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THE FIRST BOOK OF THE ASTRONOMICAL INSTITUTION

OR

THE SPHERICAL DOCTRINE.

CHAPTER I.

What the Sphere is, and of what it consists.

Since, therefore, we must begin with the Spherical doctrine, it is to be assumed that by the name of Sphere is here understood that common instrument—presently to be shown (insofar as it can be represented on a plane)—which, consisting of various circles and rings, and traversed by an axis with a small globe in the middle, is customarily used for representing both the Machine of the World and the celestial motions, and especially the First, or diurnal, motion.

For in the first place, that small globe which is supported in the middle [represents] the Earth in the center of the world-machine