The Behaviour and Eddies of River Water
Rock folds in mountains, round-falling water, and a classification of whirlpools
The page opens by observing that in every hollow of the mountain summits one finds the folded layers of the rocks, then turns to water: why a falling stream becomes round in section, and the principle that an equal quantity of water passes every cross-section of a river's length in equal time. Leonardo classifies the eddies (retrosi) of rivers into several kinds — hollowed like a concave pyramid, heaped like a raised one, some casting up matter from the bottom, others sucking down what floats, some undercutting the bank and some filling it — and explains that these whirlpools are needed to moderate a river's excess speed. He notes that although water runs at varying speeds between winding banks of different width and depth, equal quantity still passes each section in equal time. A small mountain profile is sketched at the upper right and a winding river-line at the lower right.
On this page
Folded rock layers in the hollows of mountain summits
In every concavity of the mountain tops, Leonardo asserts, one will always find the foldings of the layers of the stones. A small mountain profile drawn at the upper right accompanies the note.
Equal water passes every section in equal time
At every degree of a river's length an equal quantity of water passes in equal time. This holds even though the water runs at various slownesses and velocities between winding banks of differing width, depth and slope.
The kinds of river eddies and their purpose
The eddies of rivers are of several natures: some hollowed like a concave pyramid, some heaped like a raised one, some throwing up things from the bottom, others submerging what floats, one undercutting the bank while another fills it. These revolutions and retardations are necessary to equalize the excessive velocities of rivers, and where lateral eddies do not suffice new kinds arise that turn the surface water down to the bottom.
Why falling water becomes round
Among the questions posed is why water becomes round in its falls, that is, round in its thickness. The note stands as one of the physical problems of water Leonardo sets himself on the page.