Rule to find the centre of the arc of right angles
Compass construction for the lever-arcs; two small figures on pouring water or wind through equal holes
The left column carries a 'Rule' (Regola) for finding, with a compass, the centre of the circle whose arc touches at right angles the meeting of the pulling cord and the end of the spiritual lever that moves the weight. Leonardo directs the reader to identify which corner of the heavy body stays fixed as pole, draw a straight line from it to the point where the cord's motor acts, bisect that line, and strike the arc; the intersections give the true lever lengths, whose proportion to the contra-lever m n fixes the balance. Three large stacked diagrams of rectangles inside circles illustrate the construction. A short caption at the foot, between two funnel-shaped figures, opens a separate topic: pouring water or wind through various holes of the same width.
On this page
Compass rule for the centre of the lever-arc
To find the centre of the circle whose arc touches the right angles where cord meets lever, identify the fixed corner m (the pole), draw the straight line m to a (the motor of the cord), bisect it at c, and strike the arc a f m. Where it cuts each cord's line, a line back to m gives the lever r m, whose proportion to the contra-lever m n governs the balance.
Three stacked lever-arc constructions
Three large diagrams run down the centre of the page, each a rectangle set within a circle with a fan of lines converging on a vertex at the right and an arc swept through them. They give, in sequence, the lever and contra-lever lengths by which a weight is balanced when a cord pulls at an angle.
Pouring water or wind through holes of equal width
A caption between two funnel-shaped figures at the foot of the page announces a distinct topic: pouring water or wind through various holes of the same width. The two small vessels sketched beside it show the outlets.