efused the calls until the universi- centimeters that Lenard had found y of Wurzburg offered him the to be the maximum distance for Directorship of their Physical Insti- which cathode rays maintain their tute. In 1894 he was elected Rector power to induce fluorescence. Roent- at Wurzburg. In his inaugural ad- gen recognized the effect as wor dress, given the year before his dis- thy of his undivided attention and covery of X rays, Roentgen stated devoted the next six weeks to its that the" university is a nursery of uninterrupted study scientific research and mental edu- Historians have speculated about cation"and cautioned that " pride in why Roentgen was the first to rec- Philip Lenard, 1862-1947.(Courtesy of one's profession is demanded, but not ognize the significance of this effect. Ulstein Bilderdienst and the A/P Niels professional conceit, snobbery, or The equipment, a cathode ray tube Bohr Library) academic arrogance, all of which and a fluorescing screen, had been in grow from false egoism. " use for decades. In 1894 J Thomson Roentgens pride could rest in the had seen fluorescence in german over forty papers he had published glass tubing several feet from the from Strasbourg, Giessen, and discharge tube. Others had noted Wurzburg. These early interests fogged photographic plates. But anged widely-crystals, pyroelec- before Lenard's work, the object of trical and piezoelectrical phenomena, study was always the effects inside and the effects of pressure on liquids the tube itself, and stray ultra-ultra- and solids-but did not yet include violet light could be used to explain electrical discharges in gases. He had the fogging of photographic plates. taken his turn at measuring the Lenard's great interest was in prov- Demonstration by Crookes that cathode specific heat ratios of gases using a ing, in contradiction to the British, rays travel in straight lines: a)cathode sensitive thermometer of his own the ethereal nature of cathode rays, b)aluminum cross and anode d)dark making. He was an exact experi- and he was the first to study the shadow c) fluorescent image menter who often made his own apparatus-a skill learned during his training as an engineer in Zurich- and he was able to measure ex tremely small effects, surpassing 2b even Faradays measurement of the N rotation of polarized light in gas oentgen turned to a new interest in October of 1895: the study of cath- ode rays. In the course of repeating the experiments of Hertz and Lenard, he happened to notice a glowing flu orescent screen set off quite some distance from the cro jokes was operating. The screen sat much farther away than the six to eight Quoted in"Wilhelm Conrad Roentgen, Dictionary of Scientific Biography (New York: Scribners, 1975), p. 531 BEAM LINE 13BEAM LINE 13 refused the calls until the Universi￾ty of Würzburg offered him the Directorship of their Physical Insti￾tute. In 1894 he was elected Rector at Würzburg. In his inaugural ad￾dress, given the year before his dis￾covery of X rays, Roentgen stated that the “university is a nursery of scientific research and mental edu￾cation” and cautioned that “pride in one’s profession is demanded, but not professional conceit, snobbery, or academic arrogance, all of which grow from false egoism.”* Roentgen’s pride could rest in the over forty papers he had published from Strasbourg, Giessen, and Würzburg. These early interests ranged widely—crystals, pyroelec￾trical and piezoelectrical phenomena, and the effects of pressure on liquids and solids—but did not yet include electrical discharges in gases. He had taken his turn at measuring the specific heat ratios of gases using a sensitive thermometer of his own making. He was an exact experi￾menter who often made his own apparatus—a skill learned during his training as an engineer in Zurich— and he was able to measure ex￾tremely small effects, surpassing even Faraday’s measurement of the rotation of polarized light in gases. Roentgen turned to a new interest in October of 1895: the study of cath￾ode rays. In the course of repeating the experiments of Hertz and Lenard, he happened to notice a glowing flu￾orescent screen set off quite some distance from the Crookes’ tube he was operating. The screen sat much farther away than the six to eight centimeters that Lenard had found to be the maximum distance for which cathode rays maintain their power to induce fluorescence. Roent￾gen recognized the effect as wor￾thy of his undivided attention and devoted the next six weeks to its uninterrupted study. Historians have speculated about why Roentgen was the first to rec￾ognize the significance of this effect. The equipment, a cathode ray tube and a fluorescing screen, had been in use for decades. In 1894 J.J. Thomson had seen fluorescence in German￾glass tubing several feet from the discharge tube. Others had noted fogged photographic plates. But before Lenard’s work, the object of study was always the effects inside the tube itself, and stray ultra-ultra￾violet light could be used to explain the fogging of photographic plates. Lenard’s great interest was in prov￾ing, in contradiction to the British, the ethereal nature of cathode rays, and he was the first to study the Demonstration by Crookes that cathode rays travel in straight lines: a) cathode; b) aluminum cross and anode; d) dark shadow; c) fluorescent image. Phillip Lenard, 1862–1947. (Courtesy of Ullstein Bilderdienst and the AIP Niels Bohr Library) *Quoted in “Wilhelm Conrad Roentgen,” Dictionary of Scientific Biography (New York: Scribner’s, 1975), p. 531