OCEAN AND OCEANOGRAPHY. "Ocean" is the name applied to the great connected sheet of water which covers the greater part of the surface of the earth. But the ocean is less than the hydrosphere in so far as the latter term includes also the water lying on or flowing over the surface of the land. The conception of an encompassing ocean bounding the habitable world is found in the creation myths of the most ancient civiliza tions. The Babylonians looked on the world as a vast round mountain rising from the midst of a universal sheet of water. In the Hebrew scriptures the waters were gathered together in one place at the word of God, and the dry land appeared. The Ionian geographers looked on the circular disc of the habitable world as surrounded by a mighty stream named Oceanus, the name of the primeval god, father of gods and men, and thus the bond of union between heaven and earth.
Since the Pythagorean school of philosophy upheld the spheri cal as against the disc-shaped world, some of the ancient geog raphers, including Eratosthenes and Strabo, looked upon the hydrosphere as forming two belts at right angles to each other, one belt of ocean following the equator, the other surrounding the earth from pole to pole as in the terra quadrifida of Macro bius; while others, including Aristotle and Ptolemy, looked upon the inhabited land, or oikouniene, as occupying the greater part of the earth's surface. Until the discovery of America and of the Pacific ocean the belief was general that the land surface was greater than the water surface. (See MAP.) Only in our own days has the existence of the southern continent been demonstrated within the limits of Antarctica.
Oceanography is the science which deals with the ocean. Of re cent years the use of "hydrography" as the equivalent of physical oceanography has acquired a certain currency, but as the word is also used with more than one other meaning (see SURVEYING) it ought not to be used for oceanography. This article is restricted to general oceanography in its physical aspects and deals with phenomena common to the whole ocean.
The contents of the sailors' scientific logs were brought together by the American enthusiast in the study of the sea, Matthew Fontaine Maury (1806-73), whose methods and plans were adopted at international congresses. Many millions of observa tions are recorded in ships' logs ; this firsthand material is pre served in appropriate offices of various nations. The contents of these logs, it is true, refer more to maritime meteorology than to oceanography properly so-called.
This material for the study of the surface phenomena of the ocean has been supplemented in relation to the study of the depths of the ocean, by the records of numerous scientific expedi tions and latterly by publications embodying systematic observa tions on a permanent basis. Valuable observations were made in oceanography during the expeditions of Captain James Cook and the polar explorers, especially those of Sir John Ross in the north and Sir James Ross in the south. The period of deep sea investigation began about 185o when it became possible to measure ocean depths with precision. (See SOUNDING.) At this time, an exact knowledge of the depths of the ocean assumed an unlooked-for practical importance for the laying of telegraph cables at the bottom of the sea. Another stimulus came from the biologists, who began to realize the importance of a more detailed investigation of the life conditions of organisms at great depths in the sea.
These preliminary trips of scientific marine investigation were followed by the greatest purely scientific expedition ever under taken, the voyage of H.M.S. "Challenger" round the world under the scientific direction of Sir Wyville Thomson and the naval command of Sir George Nares. This epoch-making expedition lasted from Christmas 1872 to the end of May 1876, and gave the first wide and general view of the physical and biological con ditions of the ocean as a whole. Almost simultaneously with the "Challenger," a German expedition in S.M.S. "Gazelle" con ducted observations in the south Atlantic, Indian and south Pacific oceans; and the U.S.S. "Tuscarora" made a cruise in the north Pacific, sounding out lines for a projected Pacific cable. Since that time investigation has been carried out by ships of all nations, on a scale too extensive for detailed record.