Why the Sea Is Salt: Against Pliny's Explanations
Salt springs and salt mines as the true cause of the ocean's saltiness
A densely written text page in which Leonardo asks why sea water is salty and reviews, then rejects, the explanations given by Pliny. He argues that if the sun's heat caused it, still ponds and marshes would be saltiest, whereas experience shows their waters free of salt. His own conclusion, carried into the right-hand margin, is that the sea's saltiness comes from the many veins of water that penetrate the earth, dissolve the mines of salt they meet, and carry that salt down to the ocean.
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Salt springs meeting the mines of the earth
Leonardo's conclusion is that the sea's saltiness is born from the many veins of water that penetrate the earth, find mines of salt, dissolve them in part, and carry the salt to the Ocean and other seas. Because the clouds that sow the rivers never lift that salt back up, the sea would be saltier now than in any earlier age.
Against Pliny: still marshes are not the saltiest
Pliny held that the sun scorches and dries the sea's moisture, leaving the salt flavor behind. Leonardo objects that if this were so, lakes, ponds and marshes would be saltier the shallower and less mobile their waters are, yet experience shows such marsh waters entirely free of saltiness.
The sea's salt rendered back to the risen land
To the objection that infinite time would dry or congeal the whole sea into salt, Leonardo answers that the salt is given back to the earth: land rises up carrying its acquired salt, and the rivers render that salt again to the submerged earth. Salt thus circulates rather than accumulating without end.