Let us again refer to the centripetal force, so that we may see exactly what its governing conditions are. In Art. 18 we learned that this force might be thus expressed: "Every particle of matter in the universe attracts every other particle with a force whose direction is that of a line joining their centres of gravity, and whose magnitude is directly as the product of their masses, and inversely as the square of the distance between them." Now we have seen from the previous Art. that the centrifugal force due to the pressure of the Aether medium is the exact counterpart of this, in every way, so that if we combine the two, we get the complete statement of the universal law which governs all matter, and which we may define as follows-- "Every particle in the universe attracts and repels every other particle in the universe with a force whose direction is that of a line joining their centres of gravity, and whose magnitude is directly as the product of their masses, and inversely as the square of the distance between them." This complete law, however, only holds good when the two forces are in equilibrium. With this conception of the universal law which governs all matter, the harmony and stability of the universe becomes possible from the physical standpoint. Apart from this conjoint working of the two forces or motions, a physical explanation of Universal Gravitation is impossible, as with one force operating only throughout the universe, ultimate stability is inconceivable, and the harmony of the spheres might at any time be suddenly destroyed. With this conception of the universal law which governs all matter, the great Law of Gravitation is brought into harmony with all experience and observation. Look where we will, or at what we will, there we find forces possessing a dual character, as we have already seen proved. Professor Tyndall, as we have already learned (Art. 63), definitely states that the stability of atomic systems is preserved by the existence and operation of _two forces, one attractive and the other repulsive_, and what is true of the atomic world is equally true of solar or stellar worlds. Thus for the first time in this respect, our philosophy agrees with our experience, and the true relation of the centrifugal force or motion to the centripetal force is made manifest. So that, wherever in the solar system the centripetal force or Gravitation Attraction operates, there, with exactly equal intensity and power, the aetherial centrifugal force operates, at the respective mean distances of the planets and satellites, where the two forces are in equilibrium. If it were possible to conceive of a stationary solar system, then, by the conjoint working of the two forces, it would be equally possible to conceive of perfect stability and harmony existing between the respective planets and satellites of that system while stationary.