The oscillating motion divides into three parts, that is simple, compound and decompound. Simple is that which proceeds between two same objects; compound is that to which one oscillation joins with another oscillation; decompound is when several bodies are attached one to another and one below the other, degree by degree.

The oscillating motion in dense bodies will never be straight unless it is constrained by channels or other guides; and if it is constrained, of itself it soon consumes itself.

The oscillating motion in rare bodies, such as air and fire, can be both straight and curved; and this is because they rarefy and condense and can penetrate one another within themselves. The like can water do within water, that is, the faster penetrates within the surface of the less fast.

The compound motion soon consumes itself, and the decompound motion fails still sooner.

Such will be the proportion of the weight felt by the obliquity o p of the weight n to the remainder of that weight, as is that which the space n m has to the space m o.

Always the weight of a heavy body placed at any obliquity is distributed among its supports, that is, in the cord that does not let it descend along the obliquity, and in the obliquity that does not let it go beneath the attachment of that cord.

The weight that is sustained by the cord upon the obliquity is always to be judged at the contact made by the line that departs from the centre of gravity of the weight with the line of the said obliquity; and the angle of their contact is always right.

The unequal weights that on the arms of the balance resist each other's descent: the junction of their appendices to the beam of the balance will be made between unequal angles, and their inequality will be like the inequality of the weights that are sustained under such angles.

The weight n is 2, and the weight m is 1, that is, half of n. It follows, by the 7th of the 9th, that the angle r of the double weight is also double the angle b of the weight 1 of m; r is the centre of the world.

The flexible body does not resist a body heavier than itself. The heavy body without resistance seeks the ultimate lowness.

It follows, from what is said, that the heavy body which descends through the air or another liquid body will not stop except at the ultimate lowness; and if the water and the earth were removed, that heavy body would descend to the centre of the world, and from there it could not part, unless it rose up again; which motion would be violent.