Subsequently, Hertz showed that the cathodic rays would penetrate thin sheets of metal placed within the tube or bulb; and soon after, Paul Lenard (1894) demonstrated that the cathodic ray could be investigated as well outside of the tube or bulb as within it. He set an aluminum plate in the glass wall of the bulb opposite the cathode. Though ordinary light could not penetrate the aluminum plate, it was readily pierced by the cathodic rays, to a distance of three inches beyond its outside surface. With these rays, thus freed from their inclosure, he produced the same fluorescent effects as had been noted within the bulb, and even secured some photographic effects. These cathodic rays produced no effect on the eye, which proved their dissimilarity to light. Lenard showed further that the cathodic rays outside of the tube could be deflected from their straight course by a magnet, that they might pass through substances opaque to light, and that in so passing they might cast a shadow of objects less opaque, which shadow could be photographed. Now Professor Roentgen came upon the scene. He had been conducting his experiments in Germany, along the same lines as Lenard, and had reached practically the same results as to the penetrative, fluorescent, and photographic effects of the cathodic rays. But he had gone still further, and, in 1896, fairly set the scientific world aflame with the announcement that all the effects produced by Lenard in the limited space of a few inches could also be produced at long distances from the tube, and with sufficient intensity to depict solid substances within or behind other substances sufficiently solid to be impermeable by light. Professor Roentgen claims that his X ray is different from the cathodic ray of Lenard and others, because it cannot be deflected by a magnet. This claim has given rise to much controversy respecting the real nature of the X ray, a controversy not likely to end soon, yet one full of inspiration to further investigation. [Illustration: SCIAGRAPH OR SHADOW PICTURE. By X Ray process.]