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PISO 259 PITCAIRN ISLAND retire from the city by the conspiracy of Magacles and Lycurgus, he returned soon after by effecting a compromise, but was obliged to retire again, and suffer an exile of 11 years. In the 11th year he reappeared at the head of an army and regained his power, which he re- tained till his death, 527 B. c. He was a beneficent ruler, and did much to pro- mote the rise of Greek literature. We owe to him the poems of Homer in their present form, Pisistratus having col- lected them. PISO, an eminent Roman family, which produced some great men, as: Piso, Lucius Calpurnis, surnamed Fru- galis, on account of his frugality, con- sul 149_ B. c, who terminated the war with Sicily. He composed annals and orations, which are lost. Piso, Caius, consul 67 B. c, author of a law to restrain the factions which usually attend the elec- tion of the chief magistrates. PiSO, Cneius, consul under Augustus, and gov- ernor of Syria under Tiberius, in which situation he behaved with great cruelty. He was charged with poisoning Germani- cus; on which account he destroyed him- self, A. D. 20. Piso, Lucius, a senator, who attended the Emperor Valerian into Persia in 258. On the death of that em- peror he assumed the imperial title; but was defeated by Valens, who put him to death in 261. PISTACIO NUT, the fruit of the pis- tacia vera. The kernel is very oily, of a peculiar flavor and bright green in color, and is much used in confections, etc. PISTIL, the female organ in plants, standing in the middle of the stamens, around which again $tand the floral en- velopes. PISTILLIDIUM, a name given to cer- tain small, sessile, ovate bodies in the fructification of mosses, enveloped in a membrane tapering upward into a point. When abortive they are called para- physes. PISTOIA, or PISTOJA (ancient Pis- toria), a town of Italy; 20 miles N. W. of Florence, on a spur of the Apennines. Its^ streets are thoroughly Tuscan, and it is surrounded with walls, pierced by five gates, and has a citadel. The chief buildings are the cathedral of San Jacopo (12th and 13th centuries), con- taining a magnificent altar of silver (1286-1407) and several good pictures; the church of St. Bartholomew, with a fine white marble pulpit by Guido of Como (1250) ; St. Andrea, with Giovanni Pisano's pulpit (1301); St. John, with a font by Giovanni Pisano and terra cottas by Andrea della Robbia; the 14th century communal palace; and other palaces. The principal manufactures are iron and steel wares, and firearms — the word "pistol" in all probability takes its name through pistolese, "a dagger," from Pistoia (Pistola). Here Cataline was defeated in 62 B. c. The town was conquered by Florence and Lucca in 1306. Pop., commune about 70,000; town, about 14,000. PISTOL. See Firearms. PISTOLE, a gold coin once current in Spain, France, and the neighboring countries; average value about $3.85. PISTON, in machinery, a device so fitted as to occupy the sectional area of a tube and be capable of reciproca- tion by pressure on either of its sides. It may be of any shape corresponding accurately to the bore of the tube; but the cylindrical form is almost exclu- sively employed for both, as in the com- mon pump and the steam engine. One of its sides is fitted to a rod, to which it either imparts reciprocatory motion, as in the steam engine, or by which it is itself reciprocated, as in the pump. In the former case, it has no opening lead- ing from one side to the other, and is termed solid, though generally not really so; but in the latter, an aperture con- trolled by a valve permits the passage of the fluid from one side to the other during its downward movement; except in force pumps. A distinction is made in pumps; the solid piston being known as a plunger; the hollow piston as a bucket. The piston usually requires packing to cause it to fit closely within its cylinder and at the same time allow its free backward and forward move- ment. PITA FLAX, flax made from the fiber of the Agave Americana (called also maguey), and used for twine, rope, hammock meshes, etc. In Mexico it is also used for oakum. Labillardiere found that its strength is to that of common flax as 7 to 11%. PITCAIRN, a borough of Pennsyl- vania, in Allegheny co. It is about 15 miles E. of Pittsburgh on the Pennsyl- vania railroad. There are railroad shops and yards, machine shops and foundries, and electrical supply works. There are important coal mines in the neighborhood. Pop. (1910) 4,975; (1920) 5,738. PITCAIRN ISLAND, a solitary is- land in the Pacific Ocean, between Aus- tralia and South America, in lat. 25" 3' S. and Ion. 130° 8' W., measures 21/2 miles by 1 mile. It was discovered by Carteret in 1767, and was at that time uninhabited. In 1790 it was taken pos-