The Sphere of the World (De Sphaera)

A series of geometric diagrams are arranged in a vertical column on the left side of the page.
1. At the top, a circular diagram resembles a globe or sphere, adorned with a crown-like structure containing the letters "H", "T", and "I".
2. Below this is a cone (labeled "Piramis" [Pyramid/Cone]) with a horizontal line cutting through the top portion (labeled "curta" [shortened]).
3. Next is a cylinder (labeled "Columna" [Column] in the margin).
4. Below the cylinder is a shallow disc or drum (labeled "Timpanum" [Drum] in the margin).
5. At the bottom are three-dimensional polyhedrons: a triangular-based pyramid, a square-based pyramid, and a cube. Marginal notes identify them as "quadri lateri" [four-sided] and "trilatera" [three-sided].

De Orbi et Sphaera? On the Orb and Sphere

An orb is often understood through a sphere and conversely: hence, the earth, which is spherical, is frequently signified by an orb, as in the "orb of the lands" original: "orbis terrarum". Truly, even if every orb is a sphere, not every sphere is an orb. For an orb is a sphere which is bounded by two surfaces, namely an outer one which is necessary for a sphere, and another inner and concave one. If those two surfaces are concentric, having one center, the orb itself will be uniform and of equal thickness. But if they have two centers, the orb is found to be difform, thicker in one part and thinner in another.

An annulus ring is sometimes as if resected from an orb. It is indeed a round body, having a center, and both a concave and a convex surface, from which sometimes one is made; for then the ring is encompassed by a surface.

There are also other corporeal and regular figures: and of those which have a convex surface, there is the round pyramid referring to a cone and the column.

Euclid imagined that a sphere is caused by the revolution of a semicircle remaining firmly upon its chord until it returns to the place from which it began to be carried around.

Similarly, if a rectilinear triangle is carried around with a complete revolution while one of its sides remains stationary, a cone or round pyramid is figured, which is bounded by a convex surface terminated at a point, and which is encompassed by a circle called its base; from which, when the point is removed, the remainder is called a shortened pyramid.
curta shortened

Piramis Pyramid

In like manner, a round column is formed from a rectangular quadrilateral being circled, with one of the longer sides remaining.
Columna Column

A timpanum drum, however, is made when the shorter side remains fixed, and if another flat figure is carried around in this way, it happens that a body is made, as artisans do when turning.
Timpanum Drum

There are also corporeal figures which are made only with straight surfaces, and their number is not limited. The last of which is a triangular pyramid which is enclosed by four triangles. And those which are from four and one quadrangular base, or from five triangles and a pentagonal base, and of that kind.
quadri lateri four-sided

Likewise also a sided column: such as from two triangles and three quadrilaterals, which is accustomed to be called a sawed body, or from six quadrilateral surfaces which, when they are equal and square, render a cubic body. For a square is a superficial figure of four equal sides and four right angles.
trilatera three-sided