Motion, fire and flame, and the riddle of the infinite
Physics of moving bodies, water and fire in jolts, gravity and levity toward the centre of the world
A dense two-column physics sheet in Leonardo's mirror hand. He asks whether the straight motion of a mover always yields straight motion in the moved body, and how the body's shape or the medium interrupts it; poses the riddle of the infinite (the thing that cannot be given and, if given, would not exist); and studies why water descending through air or fire, and fire rising, move in jolts of flux and reflux. A left column headed 'figure of fire' analyses why flame divides into pyramids joined by concave curves, and a diagram at the 'centre of the world' defines gravity and levity as accidental powers. Small diagrams of rays, a flame, a numbered figure (4 6 8) and a circle accompany the text.
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Whether straight motion always yields straight motion
Leonardo asks whether the straight motion of the mover can always give straight motion to the moved body. He notes that this can be interrupted by the shape of the mobile, through the bevel of its front, its middle or its tail, and by whether it is spherical, uniform in weight, and by the medium through which it passes.
The riddle of the infinite
What is the thing that cannot be given and, if it could be given, would not exist? It is the infinite: were it given it would be bounded and finite, because whatever can be given has a boundary with the thing surrounding it at its extremities, while that which cannot be given has no boundaries.
Water and fire descending and rising in jolts
He asks why water, in descending through air or fire, moves in jolts, making flux and reflux behind its pyramid, and why fire does the same in rising. He adds that the motion of fire is slower in cold air than in warm air.
Figure of fire: flame divides into concave pyramids
The left column asks why flame is generated only above some space of smoke and strikes only with its smoke. Striking the air, the flames divide into pyramids joined by curved boundaries that are concave and not convex; air behaves the same way within water.
Gravity and levity toward the centre of the world
Beside a circle marking the centre of the world, a thing is called lower the nearer it is to that centre. Gravity and levity are accidental powers generated by one element drawn or pushed into another; no element has weight or lightness within its own element; the heavier body shows weaker resistance, the lighter is sustained by greater resistance.