The Sphere of the World (De Sphaera)

we shall also make it held firmly, and we will have the sphere oblique, and the horizon and the meridian proportional to that city; and with the horizon and meridian standing, we will be able to revolve the sphere and turn back its poles within the two said circles: and similarly to understand the motion of the prime mobile, and the rising and setting and the rest, as is to be said later in the sphere of heaven: and the varieties of the times and of the days and of the nights and of the shadows and the rest of the prime mobile which are accustomed to happen and which we might wish to consider. But if we desire to have a sphere by which we can understand the motion of the ninth and ninth sphere, we shall therefore make the common sphere from its circles as has been said: and another smaller one which can be contained and revolved inside that one, as Purbach said, which is integrated from only three circles: since they satisfy the proposal, of which two intersect each other orthogonally in two points truly diametrically opposite, where we shall establish its poles to be, through an axis penetrating them, which may protrude a little and equally outside this sphere to the quantity of half a finger, in whose middle, if we wish to understand the earth, we shall secure a small sphere on the axis itself, and then we have no need of the axis previously made which was stretching through the poles of the world; but in place of the poles of the world which the extremities of the axis previously made, two equal and round little nails shall be imprinted on the outer sphere, previously made, most firmly erected upon it, around which the meridian circle and the straight horizon, similarly made and joined to the oblique horizon as has been demonstrated before, can be led around, and with the sphere itself standing, be revolved. The third circle, however, of the enclosed sphere should be a wider circle constituted for the zodiac, divided into twelve signs and degrees similarly as the other outer zodiac is divided, but this we shall secure cutting through the middle of the other two which are called colures according to their whole [length], equally distant from the two poles of the sphere itself. And this sphere constructed from three circles will represent to us the ninth sphere with its zodiac and its poles and other circumstances. Which is fixed in the poles of the tenth sphere of the zodiac in such a way that the extremities of the axis which were made in place of its poles can be revolved. Also, similarly, you shall fashion another smaller [sphere] from the same number of circles in the same way as the second one already said, which will represent to us the eighth sphere. Of which two points diametrically opposite, namely the heads of Aries and Libra of the ninth, are revolved in the circumference of the two circles, of which the centers are the head of Aries and Libra of the ninth sphere. But it is necessary first, before one is enclosed and closed in the other, that the two small circles made and fixed around the head of Aries and Libra of the ninth sphere inside be concave equally through the whole periphery of the same, in such a way that those points of the heads, namely of Aries and Libra of the eighth sphere, having little nails fixed in them protruding, can be led around through the concavities themselves by hands, always placed from the opposite parts of the ninth sphere, and with such measure that it is neither pulled too much by the passages themselves nor [so loose] that it easily goes out. For with the zodiac of one set under the zodiac of the other, we will be able to propel these points of the eighth sphere with equal velocity from quarter to quarter of its circle in the way in which it is understood to be moved in the last chapter of the eighth sphere of Georgius Purbachius. And with this we will wish to revolve the interior sphere itself upon the axis from quarter to quarter equally proportionally as it was carried there, and there will appear the section of the two zodiacs and which signs are made northern and which meridional and how they differ and how they return to the first state and the rest. If also we shall wish to construct a sphere with fixed stars so that we can grasp their rising and setting and the middle of the sky and the figures, we shall compose a solid material sphere on whose surface we shall mark the circles...

The marginal drawing is a manicule pointing left.