Torsion, rebound, and a bombarded round fortress
Twisted cords unwinding to three-quarters, water flowing two miles an hour, and impact on walls
A page of De moto propositions with marginal diagrams of a plumb line, a two-bob pendulum, and a rebound line (figures 36, 37, 38). Leonardo states that a fully twisted weight on a cord unwinds through three-quarters of its first path, that a swing passes three-quarters beyond the centric line, and that a ball's second bounce and a knife's second tremor keep the same three-quarters proportion. He adds an aside that water with one finger of fall moves two miles an hour, and closes on impact: a round fortress struck by a bombard ball is damaged on its sides, squeezed between the ball's percussion and the resistance of the air behind it.
On this page
A twisted cord unwinds to three-quarters
A weight suspended on a cord, once entirely twisted, turns back three-quarters of its first way in the opposite twisting; a swing likewise passes three-quarters beyond the centric line of the first motion.
Rebound of a ball and tremor of a knife
The second bounce of a ball rises three-quarters of the first, and the second tremor of a knife stuck in wood keeps to the first the same proportion the two first bounces of the ball had between themselves.
Water flow from one finger of fall
An aside among the motion notes: water that has one finger of level (fall) moves two miles per hour, treating current speed as a function of gradient.
A round fortress struck by a bombard ball
A fortress of round shape struck by a bombard's blow is left damaged on its sides, because it is squeezed by the ball's percussion on one face and, on the opposite side, by the resistance of the air.
Pendulum and rebound diagrams 36-38
The right margin carries a hanging plumb line, a triangular two-bob pendulum, and a bounce line, tagged 36, 37 and 38, illustrating the torsion and rebound propositions.