Smoke in air, and the currents and percussion of water in rivers
Smoke rises like surging water; straight rivers run fastest mid-channel and rebound between their banks.
Three short notes in Leonardo's mirror-hand open by comparing the wave-like figure with which smoke enters the air to the way surging water pushes up through still water. He then observes that straight rivers move with far greater impetus in the middle of their width than at their sides. A final note describes how water striking one bank rebounds toward the centre and back again, forming a pyramidal body of water enclosed between the two percussions, slow at its base and swift toward its point. The page bears text only, with the folio number and the Bibliothèque de l'Institut stamp.
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Rivers run fastest in mid-channel
Leonardo states that rivers, when they are straight, run with much greater impetus in the middle of their width than they do along their sides. It is a concise observation about the distribution of velocity across a straight channel.
Water rebounding between the banks
After striking a bank with equal percussion, water that meets a narrower stretch rebounds toward the middle of the river, sets up a new wave-motion, and returns to the banks again. Between the first percussion at the bank and the second at mid-channel a pyramidal body of water is enclosed, slow at its base and swift near its point where it strikes the bottom before rising.
Smoke enters the air like surging water
Smoke is said to enter the air with the same wave-like figure that surging water makes with its impetus among the surrounding water. The note treats smoke and water as comparable fluids driven by impetus.