It was a question in ancient times whether they or the Egyptians had been the first to carry their investigations into the infinite depths of celestial space: when it came to be a question as to which of the two peoples had made the greater progress in this branch of knowledge, all hesitation vanished, and the pre-eminence was accorded by the ancients to the priests of Babylon rather than to those of Heliopolis and Memphis.* * Clement of Alexandria, Lucien, Diogenes Laertius, Macrobius, attribute the origin of astronomy to the Egyptians, and Diodorus Sioulus asserts that they were the teachers of the Babylonians; Josephus maintains, on the contrary, that the Egyptians were the pupils of the Chaldaeans. [Illustration: 340.jpg ASTRONOMICAL TABLE] The Chaldaeans had conducted astronomical observations from remote antiquity.* Callisthenes collected and sent to his uncle Aristotle a number of these observations, of which the oldest had been made nineteen hundred and three years before his time--that is, about the middle of the twenty-third century before our era: he could have transcribed many of a still earlier date if the archives of Babylon had been fully accessible to him. * Epigenes asserts that their observations extended back to 720,000 years before the time of Alexander, while Berossus and Critodemus limit their antiquity to 490,000 years, which was further reduced to 473,000 years by Diodorus, to 470,000 by Cicero, and to 270,000 by Hipparchus.