A Rule for How Materials Break
The corbel stays with what is fixed; a struck round tower fails on the far side
In red chalk and pen, Leonardo records a rule about how materials break. He observes that a corbel always stays with the part that does not move and detaches from the part that falls, and promises to treat such fractures in a 'seventh book,' explaining there why a round tower struck on its front breaks on the opposite side. A curved, shaded corbel carrying a member is drawn beside the text. A separate maxim adds that the extremities of all things lend them grace or gracelessness.
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Rule of fracture: the corbel keeps to what is fixed
Leonardo states that the corbel always stays joined to the part that does not move and separates from the part that falls. He files this among rules of fracture reserved for a 'seventh book,' where he means to show why a round tower struck on its front side breaks on the far side.
Corbel (beccatello) supporting a member
A curved, hatched corbel is drawn carrying a vertical member, illustrating the bracket named in the note. The shading models its projecting profile.