The Sphere of Johannes de Sacrobosco

SPHAERAE IOAN.

34 Necessity,

for if the world were of another form than round—namely, three-sided, four-sided, or many-sided—two impossible things would follow: namely, that some place would be empty, and a body would be without a place. Both of these are false, as is clear in raised and convoluted angles.

A large circular diagram at the top contains an inscribed triangle and several other concentric polygonal outlines, with a central point. Below this are four smaller circular diagrams arranged in a two-by-two grid. Each small circle contains an inscribed polygon: a six-pointed star, an octagon, a square, and a decagon. The segments between the flat sides of the polygons and the curved edges of the circles are filled in with solid black ink.

Dif. 2.

Likewise, as Alfraganus al-Farghani, an astronomer says, if the heaven were flat, some part of the heaven would be closer to us than another, namely that which would be above our heads. Therefore, a star existing there would be closer to us than a star at rising or setting. But things that are closer to us appear larger. Therefore, the Sun, or another star existing in the middle of the heaven, should appear larger than in...