Pulley rigs and the weight a cord must bear
Single- and double-pulley systems tested by experience, hung with weights of 100 and 200 pounds
Two pulley rigs are drawn at the top of the sheet: a simple single-pulley arrangement and a two-pulley system, each hung from a frame with weighted boxes. Leonardo records values confirmed 'by experience,' noting that a mid-point M pressed by 200 pounds carries 100 from above and 100 from below. In the main column he reasons that the cord running over a pulley bears and suffers twice the weight hung from it, and that, being of uniform thickness, it would break above the axle of its pulley.
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A cord over a pulley bears twice its hung weight
For every weight placed at m, two must be placed at n; the cord at m therefore sustains and suffers twice the weight attached to it. Being of uniform thickness and strength, it would break above the pole of its pulley.
Point M pressed by 200 pounds
In f M there are 100 pounds and in c M another 100, so M finds itself in the middle pressed by 200 pounds — 100 coming from above and 100 from below.
Single and double pulley rigs, tested
A simple single-pulley rig is set against a two-pulley system, each mounted on an upright frame and loaded with weighted boxes. Leonardo marks the loads (f 200 - M - c 100 100; 8 n 8 - 4 m 4) and notes the result was tested by experiment.