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408 of facts carefully considered and elucidated. We shall say a few words concerning what has been done in this line of thought by different nations, with the character which their peculiar temperament, the conditions of their past and of their present have given to their work. In fact, just as the acts of each man, physical as well as moral, are marked with the special imprint of his personality so in the domain of science every race stamps its work, the product of its collective intelligence, with an impress peculiar to it, which constitutes the very essence of its genius.

Oceanography is the study of the sea. Static oceanography deals with salt water considered independently of the movements which are manifested in it; it treats successively of the topography of the ocean beds and of their formation, their lithology. It analyzes the waters, their composition and their influence on the nature of the depths, their numerous physical properties, the effect on them caused by changes of temperature, their density, their compressibility, the way in which light is diffused throughout the superposed strata, and the different optical phenomena. The ice of the polar region offers subject matter for a chapter on the effect of cold on the sea.

In dynamic oceanography the ocean is studied in motion. We study the waves, which move the surface under the influence of the wind, and the currents, which, like the network of our arteries and veins, traverse its mass to a certain depth, and result from the simultaneous actions of heat, evaporation, the topography of the sea bottom, the geographic configuration of the surrounding continents, the climate, the force of the winds; in a word, from the total of exterior causes which, whatever they may be, all exert some influence and in turn are influenced—a constantly recurring cycle of change whose cessation would bring instant death to our planet as the last beat of the human heart terminates the life of the body. Dynamic oceanography also includes the study of the tides, whose rhythmic movements accord with those of the stars, and the examination of those processes by which the débris of the continents, swept off by winds or washed away by rivers, reach the great common reservoir, are diffused throughout its waters, descend in a shower to the very lowest depths, and there accumulate to form rocks like the greater part of those which we find now on our continents and which formed the bottom of the oceans of former ages. It deals with the phenomena that result from the contact between sea and land, seeks out the laws which control the formation of deltas or of the bars which extend across the mouths of rivers, the filling up of estuaries, the way in which waves and currents shape the contours of the shores, dunes, lagoons, and those madreporic formations—atolls and coral islands—conquests of organic life over inorganic matter, of the infinitely small, the zoophyte, over the infinitely powerful, the ocean.