In his paper on "The Velocity of Propagation of Electro-dynamic Action," he gave definite and experimental proof of the hitherto theoretical fact that the velocity of the electric waves in air was exactly the same as that of light, whereas he found that in wires the ratio was not the same, being 4 to 7. This was afterwards found out to be an error by some experiments made at Geneva, when it was discovered that the propagation in wires was the same as in the air. Among his experiments Hertz succeeded in producing very short electric waves of 30 centimetres in length, that is, about one and one-fifth of an inch. According to Maxwell's theory, such a wave ought to behave exactly as a beam of ordinary light does. Hertz proved that this was the case, and published his proofs in his paper on "Electric Radiation." In that paper he showed how such electric radiation was propagated in straight lines, like light, and that it could also be refracted and reflected. Thus he gave to Maxwell's electro-magnetic theory experimental demonstration, and placed it on a solid and immovable foundation. In summing up the results of this theory, we learn, therefore, that Hertz has conclusively proved that electric and magnetic effects are propagated through the Aether which fills all space with the same velocity that light is propagated. Further, he has conclusively proved the identity between light and electricity, and shown that electric and light radiations are essentially one and the same, and that they are both propagated by periodic wave motions of the Aether. Further, he has proved that the velocity of the propagation of light is the same as that of the electro-magnetic waves, and that these waves obey all the laws that govern light and heat. We have here, therefore, experimental proof of the identity between electricity and light, and in Art. 69 we have also proved the identity of light and heat, so that we have now experimental proof that light, heat and electricity are all due to the periodic wave motions and vibrations of the universal Aether, which not only fills all space, but which surrounds every atom and every particle of matter throughout the whole universe. Having established, therefore, the identity of heat, light and electricity, and having proved that they are all due to the periodic wave motions or vibrations of the universal Aether, it must follow as a matter of necessity that wherever in interplanetary or interstellar space we find light or heat waves we must also find electricity. We have already seen that aetherial light waves flood all space, both interplanetary and interstellar space, so that in view of the identity of the aetherial light waves and aetherial electric waves, it follows that the aetherial electric waves flood all space in the same way, and at the same time. Wherever, therefore, we find the light waves, there we find the electric waves also; and it will be impossible to find the one without the other. Thus, throughout all