POSITIVISM, the philosophy so called of AUGUSTE COMTE (q. v.), the aim of which is to propound a new arrangement of the sciences and a new theory of the evolution of science; the sciences he classes under the categories of abstract and concrete, and his law of evolution is that every department of knowledge passes in the history of it through three successive stages, and only in the last of which it is entitled to the name of science—­the Theological stage, in which everything is referred to the intervention of the gods; the Metaphysical, in which everything is referred to an abstract idea; and the Positive, which, discarding at once theology and philosophy, contents itself with the study of phenomena and their sequence, and regards that as science proper.  Thus is positivism essentially definable, in Dr. Stirling’s words, as “a method which replaces all outlying agencies, whether Theological deities or Metaphysical entities, by Positive laws; which laws, and in their phenomenal relativity, as alone what can be known, ought alone to constitute what is sought to be known.”  See Dr. Stirling’s “SCHWEGLER.”

POSSE COMITATUS, a Latin expression, signifies the whole coercive power of a county called out in the case of a riot, and embraces all males over 15 except peers, ecclesiastics, and infirm persons.  These may be summoned by the sheriff to assist in maintaining the public peace, enforcing a writ, or capturing a felon; but usually the constabulary is sufficient for these duties.

POST RESTANTE, department of a post-office where letters lie till they are called for.

POTEMKIN, Russian officer, born at Smolensk, of Polish descent; a handsome man with a powerful physique, who attracted the attention of Catharine II., became one of her chief favourites, and directed the foreign policy of Russia under her for 13 years; is understood to have been an able man, but unscrupulous (1736-1771).

POTOMAC RIVER, rising in the Alleghany Mountaine, flows 400 m. eastward between Maryland and the Virginias into Chesapeake Bay; the Shenandoah is the chief tributary.  The river is navigable as far up as Cumberland, and is tidal up to Washington, which is on its banks.

POTOSI (12), an important mining and commercial town of Bolivia, situated 13,000 ft. above sea-level on the slopes of the Cerro de Potosi; is one of the loftiest inhabited places on the globe, but a dilapidated, squalid place.  There is a cathedral, next to Lima the finest in South America, a mint, and extensive reservoirs; the streets are steep and without vehicles; the climate is cold, and the surrounding hillsides barren; the industry is silver mining, but the mines are becoming exhausted and flooded.

POTSDAM (54), 18 m.  SW. of Berlin, stands on an island at the confluence of the Nuthe and Havel, and is the capital of the Prussian province of Brandenburg; a handsome town, with broad streets, many parks and squares, numberless statues and fine public buildings; it is a favourite residence of Prussian royalty, and has several royal palaces; was the birthplace of Alexander von Humboldt; has sugar and chemical works, and a large violet-growing industry.