It is a principle laid down by Sir Isaac Newton, the correctness of which is generally admitted, that "matter attracts matter in proportion to its quantity and the squares of its distances inversely." Captain Symmes contends that gravity consists in a certain expansive quality in the molecules which constitute the aerial fluid called æther, which fills universal space, and creates a pushing, instead of a pulling power. However, let either be correct, I conceive it cannot materially affect the principles necessary to constitute concentric spheres: either principle, I apprehend, would lead us nearly to the same results. When matter was in chaos, or in a form not solid, promiscuously disseminated through universal space, suppose it then should at once receive the impression of those universal laws by which it is governed, and see what would be the consequence.
According to Sir Isaac Newton's principles of gravity, the particle of matter that happened to be the largest would attract the smaller in its neighbourhood, which would increase the power of attraction in proportion to the increase of matter, until all in the universe would be collected into one vast body in the centre of space, and there remain motionless and at rest forever. This, however, we find not to be the case; for innumerable bodies of matter, differing in magnitude, are known to exist throughout the universe, arranged at suitable distances from each other, and performing certain revolutions in obedience to certain fixed laws impressed on them.
Now suppose all the matter in our globe to be an extended liquid mass, the particles so disengaged from each other, as to take their positions according to the established laws of matter, and then see what would be the consequences resulting from motion and gravity. Taking the laws of Newton for our guide, the particles of matter in the centre would be operated on by the power of gravity equally on all sides and consequently be stationary. Suppose then a line struck through this globe of matter, so as to make a globe of half the diameter of the whole in the centre, it is plain that the inner globe would not contain more than one eighth part as much matter as the surrounding one; hence it would be attracted towards the surface more than to the centre, were it not for the attraction of the matter on the opposite side exerting an influence upon it—but this being removed to so much greater distance, would not be more than an equipoise to the other.
The diameter of our globe, according to the best observation, is believed to be about 7970 English miles, and its circumference 25,038: consequently, if it were solid, it would contain 265,078,559,622 cubic miles of matter; while a globe of only half the diameter, would contain only 33,134,819,952.[3]
Suppose our globe divided into parts of one square mile on the surface, bounded by straight lines converging to a point at the centre, as the subjoined figure represents:
and then suppose there were no other particles of matter in the universe but A and B, A containing 1,328 cubic miles of matter, and B only 166, A would attract B so as to make their centre of attraction at O, which point would become at once the common centre: but admitting the whole matter of the globe to exist, A would still exert its influence on B, but both would be operated upon by T and S and the surrounding matter, all perhaps, tending to one common centre. However, I imagine that the tending to the centre would not be so great as is contended for by the generally received theory, which alleges that matter at the centre of the earth is four times as hard as hammered iron. The Newtonian philosophy appears to contemplate a globe at rest, and not in such rapid motion as we know the earth and other planetary bodies to be in, communicating to them a centrifugal force, which tends to throw matter from the centre. The rotary motion of each planet is no doubt regulated by the quantity of matter it contains: so that at its surface centrifugal and centripetal forces are equally balanced—the rotary motion being adequate to communicate a force to counter-balance the force of gravity.
Newton ascertained by his investigations of the properties and principles of matter, the earth to be a globe flattened at the poles: and the French philosophers afterwards confirmed this fact by measuring a degree in different latitudes. This difference between the equatorial and polar diameters of the earth, and of the other planets which are also known to be of that shape, is ascribed by those philosophers who attempt to account for such a formation, to the projectile force of the globe at the equator occasioned by its rotary motion. This is admitting that the matter of our globe was once in so soft a state as to take its form from motion; for were the earth a compact solid body, and four times as hard as hammered iron at the centre, (as the Newtonian system alleges) this rotary motion round an imaginary axis could never give to the globe the form of an oblate spheroid, as is ascertained to be the fact; because a hard solid body moving in empty space, could not be supposed to yield into that shape by any law of action as yet unfolded by science.