_The Indian Ocean_ is simply the extension of the vast southern water-zone northward of parallel 40°, south latitude, where, from the Cape of Good Hope to Tasmania, it is six thousand miles in width. At this line the depth suddenly decreases, as though the edge of a submerged Antarctic plateau defined the southerly rim of its basin there. This ocean contains several large and some groups of small islands, but these are mostly near the shore, and connected with the neighboring continent by shallow waters, showing that they rise from a submerged plateau. The average depth of the Indian Ocean is about fourteen thousand feet; its surface-water is warmer and salter than that of any other; and its winds and weather are more regular and peaceful than in either the Atlantic or the North Pacific. _The Arctic Ocean_ is the well-defined body of water around and probably over the north pole. It is connected with the Pacific only by the narrow and very shallow Bering Strait, and with the Atlantic by comparatively narrow openings. It has been fairly well explored as far north as the parallel of 80°, and found to contain many islands; but it appears that there is great depth of water north of Spitzbergen and northeast of Greenland, making it probable that the trough of the Atlantic reaches to or beyond the pole itself. Most of its area is covered with drifting ice. _The Antarctic Ocean_ is regarded as the space of water within the Antarctic circle; but this is surrounded by a zone of deep ocean, unbroken almost half-way to the equator, except by the narrow southern part of South America and by New Zealand. It is an area, apparently rather shallow, of ice, fogs, and tempestuous gales, inclosing lands of unknown extent. [Illustration: WAVE-WORN CLIFFS AND PEBBLE-BEACH AT ETRETAT, FRANCE. (FROM A PAINTING BY WILLIAM P. W. DANA.)] But these geographical distinctions are merely convenient methods of speech. After all, there is only one ocean “poured round all,” and its particles are incessantly changed in place and remingled by means of a world-wide system of tides and currents, the effect of which is to keep sea-water everywhere uniform in character and perfectly pure and healthful. [Illustration: IN MID-OCEAN: A GREAT WAVE.] CHAPTER II WAVES, TIDES, AND CURRENTS Now that we have studied the ancient ocean, it is time to study its present characteristics and understand the great and important part it plays in the world.