The distances of the fixed stars are fo great, that we have no distance in the planetary system with which we can compare them; for the diameter of the Earth's orbit, which is nearly 190,000,000 miles, bears no fenfible proportion to the distance of the nearest fixed ftar from the Earth.

The diftances of the fixed stars have been the subject of investigation to feveral aftronomers. Various methods have. been devised for the purpose of difcovering the diftances of thefe heavenly bodies, but without fuccefs, on account of their almost infinite diftance; the most accurate obfervations only gave us a diftant approximation; but by the best obfervations, however, we can fafely conclude that the nearest fixed ftar is upwards of forty thousand diameters of the Earth's orbit diftant from us, or eighty thousand times farther diftant from us than the Sun is.

The magnitudes of the fixed ftars appear very different in different ftars, owing, in fome fort, to their real magnitudes, which are different, but principally owing to their different diftances from us.

The ftars are generally divided, according to their apparent magnitudes, into fix, and by fome into eight claffes. The first clafs, called ftars of the firft magnitude, are thofe that appear largeft: ftars of the fecond magnitude appear fomewhat lefs; and thus every following clafs comprehends thofe ftars next in fize to the former class: the stars of the fixth magnitude containing the fmalleft ftars vifible to the naked eye. All others that cannot be perceived, but by the help of telescopes, are called telescopic stars. It is not to be inferred from hence that Nature has divided the ftars into thofe claffes; for there are almoft as many claffes as there are ftars, fo great is their variety of magnitude and brightness!

The number of ftars is alfo very great, and appears to be almoft infinite; but aftronomers have deduced all that are visible to the naked eye into catalogues. Mr. Flamstead reduced 3000 ftars into a catalogue, which contains all that are visible to the naked eye at any time of the year, and a great

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great number that are only visible through a telescope. The number of ftars that are vifible at one time, in the clearest heaven, feldom exceeds 1000; their appearing so much more numerous arifes from their twinkling, and from viewing them confusedly, without reducing them into any order. But a good telescope will, nevertheless, bring great numbers to our view: and the more the magnifying power of the telescope is increafed, the greater will be the number of stars discovered; till the number becomes fo great as to baffle our computation.

From the great distance of the stars, we are at a loss to discover many of their properties; but from their phenomena we can with certainty deduce the following theorems concerning them:-1. That they are much greater than our Earth; for, if that were not the cafe, they could not be vifible at fuch a distance.-2. They are farther distant than the most diftant of the planets; for we often find them hidden behind the body of the planets.-And, 3. They thine with their own natural light; for though they be much farther from the Sun than Saturn is, and appear much smaller to us, yet they thine much brighter than that planet. And it is known, that the more the telescope magnifies, the lefs is the angle under which the ftar is feen; because the telescope destroys all the adventitious rays. Thus a telescope magnifying 200 times will fhow a ftar lefs in magnitude than it appears to the naked eye, infomuch, that it will appear to be only an indivifible point.

From hence we conclude, that the fixed stars are so many Suns; and that, in all probability, they are not much finaller than our Sun, but perhaps larger.

Therefore, it is generally believed that every star is the centre of a system, and has planets revolving round it in the fame manner as the Earth and the other primary planets revolve round the Sun; for our Sun, together with the orbits of all the planets, would be almoft invifible from the nearest fixed ftar.

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To imagine that the stars are formed only to afford us a faint light, would be abfurd, as we have incomparably more light from the Moon than from all the fixed stars taken together.

The fixed ftars have two apparent motions; one called the first, common, or diurnal motion; the other called the fecond or proper motion. The former of these motions arifes from the Earth's motion round its axis; by which the ftars appear to be carried round the Earth, from east to weft, in the space of 24 hours. The latter is that motion by which they appear to go backwards from weft to east round the poles of the ecliptic with a very flow motion, defcribing only one degree of a circle in the space of 71 years. This apparent motion is owing to the preceffion of the equinoxes; or, in other words, the axis of the Earth is directed to different parts of the heavens every year, describing a circle, one degree of which it describes in 71 years.

The Zodiac is an imaginary ring or zone in the heavens, in the fpace of which all the primary planets revolve in their orbits: its breadth is made different by different astronomers, but is from eight to ten degrees on each fide the ecliptic; and is divided into twelve parts, called the Twelve Signs of the Zodiac, and each fign is fubdivided into 30 degrees; the degrees are each again divided into minutes, feconds, &c. But as the ftars have a motion from weft to eaft, these conftellations, or figns of the Zodiac, do not now correspond to their proper figns; for the vernal equinox formerly happened when the Sun was in the first degree of Aries, and the Earth in the oppofite degree of the Zodiac, or first degree of Libra; whereas now, the Sun has advanced a whole fign from that point at the vernal equinox.

The twelve figns of the Zodiac are diftinguished by the following names and characters, viz. ❤ Aries, & Taurus, Gemini, Cancer, Leo, my Virgo, Libra, m Scor

pio, Sagittarius, VS Capricornus, Aquarius, Pifces: or, according to the English names, the Ram, the Bull, the Twins, the Crab, the Lion, the Virgin, the Balance, the Scorpion, the Archer, the Goat, the Water-bearer, and the Fishes.

Befides these constellations in the Zodiac, the stars in every other part of the heavens are reduced into conftella tions of fome certain figures, to which it is fuppofed each fet of ftars bears fome refemblance. In the northern hemisphere are 21 conftellations, of which the following are the names: the Little Bear, Great Bear, the Dragon, Cepheus, Boötes, the Northern Crown, Hercules, the Harp, the Swan, Caffiopeia, Perfeus, Auriga, Serpentary, the Serpent, the Arrow, the Eagle, the Dolphin, the Horfe, Pegafus, Andro meda, and the Triangle. In the fouthern hemisphere are 15 conftellations, viz. the Whale, Orion, the Eridanus, the Hare, the Great Dog, the Little Dog, the Ship, the Hydra, the Cup, the Raven, the Centaur, the Wolf, the Altar, the Southern Crown, and the Southern Fish.

This divifion was introduced by Ptolemy, and to these Bayer added 12 more, about the fouthern pole, viz. the Peacock, the Tucan, the Crane, the Phoenix, the Dorado, the Flying Fish, the Hydra, the Chamelion, the Bee, the Bird of Paradife, the Triangle, and the Indian.

To thefe, Mr. Royer has added 11 other conftellations, viz. the Giraffe, the River Jordan, the River Tigris, the Sceptre, and the Flower-de-Luce, being on the north. The following fix are on the fouth part, viz. the Dove, the Unicorn, the Cross, the Great Cloud, the Little Cloud, and the Rhomboid.

Hevelius alfo added the following new conftellations, compofed of fome unformed ftars, viz. the Unicorn, the Camelopardalis, the Sextant of Urania, the Dogs, the Little Lion, the Lynx, the Fox and Goose, Sobieski's Crown, the Lizard, the Little Triangle, and the Cerberus, to which Gregory has added the Ring and the Armilla.

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It must, however, be remarked, that fome of these conftellations introduced by Hevelius anfwer to fome of thofe of Royer; as the Camelopardalis to the Giraffe, the Dogs to the River Jordan, and the Fox to the River Tigris. The foregoing is the number of the conftellations as they stand at prefent; but an attempt has lately been made by Dr. Hill, to introduce fourteen new ones; they are, however, not yet adopted by mathematicians.

Befides the stars in the foregoing conftellations, there are a great number of ftars not included in any conftellation, and therefore called unformed ftars.

The Galaxy, or Milky Way, is that long, white, luminous tract which feems to encompafs the heavens, and is eafily feen in a clear night, when the Moon is not up. It is of a confiderable breadth, and in fome parts double. Its luminous appearance is owing to the great number of small ftars with which it is every where befpangled, and which by a good telescope may be plainly discovered.

Of Comets.

A comet is a wandering body, appearing fuddenly, and as fuddenly difappearing; and moves in its own proper orbit, like a planet.

It is ufually furnished with a long train of light, called its tail, which is always oppofite to the Sun. Comets are divided into three kinds; viz. bearded, tailed, and hairy comets: which divifion arifes from the different fituation of the comet. Thus, when the comet is eastward of the Sun, and moves from him, it is said to be a bearded comet, because the light precedes it in the manner of a beard: when the comet is weftward of the Sun, and fets after him, it iş faid to be a tailed comet, because the train of light follows it in the manner of a tail: and when the Sun and comet are in oppofition to each other, the Earth being between them, the

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