The two stars which form the eastern side of the square, come to the meridian about an hour after those in the western. The northern one has already been described as Alpheratz in the head of Andromeda, but it also belongs to this constellation, and is 14° E. of Scheat. 14° S. of Alpheratz, is Algenib, the last star in the wing, situated 161° Ē. of Markab.

Algenib, in Pegasus, Alpheratz, in Andromeda, and Caph in Cassiopeia are situated on the prime meridian, and point out its direction through the pole. For this reason, they are sometimes called the three guides. They form an arc of that great circle in the heavens from which the distances of all the heavenly bodies are measured. It is an arc of the equinoctial colure which passes through the vernal equinox, and which the sun crosses about the 21st of March. It is, in astronomy, what the meridian of Greenwich is in geography. If the sun, or a planet, or a star, be said to have so many degrees of right ascension, it means that the sun or planet has ascended so many degrees from this prime meridian. Enif, sometimes called Enir, is a star of the 3d magnitude in the nose of Pegasus, about 20° W. S. W. of Markab, and halfway between it and the Dolphin. About of the distance from Markab towards Enif, but a little to the S., there is a star of the 3d magnitude situated in the neck, whose letter name is Zeta. The loose cluster directly S. of a line joining Enif and Zeta, forins the head of Pegasus.

In this constellation, there are eighty-nine stars visible to the naked eye, of which three are of the second magnitude and three of the third.

HISTORY.-This, according to fable, is the celebrated horse which sprung from the blood of Medusa, after Perseus had cut off her head. He received his name according to Hesiod, from his being born near the sources (y, Pege) of the ocean. According to Ovid, he fixed his residence on Mount Helicon, where by striking the earth with his foot, he raised the fabled fountain called Hippocrene. He became the favourite of the Muses; and being tamed by Neptune or Minerva, he was given to Bellerophon, son of Glaucus, king of Ephyre, to aid him in conquering the Chimæra, a hideous monster that continually vomited flames. This monster had three heads, that of a lion, a goat, and a dragon. The fore parts of its body were those of a lion, the middle those of a goat, and the hinder those of the dragon. It lived in Lycia, of which the top, on account of its desolate wilderness, was the resort of lions, the middle, which was fruitful, was cov. ered with goats, and at the bottom, the marshy ground abounded with serpents. Bellerophon was the first who made his habitation upon it.

Plutarch thinks the Chimæra was the captain of some pirates who adorned their ship with the images of a lion, a goat, and a dragon.

After the destruction of this monster, Bellerophon attempted to fly up to heaven upon Pegasus; but Jupiter was so displeased at this presumption, that he sent an insect to sting the horse, which occasioned the melancholy fall of his rider. Bellerophon fell to the earth, and Pegasus continued his flight up to heaven, and was placed by Jupiter among the constellations.

"Now heav'n his further wand'ring flight confines,
Where, splendid with his num'rous stars, he shines."

Ovid's Fasti.

EQUULUS, VEL EQUI SECTIO.

THE LITTLE HORST, OR THE HORSE'S HEAD.-This Asterism, or small cluster of stars, is situated about 7° W. of Enif, in the head of Pegasus, and about halfway between it

Describe the two on the east side. What is the name of the star in the N. E. correr of the square? In the S. E. corner? In the S. W. corner? In the N. W. corner? Describe the position and magnitude of Enif. What is the whole number of stars in Pegasus? What's the magnitude of the principal ones? Describe the situat m of the the Little Hors

and the Dolphin. It is on the meridian at 8 o'clock, on the 11th of October. It contains ten stars, of which the four principal are only of the 4th magnitude. These may be readily distinguished by means of the long irregular square which they form. The two in the nose, are much nearer together than the two in the eyes; the former being 10 apart, and the latter 210. Those in the nose are uppermost, being 4° N. of those in the eyes. This figure also is in an inverted position. These four stars are situated 10° or 12° S. E. of the diamond in the Dolphin's head. Both of these clusters, are noticeable on account of their figure rather than their brilliancy.

HISTORY.-This constellation is supposed to be the brother of Pegasus, named Celeris, given by Mercury to Castor, who was so celebrated for his skill in the management of horses; others take him to be the celebrated horse which Neptune struck out of the earth with his trident, when he disputed with Minerva for superiority. The head only of Celeris is visible, and this, also, is represented in an inverted position.

AQUARIUS.

THE WATER-BEARER.-This constellation is represented by the figure of a man, pouring out water from an urn. It is situated in the Zodiac, immediately S. of the equinoctial, and bounded by the Little Horse, Pegasus, and the Western Fish on the N., the Whale on the E., the Southern Fish on the S. and the Goat on the W. It is now the 12th in order, or last of the Zodiacal constellations; and is the name of the 11th sign in the ecliptic. Its mean declination is 14° S. and its mean right ascension 335°, or 22 hours, 20 min.; it being 1 hour and 40 min. W. of the equinoctial colure; its centre is, therefore, on the meridian the 15th of October.

It contains one hundred and eight stars; of which the four largest are all of the 3d magnitude.

"His head, his shoulders, and his lucid breast,
Glisten with stars; and where his urn inclines
Rivers of light brighten the wat❜ry track."

The northeastern limit of Aquarius may be readily distinguished by means of four stars of the 4th magnitude, in the hand and handle of the urn, so placed as to form the letter Y, very plainly to be seen, 15° S. E. of Enif, or 18° S. S. W. of Markab, in Pegasus ; making with the two latter nearly a right angle.

When is it on the meridian? What is the whole number of its stars? What is the magnitude of the principal ones? How may the principal stars be distinguished! How are the two in the nose distinguished from the two in the eyes? What are their distance and direction from the Dolphin? On what account are these clusters noticea ble? How is Aquarius represented? Where is it situated? What is its present order among the constellations of the Zodiac? What are its right ascension and declination? What is the whole number of its stars? What is the magnitude of the principal ones? How may the N. E. limit of Aquarius be readily distinguished? What are the distance and direction of this letter Y, from Markab and Enif, in Pegasus ?

About 440 W. of this figure is El Melik, a star of the 3d magnitude, in the E shoulder, and the principal one in this constellation. 10° S. W. of El Melik, is another star of the same magnitude, situated in the W. shoulder, called Sad es Saud.

Ancha of the 4th magnitude, is in the right side, 8° S. of El Melik. 90 E. of Ancha, is another star of the 4th magnitude, whose letter name is Lambda.

Scheat, of the 3d magnitude, lying below the knee, is situated 83° S. of Lamb da; and 14° S. of Scheat, the brilliant star Fomalhaut,* of between the 1st and 2d magnitudes, terminates the cascade in the mouth of the Southern Fish. This star is common to both these constellations, and is one of those from which the lunar distance is computed for ascertaining the longitude at sea. It culminates at 9 o'clock on the 22d of October.

Fomalhaut, Deneb Kaitos, and Alpha in the head of the Phoenix, make a large triangle, whose vertex is in Deneb Kaitos. Those two stars of the 4th magnitude, situated 4° S. of Sad es Saud, and nearly the same distance from Ancha, are in the tail of Capricorn. They are about 20 apart. The western one is called Deneb Algedi.

The rest of the stars in the cascade are quite small; they may be traced from the letter Y, in the urn, in a southeasterly direction towards the tail of Cetus, from which the cascade suddenly bends off near Scheat, in an opposite course, and finally disappears in the mouth of the Southern Fish, 30° S. of Y.

HISTORY.-This constellation is the famous Ganymede, a beautiful youth of Phrygia, son of Tros, king of Troy, or, according to Lucian, son of Dardanus. He was taken up to heaven by Jupiter as he was tending his father's flocks on Mount Ida, and became the cupbearer of the gods in place of Hebe. There are various opinions, however, among the ancients respecting its origin. Some sup. pose it represents Deucalion, who was placed among the stars after the celebra ted deluge of Thessaly, 1500 years before the birth of our Saviour; while others think it designed to commcinorate Cecrops, who came from Egypt to Greece, founded Athens, established science, and introduced the arts of polished life.

The ancient Egyptians supposed the setting or disappearance of Aquarius caused the Nile to rise, by the sinking of his urn in the water.-In the Zodiac of the Hebrews, Aquarius represents the tribe of Reuben.

PISCIS AUSTRALIS, VEL NOTIUS.

THE SOUTHERN FISH.-This constellation is directly S. of Aquarius, and is represented as a fish drinking the water which Aquarius pours from his urn. Its mean declination is 31° S. and its mean right ascension and time of passing the meridian are the same as those of Aquarius, and it is seen on the meridian at the same time; viz., on the 15th of October. It contains 24 visible stars, of which one is of the 1st magnitude or between the 1st and 2d, two are of the 3d, and five of the 4th. The first and most beautiful of all is Fomalhaut, situated in the mouth. This is 14° directly S. of Scheat in Aquarius, and may be seen passing the meridian low down in the southern hemisphere, on the 22d and 23d of October.

*Pronounced Fo-ma-lo.

What is the name of the principal star in this constellation? What is its position? What star in the W. shoulder? Describe the situation of Ancha. What is the posi tion of Scheat and Fomalhaut? To what constellations is Fomalhaut common? Of what nautical importance is it? When does it culminate? With what other stars does it form a large triangle? How may you trace the stars in the cascade? Describe the situation and appearance of the Southern Fish. What are its mean right ascension. and declination? When is it on the meridian? What is the whole number of its stars? What is the magnitude of its principal ones? What are the name and position of the most brilliant star in the constellation? When and where does it pass the meridian?

Its position in the heavens has been determined with the greatest possible accuracy, to enable navigators to find their longitude at sea.

The mode of doing this cannot be explained here. The problem is one of some difficulty. It consists in finding the angular distance between some star whose position is well known, and the moon when she is passing near it; also, the altitude of each, at the same instant, with good sextants. These data furnish the elements of a spherical triangle, the solution of which, after various intricate corrections, is made to result in the longitude of the given place.-See note to Arieties. In 1714, the British Parliament offered a reward of 10,000 pounds ster ling, to any man who should discover a method of determining the longitude within 10, or 60 geographic miles of the truth; 15,000 pounds to the man who should find it within 40 miles, and 20,000 pounds, if found within 30 miles. These rewards in part have been since distributed among eminent mathematicians, in Europe, agreeably to the respective merits of their discoveries.

HISTORY.-This constellation is supposed to have taken its name from the transformation of Venus into the shape of a fish when she fled, terrified at the horrible advances of the monster Typhon, as we have related in the inythology of the Fishes. (See Pisces.)

CHAPTER XIII.

VARIABLE AND DOUBLE STARS-CLUSTERS-NEBULE.

1. VARIABLE STARS.-The periodical variations of brilliancy to which some of the fixed stars are subject, may be reckoned among the most remarkable of their phenomena. Several stars, formerly distinguished by their splendour, have entirely disappeared; others are now conspicuous which do not seem to have been visible to the ancient observers; and there are some which alternately appear and disappear, or, at least, of which the light undergoes great periodic changes. Some seem to become gradually more obscure, as Delta in the Great Bear; others, like Beta in the Whale, to be increasing in brilliancy. Some stars have all at once blazed forth with great splendour, and, after a gradual diminution of their light, again become extinct. The most remarkable instance of this kind is that of the star which appeared in 1572, in the time of Tycho Brahe. It suddenly shone forth, in the constellation Cassiopeia, with a splendour exceeding that of stars of the first magnitude, even of Jupiter and of Venus, at their least distances from the earth; and could be seen, with the naked eye, on the meridian, in full day! Its brilliancy gradually diminished from the time of its first appearance, and at the end of sixteen months, it entirely disappeared, and has

For what purpose has its position been very accurately determined? Describe the periodical variations of brilliancy to which some of the fixed stars are subject? Mention some of the most remarkable instances of such variations, and describe them particularly.

never been seen since. (See a more particular account of this phenomenon, page 40.)

Another instance of the same kind was observed in 1604, when a star of the first magnitude suddenly appeared in the right foot of Ophiuchus. It presented, like the former, all the phenomena of a prodigious flame, being, at first, of a dazzling white, then of a reddish yellow, and, lastly, of a leaden paleness; in which its light expired. These instances prove that the stars are subject to great physical revolutions.-Page 41. A great number of stars have been observed whose light seems to undergo a regular periodic increase and diminution. They are properly called Variable Stars. One in the Whale has a period of 334 days, and is remarkable for the magnitude of its variations. From being a star of the second magnitude, it becomes so dim as to be seen with difficulty through powerful telescopes. Some are remarkable for the shortness of the period of their variation. Algol has a period of between two and three days; Delta Cephei, of 5 days; Beta Lyræ, of 6 2-5 days; and Mu Antinoi, of 7 days.

The regular succession of these variations precludes the supposition of an actual destruction of the stars; neither can the variations be supposed to arise from a change of distance; for as the stars invariably retain their apparent places, it would be necessary to suppose that they approach to, and recede from the earth in straight lines, which is very improbable. The most probable supposition is, that the stars revolve, like the sun and planets, about an axis. "Such a motion," says the elder Herschel, "may be as evidently proved, as the diurnal motion of the earth. Dark spots, or large portions of the surface, less luminous than the rest, turned alternately in certain directions, either towards or from us, will account for all the phenomena of periodical changes in the lustre of the stars, so satisfactorily, that we certainly need not look for any other cause. ""

2. DOUBLE STARS.-On examining the stars with telescopes of considerable power, many of them are found to be composed of two or more stars, placed contiguous to each other, or of which the distance subtends a very minute angle. This appearance is, probably, in many cases, owing solely to the optical effect of their position relative to the spectator; for it is evident that two stars will appear contiguous if they are

What are such stars denominated? Describe the variations of one in the Whale. What stars are remarkable for the shortness of the period of their variations? Why may we not suppose that the stars which disappear are actually destroyed? Why may ot the variations arise from a change of distance? What is the most probable supposition in regard to their cause? How does Dr. Herschel explain these phenomena On examining the stars with a telescope of considerable power, what other peculiarity do we find? To what is this appearance, in many cases, owing?