Center of gravity of a cord over a pulley, and hovering in a scirocco
How a hanging rope sheds weight at its junction, and a bird holding still like a bridled horse
This recto (102r) pairs the rope-and-pulley mechanics of the preceding leaves with the ongoing flight study. A tall pulley figure at the top right, from which two weights hang, illustrates that a cord bearing its ends over a pulley has its greatest fatigue perpendicularly above the shared center of gravity; because of the cord's curvature at the junction, the load referred to that point is less than what the support carries, so that 4 pounds return as 2, or 8 as 4. A geometric arc figure accompanies the argument about the cord's curvature. Below, with a sketch of a gliding bird, Leonardo explains how a bird holds still against a scirocco wind by raising its head 'like a bridled horse' and setting its breast and weight obliquely against the gust, tempering with its tail when threatened with being overturned.
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A cord over a pulley bears most weight above the center of gravity
A cord hanging by its ends from a pulley has its greatest fatigue perpendicularly above the center of gravity it sustains, along the line a b, with the whole gravity of the two cords referred to point a. Because of the curvature of the cord (a n and a m), the load referred at a is less than that discharged on the support: 4 pounds of cord return 2 at a, or 8 return 4.
Pulley carrying two hanging weights
A tall pulley is drawn at the top right, a rope passing over its wheel with two boxed weights hanging at the ends, keyed by letters a, n, m, b and the numbers 4 and 4. It serves as the demonstration figure for how load is referred to the junction point above the center of gravity, and a geometric arc figure alongside illustrates the cord's curvature.
Hovering against a scirocco wind like a bridled horse
If the scirocco wind draws and the bird wishes to stay still in the air without being displaced or beating its wings, it raises its head like a bridled horse and sets its breast against the wind, which would throw it up and back. It resists the upward push by making itself oblique downward with its weight; against being driven back it inclines down and forward, and if the wind would overturn it, it raises the tail so the entering wind lowers it and it tempers itself.