Squaring the circle by rectifying the semicircumference
A rectangle equal in area to a circle, with three weights on a balanced beam
Under the heading 'Geometry,' Leonardo gives a method for constructing a rectangle equal in area to a whole circle from the circle's half-circumference and half its diameter. He proposes rolling the semicircumference along a flat surface to leave a straight trace, then joining half the diameter at right angles, so that the two lines multiplied together yield a quadrilateral of area equal to the circle. A small rectilinear triangle sits at the upper right, and below it a beam bears three weights marked 2, 1, 1, extending the folio toward the mechanics of balance.
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A rectangle equal in area to a circle
With the half-circumference of a circle and half its diameter Leonardo forms a square of capacity equal to the whole circle. He rolls the semicircumference on a flat place to leave a straight trace, then adds half the diameter at a right angle, so that the two lines multiplied together make a rectangle equal in area to the circle.
Three weights on a balanced beam
A beam near the foot of the drawing carries three suspended weights marked 2, 1 and 1, a study of equilibrium alongside the geometric construction.