Pacific Ocean, the largest of the great divisions of the ocean, occupying about one-half of the water-surface of the globe and more than one-third of the area of the world. It is almost landlocked towards the north, communicating with the Arctic Ocean by the narrow (40 miles) and shallow Behring Strait, whereas it opens widely into the deep Southern and Antarctic Oceans. Its length from north to south (the Antarctic Circle) is about 9000 miles; its greatest breadth, at the equator, is over 10,000 miles; its area is approximately 70,000,000 sq. m. It was first seen by Europeans in 1513, when Balboa, with a few followers, viewed its waters from the summit of a peak in Darien; the first European to sail upon it was Magellan (1520), who gave it the name Pacific. Sir Francis Drake was the first Englishman to sail upon it (1577). The area of land draining into it - 7,500,000 sq. m. - is less than half of that draining into the Atlantic. The largest American river flowing into it is the Yukon (2000 miles); others are the Fraser, Columbia or Oregon, Sacramento, and Colorado. The South American rivers are little more than mountain-streams. The Asiatic rivers include some of the largest rivers of the world - the Amur, Hoang-ho, Yang-tse-kiang, Mekong, and Menam. Generally speaking, the American and Australian coasts bordering the Pacific are mountainous and free from indentations, while the Asiatic coasts are low and fertile, with many gulfs and bays, and fringed with island groups.

The Pacific Ocean is remarkable for the innumerable small islands and island groups which stud its surface, but the area occupied by the truly oceanic islands is very small; they are principally congregated towards the central and western portions of its basin, while the eastern portion is comparatively free from islands. The larger islands - Borneo, New Guinea, Celebes, Java, Sumatra, etc. - are continental. The oceanic islands - the Sandwich Islands, Ladrones, Carolines, Gilbert Islands, Solomons, Fiji, Friendly Islands, Samoa, etc. - of the Pacific are all either of volcanic or coral origin, the volcanic islands within the zone of coral-reef builders being fringed with coral reefs, while many are entirely of coral formation. Some of the greatest depths in the world occur in the Pacific, in its western basin; on the whole it is deeper than the Atlantic, its mean depth being about 2500 fathoms. The eastern basin is comparatively uniform in depth, between 2000 and 3000 fathoms. The western basin is much more diversified, numerous groups of islands, shallow water, and immense depths occurring irregularly. The Challenger's deepest sounding, 4575 fathoms (nearly 5 1/4 miles), was in the sea between the Caroline and Ladrone Islands, while the American ship Tuscarora found a depth of 4655 fathoms to the north-east of Japan. The surface-currents of the Pacific Ocean depend to a great extent upon the direction of the prevailing winds, the principal of which are the two trade-winds, blowing more or less constantly, the one from the north-east, the other from the south-east. Between these two regions is what is called the equatorial belt of calms. In addition to the trade-winds, there are the monsoons, which blow with great regularity, but the direction of which changes according to the season. A cold surface-current flows constantly northwards from the Antarctic. The great equatorial current flows to the westward. The temperature of the surface-waters of the Pacific varies with the season, but in the tropical regions the variation is very small. The highest temperature occurs among the islands of the Malay Archipelago and off the Mexican coast, where the mean temperature rises to 85° F. The temperature of the water below the surface as a general rule decreases as the depth increases, the lowest temperature occurring at great depths, where the bottom temperature appears to be nearly constant all the year round, usually about 35° F.