Note on the friction of the timbers at a b
A reminder about friction between wooden pieces, with a drawn timber structure
The single line of red-chalk text reminds Leonardo to 'remember the friction that the timbers make at a b', keyed to a drawing of a wooden structure or joint below. An editorial note observes that the construction applies Euclid (XI.29 and I.37), by which parallelepipeds and triangles on the same base are, under certain conditions, equivalent — tying the sheet to the solid-geometry figures on the facing leaf.
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Remember the friction of the timbers at a b
A memorandum tells Leonardo to keep in mind the friction produced where the pieces of wood rub together at the points a and b. The note is keyed to the drawn structure beneath it.