ABSTRACT
Modern scientists and developers might misconceive the undertaking of the professor as a typical end-of-the-week Friday afternoon gambling session. However, Roentgen’s well-known custom of rigorously planning his experiments tells a different story. Shadows of objects became visible when the residual gas pressure was in the optimal range, and the voltage from the inductor reached a level of some dozen kilovolts. The spark gap emitted an audible crackle. The shadows on the paper screen pointed to the glass tube as the source of the unknown agent rather than electric leads or other items. X-rays emerged from the location on the glass wall that showed the brightest fluorescence, the area where cathode rays, later identified by Thomson as streams of electrons, hit. Neither ultraviolet radiation nor cathode rays could be the invisible agent that activated the scintillator, because he had screened the light and the cathode rays from the tube with a sheet of black cardboard.
