Balance arm in wheel vs air; the accidents of water and air
Water neither condenses nor rarefies; waves, the valley between them, and pouring water
Leonardo compares a balance with one arm inside a wheel and the other in the open air, arguing the wheel-bound arm undergoes no change of power while the airborne arm does, halving its effect as it descends. He then contrasts the "accidents" of water with those of air and fire: water can be neither condensed nor rarefied, closing behind a swimming fish as fast as it opens before it, yet it can gain gravity and levity in the making and breaking of waves. He adds that the trough between waves lies lower than the water's common surface, and that water nearest the hole of a leaking bucket runs heaviest and fastest. Balance and vessel diagrams accompany the notes (b; a c f d c, e; n; f a b c, o e).
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A balance arm in a wheel keeps its power; one in air loses it
With arm b a in the wheel and b c in the air, the wheel-bound arm has no change of power while the airborne arm does. When the air arm descends with weight c to site e, arm a c, of double length, is diminished by half, as the perpendicular power of weight b e shows.
Water can be neither condensed nor rarefied
Water in itself is neither condensable nor rarefiable: there is as much before the fish that penetrates it as behind, opening in front exactly as it closes behind. Yet it can acquire gravity and levity in the destruction and creation of the impetus that raises the wave.
The fish's impetus is shorter-lived than the bird's in air
The impetus of the fish is of shorter life than that which the bird makes in the air, even though the fish's muscles are most powerful for their quantity, since the fish is all muscle, as it must be to move in a body denser than air.
The valley between waves lies below the common surface
The valley set between the waves is lower than the common surface of the water, as seen in the water that returns backward to fill the places struck by the falls of the waters.
Water nearest the leak runs heaviest and fastest
The water nearest the hole from which it pours is heavier and faster than the rest, and the surface is lowest nearest the vent from which the water pours out of the vessel.