But to return. The earliest historic name associated with astronomy in Greece was Thales, the founder of the Ionic school of philosophers, born 639 B.C. He is reported to have predicted an eclipse of the sun, to have made a visit to Egypt, to have fixed the year at three hundred and sixty-five days, and to have determined the course of the sun from solstice to solstice. He attributed an eclipse of the moon to the interposition of the earth between the sun and moon; and an eclipse of the sun to the interposition of the moon between the sun and earth. [Footnote: Sir G. G. Lewis, Hist. of Astron., p. 81.] He also determined the ratio of the sun's diameter to its apparent orbit. As he first solved the problem of inscribing a right-angled triangle in a circle, [Footnote: Diog. Laert, i. 24.] he is the founder of geometrical science in Greece. He left, however, nothing to writing, hence all accounts of him are confused. It is to be doubted whether in fact he made the discoveries attributed to him. His speculations, which science rejects, such as that water is the principle of all things, are irrelevant to a description of the progress of astronomy. That he was a great light, no one questions, considering the ignorance with which he was surrounded. Anaximander, who followed him in philosophy, held to puerile doctrines concerning the motions and nature of the stars, which it is useless to repeat. His addition to science, if he made any, was in treating the magnitudes and distances of the planets. He attempted to delineate the celestial sphere, and to measure time by a sun-dial. Anaximenes of Miletus taught, like his predecessors, crude notions of the sun and stars, and speculated on the nature of the moon, but did nothing to advance his science on true grounds, except the construction of sun-dials. The same may be said of Heraclitus, Xenophanes, Parmenides, Anaxagoras. They were great men, but they gave to the world mere speculations, some of which are very puerile. They all held to the idea that the heavenly bodies revolved around the earth, and that the earth was a plain. But they explained eclipses, and supposed that the moon derived its light from the sun. Some of them knew the difference between the planets and the fixed stars. Anaxagoras scouted the notion that the sun was a god, and supposed it to be a mass of ignited stone, for which he was called an atheist.
[Sidenote: Socrates.]
[Sidenote: Pythagoras.]
Socrates, who belonged to another school, avoided all barren speculations concerning the universe, and confined himself to human actions and interests. He looked even upon geometry in a very practical way, so far as it could be made serviceable to land measuring. As for the stars and planets, he supposed it was impossible to arrive at a true knowledge of them, and regarded speculations upon them as useless. The Greek astronomers, however barren were their general theories, still laid the foundation of science. Pythagoras, born 580 B.C., taught the obliquity of the ecliptic, probably learned in Egypt, and the identity of the morning and evening stars. It is supposed that he maintained that the sun was the centre of the universe, and that the earth revolved around it. But this he did not demonstrate, and his whole system was unscientific, assuming certain arbitrary principles, from which he reasoned deductively. "He assumed that fire is more worthy than earth; that the more worthy place must be given to the more worthy; that the extremity is more worthy than the intermediate parts; and hence, as the centre is an extremity, the place of fire is at the centre of the universe, and that therefore the earth and other heavenly bodies move round the fiery centre." But this was no heliocentric system, since the sun moved like the earth, in a circle around the central fire. This was merely the work of the imagination, utterly unscientific, though bold and original. Nor did this hypothesis gain credit, since it was the fixed opinion of philosophers, that the earth was the centre of the universe, around which the sun and moon and planets revolved. But the Pythagoreans were the first to teach that the motions of the sun, moon, and planets, are circular and equable. Their idea that they emitted a sound, and were combined into a harmonious symphony, was exceedingly crude, however beautiful. "The music of the spheres" belongs to poetry, as well as the speculations of Plato.
[Sidenote: Eudoxus.]
Eudoxus, who was born 406 B.C., may be considered the founder of scientific astronomical knowledge among the Greeks. He is reputed to have visited Egypt with Plato, and to have resided thirteen years in Heliopolis, in constant study of the stars, communing with the Egyptian priests. His contribution to the science was a descriptive map of the heavens, which was used as a manual of sidereal astronomy to the sixth century of our era. He distributed the stars into constellations, with recognized names, and gave a sort of geographical description of their position and limits, although the constellations had been named before his time. He stated the periodic times of the five planets visible to the naked eye, but only approximated to the true periods.
The error of only one hundred and ninety days in the periodic time of Saturn, shows that there had been, for a long time, close observations. Aristotle, whose comprehensive intellect, like that of Bacon, took in all forms of knowledge, condensed all that was known in his day in a treatise concerning the heavens. [Footnote: Delambre, Hist. de l'Astron. Anc., tom. i. p. 301.] He regarded astronomy as more intimately connected with mathematical science than any other branch of philosophy. But even he did not soar far beyond the philosophers of his day, since he held to the immobility of the earth—the grand error of the ancients. Some few speculators in science, like Heraclitus of Pontus and Hicetas, conceived a motion of the earth itself upon its axis, so as to account for the apparent motion of the sun, but they also thought it was in the centre of the universe.
[Sidenote: Meton.]
The introduction of the gnomon and dial into Greece advanced astronomical knowledge, since they were used to determine the equinoxes and solstices, as well as parts of the day. Meton set up a sun-dial at Athens in the year 433 B.C., but the length of the hour varied with the time of the year, since the Greeks divided the day into twelve equal parts. Dials were common at Rome in the time of Plautus, 224 B.C.; [Footnote: Ap. Gell., N. A., iii. 3.] but there was a difficulty of using them, since they failed at night and in cloudy weather, and could not be relied on. Hence the introduction of water-clocks instead.
[Sidenote: Aristarchus.]