Force and motion: the limit of a mill wheel and the mounted crossbowman
A fixed water wheel can drive only so much work, and how a moving motor carries a shot farther
This text page on force and motion opens with a conservation argument: a wheel turned by a fixed quantity of water has a fixed output, so if it drives one mill it cannot drive two without doubling the time, and it could drive endless mills that together do in a long time only what one does in an hour. A pair of aphorisms contrasts slow causes making rapid weak movements with rapid weak causes making slow vigorous ones. The longest note argues that the longer a motor accompanies the thing it moves, the farther that thing travels, illustrated by a mounted crossbowman in whom four motions — of horse, chest, arms and bowstring — combine in one arrow.
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One water wheel, one mill's worth of work
If a wheel is turned by a fixed quantity of water that cannot be increased in course, quantity or fall, its work is fixed: driving one mill it could not turn two without doubling the time, so one mill does as much in an hour as two do in two hours.
Slow and rapid causes of movement
A slow cause makes a rapid and weak movement; a rapid and weak cause makes a slow and vigorous movement.
The longer the motor accompanies the moved thing
The more the moving force accompanies the thing moved, the longer its movement will be. As much force as you put into drawing a crossbow returns as it springs back and accompanies the arrow until the blow.
The mounted crossbowman's four motions
When a mounted crossbowman looses, he spurs the horse and thrusts his chest and arms forward while releasing at the same moment. Four motions join in one arrow — of horse, chest, arms and bowstring — and if the arrow is proportioned to them it flies very far.