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date May 28th, 585 B.C. But other modern astronomers give different dates. Thales went to Egypt to study science, and learnt from its priests the length of the year (which was kept a profound secret!), and the signs of the zodiac, and the positions of the solstices. He held that the sun, moon, and stars are not mere spots on the heavenly vault, but solids; that the moon derives her light from the sun, and that this fact explains her phases; that an eclipse of the moon happens when the earth cuts off the sun's light from her. He supposed the earth to be flat, and to float upon water. He determined the ratio of the sun's diameter to its orbit, and apparently made out the diameter correctly as half a decree. He left nothing in writing. His successors, Anaximander (610–547 B.C.) and Anaximenes (550–475 B.C.), held absurd notions about the sun, moon, and stars, while Heraclitus (540–500 B.C.) supposed that the stars were lighted each night like lamps, and the sun each morning. Parmenides supposed the earth to be a sphere. Pythagoras (569–47 o B.C.) visited Egypt to study science. He deduced his system, in which the earth revolves in an orbit, from fantastic first principles, of which the following are examples: “The circular motion is the most perfect motion,” “Fire is more worthy than earth,” “Ten is the perfect number.” He wrote nothing, but is supposed to have said that the earth, moon, five planets, and fixed stars all revolve round the sun, which itself revolves round an imaginary central fire called the Antichthon. Copernicus in the sixteenth century claimed Pythagoras as the founder of the system which he, Copernicus, revived. Anaxagoras (born 499 B.C.) studied astronomy in Egypt. He explained the return of the sun to the east each morning by its going under the flat earth in the night. He held that in a solar eclipse the moon hides the sun, and in a lunar eclipse the moon enters the earth's shadow — both excellent opinions. But he entertained absurd ideas of the vertical motion of the heavens whisking stones into the sky, there to be ignited by the fiery firmament to form stars. He was prosecuted for this unsettling opinion, and for maintaining that the moon is an inhabited earth. He was defended by Pericles (432 B.C.). Solon dabbled, like many others, in reforms of the calendar. The common year of the Greeks originally had 360 days — twelve months of thirty days. Solon's year was 354 days. It is obvious that these erroneous years would, before long, remove the summer to January and the winter to July. To prevent this it was customary at regular intervals to intercalate days or months. Meton (432 B.C.) introduced a reform based on the nineteen-year cycle. This is not the same as the Egyptian and Chaldaean eclipse cycle called Saros of 223 lunations, or a little over eighteen years. The Metonic cycle is 235 lunations or nineteen years, after which period the sun and moon occupy the same position relative to the stars. It is still used for fixing the date of Easter, the number of the year in Meton's cycle being the golden number of our prayer-books. Meton's system divided the 235 lunations into months of thirty days and omitted every sixtythird day. Of the nineteen years, twelve had twelve months and seven had thirteen months. Callippus (330 B.C.) used a cycle four times as long, 94o lunations, but one day short of Meton's seventy-six years. This was more correct. Eudoxus (406–350 B.C.) is said to have travelled with Plato in Egypt. He made astronomical observations in Asia Minor, Sicily, and Italy, and described the starry heavens divided into constellations. His name is connected with a planetary theory which as generally stated sounds most fanciful. He imagined the fixed stars to be on a vault of heaven; and the sun, moon, and planets to be upon similar vaults or spheres, twenty-six revolving spheres in all, the motion of each planet being resolved into its components, and a separate sphere being assigned for each component motion. Callippus (330 B.C.) increased the number to thirty-three. It is now generally accepted that the real existence of these spheres was not suggested, but the idea was only a mathematical conception to facilitate the construction of tables for predicting the places of the heavenly bodies.
Aristotle (384–322 B.C.) summed up the state of astronomical knowledge in his time, and held the earth to be fixed in the centre of the world.
Nicetas, Heraclides, and Ecphantes supposed the earth to revolve on its axes, but to have no orbital motion.
The short epitome so far given illustrates the extraordinary deductive methods adopted by the ancient Greeks. But they went much farther in the same direction. They seem to have been in great difficulty to explain how the earth is supported, just as were those who invented the myth of Atlas, or the Indians with the tortoise. Thales thought that the flat earth floated on water. Anaxagoras thought that, being flat, it would be buoyed up and supported on the air like a kite. Democritus thought it remained fixed, like the donkey between two bundles of hay, because it was equidistant from all parts of the containing sphere, and there was no reason why it should incline one way rather than another. Empedocles attributed its state of rest to centrifugal force by the rapid circular movement of the heavens, as water is stationary in a pail when whirled round by a string. Democritus further supposed that the inclination of the flat earth to the ecliptic was due to the greater weight of the southern parts owing to the exuberant vegetation. For further references to similar efforts of imagination the reader is referred to Sir George Cornwall Lewis's Historical Survey of the Astronomy of the Ancients; London,’ 1862. His list of authorities is very complete, but some of his conclusions are doubtful. At p. 1 13 of that work he records the real opinions of Socrates as set forth by Xenophon; and the reader will, perhaps, sympathise with Socrates in his views on contemporary astronomy: —
With regard to astronomy he [Socrates] considered a knowledge of it desirable to the extent of determining the day of the year or month, and the hour of the night,......but as to learning the courses of the stars, to be occupied with the planets, and to inquire about their distances from the earth, and their orbits, and the causes of their motions, he strongly objected to such a waste of valuable time. He dwelt on the contradictions and conflicting opinions of the physical philosophers,......and, in fine, he held that the speculators on the universe and on the laws of the heavenly bodies were no better than madmen (Xen. Mem, i. 1, 1 I-15).
Plato (born 429 B.C.), the pupil of Socrates, the fellow-student of Euclid, and a follower of Pytha