On falling: how a bird levels itself and recovers a head-down plunge
Turning the wings, raising the tail, and balancing on the air without beating
This verso (102v), headed 'On falling' (Del cadere), studies how a bird recovers control and comes safely to earth, illustrated with several sketches of birds diving and gliding at the right. Leonardo explains that a bird falling head-down levels itself by turning the faces of its wings downward toward the earth, and that raising the tail toward the back or throwing the head up (so the breast leads) helps it move along the line of that obliquity. Without a favouring wind the bird must climb by beating its wings, but once high it can stay aloft without beating if its motion is strongly oblique. A bird balanced with wings stretched in the 'site of equality' descends slowly and unharmed, and takes its motion toward whichever extremity dips lowest, always levelling a wing or the tail to curve and slow its descent.
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Recovering from a head-down fall by turning the wings
When the bird falls head downward, its remedy to level itself is to turn the faces of the wings downward, toward the earth as much as possible, so it moves along the line of the wings' obliquity. Raising the tail toward the open back helps much, as does throwing the head up so the breast remains out, obliging the bird to travel along the line of that obliquity of the breast.
Balancing on the air in the 'site of equality'
When the bird does not fly with a favouring wind it must help its ascent with wing-beats, but once high it can stay without beating if its motion is strongly oblique. Balanced with all its extremities in the site of equality, and with no wind, it descends very slowly, or falls to earth without harm; it takes motion toward whichever stretched extremity lowers, faster or slower as that extreme dips more or less.
Levelling a wing or tail curves and slows the descent
The section headed 'On falling' concludes that a bird falling along any line will always level either a wing or the tail toward the place where it descends. By this the straight motion of the descent comes to curve, and consequently to slow and to level itself. Sketches of diving and gliding birds accompany the reasoning.