P L A P L A 189 iiier, gradually shrinking through September, October, and Decem ber, Hooding in January, and continuing high and steady till June. The Uruguay rises about the middle of January (at Salto sometimes 22 feet above low water); again in April, to continue in flood for two months (30 feet at Salto); and for the third time, and with great regularity, in September or October, to last a whole month, and reach 40 to 50 feet above low water. Occasionally the flood level of the Parana is maintained throughout a whole year, or even two years in succession; and at intervals, as in 1858 and 1868, the water rises so high that the whole delta is submerged. The highest floods on record stood 24 feet above ordinnry low-water mark at Kosario, or 12 feet above ordinary high water. As a system of waterways the La Plata rivers are but partially developed. Steamers, mainly Brazilian, ascend from Buenos Ayres by the Parana, Para guay, and Cuyaba, a total distance of 2146 miles, to the town of Cuyaba in Brazil ; and the Pilcomayo and the Vermcjo, the Apa, the Jejuy, and the Tebiquary are all more or less navigable. The Parana affords a free passage for 280 miles above the confluence to the Seven Falls, except during low water, when the rapids of Apipe interfere ; and, according to Bigg- Wither, the upper Parana and its tributaries the Tibagy, Paranapanema, Tiete, Ibahy, &c. , fur nish 1290 miles of navigable stream, of which 510 could be at once utilized by steamers of light draught, while the remainder would require a certain outlay in the way of improvements. Vessels drawing 4^ feet of water can always ascend the Uruguay to Salto (200 miles), and during six months they can cross the Salto Chico, or Lesser Fall, a mile higher up ; but the Salto Grande, 8 miles farther, stops all progress except during six weeks in October and September. The whole system may be estimated to give upwards of 5000 miles of waterway, of which 3500 are accessible from the sea, without counting the secondary deltaic channels. See T. S. Page, U.S.X., La Plata, 1859 (the surveys of the " Waterwitch "); Burton, Battle-fields of Paraguay, 1870; Bigg-Wither, Pioneering in South Brazil, 1878 ; J. J. Revy, Hydraulics of Great Rivers: the Parana, the Uruguay, and the La Plata Estuary, 1874 (a series of elaborate investigations and measurements of great value) ; and other works mentioned under PARAGUAY. (H. A. W.) PLATEAU, JOSEPH ANTOINE FERDINAND, was born at Brussels in 1801, and died in 1883 at Ghent, where he had been professor of physics from 1835. He was a pupil and friend of Quetelet, who had much influence on the early part of his career. The more original investigations of Plateau refer chiefly to portions of one or other of two branches of science physiological optics and molecular forces. His doctoral thesis (Liege, 1829) had for its subject "Impressions produced by Light on the Organs of Vision"; and it was succeeded by numerous memoirs, some of much value, on the persistence of visual impressions, subjective impressions of colour, irradiation, &c. Among other results of his studies was the invention of the philosophical toy known as the " thaumatrope." We owe to him also some thing much more important, the process of studying the motion of a vibrating body by looking at it through equidistant radial slits in a revolving disk. In 1829 he imprudently gazed at the midday sun for 20 seconds, with the view of studying the after effects. The result was blindness for some days, succeeded by a temporary recovery ; but for the next fourteen years his sight gradually deteriorated, and in 1843 he became perma nently blind. This calamity did not interrupt his scientific activity. Aided by his wife and son, and afterwards by his son-in-law Van der Mensbrugghe, he continued to the end of his life his researches on vision, directing the course of the experiments which they made for him, and inter preting the bearing of the results. He also published a valuable analytical catalogue of all the more important memoirs which had been written, from the earliest times to the end of the 18th century, on his favourite theme of subjective visual phenomena. But even more extraordi nary were this blind man s investigations about molecular forces, embracing hundreds of novel experiments whose results he saw only with others eyes. These form the subject of his great work Statique experimental et theorigue des Liquides soumis (n<x seules Forces moleculaires (2 vols., 1873), which is a valuable contribution to our knowledge of the phenomena usually called capillary. To avoid, as far as possible, complications due to gravity, Plateau em ployed either films formed of a solution of soap with glycerin, or masses of oil suspended in a mixture of alcohol and water of the same density as the oil. See CAPILLARY ACTION. PLATED WARE. The plating or coating of one metal or alloy with another is extensively practised in metal working. In some cases the coating metal is a valuable protector from oxidation, &c., of the underlying metal ; in other cases the properties and advantages of two metals such as strength and lustre are combined in one object ; and more frequently a cheap and inferior body by a super ficial coating gets the appearance of a more valuable and important metal. The art of plating was originally applied to the production of imitation silver plate, whence the term " plating." The original method of silver plating consisted in attaching, by a kind of autogenous soldering, thin plates of silver to the opposite surfaces of a prepared ingot of copper alloy or of German silver. The silver plates were firmly wired to the ingot and submitted to a soldering temperature in a plating furnace, in which the surfaces became firmly united. Subsequently the ingot was rolled down to a sheet in which the relative thickness of the metals was maintained, and from such sheets " silver plated " articles were fashioned. This method of plating may be regarded as now extinct, being superseded by electro-plating (see ELECTRO-METALLURGY, vol. viii. p. 114). Recently, however, cooking vessels, &c., of iron plated in an analogous manner with nickel have come into use (see NICKEL, vol. xvii. p. 488). The plating or casing of iron with brass is extensively practised in the manufac ture of stair-rods, curtain and picture rods, and " cased " tubing for upholstery purposes generally ; and in the manufacture of pipes for conveying water the body of lead is frequently lined with a coating of pure tin. The gilding of metals is a process analogous to plating, as are also the galvanizing of iron and the manufacture of tin and terne plates. For these see IRON, vol. xiii. p. 357. PLATEN-HALLERMUND, AUGUST, GRAF VON (1796- 1835), German poet, was born at Ansbach on October 24, 1796, and died at Syracuse on December 5, 1835. His principal publications were Lyrische Blatter (1821), Sonette aus Venedig (1825), an historical fragment entitled Geschich- ten des Konigreichs Neapel 1414-43 (1833), and a poem ! in nine cantos, Die Ablasiden (1835). He wrote also a ! number of dramas, of which may be mentioned Der yldserne Pantoffel and Die Liga von Cambrai. See vol. x. p. 545. PLATINUM AND THE PLATINUM METALS. The metals platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), and osmium (Os) are united into a family by a striking similarity in chemical characters and by their association in natural occurrence. A rather rare ore, called platinum ore or polyxene, is almost the only native material which is available for their extrac tion ; it contains them all in the reguline form. Traces of platinum are found in almost all native gold. As early as the first half of the 16th century it appears to have been noticed that the gold ore in the Spanish mines of Darien includes grains of a white metal, endowed with the qualities of a noble metal and yet distinctly different from silver ; but the fact remained unknown in Europe because the Spanish Government, having found out that the new metal lent itself most admirably for the adulteration of gold, prohibited its exportation. Onlj from about the middle of last century did the metal begin to find its way to Europe and to become known there, at first as a curiosity, under its Spanish name of " platina del Pinto " (the little silver from the river Pinto). Its chemi cal individuality and qualities were established by the successive labours of Scheffer (1752), Marggraft (1757), Bergmann (1777), and others. An amateur, Count von
Sickingen, it appears, was the first who succeeded in work-