Water Striking a Mill Wheel
How impact angle and matched motion maximise a water wheel's power
A red-chalk study of a hydraulic wheel drawn from the side and edge-on, labelled a–a. The note states that water delivers its greatest power to the wheel when it strikes between equal angles, and that this impact is strongest when the flow of the water and the motion of the wheel are directed along one and the same course. Two sketches at the foot of the sheet show a spoked wheel and a vertical wheel-and-shaft assembly.
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The impact of water on the wheel at equal angles
The impact of water on the wheel is at the highest degree of its power when it strikes between equal angles. That impact is stronger still when the course of the water and the motion of the wheel run in the same direction.
The wheel drawn from the side and edge (a–a)
Two red-chalk diagrams at the foot of the sheet show the hydraulic wheel: a spoked wheel seen frontally and a wheel mounted on an upright shaft, illustrating the geometry of the striking water.