Making one cube from two equal cubes, and squaring a board
Adding two equal cubes through a cylinder into a single cube c; reducing rectangular bodies to cubic form
A proposition (numbered 9a) to make a single cube out of two equal cubes: the two cubes a and b are joined as a cylinder, which is then turned into the cube c. A following note states the general aim of reducing every rectangular body with parallel sides to cubic form, beginning by making a cylinder, and restates the problem of squaring an oblong board to a given width. The text of the last passage breaks off mid-sentence. The margin shows two small stacked cubes beneath a semicircle and a long extruded trough-like solid.
On this page
One cube from two equal cubes by way of a cylinder (a, b, c)
The two mutually equal cubes a and b are joined together in the form of a cylinder. From that cylinder Leonardo then makes the single cube c, citing the first proposition of his second book. The result is one cube equal in volume to the original pair.
Reducing every rectangular body to cubic form
A programmatic note declares that every rectangular body with parallel sides can be reduced to cubic form, and that the cylinder is made first. It restates the problem of squaring an oblong board to a given width and how far its thickness then varies, before breaking off mid-sentence.
Stacked-cube and extruded-trough diagrams
The upper right carries two small stacked cubes beneath a semicircular arc, and a long extruded trough-like solid runs across the page below. They illustrate the passage from board to cylinder to cube treated in the text.