The centre, the struck cube, and a man's leap
Defining the centre; a cube dilating into an imperfect circle; why a leaping man doubles his weight
Continuing the theory of impact, Leonardo defines the centre as the point equally distant from a body's opposite extremities and says that every part of a struck cube flees from the centre by the shortest path. He argues that a minimal cube enlarged by a blow would form a circle falling short of perfection only by the tiny difference between its centre-to-corner and centre-to-side distances, a gap no larger than a compass point. A separate note, 'On the leap made by a man,' observes that a leaping man does not weigh toward the centre but doubles his weight upon the spot he leaves, the more so the harder he thrusts himself upward. A large sketch of wooden trestle supports fills the lower part of the sheet and is not covered by the transcription.
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Definition of the centre; parts flee it under a blow
The centre is that which is equally situated from the opposite extremities of bodies. Every part of the cube, pressed by the blow, flees from the centre by the shortest way, so that the compressed body redistributes its matter outward.
A cube enlarged into a near-perfect circle
Suppose the cube is a minimal body made very large by the blow, each extremity dilating equally from its centre: it will compose a circle imperfect only by the difference between the centre-to-corner and centre-to-side distances, a gap a compass point could span. Grown by a braccio, that gap would show as a mere point in so great a circle.
A leaping man doubles his weight on takeoff
Under the heading 'On the leap made by a man,' Leonardo notes that a man in the act of leaping does not weigh toward the centre; rather he doubles his weight upon the place from which he departs, and doubles it all the more the greater the thrust he makes of himself upward.