This is the most masterly of Leonardo’s drawings of the movement of water, a recurring theme in his work. Here he studies the patterns produced by the flow of water past an obstacle, and the eddies and bubbles resulting from water falling from a sluice into a pool. The drawings exemplify Leonardo’s ability to fix a momentary impression in his mind and capture it on paper.

While the final pen drawing is a dense layering of water currents and bubbles, the under-drawing, seen for the first time in infrared light, is much simpler. It can now be understood how Leonardo built up his final image in stages. Here, he started with an underlying structure of currents in sweeping whorls, and then added the little rosettes of bubbles on the surface.

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