Bodies turning in currents, birds in the wind, and a crystal hemisphere
Notes toward a book on flight, a bird overturned by a north wind, and magnifying rays
The page opens on the motion of a body of non-uniform obliquity, which keeps turning within uniformly flowing water, while one of uniform obliquity never turns; a diagram labelled b n c, d a o e, a g, h m i, p shows an object between two currents making a lateral revolution. Leonardo reminds himself that before writing of birds he should make one book of imperceptible things that descend through the air without wind and another of those that descend with wind, and sketches two birds, one with horizontal wings and one with inclined wings. He notes that a bird flying east against a north wind will be overturned if its left wing rides above the wind unless it drops that wing beneath it. A final optical note shows that bodies seen through a crystal half-sphere reaching the eye a appear larger, because the angles of the ray r a conform better to the convex crystal.
On this page
An object between two currents makes a lateral revolution
A body of non-uniform obliquity keeps turning within uniformly flowing water, while one of uniform obliquity never turns. When the object's upper-right and lower currents are struck by an equal current it makes a lateral revolution, as shown in the diagram b n c, d a o e, a g, h m i, p.
Plan for two books on things descending with and without wind
Before writing of birds, Leonardo instructs himself to make a book of the imperceptible things that descend through the air without wind, and another of those that descend with the wind.
A bird overturned by a north wind unless it drops its left wing
For a bird moving east against a north wind, if its left wing (e, g h, f) rides above the wind it will be overturned, unless in the wind's force it puts that left wing beneath the wind and throws itself toward the north-east. Two bird figures accompany the note, one with horizontal wings a b, c d.
A crystal hemisphere magnifies the bodies seen through it
If the species of the bodies r S t on the plane t h pass through a crystal made of a half-sphere and reach the eye a, the object x appears larger than the equal object r, because the angles of the line r a are more conformable on the convex of the crystal than the angles of x.