals generally are considered to include newspapers, which usually have large, unfastened pages and contents with considerable immediacy; and magazines, or journals, which have smaller pages, are usually fastened or bound, and often have more specialized, less time- dependent contents.
periodontitis V.per-e-o-.dan-'tl-tosX Inflammation of soft tissues around the teeth (see tooth). Poor dental hygiene leads to deposition of bacterial plaque on the teeth below the gum line, irritating and eroding nearby tis¬ sues. If it is not treated, the gum margin recedes, exposing the roots of the teeth. The process eventually involves the bone anchoring the teeth, which loosen and may fall out. Removal of all plaque deposits and affected soft tissues can arrest but not reverse bone deterioration.
periosteum V.per-e-'as-te-omN Dense membrane over bones. The outer layer contains nerve fibres and many blood vessels, which supply cells in the bone. The bone-producing cells of the inner layer are most prominent in fetal life and early childhood, when bone formation is at its peak. In adulthood they are less active but vital to continuous bone remodeling. When bone is injured, they multiply profusely to produce new bone.