The circular balance and compound pulley systems
The well pulley as a balance, and how four doubled pulleys divide a weight
Folio 62r is a sustained, richly illustrated study of the pulley as a 'circular balance' and of compound pulley systems. Leonardo states that no heavy body can lift more than its own weight on a circular balance by its weight alone, identifying that balance with the roller or pulley used to draw water from wells: to raise a hundred-pound pail one must hang a hundred-and-one pounds opposite, and the whole load presses on the pulley's support. Diagrams show a single pulley (hook r, weights m 20 and n 21), a double pulley (f, d), and a quadruple system (upper rings and pulleys o, p, Q with lower pulleys l, k and counterweight x 6) in which each of four ropes bears only a fifth of the twenty-pound load, plus a red-chalk repetition balancing a 20 weight against a 5. He concludes that unequal, swifter motion is what most tires the mover.
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No weight lifts more than its own on a circular balance
No heavy body can lift more than its own weight on a circular balance by the simple force of its own weight. This heads the folio's treatment of weight and motion.
The circular balance is the well pulley
The 'circular balance' is Leonardo's name for the roller or pulley by which water is drawn from wells; with it, no more weight is ever lifted than that of the one who draws. The single-pulley sketch hangs weight m (20) against n (21) from hook r.
A weight on a circular balance presses doubly on its support
Any weight lifted by a circular balance is felt doubly on the balance's support: to draw a hundred-pound pail one must put a hundred and one pounds on the opposite side, and all this weight presses on the support of the pulley.
Four doubled pulleys: each rope feels only five of twenty pounds
Stringing the pulleys with four doubles to lift twenty pounds: rollers l and K each sustain ten, passed to upper supports o, p, and Q. Setting six at counterweight x against five at Q, each of the four ropes feels only five pounds, and the extra pound at Q-x, meeting no equal opposing weight, prevails over and moves them all.