The Cathode-Ray Tube

Every instrument before 1897 turned an electrical quantity into the position of a mechanical pointer, and a pointer has mass. That mass means inertia, and inertia means a meter cannot follow anything that changes quickly — a moving-coil movement is hopeless above a few tens of hertz. Ferdinand Braun’s tube replaced the pointer with a beam of electrons, which has almost no mass at all and can therefore be deflected as fast as you can change the voltage doing the deflecting. Suddenly a waveform could be SEEN rather than inferred, and every argument about what a circuit was really doing became settleable by looking. The same tube, given a way to build up a picture line by line, became television. This blueprint is gated because a cathode-ray tube combines high vacuum in a glass envelope with several kilovolts, and both deserve respect.