Fol. 4v

Here begin, after the theoretical notes, Leonardo’s observations of flight in nature. In his Codex he mentions two birds, the kite and the Greek partridge, but from the drawings it appears that the subject of his studies was above all the kite, a common bird of prey with a wing span of about a metre and a half. Leonardo notes the difference in behaviour between the flexible entities (i.e., feathers) and rigid entities (i.e., bones) of the bird in flight when they are subject to a force pressing down from above. The bones are one thing, but the feathers are another; these constitute entities which become increasingly flexible body as they extend towards the ends of the wing. The question that Leonardo poses is which part of the wing is most affected by the various forces of the air.

«le penne che sono più lontane dalla loro attaccatura saranno più pieghevoli. Dunque le cime delle penne delle ali saranno sempre più alte rispetto al punto in cui nascono, per cui potremo ragionevolmente dire che le ossa delle ali saranno sempre più basse di ogni altra parte dell'ala nella fase di abbassamento, e più alte nella fase di innalzamento, talché la parte più pesante è la guida del moto»
(The feathers that are furthest from the place where they are attached are the most flexible. Thus the ends of the feathers of the wings will always be higher with respect to the point from which they grow, so that we can reasonably say that the bones of the wings will always be lower than any other part of the wing in the phase of lowering, and higher in the phase of raising, because the heavier part guides the motion.)

NOTE. For each page of Leonardo’s Codex we provide a brief summary, with the quotation of one that page’s most significant passages edited in modern Italian, with an English translation.

translation by Kim Williams