The Sphere of the World with Commentaries

According to accident, however, it is divided into the right sphere and the oblique sphere. For those are said to have a right sphere who remain under the equinoctial line, if anyone can remain there. It is called "right" because neither of the poles is elevated more than the other for them, or because their horizon intersects the equinoctial and is intersected by it at right spherical angles. Those, however, are said to have an oblique sphere who live around the equinoctial or beyond. For them, one of the poles is always elevated above the horizon, while the other is always depressed, or because their artificial horizon intersects the equinoctial and is intersected by it at unequal and oblique angles.

WHAT THE FORM OF THE WORLD IS.

The universal machine of the world is divided into two: the ethereal region and the elemental region. The elemental, indeed, being continuously prone to alteration, is divided into four. For the Earth, as the center of the world, is situated in the midst of all things. Around it is water, around water is air, and around air is fire—pure there and not turbid—touching the sphere of the moon, as Aristotle says in his book on the Meteors. Thus did the glorious and sublime God dispose it. And these four elements are what are in turn altered, corrupted, and regenerated by one another. Elements, however, are simple bodies, which cannot be divided into parts of diverse forms. From their commixtion, the diverse species of generated things are made. Any three of these surround the Earth spherically on all sides, except insofar as the dryness of the Earth resists the moisture of the water in order to preserve the life of living beings. Also, all things except the Earth are mobile, which, as the center of the world, by its own weight, flees the great motion of the extremes on all sides equally and holds the middle of the round sphere.