The Crossbow-Maker's Fallacious Water-Wheel
A self-moving water-lifting device refuted, with shadow diagrams
The verso, faint and rubbed, combines a mechanical refutation with further shadow studies. Near the center a lettered wheel — the "sophistical device of the crossbow-maker" — is analyzed and shown to be a fallacy: a tube n m scoops up water g h and lifts it, but because the descending weight loses its gravity at the water's surface, the wheel stops and the adversary's claimed perpetual motion ends. A ring of balls set in a square and a screw-like device are drawn nearby. Lower figures return to optics, arguing that intersecting simple shadows are not doubled because one light cannot make two simple shadows, and that two compound shadows joined together generate a single simple shadow.
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The crossbow-maker's self-moving wheel refuted
A lettered wheel scoops water g h through the mouth of tube n m and carries it up to o while m descends to p; because p, farther from the center, weighs more, it sinks to the water's surface and there loses the gravity that drove it. The wheel therefore comes to rest, and Leonardo declares the adversary's "sophistical motion" ended — a demonstration that the proposed perpetual-motion machine cannot work.
Intersecting simple shadows are not doubled
Even when simple shadows intersect, their impacts are not doubled, because the shadow of the first opaque body is impressed on the lit part of the second where the two cross. A single luminous body with one light cannot generate two simple shadows.
Two compound shadows make one simple shadow
A short note added with the sheet turned on its left side states that two compound shadows joined together generate a simple shadow.