Man’s ability to lengthen the ultra-violet end of the spectrum is limited by his capacity to provide a diffraction grating, or a mineral prism, which can split up light-waves of increasingly greater frequency (or shortness). The width of a grating space (a fine line on speculum metal, which acts as a minute mirror) must be comparable to the wave length of the light. Previous to the discoveries of Prof. Max von Laue in Munich (now in Zurich), and Prof. William Henry Bragg, of the University of London, no grating or other material was known whose spaces were as small as the wave length of X-rays. Laue conceived the brilliant idea that the regular arrangement of the atoms in a crystal might serve the purpose. They did. Bragg, and later his son, Prof. W. L. Bragg, of the University of Manchester, followed up the work of Laue with results of immeasurable value to science. A very important relation between the atomic number of an element and its X-ray spectrum was discovered by the brilliant young English physicist, H. G. T. Moseley (1888-1915), in his 26th year, a year before his death by a Turkish bullet at the Dardanelles. While analyzing the characteristic X-rays which are given off when any kind of substance is bombarded with cathode rays, Moseley found that the atoms of all the different substances emit radiations or groups of radiations which are extraordinarily similar, but which differ in their wave lengths as we proceed from substance to substance; the frequencies (wave lengths) change by definite steps as one progresses from elements of lower to elements of higher atomic weights. Through Moseley’s epoch-making discovery we now know that each of the 92 elements, from hydrogen to uranium, is built up by successive additions of one positive charge (proton) and one negative electron, and that the atomic numbers—from 1 to 92—correspond to the number of protons and electrons in each successively heavier (and more complex) atom. FOOTNOTES: [1] This phase of our subject can only be alluded to in this little book. For an authoritative yet easily understood exposition of the subject, see Bragg, W. H. and W. L., “X-Rays and Crystal Structure”; also Kaye, G. W. C., “X-Rays”; and, for more advanced reading, deBroglie, Maurice, “X-Rays”. CHAPTER II CURATIVE VALUE OF X-RAYS In my Little Blue Book on Radium (No. 1000), it is shown that the “emanation” and the “gamma rays” of radioactive substances are being used to great advantage in our hospitals, but that certain dangers to the patient’s normal cells attended employment of these radiations. It is gratifying to note that successful X-ray treatments are now being given in cases of cancer, rays being produced—under high-tension currents—that are almost identical with the gamma rays of radium.