ASTRONOMY, is the science which treats of the motions, periods, eclipses, magnitudes, Re. of the heavenly bodies, of the laws by which these are regulated, and of the causes on which they depend. It is unquestionably the most sublime of all the sciences. No subject has been longer or more successfully studied. Al though it may be interesting to take a brief sketch of the history of this science, yet there can he no comparison drawn be tween the wide observationsof the earlier observers, and the precision and general views of modern astronomers. To ascer tain the real motions of the heavenly be dies was a difficult task, awl required the united observations of many ages. To ascertain the laws and causes of these motions demanded the exertions of pow ers almost beyond the reach of the hu man faculties. This has, however, been accomplished, and it has been demonstra ted, that the most minute movements of the heavenly bodies depend upon the same general law with the rest, and to be the consequence of it. Astronomy has therefore been highly regarded, as exhi biting one of the most remarkable in stances of the extent and powers of the reasoning faculties. It has, moreover, con ferred upon mankind the greatest bene fits, in many respects, as will be shown in the course of the present work, and may be properly considered as the teacher and guide of the art of navigation.
The early history of astronomy ad mits of no regular elucidation. It is pro bable that some knowledge of the kind must have been nearly coeval with the human race, as well from motives of cu riosity, as from the connection which it has with the common concerns oflife. Traces of it have accordingly been found among various nations, remote from each other, which shew that the most remarkable phenomena must have been observed, and a knowledge of them disseminated, at a very remote period. But in what age or country the science first originated, or by whom it was in those early times me thodized and improved, is not now known. Such, however, as wish for every infor mation that the subject admits of, we re fer to the learned and very elaborate his tory of ancient and modern astronomy, by M. Bailly, a man of the highest repu tation in the scientific world, and who was basely and cruelly murdered, in the zenith of his celebrity, by the bloodthirsty Robe spierre, whose savage ambition was, to efface from the earth every thing great, virtuous, and excellent.
M. Bailly endeavours to trace the ori gin of astronomy among the Chaldeans, Egyptians, Persians, Indians, and Chinese, to a very early period. From the re searches which he has made on this sub ject, he is led to conclude that the know ledge common to the' whole of those na tions has been derived from the same original source ; namely, a most ancient and bightly cultivated people of Asia, of whose memory every trace is now extinct, but who have been the parent instructors of all around them. The situation of this ancient people he conjectures to have been in Siberia, about the 50th degree of north latitude. Among various other co incidences, he observes that many of the European and Asiatic nations attribute their origin to that quarter, where the ci= — vil and religious rites common to each, were probably first formed.
Without going farther back, we may observe, that the Egyptians were early cultivators of this science, and that among the Greeks, Thales, who travelled into Egypt, and who was the founder of the Ionian sect, appears to have been the first who taught his countrymen the globular figure of the earth, the obliquity of the ecliptic, and the causes of solar and lunar eclipses ; which latter phenomena he is also said to have been able to predict. Thales had for his successors, Anaximan der, Anaximenes, and Anaxagoras, to the first of whom is attributed the invention of the gnomon and geographical charts ; but for which he was probably indebted to the Egyptians. He is also said to have maintained that the sun was a mass of fire as large as the earth, which, though far below the truth with respect to size, was an opinion, for those early times, that does its author much credit, though to him, as in the case of Galileo, the truths he had discovered were the cause of per secution. Both himself and his children were proscribed by the Athenians for his attempting to subject the works of the gods to immutable laws ; and his life would have paid the sacrifice of his te merity, but for the care of Pericles, his friend and disciple, who got his sentence of death changed into exile. Next after the Ionian school was that of Pythagoras; who was born at Samos, about the year 58G before the Christian xra, and who, in the celebrity he acquired, far exceeded his predecessors. Like Thales, he visited Egypt, and afterwards the Brachmans of India, from whom he is supposed to have obtained many of the astronomical trutlaS which he brought with him into Italy, to which country he was obliged to re tire, on account of the despotism which then prevailed at Athens. Here he first taught the true system of the world, which many centuries after, was revived by Copernicus: but hid his doctrines from the vulgar, in imitation of the Egyptian priests, who had been his instructors. It
was even thought, in this school, that the planets were inhabited bodies, like the earth ; and that the stars, which are dis seminated through infinite space, are suns, and the centres of other planetary sys tems. They also considered the comets as permanent bodies, moving round the sun; arid not as perishing meteors, form ed in the atmosphere, as they were thought to be in after times. From this time to the foundation of the school of Alexandria, the history of astronomy among the Greeks offers nothing remark. able, except some attempts of Eudoxus to explain the celestial phenomena: and the celebrated cycle of 19 years, which had been imagined by Meton, in order to conciliate the solar and lunar motions. This is the most accurate period, for a short interval of time, that could have been devised, for embracing an exact number of revolutions of these two lumi naries ; and is so simple and useful, that when Meton proposed it to the Greeks, assembled at the Olympic games, as the basis of their calendar, it was received with great approbation, and unanimously adopted by all their colonies. In the school of Alexandria, we see, for the first time, a combined system of observations, made with instruments proper for mea suring angles, and calculated trigonome trically. Astronomy accordingly took a new form, which succeeding ages have only brought to greater perfection. The position of the stars began at this time to be determined ; they traced the course of the planets with great care ; and the inequalities of the solar and lunar motions became better known. It was, in short, in this celebrated school, that a new sys tem of astronomy arose, which embraced the whole of the celestial Motions ; and though inferior to that of Pythagoras, and even false in theory, it afforded the means, by the numerous observations which it furnished, of detecting its own fallacy, and of enabling astronomers in later times to discover the true system of nature. It was from their observations of the princi pal zodiacal stars, that Hipparchus was led to discover the precision of the equi noxes ; and Ptolemy also founded upon them his theory of the motions of the pla nets. Next after these was Aristarchus, of Samos, who made the most delicate elements of the science the objects of his research. Among other things of this kind, he attempted to determine the 'nag nitide and distance of the sun ; and though, as may be supposed, the results he obtained were considerably wide of the truth, the methods he employed to re solve these difficult problems do great honour to his genies. The celebrity of his successor, Eratosthenes, arises, chiefly from his attempt to measure the earth, and his observations On the obliquity of the ecliptic. Having remarked, at Syene, a well, which was enlightened to its bot tom by the sun, on the day of the summer solstice, he observed the meridian height of the sun on the same day at Alexandria, and found that the celestial are continued between the two places was the 5tth part of the whole circumference ; and as their distance was estimated at 500 stadia, he fixed the length of a great circle of the earth at 250,000: but as the length of the stadium employed by this astrono mer is not known, we cannot appreciate the exactness ofhismeasurement. Among others who cultivated and improved this science we may also mention the cele brated Archimedes, who constructed a kind of planetarium, or orrery, for re presenting the principal phenomena of heavenly bodies. But of all the astrono mers of antiquity, Hipparchns of Bithynia isthe one, who, by the number and pre cision of his observations, as well as by the important result which he derived from them, is the most entitled to our esteem. He flourished at Alexandria about the year 162 before the Christian era; and began his astronomical labours by attempting to determine, with more exactness than had hitherto been clone, the length of the tropical year, which ho fixed at 365 days, 5 hours, and 55 minutes, being nearly 41 minutes too great. Like most of his predecessors, he founded his system upon an uniform circular motion of the sun ; but, instead of placing the earth in the centre of the solar orbit, he removed it to the distance of part of the radius, and fixed the apogee to the sixth degree of Gemini. By means of these data, he formed the first solar tables of which any mention is made in the his tory of astronomy ; and though defective, and even erroneous in principle, they are a durable monument of his genius, which three centuries afterwards were respect ed by Ptolemy, without his presuming to alter them. The great astronomer next considered the motions of the moon, and endeavoured to measure the exact time of her revolution, by a comparison of an cient eclipses. He also determined the eccentricity and inclination of her orbit, as well as the motion of her nodes and apogee •, and calculated all the eclipses that were to happen for 600 years to come.