OIL CITY                                                   1376                                              OKLAHOMA

great importance in the hands of Helmholtz. In 1852 Ohm was appointed to the chair of physics at the University of Munich. His most important work, by all odds, is his theorem concerning the galvanic circuit.

Oil City, Pa., a town lying on both sides of Allegheny River. It lies 133 miles northeast of Pittsburg, is in the oil-region, and is one of the largest oil-markets of the state. It has oil-refineries, engine and boiler factories and large manufactories of barrels. It has public and (R. C.) parochial schools, and among its noteworthy buildings are the Oil-Exchange, the Standard Oil Company's office, Carnegie library and several churches. In 1892 the town was visited by an unusual catastrophe : a flood of burning oil from Ti-tusville. Over $1 ,cco,poo worth of property was destroyed. Population 15,657.

Oil-Wells. See Petro'leum.

Oils, a term used to indicate a large class of compounds. The more common animal and vegetable oils, which are the fatty or fixed oils, are all compounds of glycerine with fatty acids. The t^rm fats is usually given to the solid forms, and oils to the fluid. The solid fats, however, become fluid when heated. All these fats and oils are lighter than water and will not mix with it. They penetrate paper or cloth, making it partly transparent, and leaving what is known as a grease-spot. When pure and fresh they usually have little or no taste or smell; but, when exposed to the air, they become darker in color, have a disagreeable taste and smell, and are called rancid. As examples of vegetable oils we have cottonseed-oil, linseed-oil, olive-oil, almond-oil and cocoa-butter. Linseed is brought largely from Russia and India; Africa supplies palm-oil; India and the Pacific islands cocoanut-oil ; while the best olive-oil is brought from Italy. In animal oils the principal ones are butter, lard, tallow, neatsfoot-oil and sperm-oil. Tallow is the fat of oxen and sheep, melted and purified. Lard, obtained from the hog, is one of the great products of the United States, 60,000 tons yearly being sent to Great Britain alone. Neatsfoot-cil is produced by boiling the feet of cattle. Sperm-oil and other fish-oils are obtained from different varieties of fish and sea animals, as the whale, seal, cod, shark or herring. The uses of the different oils are very numerous: as food and in the preparation of food, in soap-making, painting, machinery and in a thousand other ways they are of great importance. There is a large class of substances known as the essential or volatile oils which resemble the fats somewhat in their properties, particularly in not rhixing with water. They make a grease-spot on paper which is not permanent. These are quite varied in composition, are more or less volatile and have strong and characteristic odors. Oils of turpentine, lemon and wintergreen are examples of a great number of these products which are

largely used as solvents, for flavoring, in perfumery and in medicine. For mineral oils see Petroleum.

Ojib'ways or Chip'pewas, a large tribe of North American Indians belonging to the Algonquin family and living around Lakes Huron and Superior. They usually were at war with the Sioux and Iroquois, driving the Sioux from the sources of the Mississippi. They sided with the French, taking part in Pontiac's War; and in the Revolutionary War they fought with the British. They came as far east as Lake Erie, but gave up all their lands inOhioin 1817. They numbered about 18,000. Their lands have gradually been ceded to the United States, and most of the tribe are on lands west of the Mississippi. Their history has been written by two members of their tribe. See Peter Jones's History of the Ojibway Indians.

Oka', a river in Central Russia, the principal branch of the Volga. It flows northeast through the most fertile region of Russia, for 906 miles, to the Volga. It is navigable for part of the year only

Okhotsk {Õ-kštsk'), Sea of, an arm of the Pacific, on the eastern coast of Siberia. It is 1,000 miles long and 600 broad, and contains several islands. It is seldom navigated.

Oklaho'ma (a Comanche Indian word signifying Land of the Fair God), until recently a territory (organized on May 2,1890), with an area of 39,030 square miles and a population of 398,331 in 1900, but on Nov. 16, 1907, admitted as a state, with the adjoining Indian Territory (set apart for the Indians in 1832, organized on June 30, 1834, with an area of 31,400 square miles, and a population of 392,060 in 1900) Theareaof this 46th state is 70,430 square miles, with a population, according to the census of 1910, of 1,657,155. Oklahoma City is the capital, with a population (census 1910) of 64,205. The other important cities are Guthrie, Tulsa, Ardmore, El Reno, Enid, Lawton, Muskogee, Shawnee, South Mc-Alester, Chickasha, Hobart, Stillwater and Vinita. The state, which lies in the South-central group, is bounded on the south by Texas, on the east by Arkansas and Missouri, on the north by Kansas and Colorado and on the west by New Mexico and Texas. The rise of Oklahoma to statehood within so brief a period as 18 years, when it was a vast cattle-range and Indian hunting-ground, is phenomenal, and bodes well for a still greater and more prosperous future.

Surface and Climate. With the exception of the Wichita Mountains in the south and the Chautauqua range near the center of the state, Oklahoma is a vast unbroken prairie plain, about 1,100 feet above the sea, the drainage being chiefly to the southeast by the Arkansas, Canadian and Red Rivers and their feeders. In the east and southeast there is some timber-land, but not much of