Weights Held by Cords Wound on Rollers
Counter-lever and centre of gravity in cord-and-pulley systems
Several diagrams of weights hung from cords wound around rollers and passed over pulleys, labelled o-r, a b c d, n m and 2 4. Leonardo argues this arrangement moves more easily than the previous one because the cords wind onto a smaller winding-beam. He develops the rule that the centre of every weight lies perpendicularly below the centre of the cord that suspends it, and treats the counter-lever c d as half (subdouble) of the lever a c.
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Centre of gravity and the subdouble counter-lever
The centre of every weight sits perpendicularly beneath the centre of the cord that suspends it, as seen in d 4, the central line of weight 4 and of the whole cord d 4. Hence c d is the counter-lever of a c, and this counter-lever is half of its lever.
Cords wound on a smaller winding-beam
The apparatus of drums (subbio) and pulleys is drawn across the sheet; winding the cords onto a smaller beam makes the motion easier than in the arrangement above. One must reckon half the moving cord plus half the winding-beam as counter-lever.