On Percussion: Air Compressed Beneath a Falling Body
Oblique descent, air rarefying and condensing, and a test of a melting varnish
Under the heading 'On percussion', Leonardo studies a body falling obliquely through air: the air that compresses beneath it escapes more from its upper side than from below. A companion figure with two oblique objects (labelled b a and c d) argues that where air rarefies on one side it condenses on the other, so the rear of the falling body descends with greater impetus and its once-low front rises at the end of the motion. A closing note proposes testing whether a non-tarnishing varnish, once melted by fire, will run on sloping surfaces, and directs that it be spread flat with an even brush.
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Air compressed beneath an oblique falling body
The air that condenses beneath a body descending through it in an oblique position escapes more from the body's upper part than from its lower part. This uneven escape of compressed air governs how the body settles as it falls.
Rarefied and condensed air steer the descent (b a / c d)
Continuous air rarefies on one side as much as it condenses on the other; rarefied air resists less as condensed air resists more. So the rear part b descends with greater impetus than the front, and the front a, which was at first low, rises up at the end of the reflected motion.
Test of a melting varnish for the template
Leonardo proposes an experiment to see whether the non-tarnishing varnish, once liquefied by fire, runs on oblique surfaces if it is not too thick. Once melted, the varnish must be spread flat with an even, continuous brushstroke.
Curved sheets drawn falling obliquely
The right and centre of the sheet carry scroll-like curved shapes representing the thin sheets or cards descending on the slant. A small latticed panel is drawn at the lower right beside them.