The Sphere of the World (De Sphaera)

side, around which the sphere can be revolved. On the outside, from the part of the south pole of the sphere, we shall secure a wooden handle around the axis, so that the artificial sphere can be held more conveniently by hand. But first, we will firmly set a small wooden sphere around the axis in the middle of the sphere, which may represent for us the mass of the earth, upon whose surface we will pre-mark five regions of the sky related to the regions, or twelve zones properly: which denote the seven climates and five habitable zones, and similarly the rest of the extremes as it is explained in the second chapter of this work, with their names; marking in the same [sphere] the longitudinal and latitudinal circle if we wish to have a more complete thing. And we paint in green color all that is the hemisphere from the part opposite the climates and its two extreme zones and the remainder of that southern [part] which adheres to the torrid zone, so that by it we may understand all the habitable earth through the waters of the ocean sea. Furthermore, it is necessary to arrange three other revolving circles around the sphere on the outside for greater convenience: but the first two of them, one nearly touching the other, which can be revolved around the sphere and the axis, with them being firmly held. And let one of them be held for the meridian circle, and properly the outer one, of which each half, precisely that which is from pole to pole, is divided into 180 degrees and its fractions. The other, however, similarly [is that] which is marked for the straight horizon. And to this circle, we shall join a third interior circle by appropriate ingenuity, through two little axles made in holes in them around two points opposite, equally distant from the poles of the revolution of the sphere, which is precisely in the direct line of the equinoctial circle of the sphere, so that around these two little axles the third circle itself, with the other held, can be led around the sphere from one pole of the sphere to the other. And we shall not make the little axles protruding, lest they impede this motion or the motion of the meridian. We shall also mark this circle for the oblique horizon, which, just as the others, we shall divide into degrees. And so the artificial sphere will be constructed, as it is commonly in use, made from material circles. And when we wish to have the straight or oblique horizon duly arranged on the sphere, let us make that horizon held firmly in such a way that no part of its circumference is higher than another. For then it will be truly equidistant to the surface of the true horizon. And it will be good, although it is not necessary, that the northern part of the sphere be towards the north, and the southern towards the south, with this, that the eastern part of this sphere be towards the east, and the western towards the west. And it is convenient with this that the meridian circle be raised so that both the part of it which indicates the meridian, and the lowest [part] which denotes the angle of the night, be distant from the east of the horizon and the west of the same equally by all means, that is by a fourth part of the equinoctial or by ninety degrees. And thus we have the location of the zenith at the top of the meridian, equidistant everywhere from the horizon itself. And its nadir at the bottom of it. And if we wish to have the elevation of the pole above the oblique horizon according to the latitude of any place on earth, as for example for a city whose latitude is known, first we shall secure the oblique horizon and the meridian, each in its place as has been said, and we shall make the horizon itself held strongly; and then we revolve the sphere not around its poles from east to west nor vice versa, but from its north to south around the little axles set on the horizon, elevating its northern pole if the latitude of the city is northern, or the southern pole if that latitude is southern, precisely by as many degrees of the meridian set at distances from the oblique horizon itself, as are the degrees or minutes of the latitude of that city: and in this state of the meridian...