Odometer (Gr., a road, and pov, a measure), an instrument for determining the distances passed over in travelling, also known as pedometer, perambulator, etc. Odometers attached to the wheels of carriages were employed by the ancient Romans. This kind of odometer records by a mechanical contrivance the number of revolutions of a wheel in passing from one place to another. The odometer carried by pedestrians, and designed for recording the number of steps, is generally called a pedometer. It resembles a watch in size and shape, and may be worn in the vest pocket. Its machinery is so constructed that by the rising and sinking of the body with each step a lever is made to vibrate, which moves the index hand connected with it.
Oesel, an island in the Baltic, at the mouth of the gulf of Riga, in the Russian government of Livonia; length about 60 m., breadth from 3 to 50 m.; area, 1,200 sq. m.; pop. about 46,000, mainly Lutherans. It has a bold, high coast, and a diversified surface. The climate is more temperate than on the mainland, but violent storms are frequent in spring and autumn. The soil is not naturally fertile, but is watered by many small streams. A great part of the island is covered with forests, and much of it is used as pasture. Grain is raised for exportation. The only important manufacture is tar. The fisheries, chiefly of seals, are valuable. Oesel once belonged to the Teutonic knights, but was seized by the Danes at an early period, and ceded by them to Sweden in 1645. In the beginning of the 18th century Russia took possession of it, and in 1721 it was formally ceded to that power. Chief town, Arensburg.
Offa, a king of Mercia, Britain, who reigned for about 40 years in the second half of the 8th century. He conquered various territories, and compelled the king of Kent to acknowledge his authority. Charlemagne called him the most powerful of the Christian kings of the West, and maintained friendly relations with him except during a short period when the traders in Offa's dominions committed depredations upon Prankish merchants. At the instigation of Cynedrida, his wife, he put to death Etheibert, king of East Anglia, and seized his states. He soon died, overcome by remorse, and was succeeded by his son Egferth, who reigned only a few months. Offa compiled the laws of his dominions, which are mostly included in the Anglo-Saxon code of Alfred the Great - See "Essay on the Life and Institutions of Offa," by Mackenzie (London, 1840).
Offenbach, the chief manufacturing town of the grand duchy of Hesse, Germany, on the S. bank of the Main, 4 m. E. of Frankfort; pop. in 1871, 22,691. It contains a castle, and has manufactories of cottons and woollens, carriages, cards, musical instruments, jewelry, and other wares.