a uniform distance, and all in perfect harmony. We shall afterwards explain the manner in which the gravity of the sun acts in controlling the planetary motions. For the present, let us content ourselves with reflecting upon the wonderful force which the sun must put forth to bend out of their courses into circular orbits such a number of planets, some of them more than a thousand times larger than the earth. Were a ship of war under full sail, we can easily imagine what a force it would require to turn her from her course by a rope attached to her bow-especially were it required that the force should remain stationary, and the ship be so held as to be made to go round the force as round a centre. Somewhat similar to this, but on a much grander scale, is the action which is exerted on the earth in its journey round the sun. By an invisible influence, which we call gravitation, the sun turns all the planets out of their course, and bends them into a circular orbit round himself, though they are all many millions of times more ponderous than the ship, and are moving many thousand times more swiftly.

WHAT IS GRAVITATION?

It was at one time supposed that we could never reason respecting the laws that govern the heavenly bodies from what we observe in bodies around us,-that motion is one thing on the earth and quite another thing in the skies; and hence, that it would be impossible for us, by any inquiries into the laws of terrestrial nature, to ascertain how things take place among the heavenly bodies. Galileo and Newton, however, proceeded on the contrary supposition, that Nature is uniform in all her works,—that the same Almighty arm rules over all, and that he works by the same fixed laws through all parts of his boundless realms.

We discover in nature a tendency of every portion of matter towards every other. This tendency is called the law of gravitation. In obedience to this power, a stone falls to the ground, and a planet revolves around the sun. The former is an example of what we call gravity; the latter, an example of universal gravitation. The

laws of terrestrial gravity were first investigated by Galileo; those of universal gravitation, by Sir Isaac Newton. Terrestrial gravity is only an individual example of universal gravitation, being the tendency of bodies towards the centre of the earth. We are so much accustomed, from our earliest years, to see bodies fall to the earth, that we imagine they must of necessity fall "downwards;" but when we reflect that the earth is round, and that bodies fall towards the centre on all sides of it,—and that, of course, on opposite sides of the earth they fall in precisely opposite directions, and towards each other,—we perceive that there must be some force acting to produce this effect. Every motion implies some force which produces it; and the fact that bodies fall towards the earth, on all sides of it, leads us to infer that that force, whatever it is, resides in the earth itself. We therefore call it attraction. We do not, however, say what attraction is, but what it does. We must bear in mind, also, that this attraction is mutual-that when a stone falls towards the earth, it exerts the same force on the earth that the earth exerts on the stone; but the motion of the earth towards the stone is as much less than that of the stone towards the earth as its quantity of matter is greater, and therefore its motion is quite imperceptible.

But although we are compelled to acknowledge the existence of such a force as gravity, causing a tendency in all bodies towards each other, yet we know nothing of its nature, nor can we conceive by what medium bodies at such a distance as the sun and the earth exercise this influence on each other. Yet we know that it

is this which, acting across an interval of ninety-five millions of miles, holds the earth as surely in its orbit as if it were connected by a chain to the sun; and the same force holds all the other planets in their orbits.

It is a law of nature that a body when at rest remains so, unless some force puts it in motion; but when once in motion it will continue to move for ever, unless something stops it. When a ball is rolled on the ground, the friction of the earth and the resistance of the air soon stop its motion; when rolled on smooth ice it will go much further, because the ice opposes much less resistance than

the ground, and were there no impediment to its motion it would continue to move for ever. The earth, and all the other planets which revolve around the sun as their common centre, are actually in this condition. They would fly off into space, and continue to move for ever in a straight line; but, held in check, in obedience to the laws of Him who created them and gave them motion, they circulate in their appointed orbits.

"The spacious firmament on high,

With all the blue ethereal sky,

And spangled heav'ns, a shining frame,
Their great Original proclaim.

Th' unwearied sun, from day to day,
Does his Creator's power display;
And publishes to ev'ry land
The work of an Almighty hand.

Soon as the ev'ning shades prevail,
The moon takes up the wondrous tale,
And, nightly to the list'ning earth,
Repeats the story of her birth;

While all the stars that round her burn,
And all the planets in their turn,
Confirm the tidings as they roll,

And spread the truth from pole to pole.
What though in solemn silence all
Move round the dark terrestrial ball?
What though no real voice, nor sound,
Amidst their radiant orbs be found?
In Reason's ear they all rejoice,
And utter forth a glorious voice;

For ever singing, as they shine,

"The hand that made us is divine."

THE STELLAR WORLD.

ADDISON.

VAST as the solar system appears to us, it forms but a single star system in the stellar world. What we call the fixed stars are sung

like our own, each attended by a retinue of planetary orbs, and guided by the same laws that regulate our own solar system. The number and distances of these systems of stars far exceed man's powers of comprehension.

"If," says an eloquent writer, "there be anything which can lead the mind upward to the Omnipotent Ruler of the universe, it is to be found in the grandeur and beauty, of his works. If you would know his glory, examine the interminable range of suns and systems which crowd the Milky Way. Multiply the hundred millions of stars which belong to our own 'island universe,' by the thousands of those astral systems that exist in space within the range of human vision, and then you may form some idea of the infinitude of his kingdom; for, lo! these are but a part of his ways. Examine the scale on which the universe is built. Comprehend, if you can, the vast dimensions of our sun. Stretch outward through his system, from planet to planet, and circumscribe the whole within the immense circumference of Neptune's orbit. This is but a single unit out of the myriads of similar systems. Take the wings of light, and flash with impetuous speed, day and night, and month and year, till youth shall wear away, and middle age is gone, and the extremest limit of human life has been attained;-count every pulse, and at each speed on your way a hundred thousand miles, and, when a hundred years have rolled by, look out, and, behold! the thronging millions of blazing suns are still around you, each separated from the other by such a distance that, in this journey of a century, you have only left half a score behind you.

"Would you gather some idea of the eternity past of God's existence, go to the astronomer, and bid him lead you with him in one of his walks through space; and, as he sweeps outward from object to object, from universe to universe, remember that the light from those filmy stains on the deep pure blue of heaven, now falling on your eye, has been travelling space for a million of years.

"Would you gather some knowledge of the omnipotence of God, weigh the earth on which we dwell, then count the millions of its inhabitants that have come and gone for the last six thousand

years. Unite their strength into one arm, and test its power to move this earth. It could not stir it a single foot in a thousand years; and yet, under the omnipotent hand of God, not a minute passes that it does not fly far more than a thousand miles. But this is a mere atom-the most insignificant point among his innumerable worlds. At his bidding, every planet, and satellite, and comet, and the sun himself, fly onward in their appointed courses. His single arm guides the millions of sweeping suns; and around his throne circles the great constellation of unnumbered universes.

"Would you comprehend the idea of the omniscience of God, remember that the highest pinnacle of knowledge reached by the whole human race, by the combined efforts of its brightest intellects, has enabled the astronomer to compute approximately the perturbations of. the planetary worlds. He has predicted, roughly, the return of half a score of comets. But God has computed the mutual perturbations of millions of suns, and planets, and comets, and worlds without number, through the ages that are past, and throughout the ages which are yet to come, not approximately, but with perfect and absolute precision. The universe is in motion-system rising above system, cluster above cluster, nebula above nebula-all majestically sweeping around under the providence of God, who alone knows the end from the beginning, and before whose glory and power all intelligent beings, whether in heaven or on earth, should bow with humility and awe.

"Would you gain some idea of the wisdom of God, look to the admirable adjustments of the magnificent retinue of planets and satellites which sweep around the sun. Every globe has been weighed and poised, every orbit has been measured and bent to its beautiful form. All is changing; but the laws fixed by the wisdom of God, though they permit the rocking to and fro of the system, never introduce disorder, or lead to destruction. All is perfect and harmonious, and the music of the spheres that burn and roll around our sun is echoed by that of ten millions of moving worlds, that sing and shine around the bright suns that reign above."