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POWERS

1542

PRAGUE

does the same amount of work whether the hoist be made in one minute or in one hour. Yet there is a very great difference between these eases; and we say that it requires a much more "powerful" engine to make the hoist in one minute. Accordingly, we define the power of an agent as the rate at which it does work, that is, the ratio of the work divided by the time. Activity is used as a strict synonym for power.

The unit of power most frequently employed in England and America is the horsepower, introduced by James Watt and defined as the activity of an agent capable of raising 550 pounds through a vertical distance of one foot in one second. The French horse-power is such that it will raise 75 kilograms one meter per second. In purely scientific work the unit of power is that which will accomplish the work of one joule per second. This unit is called a watt; and is numerically equal to io7 ergs per second. In electrical work the kilowatt (1,000 watts) is the unit most frequently used. Electrical energy, whether for lighting or for power purposes, is sold at so much per*kilowatt-hour. It is important to remember that one horse-power equals 746 watts.

Powers, Hiram, a distinguished American sculptor, was born at Woodstock, Vt., July 29, 1805. While a boy he went to Cincinnati, O., and became an apprentice to a clock-maker. About the same time he formed the acquaintance of a German sculptor, who taught him to model in clay. In 1835 ^e went to Washington, where he executed the busts of several distinguished persons. Two years later he went to Italy to study his art, and resided in Florence until his death on June 27, 1873. There he produced his statue of Eve and numerous other works; but the famous production of his genius was the Greek Slave, of which six copies in marble and innumerable cast copies were produced.

Powhatan (poufha-tdnf}. See POCAHON-TAS.

Pozzuoli (pot'soo-o'le), formerly Puteoli, a city of southern Italy on the Bay of Naples, seven miles from the city, with which it is connected by a tramway. Pozzuoli is interesting from its memorials of ancient times. Its cathedral was the temple of Augustus. There are the remains of an amphitheater which seated 30,000 persons, in which Nero fought as a gladiator; of temples to Diana and Neptune; and of the ancient harbor. Population 22,830.

Praetor, originally the official title of the consuls of ancient Rome as leaders of the armies; but specially employed to designate a magistrate whose powers were scarcely inferior to those of a consul. The praetor's functions were chiefly judicial, his principal business (although he sometimes commanded armies in the field) being the administration -$» justice in matters both civil and criminal;

and to the edicts of successive praetors the Roman law owed much of its development. Originally there was but one pra?tor; but in 246 B. C. a second praetor was appointed to settle disputes that might arise between Romans and foreigners temporarily residing in Rome. In 227 B. C. two new praetors were appointed to administer affairs in Sicily and Sardinia. A few years later there were two for the Spanish provinces. Sulla increased the number to eight and Julius Caesar to 16.

Praeto'rian Guard, a special body of soldiers organized for protecting the person and upholding the power of the Roman emperors. We read of a select guard of soldiers attached to the person of Scipio Afri-canus, but it was by Augustus that they were first organized as a separate force. He formed nine or ten cohorts of i ,000 men each, but kept only three at Rome. Tiberius, however assembled the nine cohorts in a permanent camp at Rome, while Vitellius increased their number to 16. They soon acquired great power, which they often exercised most unscrupulously, elevating and deposing emperors at pleasure. Candidates for the imperial dignity found it necessary to bribe them largely; while those who attained the position were accustomed to purchase their favor by liberal donations. After the death of Pertinax (193 A. D.) they sold the imperial purple to Didius Julianus for a sum of money; but in the same year their organization was broken up by Sever us, who formed new cohorts out of the best legions serving on the frontiers, which he increased to four times the number of the old ones. After several other changes the prse-torian guard was finally dispersed among the other Roman legions by Constantine the Great in 312.

Pragmatic Sanc'tion, a solemn ordinance of the head of a kingdom relating either to affairs of church or to those of state. The term originated in the Byzantine empire, and signified a public and solemn decree by a prince, in distinction from the simple rescript, which was a mere declaration of law in answer to an individual. This name is applied to several important treaties, of which the chief ones are (i) that of St. Louis in 1269 and (2) that of Charles VII in 1437, in both of which the rights of the Gallican church were asserted; (3) the instrument which settled the Holy Roman empire in the Hapsburg house of Austria in 1439; (4) the ordinance by which Charles VI of the Holy Roman empire settled his dominions on Archduchess Maria Theresa, his daughter; and (5) the settlement of the succession of the kingdom of Naples, which was ceded by Charles III of Spain in 1759 to his third son and his descendants.

Prague, the capital of Bohemia and the third largest town in Austria-Hungary, is situated on. the Moldau, 220 miles from