Every heavy body removes itself as far as it can from the light, and its centre comes to rest in the centre of the elements. Falling freely toward it, it directs itself by the shortest way; and the heavier it is, the sooner it descends; and the more it descends, the faster it becomes; and the more oblique the descent, the more the weight loses of its heaviness; and losing of its heaviness it loads its support. And that... Just as the levity of fire is not of such force that it can sustain the heaviness of the air, and likewise... Just as fire is the lightest element, so it is of least resistance; and if it were possible to carry some quantity of air to its greatest height, that air would pierce through that element without ever giving rest to its descent, until it were brought to its own sphere. Likewise, air being of greater levity than water, that air is of less resistance. Whence, when the water that vaporizes up there returns to its simple nature, from there it descends, piercing the air which below cannot resist it, and makes its way to its element by the shortest path. Likewise the earth, heavier than water, if it be placed on the surface of that water, the water, being lighter, cannot resist it, whence that earth makes its way to the bottom of the water by the shortest path. And if this whole sphere of the earth were water or air, one would see that gravity... Aristotle says that everything desires to maintain its nature. Gravity, being driven back by light things, desires such a place where it no longer weighs, so that its density remains without weight; which once found, it weighs no more and moves no more of itself. Gravity and force desire not to be, and therefore each maintains its being by violence. The thing set in motion desires to follow the line begun by its mover. Gravity, daughter of motion, like force, desires to undo itself, and therefore each maintains its being by violence. And if it were possible to give a diameter of air to this sphere of the earth, in the likeness of a well showing from one surface to the other, and through that well a heavy body were let fall, even though that body wished to stop at the centre, the impetus would be that which for many years would prevent it from doing so.

The impetus that is born from motion often delays the desire of the thing that has been moved.

Gravity and force, daughters of motion and sisters of impetus and percussion, of which I intend to treat somewhat, always stand in a continual desire not to be. But weight, of which I first intend to treat as a corporeal and palpable thing, is that which, not being sustained by any element — rather, as much as they can, they equally drive it away from afar.

No part of an element can weigh within its own sphere. The heavy element cannot be sustained by the light. Weight, force, blow, and impetus are sons of motion, because they are born from it. Weight and force always desire their death, and each is maintained by violence. Impetus is many times the cause that motion prolongs the desire of the thing moved.