Eddies and the Middle Water in a Canal
Where vortices form, and the middle water between incident and reflected flow
In red chalk Leonardo studies the 'middle water' (acqua media) of a canal, stating that eddies always arise there, above the mouth where the water bends crosswise near the head of the channel. A second note places this middle water between the incident and the reflected water. A short jotting in the right margin records a 'little toll of Porta Nuova,' a memorandum unrelated to the water study; small red-chalk sketches of curling water accompany the notes.
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Eddies generated in the middle water
Leonardo states that the eddies of water always form in the 'middle water.' This middle water lies above the mouth of the flow that bends crosswise near the head of the canal where it runs.
Middle water between incident and reflected water
A companion note locates the middle water in the region between the incident water and the reflected water, framing it as the zone where the two currents interact.
Marginal note: toll of Porta Nuova
A note in the right margin, separate from the water studies, records a 'little toll of Porta Nuova' (Dazietto di Porta Nova), a brief memorandum referring to the Milanese city gate.