"[A]s to the spherical shape of the earth... Aristotle begins by answering an objection raised by the partisans of a flat earth... His answer is confused... He has, however, some positive proofs based on observation. (1) In partial eclipses of the moon the line separating the bright from the dark portion is always convex (circular)—unlike the line of demarcation in the phases of the moon, which may be straight or curved in either direction—this proves that the earth, to the interposition of which lunar eclipses are due, must be spherical. ...[H]is explanation shows that he had sufficiently grasped this truth. (2) Certain stars seen above the horizon in Egypt and in Cyprus are not visible further north, and... certain stars set there which in more northern latitudes remain always above the horizon. ...[I]t follows not only that the earth is spherical, but also that it is not a very large sphere. He adds that this makes it not improbable that people are right when they say that the region about the is joined on to India, one sea connecting them. It is here, too, that he quotes the result arrived at by mathematicians of his time, that the circumference of the earth is 400,000 stades. He is clear that the earth is much smaller than some of the stars. On the other hand, the moon is smaller than the earth. Naturally, Aristotle has a priori reasons for the sphericity of the earth. Thus, using once more his theory of heavy bodies tending to the centre, he assumes that, whether the heavy particles forming the earth are supposed to come together from all directions alike and collect in the centre or not, they will arrange themselves uniformly all round, i.e. in the shape of a sphere, since, if there is any greater mass at one part than at another, the greater mass will push the smaller until the even collection of matter all round the centre produces equilibrium."