Gravity.

a m o - n - q p c - b - d - e - f. d is the centre of natural gravity. e is the centre of accidental gravity. Of the two cords of differing lengths which, descending obliquely, meet to create the angle from which descends the cord that supports a weight.

The intercentric line is that which is born from the centre of the world and, rising from it in continuous straightness, passes through the centre of the suspended weight for an infinite quantity of space. This is proved: let the weight suspended at d give passage to the intercentric line f d. Although the adversary may say, «such a line cannot pass through those centres f d», one will bring against him the two supports of differing lengths, which are the lines a b and c b, and the angle a b c of these will be divided by the intercentric line, which has divided the angle a b c into two other angles. But to argue more briefly against the adversary: if the intercentric line did not pass through the centre of the suspended gravity, it could not pass through the cord, the appendage of that gravity, nor even through the real angle a b c, nor again through the angle of semi-real sides a b o, in which judgement is given upon its base a m and m o.

The base of this triangle a o b may be imagined to be remote in infinite space, remote from its angle b, and for this reason it does not fail that the intercentric line divides its base in the same proportion as that in which the weight is divided among the cords, the sides of that triangle.