The Sphere of Johannes de Sacrobosco

SPHÆRÆ IOAN.

are equal, and that point is called the center of the sphere. A straight line, however, passing through the center of the sphere, applying its extremities to the circumference on both sides, around which the sphere revolves, is called the axis of the sphere. The two points terminating the axis are called the poles of the sphere.

Two woodcut illustrations are presented side-by-side. The left diagram shows a dark globe mounted on a horizontal axis supported by two ornate pillars. The right diagram shows a dark hemisphere similarly mounted on a horizontal axis between two pillars. Below the globes are stylized terrain lines with small human figures positioned near the base of the pillars.

THE DIVISION OF THE SPHERE OF THE WORLD.

3The sphere of the world is divided in two ways: according to substance and according to accident. According to substance, it is divided into nine spheres: namely, the ninth sphere, which is called the first motion or the primum mobile the first moved/prime mover; the sphere of the fixed stars, 4 which is called the firmamentum firmament; and the seven spheres of the seven planets, some of which are larger and some smaller, according to how much they approach or recede from the firmament. Hence, among those