OPORTO (140), at the mouth of the Douro, 200 m.  N. of Lisbon, the chief manufacturing city of Portugal, and second in commercial importance; is the head-quarters of the trade in port wine; the industries include cloth, silk, hat, and porcelain manufacture, tobacco, metal-casting, and tanning; besides wine it exports cattle, fruit, cork, and copper.  There are many old churches, schools, a library, and two picture-galleries.

OPPORTUNIST, name given to a politician whose policy it is to take advantage of, or be guided by, circumstances.

OPTIMISM, the doctrine or belief that in the system of things all that happens, the undesirable no less than the desirable, is for the best.

OPUS OPERATUM (i. e. the work wrought), a Latin phrase used to denote the spiritual effect in the performance of a religious rite which accrues from the virtue inherent in it, or by grace imparted to it, irrespectively of the administrator.

ORAN (74), the busiest port in Algeria, is 260 m.  W. of Algiers; it has a Roman Catholic cathedral, a mosque, a school, a college, and two castles, and exports esparto grass, iron ore, and cereals.

ORANGE RIVER or GARIEP, chief river of South Africa, rises in the eastern highlands of Basutoland, and flows 100 m. westward to the Atlantic, receiving the Vaal and the Caledon as tributaries, and having Cape Colony on the S. bank and the Orange Free State, Griqualand West, Bechuanaland, and German Namaqualand on the N.; a bar at the mouth and the aridity of its lower course make it unfit for navigation.

ORANGE RIVER COLONY, formerly Orange Free State (380), lying between the Vaal and the Orange Rivers, Griqualand West, and the Drakenberg Mountains; has an area nearly the size of England, with a healthy, temperate climate; undulating plains slope northward and southward, from which rise isolated hills called kopjes.  The chief industries are the rearing of sheep, cattle, horses, and ostriches; coal-mining in the N. and diamond-seeking in the SW.; the exports comprise wool, hides, and diamonds.  Founded by Dutch Boers from Natal, it was annexed by Britain in 1848, but granted independence in 1854.  The capital, Bloemfontein (3), is connected by a railway with Johannesberg and with the Cape.  Having made common cause with the South African Republic in the Boer War, it was annexed by Great Britain in 1900.  At present (1905) it is under the supreme authority of the Governor of Orange River and the Transvaal Colonies, assisted by a Lieutenant-Governor and an Executive Council.

ORANGEMEN, a name given to an association of Protestants in Ireland instituted to uphold the Protestant succession to the crown, and the Protestant religion as settled at the Revolution of 1688, and which derives this name from William, the Prince of Orange, on whose accession to the throne Protestantism was established; it became dormant for a time after its institution, but it has shown very decided signs of life at political crises when Protestantism seemed in danger, such as often to call for some firm handling.