Physics of Flame in the Bombard and the Rocket
How fire grows, seeks least resistance, and drives a rocket backward
The sheet studies the behaviour of flame inside a bombard and a rocket, arguing that fire gains quantity and power over time and extends toward whatever offers least resistance. Leonardo reasons that the concavity of air clothing the flame condenses and itself acts as a bombard, so that igniting powder drives the piece or the rocket backward by breaking every obstacle. He concludes that the flame does not flee from the rocket, but the rocket flees from the flame. Small sketches of a bombard (labelled b, a, c) and a rocket accompany the mirror-script notes, with further device sketches in the margins.
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Fire grows and extends toward least resistance
At every degree of time the flame kindled in the bombard acquires degrees of quantity and power, while a fire nourished by less fuel has less life. The growing fire condenses against whatever objects prevent its increase and extends toward the quarter where it meets least resistance.
How igniting powder drives the bombard back
The hollow of air that clothes the flame fleeing the bombard condenses and itself becomes a bombard. The powder it holds, which at first did not ignite in the piece, now catches fire and drives that bombard backward, breaking every obstacle.
The rocket flees from its flame
Leonardo argues that the flame penetrating the air is not what drives the rocket in contrary motion; only the flame that first strikes the air does so. He states the principle that the flame does not flee from the rocket, but the rocket flees from the flame, to be proved by means of the galley trumpet.
Sketches of a bombard and a rocket
A small bombard is drawn with the letters b, a, c marking its parts, tied to the note on the flame within it. A rocket and further small arms sketches appear in the margins of the leaf.