A decorative woodcut headpiece features a central grotesque mask flanked by scrolling foliage, floral motifs, and two seated figures at the far ends.

BOOK ONE

ON THE

SPHERICAL DOCTRINE

OF ASTRONOMY.

CHAPTER ONE.

What the Sphere is, and of what it consists.

Since we must begin with the doctrine of the Sphere, it should be assumed that by the name "Sphere" we mean that common instrument. This instrument, which will soon be shown as it can be represented on a flat surface, consists of various circles or rings original: "armillis". It is pierced by an axis with a small globe in the center. It is used to represent both the Machine of the World and the celestial motions, especially the First, or diurnal, motion.

For first, that little globe held in the middle represents the Earth, placed at the center of the World Machine. The ends of the axis passing through it, upon which the rotation occurs, represent the two Poles. These are called the North Pole original: "Boreum" and the South Pole original: "Austrinum". Upon these, the whole Machine of the Heavens turns in a motion completed in twenty-four hours. This is called "diurnal" by the Latins and nychthemeros original: "νυχθήμερος," meaning "night-day" by the Greeks, because it encompasses the span of a day and a night.

A detailed woodcut illustration shows an armillary sphere mounted on a decorative stand. The sphere includes various rings representing astronomical circles: the Meridian, the Rational Horizon, the Equator, the Zodiac (labeled with signs of the zodiac), the Tropics of Cancer and Capricorn, and the Arctic and Antarctic Polar Circles. The poles are labeled as the North Pole and South Pole. A small globe representing Earth sits at the very center.

Gassendi's Observations.

And indeed, the Sphere is not constructed from as many physical orbs as the heavens we previously described. However, the entire structure of the heavens can be understood from this simple framework of circles: to the extent that