A rectangle's thickness when stretched to a set length
Rectangle a d f g reshaped to the length a h through an equilateral square (prop. 8)
The page continues the treatise on turning a rectangle into an equivalent one (proposition 8). Leonardo stretches the oblong a d f g along its length to the given length a h and asks how much its breadth narrows, solving it by reducing the figure to an equilateral square and then, by his sixth proposition, rebuilding the rectangle a c h i to recover the due thickness in the space a c. A second heading opens the converse problem of shortening a rectangle to a given length. A large semicircle enclosing an inscribed rectangle is drawn across the top.
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Stretching rectangle a d f g to the length a h
The oblong a d f g is stretched along its length to a h, and its narrowing in breadth is sought. Leonardo first makes the equilateral square from the rectangle, then by the sixth proposition makes from that square the rectangle a c h i to the given length, finding the due thickness in the space a c.