periods, about forty days, during which time the cluster would be invisible owing to its proximity to the sun, corresponds with the preceding statement. Hesiod likewise observes, that when the Pleiades rise from the dark seas, sailing is dangerous, and that, on account of violent winds and rain, it is necessary to have large vessels, well provided with ballast, and to work much at the pumps. Here, he evidently alludes to what is called the acronical rising of the stars, which takes place at the setting of the sun. This would happen in his day soon after the autumnal equinox, in the case of the group named; and at that season, we know that storms are common in the Grecian seas. The names of several of the constellations occur in Homer. In the fifth book of the Odyssey, he makes Ulysses, upon leaving the island-goddess for his bark, speak of the "Pleiades and Bootes, the Hyades, and bold Orion, the Bear, which is called the Wain, the unwearied sun, and the full moon, and all the stars, by which, like a crown, the heavens are surrounded." He mentions Sirius also, and Hesiod in addition introduces Arcturus; but neither of these writers take any notice of the planets. The reference, in the fine passage descriptive of Tydides in the Iliad, is doubtful:

66

:

High on his helm celestial lightnings play,
His beamy shield emits a living ray;
The unwearied blaze incessant streams supplies,
Like the red star that fires the autumnal skies,
When fresh he rears his radiant orb to sight,
And bath'd in ocean shoots a keener light."

Some conjecture Venus to have been intended, others Sirius; and it may here be mentioned, as a singular physical fact, that Sirius, now so brilliantly white, was known as a red star to the ancients-a change of aspect which is not a solitary instance of the phenomenon. By THALES

the founder of the Ionic school the basis was laid, of whatever profi

ciency the Greeks attained in astronomical science, for they were never distinguished as a people by the study of physical nature. Of him, the familiar story is related, that when a boy at Miletus, his native city, he fell into a ditch while contemplating the stars, upon which Thressa, his conductress, exclaimed, "Why, O Thales, do you seek to comprehend the things which are in the heavens when you are not able to see those before your eyes?" The truth of this anecdote has been doubted, but the remark harmonises with what we know to have been the general tone of the Grecian mind. The great men of the country were chiefly poets, warriors, statesmen, orators, and moral rather than natural philosophers. It was not the spirit of scientific enquiry, but a love of speculative and tasteful sentiment, that elevated the soul of Plato into communion with the skies, and inspired the thought, that because the flight of birds, and the movement of every body through space, produced a vibrative sound, that therefore the motion of the celestial objects must occasion a ravishing harmony, fitly called the music of the spheres an idea to which Shakspeare gives expression in the address of Lorenzo in the grove to Jessica:

"How sweet the moonlight sleeps upon this bank!
Here will we sit, and let the sounds of music
Creep in our ears; - soft stillness and the night
Become the touches of sweet harmony.

Sit, Jessica; look how the floor of heaven

Is thick inlaid with patterns of bright gold:

There's not the smallest orb, which thou behold'st,

But, in his motion, like an angel sings,

Still quiring to the young-eyed cherubim.

Such harmony is in immortal souls.”

It was the tendency in general of the Attic mind to study with ardour, morals, politics, and religion, but to play with physical phenomena: regarding only the graceful and poetic sentiments they suggested. Thales, an Ionian, and his successors, were exceptions to this rule of their countrymen, and arrived at conceptions respecting the constitution of the universe which strongly sympathise with the hypotheses that are now admitted. The most prominent circumstances concerning him are, that while the Greeks were contented with the rough approximation to the north afforded by the Great Bear, he introduced the knowledge of the Little Bear, by which the Phoenician mariners had long been accustomed to steer; that he made a near approach to the diameter of the sun, taken at a mean; taught the sphericity of the earth; and predicted a great solar eclipse, which occurred at the time announced. We may regard this last-mentioned particular as the greatest astronomical achievement, resting upon good authority, that had hitherto transpired. Herodotus, whose relation may be substantially confirmed by other testimonies, observes, that in the midst of an action between the Medes and Lydians, the day was suddenly changed into night. He adds, that Thales the Milesian had predicted the year in which the eclipse would happen, and that the hostile armies, when they saw the darkness, desisted from the battle. According to the calculations of Bailly, the centre of the moon's shadow passed in a right line over the north-eastern part of Asia Minor, the scene of the war, through Armenia into Persia, on the morning of September 30th, B. c. 610. Want of minuteness in the historian probably led to the statement that the prediction referred only to the year in which the eclipse would take place, for, as it was total, or nearly so, Thales must have been able to come much nearer to the time. It follows, also, that such a prediction could only have been made with certainty by one in possession of a long series of observations derived from some foreign source, as the Greeks themselves had not originated any in all likelihood from Chaldea, where the requisite materials might be found.

The opinions held by the successors of Thales are in several respects remarkably accordant with modern ideas. Anaximander maintained the tenet of the earth's movement about its axis, and of the moon's light being reflected from the sun. Anaxagoras, who transferred the Ionic school from Miletus to Athens, in addition offered a conjecture that, like the earth, the moon had habitations, hills, and valleys. All these truths were taught upon a more extended scale by PYTHAGORAS, who appears to have reached the sublime conception of the earth's motion round the sun, which Philolaus, his successor in the Crotonian school, is generally believed to have taught openly. According to the Pythagoreans, not only the planets, but the comets themselves, are in motion round the sun, and not floating meteors formed in the atmosphere. But such philosophic views as these, instead of obtaining the suffrages of antiquity, met with little acceptance, because opposed to the evidence of the senses; and they slumbered for eighteen centuries, owing to the powerful confirmation given to the doctrines of Aristotle by the apparent motions of the heavenly bodies. These gleams of truth vanished from the world with the existence of the Ionic and Crotonian schools. A blind submission was yielded for ages to the dogmas of the Peripatetics, who held the earth to be the quiescent centre of the universe, the

celestial bodies its servants, moving in circular orbits, and with uniform velocities, and

comets simply meteors generated in the terrestrial atmosphere. The divine Plato indeed, the master of Aristotle, is said to have renounced his opinion upon one of these points in his old age, and to have admitted that the centre ought to be appropriated to some more noble object than the earth, or, rather, than terrestrial substance. It is a plausible conjecture, that the elements of his own system were first suggested to the mind of Copernicus by notices of the opinions of the disciples of Thales and Pythagoras. They won few converts, however, among the Greeks, and in some instances exposed their professors to persecution. The Athenians condemned

Anaxagoras to death for his philosophical views, a fate from which he was saved by the interest of Pericles, but he was sentenced to perpetual banishment, and died in an obscure town on the Hellespont. Philolaus also suffered persecution on account of his doctrine of the earth's annual revolution, which so shocked the prejudices of men as to subject him who maintained it to the suspicion of impiety.

Egypt became the chief seat of astronomical science in the ancient world soon after the age of Aristotle. Alexandria had risen by the delta of the Nile at the command of the conqueror from whom its name is derived, and under the superintendence of the architect who proposed cutting mount Athos into the figure of a man. Upon the death of Alexander it became the capital of one of the kingdoms formed out of the ruins of his empire. The first of the Ptolemies laid the foundation of its celebrated library-perhaps the most extensive collection of books ever brought together before the invention of printing. His successor established in connection with it a college for the cultivation of the pure sciences, invited the most accomplished of the Greeks to repair to it, supplied them with whatever instruments could be furnished necessary to their pursuits, and thus arose the Alexandrian school, which received the flattering epithet of Divine, on account of the acquirements of its professors, and the philosophical character of its investigations. It originated a connected series of observations relative to the constitution of the universe. The positions of the fixed stars were determined, the paths of the planets carefully traced, and the solar and lunar inequalities more accurately ascertained. Angular distances were calculated with instruments suitable to the purpose by trigonometrical methods, and, ultimately, the school of Alexandria presented to the world the first system of theoretical astronomy that had ever comprehended an entire plan of the celestial motions. The system we know to be false, and inferior to the Pythagorean notions; but it had the merit of being founded upon a long and patient observation of phenomena, a principle which finally brought about its own destruction, while the previous theories were the results of pure hypothesis.

E

The most interesting circumstances connected with the early history of the Alexandrian school are the attempts made to determine the distance of the earth from the sun, and the magnitude of the terrestrial globe. Aristarchus of Samos is the author of an ingenious plan to ascertain the former. Suppose the centre of the circle s to represent the centre of the sun, M that of the moon, and at E the position of an observer on the surface of the earth. It is easy to perceive that, when the moon has half her disc illuminated by the sun, a line drawn from E to M will be perpendicular to another line drawn from s to M, making with each other a right angle. The plan of Aristarchus was, that the angular distance S E M should at that time be taken, which is possible, because both the sun and moon may then be seen at once above the horizon, from whence the ratio of E S to E м may be determined. He obtained the general result, that the distance of the sun from the earth is about nineteen times as great as that of the moon from the earth. We now know that the distance is much greater; but notwithstanding the inaccuracy of the result, the method employed is undoubtedly just, and reflects the highest honour upon the genius of its proposer. He failed in practice, owing to the difficulty of ascertaining the exact time of the bisection of the moon's disc, and the imperfect instruments then in use for the measurement of angular distances. The determination of the sun's distance from the earth, with any thing like precision, is only of recent date, and has been effected by means of which the ancients could have had no conception. Aristarchus held the Pythagorean doctrine of the motion of the earth in space, and gave the right answer to the formidable objection long afterwards made to it, that of the non-existence of an annual parallax. The answer recognised the earth's orbit as being an insensible point in comparison with the vast distance of the fixed stars. The boundaries of the universe were thus extended to his mind far beyond any limits conceived by his predecessors. There is great obscurity resting upon his life. The era of his birth and death is unknown; but he was alive B. C. 280, as an observation of the solstices made by him at that date has been preserved. The Greek text of his only surviving work, "On the Magnitudes and Distances of the Sun and Moon," was edited in this country by Dr. Wallis in 1688. He estimated the apparent diameter of the sun at 30',—about 2' too little.

The attempt to determine the magnitude of the earth was made by Eratosthenes, and we have reason to believe this was the first attempt ever made to solve the problem, as certainly it was to do it upon a true principle. Syene, in Upper Egypt, then a flourishing city, now Assouan, has acquired an interest from its connection. with this experiment. It was supposed to lie exactly under the tropic of Cancer, as it had been observed that, on the day of the summer solstice, at noon, a well there was enlightened to the bottom, while vertical bodies threw no shadow for the space of about three hundred stadia around it. At Alexandria, therefore, which was conceived to lie under the same meridian, on the same day at noon, when the sun was believed to be vertical at Syene, Eratosthenes measured his zenith distance, or the value of an arc of the meridian between the two cities.

Let E be the centre of the earth, a Alex-
The celestial arc contained between the

andria, s the sun, and s' Syene. zeniths of the two places, Alexandria and Syene, was found to be equal to th of the circumference of a circle, that is, to 7° 12'. Now, admitting the earth to be of a spherical form, Eratosthenes would obtain the measure of its circumference, by multiplying fifty times the distance between the cities. This distance was ascertained by order of the government to be 5000 stadia, and consequently the result obtained for the length of the

whole terrestrial circumference was 250,000 stadia. The great uncertainty that exists, as to the value of the stadium in question, prohibits any appreciation of the measurement: but several important errors were committed in the practical application of a right principle. No allowance was made for the solar parallax, and instead of Syene being under the tropic of Cancer and on the meridian of Alexandria, it is about 50′ north of the former, and nearly 3° east of the latter. The principle of the method employed is, however, precisely the same as that which has been acted upon in modern times; and our more accurate results in determining the magnitude of the earth are owing to greater nicety in observation, attention to all the elements which the solution of the problem requires, and more perfect instruments for the measurement of linear and angular distances. The inventor of the method was born at Cyrene, in the year 276 B. C. The third Ptolemy invited him to his capital, giving him the charge of its library; but becoming weary of life at the advanced age of eighty, he died by voluntary starvation, and was succeeded in his office of librarian by the author of the Argonautics.

We now come to the greatest astronomical name in antiquity—that of Hipparchus who may be properly regarded, on account of the plans he pursued and the results he obtained, as the father and founder of real astronomy. The invention of spherical trigonometry is supposed to be due to him, and undoubtedly the first application of it is, by which the places of the celestial bodies may be fixed, and the variations of their movements exhibited with precision. He approximated also closely to the true length of the tropical year, which had been previously held to be 3654 days. This he discovered to be an error in excess, by comparing one of his own observations of the summer solstice, with another made by Aristarchus of Samos, 145 years before. His own determination of 365 days, 5 hours, 55 minutes, 12 seconds, exhibits a value greater than the truth by 6′ 13′′ only, as according to Laplace, the length of the tropical year at that time must have been about 4"-2 shorter than in the present age. The error can occasion no surprise. It must be remembered, in behalf of the ancients generally-to use the words of Delambre, that their astrolabes were nothing but armillary spheres, of no great diameter, and with very small subdivisions of a degree; and that they had neither telescope, vernier, nor micrometer. "What should we do," he goes on to remark, "even now if deprived of these helps, and if we knew neither the refraction nor the true altitude of the pole, on which point, even at Alexandria, and with armillæ of every sort, an error of a quarter of a degree was committed?" At this day we dispute about a fraction of a second; they could not then answer fraction of a degree, and might be wrong by a whole diameter of the sun and The appearance of a new star in the time of Hipparchus is said to have induced him to make a catalogue of the fixed stars, in order that posterity might be able to recognise any changes that might take place in the appearance of the heavens. He was well aware of the importance of such a catalogue, especially for observations of the moon and planets; and in executing the task he rendered essential service to astronomy, and made his most remarkable discovery. Comparing the place of the star Spica Virginis, as determined by himself, with that assigned to it about 170 years previously by two distinguished Alexandrians, he found that this star was six degrees distant from the autumnal equinox, whereas the before-mentioned astronomers had found it eight degrees from the equinox. He saw that there must have been either a movement of the star in longitude during the interval, or a contrary movement of the equinoctial point in the heavens. The same phenomenon was observed in relation to other stars; that while their latitudes had been retained unaltered, they had advanced in longitude; and hence the retrogradation of the equinoctial points along the ecliptic was inferred, the cause of which remained a secret till the age of Newton.

for any

moon.

The catalogue formed by Hipparchus contained 1080 stars.

The labour it involved,