Visual pyramids, bird flight, and a worm-screw mechanism
Two fragments: the geometry of sight and a lit sphere; birds against the wind; a worm-and-rack
The larger fragment is given to the science of vision: schemes of visual 'pyramids' whose base is the picture-plane, a note that a curved plane yields the truest image, and a study of a gilded ball lit by the sun and observed from points a, b, c, d. A balance problem for a four-braccia rod and a remark on cast shadows sit at the left. The lower strip turns to the flight of birds inclining against and beneath the wind, and to a worm-screw driving a toothed rack (b, a).
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Visual pyramids and the seeing eye
The object generates the visual pyramids while the plane (pariete) forms their base, drawn as converging cones of rays. Leonardo notes that the base is rather a privation than a creation of lines, and that a curved plane, with the eye at its centre, gives the truest clarity of the things seen.
A gilded ball lit by the sun (a, b, c, d)
A sphere is shown lit by the sun over its hemisphere, with rays marked a, b, c, d. Moving from place to place, the observer sees the cause of the ball's light shift from a to b, c and d.
Balancing a four-braccia rod, and cast shadow
Leonardo balances a rod of four braccia divided into unequal arms of 1 and 3, working out how a weight fixed at the shorter arm restores equilibrium. A paired note observes that a shadow's form appears clearest on the wall when its cause is near the surface struck and far from the light.
A bird climbing obliquely against the wind
A bird figure inclines against the wind. The oblique motion makes the bird's weight more powerful than the wind striking it in front, so that its advance against the wind is swift.
A bird descending beneath the wind
A bird descending under the direct oncoming of the wind turns its wing over somewhat, from the shoulder to the tip. It does so to gain purchase in as oblique a motion against the wind as possible.
Worm-screw driving a toothed rack (b, a)
A mechanism couples an endless screw to a toothed rod, marked b and a. If the little ladder-like rack a b were a chain, Leonardo notes, it would turn about the wheel's pole and the screw could no longer do its work.