A Wind-Driven Wheel and the Rim That Outruns the Air
A parallel circle cast oblique toward the south, drawing the east wind (n, m, r, a, b), with a short sum
In red chalk a curved sail-like blade drops to a small wheel or disc set on an axle, its rim marked with the letters n, m, r and the shaft ending at d. The note argues that a 'parallel circle' cast obliquely (n m) toward the south while drawing the east wind will not be overturned, because the rim-point r travels faster than the wind a b that drives against it like a wedge. A short multiplication (375 x 2 = 750) is jotted at the lower left. Faint show-through from the facing leaf appears at the top.
On this page
The rim-point r outpaces the driving wind a b
If the parallel circle, cast with the obliquity n m toward the south, draws the east wind, that wind will not overturn it even as it enters underneath, because the point r on the periphery moves faster than the wind. The wind a b is described as acting on the wheel like a wedge. The reasoning compares the speed of a point on the turning rim with the speed of the air.
Wind directions and letter-labels around the wheel
The drawing is annotated with the direction 'levante' (east) and the letters n, a, m, r, b placed around the disc and its axle. These fix the geometry of how the oblique wheel meets the wind. The label d marks the far end of the horizontal shaft.
A small doubling sum
At the lower left a brief calculation doubles 375 to 750, repeated as an addition of 375 and 375. It stands apart from the wind argument above.