Identifier: elementaryphysic00tarr (find matches)
Title: Elementary physical geography
Year: 1907 (1900s)
Authors: Tarr, Ralph S. (Ralph Stockman), 1864-1912
Subjects: Physical geography
Publisher: New York, The Macmillan company
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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the New Englandcoast, the water in summer is warm enoughfor purposes of bathing, while in winter it isnot uncommonly frozen in the shallow har-bors. Even at a distance of a number ofmiles from the shore, this variation fromsummer to winter is quite marked; but inthe mid-ocean, and in the tropical and arcticzones, the summer and winter temperaturesare very nearly the same. In the ocean there is a vertical change intemperature. Since water warms very slowly,the effect of the sun extends only to a dis-tance of a few score of feet, even in the trop-ics ; and below this, the temperature throughout the year ispractically uniform, while it rapidly descends until the coldwaters of the great ocean depths are encountered (Fig.83). Because radiation from a water surface is a slowprocess, the temperature of the water does not becomerapidly lowered during the night. Therefore there is very Via. So. Diagram to showthe normal de-scent of temper-ature in a col-umn of waterin the ocean atthe equator.
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Plates 15. 182 PHYSICAL GEOGRAPHY. little reason for decided changes in temperature, eitherbetween the day and night, or between the seasons. Ocean Currents: Planetary Circulation. — As a result ofdifferences in temperature between polar and tropical re-gions, the air is engaged in a series of great movements.There are many reasons for believing that a similar circu-lation exists in the ocean. The fact of the difference intemperature suggests the probability of such a circulation,which would consist of a rising of the water under theequator, a surface outflow from equatorial to polar regions,and then a downsinking to the bottom, from which therewould be a return to the equatorial regions along the oceanbottom. That this theoretical circulation actually exists, is sug-gested by the fact that the bottom of the sea is inhabited bylarge numbers of animals. If some such circulation as thisdid not exist, it would be difficult to account for the supplyof oxygen which these creatures need f

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