Bird's Wings, Air Resistance and the Motion of Air and Water
Flight studies with gold-leaf buoyancy, river vortices and small domed-church sketches
A dense study sheet linking the behaviour of air and water to the mechanics of flight. Leonardo notes how waters meeting at an angle deflect upward and whirl back to the riverbed, argues that a body weighs less the greater the width of air supporting it (the beaten gold-leaf example), and observes that moving air against a still body is equivalent to a moving body in still air, as ships' sails and rudders taught him. A labelled bird with open wings (d, c, a, b) illustrates how the wing-concavities near the root catch the air, while several small pen sketches of centrally-planned domed buildings appear in the lower part of the sheet.
On this page
Wing concavities and the power of the wing-root
A bird drawn with open wings, marked d c a b: the concavities of the wings beneath the shoulders receive the revolution of the air near the root of the wings. Nature so conditioned them near the wing-root because, by the fourth proposition of weight, 'that part of the support is more powerful which is nearer to its root.'
A body weighs less on a wider bed of air (gold leaf)
That body weighs less upon the air which rests upon a greater width of air. The example is the coin of very heavy gold which, once beaten into a thin gilding leaf, is held up on the air by the least of its movements.
Waters meeting at an angle deflect and whirl to the bottom
Waters that meet one another forming any angle always deflect backwards, rising toward the sky, and with a whirling (vortiginous) motion turn back down toward the bottom. Material carried by the motion strikes the riverbed and is thrown back by the reflected motion.
Equivalence of moving air and moving body; the ship analogy
The motion of the air against a motionless object does as much as the motion of a moving body against motionless air. The same holds in water, which taught Leonardo the like is true in air, by means of ships' sails accompanied by the lateral resistance of the rudder.
Small sketches of domed, centrally-planned buildings
In the lower part of the sheet are several small, rapid pen elevations of churches or palaces crowned with domes and lanterns. These architectural jottings are not covered by the transcription and are noted here from the drawing itself.