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.