The waterwheel as a motor of constant power
A cascade drives a wheel labelled 'Water,' with a note on why the moved body stays slower than its motor
A wheel struck by a falling cascade is drawn at the right, the stream labelled 'Water.' Under the heading 'On the motor of constant quality of power,' Leonardo argues that the moved body can never be more rapid than its motor: were their speeds equal, the water would deliver no percussion. Such a motor could then move only as much weight as equalled the quantity of water following the wave that propels it.
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A motor of constant power and the need for percussion
Leonardo holds that a body moved by this constant-power motor can never be otherwise than slower than the motor itself, since equal speeds would leave the water unable to deliver a percussion. In that case it could move only as much weight as equalled the quantity of water that follows the propelling wave.
Cascade striking the wheel, labelled 'Water'
The drawing shows water falling as a cascade onto the rim of a wheel, the stream marked 'Water,' representing the moving water as the motor of the system. The propelling 'wave' of water named in the text is the force that turns the wheel.
Wheel with an axle struck by the water
A wheel with a hatched rim is set so that the falling water strikes it, an axle projecting at its centre. It is taken as the 'motor' of the discussion, its steady turning standing for a source of constant power.