Thinning a Square Slab and Its Growth in Area
Stereometry: keeping a slab square while reducing its thickness, and squaring a pyramid's base
The problem: from a square slab thinned to a given thickness, find the increase of its squared area. Leonardo traces the stages through lettered figures — the given square slab, its conversion into the square d, its reduction into the thinner slab f (now longer than wide), and finally back into a square h of the same thinness. A marginal note treats squaring the non-square face n that represents the base of a shortened pyramid, so that the largest inscribable pyramid can be drawn on base m.
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Thinning a square slab yet keeping it square
From a square slab thinned to a given thickness, the increase of its squared area is sought. The square slab is converted into square d, reduced into the thinner slab f (longer than it is wide), and finally brought back into the square h of the same thinness — 'and this is what we were seeking.'
Squaring the base of a shortened pyramid
The margin note obtains the height of o n by the sixth of the first; because the face n giving the width of the shortened pyramid's base is not square, it is squared by the first of the first to complete the solid, from which the largest pyramid that fits is drawn, making m the base.
