Wind striking a wheel; further rectangle constructions
Notes on the transit of wind and a wind-driven wheel, beside area-preserving geometry
Folio 75 recto continues the study of wind alongside the geometry series. Leonardo notes that wind is more powerful where it has an exit than where it strikes with none, and sketches wind a b c d striking the side of a wheel d c, with two figures labelled 'passage of wind' and a paddle-wheel struck by radiating gusts. The lower part returns to transforming rectangles: the surface a b c d of unknown quantity is lengthened to a given height f using a tangent f c, the arc f i and a perpendicular e d to find its remaining width, followed by a proof adding equal parts to equal quantities. Diagrams include a wind-struck wheel, a hatched frame, and quarter-arc and triangle constructions.
On this page
Wind is stronger where it has an exit; transit of wind
The wind is more powerful where it has its exit than where it strikes without an exit. Two figures are labelled 'passage of wind', studying how a current flows through and past obstacles.
Wind striking the side of the wheel d c
The wind a b c d strikes the side of the wheel d c and does not have... (the note breaks off). The accompanying diagram shows a spoked paddle-wheel met by radiating streams of wind, a study of a wind-driven wheel.
Lengthening rectangle a b c d to the height of point f
The rectangle a b c d of unknown quantity is lengthened to the height of the given point f, and its remaining width sought. Leonardo draws the tangent f c to the surface's side, extends a b to a i, swings the arc f i to meet it, draws c i where the circle cuts a i, and drops the perpendicular e d from the right angle d to c i, which gives the width.