“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.,[419] 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.[420]” “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. The Meridian, always variable, because it passes through all points of the equator, cutting it perpendicularly, designates the longitude, and it is on it that the latitudes are marked.” +Of Latitude.+ After having well explained the armillary sphere with all its parts, and their use according to the system of Ptolemy, the author goes on to teach the method of taking the altitude of the pole, on which the latitude is calculated; fixing the pole at 0° and the equator at 90°. “The Polar star,” he says, “is not precisely on the point corresponding to the axis of the earth; but it turns round it, as do all the other stars. In order to know its true position with regard to the pole, it must be observed where the Guard stars[421] stand. If these are on the western arm,[422] the polar star stands one degree above the pole: if they are on the line[423] the pole star stands 3 deg. 30 min.[424] below the pole: if they are on the eastern arm the pole star is one degree below the pole. When one wishes to take the altitude of the pole star, in whichever of the above-mentioned four places the Guard stars may be, the degrees which the pole star has above the pole will be subtracted from its altitude, or those which it has below the pole will be added to it. I have spoken in the account of the voyage of the stars of the Antarctic Pole.”