CHAPTER VIII.

ORIGIN OF ASTRONOMY AMONG THE GREEKS.

A theory of the celestial movements developed in the Greek astronomy.The Greek astronomy probably derived from the Egyptian.-Thales established the first school of Greek philosophy.-Works ascribed to him.-He predicts an eclipse of the sun.-Tenets of Anaximander.-Removal of the school of Thales to Athens.-Theory of the universe ascribed to Anaxagoras.-Opinions of this philosopher concerning the stability of the heavenly bodies.-Sentiments of the Greek astronomers concerning the sun and moon.-A supposed change in the position of the earth's axis.-An opinion concerning meteoric stones. - Doctrines of Anaximenes.-The school of Pythagoras in Italy.-Opinion of the mobility of the earth.--Of an antochthone and invisible planets.-Harmony of the celestial spheres.--Hypothesis of vortices proposed by Democritus.-The lunar cycle of Philolaus.-The cycles of Meton and Calippus.

In attempting an account of the ancient astronomy of the East we have been compelled, from the paucity of documents, to describe the probable rather than the real march of discovery, and to reason from conjectures rather than from facts: we now proceed to consider the astronomy of the Greeks and later Egyptians whose yet existing works exhibit the progress of the human mind in investigating the laws of the celestial movements, and in inventing a mechanism which may represent them. We must not, indeed, expect to find a complete development of that principle by which, in the age immediately preceding our own, the true cause of those movements has been explained and the constitution of the universe made evident; yet we shall perceive so many hints, obscurely indeed announced, but indicating a conception of the hypotheses now generally admitted, and of the facts which recent observations have confirmed, as almost to justify the opinion entertained by a late French author that the most important discoveries ascribed to the moderns originated, or were recognized, in the schools of Greece. But though it is certain that such an opinion is not supported by a reasonable interpretation of the expressions used by the ancient philoso

phers, yet we shall find sufficient cause to admire the sagacity which, with observations of so rude a nature as those they had it in their power to make, and with a calculus so far inferior to that which we now possess, enabled them to account for so many of the phenomena of the heavens, and to offer so feasible a solution of the great problem of the celestial motions. It must also be observed that the system of the universe invented in those schools maintained its ground during more than two thousand years, and only yielded to the improvements made in the instruments of observation since the revival of learning in Europe. These improvements, joined to the happy adoption of a principle either unknown or but little regarded before his time, permitted Newton to unfold a theory which is not likely to be shaken during the continuance of that order of things which it has so satisfactorily explained.

All the more ancient hypotheses may be said to have had their use in connecting together the results of individual observations; and thus, have contributed, in some measure, to the progress of science; but it was impossible that they should stand when, by multiplied observations, the minute irregularities in every part of the orbit of the Moon, or of each planet, were discovered. The first two principles, the circular and uniform motions of celestial bodies, were arbitrary assumptions, and the original system formed upon them was insufficient to account for any but the most obvious phenomena; and, instead of being able to deduce from it the explanation of any newly observed inequality of motion, astronomers were obliged, for this purpose, to make additions, in the nature of excrescences, to the machinery before imagined. These additions, however, did not, as may be supposed, combine with each other and with the original hypothesis so as to satisfy the different phenomena; and, in fact, it happened that while one inequality of motion was explained by them another was contradicted; they, moreover, at length rendered the machinery of the heavens unmanageably complex, and, therefore, nearly useless for the purpose of facilitating astronomical computations, long before it was superseded by the modern theory of gravitation.

The writings of Homer and Hesiod contain all that is known

of the first state of astronomy in Greece: and this amounts, as we have said, to little more than the names of a few constellations, the principal of which Homer has introduced in the fifth book of the Odyssey, where Ulysses, in his bark, on leaving Calypso, is made to observe," 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." We may, therefore, conclude that, in the age of those poets, the science was at its birth in that country; or that the Greeks had just then received its elements from some other people.

Little doubt can be entertained that the Greeks derived their first notions of the sciences, particularly of astronomy, from Egypt or Syria, either by means of intelligent men of their nation who travelled into those countries to seek for information, or by means of the chiefs who, for the purpose of conquest or colonization, conducted their warlike bands from thence towards the west. We are aware that the expeditions, and even the existence of such men as Uranus and Atlas as well as the exploits of Sesostris, have been called in question, but surely without sufficient reason; since, during the many ages in which the profession of arms enjoyed the highest consideration, and when the rapid increase of the human race rendered emigrations absolutely necessary, it is impossible that multitudes should not have abandoned their native soil, though no account of their movements has been preserved; on the contrary, it is in the highest degree probable, not only that the tide of conquest should have flowed into the remotest accessible regions, but that the arts and sciences of the more enlightened people should, by such means, have been communicated to those who were less so: on this account we cannot hesitate to admit that what is related by Diodorus Siculus concerning those personages may have some foundation in truth. In his third book he informs us that Uranus, who held in subjection a great portion of the earth, towards the west and north, applied himself to the observation of the risings and settings of stars; that, from the movements of the sun and moon, he taught the length of the year and its division into months; and that, in consequence of the admira

tion excited by his knowledge of celestial things, divine honours were paid to him and the universe was called by his name. In the same book it is related that Atlas extended his conquests to the regions in Africa bounding the Western Ocean, and gave his name to a mountain in that part of the world. It is added, as a report however, that he had an exact knowledge of astronomy and that, because he had executed an artificial sphere representing the heavens, he was supposed, and the opinion is alluded to by Eschylus, to have carried the universe on his shoulders. In the fourth book it is stated that Hercules introduced the knowledge of the celestial sphere to the people of Greece, and that he was said to have received the burthen of the universe from Atlas; which seems to imply that one of the labours of the hero consisted in communicating to the Greeks a knowledge of the sciences which he had acquired in some expedition towards the west.

It is evident, however, that astronomy could not have been in a state of maturity in the East at the time the Greeks received it from such of their countrymen as had studied among the Egyptians or Asiatics; since, if it were so, those persons would have imparted it in a more advanced condition than, by the accounts which have been transmitted to us, we find it to have been; for what they taught on their return appears to have consisted only of a few simple and elementary circumstances, and there is no hint given that they had acquired the knowledge of any thing more profound.

a

The first intimation we have of any Greek professing the science of astronomy is contained in the works of Herodotus, and consists in the mention of an eclipse of the sun which had been predicted by Thales, a native of Miletus in Asia. A short account of the life of this philosopher is given by Diogenes Laertius, who relates of him that, when a youth, he was one day led out of the house for the purpose of contemplating the stars and, falling into a ditch, 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 story, which is alluded to by Socrates in Plato's dialogue

a In vita Thaletis.

L

Theaetetus, has the air of an invention, but something remarkable is generally related concerning the early life of persons who have distinguished themselves by superiority of talent, and there is nothing to prevent our giving as much credit to this as to many others of a similar nature: if true, the exclamation may indicate either a sarcastic, or a moralizing spirit in Thressa, the attendant, and it affords, at the same time, a proof of the inclination of her young charge to philosophical pursuits.

After performing the duties of a citizen Thales employed himself in the study of the system of nature, but Diogenes observes that he left behind him no monument of his discoveries, and that whatever is known concerning him is drawn from the works of Phocas the Samian. He is said, for the purpose of acquiring information in philosophy, to have made a voyage to Egypt; yet, by a strange inconsistency, it is asserted that he taught those who were his masters in the sciences how to measure the height of the Pyramids by the length of the shadows they cast, which is one of the most simple examples of practical geometry: the truth probably is that, in Egypt, Thales learned this, among other subjects connected with the elements of astronomy. On his return to his native country he made a profession, after the manner of learned men in those times, of giving public instructions to such as chose to become his disciples, on which account he is spoken of as the founder of the Ionian school and the father of the Greek philosophy.

If we may depend upon the obscure hints contained in the works of those authors who have incidentally made mention of this philosopher, it would appear that, in his time, the form of the earth was recognized, for he is said to have asserted that it was globular and that it was situated in the centre of the universe. It is added that he supposed the fixed stars to be attached to the surface of a sphere, and, according to Plutarch, he divided the earth into five zones and described the situations of the Equator, the Tropics, the Arctic and Antarctic circles: if these circumstances be true they prove that this manner of dividing the visible heavens, for the purpose of distinguishing the relative positions of the stars, had then been adopted; the last two

De Placitis Philosophorum, Lib. II. cap. 12.