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nomena were lost, the isolated, unconnected facts, rules of calculation, and phenomena themselves, remained.

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 emperor was so irritated against the great officers of state for neglecting to predict the eclipse, that he caused them to be put to death. The Chinese have, from time immemorial, considered Solar Eclipses and conjunctions of the planets, as prognostics of importance to the Empire, and they have been predicted as a matter of state policy.

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 cele brated 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 2284 years before the birth of Christ, or to about the time of the dispersion of mankind by the confusion of tongues.

316. The Greeks, in all probability, derived many notions in regard to this science, 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. 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 centers of distant systems. Some of them, however, maintained that the Earth was flat, and others that, though round, it was at rest in the center of the universe.

317. When that distinguished school of philosophy was established at Alexandria, in Egypt, by the munificence of the sovereigns to whom that portion of Alexander's empire had fallen, astronomy recived 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

816. Of the Greeks? Who first taught astronomy among them? Date? Who next? State some of their doctrines? 817. What record of this science? What of Ptolemy and his works?

who had preceded him, spread out before him, composed a work in thirteen books, called the Meyaλn Evvτağıç, or Great System.

318. Rejecting the doctrine of Pythagoras, who taught that the Sun was the center 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 endeavored to account for the celestial phenomena, by supposing the Earth to be the center 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."

319. 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 epicycles, 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 18th 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.

320. 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 medicine, and devoted himself with the most intense ardor 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."

318. His system of astronomy? What singular idea and reasoning? 819. What difficulty did he meet with, and how explain it? What further difficulty? How long did this theory prevail? What anecdote of the King of Castile ? 820. What distinguished student of astronomy now arose? His impressions in regard to the Ptolemaic theory? His own earlier convictions? What other theories did he study?

In the opinions of the Egyptian sages, in those of Pythagoras, Philolaus, Aristarchus, and Nicetas, he recognized his own earliest conviction that the Earth was not the center 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 round him as a center, 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 center of the universe.

321. The examination, however, of various hypotheses, by Copernicus, gradually expelled the difficulties with which the subject was beset, and after the labor of more than thirty years, he was permitted to see the true system of the universe.The Sun he considered as immovable, in the center 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 Distances of the Planets' Orbits, Map 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."

322. Soon after the death of Copernicus, arose Tycho Brahe, 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 2,000 crowns per annum. He added to this sum a pension of 1,000 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 immovable in the center 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 so simple as that of Copernicus, and involved the absurdity of making the Sun, planets, &c., revolve around a body comparatively insignificant.

321. How was Copernicus led to discover the true system of astronomy? What is that system? Does it account for the stations and retrogradations of the planets? 822. What distinguished astronomer next arose? What said of his detention in Denmark? His observations? His theory

323. 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.

324. 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 were discovered revolving about Jupiter; and Venus, as Copernicus had predicted, was seen exhibiting all the different phases of the Moon, waxing and waning as she does, through various forms.

Many minute stars, not visible to the naked eye, were described in the Milky-Way; and the largest fixed stars, instead of being magnified, appeared to be small brilliant points, an incontrovertible argument in favor of their immense distance from us. All his discoveries served to confirm the Copernican theory, and to show the absurdity of the hypothesis of Ptolemy.

325. Although the general arrangement and motions of the planetary bodies, together with the figure of their orbits, had been thus determined, the force of power which carries them around in their orbits, was as yet unknown. The discovery of this was reserved for the illustrious Newton, though even his discovery was in some respects anticipated by Copernicus, Kepler and Hooke. By reflecting on the nature of gravity— that power which causes bodies to descend toward the center of the earth-since it does not sensibly diminish at the greatest distance from the center of the earth to which we can attain, being as powerful on the loftiest mountains as it is in the deepest caverns, he was led to imagine that it might extend to the Moon, and that it might be the power which kept her in her orbit, and caused her to revolve around the Earth. He was next led to suppose that perhaps the same power carried the


323. What two noted astronomers next arose? What did Kepler discover? Galileo and his discoveries? What theory did they serve to establish? 325 What great discovery next made, and by whom? How led to it? Successive steps!

primary planets around the Sun. By a series of calculations, he was enabled at length to establish the fact, that the same force which determines the fall of an apple to the Earth, carries the moons in their orbits around the planets, and the planets and comets in their orbits around the Sun.

To recapitulate briefly: The system (not hypothesis, for much of it has been established by mathematical demonstration) by which we are now enabled to explain with a beautifu' simplicity the different phenomena of the Sun, planets, moons, and comets, is, that the Sun is the central body in the system: that the planets and comets move round him in elliptical orbits, whose planes are more or less inclined to each other, with velocities bearing to each other a certain ascertained relation, and in times related to their distances; that the moons, or secondaries, revolve in like manner about their primaries, and at the same time accompany them in their motion around the Sun; all meanwhile revolving on axes of their own; and that these revolutions in their orbits are produced by the mysterious power of attraction. The particular mode in which this system is applied to the explanation of the different phenomena, will be exhibited as we proceed to consider, one by one, the several bodies above mentioned.

326. These bodies, thus arranged and thus revolving, constitute what is termed the Solar System. The planets have been divided into two classes, primaries and secondaries. The latter are also termed moons, and sometimes satellites. The primaries are those that revolve about the Sun, as a center. The secondaries are those which revolve about the primaries. There have been discovered to this date (1854), thirty-five primary planets, viz.: Mercury, Venus, the Earth, Mars, Flora, Clio, Vesta, Iris, Metis, Eunomia, Psyche, Thetis, Melpomene, Fortuna, Massilia, Lutetia, Calliope, Thalia, Hebe, Parthenope, Irene, Egeria, Astræa, Juno, Ceres, Pallas, Hygeia, Jupiter, Saturn, Uranus, Neptune, and four other Asteroids, whose names and places have not yet been determined. Mercury is the nearest to the Sun, and the others follow in the order in which they are named. The seventeen small planets from Flora to Hygeia, inclusive, were discovered by means of the telescope, and, because they are very small, compared with the others, are called Asteroids. Neptune, also, is a telescopic planet, though much larger than any of the Asteroids.

There have been discovered twenty secondaries. Of these, the Earth has one, Jupiter four, Saturn eight, Herschel six, and Neptune one. All these, except our Moon, as well as the Asteroids and Neptune, are invisible to the naked eye.

Map I. of the Atlas, "exhibits a plan of the Solar System," comprising the relative magnitudes of the Sun and Planets; their comparative distances from the Sun, and from each other; the position of their orbits, with respect to each other; the Earth and the Sun; together with many other particulars which are explained on the map. There, the

Describe the Copernican theory? 826. What do the bodies mentioned constitute? How are the planets divided? Describe each? What number of primaries? Name them in order from the Sun? Which are the Asteroids? Which telescopic? How many secondary planets? How distributed? Are they visible to the naked eye? What sald

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