Heat makes bodies lighter; and the current at the Strait of Spain
Balance experiments with heated copper balls, the moon and tides, and why straits run faster
Leonardo opens with the distilling of quicksilver in an alembic, where heat lifts even so heavy a substance before it falls again as smoke, then proposes a balance experiment: two equal copper balls hang from the beam, and when one is made red-hot it is shown to weigh less, proving that heat makes weighty bodies light. He rejects the idea that the moon, as a cause of cold, could raise and lower the sea every six hours, reasoning that like does not draw like, and adds that water is lighter than earth because a heavy porous body lets liquid seep into the spaces its air abandons. A bird's-eye map of the Mediterranean and the Strait of Spain accompanies the rule that a river of equal depth runs faster through a narrower channel, the narrowing measured in units n along intervals f, g, h and a, b, c, d, e.
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Heat makes weighty bodies lighter (balance of copper balls)
Of two things of equal weight on the balance, the one on fire is lighter than the cold one. Hang two little copper balls by iron wires from the balance; put one into the fire and make it red-hot, then take it out so the rising vapor does not push the weight up, and you will see that the ball, before equal, has been made light by the heat.
The moon cannot raise the sea by likeness
If someone alleged that the moon, which augments cold, made the sea grow and shrink every six hours, this would seem impossible, since a thing does not draw its like by similarity but through want of conformity — hot dry fire draws not fire but the cold and humid, and water does not draw other water to itself.
Distilling quicksilver: heat lifts a heavy body
Heat, in its desire to return to its element, carries the heated humors with it. You may see this if you distil quicksilver in an alembic: though so heavy, when mixed with the fire's heat it rises, then falls again as smoke into the second receptacle, back to its former nature.
Why the current is stronger in the Strait of Spain
A river of equal depth flows faster through a narrower tract than a wider one, in the proportion the greater width exceeds the lesser. Where the river is five miles wide, each of the five square miles gives a fifth of itself to replace the square mile of water missing in the strait; where it is three miles wide, each gives a third, as shown at f g h for mile n.
Bird's-eye map of the Mediterranean and the Strait
A schematic bird's-eye plan shows the Mediterranean Sea narrowing to the Strait of Spain between Spain and Africa; the strait's width is marked n, and two expanses (x–y and r–l) are divided into intervals of that width, labelled f, g, h and a, b, c, d, e, to compare the volumes of water passing through.