We will next proceed by the lamp of experience, consulting with care the observations deposited in the records of astronomy.
We will found our hypothesis in the general laws of motion, whose effects are every where the same, and whose influence extends to the utmost limits of matter.
If in two ellipses having a common major axis we take two such arcs that their chords are equal, and that also the sums of the radii vectores, drawn respectively from the foci to the extremities of these arcs, are equal to each other, then the sectors formed in each ellipse by the arc and the two radii vectores are to each other as the square roots of the parameters of the ellipses.