Page:The Gradual Acceptance of the Copernican Theory of the Universe.djvu/115

 

APPENDIX A.

Ptolemy: Syntaxis Mathematica (Almagest)

"That the earth has no movement of rotation," in Opera Quæ Exstant Omnia, edidit Heiberg, Leipsic, 1898, Bk. I, sec. 7: (I, 21-25); compared with the translation into French by Halma, Paris, 1813.

By proofs similar to the preceding, it is shown that the earth cannot be transported obliquely nor can it be moved away from the center. For, if that were so, all those things would take place which would happen if it occupied any other point than that of the center. It seems unnecessary to me, therefore, to seek out the cause of attraction towards the center when it is once evident from the phenomena themselves, that the earth occupies the center of the universe and that all heavy bodies are borne towards it; and this will be readily understood if it is remembered that the earth has been demonstrated to have a spherical shape, and according to what we have said, is placed at the center of the universe, for the direction of the fall of heavy bodies (I speak of their own motions) is always and everywhere perpendicular to an uncurved plane drawn tangent to the point of intersection. Obviously these bodies would all meet at the center if they were not stopped by the surface, since a straight line drawn to the center is perpendicular: to a plane tangent to the sphere at that point.

Those who consider it a paradox that a mass like the earth is supported on nothing, yet not moved at all, appear to me to argue according to the preconceptions they get from what they see happening to small bodies about them, and not according to what is characteristic of the universe as a whole, and this is the cause of their mistake. For I think that such a thing would not have seemed wonderful to them any longer if they had perceived that the earth, great as it is, is merely a point in comparison to the surrounding body of the heaven. They would find that it is possible for the earth, being infinitely small relative to the universe, to be held in check and fixed by the forces exercised over it equally and following similar directions by the universe, which is infinitely great and composed of similar parts. There is neither up nor down in the universe, for that cannot be imagined in a sphere. As to the bodies which it encloses, by a consequence of their nature it happens that those that are light and subtle are as though blown by the wind to the outside and to the circumference, and seem to appear to us to go up, because that is how we speak of the space above our heads

107