The law of inertia has often been discussed, and nearly always the questionable, hollow idea of absolute space has interfered to obscure matters. Absolute space is merely a figment of the mind, which cannot be evidenced by experience.

By referring to the experiment with the rotating water vessel, Newton believes that he is able to establish an absolute rotation. All that Newton’s experiment with the rotating water vessel demonstrates is that the relative rotation against the sides of the vessel does not evoke any noticeable centrifugal forces, but that these are evoked by the relative rotation against the mass of the Earth and the other celestial bodies. No one can say what the qualitative and quantitative outcome of the experiment would be if the walls of the vessel were to become progressively thicker and more massive until, finally, they are several miles thick.