River pits, cataracts, and the erosion of riverbeds
Why falling water hollows out pits and why a river's surface mirrors its bed
Folio 59v continues Leonardo's study of moving water, analyzing how falling water and cataracts scour and widen pits in riverbeds. Side-view diagrams show a cataract dropping into a basin ('Water falling with air') and an engorged river whose fuller flow strikes the basin as a united diagonal stream, alongside notes on why bumps and hollows appear on a river's surface. A closing remark observes that the lowest part of the earth's whole machine is the region submerged beneath the sea. The dense mirror-script fills the page and is carried in the bundle's five blocks.
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Full rivers make shorter, united falls that scour the bottom
When rivers are full their waterfalls are lower: the falling water meets the water below, which resists it, so the fall is shortened and encloses little air. With nothing to throw its blow upward, the weight of the water goes united to the bottom, stripping the earth from the stones and widening the depths of the water.
Why pits form along the course of a river
Various sizes of stones lie on a riverbed; the water finds the largest, pours down behind it, and its blow sweeps the smaller stones from the struck spot. The pit grows, the fall becomes more powerful, and it digs ever deeper, because rivers constantly erode the mud and bare the lower parts of the stones.
A river's surface reveals its bed like a stocking on a leg
Just as stockings that clothe the legs show from outside what is hidden within, the surface of the water reveals the quality of its bottom. The water furrowing the bed meets protuberances of stone, strikes them, and bounces upward, lifting with it all the water that lay above.
The lowest part of the earth's machine lies beneath the sea
Of the entire universal machine of the earth, the lowest part is the one submerged under the sea. Leonardo sets this cosmological remark at the foot of the folio, framing the water studies within the body of the earth.