The sphere of air and how a bird hangs still on the wind
Circular undulations in air and water; soaring against the wind
A closely written sheet, its right column struck through, opening a treatise on the effects of air within and beyond its own sphere, placed between fire and water. Leonardo argues that air rising into the region of fire gains weight, falls back with impetus, and generates spreading circular undulations, and that the like circular waves are produced when air descends into water. The left column turns to flight, analysing how a bird holds itself motionless upon the wind by balancing the wind's force with the tilt of its wings and body and by rowing backward. The bundle notes that portions of the leaf (the Nantes and Govi fragments) were torn away and are supplied here from other transcriptions, since they are not present in the image.
On this page
The sphere of air between fire and water
The sphere of air lies between water and fire. The part that rises and penetrates into the element of fire gains weight and, finding no support, falls back with impetus, striking the surrounding air and making circular undulations about the line of its motion. These circles are created successively until the motion ends.
How a bird holds itself motionless on the wind
If the wind striking in front of the bird equals the bird's tendency to fall toward it, the bird stays without motion, the wind doing the work in the opposite direction. When the wind comes from below and in front and exceeds the bird's weight, the wings must draw in to occupy less air and the bird must row somewhat backward; turning its beak to the wind, it remains fixed in place.
Circular undulation passing through water
When air descends into the element of water it makes heavy the water resting upon it, which falls back with impetus, drives the air upward, and penetrates the water beneath. This penetration generates a circular undulation along the whole length of its motion, which widens and loses a degree of power at every degree of motion.