Harnessing a Tall, Thin Waterfall to Drive a Bucket Wheel
Weighing the dead weight and the percussion of the falling stream
Leonardo describes a fall of water that is high but narrow, which he would put to useful work by leading it down a bottomless pipe onto a wheel. He counts on two effects together: the dead weight of the water settling in the buckets m o p r t v and the percussion of the falling column, whose combined imbalance could move any great load. He then asks which blow strikes with greater force, water on the water already in a bucket or water on the bare wooden paddle, concluding that a stroke on the denser wood counts for more. Two small figures at lower right illustrate the two cases.
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A pipe leading a thin fall onto a bucket wheel
To use a fall of great height but small thickness, Leonardo sets a pipe as wide as the water's stream and as tall as the fall. The water fills the bottomless pipe and settles or strikes on the wheel, and also fills all the buckets m o p r t v, so the loaded side outweighs and turns the wheel.
Weight and percussion joined as two powers
Once water fills a bucket it gives all its weight to that side of the wheel, and to this is added the percussion of the water falling upon it: two powers joined, percussion and weight. Yet a blow on the water is weaker than a blow on the denser wood of the paddles.
Blow on wood versus blow on water
One small figure is labelled as the blow of water upon wood, that is the paddles of mill wheels; the other as the blow of water given upon the water already standing in the buckets of such wheels.