PLANETS, bodies resembling the earth and of different sizes, which revolve in elliptical orbits round the sun, and at different distances, the chief of them eight in number, two of them, viz., Mercury and Venus, revolving in orbits interior to that of the earth, and five of them, viz., Mars, Jupiter, Saturn, Uranus, and Neptune, exterior, the whole with the PLANETOIDS (q. v.) and comets constituting the solar system.

PLANTAGENETS, the name attached to a dynasty of kings of England, who reigned from the extinction of the Norman line to the accession of the Tudor, that is, from the beginning of Henry II.’s reign in 1154 to the end of Richard III.’s on Bosworth Field in 1458.  The name was adopted by Geoffrey of Anjou, the husband of Matilda, the daughter of Henry I., whose badge was a sprig of broom (which the name denotes), and which he wore in his bonnet as descended from the Earl of Anjou, who was by way of penance scourged with twigs of it at Jerusalem.

PLANTIN, CHRISTOPHE, a printer of Antwerp, born near Tours, in France; celebrated for the beauty and accuracy of the work that issued from his press, the most notable being the “Antwerp Polyglot”; he had printing establishments in Leyden and Paris, as well as Antwerp, all these conducted by sons-in-law (1514-1589).

PLASSEY, a great battlefield in Bengal, now swept away by changes in the course of the river, scarcely 100 m.  N. of Calcutta; was the scene of Clive’s victory in 1757 with 800 Europeans and 2200 unreliable native troops over Suraj-ud-Dowlah, the ruler of Bengal, which laid that province at the feet of Britain, and led to the foundation of the British Empire in India.

PLASTER OF PARIS, a compound of lime, sand, and water used for coating walls, taking casts, and forming moulds.

PLATAEA, a city of ancient Greece, in western Boeotia, neighbour and ally of Athens, suffered greatly in the Persian and Peloponnesian Wars.  It was destroyed by the Persians 480 B.C., by the Peloponnesian forces 429 B.C., and again by the Thebans 387 B.C.  Philip of Macedon restored the exiles to their homes in 338 B.C.

PLATO, the great philosopher, born in Athens, of noble birth, the year Pericles died, and the second of the Peloponnesian War; at 20 became a disciple of Socrates, and passed eight years in his society; at 30, after the death of Socrates, quitted Athens, and took up his abode at Megara; from Megara he travelled to Cyrene, Egypt, Magna Graecia, and Sicily, prolonging his stay in Magna Graecia, and studying under Pythagoras, whose philosophy was then at its prime, and which exercised a profound influence over him; after ten years’ wandering in this way he, at the age of 40, returned to Athens, and founded his Academy, a gymnasium outside the city with a garden, which belonged to his father, and where he gathered around him a body of disciples, and had Aristotle for one of his pupils, lecturing there with undiminished mental power till he reached