Cones on oblique bases and the equality of triangle sections
Solid geometry: pyramids brought to a point, and triangles of equal base between parallels
A sheet of solid geometry crowded with cone-and-triangle diagrams, several carrying letter labels. Leonardo notes that a cone (a 'round pyramid') can be brought to a point on a most oblique base by the same rule as on an upright base, and that a cone raised from a ring (torus) converges to a point while remaining hollow except at that point. Further notes assert that triangles of equal base placed between parallel or curved lines are always equal, and that the equal curved figures a b c d e, whose sides a e and o 7 are parallel, enclose equal areas.
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A cone brought to a point on a very oblique base
The round pyramid (cone) can be made to converge entirely upon a most oblique base, by the very same rule by which it is made upon an equiangular, upright base.
A hollow cone raised from a ring to a single point
The pyramid born of the ring (torus) can be made to converge to a point, taking the whole ring as its base; but it will be a hollow pyramid, solid only at the point.
Triangles of equal base between parallels are always equal
As above the line, so below: equal spaces can be laid out above the line h f as above the line h g. Triangles of equal base placed between parallel lines, straight or curved, are always equal, and their sections or divisions made between such lines will likewise always be equal.
Equal curved figures a b c d e with parallel sides a e and o 7
Let a b c d e be equal in their spaces, in curvature, and in one same proportion with their bases, and let the area enclosed within their four sides be equal, the lines a e and o 7 being parallel.