How a Moving Body Generates Waves in the Air
The air wave runs ahead of its mover and prepares its path, multiplying at every instant; compressed air becomes heavier than free air.
Four linked propositions describe how a body moving through air throws off waves. Leonardo asserts that the air wave a moving body generates travels considerably faster than the body itself, because air is very agile and easily set in motion: the first stroke makes one wave, which begets another and that another, so that at every instant the body multiplies waves beneath it which, by their flight, prepare the path for its motion. He restates that the successively generated air wave clears the way for its mover, and adds that air compressed by force becomes heavier than air left at liberty. The lines of the first and last notes are gathered by a pen-stroke, and the third note is written in a different nib and ink.
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The air wave outruns the body that makes it
The wave of air generated by a body moving through the air is quite a bit faster than the body that moves it. Because air is very agile and easily moved, the body makes a first wave at its first motion, which cannot but generate another after it, and that another, so that at every degree of time the moving body produces multiplications of waves beneath itself.
The waves prepare the path for their mover
The multiplied waves, through their flight, prepare the way of the motion for their motor; the air wave, by being successively generated, clears the path of motion for the body that moves it. Air enclosed by force, moreover, becomes heavier than air that remains at liberty.