ART. 99. _Second Law of Motion._--According to Newton's Second Law of Motion, "Change of motion is proportional to the impressed force, and takes place in the direction in which the force is impressed." From a consideration of this Law (Art. 15) we saw that the impressed force was a compound quantity, being regulated by the mass of the moving body which exerted the impressed force, and that it was also proportionate to the velocity of the moving body; so that if either of these quantities are changed, the total impressed force would be changed also. We have now to show that our aetherial medium agrees with this second law of motion in so far as the second law of motion agrees with experience and experiments. To do this, we must review our conception of the universal Aether, and remember that Aether is matter, and being matter, it is atomic and gravitative, possessing density, elasticity, inertia, and kinetic energy, the same as any other moving matter. In this Aether medium we have, according to this conception, something that can both push and pull, or exert force upon any body with which it comes into contact. Further, the inertia and kinetic energy of the Aether at any part of space will be regulated by its mass in that particular part, and if its mass is denser in some parts than others, that part of the aetherial medium possessing the greatest mass will also possess the greatest capacity for impressing force upon any body that exists in the medium. Now we have learned from Art. 45 that Aether being gravitative, it is denser nearer to the sun, getting gradually less and less dense, the further it recedes from the central body, except where it is bound or associated to some other planet or satellite, and there it gradually gets denser, for the same reason that it is denser nearer to the sun. As, therefore, the Aether gets gradually less dense as it recedes from the sun, the density of the Aether at the mean distance of Mercury, 35,900,000 miles, would not be so great as near the sun's surface; while the density of the aetherial medium at the distance of Venus, 67,000,000 miles, would be less than the density of the aetherial medium at the distance of Mercury. This principle may be applied right through the sun's aetherial electro-magnetic field, until we come to the mean distance of Neptune, which is 2,780,000,000 miles, and there the density of the Aether would be less than at any other part of the aetherial electro-magnetic field around the sun.