Glowing tubes, cathode rays, the electron, and vacuum valves.
How gases are made to conduct, the discharge tube, sparking potential and Paschen's law, the glows and dark spaces at falling pressure and their explanation, cathode rays and canal rays, Thomson's e/m and Millikan's oil-drop experiments, thermionic emission and the Richardson–Dushman equation, the diode valve and rectification, and the triode and its use as an amplifier.