There are some stars, whose situation and place were heretofore known and marked with precision, that are no longer to be seen; new ones have also been discovered, that were unknown to the ancients, while numbers seem gradually to vanish. There are others which are found to have a periodical increase and decrease of magnitude; and it is probable, that the instances of these changes, would have been more numerous, if the ancients had possessed the same accurate means of examining the heavens as are used at present.

New stars offer to the mind a phenomenon more surprising, and less inexplicable, than almost any other in the science of astronomy. I shall select a few instances of the more remarkable ones, for the instruction of the young pupil: a consideration of the changes that take place, at so immense a distance as the stars are known to be from him, may elevate his mind to consider the immensity of his power, who regulates and governs all these wide extended motions; "who hath measured the waters in the hollow of his hand, and meted out heaven with a span."

It was a new star discovered by Hipparchus, the chief of the ancient astronomers, that induced him to compose a catalogue of the fixed stars, that future observers might learn from his labours, whether any of the known stars disappeared, or new ones were produced. The same motives engaged the illustrious Tycho Brahe, to form, with unremitting labour and assiduity, another new catalogue of the stars.

Of new stars, the first of which we have a good

account, is that which was discovered in the constellation Cassiopea, in the month of November, of the year 1572; a time when astronomy was sufficiently cultivated, to enable the astronomers to give the account with precision. It remained visible about sixteen months; during this time, it kept its place in the heavens, without the least variation. It had all the radiance of the fixed stars, and twinkled like them; and was, in all respects, like Sirius, excepting that it surpassed it in brightness and magnitude. It appeared larger than Jupiter, who was at that time in his perigree; and was scarce less bright than Venus.

It was not by degrees that it acquired this diameter, but shone forth at once of its full size and brightness, as if of instantaneous creation. It continued about three weeks in full and entire splendor, during which time it might be seen even at noonday, by those who had good eyes, and knew where to look for it. Before it had been seen a month, it became visibly smaller, and from thence continued diminishing in magnitude till March 1574, when it entirely disappeared. As it decreased in size, it varied in colour; at first, its light was white, and extremely bright; it then became yellowish, afterwards of a ruddy colour, like Mars; and finished with a pale livid white, resembling that of Saturn.

In August 1596, Fabricius observed a new star in the neck of the Whale. In 1637, Phocyllides Holwarda observed it again, and, not knowing that it had been seen before, took it for a new discovery:

he watched its place in the heavens, and saw it appear again the succeeding year, nine months after its disappearance. It has been since found to be every year very regular in its period, except that in 1672 it was missed by Hevelius, and not seen again till 1676. Bullialdus determined the periodical time between this star's appearing in its greatest brightness, and returning to it again, to be about 333 days; observing further, that this star did not appear at once in its full magnitude and brightness, but by degrees arrived at them.

Three changeable, or re-apparent stars have been discovered in the constellation of the Swan; the first was seen by Jansonius, in 1600; the second was discovered in 1670; the third by Kirchius, in 1686.

In the latter end of September, 1604, a new star was discovered, near the heel of the right foot of Serpentarius. Kepler, in describing it, says, that it was precisely round, without any kind of hair or tail; that it was exactly like one of the stars, except that in the vividness of its lustre, and the quickness of its sparkling, it exceeded any thing he had ever seen before. It was every moment changing into some of the colours of the rainbow, as yellow, orange, purple, and red; though it was generally white, when it was at some distance from the vapours of the horizon. Those in general who saw it, agreed that it was larger than any other fixed star, or even any of the planets, except Venus; it preserved its lustre and size for about three weeks; from this time it grew gradually smaller. Kepler

supposes that it disappeared some time between October, 1605, and the February following, but on what day is uncertain.

Besides these several re-apparent stars, so well characterized and established by the earliest among the modern astronomers, there have been many discovered since, by Cassini, Maraldi, and others; Mr. Montanere speaks of having observed above one hundred changes among the fixed stars.

The star Algol, in Medusa's head, has been observed long since to appear of different magnitudes, at different times. The period of it has been lately settled by J. Goodrick, Esq. of York. It periodically changes from the first to the fourth magnitude: the time employed from one greatest diminution to the other, was, anno 1783, at a mean 2 days, 20 hours, 49 minutes, 3 seconds.

The causes of these appearances cannot be assigned at present, with any degree of probability; perhaps they have some analogy to the spots on the sun, which at some times appear in greater numbers than at others, some of them bigger than the whole earth; or perhaps they are owing to some real motions of the stars themselves.

There are several stars that appear single to the naked eye, which are, on examination with a telescope, found to consist of two, three, &c. The number of double stars observed before the time of Dr. Herschel, was but small; but this celebrated astronomer has noted upwards of four hundred ; among these, some that are double, others that are

treble, double double, quadruple, double treble, and multiple; his catalogue gives the comparative size of these stars, their colour, as they appeared to him, with several other very curious particulars.

OF NEBULÆ, AND OF HERSCHEL'S IDEAS RESPECTING THE CONSTRUCTION OF THE UNIVERSE.

Besides, those appearances of the fixed stars, already noticed, there is another which deserves particular attention; namely, the nebulæ, or parts of the heavens which appear brighter than the rest. The most remarkable among these is, that large irregular zone, or band of whitish light, which crosses the ecliptic in Cancer and Capricorn, and is inclined thereto in an angle of about 60 degrees; it is a circle bisecting the celestial sphere, irregular in breadth and brightness, and in many places divided into double streams. The principal part runs through the Eagle, the Swan, Cassiopea, Perseus, and Auriga: it continues its course by the head of Monoceros; along by the greater Dog, through the Ship, under the Centaur's Feet; till having passed the Altar,the Scorpion's Tail, and the Bow of Aquarius, it ends at last where it began.

This curious appearance is owing to a multitude of small stars, which are too minute to be distinguished by the naked eye; yet, blending their light together, form that whiteness which occupies so large a tract of the heavens. The milky-way may be