Radio broadcast .. (1922-30)

AUGUST, 1926 ONE BILLIONTH OF A METER 289 ATOMIC ARRANGEMENT IN SOLID BODIES Is indicated by these atomic models which, of course, are magnified millions of times. From left to right, the models represent the diamond, magnesium, and cakite a crystal were made were arranged in successive tiers, layer cake fashion, each .aver being one molecule deep. Laue thought then, that he might obtain his grating by using the molecular planes of a crystal. At his suggestion, two of his colleagues, Friedrich and Knipping, tried this, and were successful, thereby killing two birds with a single experiment, for not only did they show that the X-rays were actual forms of wave motion, but also that the structure of the crystals was the same as theory had predicted. Three years later, two English physicists, Sir William Bragg and his son W. L. Bragg, collaborated in a very careful and exhaustive series of experiments which culminated, in 1915, in the publication of their book "X-rays and Crystal Structure," and which won for them the joint award of the Nobel prize in physics the same year. From this beginning there developed a new method of studying X-rays. Just as the invention of the spectroscope by Fraun:iol'er, in 1814, enabled scientists to studslight in a way they had been unable to do Before, so did the work of Laue, and the Braggs, which led to the X-ray spectrometer, lead to new methods of studying materials of all kinds as well as the X-rays themselves. Resembling the optical spectroscope, except that a crystal of rock salt replaces the glass prism, many laboratories are now equipped with the X-ray spectrometers as an aid to analysis. In fact, this instrument is now manufactured and carried in stock by one large manufacturer, even though it was only a very few years ago that the first crude form was invented. All solid metals consist of crystals, and so, though the work of Laue and Bragg might not have seemed at that time to have any practical value, it has now opened tremendous possibilities in metallurgical research. The way the atoms and molecules are put together is just as much a characteristic of a metal, and just as important, as its density or melting point; indeed, it is the arrangement of the atoms that determine its physical properties. For example, metals, like human beings, A PORTABLE X-RAY OUTFIT It is used to produce diffraction patterns from crystals. A narrow pencil-like beam of the rays is permitted to pass through the crystal, after which it emerges in a spread-out condition. It is thrown onto the small screen, and is visible as a series of rings of spots show fatigue. A piece of brass may be bent a certain number of times before it breaks, but after it has been bent a hundred times, though it may have its surface polished, and look the same as a fresh piece on the outside, it will not be nearly as strong. By the use of the X-ray spectrometer, however, the difference in the lines in the photograph shows a great difference between the fresh piece and the one that has been fatigued, for the one shows the lines sharp and distinct, while in the other they are hazy and ill defined. Such studies have shown why steel, and various alloys, are stronger than iron, or, perhaps, than any of the metals of which they are made. In such metals as aluminum, silver, copper, and gold, X-ray studies indicate that they consist of closely packed atoms, the plan of the crystal being simply the direction in which the packing is most dense. If it breaks, it does so most easily along one of these planes, but if the metal consists of a mass of crystals, rather than a single one, the planes of weakness lie in different directions, and so it is not so easy to break. Now, if a number of atoms of another substance are mixed with them, as carbon atoms in steel, which apparently tend to fill up the interstices between the iron atoms, they lessen the possibility of the atoms slipping over each other, and the mixture is harder than either iron or carbon. HOW THE X-RAY TUBE WORKS HP HE ether vibrations called X-rays ' result when cathode rays — rapidly moving electrons produced when a hightension electric current is passed through a highly evacuated tube — are suddenly stopped. In the Crookes tube, which produced these rays, and which Rontgen was using when he made his discovery, the cathode rays are stopped by the glass wall of the tube, but early in the history of X-rays it was found that if the cathode rays were focussed on a target of a dense metal, such as platinum, far more copious amounts of the rays were produced. There was another advantage in focussing the rays on such a target, for the X-rays all radiate from a small point, PROF. AND SIR WILLIAM BRAGG Father and son. Professor W. L. Bragg is of the University of Manchester, England, while Sir William is of the Royal Institution, London. They were jointly awarded the much coveted Nobel prize for physics in 1915'