eye they seem to be innumerable, but this is a deception occasioned probably by the refraction of our atmosphere. The fixed stars comprehend all the celestial objects, excepting the sun, the moon, and the planets, and some comets, which appear but seldom. The stars, on account of their apparently various magnitudes, have been distributed into several classes or orders. Those which appear largest, are called stars of the first magnitude; the next in lustre, stars of the second magnitude; and so on to the sixth, which are the smallest visible to the naked eye. This distribution having been made long before the invention of telescopes, the stars which cannot be seen without the assistance of these instruments, are termed telescopic stars. They are also distinguished, with regard to their situation, into asterisms, or constellations; which are assemblages of several neighbouring stars, considered as constituting some determinate figure, as an animal, &c. from which each is named. The number of constellations, in the northern hemisphere, is thirty-three; in the southern, forty-five; and in the ecliptic, twelve. The most complete series of observa tions ever made upon the fixed stars, is that some time since announced by Lalande the elder, and his nephew Francis Lalande, who with the assistance of the ingenious and enterprizing wife of the latter, have determined the places of fifty thousand stars, from the pole to two or three degrees below the tropic of capricorn.

12. The twelve constellations which surround the ecliptic, commonly called the twelve signs of the zodiac, are aries, the ram; taurus, the bull; gemini, the twins; cancer, the crab; leo, the lion; virgo, the virgin; libra, the balance; scorpio, the scorpion; sagittarius, the archer; capricornus, the goat; aquarius, the water-bearer; and pisces, the fishes. The first six are called northern, and the others, southern signs; because the former possess that half of the ecliptic which lies to the northward of the equinoctial; and the latter, that which lies to the southward. The northern are summer, the southern, winter signs. The division of the ecliptic into twelve equal parts was, as Pliny informs us, (lib. ii. cap. 8,) the invention of Cleostratus Tenedius. The idea of attributing to the stars different forms, probably originated with the Egyptian shepherds, who, during the silent watches of the

night, (as they slept in the open air) had no other objects than the starry heavens to contemplate. A fertile imagination assisted them in tracing a resemblance between the objects most familiar to them, and the heavenly bodies. The shepherds having thus conceived the figures of animals, &c. to exist in the firmament, the poets embellished the illusion with the fictions of mythology, till the heavens were filled with these imaginary creatures.

13. Those stars, which are not included in any constellation, are denominated unformed. Besides the names of the constellations, the ancient Greeks gave particular appellations to some single stars, or small groupes of them; thus those in the neck of the bull were called pleiades; five in the bull's face, hyades; a bright star in the breast of leo, the lion's heart; and one between the knees of bootes, arcturus. Those clusters of stars which are so distant as not to be distinctly seen, are, from their cloudy appearance, comprised under the name of nebula. The via lactea, galaxy, or milky way, is a broad belt or zone, of a whitish appearance, which consists of an infinite number of small stars, not to be discerned but by a very large telescope. Dr. Herschel is of opinion that the universe is full of these nebulæ or systems of stars, and that the milky way is the nebula in which our system is situated.

14. The fixed stars are so extremely remote, that no distances in the planetary system can be compared with them. The distance of the star Draconis (a star of the fifth magnitude) appears, by Dr. Bradley's observations, to be at least 400,000 times that of the sun, and the distance of the nearest fixed star not less than 40,000 diameters of the earth's annual orbit; that is, the distance from the earth, of the former at least 38,000,000,000,000 miles, and the latter not less than 7,600,000,000,000 miles. A cannon-ball, supposing it could preserve the same velocity, would not reach the nearest of the fixed stars in 600,000 years. Astronomers long since ascertained the number of stars visible to the eye. Of the 3000 contained in Flamstead's catalogue, there are many only visible through a telescope; and a good eye scarcely ever sees more than five hundred, at the same time, in the clearest heaven. Above 2000 stars have been observed in the single constellation of Orion; 188 in the Pleiades; 80 in the space of

year

the belt of Crion's sword; 21 in the nebulous star of his head, and above 500 in another part of him. The stars in the milky way are in prodigious numbers: in the 1792, not less than 258,000 passed through the field of view, in Dr. Herschel's telescope, in the space of forty-one minutes. Some of the largest stars have not the same situations observed by ancient astronomers; and new stars have appeared, while others, formerly described, are no longer seen. Some stars have a periodical increase and decrease: and many of the fixed stars, upon examination by the telescope, are found to consist of two.

15. The sparkling appearance of the fixed stars, most clearly demonstrates that they shine by their own light. On account of their being visible to us, notwithstanding their immense distance from our earth, we may fairly infer that some of them surpass even the sun himself, in magnitude. If they were only designed to serve as nocturnal lights to us, they could be of no use during the greater part of the year. The cloudy atmosphere which often surrounds us, together with the short nights which are bright enough without their assistance, would render them useless. Besides, the stars which we cannot perceive by the naked eye, because of their vast distance, would be absolutely superfluous; and their supposed destination would be more completely accomplished by a single star bearer to us, than by so many millions at such a distance. As we may apply the same mode of reasoning to the whole of that use which we make of the stars, whether for navigation or any other purpose, we must confess, that it would be utterly impossible for us to see the utility of so many suns, if no creatures beyond our globe profited by their light and heat; or if they themselves were not the abode of different beings.

16. This consequence will appear still more reasonable, if we consider our solar system more attentively.. We have seen that the moon, in many respects, resembles our earth: that in her, as well as on our globe, there are continents and seas, mountains, vallies, islands, aid gulfs. Such striking similitudes authorize us to admit others, and to conclude that in the moon, there are minerals and vegetables, animals and rational creatures. The analogy between the moon and the other

planets, leads us to extend the same conjectures to them : and as each fixed star has, according to all appearance, like our sun its particular planets, so these planets undoubtedly resemble ours. Thus, we see around us an innumerable multitude of worlds, each of which has its peculiar arrangement, laws, productions, and inhabitants. In what glory do the divine perfections appear, when we for a moment, consider the stupendous spectacle of " thou sands of thousands of suns, multiplied without end, and at immense distances from each other-attended by ten thousand times ten thousand worlds, all hung LOOSE as it were, in boundless space-yct preserved in their rapid course, calm, regular, and harmonious-invariably keeping the paths assigned them by the CREATOR."

As

17. The principal cause of tides is the attraction of the moon, by which that part of the water in the ocean, nearest the moon, being most strongly attracted, is raised higher than the rest; and the part opposite to it, on the contrary side, being least attracted, is also higher than the rest. And these two opposite rises of the surface of the water in the great ocean, following the motion of the moon from east to west, and striking against the coasts of the continents that lie in its way, rebound, and cause floods and ebbs in narrow seas, and rivers remote from the ocean. the earth, by its daily rotation round its axis, goes from the moon to the moon again, (or the moon appears to move round the earth from a given meridian to the same again) in about twenty-four hours, hence in that period there are two tides of flood and two of ebb, and this alternate ebbing and flowing continues without intermission. If the tide be now at high-water mark, in any port, or harbour, which lies open to the ocean, it will presently subside, and flow regularly back, for about six hours, when it will be found at low-water mark. It will then again gradually advance for six hours, and return back, in the same time, to its former situation; rising and falling alternately, twice a day, or in the space of about twenty-four hours. The interval between its flux and reflux is, however, not precisely six hours, but about eleven minutes more; so that the time of high-water does not always happen at the same hour, but is about three quarters of an hour later every day, for thirty days; when it again recurs as before.

18. Spring and neap tides. The attraction of the sup also produces a similar rising and falling of the water of the ocean, but on account of its distance, it is not so considerable as that produced by the moon. According to the different situations of the sun and the moon, the tides, which are raised by their respective attraction, will either conspire with, or counteract each other, in a greater or less degree. When they conspire together, the tides rise higher, and their mutual action produces what are called spring tides. When they counteract each other, they produce neap tides. The tides are so retarded in their passage through channels, and so affected by capes and headlands, as to happen variously at different places. The tide raised in the German Ocean when the moon is three hours past the meridian, takes three hours to arrive at London bridge. Lakes have no tides, because every part is attracted alike. The Mediterranean and Baltic seas have but small elevations, on account of the narrowness of the inlets by which they communicate with the ocean. But for a full explanation of this curious and intricate subject, the reader must consult the writers on physical astronomy.

Select Books on Astronomy.

Keill's Astronomy, Dr. David 'Gregory's, Ferguson's, Bonnycastle's, Vince's, Dr. Olinthus Gregory's, Woodhouse's; Mr. Pond's Translation of Laplace's System of the World.

The best French works on the subject are those by Lalande, Laplace, and Biot.

CHAP. IX.—MAGNETISM.

1. THE magnet or loadstone is a hard mineral body, of

a dark brown, or almost black colour, and when examined, is found to be an ore of iron. The magnetic power may be communicated from the loadstone to iron or steel, by the touch or gentle friction, or from one piece of iron to another. These artificial magnets are even capable of being made more powerful than the natural ones. All magnets attract iron, and this in consequence of their attractive power. The directive power is, when a magnet is placed so as to be at liberty to move freely in every direction, its ends point towards the poles of the earth, or very nearly