Leucippus affirms that the earth vergeth towards the southern parts, by reason of the thinness and fineness that is in the south; the northern parts are more compacted, they being congealed by a rigorous cold, but those parts of the world that are opposite are enfired. Democritus, because, the southern parts of the air being the weaker, the earth as it enlarges bends towards the south; the northern parts are of an unequal, the southern of an equal temperament; and this is the reason that the earth bends towards those parts where the earth is laden with fruits and its own increase. 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. CHAPTER XIV. INTO HOW MANY ZONES IS THE EARTH DIVIDED? Pythagoras says that, as the celestial sphere is distributed into five zones, into the same number is the terrestrial; which zones are the arctic and antarctic, the summer and winter tropics (or temperate zones), and the equinoctial; the middle of which zones equally divides the earth and constitutes the torrid zone; but that portion which is in between the summer and winter tropics is habitable, by reason the air is there temperate. CHAPTER XV. OF EARTHQUAKES.