To be consistent, therefore, we must either cease to call Aether matter, or else admit that Aether, like all other matter, is gravitative. It is absolutely impossible to be strictly logical and admit that Aether is matter, and not to admit that it is subject to the most universal law that governs matter, as the Law of Gravitation distinctly states that "every particle or atom of matter attracts every other particle." This universal law in view of a gravitationless Aether would have to be amended to "Some particles of matter attract some other particles." Thus the universal Law of Gravitation ceases at once to be a universal law, and such a result is opposed to all experience and experiment. Again, let us apply our third Rule of Philosophy to this supposed gravitationless Aether, and see what the result is. Our third rule states, that any hypothesis put forward must satisfactorily account for the phenomena sought to be explained and accounted for. The Aether was conceived in order to explain the phenomena of light, and one of the properties it was conceived to possess was elasticity, yet that very conception was devoid of the most fundamental property of matter, without which there is no elasticity, that is, that it was not atomic. I have already shown in Art. 44, that Aether is atomic, and therefore there is given to the Aether a structure which is capable of exhibiting elasticity, inertia, density, and even Gravitation, while at the same time, the conception is fully in harmony with philosophical reasoning and Newton's Rules of Philosophy. Let us consider the question whether Aether is, or is not gravitative, from another aspect. For several hundred years, the physical cause of Gravitation has been outstanding, while the world has held the conception that Aether is a gravitationless and frictionless medium. The earth has been rolling on in her orbit year in, year out, together with all the other planets in their annual march round the sun, and yet through all that time no one has been able to suggest, or give any satisfactory or adequate physical explanation, as to what moves the earth along. I am fully aware that Newton suggested and proved, that it was because of the Law of Gravitation. But I look upon that as a mathematical explanation and not as a physical one. Now I venture to predict this, that on the assumption of a gravitationless medium, the physical explanation so longed for will always be outstanding, as a gravitationless Aether is synonymous with a frictionless medium, and so long as we admit that there is a frictionless medium, so long will the physical cause of Gravitation, and therefore the physical cause of all the movements of the planets and comets, be outstanding and unexplained.