Chapter XIII.

Of the Motion of the Earth.

Most of the philosophers say that the earth remains fixed in the same place. Philolaus the Pythagorean, that it is moved about the element of fire, in an oblique circle, after the same manner of motion that the sun and moon have. Heraclides of Pontus and Ecphantus the Pythagorean assign a motion to the earth, but not progressive, but after the manner of a wheel being carried on its own axis; thus the earth (they say) turns itself upon its own centre from west to east. Democritus, that when the earth was first formed it had a motion, the parts of it being small and light; but in process of time the parts of it were condensed, so that by its own weight it was poised and fixed.