Thus, if every planet and satellite could be conceived to be motionless in space, and these two forces could be set in operation without producing rotation or translation in space, which is impossible, then every planet and satellite would occupy, by the joint exercise of these two forces, the same position in relation to the sun represented by their mean distances, as long as the solar system existed as a separate system in the realm of aetherial space. We have therefore discovered by strict philosophical reasoning, based on Newton's Rules of Philosophy, a real tangible centrifugal force existing throughout the universe; because it is entirely due to the pressure of an universal Aether, whose operation is ever directed from a central body, which force was indicated by Herschel, and its existence to his mind was demonstrated by the repulsion exhibited in connection with the tails of comets. We have now to go a step further, and show that the same pressure also includes the magnetic phenomena, as indicated by Clerk Maxwell, and that magnetic phenomena are also due to the aetherial medium, and then we shall have linked together in one common medium the majority of the forms of energy, as light, heat, electricity and magnetism, with which we are familiar. If it be demonstrated that these two forces, the centrifugal force and the centripetal force, can conjointly account for all the motions of the celestial bodies, then we shall have conclusive evidence that one of the forces is physical and due to the pressure of a physical medium. After that it will be comparatively easy to show that the centripetal force is also due to the same aetherial medium, and then we shall have accomplished that which we set out to accomplish, viz. the establishment of a physical cause for universal Gravitation, which physical cause is alone to be found in the pressures, tensions and motions of an universal Aether. CHAPTER IX AETHER AND MAGNETISM ART. 86. _Electro-magnetism._--We have now to look at the relation of magnetism to electricity, or, in other words, to prove the identity that exists between magnetism and electricity. In Art. 78 we have proved the identity between electricity and light, so that if we can now prove the identity between electricity and magnetism, then, wherever we get aetherial light waves, we must also get aetherial electro-magnetic waves. As the light waves due to the vibrations of the Aether are practically universal in extent, then it must follow, if the identity of the light waves with electro-magnetic waves is established, that the universality of electro-magnetic waves is established also, with the natural result, that, wherever we get these electro-magnetic waves, there we shall have the conditions by which all electro-magnetic phenomena are produced.