The Right-Angle Blow: Impact, Recoil and the Bombard's Sound
A perpendicular strike is strongest; an oblique one glances off, and the report comes from flame striking air
Leonardo states that a blow meeting its object at a right angle is at its maximum power, because the three powers of force, weight and motion then lie in a straight line through the ball's center. A more oblique blow is weaker and rebounds with two different motions: the ordinary forward course and a spinning about itself that runs faster and farther, as an unequally loaded balance tips. A final note explains the bombard's sound as the percussion of its flame against the air, and observes that the harder the bombard recoils against its housing the better it drives the ball, like a man who braces his back against a wall to push with his hands. Three sketches show the ball striking the wall, the wall collapsing along an oblique line, and a detailed exploding bombard shooting its ball through plumes of smoke.
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A right-angle blow is at maximum power
A blow striking its object at a right angle is at its maximum degree of power, because the centers of the powers, force, weight and motion, then lie in a straight line. The forward part of the ball striking the wall is in line with these centers and equally surrounded by the whole sum of the powers, so all the weighty parts bear on the place struck.
The oblique blow glances off and spins
A more oblique blow does little damage, because the weight above the center of percussion so exceeds that below it that the ball tips after the blow, like a balance with unequal weights. This produces two motions: the ordinary straight course, and a turning about itself of much greater speed and longer path than the straight motion.
The bombard's report and the value of recoil
The sound of the bombard is caused by the percussion of the flame against the air, and the more forcefully the bombard recoils against its housing, the better it thrusts its ball. Leonardo likens it to a man who leans his back against a wall and pushes with his hands: the more he pushes with his hand, the more force his back makes against the wall.
Exploding bombard shooting through plumes of smoke
A smaller, detailed sketch at the foot shows an exploding bombard, with the housing and flanges at the mouth and tube joint. The ball shoots straight forward through plumes of smoke from the explosion.