True proof of the square: four equal circles on one circle
Four circles centred on a single circle divide it into four and yield the inscribed square
Under the heading 'True proof of the square,' Leonardo shows that if four circles are set with their centres on the line of a single circle, each circumference passing through the others' centres, the four circles are equal. The central circle is then divided into four equal parts, is half of each of the four, and receives an inscribed square of equal angles and sides. The proof is drawn below as a symmetrical rosette of overlapping circles.
On this page
Four circles centred on one circle yield the inscribed square
Four circles are placed with their centres upon the line of a single circle, each circumference passing through the others' centres, so all four are equal. The central circle where they intersect is divided into four equal parts, is half (subduple) of each of the four, and within it the square is inscribed with equal angles and sides.