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great, but uncertain ; the elements of 98 of them only being determined with anything approaching a definite knowledge. Of these, 24 pass between the sun and the orbit of Mercury, 33 between Mercury and Venus, 21 between Venus and the earth, 16 between the earth and Mars, 3 between Mars and Ceres, and one between Ceres and Jupiter. These are so far known to astronomers, that they are able to calculate their returns, the periods of which are very various ; Encke's comet revolving in three years four months, and Halley's in 75 or 76 years. Comets have often come very near the earth, and have occasioned no small alarms, though from their extreme tenuity we need be under little dread on their still nearer approach ; for the comet of 1770 actually got entangled among the satellites of Jupiter, without their experiencing the slightest derangement.
The vapoury portion, or tail, as it is commonly called, is always in the direction towards the sun, so that sometimes it is in advance, sometimes behind, and sometimes surrounding the nucleus, or more solid part. In the first case the comet is called bearded, in the second tailed, and in the last case hairy. This arises from the attraction of the sun. Notwithstanding the great velocity of comets on their approaching the sun, their tenuity is such that their more vapoury parts are attracted by the sun, and advance before the nucleus; but as the nucleus is going in the same direction as its vapour is being attracted by the sun, the length of its tail or beard must be consequently lessened. On the comet's leaving the sun, however, its tail is then attracted in the contrary direction to the comet's path, and therefore it then assumes its greatest length. The tail of the comet of 371 B.C. occupied one-third of the hemisphere, or 60 degrees. That of 1618 had a tail extending 104 degrees. That of 1680 Newton calculated to be 163 million miles. That of the great comet of 1769 was 48 million miles ; and that of 1811 was 108 million miles long, and 15 millions broad. All comets, however, do not have tails, while some comets have several tails; thus that of 1744 had six tails, nearly 30 degrees long.
We now leave the consideration of our solar system, to take a glimpse of the vast expanse beyond, from whence our whole system appears no bigger than a point, and of such insignificance that its total destruction would not be noticed amidst the countless host that lie around.
The Fixed Stars are divided into various classes or orders, according to their respective apparent diameters. There are six classes or degrees of magnitude visible to the naked eye. Those which appear the largest and brightest are said to be of the first magnitude ; those next to them in lustre and size are of the second ; and so on to the sixth. Those that cannot be seen by the naked eye are called telescopic stars, and are said to be of the seventh, eighth, and ninth magnitudes, according to their appearance.
The nearest may be computed at 32 millions of miles' distance, which is further than a cannon ball would fly in seven millions of years. If our sun were seen from such a distance, it would not appear as big as a star of the first magnitude.
It is impossible that these bodies could receive and reflect, through such an immense distance, sufficient light to render them visible, wherefore they do not sbine by reflection as the planets, but by their own light. As we have much more light from the moon than from all the stars together, it is the greatest absurdity to imagine that the stars were made for no other purpose than to cast a faint light upon the earth, especially since there are so many stars which can only be seen by a telescope. From all this it is highly probable that each star is a sun to a system of worlds moving round it, though unseen by us.
The number of the stars visible to the naked eye is said to be as follows:-20 of the first magnitude, 65 of the second, 206 of the third, 486 of the fourth, 652 of the fifth, and 1424 of the sixth ; making in the whole 2833. By the aid of telescopes, however, myriads of stars are seen which before were invisible.
De la Lande formed a catalogue of more than 50,000 stars: 188 have been counted in the pleiades, though there are only six seen by the naked eye. Many stars which appear single are discovered by the telescope to consist of two or more, and hence denominated double, triple, quadruple, and multiple stars. Mr. Whewell says there are 3000 and more double stars discovered already. There are about 100 constellations distributed over the heavens, and the stars in them are marked by the letters of the Greek and Roman alphabets, and by numerals. Besides the double and multiple stars, there are binary stars, which revolve round each other ; periodic stars, which have a periodical increase and decrease of lustre; and coloured stars, where double stars partake of two different colours. This arises often by contrast; for if the brighter star is crimson, the other will assume a green appearance; if the brighter
star appear yellow, the other will assume a blueish tint. The former instance is exhibited by y, Andromedæ; the latter by v, Caneri. Some stars are continually moving in a straight line, as M, Capiopeiæ ; some as B, in Cæti, are constantly increasing in splendour; and others, as o, Ursæ, ás constantly diminishing. veral stars recorded by ancient astronomers are not now seen, while we see others not noticed in ancient catalogues.
Sir W. Herschell states our system to be in the centre of the Galaxy, or ‘milky way,' which is an immense nebula of fixed stars. Of what extent must it be, if each star is as remote from its nearest as our sun appears to be. He also supposes that the starry firmament, instead of being scattered through indefinite space, may form a stratum, whose thickness is small in comparison to its length and breadth, and to resemble a narrow letter Y, in the centre of which is the Galaxy or milky way.
Besides those mentioned, there are also nebulæ' and 'globular clusters. The latter sometimes consist of 10 or 20 thousand stars at least, compacted and wedged together in a round space. Nebulæ, according to Dr. Herschell, may consist of a selfluminous fluid, distributed through space in immense quantities, and that its various appearances may be caused by the various degrees of solidity it may have acquired through gravitation and rotation, until at length it forms either a comet or planet; or, being still further condensed, becomes a self-luminous star.
We have thus taken a slight view of the heavenly host,' which we find to consist of such an inconceivable number of suns, systems, and worlds, that we
find ourselves lost in the contemplation of the wonderful works of God. If, therefore, our solar system, as we before considered, with all its planets, &c. were annihilated, it would scarcely be a sensible blank in the universe. We may conclude, from what has been already stated, that the planets of our system, together with their satellites, are of nearly the same nature as our earth, and consequently inhabited. For they all have regular returns of seasons, and of day and night. Such of the planets, also, as are furthest removed from the sun, have satellites to revolve round and enlighten them; thus compensating for his diminution of light and heat. It is remarkable, that of all the bodies, that which we would naturally consider least habitable, viz. the sun, been thought to be so by astronomers; while the moon, which we might consider most habitable, is thought to be the least so. This arises from her possessing little or no atmosphere or water.
Still we must consider, that though we might not be able to reside in the globes of the sun, planets, &c., yet beings may be created by God, to whom they shall be perfectly adapted. We may therefore suppose, either that the creatures are made of a nature to inhabit these bodies, or that these bodies are suited and calculated for the residence of such creatures.
We will now conclude with a few remarks taken the sacred writers and eminent divines.
They who view these 'wonders of creation,' with
1 Tully, the Roman philosopher, remarked, in his De Nat. Deorum, * Shall we, when we see an artificial engine, a sphere, a dial, for instance, acknowledge, at first sight, that it is the work of art and understanding; and yet when we behold the heavens, make any doubt that these are performances not only of reason, but of a most excellent and divine reason?'