Definitions of the sphere after Euclid and Theodosius
Many restatements of how a sphere is generated by revolving a semicircle about its fixed diameter
A page densely written in two columns and given over almost entirely to defining the sphere, with a small sectional diagram of a hemisphere. Leonardo copies and reworks classical definitions, crediting Euclid (the solid described by the arc of a semicircle carried around) and Theodosius (the body from a single surface with a central point equidistant to the circumference, its axis ending in the poles of the world). He then drafts more than a dozen of his own restatements: the sphere as the revoluble motion of a semicircle's arc about its immobile diameter, and as the body which, cut by any straight plane, is bounded by two circles.
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The sphere defined by Euclid and Theodosius
Euclid: the sphere is a round solid body described by the arc of a semicircle carried around. Theodosius: it is a solid contained by a single surface, in whose middle is a point from which all lines to the circumference are equal, its center; the straight line through that center meeting the circumference on both sides is the axis, and the two points ending the axis are called the poles of the world.
The sphere as a revolving semicircle, cut into two circles
The spherical body is figured by the revoluble motion of a semicircle's arc about its immobile diameter, with the ends of the arc joined to the ends of the diameter. It is a round body clothed in a single surface, everywhere equally distant from its center and terminated in itself without any angle. If it is cut by a straight plane in any direction, into equal or unequal parts, the boundary of the parts at the cut will be two circles.