visitors from all parts of the world. See Miracle-Plays and Homes of Ober-Ammer-gau by Greatorex.

O'b'erlin, O., a town in Lorain County, near Lake Erie, 34 miles west of Cleveland. It is a college town, with some factories and business blocks. It is the seat of Oberlin College, established in 1833 and chartered as Oberlin Collegiate Institute. In 1850 the name was changed to Oberlin College. It is a coeducational institution, and, besides the college, theological seminary and academy, provides courses for graduate students. The number of instructors in all departments including the conservatory of music, is 142, the students in attendance 2,025, an& the number of volumes in the library about 125,000. Population 4,365.

Obi (o'be) or Ob is the great river of western Siberia. It rises in two branches in the Altai Mountains in the Chinese dominions, and flows north, 2,120 miles, into the Gulf of Obi in the Arctic Ocean. It is very little used for navigation, but with the growth of the country will probably become one of the great water-routes for commerce. Its chief tributary is the Irtish.

O'Brien, Most Rev. Cornelius, D.D., Ph.D., F.R.S. Can., Roman Catholic Archbishop of Halifax since 1882, was born in New Glasgow, Prince Edward Island, on May 4, 1843, and was educated at St. Dun-stan's College in Charlottetown and at the Propaganda in Rome. He has been president of the Royal Society of Canada, for which he wrote The Supernatural in Nature and other papers His published works include The Philosophy of the Bible, Memoirs of Bishop Burke; and Cabot's Landfall.

Observ'atory, an institution equipped for the study of astronomical or meteorological phenomena. In distinction from a laboratory, which is a place where phenomena can be brought to pass and experiments tried, an observatory is a place for the observation of phenomena over which we have no control, as an eclipse of the moon or a sudden variation in the earth's magnetism. Those institutions which are exclusively devoted to observational work are the purely astronomical observatories. Scarcely any other kind existed previous to the invention of the spectroscope by Kirchhofī and Bunsen. Recently, however, a number of astrophysical observatories have been established — notably at Potsdam in Germany, Meudon in France, Tulse Hill in London and Cambridge, Washington, Allegheny, Columbus, Lake Geneva and Mount Hamilton in America. In these institutions many experiments have to be tried as well as many observations made; for the spectra of stars, planets, nebulas, comets have to be interpreted as well as described. And their interpretation can be given only after experiment has shown how to duplicate them. Hence an astrophysical observatory

is generally also a laboratory, provided with electrical, photographic and spectroscopic apparatus. The same is more or ■ less true of a magnetic observatory.

The typical astronomical observatory is equipped with a clock and an instrument for correcting this clock from the passage of stars over the meridian of the place. It is provided also with a telescope, housed in a dome which can easily be opened to the sky on one side and easily rotated. The more important observatories of the world are : Yerkes Observatory at Lake Geneva, with a refracting telescope whose object glass is 40 inches in diameter; Lick Observatory at Mount Hamilton, Cal., with an objective of 36 inches diameter; Harvard Observatory at Cambridge, Mass.. with a branch in Arequipa, South America; this institution employs between 30 and 40 workers and is making a superb spectroscopic survey of the heavens; Naval Observatory at Washington and Mcăormick at the University of Virginia each have 2 6 inch glasses, while Halstead Observatory at Princeton University follows with one of 23 J inches. Greenwich Observatory in England is a national institution, which has a brilliant history and is doing a great variety of work. The corresponding institution for France is Paris Observatory, and, like Greenwich in England and Pulkowa in Russia, it has a history of which it may well be proud.

Obsid'ian, a natural glass, a variety of lava. It is hard, brittle, with a glassy luster, partially transparent, and with sharp edges that cut like glass. It is black, dark gray, green, red, brown, striped or spotted, a specimen usually having but one of these various colors. It is used for jewelry and ornamental articles, and in early times was employed for arrowheads, knives and mirrors. It is found in Yellowstone Park and other localities in the United States; in Iceland, the Lipari Islands, Vesuvius, Sardinia, Hungary, Spain, Mexico and South America.

0'cean=Cur'rents. There are some very remarkable currents in the great seas. Some are surface-currents and some move along on the very bottom of the sea. The latter are the great inflows of cold water from the polar regions. The surface-currents are caused by the winds, and are warm or cold according as they pass from a warmer or colder climate. The effect of these currents upon climatic conditions makes them of great importance. They may be considered as constituting two great and somewhat similar systems, the Atlantic and the Pacific, which may be subdivided into the North and the South Atlantic and the North and the South Pacific respectively. The currents of the North Atlantic are the North Equatorial current, the Gulf Stream (q. v.) and the North African current, which form a great circle with a large Sargasso Sea in