Groynes in a river bend and a lettered proportion figure
How a spur set before, at, or beyond a bend sorts the water's load; a geometric proportion
One leaf carries a geometric construction of converging lines meeting a circle, labelled with letters, beside the note that a b enters into c d as many times as n a enters into c n. The facing leaf explains how a spur or groyne set at the start of the water's bend breaks the bank behind its shoulders and deepens the bed, while one set at the end of the bend collects timber and roots, and one beyond the bend gathers mud and useful soil. Leonardo concludes that, placed in different sites, the current deposits or carries off different materials, from stones and fine gravel to sand. The observation treats groynes as instruments for controlling erosion and sedimentation.
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Where a spur set in a bend deposits the river's load
A spur set at the beginning of the water's bend breaks the bank behind its shoulders and deepens the bed; one set at the end of the bend gathers timber, roots and other light matter behind it; one set beyond the bend gathers mud and useful soil. Placed in various sites, the current thus deposits or removes stones, fine gravel, sand and other kinds of material.
Proportional relation among the lettered segments
The note states that as many times as a b enters into c d, so many times n a enters into c n, fixing a proportion among the segments of the figure. The accompanying drawing is a pyramid of straight lines converging from an upper point down onto a circle, with the letters set at its vertices.