had remarked the difference between the sidereal and tropical year, and that they were acquainted with the use of the gnomon and sundial. And finally, some of them were led from considering the spectacle of nature, to suppose that comets, like planets, are subject to fixed periods, which are regulated by external laws.

Astronomy is not less ancient in Egypt than in Chaldea, The Egyptians were acquainted, long before the christian æra, with the excess of the year, of one quarter of a day beyond 365 days: on this knowledge, they formed the sothic period of 1460 years, which, according to them, brought back the same seasons, months, and festivals of their years, whose length was 365 days. The exact direction of the sides of their pyramids with the four cardinal points, give us a very advantageous idea of their accuracy of observation. It is probable that they had also methods of calculating eclipses. But that which reflects most honour to their astronomy, was the sa gacious and important observation of the motion of Mercury and Venus about the sun. The reputation of their priests attracted to them the greatest philosophers of Greece; and, according to all appearance, the school of Pythagoras is indebted to them for the sound notions they professed relative to the system of the universe.

Among these people, astronomy was only cultivated in their temples, and by priests, who made no other use of their knowledge than to consolidate the empire of superstition, of which they were the ministers. They carefully disguised it under emblems, which presented to credulous ignorance, heroes and gods, whose actions were only allegories of celestial phenomena, and of the operations of nature; allegories which the power of imitation, one of the chief springs of the moral world, has perpetuated to our own days, and been mingled with our religious institutions. The better to enslave the people, they profited by their natural desire of penetrating into futurity, and created astrology. Man being induced, by the illusions of his senses, to consider himself as the centre of the universe, it was easy to persuade him, that the stars influenced the events of his life, and could prognosticate to him his future destiny. This error, dear to his self-love, and necessary to his restless curiosity, seems to have been co-eval with astronomy. It has maintained itself through a very long period, and it is only since the end of the last century, that our knowledge of our true relations with nature, has caused them to disappear. In Persia and in India, the commencement of

astronomy is lost in the darkness which envelops the origin of these people. In no country do they go back so far as in China, by an incontestable series of historical monuments.

The prediction of eclipses, and the regulation of the calendar, were always regarded as important objects, for which a mathematical tribunal was established; but the scrupulous attachment of the Chinese to ancient customs, which extended even to their astronomical rules, has contributed among them to keep this science in a perpetual state of infancy.

The Indian tables indicate a much more refined astronomy; but every thing shows that it is not of an extremely remote antiquity. And here, with regret, I differ in opinion from a learned and illustrious astronomer, who, after having honoured his career by labours useful both to science and humanity, fell a victim to the most sanguinary tyranny, opposing the calmness and dignity of virtue to the revilings of an infatuated people, who wantonly prolonged the last agonies of his existence".

The Indian tables have two principal epochs, which go back, one to the year 3102, the other to the year 1491 before the Christian æra. These epochs are connected with the mean motions of the sun, moon, and planets, in such a manner, that one is evidently fictitious; the celebrated astronomer, above alluded to, endeavours, in his Indian astronomy, to prove, that the first of these epochs is founded on observation. Notwithstanding all the arguments are brought forward with that interest he so well knew how to bestow on subjects the most difficult, I am still of opinion, that this period was invented for the purpose of giving a common origin to all the motions of the heavenly bodies in the zodiac. In fact, computing, according to the Indian tables, from the year 1491, to 3102, we find a general conjunction of the sun and all the planets, as these tables suppose, but their conjunction differs too much from the result of our best tables to have ever taken place, which shows that the epoch to which they refer, was not established on observation. But, it must be owned, that some elements of the Indian astronomy seem to indicate that they have been determined even

* Lavoisier, the great founder of the nomenclature of modern chemistry. He was born at Paris, Aug. 26, 1743, and was guillotined May 8, 1794, during the tyranny of Robespierre.—Editor

before this first epoch. Thus the equation of the centre of the sun, which they fix at 20.4173, could not have been of that magnitude; but at the year 4300 before the Christian ara. But, independently of the errors to which the Indian observations are liable, it may be observed, that they only considered the inequalities of the sun and moon, relative to eclipses, in which the annual equation of the moon is added to the equation of the centre of the sun, and aug. ments it about * 22′, which is very nearly the difference between our determinations and those of the Indians. Many elements, such as the equations of the centre of Jupiter and Mars, are so different in the Indian tables, from what they must have been at their first epoch, that we can conclude nothing in favour of their antiquity from the other elements.

The whole of these tables, particularly the impossibility of the conjunction, at the epoch they suppose, prove on the contrary, that they have been constructed, or at least rectified in modern times. Nevertheless, the ancient reputation of the Indians does not permit us to doubt, that they have always cultivated astronomy, and the remarkable exactness of the mean motions which they have assigned to the sun and moon, necessarily required very ancient obser

vations.

The Greeks did not begin to cultivate astronomy till a long time after the Egyptians, of whom they were the disciples.

It is extremely difficult to ascertain the exact state of their astronomical knowledge, amidst the variety of fable which fills the early part of their history. It appears, however, that they divided the heavens into constellations, about thirteen or fourteen centuries before the Christian æra; for it is to this epoch that the sphere of Eudoxus should be referred. Their numberless schools for philosophy produced not one single observer before the foundation of the Alexandrine school. They treated astronomy as a science purely speculative, often indulging in the most frivolous conjectures.

It is singular, that at the sight of so many contending systems, which taught nothing, the simple reflection, that the only method of comprehending nature is to interrogate her by experiment, never occurred to one of these philosophers, though so many were en

* 11′ 52".

dowed with an admirable genius. But we must reflect, that the first observation only presenting insulated facts, little suited to attract the imagination, impatient to ascend to causes, they must have succeeded each with extreme slowness. It required a long succession of ages to accumulate a sufficient number, to discover, among the various phenomena, such relations, which, by extending themselves, should unite with the interest of truth, that of such general speculations as the human understanding delights to indulge in.

Nevertheless, in the philosophic dreams of Greece, we trace some sound ideas, which their astronomers collected in their travels, and afterwards improved. Thales, born at Miletus, 640 years before our æra, went to Egypt for instruction: on his return to Greece, he founded the Ionian school, and there taught the sphericity of the earth, the obliquity of the ecliptic, and the true causes of the eclipses of the sun and moon; he even went so far as to predict them, employing, no doubt, the periods which had been communicated to him by the priests of Egypt.

Thales had for his successors-Anaximander, Anaximenes, and Anaxagoras; to the first is attributed the invention of the gnomon and geographical charts, which the Egyptians appear to have been already acquainted with.

Anaxagoras was persecuted by the Athenians for having taught these truths of the Ionian school. They reproached him with having destroyed the influence of the gods on nature, by endeavouring to reduce phenomena to immutable laws. Proscribed with his children, he only owed his life to the protection of Pericles, his disciple and his friend, who succeeded in procuring a mitigation of his sentence from death to banishment. Thus, truth, to establish itself on earth, has almost always had to combat established prejudices, and has more than once been fatal to those who have discovered it. From the Ionian school arose the chief of one more celebrated. Pythagoras, born at Samos, about 590 years before Christ, was at first the disciple of Thales. This philosopher advised him to travel into Egypt, where he consented to be initiated into the mysteries of the priests, that he might obtain a knowledge of all their doctrines. The Brachmans having then attracted his curiosity, he went to visit them, as far as the shores of the Ganges. On his return to his own country, the despotism under which it groaned, obliged him again to quit it, and he retired to Italy, where he

founded his school. All the astronomical truths of the Ionian school, were taught on a more extended scale in that of Pythagoras; but what principally distinguished it, was the knowledge of the two motions of the earth on itself, and about the sun. Pythagoras carefully concealed this from the vulgar, in imitation of the Egyp tian priests, from whom, most probably, he derived his knowledge; but his system was more fully explained, and more openly avowed by his disciple Philalaus.

According to the Pythagorists, not only the planets, but the comets themselves, are in motion round the sun. These are not fleeting meteors formed in the atmosphere, but the mighty works of nature. These opinions, so perfectly correct on the system of the universe, have been admitted and inculcated by Seneca, with the enthusiasm which a great idea, on the subject the most vast of human-contemplation, naturally excited in the soul of a philosopher.

"Let us not wonder," says he, " that we are still ignorant of the law of the motion of comets, whose appearance is so rare, that we neither can tell the beginning nor the end of the revolution of these bodies, which descend to us from an immense distance. It is not fifteen hundred years since the stars have been numbered in Greece, and names given to the constellations. The day will come, when, by the continued study of successive ages, things which are now hid, will appear with certainty, and posterity will wonder they have escaped our notice.

The same school taught that the planets were inhabited, and that the stars were suns disseminated in space, being themselves centres of planetary systems. These philosophic views should, from their grandeur and justness, have obtained the suffrages of antiquity; but having been taught with systematic speculations, such as the harmony of the heavenly spheres, and wanting, moreover, that proof which has since been obtained, by the agreement with observations, it is not surprising that their truth, when opposed to the illusions of the senses, should not have been admitted.

[La Place, Exposition du Systême du Monde.]