Reflex and incident wing-motions of birds in the wind
How a bird's oblique descent and recovery shift downwind and upwind
This page opens Leonardo's account of the four 'reflex and incident' motions a bird makes as the wind strikes it from different quarters (text 1). He argues that an oblique descent made against the wind carries the bird downwind while its recovering reflex-climb carries it upwind, and he traces where the bird ends up facing when a north (tramontane) or south wind reigns, noting a 'long dispute' about whether a reflex is even possible in one case (texts 2-3). A closing note describes how a bird climbing against the wind overshoots its natural impetus, the wind acting beneath it as a wedge, and rights itself by lowering one wing to curve away in a half circle (text 4). Three small pen sketches of birds in flight accompany the notes down the right margin.
On this page
The four reflex and incident motions in the wind
Leonardo announces the subject of the page: the four reflected and incident motions that birds make according to the different aspects from which the wind meets them. This heading frames the wind-response analysis that follows across the sheet.
Descent downwind, recovery upwind
An oblique descent made against the wind is carried downwind, while the recovering reflex-motion is carried upwind. If the incident motion is made toward the east while a north wind blows, the north wing lies downwind, so that at the end of the reflex the bird finds itself facing north.
The wind as a wedge that overshoots the climb
When the bird makes its reflex against the wind it rises far more than its natural impetus warrants, because the wind enters beneath it and acts as a wedge (coneo). Once the impetus is spent, only the wind's push remains, striking the breast and threatening to overturn it, unless the bird lowers the right or left wing to turn away in a half circle.