Water leaps and why bombards outrange small guns
On motion: percussion of water and the scaling of firearms
Leonardo first observes that when falling water strikes standing water, the leaps it throws up do not rebound at equal angles but spring to the surface by the shortest path, driven by the air dragged under with the water. Under the heading 'On motion' he then asks why a bombard does not obey the same rule as a small firearm. He proposes a thought-experiment: scale a gun up from a one-ounce ball fired with an ounce of powder, which carries a mile, all the way to a thousand-pound ball, keeping the powder equal to the ball's weight and every proportion fixed, and concludes that the heavier the ball, the farther it travels.
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Scaling a firearm and the range of the ball
Under the heading 'On motion', Leonardo imagines enlarging a gun from a one-ounce ball fired by an ounce of powder, which carries a mile, up to a thousand-pound ball, always giving powder equal to the ball's weight and holding every proportion fixed. He concludes that the heavier the ball, the greater the distance it travels.
Why a bombard does not obey the harquebus's rule
The passage poses the question of why a bombard does not follow the same rule as the small firearm (scoppietto), and works it out by scaling the weapon and its charge together up to enormous size. It treats the bombard as a scaled-up gun whose behaviour changes with size.
Leaps thrown up by water striking water
Leonardo notes that when water falls onto other water, the leaps it raises do not rebound between equal angles but rise to the surface by the shortest way, because of the air submerged together with the water.