Flight of birds: turning, bounding and circling in the air
Bird-flight notes with sketches of birds, plus observations on impetus, the elements and the rainbow
A crowded sheet of flight studies with many small sketches of birds in flight arranged around three columns of text. Leonardo analyzes how a bird turns its straight course into a curve by beating one wing more than the other, how it flies in bounds gaining impetus in the descent, and how it rises and circles by holding the wings oblique. A central column states principles of gravity, condensation of air and fire, and impetus in a rare medium, while a lower passage turns to the rainbow, describing four kinds of 'celestial arc' formed by the sun's rays through gaps in the clouds.
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Turning course by unequal wing-beats
To turn a straight course into a curve without rising or falling, the bird beats the wing on the convex side of the curve more often than the wing on the concave side. Elsewhere, the bird bends its course toward whichever wing lowers more, as though that wing were more struck by the wind, and it raises the shoulder of the beating wing more in front than behind to gain motion.
Flying in bounds and the reflex motion
Of the bird that flies in bounds: closing its wings in the descent it gains heaviness and so becomes swift, making the rebounding (reflex) motion more powerful. Adding the wing-beat doubles that power, so the reflex motion carries farther than it would unaided, and the flight balances equally in its low and high phases.
Rising from the ground and circling in the air
Rising from the ground, the bird leaps and snaps its open wings shut, raising a wave of air that strikes its breast from below and lifts it while it beats repeatedly. When it climbs in a circle it holds its wings oblique across their breadth: the more oblique the set, the wider the circle; the less oblique, the tighter.
Gravity, condensation and impetus in a rare medium
The central column argues no element has gravity in itself except along the line of its motion, heavier or lighter as it is swifter or slower. Air and fire are condensable toward the infinite, as seen in bombards and in lightning; and impetus is swifter and more lasting the rarer the medium through which it passes.
The rainbow: four kinds of celestial arc
The lower passage treats the 'celestial arc', greater than a half-circle when the sun is low and smaller when high, and a cloud reddened at sunset. A lettered figure (points abcde, aperture n, intersections c and f) explains that the arcs are of four kinds, one born from the sun's body alone and others doubled around one centre, the inner of most excellent colours, formed by rays intersecting at the lit lips of a gap in the cloud.
Bird carried and pushed by the wind
A bird pushed by the wind, rising without beating its wings, prolongs the whirling motion more in the incident phase than in the reflex, rising in the reflex and descending in the incident. Descending against the wind it lowers its feet, where the wind strikes, so as not to disorder the tail from the straight line of its body.