We have seen also that Radiant Energy could be communicated or transmitted from one body of Substance to another. And that the communication of transmission might be accomplished not only by close contact of the bodies, but by "waves" of some sort which were caused in some "medium" (the Ether) by the vibrations of the Particles of the body, and which "waves," when they reached the other body, were transformed into vibrations of the Particles corresponding to those manifested in the first body. The idea has been illustrated by the sending telephone, the sound waves in the diaphragm of which were transformed into waves of the Electric current, and thus passing along the wires were transformed again into sound-waves by the diaphragm of the receiving instrument. We have seen, also in the preceding chapter, that the medium by which these vibrations were transferred, transmitted, or communicated, might be supposed to be Mind, the operation being akin to Thought-transference. Now let us examine into the workings of the matter. In the first place, we assume a certain state of vibration, existing in a certain body of Substance--Heat, or Electricity for instance (either illustration will answer.) Another body of Substance is brought in close contact with the first body, and the vibrations of Energy pass on to the second, not by "waves" but by a seeming actual passing of vibrations without the need of intervening "waves." This, Science calls transmission by Conduction, the theory being that the particles rapidly "pass on" the vibrations from one to another. Convection or conduction along other forms of Substance, such as hot-air, hot-water-steam, etc., is but a variation of the above, as Substance is the medium in both cases. The third form of transmission is by Radiation, whereby the vibrations are transmitted by "waves" in some medium other than Substance (according to the theory), as we have described in a preceding paragraph, as well as in previous chapters. As a matter of fact, a careful analysis of the matter will show that even in the "Conduction" of the most solid Substance, there must be a "_medium not Substance_" between the Particles of the Substance, _for the Particles always have Space between them_--this being true of the Particles of Air, as well as those of Iron. _So there is always Space to be traversed by a "medium not Substance."_ But we need not stop to split-hairs regarding this question, for the general explanation will explain this also.