To meet the requirements of the case, Science says that The Universal Ether must be Substance infinitely more rare and evanescent than the finest gas or vapor known to Science, even in its rarest condition. It must convey Heat in the manner of an infinitely Solid body--and yet it must not be a Solid. It must be transparent and invisible. It must be Frictionless, and yet Incompressible. It cannot be a Fluid. It cannot have Attraction for Substance, such as all Substance has. Nor can it have Weight--that is, it is not subject to Gravitation. It is beyond the reach of any known scientific instrument, even of the greatest power, and it refuses to register itself in any way, either to senses or instruments. It cannot be known "of itself," but may only be recognized as existent by the "things" for which it acts as a medium or transmitting agent. It must convey Energy and Motion, yet it must not take up any part of either from the Matter in its midst. It must not absorb any of the Heat, Light or Electricity. It must fill up the spaces between the worlds, as well as the most minute space between the Molecules, Atoms and Corpuscles, or any other minute particle of Substance, either known by name to Science now or which may be discovered or imagined later as a necessity of some conception regarding the nature of Substance. In short, The Universal Ether, in order to do the things attributed to it, must be more solid than Solids; more Vapor-like and Gas-like than Vapor or Gas; more fluid than Fluids; infinitely less rigid than steel, and yet infinitely stronger than the strongest steel. It must be a substance having the qualities of a vacuum. It must be continuous and not composed of Particles, Atoms or Molecules. It must be an "everything" in some respects, and yet a "nothing" in others. It must not be Substance, and yet it must carry Substance within its ocean of dimensions, and, besides, interpenetrate the most minute space between the particles of Substance. It must not be Energy or Force, and yet Science has been considering Energy and Force as but "interruptions of rest" or "agitations" within, and of, itself.