from its orbit, and to take the same rapid flight over this immense tract, it would not have arrived at the termination of its journey, after taking all the time which has elapsed since the creation of the world. These are great numbers, and great calculations; and the mind feels its own impotency in attempting to grasp them. We can state them in words. We can exhibit them in figures. We can demonstrate them by the powers of a most rigid and infallible geometry. But no human fancy can summon up a lively or an adequate conception-can roam in its ideal flight over this immeasurable largeness can take in this mighty space in all its grandeur, and in all its immensity-can sweep the outer boundaries of such a creation-or lift itself up to the majesty of that great and invisible arm on which all is suspended. But what can those stars be which are seated so far beyond the limits of our planetary system? They must be masses of immense magnitude, or they could not be seen at the distance of place which they occupy. The light which they give must proceed from themselves, for the feeble reflection of light from some other quarter would not carry through such mighty tracts to the eye of an observer. A body may be visible in two ways. It may be visible from its own light, as the flame of a candle, or the brightness of a fire, or the brilliancy of yonder glorious sun, which lightens all below, and is the lamp of the world; or it may be visible from the light which falls upon it, as the body which receives its light from a taper, or the whole assemblage of objects on the surface of the earth, which appear only when the light of day rests upon them, or the moon, which, in that part of it that is towards the sun, gives out a silvery whiteness to the eye of the observer, while the other part forms a black and invisible space in the firmament, or as the planets, which shine only because the sun shines upon them, and which, each of them, present the appearance of a dark spot on the side that is turned away from it. Now apply this question to the fixed stars. Are they luminous of themselves, or do they derive their light from the sun, like the bodies of our planetary system? Think of their immense distance, and the solution of this question becomes evident. The sun, like any other body, must dwindle into a less apparent magnitude as you retire from it. At the prodigious distance even of the very nearest of the fixed stars, it must have shrunk into a small indivisible point. In short, it must have become a star itself, and could shed no more light than a single individual of those glimmering myriads, the whole assemblage of which cannot dissipate and can scarcely alleviate the midnight darkness of our world. These stars are visible to us, not because the sun shines upon them, but because they shine of themselves, because they are so many luminous bodies scattered over the tracts of immensity-in a word, because they are so many suns, each throned in the centre of his own dominions, and pouring a flood of light over his own portion of these unlimitable regions. At such an immense distance for observation, it is not to be supposed that we can collect many points of resemblance between the fixed stars, and the solar star which forms the centre of our planetary system. There is one point of resemblance, however, which has not escaped the penetration of our astronomers. We know that our sun turns round upon himself in a regular period of time. We also know that there are dark spots scattered over his surface, which, though invisible to the naked eye, are perfectly noticeable by our instruments. If these spots existed in greater quantity upon one side than upon another, it would have the general effect of making that side. darker; and the revolution of the sun must, in such a case, give us a brighter and a fainter side, by regular alternations. Now, there are some of the fixed stars which present this appearance. They present us with periodical variations of light. From the splendour of a star of the first or second magnitude, they fade away into some of the inferior magnitudes and one, by becoming invisible, might give reason to apprehend that we had lost him altogether-but we can still recognise him by the telescope, till at length he reappears in his own place, and, after a regular lapse of so many days and hours, recovers his original brightness. Now, the fair inference from this is, that the fixed stars, as they resemble our sun in being so many luminous masses of immense magnitude, resemble him in this also, that each of them turns round upon his own axis; so that if any of them should have an inequality in the brightness of their sides, this revolution is rendered evident, by the regular variations in the degree of light which they undergo. Shall we say, then, of these vast luminaries, that they were created in vain? Were they called into existence for no other purpose than to throw a tide of useless splendour over the solitudes of immensity? Our sun is only one of these luminaries, and we know that he has worlds in his train. Why should we strip the rest of this princely attendance? Why may not each of them be the centre of his own system, and give light to his own worlds? It is true that we see them not; but could the eye of man take its flight into those distant regions, it would lose sight of our little world before it reached the outer limits of our system-the greater planets would disappear in their turn before it had described a small portion of that abyss which separates us from the fixed stars, the sun would decline into a little spot, and all its splendid retinue of worlds be lost in the obscurity of distance he would at last shrink into a small indivisible atom, and all that could be seen of this magnificent system would be reduced to the glimmering of a little star. Why resist any longer the grand and interesting conclusion? Each of these stars may be the token of a system as vast and as splendid as the one which we inhabit. Worlds roll in these distant regions; and these worlds must be the mansions of life and of intelligence. In yon gilded canopy of heaven, we see the broad aspect of the universe, where each shining point presents us with a sun, and each sun with a system of worlds-where the Divinity reigns in all the grandeur of His attributes-where He peoples immensity with his wonders; and travels in the greatness of His strength through the dominions of one vast and unlimited monarchy. THE COMETARY WORLD. (From Comstock's "Manual of Natural Philosophy.") Orbit, n. (L. orbis), the path of a thing about which matter is Per-i-he'-li-on, (n. Gr. peri, helios), BESIDES the planets which move round the sun in regular order, and in nearly circular orbits, there belongs to the solar system an unknown number of bodies called comets, which move round the sun in orbits exceedingly eccentric, or elliptical, and whose appearance among our heavenly bodies is only occasional. Comets, to the naked eye, have no visible disk, but shine with a faint, glimmering light, and are accompanied by a train or tail, turned from the sun, and which is sometimes of immense length. They appear in every region of the heavens, and move in every possible direction. It had been supposed that comets moved in straight lines, coming from the regions of infinite, or unknown space, and merely passing by our system, on their way to regions equally unknown and infinite, and from which they never returned. Sir Isaac Newton was the first to demonstrate that the comets pass round the sun, like the planets, but that their orbits are exceedingly elliptical, and extend out to a vast distance beyond the solar system. The number of comets is unknown, though some astronomers suppose that there are nearly 500 belonging to our system. Ferguson, who wrote in about 1760, supposed that there were fewer than 30 comets which made us occasional visits; but, since that period, the elements of the orbits of nearly 100 of these bodies have been computed. Of these, however, there are only three whose periods of return among us are known with any degree of certainty. The first of these has a period of 75 years; the second a period of 129 years; and the third a period of 575 years. The third appeared in 1682, and therefore cannot be expected again until the year 2257. This comet, in 1682, excited the most intense interest among the astronomers of Europe, on account of its great apparent size and near approach to our system. In the most remote part of its orbit, its distance from the sun was estimated at about eleven thousand two hundred millions of miles. At its nearest approach to the sun, which was only about 50,000 miles, its velocity, according to Sir Isaac Newton, was 880,000 miles in an hour; and supposing it to have retained the sun's heat, like other solid bodies, its temperature must have been about 2000 times that of red hot iron. The tail of this comet was at least 100 millions of miles long. In the Edinburgh Encyclopedia, article 'Astronomy,' there is the most complete table of comets yet published. This table N contains the elements of 97 comets, calculated by different astronomers, down to the year 1808. From this table it appears that 24 comets have passed between the sun and the orbit of Mercury; 33 between the orbits of Venus and the Earth; 15 between the orbits of the Earth and Mars; 3 between the orbits of Mars and Ceres; and 1 between the orbits of Ceres and Jupiter. It also appears by this table that 49 comets have moved round the sun from west to east, and 48 from east to west. Of the nature of these wandering planets very little is known. When examined by a telescope, they appear like a mass of vapours surrounding a dark nucleus. When the comet is at its perihelion, or nearest the sun, its colour seems to be heightened by the intense light or heat of that luminary, and it then often shines with more brilliancy than the planets. At this time the tail or train, which is always directly opposite to the sun, appears at its greatest length, but is commonly so transparent as to permit the fixed stars to be seen through it. A variety of opinions have been advanced by astronomers concerning the nature and causes of these trains. Newton supposed that they were thin vapour, made to ascend by the sun's heat, as the smoke of a fire ascends from the earth; while Kepler1 maintained that it was the atmosphere of the comet driven behind it by the impulse of the sun's rays. Others suppose that this appearance arises from streams of electric matter passing away from the comet, &c. The comet above noticed has been named from Edmund Halley, who considered it the same as that which had appeared in 1531 and 1607. He accordingly predicted its reappearance about the year 1759, and on the 12th of March in that year it actually re-appeared. This is the first comet whose periodicity was foretold, and the truth of the prediction verified. Its next return to the perihelion was calculated by M. Damoiseau, and fixed for the year 1835. The intervals of its returns are therefore 75 or 76 years. The comet named from Professor Encke, of Berlin, completes its orbit in about 3 years. Its return was calculated in 1819, and the result of the calculation verified by its several reappearances in 1822, 1825, 1828, &c. The comet of Biela is identical with that which appeared in 1 Kepler, one of the greatest philosophers that ever lived, born at Wiel near Wirtemberg 1571. He was the first who discovered that the planets move not in a circle, but in an ellipse. 2 Halley, the celebrated astronomer, born in London 1656. |