Thus the motion of Mercury or any other planet through space would not be uniform, but would gradually decrease, and such a result is perfectly in harmony with all experience and experiment in relation to moving bodies on this earth. This effect of the Aetherial electro-magnetic light waves upon a planet is in harmony with Newton's nineteenth query in _Optics_, and is indeed the physical illustration of that query in its corrected form which we have already referred to in Art. 46, where Newton says: "Doth it (Aether) not grow denser and denser, etc.; every body endeavouring to go from the denser parts of the medium towards the rarer?" That the Aether does grow denser and denser nearer to a body we have already seen in Art. 46, and now we learn that a body, when under the influence of the centrifugal force only, would pass from the denser parts of a medium to the rarer parts, as suggested by Newton. We will now suppose that Mercury has been repelled, by the pressure due to the aetherial waves generated by the sun, to the distance of Neptune, a distance of 2,780,000,000 miles; and that at this point the centrifugal force is cancelled, and in its place is put the centripetal force of Gravitation. What will be the effect upon Mercury then? At first sight the effect will be exceedingly slight, but slowly, yet surely, the attractive power of the sun would begin to make itself manifest, and we should find Mercury retracing its path along exactly the same straight line that it had taken in its outward journey. Not only so, but its motion would be accelerated just in the same proportion that it had decreased on its outward journey. On and on through the intervening space the planet would rush, and if there were no centrifugal force in existence, the planet would ultimately rush into the central body, the sun, and being swallowed up by it, would maintain for a time the heat thereof.