Waves in a canal: reflected motion and the semicolumnar wave
Why smooth channels raise no waves, and how a bankside obstacle forms a half-column wave
Three linked notes on why waves form in flowing water. Leonardo argues that a straight, clean channel raises no waves, since a wave arises only from reflected motion born where the current strikes a particular obstacle on the bed or banks; he then describes the 'simple semicolumnar wave' raised at a small obstacle a on the bank of a canal n o m p. The right margin carries parallel-line flow figures and diagonal wave diagrams, and a closing note that the two lower figures are transposed and must be corrected in the principal book.
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A smooth channel raises no wave
Water flowing between a straight, clean bank and bed makes no wave of any kind, because a wave arises only from reflected motion, which is born where the incident flow strikes a particular obstacle on the bed or sides. Where no such obstacles exist, the water rises only in minute upwellings that reach the surface without forming waves.
Waves born of incident and reflected motion
A wave is generated by reflected motion, and the reflected motion is produced by the percussion of the incident motion against an obstacle. Without a particular obstacle to strike, no reflected motion and therefore no wave is created.
The simple semicolumnar wave at obstacle a
At any minute obstacle a joined to the bank n o of the canal n o m p, the striking water raises a long half-column wave that runs obliquely toward the opposite shore, where it dies and is reborn. Continually recreated, the wave would persist were it not pushed straight again by the canal's ordinary current.
Note on the two transposed figures
Leonardo notes that the two lower figures, labelled m c, S and q r f, are transposed both in the description and in the drawing, and reminds himself to set them right in the principal book.