The order of your book must proceed on this plan: first simple
beams, then (those) supported from below, then suspended in part,
then wholly [suspended]. Then beams as supporting other weights
[Footnote: 4. Leonardo's notes on Mechanics are extraordinarily
numerous; but, for the reasons assigned in my introduction, they
have not been included in the present work.].

General introductions to the book on Painting (9-13).