Inequalities of the Earth’s Surface
The earth is a spherical body, or, more correctly, an elliptic spheroid. Its surface, therefore, may be considered equidistant from its centre point within, and of uniform curvature. This is so as regards the ocean, which is
“Unchangeable save to its wild waves’ play;”
but the surface of the land is very diversified. In parts it is spread out into plains; in others, into easy undulations. Here and there it rises into hills, with valleys and extensive basins between them; while at places chains of mountains appear at varying altitudes, some of which penetrate the clouds.
Although the irregularities of the small portion of land which we can see at one view seem very considerable, and more especially the largest mountains, yet these protuberances are insignificant when compared to the magnitude of the earth itself.
Mount Everest, in Nepaul, is the loftiest point of the Himalaya chain, and the highest mountain in the world. It rises 29,002 feet—equal to 5·49 miles,—above the level of the sea. This height is only
( 7912·40
————
5·49 ) 1
————
1441
part of the earth’s diameter; or equal to 1 inch placed on a globe
( 1441
——
12
=
)
120 feet in diameter. It therefore bears the same proportion to the diameter of the earth that a grain of sand, the ninetieth part of an inch in diameter, does to a globe
( 1441
——
90
=
)
16 inches in diameter.
“If we would construct a correct model of our earth, with its seas, continents, and mountains, on a globe 16 inches in diameter, the whole of the land, with the exception of a few prominent points and ridges, must be comprised on it within the thickness of thin writing paper; and the highest hills would be represented by the smallest visible grains of sand.”17
Astronomers have measured the distances and weighed the masses of the planets, yet the height of the atmosphere and the depths of the ocean are unsolved problems. The bottom of “blue water” is almost as unknown to us as the interior of the earth. It is a common opinion that the greatest depths of the sea are about equal to the greatest heights of the mountains. Attempts have been repeatedly made to sound out its depths, but no reliance can be placed on any reports of soundings beyond 8000 or 10,000 feet. One ran out his sounding-line 34,000 feet, and did not touch bottom; another 39,000 feet with the same result; one reported bottom at 49,000 feet, another at 50,000 feet. But there are no such depths. There are currents and counter-currents in the ocean, as in the air, which operate upon the bight of the sounding-line, and cause it to run out after the weight has reached the bottom, so that the shock cannot be felt.
The oceanic circulation is as complete as that of the atmosphere, and is possibly subject to, or governed by, the same laws; and there appears to be a law of descent through “blue water,” the same as there is a law of ascent through “blue air.” The one increases in density downwards as the other decreases in density upwards; and the development of this law proves that the sea is not so deep as reports made it.
There is a set of currents in the sea by which its waters are conveyed from place to place through regular and certain channels, traversing from one ocean to the other with the regularity of the machinery of a watch. The chief motive power of marine currents is caused by heat. But an active agency in the system of circulation is derived from the salts of the sea-water, by winds, marine plants, and animals. These give the ocean great dynamical force.
The only reliable deep-sea soundings are those obtained by Brooke’s plummet; and the greatest depths at which the bottom of the sea has been reached with this plummet are in the North Atlantic Ocean, and do not show it to be deeper than 25,000 feet, the deepest place being immediately to the south of the Grand Banks of Newfoundland. Thus, from the top of Mount Everest to the deepest reliable sea bottom reached by sounding, we have a vertical height of nearly 10¼ miles, equal to
( 7912·40
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10·23 ) 1
——
773
rd part of the earth’s diameter.—The Builder.