Wheels Driven by Falling Counterweights
Motion increased by impetus and by a cord unwinding from the wheel's centre
Leonardo analyses how a falling weight drives a wheel and gathers force as it descends. The notes say the motion is first increased by impetus, since the falling stone grows faster and heavier as it drops, and further increased because the cord unwinding from the wheel moves ever farther from the centre of rotation, so it weighs and thrusts more. Three sketches show wheels and a semicircle mounted on stands and turned by counterweights hung from cords.
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Motion increased by impetus and by the falling stone
The driving weight increases the motion by impetus: as the stone falls it continually gains speed and effective heaviness. This first cause makes the descent grow ever more forceful.
A cord unwinding from the wheel's centre
A second cause is geometric: as the cord unwinds from the rim it acts ever farther from the centre of rotation. The greater this distance, Leonardo argues, the more the weight tells and the more impetus it acquires.
Wheels and semicircle on counterweighted stands
Three mechanisms are drawn: wheels and a semicircle set on upright stands, each turned by a stone or weight hung from a cord wound about it. They embody the counterweight drive described in the text.