Again, Lord Kelvin in his Address to the British Association, 1901, on the "Clustering of Gravitational Matter in any part of the Universe," states: "Aether we relegate to a distinct species of matter which has inertia, etc." Aether, therefore, according to Tyndall, "is a substance or medium endowed with inertia, and capable, in accordance with Newton's Laws of Motion, of imparting its motion to other substances." If, however, the Aether is frictionless, as has generally been supposed, then it cannot possess inertia, because to the extent that a body possesses inertia, to that extent it is opposed to being frictionless. Inertia is really the equivalent of mass, or the amount of matter measured by gravity, and if Aether possesses mass in any sense at all, as it must do if it is matter, then, possessing mass or weight, it must offer resistance to any body moving through it, and to that extent cannot be frictionless. To suppose that the Aether is frictionless, and yet possesses inertia, is to suppose something altogether opposed to all the Rules of Philosophy and therefore of experience. I have already shown that a frictionless medium is opposed to all philosophy and experience, and is an anomaly in the universe. On the strictly philosophical assumption that Aether is matter, and therefore atomic and gravitative, the whole question of the inertia of the Aether is reduced to one of common experience. It is, at least to my mind, difficult to conceive of mass without weight or without atomicity, and yet that is the unphilosophical position of the present state of science in relation to the Aether. In other words, while the Aether is supposed to possess inertia, which is dependent upon mass, as measured by gravity, yet it is supposed not to be gravitative, that is, that the mass of the Aether has no weight at all, and therefore is not mass, which assumption contradicts itself. From Arts. 44 and 45, however, we have seen, to be strictly philosophical, that Aether must be atomic and also gravitative. It can now be easily understood how it can possess inertia like any other matter, and is therefore capable of receiving motion from other matter, and also of imparting that motion to other matter. So that, wherever there is motion of any kind in the Aether, either in the form of vibratory motion as heat, or undulatory motion as light, or rotatory motion as electricity, those motions will affect adjoining matter in the same way that the motion of any other moving matter affects any body with which it comes into contact.