It is, perhaps, only necessary to say, regarding the perfection of the elasticity of the Aether medium, that though it takes from 40,000 to 69,000 waves to complete the space of one inch in extent, yet it is done with such miraculous rapidity, as to speed the distance of 186,000 miles in the short space of a second of time; or, taking the number of Aether-waves to complete an inch as 50,000, its elasticity is such that it makes 50,000 × 186,000 × 12 × 5280 vibrations in one second of time. We have already seen in Art. 39, that according to Boyle and Marriotte's Law, the velocity of a wave-motion, as sound in the air, is determined by the relation of the elasticity of the medium to its density. If the temperature of the atmosphere remains the same, then the _elasticity_ varies in the same proportion as its density. According to Art. 45, Aether is gravitative, and that fact produces different degrees of density in the aetherial atmosphere of an atom or planet or meteor, sun or star; that part of the Aether being densest nearest the central body, and rarer the further we go away from that body. Now the question at once arises, what is the effect of the increased density of the Aether near the body upon the elasticity of the Aether? From the analogy of sound in air, we arrive at the conclusion that Boyle and Marriotte's Law equally applies to the Aether, as it does to the atmosphere of any planet. That is, if the temperature of any stratum or layer of the Aether remains the same, then the elasticity of the aetherial medium in that layer is proportionate to its density, so that while the gravitating property of the Aether makes it denser nearest the central body, the fact that the elasticity is proportionate to the density, does not affect the transmission of any wave-motion. [Footnote 6: _Phil. Trans._, 1802.] ART. 48. _Aether possesses Inertia._--From Art. 40 we have seen that all matter possesses inertia, inertia being that property of matter by which it cannot of itself change its state of motion or of rest. If Aether be matter, therefore, then it must also possess inertia. This property of inertia is already postulated for Aether by scientists, and to that extent is conformable to the Rules of Philosophy. Professor Tyndall, with reference to the inertia of the Aether, writes: "The motion of Aether communicated to material substances throws them into motion. It must be therefore itself a substance. Aether is a substance endowed with inertia, and capable, in accordance with the established laws of motion, of imparting its motion to other substances."[7]