places in the concave itself. Sometimes they are stationary; sometimes they appear to be moving from west to east, and sometimes to be going back again from east to west; being seen at sunset sometimes in the east, and sometimes in the west, and always apparently changing their position with regard to the earth, each other, and the other heavenly bodies. From their wandering as it were, in this manner, through the heavens, they were called by the Greeks Tavnra, planets, which signifies wanderers.

There also sometimes appear in the heavens, bodies of a very extraordinary aspect, which continue visible for a considerable period, and then disappear from our view; and nothing more is seen of them, it may be for years, when they again present themselves, and take their place among the bodies of the celestial sphere. They are distinguished from the planets by a dull and cloudy appearance, and by a train of light. As they approach the sun, however, their faint and nebulous light becomes more and more brilliant, and their train increases in length, until they arrive at their nearest point of approximation, when they shine with their greatest brilliancy. As they recede from the Sun, they gradually lose their splendour, resume their faint and nebulous appearance, and their train diminishes, until they entirely disappear. They have no well defined figure; they seem to move in every possible direction, and are found in every part of the heavens. From their train, they were called by the Greeks Kopnra, comets, which signifies having long hair.

The causes of these various phenomena must have early constituted a very natural subject of inquiry. Accordingly, we shall find, if we examine the history of the science, that in very early times there were many speculations upon this subject, and that different theories were adopted to account for these celestial appearances.

The Egyptians, Chaldeans, Indians, and Chinese, early possessed many astronomical facts, many observations of important phenomena, and many rules and methods of astronomical calculation; and it has been imagined, that they had the ruins of a great system of astronomical science, which, in the earliest ages of the world, had been carried to a great degree of perfection, and that while the principles and explanations of the phenomena were lost, the isolated, unconnected facts, rules of calculation, and phenomena themselves, remain. ed. Thus, the Chinese, who, it is generally agreed, possess the oldest authentic observations on record, have recorded in their annals, a conjunction of five planets at the same time, which happened 2461 years before Christ, or 100 years before the flood. By mathematical calculation, it is ascertained that this conjunction really occurred at that time. The first observation of a solar eclipse of which the world has any knowledge, was made by the Chinese, 2128 years before Christ, or 220 years after the deluge. It seems, also, that the Chinese understood the method of calculating eclipses; for, it is said, that the Whence do they derive their name? Describe the comets. Whence is their name derived? What oriental nations early possessed many important astronomical facts, observations, and rules? Whence is it supposed that they obtained them?

emperor was so irritated against the great officers of state for neglecting to pre dict the eclipse, that he caused them to be put to death.*The astronomical epoch of the Chinese, according to Bailly, commenced with Fohi, their first emperor, who flourished 2952 years before the Christian era, or about 350 years before the deluge. If it be asked how the knowledge of this antediluvian astronomy was preserved and transmitted, it is said that the columns on which it was registered have survived the deluge, and that those of Egypt are only copies which have become originals, now that the others have been forgotten. The Indians, also, profess to have many celestial observations of a very early date. The Chaldeans have been justly celebrated in all ages for their astronomical observations. When Alexander took Babylon, his preceptor. Callisthenes, found a series of Chaldean observations, made in that city, and extending back with little interruption, through a period of 1903 years preceding that event. This would carry us back to at least 2234 years before the birth of Christ, or to about the time of the dispersion of mankind by the confusion of tongues. Though it be conceded, that upon this whole period in the history of the science, the obscurity of very remote antiquity must necessari. ly rest, still it will remain evident that the phenomena of the heavenly bodies had been observed with great attention, and had been a subject of no ordinary interest.

But however numerous or important were the observations of oriental antiquity, they were never reduced to the shape and symmetry of a regular system.

The Greeks, in all probability, derived many notions in regard to this sci. ence, and many facts and observations, from Egypt, the great fountain of ancient learning and wisdom, and many were the speculations and hypotheses of their philosophers. In the fabulous period of Grecian history, Atlas, Hercules, Linus, and Orpheus, are mentioned as persons distinguished for their knowledge of astronomy, and for the improvements which they made in the science. But in regard to this period, little is known with certainty, and it must be considered, as it is termed, fabulous.

The first of the Greek philosophers who taught Astronomy, was Thales, of Miletus, He flourished about 640 years before the Christian era. Then followed Anaximander, Anaximenes, Anaxagoras, Pythagoras, Plato. Some of the doctrines maintained by these philosophers were, that the Earth was round, that it had two motions, a diurnal motion on its axis, and an annual motion around the Sun, that the Sun was a globe of fire, that the Moon received her light from the Sun, that she was habitable, contained mountains, seas, &c.; that her eclipses were caused by the Earth's shadow, that the planets were not designed merely to adorn our heavens, that they were worlds of themselves, and that the fixed stars were centres of distant systems. Some of them, however, maintained, that the Earth was flat, and others, that though round, it was at rest in the centre of the universe.

When that distinguished school of philosophy was established at Alexandria, in Egypt, by the munificence of the

* It is well known that the Chinese have, from time immemorial, considered Solar Eclipses and Conjunctions of the planets, as prognostics of importance to the Empire, and that they have been predicted as a matter of State policy.

Give some instances. Were these facts, however, reduced to a science? Whence, is it probable, that the Greeks derived their first notions of astronomy? What is the name of the first of the Greek philosophers who taught astronomy? At what time did he flourish? What Greek philosophers after him taught upon the same subject? Mention some of the doctrines which they maintained.

sovereigns to whom that portion of Alexander's empire had fallen, astronomy received a new impulse. It was now, in the second century after Christ, that the first complete system or treatise of astronomy, of which we have any knowledge, was formed. All before had been unconnected and incomplete. Ptolemy, with the opinions of all antiquity, and of all the philosophers who had preceded him, spread out before him, composed a work in thirteen books, called the Meyan Euvragis, or Great System. Rejecting the doctrine of Pythagoras, who taught that the Sun was the centre of the universe, and that the Earth had a diurnal motion on its axis and an annual motion around the Sun, as contrary to the evidence of the senses, Ptolemy endeavoured to account for the celestial phenomena, by supposing the Earth to be the centre of the universe, and all the heavenly bodies to revolve around it. He seems to have entertained an idea in regard to the supposition, that the Earth revolved on its axis, similar to one which some entertain even at the present day. "If," says he, "there were any motion of the Earth common to it and all other heavenly bodies, it would certainly precede them all by the excess of its mass being so great; and animals and a certain portion of heavy bodies would be left behind, riding upon the air, and the Earth itself would very soon be completely carried out of the heavens."

In explaining the celestial phenomena, however, upon his hypothesis, he met with a difficulty in the apparently stationary attitude and retrograde motions which he saw the planets sometimes have. To explain this, however, he supposed the planets to revolve in small circles which he called epi cycles, which were, at the same time, carried around the Earth in larger circles, which he called deferents, or carrying circles. In following out his theory and applying it to the explanation of different phenomena, it became necessary to add new epicycles, and to have recourse to other expedients, until the system became unwieldy, cumbrous, and complicated. This theory, although astronomical observations continued to be made, and some distinguished astronomers appeared from time to time, was the prevailing theory until the middle of the 15th century, It was not, however, always received with implicit confidence; nor were its difficulties always entirely unappreciated.

Alphonso X., king of Castile, who flourished in the 13th century, when contemplating the doctrine of the epicycles, exclaimed, "Were the universe thus constructed, if the deity had called me to his councils at the creation of the world, I could have given him good advice." He did not, however, mean any impiety or irreverence, except what was directed against the system of Ptolemy.

About the middle of the 15th century, Copernicus, a native of Thorn in Prussia, conceiving a passionate attachment to the study of astronomy, quitted the profession of

When was the first complete system of Astronomy written, and by whom? In how many books was it comprised, and what was the work called? What was the system of Ptolemy? How did Ptolemy explain the stations and retrogradations of the plancis? How long was the system of Ptolemy the prevailing system? Was it always received with implicit confidence? Who established a new System of Astronomy about the middle of the 15th century?

medicine, and devoted himself, with the most intense ardour, to the study of this science. "His mind," it is said, "had long been imbued with the idea that simplicity and harmony should characterize the arrangements of the planetary system. In the complication and disorder which, he saw, reigned in the hypothesis of Ptolemy, he perceived insuperable objections to its being considered as a representation of

nature.

In the opinions of the Egyptian sages, in those of Pythagoras, Philolaus, Aristarchus and Nicetas, he recognised his own earliest conviction that the Earth was not the centre of the universe. His attention was much occupied with the speculation of Martinus Capella, who placed the Sun between Mars and the Moon, and made Mercury and Venus revolve around him as a centre, and with the system of Appollonius Pergous, who made all the planets revolve around the Sun, while the Sun and Moon were carried around the Earth in the centre of the universe.

The examination, however, of these hypotheses, gradually expelled the difficulties with which the subject was beset, and after the labour of more than thirty years, he was permitted to see the true system of the universe.The Sun he considered as immoveable, in the centre of the system, while the earth revolved around him, between the orbits of Venus and Mars, and produced by its rotation about its axis all the diurnal phenomena of the celestial sphere. The other planets he considered as revolving about the Sun, in orbits exterior to that of the Earth. (See the Relative Position of the Planets' Orbits, Plate I. of the Atlas.)

Thus, the stations and retrogradations of the planets were the necessary consequence of their own motions, combined with that of the Earth about the Sun. He said that "by long observation, he discovered, that if the motions of the planets be compared with that of the Earth, and be estimated according to the times in which they perform their revolutions, not only their several appearances would follow from this hypothesis, but that it would so connect the order of the planets, their orbits, magnitudes, and distances, and even the apparent motion of the fixed stars, that it would be impossible to remove one of these bodies out of its place without disordering the rest, and even the whole of the universe also."

Soon after the death of Copernicus, arose Tycho Brahe,

What led him to doubt the system of Ptolemy? How long was he employed in the ex amination of different hypotheses before he came to a satisfactory result? What was the system of Copernicus? What distinguished astronomer, soon after the time of Copernicus, enriched astronomy with many valuable observations?

.

born at Knudstorp, in Norway, in 1546. Such was the distinction which he had attained as an astronomer, that when dissatisfied with his residence in Denmark, he had resolved to remove, the king of Denmark, learning his intentions, detained him in the kingdom, by presenting him with the canonry of Rothschild, with an income of 2000 crowns per annum. He added to this sum a pension of 1000 crowns, gave him the island of Huen, and established for him an observatory at an expense of about 200,000 crowns. Here Tycho continued, for twenty-one years, to enrich astronomy with his observations. His observations upon the Moon were important, and upon the planets, numerous and precise, and have formed the data of the present generalizations in astronomy. He, however, rejected the system of Copernicus; considering the Earth as immoveable in the centre of the system, while the Sun, with all the planets and comets revolving around him, performed his revolution around the earth, and, in the course of twenty-four hours, the stars also revolved about the central body. This theory was not as simple as that of Copernicus, and involved the absurdity of making the Sun, planets, &c. revolve around a body comparatively insignificant.

Near the close of the 15th century, arose two men, who wrought most important changes in the science, Kepler, and Galileo, the former a German, the latter an Italian.

Previous to Kepler, all investigations proceeded upon the supposition that the planets moved in circular orbits, which had been a source of much error. This supposition Kepler showed to be false. He discovered that their orbits were ellipses. The orbits of their secondaries or moons he also found to be the same curve. He next determined the dimensions of the orbits of the planets, and found to what their velocities in their motions through their orbits, and the times of their revolutions, were proportioned; all truths of the greatest importance to the science.

While Kepler was making these discoveries of facts, very essential for the explanation of many phenomena, Galileo was discovering wonders in the heavens never before seen by the eye of man. Having improved the telescope, and applied it to the heavens, he observed mountains and valleys upon the surface of our Moon; satellites or secondaries

What inducements did the king of Denmark offer him to remain in the kingdom? How long did he continue to make observations in his observatory in the island of Huen? How were the heavenly bodies arranged, in his system? What absurdity did it involve? What two illustrious astronomers made several very important discoveries soon after the time of Tycho Brahe? What were the discoveries of Kepler? What were the discoveries of Galileo ?