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the final result of all these operations is very nearly what we have stated above.
But while we have thus found out the general dimensions of the earth, we have discovered that the form is not exactly that of a sphere. The length of a degree increases as we proceed from the equator toward either pole. We hence infer that the earth is flattened about the polar regions, and more convex between the tropics. The average length of a degree is 6915 miles. But the length of a degree in latitude 66°, is about two-thirds of a mile greater than at the equator. The same phenomenon is indicated also by the pendulum. A clock which keeps correct time at the equator, is found to gain more and more as it is carried toward either pole in consequence of a quicker motion of the pendulum, resulting from a nearer approach to the centre, and a greater power of gravity.
The results of calculations founded upon observations of the pendulum agree pretty nearly with those derived from actual measurement; and the conclusion from the whole is, that the degree of flattening amounts to about sig of the whole diameter of the earth, that is, a line drawn through the centre of the earth, from pole to pole, is zio (or 26 miles) shorter than a similar line in the direction of the equator.
III. DENSITY OF THE EARTH.
Is the earth solid or hollow, and if solid, how dense is it? Would it be equivalent to so much water, or would it exceed it, and how much would it exceed it? It may seem very difficult to answer these questions, and yet they have been answered most satisfactorily. It is now abundantly proved not only that the earth is solid, but that the interior parts are more and more compact the nearer we approach to the centre, as we should naturally suppose. We are able to estimate the influence which a mountain exerts upon a plumb-line by observing how much it is drawn out of the direction of an exact perpendicular; and then, by comparing the size of the mountain with the size of the earth, knowing at the same time of what materials the mountain is composed, we are able to say how much the matter of the whole earth exceeds that of the mountain. It is thus ascertained that the matter composing the earth is about five times as dense as water, or, in other words, would weigh, under the same cir. cumstances, five times as much as the same bulk of water. Now we know that the matter near the surface, is, for the most part, either water or earthy and stony substances, only two or three times as heavy as water. The density of the interior parts, therefore, must greatly exceed that at the surface, in order that the average may amount to five times the density of water, as is ascertained by actual observation.
It may be thought, that the above method of determining the quantity of matter in a mountain is liable to great uncertainty. It should be
TEMPERATURE OF THE INTERIOR OF THE EARTH.
known that we do not rely upon a single experiment, or even upon one single method, for so important a result. A balance has been contrived, depending upon the twisting and untwisting of an extremely fine wire suspended perpendicularly,* by which the mutual tendency (or relative weight) of two balls of lead, has been accurately estimated and compared with the force exerted by the great mass of the earth; and these delicate experiments have afforded a striking confirmation of the result above stated.
IV. TEMPERATURE OF THE INTERIOR OF THE EARTH.
The circumstance of the earth's being flattened at the poles and protuberant at the equator, is the natural and necessary result of its rotation on its axis. But in order that it might yield to the force resulting from such a motion, the matter of which it is composed, must have been soft. Now, although water is capable of being compressed, and so far as we can judge, of taking any degree of density, according to the force exerted upon it, still the shape of the earth is not that which would have resulted from such a mass of water. There may be particular portions of the sea that extend to the depth of several miles, as there are particular points of the solid crust of continents, that rise to this height above the general level. Still we have reason to believe, that the average depth of the ocean does not much exceed three thousand feet. It is thought that heat may have been the original cause of the fluidity of the earth, and that there may still remain enough to keep the interior portions in the same state. The more this subject has been examined, the more the evidence has accumulated in favor of the position that the temperature increases as we descend below the surface. There are numerous instances in which we have been able, by means of natural or artificial excavations, to penetrate to the depth of from 1300 to 1600 feet. The general inference from all the observations made in different parts of the earth is, that there is an increase of heat amounting to about 1° of Fahrenheit for every 46 feet in depth; that at the depth of 10,000 feet the heat would be sufficient to boil water, and that at the depth of about 100 miles, or do part of the distance to the centre, the heat would be intense enough to melt most of the earths and stones that are known to enter into the composition of the globe. These facts and inferences have an important bearing upon the phenomena of earthquakes and volcanoes, and open a wide field of speculation to the natural historian and geologist.
* A balance of this construction, applied to electrical forces, has been estimated to weigh to the sixty-thousandth part of a grain.
I. DECLARATION OF INDEPENDENCE.
JULY 4, 1776.
[From the Journals of Congress.] A Declaration by the Representatives of the United States of America
in Congress assembled.
WHEN, in the course of human events, it becomes necessary for one people to dissolve the political bands which have connected them with another, and to assume, among the powers of the earth, the separate and equal station to which the laws of nature and of nature's God entitle them, a decent respect to the opinions of mankind requires that they should doclare the causes which impel them to the separation.
We hold these truths to be self-evident :-that all men are created equal ; that they are endowed by their Creator with certain unalienable rights ; that among these are life, liberty, and the pursuit of happiness; that to secure these rights, governments are instituted among men, deriving their just powers from the consent of the governed; that whenever any form of government becomes destructive of these ends, it is the right of the people to alter or to abolish it, and to institute new government, laying its foundation on such principles, and organizing its powers in such form, as to them shall seem most likely to effect their safety and happiness. Prudence, indeed, will dictate, that governments long established should not be changed for light and transient causes; and accordingly all experience hath shown, that mankind are more disposed to suffer while evils are sufferable, than to right themselves by abolishing the forms to which they are accus tomed. But when a long train of abuses and usurpations, pursuing inváriably the same object, evinces a design to reduce them under absolute des. potism, it is their right, it is their duty, to throw off such government, and to provide new guards for their future security. Such has been the patient sufferance of these colonies ; and such is now the necessity which constrains them to alter their former systems of government. The history of the present king of Great Britain, is a history of repeated injuries and usurpations, all having in direct object the establishment of an absolute tyranny over these states. To prove this, let facts be submitted to a candid world.