How Eddies Form and Consume the Water's Impetus
Two motions of an eddy: its own revolution and its drift downstream
A dense page of text traces how eddies (retrosi) arise in a swift current. The sluggish fronts of struck water are suddenly forced into the swifter motion, dragging the water attached behind them; unable to be received by the first course, the water must turn back and consume its swift motion within itself. Leonardo concludes that each eddy makes two motions at once: a revolution about itself, and a drift following the water's course that carries it along until it dissolves.
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How swift currents generate self-consuming eddies
The sluggish fronts of struck water are suddenly transmuted into the swift motion, and the water attached behind is dragged and torn away. Unable to be received by the first course unless it rises above it, the water must turn back and consume its own swift motions in circulations called eddies.
The two motions of an eddy
Once generated, an eddy does not stand still but is carried whirling by the impetus of the water in the same shape. It therefore makes two motions: one in itself by its own revolution, the other following the course of the water that transports it until that flow undoes it.