It is easy to exonerate Aristotle. We can say that he only lent his weight to one side of the scales which had been about evenly balanced, that he did it with purer logic than Plato, and that he could not know how abruptly Greek science was to perish, leaving only the most persistent doctrines to the succeeding ages. The fact remains that the scales were tipped, the course of astronomy was set back for two thousand years, and the scientific Aristotle is the arch villain in the story.
The heliocentric theory flickered on for a while in Plato's academy, but the voices of science were too much for it. Archimedes was practical enough to set fire to the Roman ships with a burning glass, and impractical enough to run naked through the streets of Syracuse, shouting, "Eureka," when he succeeded in another famous experiment; but even he criticized and rejected the theory of Aristarchus with scorn. "If the Earth were really moving around the Sun," he asserted, "the apparent position of the stars would change." His arguments sounded well, but he had forgotten his predecessor's view of distance. To a man driving through the mountains, the near-by scenery constantly varies; but to a man turning in small circles a hundred miles away, the mountains are as invariable as the stars are to us.
Mark Twain, in his autobiography, told of a lie which he perpetrated in his boyhood, and tried many times afterward to contradict, only to be told by others that they knew better. It has been said that a lie never lives, but Mark Twain ended by saying that he was very glad he did not have life-insurance premiums to pay on the lie which he had told.
The life of Mark Twain's lie was relatively short. At least he was able to prove the contrary before his death, and no one else suffered. Aristarchus had no such luck. He laughs best who laughs last; but for that final triumph Aristarchus had to wait more than two thousand years.
The arguments for a stationary Earth were given by Claudius Ptolemy in 150 A. D. He argued that, if the Earth were rotating, objects would fly off into space. "Matter which is in violent rotation does not seem fit to be massed together, but rather dispersed." He added that long before his time the Earth would have been dissipated over the heavens themselves; furthermore a stone dropped to Earth would not reach its destined place as the Earth would have moved from under it.
All Ptolemy's arguments, except the last, have been proved wrong by later scientists. Curiously Ptolemy was right that a stone would not reach its appointed place, but for just the opposite reason from the one Ptolemy stated. The experiment has been proved by stones dropped carefully down a deep vertical mine shaft. In not a single case did they reach the bottom; they continued to move eastward during their fall with a velocity equal to the velocity of the Earth's surface from which they started, but the mine shaft some 4,000 to 5,000 feet below was revolving more slowly, and in every case the stone struck the east side of the shaft before it reached the bottom.
Claudius Ptolemy was the last of the great astronomers, and his work survived when all the others were lost or burned in the religious fires of persecution. His theory was ingenious, remarkably useful in spite of its falsity, the result of careful observation and accurate mathematics. But it was exceedingly complicated. He held that the Earth was spherical but stationary, and that all the stars and planets revolved around the Earth in circular orbits at uniform velocities. They were situated in ten vast crystal spheres, perfectly transparent, and each sphere had its own special motion. The first seven were for the Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn. Apian, in 1540, described the other three:
"It is known to all that outside the seven orbits of the wandering stars, three spheres exist beyond them, namely the eighth, in which are the fixed stars, the ninth again beyond that and the tenth, which is the last.
"The tenth sphere revolves from east to west in 24 hours, as appears daily to our eyes. We see then how the Sun and other stars (which follow one another very rapidly) rise and set.
"The ninth sphere rises in the west and travels to the zenith in the direction opposite to that of the tenth and makes its revolution in 49,000 years.
"In the middle of this course, we imagine the ecliptic. . . .
"In this ecliptic of the ninth sphere, you can place the 12 signs if you like, but they have no use, except the first point of Aries . . .
"Understand that the eighth sphere is under the ninth (whose center the ecliptic sometimes occupies) . . . .
"The Equinoctial is equidistant from both poles and its surface bisects the whole mechanism of the world. Leaving the eighth sphere, we go through it to the tenth sphere. There, at last, I have shown the true ecliptic."
Ptolemy added yet further complications, such as epicycles at the first point of Aries and Libra, and the Arabians added trepidation as an extra decoration to a system already sufficiently involved. The three outer spheres were particularly designed to show the motion of precession and the separation of the signs of the zodiac from the constellations which bore the same names.
The Ptolemaic theory suited the intricate minds of the Orient. The Greeks had adopted science from the east in the first place, and purified it with their logic. The east was ready and willing to welcome it back. Therefore when the heretic Christians, who insisted on studying science, took their books under their arms and fled into Persia, the eastern countries accepted their theories at least; and the Ptolemaic system grew up in an atmosphere where angels and devils inhabited the spheres of the planets, and dragons still caused eclipses of the Sun and the Moon. The books brought from Greece were translated not only into the various languages of their new homes, but into accord with the doctrines which their new masters loved.
In spite of its false basis, and curiously fantastic surroundings, the Ptolemaic theory did not altogether suffer in the hands of the Easterners. Their very love of intricacy led scientists to perfect instruments of great precision, and their calculations were amazingly accurate. At the highest point of Ptolemaic astronomy, the Arabians could approximate the movements of the planets; and, if they needed greater refinement, they obtained it with the aid of epicycles and eccentrics. The mean motion of the planets was determined with errors of only minutes of arc in centuries of time, and eclipses of the Moon were found with errors not exceeding one and one-half hours in seventeen hundred years. Working with a premise that was basically false, without telescopes, verniers, or chronometers to correct their measurements, the Ptolemaic astronomers achieved the most extraordinary precision.