OHIO RIVER, formed by the confluence of the Alleghany and the Monongahela, pursues a westward course of 1000 m., separating Ohio, Indiana, and Illinois from West Virginia and Kentucky, and after receiving sundry tributaries joins the Mississippi, being the largest and, next to the Missouri, the longest of its affluents; it is navigable for the whole of its course; on its banks stand Pittsburg, Cincinnati, Louisville, and Madison.
OHM, GEORG SIMON, a German physicist, born at Erlangen; discovered the mathematical theory of the electric current, known as Ohm’s Law, a law based on experiment, that the strength of the electric current is equal to the electro-motive force divided by the resistance of the wire (1787-1854).
OHNET, GEORGES, French novelist, born in Paris; author of a series of novels in a social interest, entitled “Les Batailles de la Vie;” b. 1848.
OIL CITY (11), on the Alleghany River, Pennsylvania, by rail 130 m. N. of Pittsburg, is the centre of a great oil-trade and oil-refining industry; there are also engineer and boiler works; it suffered severely from floods in 1892.
OKA, a river of Central Russia, which rises in Orel and flows N., then E., then N. again, joining the Volga at Nijni-Novgorod after a course of over 700 m., navigable nearly all the way; on its banks are Orel, Kaluga, and Riazan, while Moscow stands on an affluent.
OKEN, LORENZ, German naturalist; was professor first at Jena, then at Muenich, and finally at Zurich, his settlement in the latter being due to the disfavour with which his political opinions, published in a journal of his called the Iris, were received in Germany; much of his scientific doctrine was deduced from a transcendental standpoint or by a priori reasonings; is mentioned in “Sartor” as one with whom Teufelsdroeck in his early speculations had some affinity (1779-1851).
OKHOTSK, SEA OF, an immense sheet of water in Eastern Siberia, lying between the peninsula of Kamchatka and the mainland, with the Kurile Islands stretched across its mouth; is scarcely navigable, being infested by fogs.
OKLAHOMA (62), a United States territory, stretching southward from Kansas to the Red River, with Texas on the W. and Indian Territory on the E., is a third larger than Scotland, and presents a prairie surface crossed by the Arkansas, Cimarron, and Canadian Rivers, and rising to the Wichita Mountains in the S. There are many brackish streams; the rainfall is light, hence the soil can be cultivated only in parts. Ceded to the United States under restrictions by the tribes of the Indian Territory in 1866, there were various attempts by immigrants from neighbouring States to effect settlements in Oklahoma, which the Government frustrated by military interference, maintaining the treaty with the Indians till 1889, when it finally purchased from them their claim. At noon on April 22, 1889, the area was opened for settlement, and by twilight 50,000 had entered and taken possession of claims. The territory was organised in 1890; embedded in it lies the Cherokee Outlet, still held by the Indians, but on the extinction of their interests to revert to Oklahoma. The chief town is Oklahoma (5).