Compound pulleys, rope motion, and a half-lit aperture
The swifter rope tires the mover most; a half-closed opening seen like the half moon
Folio 61v combines a mechanics study of pulleys with an optical note. A compound pulley of five wheels on a single cord (topmost a, lowest b) heads the principle that, among things moved by one cause, the fastest-moving one most wears out its motor. A rope-and-staves experiment — the cord passing over an upper staff at a, c, e, g and under a lower staff at b, d, f, h — shows that when one braccio of rope moves at b, two move at d and three at f, so f endures three times the effort, just as a swiftly thrown weight tires the mover more than a slow one. At the foot, drawn with a finer nib, an eye peers through a round aperture whose lower half (n) is closed while the upper half (c) admits light, between limits a and b — the same effect, Leonardo notes, as the half-lighted moon.
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The swifter of things moved by one cause most tires its motor
Among things moved by one same cause, the one of quickest motion causes the greatest detriment to its motor. The five-wheel compound pulley (uppermost a, lowest b) illustrates the principle for a single cord.
Rope through a pulley: three braccia move at f for one at b
Raising the lower staff b-h to line m-n requires lowering part g-h of the rope. When one braccio of rope moves at angle b, two move at d and three at f, so f endures three times the effort of b because it moves three times as fast; the unequal, swifter movement tires the mover more.
A half-closed round opening, and the half-lit moon
A round opening half closed appears in the form a-b, where part c is the light and n is the part closed off. This is the same effect that occurs with the half-lighted moon.