rora of the northern sky. After Geissler came Prof. Crookes, and other physicists, who varied their queries in many ingenious ways. They replaced air with other gases, they brought exhaustion to a close approach to perfection, they changed the forms of tubes, the material of the electrode or current carriers, they increased and diminished the intensity of the electric discharge. Most significant of all, they placed fluorescent substances in the tubes, and brought them to vivid radiance.
Now came the epoch-making experiments of Hertz, which demonstrated Maxwell's theory that light is an electro-magnetic phenomenon; that light and electricity move through the same medium and at the same rate. Incidentally, Hertz produced electric waves of new amplitudes, which readily took their way through wooden doors and stone walls. In his vacuum tubes, by their capacity to excite fluorescence, he found that cathode rays penetrated thin sheets of gold, copper, aluminum, and other metals, while, strange to say, they were arrested by the glass of the tube itself. Hertz had abundant reason to think that, given a concordant ray, any substance whatever offers it a free and open path. His researches, cut short by his lamented death, were continued by his assistant. Prof. Paul Lenard, who inserted in the wall of a vacuum tube a tiny window of aluminum. Through this window he succeeded in bringing a cathode ray into the outer air for a distance of some three inches. This ray had all the characteristic tokens of light; it was capable of reflection, refraction, and polarization; it excited fluorescence; it had photographic power.
At this point Prof. Röntgen comes upon the scene, repeats the experiments of Prof. Lenard, and, by such a stroke of good fortune as befalls only the man who earns it, he incloses an excited vacuum tube in blackened cardboard treated with barium platinocyanide. To his delight he discovers that the cathode beam is accompanied by a radiance hitherto unknown, which, although of fluorescent and photographic quality, can scarcely be any form of light. It is not susceptible of refraction or polarization; indeed, it seems as if it might be a stream of infinitesimal particles, since its path is less impeded in a light metal, aluminum, than in a dense one, such as platinum.
Thus culminate the experiments of two companies of students—those devoted to inquiry regarding phosphorescence, and fluorescence and those who investigated the conduct of attenuated gases excited by electricity in vacua. It was many a weary day before the explorers came within sight of each other, before they could join hands on the common ground where all research meets at last in Nature's fundamental unity. At every step but the final one, the observer intent solely on "results" might well have asked, "What's the good?" And yet results of profound import to science and art lay bound up in quests not to be suspected of the most averted wooing of utility. The eye and its wonderful supplement, the photographic plate, now find disclosed what had been deemed forever hidden from sight and light. The physician and the surgeon rejoice in new powers of relieving pain and saving life. The physicist enlarges his conceptions of both matter and energy; he explores by a new path the mazes of molecular structure and motion. Once more it is emphasized that Truth is won only by her disinterested lovers, who, nevertheless, ever find her dowered with wealth greater than fortune-hunter ever dared pursue.