Water wheels: which the current drives best
Mill wheels on an incline, and the rule that a straighter, longer blow strikes harder (a n vs p q)
A red-chalk row of mill wheels set along a sloping line accompanies notes on how running water drives a wheel. Leonardo argues that a wheel is best turned when the water striking it does not rebound after impact. He adds that a blow has greater force the straighter and longer the motion that causes it, so that the stroke a n is better than p q in proportion as it is longer.
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The wheel the water turns best
A wheel is best turned by water when the water that turns it does not leap back after striking it.
Row of mill wheels on an incline
Several mill wheels are drawn along a sloping line, labelled with the letters a, p, m, q, o and n, illustrating the notes on driving a wheel by water.
A longer, straighter blow strikes harder (a n, p q)
A blow is of greater force the straighter and longer the motion that causes it. Thus a n is a better blow than p q by as much as it is longer.