There have been three great schools of astronomy, the Chaldæan, the Ægyptian, and the Grecian. To these has been added a fourth school, which was established by the Dictator Cæsar among ourselves, and to which was entrusted the duty of regulating the year in conformity with the sun’s revolution,[417] under the auspices of Sosigenes, an astronomer of considerable learning and skill. His theory, too, upon the discovery of certain errors, has since been corrected, no intercalations having been made for twelve[418] successive years, upon its being found that the year which before had anticipated the constellations, was now beginning to fall behind them. Even Sosigenes himself, too, though more correct than his predecessors, has not hesitated to show, by his continual corrections in the three several treatises which he composed, that he still entertained great doubts on the subject. The writers, too, whose names are inserted at the beginning of this work,[419] have sufficiently revealed the fact of these discrepancies, the opinions of one being rarely found to agree with those of another. This, however, is less surprising in the case of those whose plea is the difference of the localities in which they wrote. But with reference to those who, though living in the same country, have still arrived at different results, we shall here mention one remarkable instance of discrepancy. Hesiod—for under his name, also, we have a treatise extant on the Science of the Stars[420]—has stated that the morning setting of the Vergiliæ takes place at the moment of the autumnal equinox; whereas Thales, we find, makes it the twenty-fifth day after the equinox, Anaximander the twenty-ninth, and Euctemon the forty-eighth. As for ourselves, we shall follow the calculations made by Julius Cæsar,[421] which bear reference more particularly to Italy; though at the same time, we shall set forth the dicta of various other writers, bearing in mind that we are treating not of an individual country, but of Nature considered in her totality. In doing this, however, we shall name, not the writers themselves, for that would be too lengthy a task, but the countries in reference to which they speak. The reader must bear in mind, then, that for the sake of saving space, under the head of Attica, we include the islands of the Cyclades as well; under that of Macedonia, Magnesia and Thracia; under that of Egypt, Phœnice, Cyprus, and Cilicia; under that of Bœotia, Locris, Phocis, and the adjoining countries; under that of Hellespont, Chersonesus, and the contiguous parts as far as Mount Athos; under that of Ionia, Asia[422] and the islands of Asia; under that of Peloponnesus, Achaia, and the regions lying to the west of it. Chaldæa, when mentioned, will signify Assyria and Babylonia, as well.