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 308 PERNAU PERPETUAL MOTION era portions is into the Sao Francisco, some of the streams being quite large. The chief rivers emptying into the ocean are the Una, Ca- pibaribe, Ipojuca, Serenhaem, and Pirapama; none of them are navigable, being almost en- tirely dry during the dry season, and greatly swollen in the rainy season. The climate on the coast is damp, but the excessive heat is here somewhat modified by sea breezes, while in the interior no tempering influence exists. There are extensive and valuable forests. The region of the mattas produces large quantities of sugar, molasses, and rum, and cotton is also extensively cultivated and of fine quality ; but the system of agriculture is very inefficient. Mandioca and cocoanuts are the only other important productions, the latter from large groves planted on the coast. Cattle rearing is largely carried on in the sertao ; and there are in the coast region numerous mills for pro- ducing mandioca flour. Public instruction is flourishing. In 1873 there were 466 primary schools and 25 grammar schools, with IV, ITS pupils; and there are several higher schools in the capital. The principal towns are Re- cife, Monteiro, Goyanna, Tamandare, Rio For- mozo, and Serenhaem. II* A city, capital of the province. (See RECIFE.) PERNAU, a seaport town of Russia, in Livo- nia, at the mouth of the Pernau, on the gulf and 100 m. N. by E. of the city of Riga ; pop. in 1867, 9,527. It has two Lutheran church- es, a Greek church, and several schools. The principal trade is in flax, hemp, various seeds, grain, wood, and leather. The shipping in 1873 comprised 240 vessels; value of imports, 287,217 rubles; of exports, 7,006,317 rubles. PERON, Francois, a French traveller, born at Oerilly, Bourbonnais, Aug. 22, 1775, died there, Dec. 14, 1810. He enlisted as a volunteer in 1792, was wounded at the siege of Landau, and made a prisoner at the battle of Kai- serslautern, taken to the citadel of Magde- burg, and released in 1794. In 1800 he was attached in the capacity of zoologist to the ex- pedition sent by the French government under Oapt. Baudin to explore Australia, and wrote Voyage de decouvertes aux terres australes pendant les annees 1800-1804 (3 vols. 4to, with an atlas, Paris, 1807-'16). The third volume was prepared after his death by M. de Frey- cinet. He had previously published Observa- tions sur Vanthropologie (Paris, 1799). See F. Peron, naturaliste voyageur aux terres aus- trales, by Maurice Girard (Paris, 1857). PEROME, a town of France, in the depart- ment of Somme and on the right bank of the river Somme, 27 m. E. by N. of Amiens ; pop. in 1866, 4,262. It is strongly fortified, and acquired historical importance under the reign of Louis XL, who was imprisoned here by Charles the Bold (1468). In 1536 the town won the designation of la Vierge or the im- pregnable by a successful resistance to the besieging imperialists. The league was signed at Peronne in February, 1576. In 1815 it sur- rendered to Wellington, and on Jan. 9, 1871, to the Germans after 13 days' resistance. PEROISE, La. See LA PEKOUSE. PERPETUAL MOTION, in mechanics, a machine which when set in motion would continue to move without the aid of external force and without the loss of momentum, until its parts became deranged or worn out. Although the impossibility of constructing such a machine has long been demonstrated, many attempts have been made, an interesting history of which has been given by Henry Dircks, " Per- petuum Mobile, or a History of the Search for Self -motive Power " (London, 1870). The ear- liest record of a contrivance for effecting me- chanical perpetual motion was by Wilars de Honecourt, an architect of the 15th century, whose sketch book containing the accompany- ing cut, fig. 1, is in the ecole des chartes at Paris. This contains the imaginary principle upon which most of the perpetual motion machines FIG. 1. Facsimile of Sketch by Wilars de Honecourt. having any plausible appearance of effecting the object have been constructed. The design will be made more apparent by fig. 2, a revival of the same plan by Capra (Bologna, 1678), in which the weights by reason of their mode of attachment take a position further from the centre of motion when descending than when ascending. It will be readily seen that this dispositon of the weights may be effected, but the result will be that of those which are on the ascending side there will be a greater num- ber at any one time than of those on the de- scending side, and it may be computed that the mechanical force of the ascending will ex- actly balance that of the descending weights. The machine of the marquis of Worcester, which has great historical prominence on ac- count of the rank of its inventor, was a wheel ostensibly moved in a similar manner. An ac- count of it and of the attention it commanded,