Great were, undoubtedly, the improvements in astronomy, made by the Greek philosophers of early ages, on such of its rudiments as were handed down to them from those nations by whom it was first cultivated:[16] Yet it can scarcely be conceived, that, until the celebrated Euclid of Alexandria,[17] and his followers, had reduced the mathematics of Thales and others of those philosophers, into regular systems of arithmetical and geometrical science, the true principles of astronomy could be ascertained. In fact, seventeen centuries and an half had elapsed, from the time of that great geometrician, before Copernicus appeared: when this wonderful genius, availing himself of such remnants of the ancient philosophy, as the intervening irruptions of the barbarous nations of the north upon the then civilized world had left to their posterity, opened to the view of mankind the real system of the universe.[18]—So vast was the chasm, during which the nobler branches of physics remained uncultivated and neglected, that, from the age of Euclid, fourteen centuries passed away, before Roger Bacon, an English Franciscan friar, began his successful enquiries into experimental philosophy.—This extraordinary man is said to have been almost the only _astronomer_ of his age; and he himself tells us, that there were not, then, more than three or four persons in the world who had made any considerable proficiency in the _mathematics_! ----- Footnote 16: The Greeks derived their knowledge of astronomy from the Egyptians and Chaldeans. According to Plutarch, the sciences began to unfold themselves about the time of Hesiod, the Greek poet, who flourished upwards of nine centuries before the Christian era; but their progress was very slow, until the time of Thales, which was about three centuries later. And although this celebrated philosopher of antiquity rendered himself famous by foretelling an eclipse of the sun, he only predicted the _year_ in which it was to happen. Even this, it is remarked by Mr. Vince (in his invaluable work, entitled, _A Complete System of Astronomy_,) he was probably enabled to do by the _Chaldean Saros_, a period of 223 lunations; after which, the eclipses return again nearly in the same order. Philolaus, a disciple of Pythagoras, lived about four hundred and fifty years before Christ, and is said to have taught the true solar system,—placing the sun in the centre, with the earth and all the planets revolving about it; a system which, it is believed, Pythogaras himself had conceived, and was inclined to adopt.