Weight or percussion: which drives a projectile farther
An experimental method to separate the cause of motion and refute a false rule of proportion
This text-only page, written in mirror script with no diagram, sets out an experimental method for isolating the cause of a body's motion. Leonardo has the reader find the weight thrown farthest first by percussion, then by simple weight without percussion, so as to see what difference the cause of motion makes. Weighing each mobile and comparing the distances travelled yields a general rule relating the two powers. He rejects the claim of earlier writers on proportion that halving a weight lets the same power move it twice as fast.
On this page
Percussion versus simple weight as the cause of motion
Leonardo proposes finding the weight that moves farthest from the start of the motion, first using percussion with every care, then repeating with simple weight and no percussion. Comparing the two reveals what difference the cause of the motion makes, whether it be weight or percussion. He varies the mobile bodies until one is found proportionate to the power of the mover, namely the ball thrown farthest from it.
Against the rule 'half the weight, twice the speed'
The reader is told to weigh each mobile, consider the distances they have moved, and so derive a true general rule between the two powers. Halving the mobile, as the writers on proportion agree, cannot make the same power drive it twice as fast; were it twice as fast, it would travel proportionately farther still.