The Spectator., 1914-12-15
THE X-RAY.

The discovery of the X-ray burst upon the world without the slightest warning and completely astounded even the most astute and learned scientists of the time. But we can now see that it was the perfectly logi- cal sequence of a long series of dis coveries, following numberless experi- ments by many individuals with a scientific toy known as the Geissler tube. Geissler had demonstrated the peculiar behavior of electric dis charges through different gases con- fined in sealed tube and under vari- ous degrees of vacuum, whereby the spark became a more or less steady stream.
 Following Geissler, Sir William Crookes became the chief investigator along these lines, and by means or miniature wind-wheels and turbines in his improved tubes, now known as Crookes tubes, demonstrated that the current of electricity flowing from the negative pole and known as the cath ode stream could be transformed into kinetic energy. Radiant matter was the term used by Crookes to describe the highly rarefied gas, or ultra gase- ous matter" which he found to pro duce certain peculiar mechanical and luminous effects when charge of high l potential electricity was passed 1 through it.
 As with all new thoughts. the idea was fercely attacked by many of the scientific men of the time, who strenu- ously argued against it and endeavored to prove that both the theory and the | demonstrations amounted to nothing l But few choice spirits pressed on.
 Lenard demonstrated that the cath ode stream could be detected outside the tube as we'll as within 1t and that it could be deflected or attracted by a magnet A professor of physics in the University of Wurzburg, in Ba- varia. w K Roentgen. noted in 1895 | that substances such as potassium platinocyanide became luminous when | brought near to a tube exhausted to vacuum so that the glass was brightly l phosp phorescent. About this time also he noticed that a large number of pho- tographic plates placed within range of a Crookes tube with which he was experimenting were logged, although they were simply protected from light by the usual light-tight plate holders. and he began to suspect connection between the two phenomena. A few more experiments and the idea crystal lized-he viewed his own bones through the flesh of his hand and knowledge of the new ray was born November s, 1895.
 Because the ray which produced fuorescence showed him the bones in the living human body, affected photo graphic plates while inclosed in light tight boxes and could not be reflect ed refracted nor defected by mag net, Roentgen knew that he had dis covered a new and unbroken ray and he therefore called 1t the X-ray.
 It was Domenici who discovered that the X-rays as they emanate from the tube are in fact mixture of rays of different qualities, so the minds of investigators were turned to still fur ther improving the X-ray tube. Mean time the radioactive elements were discovered and the electron was dem onstrated in 1899.
 It may be asked how it is possible to distinguish between such radiations of different wave lengths This is achieved through demonstrating by means of photography, or fuorescent screen. or the electroscope, the "pene- trating power" or hardness" of the short wave emanations after travers- ing various thicknesses of medium which absorbs X-rays, such as, for ex- ample, aluminium. The shorter the wave length the harder" the ray. and the harder" the ray the greater its penetrating power. Soddy has dem onstrated the penetration of one-half inch steel, This discovery of the com plex character of the X-ray tube ema- nations and those from radiant sub- stances in general created the need of a system for designating the differ ent rays, and they have therefore been named alpha. beta, gamma from the Greek alphabet corresponding with our a, b and c.
 The original X-ray tube shot the rays from the cathode directly against the glass at the opposite end; subse- quently n metal target known as the anti-cathode was introduced to re- ceive the rays, but the bombardment from the stream of corpuscles or cleo. irons was so intense that the target was soon raised to white heat. and it would become necessary to stop the action. For these and other reasons which we will discover later radium with its gamma rays seemed to offer certain advantages over the X-ray tube. but recently Dessauer of Frank fort.on-Main has perfected tube by which hN can produce rays practically identi with the gamma ray from radium mesothorium, the ratio of