The Eleatic school was chiefly famous for the study of logic, or the art of ratiocination, first invented by Zeno. Those of this sect paid but little attention to science, or the study of Nature. Philosophy was anciently divided into three parts, natural, moral, and the art of reasoning. Xonophanes was succeeded by Parmenides, his scholar, who, in addition to his master’s absurdities, taught that the earth was habitable in only the two temperate zones; that the earth was suspended in the middle of the universe, in a fluid lighter than air; that all bodies left to themselves light on its surface. This bore a slight resemblance to the Newtonian doctrine of attraction.
Democritus, of Abdera, a scholar of Leucippus, who flourished four hundred and fifty-six years before Christ, was the first publisher of the Atomic Cosmogony, invented by Mochus, the Phœnician, said to have been received by his master Leucippus. Both admitted plurality of worlds. Democritus was the first who taught that the milky way is occasioned by the confused light of an infinite number of stars; which doctrine is still maintained by the best informed of philosophers. He also extended that idea to comets; the number of which Seneca says the Greek philosophers did not know; and that Democritus suspected there were more planets than we could see. This was also the opinion of many others, the truth of which has been verified in the discoveries of Pallas, Juno, Vesta, and the Georgium Sidus.
Democritus is considered as the parent of experimental philosophy; the greatest part of his time was devoted to it; and he is said to have made many discoveries. He, like Meteon, and Newton, maintained the absurd idea of the existence of a vacuum, which was denied by Thales and Descartes. Democritus also maintained that the sea was constantly diminishing. He declared that he would prefer the discovery of one of the causes of the works of Nature, to the possession of the Persian monarchy. Often laughing at the follies of mankind, he was thought by the vulgar to be out of his mind; but Hippocrates, being sent to cure him, soon found him to be the wisest man of the age; and Seneca reckons him the most acute and ingenious of the ancients, on account of his many useful inventions; particularly his ingenious making of artificial emeralds, tinging them of any colour; of softening ivory, dissolving stones, &c.
Although the chief attention of Plato and Aristotle was directed to other grand objects, yet they much contributed to the improvement of astronomy. Notwithstanding the most famous in this respect was Eudoxus, the scholar of Plato, who was famous for his skill in astrology, natural and judicial, or the art of foretelling future events by the relative situations of the stars, of their various influences, an art which prevailed for many ages among the ancients, and is yet assiduously cultivated by the modern Arabians and other orientals, although in a great measure exploded in European nations. By the former or which divisions in this science are foretold the changes of seasons, rain, wind, thunder, cold, heat, famine, diseases, &c., from a knowledge of the causes that are believed to act upon the earth and its atmosphere; whilst the latter foretold the characters, fortunes, &c., of men, from the stellary disposition at the moment of their respective nativities.
The philosopher, Eudoxus, spent much of his time on the top of a high mountain, to observe the motion of the stars. He regulated the Greek year as Cæsar did the Roman. Had the ancient Grecian astronomers been equally attached to experiment with Democritus, they might have arrived at more certain conclusions; but they were content with speculative theory, and spoke rather from conjecture than observation; whence both Strabio and Polybius treated as fabulous the since recognised assertion of Pythius, a famous navigator to the north, who had sailed to a country supposed to be Iceland, where he said the sun, in the middle of summer, never set.
The most important improvements in astronomy were made in the school of Alexandria, founded by Ptolemy Philadelphus; and which seminary flourished for nine hundred and twenty-three years, till the invasion of the Saracen army, under the command of Amrou. Those astronomers were chiefly Greeks, or of Grecian extraction—the most learned men being invited here by the liberality of the Ptolemies. The first who distinguished themselves were Timocarus and Aristillus, prior to the foundation of the library, which was founded three hundred years before Christ. Those two men endeavoured to determine the places of the different stars, and thus to trace the course of the planets. The next and most eminent man was Aristarchus, about two hundred and sixty-four years before Christ; who taught, that the sun was about nineteen times further from the earth than the moon (which is not the twentieth part of its real distance), although the philosophers of the Pythagorean school did not consider it above three times, and perhaps only one and a half further distant. Aristarchus also taught, that the moon was fifty-six diameters of our earth from this globe, which opinion comes near to the truth: he believed it to be scarcely one-third of its real size. He was widely erroneous in his conception of the sun’s dimensions. He also, in conformity to the doctrines of Pythagorus and Philolaus, supposed the sun to be placed in the centre, and that the earth moved round it; on which account he was accused of impiety, as disturbing the repose of the Vesta and the Lares. This opinion was not, however, retained by his successors in the Alexandrian school. Contrary to the doctrine of the Greek philosophers, he taught that the stars were at different distances, and that the orbit of the earth round the sun was an insensible point, in consequence of the immense distance of the stars. The only work of Aristarchus which remains, is on the magnitude and distance of the sun and moon.
Very nearly contemporary with Aristarchus was Euclid, the celebrated geometrician of Alexandria; Manetho, an astrologer and historian; and Aratus and Cleanthus, disciples of Zeno, the stoic philosopher; all of whom contributed to the enlargement of astronomical knowledge; but particularly the two first named.
Eratosthenes, born at Cyrene, succeeded Aristarchus, being invited by Ptolemy Euergetes. This professor is said to be the inventor of the Armillary sphere, an instrument or machine composed of moveable sides, representing the equator, the two colures, with the meridian; all of which turned round on an axis directed to the two poles of the world, each of which circles were anciently called armilla, and the whole machine, astrolabus. All instruments which could be contrived for the promotion of this science, were furnished at the public expense, and placed within the observatory of Alexandria. Assisted by these instruments, Eratosthenes first undertook to measure the obliquity of the ecliptics, or rather the double of that obliquity, that is, the distance from the tropics, which he made to be about 47 degrees; the obliquity, or half of this distance, 23½ degrees. This grand attempt was to ascertain the exact distance of a degree of the meridian, and thus to determine the circumference of the earth; which he accomplished with wonderful exactness, considering the period at which he lived; and he performed this by the same method since adopted by the moderns who have succeeded him. He is also said to have discovered the true distance of the sun from the earth.
The great Archimedes lived contemporary with Eratosthenes, that eminent geometrician of Syracuse, whose inventive genius in mechanics had constructed engines which protracted the fall of that capital, with its Island Sicily, to the almost omnipotent power of Rome for a considerable period.
The most illustrious astronomer which had as yet appeared at Alexandria was Hipparchus, who flourished between one hundred and sixty and one hundred and twenty-five years before Christ. He first brought this science into a tangible elementary form, rendering it systematic. He discovered, or was the first who observed the difference between the autumnal and the vernal equinox; the former being seven days longer than the latter, which proceeds from the eccentricity of the earth’s orbit, first discovered from observing the inequality of the solar motion. He framed tables for what is called equation of time, or to ascertain the difference between the shade on a well constructed dial and a perfectly regulated clock. He made great progress in explaining the motions and phases of the moon; however, he was not so successful with respect to the planets.