OBY, or OB, a river of the Russian empire in Asia, which rises in the desert of Ilichinska, and, running north, joins the Irtysh near Tobolsk; and, still keeping its name, continues its course north, and falls into a deep bay called Obskaya, in about 63 degrees of latitude. The exact course of this river was unknown, till the country was surveyed by the Russians; who have given us good maps of it and of all Siberia. The Oby forms the boundary between Europe and Asia, and its course is upwards of 2000 miles in length.