An Instrument to Test the Motion of Air and Water
Wind blown through pyramidal holes turns a wheel, letting the power of moving air and water be measured
The left leaf (238v) is blank; all the work is on folio 241r, where Leonardo describes and figures an instrument for making experiments on the motion of air and water. A board pierced with pyramidal holes is turned to face the wind, which drives a wheel on its axle; by stopping all but one hole and noting the weight the wheel lifts, then comparing holes of different sizes, one measures the power of the blowing. He proposes testing whether a hole b, some multiple larger than hole a, lifts a proportionally greater weight, adds a vane to check that the wind is steady, and notes the mouths a, b, c and d with their sizes in braccia. The same tests, he adds, can be repeated with water to reveal the power of its motion.
On this page
Measuring the power of blowing by the weight a wheel lifts
Make an instrument as figured and turn the pierced board toward the wind. Stop the smaller hole and note the weight the wheel gathers on its axle, driven by the pyramidal hole a; then stop a and open the larger hole b, and consider: if hole a makes the wheel lift 4 pounds, and b is 5 times greater than a, will it lift 5 times as much on the same wheel? Note the differences with diligence.
The pierced board, wheel, axle and vane
The lower right of the leaf is figured with the apparatus: benches or boards carrying pyramidal openings, a wheel turning on its stile, and a vane. Two figures with letters and numbers and two figures with letters accompany the text but are not themselves transcribed.
Comparing four blowing-mouths of different bore
Note all the differences of the powers of the blowings, these four mouths being of equal size, and let the pyramidal hole a be one braccio, hole b eight braccia, c six braccia and d six braccia. A vane, figured above, guards against the wind itself varying during the trial.
The same trials repeated with water
Leonardo closes by noting that all these same tests can be made with water, so that one may see the power of its motion just as with the wind. The instrument thus serves to compare the forces of moving air and moving water alike.