Which fall of water strikes a wheel hardest
Comparing four water-falls for impact and weight, with a wheel to test them
A tall vessel of water (labelled acqua, its corners a b c d) discharges through openings at different heights, and Leonardo asks which fall delivers the greater percussion and power for turning a wheel. Not yet having tested it, he reasons that the falls should be of equal power, since a high fall gains impact but lacks the backing weight that a low outlet enjoys, so where percussion is wanting the weight of the water makes it up. To settle the question he proposes a test wheel A that raises a weight above its centre, fed from a reservoir kept at constant level, and a lower diagram compares four falls a, m, n, o descending an incline.
On this page
Percussion versus weight in four falls of water
The vessel marked acqua feeds falls a, b, c and d; the question is which turns a wheel with greater force. Leonardo argues that a high fall has great percussion but little backing weight, while a low fall has less impact but the whole column of water behind it, so the two effects may balance out.
A test wheel fed from a constant reservoir
The wheel A is to be built so that each fall raises a weight above its centre equal to the fall's power. All falls must be taken at equal distance from their outlet, and a neighbouring reservoir must keep the flow constant, so that a general rule can be drawn.
A second comparison of falls a, m, n, o
A lower diagram sets four jets descending an incline to points a, m, n and o, repeating the question of which fall will give the greater percussion.