This approximate determination of the size of the earth tended to depose her from her dominating position, and gave rise to very serious theological results.  In this the ancient investigations of Aristarchus of Samos, one of the Alexandrian school, 280 B.C., powerfully aided.  In his treatise on the magnitudes and distances of the sun and moon, he explains the ingenious though imperfect method to which he had resorted for the solution of that problem.  Many ages previously a speculation had been brought from India to Europe by Pythagoras.  It presented the sun as the centre of the system.  Around him the planets revolved in circular orbits, their order of position being Mercury, Venus, Earth, Mars, Jupiter, Saturn, each of them being supposed to rotate on its axis as it revolved round the sun.  According to Cicero, Nicetas suggested that, if it were admitted that the earth revolves on her axis, the difficulty presented by the inconceivable velocity of the heavens would be avoided.

There is reason to believe that the works of Aristarchus, in the Alexandrian Library, were burnt at the time of the fire of Caesar.  The only treatise of his that has come down to us is that above mentioned, on the size and distance of the sun and moon.

Aristarchus adopted the Pythagorean system as representing the actual facts.  This was the result of a recognition of the sun’s amazing distance, and therefore of his enormous size.  The heliocentric system, thus regarding the sun as the central orb, degraded the earth to a very subordinate rank, making her only one of a company of six revolving bodies.

But this is not the only contribution conferred on astronomy by Aristarchus, for, considering that the movement of the earth does not sensibly affect the apparent position of the stars, he inferred that they are incomparably more distant from us than the sun.  He, therefore, of all the ancients, as Laplace remarks, had the most correct ideas of the grandeur of the universe.  He saw that the earth is of absolutely insignificant size, when compared with the stellar distances.  He saw, too, that there is nothing above us but space and stars.

But the views of Aristarchus, as respects the emplacement of the planetary bodies, were not accepted by antiquity; the system proposed by Ptolemy, and incorporated in his “Syntaxis,” was universally preferred.  The physical philosophy of those times was very imperfect—­one of Ptolemy’s objections to the Pythagorean system being that, if the earth were in motion, it would leave the air and other light bodies behind it.  He therefore placed the earth in the central position, and in succession revolved round her the Moon, Mercury, Venus, the Sun, Mars, Jupiter, Saturn; beyond the orbit of Saturn came the firmament of the fixed stars.  As to the solid crystalline spheres, one moving from east to west, the other from north to south, these were a fancy of Eudoxus, to which Ptolemy does not allude.