We have therefore arrived at exactly the same result that Newton arrived at, except that he had to introduce a third factor, viz. the Parallelogram of Forces, while we have produced the result by a simpler method, which, according to his own rules, is more philosophical, as all effects are produced by the simplest causes, as Newton himself stated in Rule 1. Thus it is the rotatory electro-magnetic Aether currents that urge the planets round the sun; and, as will be shown later, it is the same Aether currents in combination with the other motions that give rise to the physical cause of Kepler's Laws. It is the electro-magnetic Aether currents that produce the regular decrease in the velocity of the planets in their orbits, because of the regular decrease of the mass and velocity of the Aether currents themselves. We have now a physical cause as well as a mathematical explanation of the decrease of the velocity of a planet in its orbit, which physical cause is in perfect harmony with all philosophical rules. The following table shows the gradual decrease in the velocity of each planet as the various planets recede from the sun-- MEAN PERIOD OF VELOCITY IN DISTANCE. REVOLUTION. ORBIT PER HOUR. Mercury 35,900,000 87.9 days Venus 67,000,000 224.7 77.000 Earth 92,700,000 365.2 66.500 Mars 141,000,000 686.9 53.000 Jupiter 482,000,000 4,332.6 28.744 Saturn 884,000,000 10,759. 21.221 Uranus 1,780,000,000 30,687. 14.963 Neptune 2,780,000,000 60,127. 11.958 ART. 100. _Aether and Third Law of Motion._--We have seen (Art. 16) that action and reaction are equal and opposite, and that it is true of the centripetal force in its application to all matter throughout the universe. If, therefore, the centrifugal force is the exact opposite of the centripetal force, then the Third Law of Motion should equally hold good in relation to that force also. We have, therefore, to form a physical conception of the application of the third law of motion, as it relates to the centrifugal force. As we have already learned, this force is due to the universal electro-magnetic Aether, which being gravitative, surrounds all atoms and molecules that may exist throughout the whole universe. It can readily be seen, therefore, that if the Aether surrounds every atom and molecule, then each atom repels another atom or molecule when the two forces are in equilibrium with exactly the same intensity with which the atom and molecule attract each other. But the centrifugal force in each case is due to the pressure of the Aether, which presses always proportionately to the density of the Aether surrounding the atom or molecules, as suggested by Professor Challis.