POROSITY

1529               PORT ARTHUR SHIP-CANAL

body, about forty inches long, with a short tail. The hair is dark brown, and the spines are from four to six inches long. They are almost hidden in the hair. It is found in New England, New York, Pennsylvania, Ohio and northward and northwestward. It should never be called hedgehog, for the latter is not a gnawing animal but an insect-eater, smaller, weaker and not found in America. Porcupines are slow-moving and slow-witted creatures. The idea that they can shoot their quills is a mistaken one, but when attacked they strike with the tail, and quills are thus driven into the disturber. When alarmed, the quills are raised erect, the animal presenting its bristling appearance. The tree-porcupine of tropical South America and Mexico is of slighter build, and has a tail capable of grasping.

Poros'ity, a term by which we express the fact that no body of matter, whether solid or liquid, completely fills the space it occupies, as the particles or molecules of all bodies have spaces between them filled with air, and these spaces are called pores. Many objects, as wood and cloth, show their porosity by the readiness with which they absorb water or any other liquid. Under heavy pressure water has been forced through iron, silver and other metals; and the porosity of water itself has been proven by mixing it with alcohol and noting the fact that the bulk of the mixture is much less than the sum of the two bulks before the mixture.

Porphyry (pr'f-rŷ), igneous rocks made of large and distinct crystals imbedded in a matrix of small and often indistinct crystals. The term also is sometimes applied to lavas, the matrix of which is but partly crystalline. The name, therefore, refers to the structure of the rock, not to its composition. A granite would be called porphy-ritic if some of its crystals, for example some of its feldspar crystals, were conspicuously larger than others. A quartz porphyry is one in which the conspicuous crystals (phenocrysts) are all quartz. Light-colored igneous rocks are more commonly porphy-ritic than dark ones.

Porpoise (par'pus), a sea-mammal belonging to the group of toothed whales. They are similar in general appearance to dolphins, but have a shorter snout. They are dark above and whitish below. Porpoises are common in the North Atlantic near shore, and often ascend rivers. They feed on such fish as mackerel and herring, for the capture of which their teeth are well-adapted. The bay-porpoise of the Pacific coast is the

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porpoise

smallest of the whale family, being often not more than four or five feet long. Some other species reach a length of about nine feet. Their very thick hide is beaten down and made into soft leather. Their fat yields oil of fine quality. '

Port Ar'thur, called by the Chinese Lu-shun-k'ow, is a naval station on the northern coast of China, in the province of Shing-king, about 275 miles east of Peking. Up to 1881 it was merely a harbor of refuge for coastwise sailing vessels; but in that year China determined to make it a naval port for her northern squadron. It is entirely surrounded by hills; and at great expense it was fitted with dry docks, foundries for casting heavy ordnance and everything needful to constitute an important station. It grew from a mere handful of mud huts in 1881 to a place of 6,000 inhabitants in 1893. In 1894 it was destroyed by the Japanese as a result of the war with China. In 1898 Russia obtained a lease of this harbor for twenty-five years, subject to renewal ; and with it was obtained possession of the adjacent seas and all the Chinese territory to the north. Port Arthur, though small, is naturally impregnable; and its many fortifications were made still more formidable by the Russian authorities. The acquisition of Port Arthur by Russia led to the occupation of Wei-Hai-Wei by Great Britain. In 1905 Japan captured Port Arthur from Russia after a long and terrible siege, and China, after the conclusion, of peace between Japan and Russia, ceded Port Arthur to Japan. See Chinese Empire, Japan and Russia.

Port Arthur, Can., a city on the western shore of Thunder Bay, in Lake Superior, Ontario. It is a divisional point on the Canadian Northern Railway and is the main line of the Canadian Pacific. It and Fort William (g. v.), twin cities almost joining, are at the head of lake-navigation. It, therefore, is a point of transhipment for much of the merchandise consigned by merchants east to the settlers on the western plains and for the grain from Canada's western wheat-belt, which is transhipped to the lake-vessels. The prosperous future of the west is assured, and therefore the location must bring prosperity to these twin cities. The elevators at Port Arthur will handle 9,000,000 bushels of grain. It is the terminus of the Northern Navigation Co., the Booth and White line and the Montreal and Lake Superior Steamships. Port Arthur has an extensive blast-furnace and immense docks; falls in its immediate vicinity can supply 150,000 horse-power. Its lumbering interests are very important. Population 14,000.

Port Arthur Ship=Canal, Tex., is an artificial waterway deriving its name from the town on Sabine Lake. This, which is three miles long and ten wide, marks the.