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before him — Michael Faraday, Johann Heinrich Wilhelm Geissler, Johann Wilhelm Hittorf, and William Crookes, for example — as well as the more current work of fellow German scientist Philipp Lenard. These scientists and others had studied luminescence in gases and solids using a partially evacuated tube, popularly known as a crookes tube (Glasser 1934). This was typically a pear-shaped glass tube, containing two electrodes. When a high voltage was put between the electrodes, the positively charged ions from the gas bombarded the negative electrode, causing the release of electrons, then called cathode rays. The electrons caused luminescence in the partial gas filling, in the glass walls of the tube, or in other materials placed in their path. Discovery Röntgen had a covered tube in his darkened laboratory when he energized the cathode ray tube and noticed luminescence from a barium platino- cyanide screen on a table about 2 m (7 ft) away. The luminescence was definitely associated with the tube, turning on only when the tube was energized. Röntgen knew the effect could not be cathode rays, because they penetrate only a short distance in air. He was intrigued; he investigated. He quickly learned about the penetrating power of these new rays; they penetrated paper, wood, metal, and f lesh. The rays made shadow pictures on f luorescent screens and on film. Nevertheless, he was skeptical about his discovery. He knew he must report his findings and obtain feedback from fellow scientists. Because the new rays darkened a photographic plate, he could take pictures and share them with others. One of these early pictures in December 1895 was a 15 min exposure showing the bones in the hand of his wife, Bertha. He recognized that he must publish his results so that they could be shared with others in the scientific community. His first technical paper on X-rays, “On a New Kind of Rays: A Preliminary Communication,” was published in the annals of the Würzburg Physical Medical Society in December 1895 (Röntgen 1895).

Fame Röntgen was apprehensive as he sent reprints of his article and pictures to colleagues in January 1896, but he probably had no idea of what was in store for him. There was tremendous interest in his new rays, both from the scientific community and the general public. Once the news was out, there were many offers of honors, lectures, and visits. However, Röntgen turned down most such overtures. One he could not turn down, however, was a call from his own university. In January 1896, he lectured on his discovery before the Physical Medical Society in Würzburg and gave the first public demonstra- tion before an overf lowing audience. The image of Röntgen’s lecture was captured in a 1961 painting (Figure 14). During the lecture, Röntgen radiographed the hand of his fellow university professor and well-known anatomist, Albert von Kolliker. Kolliker was so excited by the discovery that he announced that the new rays should be called roentgen rays , as they are still called in Europe and within the medical community. The lecture and demonstration were greeted with enthusiastic applause. It was Röntgen’s only formal public lecture on X-rays.

Figure 14 Röntgen demonstrates X-rays in 1896.

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Part 2