word, and no resting-place for his hopes, but in the life and immortality which have been brought to light in the Gospel of Jesus. FOURTH WEEK-TUESDAY. II. THE STARRY HEAVENS.-GRAVITATION AND INERTIA. Ir it be true, as there is every reason to believe, that the fixed stars which sparkle in the heavens, are suns like our own, shining, as they certainly do, by their own light, and shedding their radiance on other worlds, a view of creation is opened to us, which it is both delightful and overwhelming to contemplate; and to this view we shall afterwards turn. At present, let us take a rapid survey of the system of which we ourselves form a part. Our star (for the sun, considered with reference to the universe, deserves no higher name) appears larger than other stars to us, only on account of its nearness; but when we call it near, we speak relatively; for it is known to be separated from us by the amazing distance of 95,000,000 of miles. It is the centre of our planetary system; that is to say, there are certain bodies similar to our own globe, which bear to the sun the same relation, being, like the earth, attracted to it by the all-pervading law of gravitation, and only kept from falling into it,—as a stone when thrown falls to the ground, by the velocity with which they move in a different direction. The two wellknown laws, so simple in their nature, and yet so vast in their effects, by which the whole creation is moulded and regulated, have, ever since their discovery as universal agents, been most justly regarded with the highest admiration; and it is not easy to conceive any thing capable of impressing on the mind a more exalted view of the power and wisdom of the Creator. It would be inconsistent with our plan to enter deeply into this subject; but some cursory observations on a matter of such intense interest, and so directly illustrative of the perfections of God, cannot be considered out of place. Every one is familiar with the law of gravity or weight, -that mysterious power, which, acting uniformly, draws all things downwards, toward the centre of the earth. It is in virtue of this law, that, were I to open my fingers, the pen with which I write would fall flat upon the paper. It is the same law, which causes the ink to flow upon the paper from my pen, the paper to lie steadily on my desk, and the desk itself to stand firmly on the floor. Nay, it is this very law which gives solidity to the ground on which I tread, which has formed it into a globe, and which prevents it from breaking up into shapeless and unconnected masses. The properties of this unseen agent are too palpable, in relation to our own sphere, to have escaped the attention of the earliest inquirers into Nature. But it was reserved to a far later period to demonstrate, or even to conjecture, that the very same power, which produces such salutary effects in the earth, is not only an essential property of all matter, but acts at the greatest distances, and preserves the balance of the universe. The other property, which, combined with gravitation, is employed in regulating the machinery of creation on the great scale, is also familiar to the most ignorant, in regard to some of its qualities. Every child knows, that a stone thrown forcibly from the hand, or an arrow shot from a bow, will continue for some time to move forward in the direction in which it has been projected; but, then, this power of continued motion, as it comes under ordinary observation, is only very limited in its operation, because it is counteracted both by the attraction of the earth and the resistance of the air, and no force which human skill can apply, is sufficiently powerful to give an impetus to any body, capable of overcoming, for a length of time, these opposing forces. In the principle itself, however, there is no limit; and the law is simply this, that while a body at rest will, if not disturbed, re main for ever in that state,-a body once set in motion, will, when not acted on by some modifying or counteracting force, move on continually without deviation or intermission, in a straight line. This is the law of inertia, [or inertness,]-a law which is not less universal than that of gravitation. Now, to understand the operation of these two laws in relation to each other, first, suppose a small body, placed at rest, in the neighborhood of a large one, also at rest, both of them in empty space. The mutual attraction would immediately begin to operate, and they would move toward each other till they met, and that with a rapidity proportioned to the quantity of matter contained in each, the larger most powerfully attracting the smaller. Suppose, again, that the smaller body, instead of being placed at rest, was projected with a certain velocity in a direction different from that in which the other was situated. That velocity might be very great; and then, after a mutual disturbance, arising from the reciprocal attraction, the moving body would disengage itself from the other, and fly off into boundless space; or it might be very small, and then the vis inertia would be overcome, and the two bodies would fall toward each other, and unite; but, if the projecting force were, within certain limits, proportioned to the gravitating force, the consequence would be, that there would be a certain point in the progress of the moving body, in which the two powers would balance each other, and .hen, that body would continue to move, indeed, but in a constant circuit round the attracting force, which would thus become its centre of motion, and its course would be in an oval or in a circle, according to the force and direction of the motion originally impressed. This is, in fact, the principle by which the whole planetary system is governed. The sun, a body of vast dimensions, is the centre of attraction to which all the planets gravitate, and into which they are prevented from falling only by the opposite power of inertia. The two forces, with the nicest exactness, balance each other the former, in reference to this principle, being called the centripetal, and the latter the centrifugal motion; and thus, the great machine is kept in action, and the planets wheel steadily in their respective orbits, and perform their various beneficent functions. I may add, that this is the principle, not of the solar system only, but of the system of the universe. "O, unprofuse magnificence divine! O, wisdom truly perfect! thus to call THOMSON. FOURTH WEEK-WEDNESDAY. III. THE STARRY HEAVENS. THE PLANETARY SYSTEM. In the account of the creation given by Moses, the heavenly bodies are spoken of merely with reference to the earth, and the living beings which were created to inhabit its surface. Any other view would seem to have been inconsistent with the design of Revelation. The words of the inspired writer, therefore, are, "God said, Let there be lights in the firmament of the heaven, to divide the day from the night; and let them be for signs, and for seasons, and for days, and years: and let them be for lights in the firmament of the heaven, to give light upon the earth and it was so. And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: He made the stars also." This account very accurately and distinctly enumerates the uses of the sun, moon, and stars, so far as the inhabitants of our planet are concerned; but there is another, which may be called the philosophical view of the subject, on which man was wisely left to exercise his own powers. This treats of the heavenly bodies, with reference to each other, and to the universe. Here, a new and most wonderful scene opens to our view, bright with the glory of the Divine perfections; and this, is the scene which now presents itself for our consideration. Keeping in mind that our object is not to write a treatise on astronomy, but merely to point out some remarkable facts in the construction of Nature, which can only be referred to an intelligent and benevolent First Cause, let us look more minutely at the appearances of the starry heavens. Besides the moon, which shall be afterward considered, one of the first things which strike an observer, is, that the great mass of the stars, though apparently in constant motion round a point from east to west, occasioned by the diurnal movement of the earth, are yet stationary,—or, in other words, preserve, generally speaking, the same relative position,-with reference to each other; but that there are a very few of those lamps of night which follow a different law, continually changing their place, and making progress among the rest, from west to east, with different degrees of velocity. It was discovered, too, as soon as the telescope was applied to the heavens, that, while no known magnifying power could increase the apparent dimensions of the fixed stars, these moving bodies were readily affected by that instrument. Such circumstances indicated an essential difference in the nature of the two classes of stars; and, in the progress of science, it was found that the latter were no other than bodies partaking of the conditions of our own globe, and moving, like the earth, in a constant orbit round the sun. These are called planets. To the ancients only five planets were known,-Mercury, Venus, Mars, Jupiter, and Saturn. To this list, modern science has added the Earth,-which takes its place, with relation to its distance from the sun, between Venus and Mars,—and Uranus, or Georgium Sidus, [or Herschel,] which is the most distant of them all. Besides these, a still later discovery has been made, of four other planetary bodies, which move in orbits considerably more eccentric than the rest, and are of much smaller dimensions, whose situation has been found to be between Mars I. 9 VII. |