A bird raising and lowering its wings in wind
Climbing in circles with wings held high, then descending with wings low as the wind wedges above
Two small ink sketches of a bird accompany the notes: one with wings raised high, another with wings pressed down. Climbing in spirals with the wind, Leonardo writes, the bird keeps its wings very high so that the 'wedge' of the wind and its impetus lift it. Going down, it lowers its wings for two reasons: less air then supports it, and the wind forms a wedge above that presses it downward.
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Wings held high to climb with the wind
In mounting in circles with the wind, the bird keeps its wings very high. This is so that the wedge of the wind and of its impetus should lift it upward. The raised-wing sketch illustrates this ascending posture.
Wings lowered to descend
In going down the bird lowers its wings for two reasons. First, less air then holds it up; second, the wind makes a wedge above it that pushes it down and keeps lowering it. The lower sketch shows the depressed wings.