The Percussion of Falling Water
Water dropping through a pipe and cascading down steps, with its rebounding eddies
Under the heading "percussion of falling water upon various objects," Leonardo describes water falling vertically through a round pipe onto a flat surface, where it spreads into a swift thin sheet ringed by a circular wave that rebounds toward the point of impact. A lettered figure and its caption then treat water cascading down a flight of steps: the part clear of the step keeps its simple fall, while the part striking each tread rebounds in eddies (p a, b c, a h c, c b, d a, c e) trapped between the tread and the step above. Central sketches show a jet dropping into circular basins, and Leonardo advises observing such eddies in water enclosed between two thin plates of white glass. A small decorative arch is sketched in the upper corner of the right folio.
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Falling water makes a circular wave on a flat surface
Water falling in a perpendicular line through a round pipe onto a flat place forms a circular wave around the point of impact. Within that ring the water is of very swift and thin thickness, and finally it strikes back against the wave it has generated, which seeks to return to the place of the impact.
Water cascading down steps and its rebounding eddies (p a, b c, a h c, c b, d a, c e)
Water falling upon steps arranged like a staircase keeps its simple motion where it clears the tread, but where it strikes the flat of the step it rebounds with varied reflections between that flat and the wall of the step above. Falling from step p a onto step b c with the part a h c and striking at c, it leaps back to c b and from b to a with various eddies, none penetrating the simple course d a, c e without at once straightening with that backflow.
Sketches of a jet dropping into circular basins
In the central column of the right folio a slender vertical jet is shown falling from above into shallow round dishes, spreading into concentric ripples and a bulbous swelling of disturbed water. The drawings visualise the circular wave and returning eddy that the accompanying text analyses; the transcription flags the block only as a figure with letters.
Marginal sketch of a decorated arch
In the upper right corner of the right folio a small pen sketch shows the springing of an arch with foliate ornamental scrollwork, unrelated to the water text. It is a marginal doodle rather than a developed study, and no transcription accompanies it.