Fol. 18r

Leonardo describes in detail, with drawings and above all in the text, how the flapping of birds’ wings occurs: the initial thrust, the extension and position of the profile of the wing during the phase of ascent, the strategy for the least friction during the transition from one flap to the next.

«Sempre quando la mano si alza il gomito s'abbassa e preme l'aria, e quando la mano s'abbassa il gomito si alza e rimane di taglio per non impedire il moto dovuto all'aria che vi batte»
(Always, when the hand is raised the elbows goes down and presses the air, and when the hand goes down the elbow is raised, and it remains edgewise so that it does not impede the motion due to the air striking.)

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