Compound screw with seven nuts and the 'sophistic wheel'
Seven mother-nuts a-g driven by a handle S, and a critique of the false perpetual-motion wheel
The top diagram shows a compound 'segmented screw' whose seven mother-nuts a, b, c, d, e, f, g are driven by a single handle S, so that one full turn advances the last nut by a space equal to seven teeth. Leonardo judges the invention ingenious but too intricate, preferring ordinary multi-turn screws that do the same work with the same effort and far less labour to make. A further note treats several movers pulling on one weight, the load falling most on whoever pulls hardest or sits directly beneath the pulley, and the lower-right figure lettered d, b, n, a, f is captioned 'sophistic wheel', his term for a deceptive perpetual-motion device.
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Compound screw with seven mother-nuts a-g on handle S
The seven mother-nuts a to g grip a reversed screw; with nut a held fixed, one whole turn of the handle S advances a nut by two teeth, the next by three, and so on, until the last screw moves seven teeth because there are seven nuts in all.
The sevenfold screw offers no real gain in effort
Though this single-turn screw is ingenious, it feels effort equal to a sevenfold screw and is too intricate and difficult. Leonardo advises using ordinary multi-turn screws instead, since the motion and effort of the mover are the same while the manufacture is far simpler.
Several movers on one weight share the load unequally
If several movers pull one weight by different cords or levers, the pulling is discordant and the one that pulls most bears all the weight. If many are tied to the same cord over a pulley, the one nearest beneath the pulley's centre feels the most weight, each otherwise feeling its proportional share.
The 'sophistic wheel' d, b, n, a, f
The overbalanced wheel at the lower right, its arms lettered d, b, n, a, f, is captioned 'sophistic wheel'. The term is Leonardo's name for a device that only feigns perpetual motion.