OCEAN

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OCEAN ; the great mass of waters which surrounds the land, and which probably extends from pole to pole, covering nearly three quarters of the globe. For the sake of convenience, we distinguish different parts of it under the names of seas, bays, gulfs, sounds, and even give the name of ocean to large portions which are partially divided from each other by the continents. But these divisions are arbitrary. The following classification, adopted by MalteBrun, in his System of Geography, has, at least, the advantage of showing, in a striking manner, the connexion which exists between the great masses of water. Its limits are a line drawn from cape Horn to the cape of Good Hope, by Van Diemen's Land, and the south of New Zea land, back to cape Horn. ( a. The Great Archipelago (Oceanica), comprised between the Austral ocean, the Marquesas, the straits of Malacca, and the latitude of Formosa.b. The Northern Oriental ocean, between Asia and North America.c. Southern Oriental ocean, between the Great Archipelago and South America. The Western Basin, forming a sort of channel between the two continents.4. Western \ ocean.( a. Northern ocean, or Frozen ocean (Arctic ocean). &. Atlantic ocean, lying between Europe and North America, and extending south to the nearest points of Brazil and Guinea. c. The Ethiopic ocean, between the At^ .antic and Austral oceans.It has been calculated that the land of the northern hemisphere is to the sea of the same as 419 to 1000 ; in the southern hemisphere, the proportion is" as 129 to 1000. To account for this great dispro portion, it has been conjectured that there is a great southern continent surrounding the south pole ; but the voyages ofnavi gators have not revealed the existence of such an extent of land. The bed of the ocean presents the same irregularities of aspect as the surface of the land. It is diversified by rocks, mountains, plains, and deep valleys. In some places it has been found impossible to reach the bottom; but the notion that it is any where without a bottom is incompatible with the spherical figure of the earth. The mean depth of the ocean has been shown, by Laplace, to be about the same as the mean height of the continents and islands above its surface, which does not much exceed 3000 feet. This distance is but a small fraction of the excess of the equatorial over the polar radius, which is about 60,000 feet. The greatest depth that has ever been sounded is 7200 feet (by Scoresby, in 1819). But it is probable that there are deep cavities or valleys in the bed of the ocean corresponding to the elevation of the mountains on the surface of the earth. Seawater is well known to contain foreign substances mixed with it; its saltness and bitterness give it an extremely disagreeable taste. Its specific gravity varies from 1.0269 to 1.0285. The degree of saltness differs according to different localities; but the difference is not very great. In 100 parts of seawater the greatest proportion of salt is 3.77, and the smallest 3.48. The experiments of Sparmann go to show that the water of the surface, while it is less salt than that at a considerable depth, is much more bitter. Gulfs or inland seas, such as the Baltic, are less salt than the main ocean, on account of the quantity of fresh water poured in by rivers, The polar seas are less salt than the equatorial, owing to the low temperature of the former, which disposes them to deposit the saline substances. Naturalists have endeavored to account for' the saltness of the sea ; some have supposed it to be caused by primitive banks of salt at the bottom; but if such banks exist, they have probably been formed by deposits from the water, rather than been the cause of its saltness ; others have ascribed it to the corruption of vegetable and animal matter conveyed to the sea by rivers ; but if this is true, the saltness would be increasing. Some have conceived the ocean to be the residue of a primitive fluid, which held in solution all the substances of which the earth is composed, and on depositing the others, retained the saline principles which it stfll contains. The only method of freeing seawater from its salt is by distillation; snd the process is so slow that it can rarely be applied to any practical purpose. Even after distillation it retains its bitter taste. This bitterness, which renders seawater so nauseous, probably proceeds from animal and vegetable matter in a state of decomposition. The most common ingredients found in it are muriatic acid, sulphuric acid, soda, lime and magnesia. These substances in combination may form six salts; but it is not probable that all of these latter actually exist at the same time. They are muriate of soda, or common salt, muriate of magnesia, or Epsom salt, sulphate of soda (Glauber's salt), &c. The saltness of the seawater does not preserve it from corruption, as is shown by the water in a ship's hold, and sometimes even in the equatorial seas after a long calm. Many substances are corrupted more rapidly by being plunged into it; and its odor, when corrupted, is extremely offensive. It is preserved pure by its constant motion. The general color of the sea, in the open ocean, is a deep greenishblue ; the blue tint, which is predominant, seems to proceed from the same cause as the color of the sky; the blue rays being reflected in the greatest quantity on account of their superior refrangibility. The other shades, which have sometimes been observed in different seas, seem to be owing to local causes, and often, perhaps, to optical illusions. In approaching soundings, the water assumes a lighter shade. The luminous appear ance of the sea by night is an imposing and magnificent phenomenon. It has been ascribed by some to animals of the zoophyte and mollusca classes, which are said to possess phosphorescent qualities ; some attribute it to the phosphorescence of decajang animal and vegetable substances ; others to the spawn of fish. Some have explained it to be the effect of friction. But the appearances are extremely different at different times, and all these causes probably operate to produce them. Observations made on the temperature of the sea, show that the sun's rays rarely penetrate below the depth of 45, or, according to some, of 113 fathoms, below which the sea receives no light, and consequently little or no direct heat from the sun; and that the temperature increases with the depth to a certain degree, but never to freezing. The constant motion of the sea contributes in some measure to render its temperature equable. (See Ice.) " We must distinguish," says Humboldt, " four different phenomena with respect to the oceanthe temperature of the water at the surface in different latitudes, the decrease of temperature in the lower strata; the effect of waves on the temperature of the surface; and the temperature of currents. The region of warmest water is between 5° 45; N. and 6° 15' S. lat.; and different observations give from 82 to 84 as the maximum. In the parallel of warmest waters the temperature of the surface of the sea is from 3° to 5° higher than that of the superincumbent air." The observations of Humboldt also show that both in the Atlantic and Pacific, in changing the latitude and longitude, the waters often retain nearly the same temperature over a great extent, and that between 27° N. and 27° S. lat. the temperature of the sea is entirely independent of the changes in the atmosphere. From the equator to 25° or 28° N. there is a remarkable constancy of temperature, but in higher latitudes there is more change. (See Temperature.) The great periodical oscillations of the sea, caused by the attraction of the sun and moon, are treated of in the article Tides; the particular movements, which prevail in different parts of the ocean, and set in different directions, are described in the article Currents. (See, also, Winds.) In some places springs of fresh water are observed to issue from the sea, entirely unaffected by the salt water. The most remarkable of these phenomena are in the gulf of Spezia, in the Persian gulf, and in the bay of Xagua, on the south coast of Cuba. It is probable that these are subterraneous streams, which find their way under the bed of the ocean, until they encounter a fissure, into which they are impelled in the same manner as spouting springs on land. A variety of plants are nourished by the ocean, to which are given the general denomination of fuei, and which are vulgarly known by the names of seaweed and rockweed. Some species adhere to the bottom, while others rise to the surface even from a depth of 60 fathoms. In the North Atlantic there is a space extending between lat. 20° and 40° N., and Ion. 20° and 45° W., which is at all seasons covered with a species of weed (fucus natans) of a beautiful green color, whence the Dutch navigators called this tract Kroos Zee, Duckweed sea. (See Fuci.) The great divisions of the sea appear to be inhabited by their peculiar fish, mollusca, zoophytes, &c, and to be frequented by peculiar species of birds. The level of the seas is, generally speaking, every where the same. This arises from the equal pressure, in every direction, which the particles of a fluid exercise upon each other. The 31* ocean, therefore, considered as a wholehas a spherical or a spheroidal surface, which may be considered as the true surface of our planet. Exceptions to this general rule are often, however, to be found in gulfs and landlocked bays, where the waters become accumulated, and stand higher than in the open ocean. (See Islands ; see also Atlantic, Pacific, and Indian Ocean.)