English: Drawing of the first cathode ray tube invented by German scientist Ferdinand Braun in 1897. It was a cold cathode tube, developed from the Crookes tube and so did not have a heated filament to produce electrons. Instead it produced electrons by ionization of residual gas in the tube with a high voltage. The tube contains a platinum cathode electrode (right end), an anode electrode consisting of an open tube in the neck to focus the electrons into a narrow beam (center right), a pair of flat deflection plates (center left), and a paper screen (left) painted on the inner side with a fluorescent chemical like zinc sulfide or calcium tungstate. When a high voltage is applied between the cathode and anode, it creates positive ions which are attracted to the negative cathode. When they strike the cathode they knock out electrons (cathode rays) which are accelerated down the tube to the left, through the anode tube, between the deflection plates, and strike the fluorescent screen at the left end, producing a glowing spot. If a second voltage is applied between the deflection plates the electron beam will be repelled by the positive plate and attracted toward the negative plate, so the spot on the end screen will move toward the positive plate.