Fol. 14v

More studies of the structure and functions of the wing, together with a ‘problem’ of flight: what happens, Leonardo asks himself, to a bird that flies downwards at a certain speed with the wind against it? The animal will follow a trajectory following a line that is the resultant of the various variables in play, such as weight, velocity and the strength of the wind.

«Supponiamo che la spinta del vento sia di 6 e l'uccello pesi 6, e a metà del movimento la spinta del vento scenda a 3 e il peso rimanga 6. L'uccello verrebbe a scendere lungo il diametro del quadrato, mentre l'ala obliqua in posizione opposta non lascia discendere tale peso e il peso non lascia salire l'uccello, che per conseguenza si muove lungo una retta»
(Let us suppose that the thrust of the wind is 6, and that the bird weighs 6, and that at halfway through the movement the wind goes down to 3, while the weight remains 6. The bird would descend along the diameter of the square, but the oblique wing in the opposite position would not allow such a weight to descend and the weight would not allow the bird ascend, with the consequence that the bird would move along a straight line.)

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