The armillary sphere, of which the author gives a drawing, serves to explain the system of the world according to Ptolemy, and could also serve as an astrolabe, for one sees at the top of it a kind of handle or ring, by which to hold it suspended, as is seen in the above-mentioned drawing. He begins his treatise by giving us an idea of that system, as have done all those after him, who have written of the elements of the nautical art and of pilotage.

“The earth is round,” he says, “and remains suspended and immovable in the midst of all the celestial bodies. The first index fixed on two poles, the arctic and antarctic, which are supposed to correspond with the poles of the earth. It runs from East to West, and transports with itself all the planets and stars. Besides this there is the eighth sphere, the poles of which are at 23 deg. 33 min., it runs from West to East.

“It is supposed that all the circumference of the earth is divided into 360 degrees; and each degree is of 17 leagues and a half, consequently the circumference of the earth is 6, 300 leagues. Land leagues are of three miles and sea leagues of four miles.

“The ten circles of the armillary sphere, of which the six major pass through the center of the earth, serve to determine the situation of countries and climates. The Ecliptic determines the movement of the sun and the planets: the two Tropics indicate the point to which the sun declines from the equator towards the North in summer, and towards the South in winter.