Thrushes flying against the wind, with a wing study and a jest
Notes on how small birds fly upwind, a labelled wing figure, mechanical linkages and columns of figures
The sheet mixes observation, mechanism and play. At the upper right Leonardo explains how thrushes and other small birds cross against the wind by flying in leaps, running downwind with wings half closed and then climbing again on the reflected wind, with small looping trajectory curves sketched above. A wing figure is labelled a (toe) and b (heel), and the centre carries articulated mechanical linkages with two small circle-and-triangle diagrams at the left. The upper left holds a witty jesting passage addressed to Sandro, and the lower half is filled with columns of numbers and multiplications.
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How small birds fly against the wind
Thrushes and other small birds make their passage against the wind by flying in leaps: they run a long way downwind, descending obliquely toward the earth with wings half closed, then open their wings to receive the wind with a reflected motion and so climb high again, repeating the cycle.
Wing figure labelled a and b
A small wing is drawn and lettered a to b, where a marks the point of the toe (punta di pie) and b the heel (calcagno), transferring the terms of the foot to the parts of the wing.
Articulated linkage mechanisms
The middle of the sheet is worked over with articulated rods and jointed linkages drawn in both ink and faint underdrawing, together with two small circle-and-inscribed-triangle diagrams at the left, apparently studies toward a moving apparatus.
Jesting note addressed to Sandro
A playful literary passage likens a certain simpleton to a gourd or melon grown fat in the shade from too much moisture, then turns to a companion, Sandro, asking what he thinks, and concludes that 'it hasn't come off for me'.
Columns of figures and multiplications
The lower part of the sheet is filled with paired columns of numbers and long multiplications running into the millions, with results such as 5625 noted in the margins.