The motion of birds, and the earth seen from the moon
Gliding descent, a four-book plan on flight, and the rebound of the swimmer's hand and the bird's wing
This folio joins cosmology to the study of flight. It first argues that the earth is not at the centre of the sun's circle or of the world but at the centre of its own elements, and that seen from the moon the earth with its water would shine and serve as the moon does for us. Under the heading 'On the motion of the bird' Leonardo studies gliding descent along a straight and curved path, shown in the trajectory diagram, and lays out a four-book plan on air resistance, the bird's anatomy, the feathers' action, and steering without flapping. A margin note tells him to dissect the bat to design his flying instrument and states that of two colliding forces the faster rebounds, as with a swimmer's hand or a bird's wing.
On this page
The earth seen from the moon, as the moon is to us
The earth stands at the centre of its own elements, not of the sun's circle or of the world. Seen from the moon, when the moon lies with the sun beneath us, the earth with its element of water would shine and serve as the moon does for us.
A four-book plan for the study of bird flight
Leonardo sketches four books for the study of flight: first the resistance of the air, second the anatomy of the bird and its feathers, third the action of the feathers in their various motions, fourth the power of wings and tail to steer without flapping, aided by the wind. The trajectory diagram sets out the straight and curved path of a gliding descent.
Dissect the bat to design the flying instrument
A note in the right margin directs him to dissect the bat, hold to it, and base the design of the flying instrument upon it.
Of two colliding forces, the faster rebounds
Whenever two powers strike against each other, the faster springs back: the swimmer's hand pressing on the water drives the body the opposite way, and the bird's wing does the same in the air.