THE INFLUENCE OF THE OCEANS features of man's geographical surroundings are more impor tant than the division of the earth's surface into continents and oceans. At first thought one might say that only the lands are really necessary. We live on the lands; their soil yields food for man and beast; the lands contain mines from which we extract minerals; we travel chiefly upon the lands; and even when we traverse the oceans it is only to reach some other point upon the lands. It would seem that the ocean merely covers three-fourths of the earth's surface which might otherwise form fertile plains supporting millions upon millions of people. Such a view is wrong, however, for the oceans are as neces sary to man as are the lan4 They are of the greatest service in the following five respects: (1) as a source of rain; (2) as regulators of temperature; (3) as an aid to health; (4) as a source of minerals; and (5) as a source of food. Oceans also serve (6) as barriers, and (7) as carriers of commerce. In these two respects the relation of the oceans to transportation is the reason for their profound effect upon man's life. In most respects large lakes act in the same way as oceans.
Why the Oceans are Important.—(1) As a Source of Water for Clouds and in the heart of a continent much of the rain consists of moisture wafted thither by winds from the ocean. If the crops depended only on moisture evaporated from the lands including their lakes and rivers, they would be as scanty as in deserts. Nebraska and the Dakotas, although in the middle of a continent, raise millions of bushels of wheat by means of water from oceans over 1000 miles away. Practically all the world's corn crop depends on summer rains from oceans 500 to 1500 miles away. This is not surprising for two chief reasons: (a) The evaporation from the land is usually less than from the same area of water, as is evident from the dampness of a sea breeze compared with the dryness of a land breeze; (b) the area of the oceans is two and a half times that of the lands, and two hundred times that of all the lakes, rivers, swamps, and other bodies of water on the lands, including the great Caspian Sea. If all
the lakes in the world should be evaporated they would supply only one-fifteenth of the rain that falls each year on the lands.
(2) Oceans as Regulators of Temperature.—In addition to supply ing moisture the oceans prevent the land from becoming too hot or too cold. Water becomes warm much more slowly than the materials that form the land, and is correspondingly slow in cooling. Moreover since water is easily movable it is blown about in the form of currents which carry warm water from the torrid zone toward the poles and cold water from polar regions toward the equator. Because water heats and cools slowly and because the warm and cool parts are mixed by currents, the ocean is warmer than the lands in winter and cooler in summer. Hence winds that blow across the oceans are warmed by the water in winter, and cooled in summer. Thus when they reach the lands they make the summers cooler and the winters warmer than they wouki otherwise be. How great this effect is may be seen by comparing Seattle, Washington, where the Pacific Ocean influences the temperature, with Bismarck, North Dakota, which is far from either ocean. In January while the farmers around Seattle are plowing in an average temperature of about F. for day and night together, those around Bismarck, where the average is only about can do little except feed their cattle and protect them from bliz zards. In July, on the contrary, the average at Seattle is and at Bismarck so that wheat grows much better at Bismarck than at Seattle. If there were no oceans all parts of the United States would have extremes much greater than those of Bismarck so that the summers would be unbearably hot and the winters unbearably cold. It is well that the continents are surrounded by great oceans.