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located, would scarcely fall beyond the limits of the sun's surface. At a mean distance of 36,000,000 of miles from the sun we meet the nearest planet, Mercury, revolving in an orbit of considerable eccentricity, and completing its circuit around the sun in a period of about eighty-eight of our days. This world has a diameter of only 3,140 miles, and is the smallest of the old planets. Pursuing our journey, at a distance of 68,000,000 of miles from the sun, we cross the orbit of the planet Venus. Her magnitude is nearly equal to that of the earth. Her diameter is 7,700 miles, and the length of her year is nearly 225 of our days. The next planet we meet is the earth, whose mean distance from the sun is 95,000,000 of miles. The peculiarities which mark its movements
. and those of its satellite, have been already discussed. Leaving the earth, and continuing our journey outward, we cross the orbit of Mars, at a mean distance from the sun of 142,000,000 of miles. This planet is 4,100 miles in diameter, and performs its revolution around the sun in about 687 days, in an orbit but little inclined to the plane of the ecliptic. Its features, as we shall see hereafter, are more nearly like those of the earth than any other planet. Beyond the orbit of Mars, and at a mean distance from the sun of about 250,000,000 of miles, we encounter a group of small planets, eight in number, presenting an anomaly in the system, and entirely different from anything elsewhere to be found. These little planets are called asteroids. Their orbits are, in general, more eccentric, and more inclined to the ecliptic, than those of the other planets; but the most remarkable fact is this :—that their orbits are so nearly equal in
size, that when projected on a common plane, they are not enclosed, the one within the other, but actually cross each other.
We shall return to an examination of these wonderful objects hereafter.
mean distance of 485,000,000 of miles from the sun, we cross the orbit of Jupiter, the largest and most magnificent of all the planets. His diameter is nearly 90,000 miles. He is attended by four moons, and performs his revolution round the sun in a period of nearly twelve years.Leaving this vast world, and continuing our journey to a distance of 890,000,000 of miles from the sun, we cross the orbit of Saturn, the most wonderful of all the planets. His diameter is 76,068 miles, and he sweeps round the sun in a period of nearly twenty-nine and a half years. He is surrounded by several broad concentric rings, and is accompanied by no fewer than seven satellites or moons. The interplanetary spaces we perceive are rapidly increasing. The orbit of Uranus is crossed at a mean distance from the sun of 1,800,000,000 of miles. His diameter is 35,000 miles, and his period of revolution amounts to rather more than eighty-four of our years. He is attended by six moons, and pursues his journey at a slower rate than any of the interior planets. Leaving this planet, we reach the known boundary of the planetary system, at a distance of about 3,000,000,000 of miles from the sun. Here revolves the last discovered planet, Neptune, attended by one, probably by two mcons, and completing his vast circuit about the sun in a period of one hundred and sixty-four of our years.His diameter is eight times greater than the earth's, and he contains an amount of matter sufficient to form one hundred and twenty-five worlds such as
Here we reach the known limit of the planetary worlds, and standing at this remote point and looking back towards the sun, the keenest vision of man could not descry more than one solitary planet along the line we have traversed. The distance is so great, that even Saturn and Jupiter are utterly invisible, and the sun himself has shrunk to be scarcely greater than a fixed star.
There are certain great characteristics which distinguish this entire scheme of worlds. They are all nearly globular—they all revolve on axes-their orbits are all nearly circular—they all revolve in the same direction around the sun—the planes of their orbits are but slightly inclined to each other, and their moons follow the same general laws. With a knowledge of these general facts, it is proposed to trace the reciprocal influences of all these revolving worlds, and to learn, if it be possible, whether this vast scheme has been so constructed as to endure while time shall last, or whether the elements of its final dissolution are not contained within itself, either causing the planets, one by one, to drop into the sun, or to recede from this great centre, released from its influence, to pursue their lawless orbits through unknown regions of space.
Before proceeding to the investigation of the great problem of the stability of the universe, let us examine how far the law of gravitation extends its influence over the bodies which are united in the solar system. A broad and distinct line must be drawn between those phenomena, for which gravitation must render
a satisfactory account, and those other pheromena, for which it is in no wise responsible. In the solar system we find, for example, that all the planets revolve in the same direction around the sun, in orbits slightly elliptical, and in planes but little inclined to each other. Neither of these three peculiarities is in Any way traceable to the law of gravitation.
Start a planet in its career, and, no matter what be the eccentricity of its orbit, the direction of its movement, or the inclination of the plane in which it pursues its journey, once projected, it falls under the empire of gravitation, and ever after, this law is accountable for all its movements. We are not, therefore, to regard the remarkable constitution of the solar system as a result of any of the known laws of nature.
If the sun were created, and the planetary worlds formed and placed at the disposal of a being possessed of less than infinite wisdom, and he were required so to locate them in space, and to project them in orbits, such that their revolutions should be eternal, even with the assistance of the known laws of motion and gravitation, this finite being would fail to construct his required system.
Let it be remembered, that each and every one of these bodies exerts an influence upon all the others. There is no isolated object in the system. Planet sways planet, and satellite bends the orbit of satellite, until the primitive curves described, lose the simplicity of their character, and perturbations arise, which may end in absolute destruction. There is no chance work in the construction of our mighty system. Every planet has been weighed and poised, and placed pre. cisely where it should be. If it were possible to drag Jupiter from its orbit, and cause him to change places with the planet Venus, this interchange of orbits would be fatal to the stability of the entire system. In contemplating the delicacy and complexity of the adjustment of the planetary worlds, the mind cannot fail to recognize the fact that, in all this intricate balancing, there is a higher object to be gained than the mere perpetuity of the system.
If stability had been the sole object, it might have been gained by a far simpler arrangement. If God had so constituted matter that the sun might have attracted the planets, while these should exert no influence over each other—that the planets might have attracted their satellites, while these were free from their reciprocal influences—then, indeed, a system would have been formed, whose movements would have been eternal, and whose stability would have been independent of the relative positions of the worlds, and the character of their orbits.
Give to them but space enough in which to perform their revolutions around the sun, so that no collisions might occur, freed from this only danger, every planet, and every satellite, will pursue the same undeviating track throughout the ceaseless ages of eternity.
If this statement be true, it may be demanded, why such a system was not adopted. It is impossible for us to assign all the reasons which led to the adoption of the present complicated system. Of one thing, however, we are certain :-If God designed that in the heavens his glory and his wisdom should be declared, and that in the study of his mighty works, his intelligent creatures should rise higher and higher too