THE INTERIOR OF THE EARTH.
By Rev. B. J. WESXfeaooKE. No. 111. There ax*e two principal roosomp for* believing that the interior of the e«coh is not molten. The first—but not tlx* most important—l propose now to review. It may be briefly stated thus :—The interiorof the earth must be subject to immense pressure from the super incumbent matter. Now, it is thought that pressure exercises, a great influence over the fusing point of ’ bodies, and it is thought that this principle* may greatly modify the results of the* groat heat in the interior of the earth. Perhaps this will be better undei'stood 1 if the difference between gases, liquids,. and solids, be explained ; for it must be' understood that I do not presume to* write for men we 1 l read in science, 'Sut* simply for ordinary readers. Well, then,, each of these bodies consists of uktinatej particles, or- atoms (i.e., not mnfc' or ■ divided), and, in each of the three:—gases,-, liquids, and snKds—the particles emuport: themselves differently. In gases the = particles repel each other, so that if a >*ery ■ small cp'WM)ity of gas bo placed in a very - large vessel 1 the particles wiM get is far * away- from each other aa the: size o’ the » vessel-will allow, and the particles wll be • so diffused throughout it that the grs nay bo said to fill the vessel-.. The ato ■ a of gases are constantly tending to get -u>. far - away from each othea- as possible. In liquids, on the other-hand, the par lea • attract each other* but not ao strongly but that they are const tly moving in and out in a wavy path r all directions, so that a particle at one p r of’ the liquid will, at a certain, time, '• sve - traversed all the different parts ono ter another. But in the case of solids the attra ion . is stronger, and the particles are al ayswitlxin the range of each other's a on,. and, although it is thought by m n of science that each particle can oso late* about its mean position, and even pin. about any axis in that position/ afl i the > case of vibration or contusion (beet iap
Simply of the atoms of a body) yet those^lrtides wo not able to change that position timlly and go and take up another position, as in gases and liquids. But when a certain amount of heat is applied, the cohesion of particles is overcome, and they move as in a liquid state. Now it will, I think,be seen that whenjieat is applied under circumstances of great pressure the pressure tends to prevent the free action of particles in that wavy movement which characterizes the particles of a liquid simply for the want of room to move. The greater the pressuse, the greater must be the heat before a body can become molten. Thus, sulphur, for example, has its fusing point raised from 237 deg. Fah., at the ordinary atmospheric pressure, to 285 deg. at 519 atmospheres (an atmosphere is 16 pounds to the square inch); and zinc heated 1 deg. C. occupies more bulk by one thousandth part of its original bulk; while glass is increased by a four thousandth of its bulk Now, it is held that the pressure of superincumbent matter upon the centoe of the earth is so immense that it presses upon the ultimate particles and forces them together, and, overcoming the tendency of heat to liquify, holds them as rigid as a solid body. How great this pressure is at the centre of the earth may be gathered from Professor Leslie's statement, “ That at a depth of 34 miles, air would be as heavy as water ; and water at 362 miles as heavy as mercury.” The astounding statement has also been made that at the centre of the earth cold steel would be compressed by this immense pressure into a fourth of its bulk, and ordinary stone into one eighth. Under the heading “The Earth’s Density,” Sydney B. J. Skertchley makes the following calculation, which bears somewhat upon this subject of pressure : “Water is one of the most incompressible of substances, and was, indeed, for a long time deemed to be absolutely rigid. Refined experiments have shown, however, that the pressure of an atmosphere reduces the bulk of sea-water one 44millionth. Now a column of water 32ft. high and of one inch sectional area, weighs 16 pounds. Suppose the earth to be made of sea-water, having the ordinary density at the surface, which density we will call 1. Taking the earths radius at 4,000 miles we have 660,000 atmospheres at the centre. The water at the centre will consequently be compressed into (660,000 x 0 000044, 29-040) one twenty ninth of its bulk at the surface. . . Or to vary this illustration : If we take the area of the ocean at 146,000,000 square miles, and the mean depth at 2 miles, it could be poured into a cavity 2\ miles square, reaching from the surface to the centre of the globe.” I think I have said enough to show that pressure of superincumbent raatteris, at the the centre of the earth, immense ; and may account for the -earth, in its obedience to the laws of gravitation, showing signs of being rigid to the centre, but I must defer this aspect of the question until my next.
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