Gravity.

The nature of weights with their supports.

That weight shows itself heavier which has the weaker support, and that support is weaker which, more distant from its fixed point, is loaded.

And such will be the proportion of the weaknesses as is that of the distances they have from their fixed points.

And the proportion of the weights and of the weaknesses of their supports is one and the same, that is, c being twice less resistant than b, it sustains twice less weight than b.

That weight shows itself heavier which has less resistance, and that resists which is more remote from its fixed point, and such will be the proportion from resistance to resistance as is that from distance to distance from its fixed point. But it is an inverse proportion, that is, the lesser power at the greater distance and the greater at the lesser distance. But the proportion of the weights and of the resistances that suspend them is one and the same.

That weight seems greater which has less resistance.

The gravity of a weight increases as much as its resistance diminishes, and the resistance diminishes as much as it moves away from its fixed point. Therefore the proportion of the resistances is equal to that of the weights and one and the same, and the same is that of the weights and of the distances; but it is inverse.

No element has gravity or levity in its own sphere.

Vaporized elements remain for some time one within another, but in united quantity.

Weight is an accidental power created by the motion of one element drawn into another, and its motion is to descend toward the center or to flee from it; and it divides into two parts, taking two names, that is, levity and gravity. Levity is that which goes upward, and gravity is that which goes downward, and they are of equal power placed in a middle element, as air and earth placed within water, or water and fire placed within air, so that the one is heavier than water and the other lighter, and thus in the second the one is heavier than air and the other lighter. And if to a weight under water air is joined, it will make a mixture of lesser temper than the weight of the water, and if the weight is greater than the air, it will remain at the bottom, and if it is less, it will go up.

The heavier part of one and the same body that descends always stays below the lighter.

The victorious weight placed in the arms of the balance diminishes as much as it descends, so that in minute weights it becomes so light that it does not descend below its support.

Weight is an accidental power created by a scarcity of counterpoise and resistance, like the water that is generated in the air by condensation of humid vapor, which is as it were water drawn up.

a b is the river driving the wheel of the first motion, and its water falls at m; f is the wheel that draws the water of the marsh t up to the height m.

No surface of river water is lower than the surface of the sphere of water, except that which pours into the bottom of ships.

Only that water has weight which is raised above the other water, save the evaporated.

Let the wheel be wide, so that the water spreads little toward the center of the wheel, and thus the center of gravity of the water will be quite remote from the center of its wheel.

Let a ditch be made two braccia wide at the bottom and wide at the mouth in such a way that the banks do not collapse into it.

And this extends from the sea to the first mill that can be made on the river that pours into the marsh, and to that mill let the water of the marsh run.

A river will throw out so much the more as the motion of the water that is raised is less, that is, if the water that moves has 8 of downward motion, and that which is raised has 4 of rising, the water that flees is double that which gives the flight; the water that is raised will be poured out as high as the backflow is high. Let the water that is raised be wide and thin in its box, so that it does not have to raise itself too much.