The Sphere of the World with Commentaries

the firmament more in one part than in another, someone existing in another part of the surface of the Earth that approached the firmament more closely would not see half of the sky, but this is contrary to Ptolemy and all philosophers who say that wherever a man exists, six signs rise for him and six set, and half of the sky always appears to him, while the other half is hidden. That also is a sign that the Earth is as a center and a point with respect to the firmament, because if the Earth were of any magnitude with respect to the firmament, it would not happen that half of the sky is seen. Likewise, if one understands a flat surface above the center of the Earth dividing it into two equal parts, and consequently the firmament itself, an eye therefore existing at the center of the Earth would see half of the firmament. And the same eye existing on the surface of the Earth would see the same half. From these it is gathered that the quantity of the Earth which is from the surface to the center is insensible, and consequently the quantity of the whole Earth is insensible with respect to the firmament. Alfraganus also says that the smallest of the visible fixed stars is larger than the whole Earth, but the star itself with respect to the firmament is as a point; therefore, with much more reason [is] the Earth, since it is smaller than that [star].

ON THE IMMOBILITY OF THE EARTH.

That the Earth is held motionless in the middle of all things, since it is supremely heavy, its gravity seems to be persuaded in this way: for every heavy thing tends naturally to the center. The center is indeed a point in the middle of the firmament; the Earth, therefore, since it is supremely heavy, naturally tends to that point. Likewise, whatever is moved from the center towards the circumference of the sky ascends. The Earth is moved from the center, therefore it ascends, which is left as an impossibility.

ON THE ABSOLUTE QUANTITY OF THE EARTH.

However, the whole circumference of the Earth is defined by the authority of Ambrosius Theodosius Macrobius and Eratosthenes the philosophers as containing 252,000 stadia, assigning 700 stadia to each of the 360 parts of the zodiac. For having taken