Pacific Ocean, the largest ocean on the globe, bounded E. by the American continent, N. by the same and by the chain of the Aleutian islands (Behring sea not being properly oceanic in its character), and W. by the chain of continental islands and peninsulas lying off the coast of Asia, the chain of the Melanesian islands, and the continent of Australia. This whole boundary, starting from the S. part of Chili, following up the line of the Cordilleras through Central and North America, the Aleutian islands, and the islands E. of Asia, and continuing it from Papua through the New Hebrides and New Caledonia to New Zealand, is remarkable as being, with some interruptions, the great zone of volcanoes; no fewer than 400, extinct and active, being known on that line. The southern limit, as in the Atlantic and Indian oceans, is an artificial one, the Antarctic circle. The first European discoverer of the Pacific ocean was Vasco Nunez de Balboa, who on Sept. 26, 1513, saw it from one of the mountains near the isthmus of Da-rien. It was first traversed by Magalhaens, from the strait bearing his name to the Philippine islands (1520-'21). From him it received its name of Pacific, on account of the constant fair weather which accompanied him during his voyage.

It is also called the Great ocean with more propriety, or the South sea, a title now nearly obsolete. The E. or American shore is remarkably uniform and almost unbroken, except by the fiords of Patagonia, British America, and Alaska, and by the gulf of California. The N. and W. shores are broken into innumerable islands, separating its waters from a chain of inland seas, such as Behring sea, the Okhotsk, Japan, and Yellow seas, the E. and S. China seas, and the Banda, Arafura, and Coral seas. This configuration has had a great influence on the migration of the populations, and on the comparatively high and early civilization of some of them, such as the Chinese and Japanese. - The depth of this ocean is not yet known in much detail. By means of the recorded time of transmission to California of the waves produced by an earthquake in Japan, Prof. Bache calculated the depth as between 2,000 and 2,400 fathoms. Another calculation based on the movement of the waves of the great South American earthquake of 1868, by Prof. Hoch-stetter, gave somewhat less than 2,000 fathoms.

The soundings made in 1874 by Com. Belknap in the United States steamer Tuscaro-ra, between California, the Hawaiian islands, and Japan, give an average very near Prof. Bache's results, a brilliant confirmation of Prof. Airy's formula on which the calculations were based. The maximum depth is about 3,000 fathoms. Similar depths were found by the Challenger expedition (1874) in the south Pacific, and in the Melanesian, Celebes, and Sooloo seas; in these latter the decrease of temperature with depth ceased at a point of equal depth with the lowest part of the rim of the submarine basin enclosing them, and below this the temperature remained constant; a phenomenon similar to that observed in the Mediterranean. The soundings of the Challenger in the Pacific confirm the observations made by the same party in the Atlantic, viz., that below 2,250 fathoms on an average the gloligeriva deposits are no longer found, the bottom consisting of red clay. - The currents resolve themselves into two systems, as in the Atlantic. The southern one in its general features forms a revolving stream turning from right to left, the northern one revolving in the contrary direction.

The former originates in the southwest and south by the combination of the south Australian current, coming from the Indian ocean, with the great antarctic drift. This current moves E., crossing the whole breadth of the ocean toward the coast of South America; before reaching it, it divides into two branches, the northern or current of Mentor trending 1ST. E. until it reaches about lon. 78° W., when it turns W. in a wide sweep to join the S. equatorial current. The southern branch strikes the American coast, gives off the Cape Horn current, passing around that cape into the Atlantic, then runs N, hugging the coast under the name of the Humboldt or Peruvian current, nearly up to the equator, where it turns W. and crosses the whole of the ocean as the S. equatorial current, following nearly the parallel of 10° S. The Humboldt current, receiving much of its water from the antarctic regions, is cold, and reduces the temperature of the South American coast much below the degree due to the latitude.

At the Galapagos islands Capt. Fitzroy found the temperature of the water only 60°, while just outside the group on the north it was 80 in the water coming from the direction of the bay of Panama. The S. equatorial current divides into several branches in the vicinity of the Tonga islands, one of them running into Torres strait, and another along the E. coast of Australia, sweeping round toward New Zealand. A little N. of the equator, a counter current is found running E. across the whole ocean and separating the N. and S. equatorial currents; this is the belt of the equatorial calms. The N. equatorial current strikes the coast of Asia near the island of Formosa, and is deflected N. and N. E., forming the Japan current (Kuro-Siwo or Black stream), the counterpart of the Gulf stream of the Atlantic. It gives off the Kamtchatka current, running up toward Behring strait, but the main body crosses over toward Alaska, carrying warmth and moisture to that country, then runs S. as the coast current of California, and off the coast of Mexico returns into the equatorial circulation. - The trade winds are found to blow with regularity only in that part of the ocean most free of islands.

Thus the S. E. trades can be depended on only between the meridians of the Galapagos and Marquesas islands, and between the tropic of Capricorn, or at the most 30° S., and the equator or even a little N. of it. The N. E. trades are chiefly confined between lat. 30°. and 10° N., these limits varying somewhat with the sun's declination. In longitude they are encountered about 200 leagues off the coast of America, and as far as the Ladrone islands. A belt of calms and variable winds is encountered a few degrees N. of the equator. Along the coast of America. and among the islands of Polynesia, including Melanesia and Micronesia, there are areas of periodical winds, in some parts as regular as the monsoons of the Indian ocean. On the coast of Chili northerly winds prevail from May to September, and southerly from October to May. On the coast of California it blows from N W. during the summer months, and from S. E. to S. W. in winter. Among the islands of Polynesia situated in the region of the S. E. trades, this wind blows regularly between March and October, while westerly winds prevail the rest of the year, with occasionally violent storms. Between the Ladrone and Philippine islands the monsoon is more regular, N. E. from May to April, and 8. W. during the other months.

As in the Indian ocean, the change of the monsoons is accompanied by storms; but hurricanes of the type of those of the West Indies or Mauritius are not known in the greater part of the Pacific, the exception being the region W. of the Ladrone archipelago, into which the typhoons of the China seas sometimes extend. They occur most frequently in May and June, October and November. - The tides of the Pacific exhibit in a much larger degree than those of the Atlantic the diurnal inequality (see Tides) by which one of the tides of the day is rendered much higher than the other. In some places this is so marked that to ordinary observation there appears to be but one tide in 24 hours. At Tahiti the solar tide exceeds the lunar, a phenomenon which has thus far not been observed in other parts of the world, though it probably prevails throughout that part of Polynesia. - The Pacific ocean is noted for the great number of its islands. We have already mentioned the continental islands forming its western limits. The others, called oceanic islands, are grouped according to certain principal directions, like the summits of submerged chains of mountains. As in these, the direction is not perfectly constant, and the chains are formed by several parallel courses.

According to Dana, there are two principal trends in these islands, a northwesterly and a northeasterly one, crossing each other at right angles. The former is the prevailing one. To it belong the Hawaiian chain, in the prolongation of which, though without connection, are found the Galapagos. The great Polynesian chain is formed of a number of links, parallel or overlapping, beginning in the west with the Pelews, and continuing through the Caroline, Ralick, Radack, Kingsmill, Samoa, Society, and Paumotou islands; in the continuation are found Easter island, and at a long distance Mas á Fuera and Juan Fernandez. The Marquesas and Fanning islands form a parallel chain. The Australasian or Melane-sian system is connected with the continent of Asia through Java and Sumatra; it comprises Papua, the Admiralty, Louisiade, Solomon, New Hebrides, and Loyalty groups, New Caledonia, and the northern part of New Zealand. To the northeasterly system of trend belong the main part of New Zealand with the Auckland and Macquarie islands, and as a parallel chain Chatham, Bounty, Campbell, and Emerald islands. The Feejee. islands lie near the intersection of several chains, and are difficult to associate with either. The Ladrone and Bonin islands belong also to the northeasterly system.

All the oceanic islands of the Pacific are either volcanic or formed of coral; in fact they may all be referred to the former origin, those formed only of coral marking the place of a volcanic peak in an area of subsidence. Dana has given, in his "Corals and Coral Islands/' what are supposed to be the areas of subsidence and elevation in the Pacific - The inhabitants of the Pacific islands belong to two distinct races, the Malaysian and the Polynesian. (See Malayo-Polynesian Races.) Their distribution is one of the most interesting chapters of ethnology, connected as it must be with the prevailing course of winds and currents. They have carried with them almost everywhere the dog, the pig, and the domestic fowl. In many of the groups of islands the natives have at the present day generally embraced Christianity, but at the same time have received the curses apparently inseparable from the introduction of civilization among savage nations, under the influence of which the population is diminishing with fearful rapidity.

The white race is rapidly encroaching, and displacing the natives, particularly since the more progressive Anglo-Saxon branch has occupied the shores of this ocean, and established new centres of civilization in Australia, California, and New Zealand. Lines of coasting steamers are established along the whole coast of America, from Alaska to the straits of Magellan, and the coasts of Australia and New Zealand; and transatlantic lines have brought into close connection California, the Hawaiian islands, Japan, China, and Australia. - The marine mammalia of the Pacific have played an important part in the commercial history of the world, but they are being rapidly destroyed. The fur of the sea otter, formerly very common on the northern shores of America and Asia, was at the beginning of this century a most valuable article of trade. Ships used to be fitted out, particularly in Boston, for the purpose of buying these furs from the natives, carrying them to China, where the highest price could be procured, and investing the profits in silks and teas for the return voyage. This trade has entirely ceased.

Eared seals, to which division of the family the sea lions and fur seals belong, are found on the coast of South America as far north as the Galapagos islands, the cold current of the coast of Peru proving thus congenial to them as far as the equator. The huge sea elephant, which formerly abounded on the S. coast of Chili and at Juan Fernandez, has been so much hunted for its oil that it has almost entirely disappeared from these parts; but it is still found in the islands bordering on the Antarctic circle. The northern fur seal is now protected by law. The dugong is found on the N. coast of Australia; an allied animal, Steller's sea cow, formerly inhabited the westernmost Aleutian islands, but is now entirely extinct. The whale fishery is still extensively pursued in the Pacific, though the profits are diminishing every year. The right whale of the north is not found on the American coast further south than Vancouver island, but on the Asiatic side it reaches the south of Japan; the sea of Okhotsk is a favorite resort of the whalers in pursuit of it.

Another species is found S. of the tropic of Capricorn. In the warmer parts of the ocean it is replaced by humpback and other whales of the tinner family, which are taken in considerable numbers on the coast of California. Sperm whales formerly abounded in the tropical regions, certain parts being more frequented than others. They are said by Maury to cross into the Atlantic around Cape Horn. They are not found near the American shore north of Panama, nor in the Asiatic seas bordering on the Pacific. Fish are abundant everywhere, and constitute an important item in the food of the populations, but do not yet form an article of commerce comparable to the cod and herring of the Atlantic. Mollusks and Crustacea present a great variety, the shells being particularly noted for their beauty. Among the echinoderms the holothurm or sea slugs deserve mention as forming an article of trade for the China market under the name of tripang or biche de mer. The corals have been mentioned as forming a large part of the Polynesian islands; others they surround by fringing and barrier reefs. Their geographical distribution is dependent on the temperature of the currents.

Thus on the American coast no corals are found S. of the equator, on account of the cold Peruvian current, nor on the North American coast S. of the extremity of the Californian peninsula. But in the western part of the ocean coral reefs are found in abundance in a range of latitude extending from 24° S., the extremity of the great Australian reef, and 25° S. among the Paumotou islands, to 28° 30' N. among the small islands N. W. of the Hawaiian group. - The North Pacific has its Sargasso sea, bearing the same relation to the Japanese and North Pacific currents which the Atlantic Sargasso sea bears to the Gulf stream. (See Atlantic Ocean.) It is situated N. of the Hawaiian islands, but is little known in its details. Our knowledge is still more scanty with regard to an accumulation of seaweed to the eastward of New Zealand.