POTLATCH. 31T POTOMETEB. according to his rank. There is a farewell feast and the visitors return to their canoes and their homes. POTOCKI, p6-t6ts'ke. The name of a Polish family of high rank, possessing large estates in Galicia and the Ukraine. After the sixteenth century several members of tlie family held im- portant places in State and Church. Among the most noteworthy may be mentioned : ( 1 ) Count Stanisla.s Felix Potocki (1745-1805), chief of the Polish artillery. In 1792 he joined Branicki and Rzewuski in issuing the manifesto of the confederation of Targovitza (q.v. ). The ne.xt year he attempted, with the aid of Catliarine II. of Russia, to carry out the objects of the confederation. The insurrec- tion of 1794 forced liim to leave Ppland, and he fled to Russia. In his absence he was sentenced to death for treason, but the success of Suvaroff enabled him to return to Poland. He was ap- pointed Russian field-marshal bv Catharine in 1795. (2) Count Ignazt Potocki (1751-1809), grand marshal of Lithuania, a cousin of Stan- islas Felix. He helped to form the Constitu- tion of 1791; fled to Prussia upon the inva.sion of Poland by the Russians, but returned after the success of Kosciuszko, and became a member of the new Government. He was made pris- oner by Suvaroff, and confined in Schliissel- burg. Released in 1796, he lived in Galicia till the approach of Xapolcon's army in 1800, Avhen he was again imprisoned for a short time. (3) Count Staxi.sl.s KosTK. Potocki (1752- 1821 ), brother of Ignazy, was prominent in draw- ing up the Constitution of 1791, and after the sec- ond partition of Poland was for a short time un- der arrest. After his release he became a de- voted patron of science and literature. In 1807 he became head of the educational system in the Duchy of Warsaw; and after the Kingdom of Pohind was reorganized (1815), became Minister of Public Instruction. He wrote a treatise on the Art of the Ancients and On Eloquence and Htyle (1815). (4) Count Jan Potocki (1701-1816) was emi- nent as a student of Slavic antiquities and wrote several historical works, among them Fracfinents liistoriques ct gcogrnphiques sur la Scythie, la Hfirmatie et les Shn^es (4 vols., Brunswick, 1795) ; Histoire primitive des peuples de Russie (Saint Petersburg, 1802). He also wrote me- moirs upon Egyptian antiquities and Toi/age dan3 I'Enipire dc Muroc (Warsaw, 1792). These works were printed in editions of but one hun- dred copies, and arc therefore very rare. They have some value as collections of material. (5) Count Alfred Potocki (1817-89) rose to prominence as a member of the Galician Diet and the Austrian House of Peers. From 1867 to 1870 he was Austrian Minister of Asriculture, and from April, 1870, to February, 1871, head of the Cabinet. POTOCKI, Waclaw (c. 1622-97). The most prolific Polish poet. He ser-ed in the army, fighting in the war against the Cossacks (1653)* ; m 1683 was appointed commissioner to map the boundary of Silesia: and lived his last years on his hereditary estate of Luzna. Potocki is known in our time for an epic, Wojnn Chocim.ikfi. on the victory over the Turks at Chocim in 1621, a poem which received no recognition from his contempo- raries and was lost until 1850. It is an epic of much merit, with many satiric contrasts between the heroic simplicity of old times and the luxury of the new. Potocki's contemporary fame rested on Poczet lierhow (1696), a heraldry in verse; some devotional poems (1690); Jovialitates (1747), consisting of witty epigrams; Syloret ( 1764), a tale; and a version of Barclay's A rjenis (1697). POTO'MAC. One of the most important riv- ers of the Eastern United States, forming through- out its course the boundary between Marjiand on the north and east, and West Virginia and Virginia on the south and west (Map: Jlaryland, K 8). It rises in two branches, the Xorth Branch in the western Alleghanies on the bound- ary of Maryland, and the South Branch in the central Alleghanies in western Virginia, the junc- tion of the headstream being 14 miles southeast of Cumberland, Md. Thence the main stream flows in a much winding southeast course till it empties into Chesapeake Bay, 75 miles from the Atlantic Ocean. Its total 'length is about 400 miles, and its chief tributaries, besides the South Branch, are the Shenandoah from the south and the Monocacy from the north. The scenery along its upper course is remarkably picturesque, espe- cially where it breaks through the Blue Ridge at Harper's Ferry. There are several falls in its passage through the mountains and through the Piedmont Plain below, the Great Falls being about 10 miles above Washington. At that city, 125 miles from its mouth, the river becomes a tidal stream, navigable for large ships, and for the last 100 miles it is a magnificent estuary from two to seven miles wide. The Chesapeake and Ohio Canal follows its course from George- town to Cumberland. The whole region through which the river flows is full of historic landmarks. Opposite Washington is Arlington (q.v.), and a short distance below are Alexandria and !^tount Vernon. POTOMAC FORMATION. A name applied to a series of deposits which are chiefly of Lower Cretaceous age, but may be also partly Jurassic. The formation is found along the Atlantic border of the United States from Martha's Vineyard to Georgia, and also up the Mississippi Valley to Tennessee. It consists of a series of sands, grav- els, and clays. The latter are worked at many points, notably in New Jersey, and certain mem- bers of the series supply iron ore and gla.ss sand. Consult : White, "Correlation Papers, Cretace- ous," Bulletin United States Geological Survey No. S2 (Washington, 1893). See Cretaceous System. POTOM'ETER (from Gk. vroTiSi-.po/on, drink + jJ-irpov, mrtron, measure). An instrument for observing the rate at which plants evaporate water. The simple form used in physiological laboratories consists essentially of a graduated capillary glass tube (c in the figure), to which is connected a transpiring shoot. The tube is filled with water and the lower end dipped into water. As evaporation from the leaf surface proceeds water is drawn up the tube, whose narrow bore ac- celerates the rate of flow. This may be made evi- dent by lifting the end of the tube for an instant and allowing air to enter. On replacing the tube water again enters, and as the short bubble trav- els along the tube its rate may be observed and
