Plan for the water treatise; impetus and how birds ride air
A page of notes: order the study of water, wind-waves in the corn, and the air struck by a falling body
A full page of mirror-script with no diagrams. Leonardo sketches the plan of his treatise on water, then turns to the physics of moving fluids: impetus travels far faster than the water itself, just as a wave runs across a field of ripening corn while the grain stays put. A final passage argues that a heavy body falling through air drives the air aside in a curved path, condensing it beneath the falling body and rarefying it above, which is why birds can beat and rest upon the air. The note ends by directing the reader to turn the leaf over.
On this page
How to order the treatise on water and its waves
First write of all the water in each of its motions, then describe its beds and their materials, always citing the propositions already set down, so that the work keeps good order and is not confused. Then describe every figure the water makes, from its greatest to its smallest wave, together with their causes.
Impetus outruns the water, like wind-waves in the corn
Impetus is much faster than the water, for often the wave flees the place of its creation while the water itself does not move from its site. This is like the waves made in May by the wind in the standing corn, where the waves are seen to run across the fields yet the corn does not shift from its place.
Air condenses beneath a falling body, so birds can rest on it
A heavy body descending through the air drives the air the contrary way to fill the place it leaves; that air moves in a curved path, since wishing to rise by the shortest line it is blocked by the falling body and must bend around and back to fill the void. Because the air condenses beneath its striker and rarefies above, birds are able to sustain themselves upon the air they beat.