Television

A television picture is a lie the eye agrees to believe. There is never a whole image anywhere in the system — only a single spot of brightness racing across a screen, line after line, thirty times a second, too fast for the eye to catch it moving. The trick is to read a scene the same way at the sending end: measure its brightness one point at a time, in a fixed zigzag path, turn each reading into a radio signal, and steer an identical spot in perfect step at the receiver. Get the two spots marching together and a face appears out of pure timing.

Radio had already put sound through the air to everyone at once. Television did the same for sight — the first medium to carry live moving pictures into the home, and for most of the twentieth century the dominant one. It reshaped politics, war, sport, and memory: hundreds of millions watched the same event at the same instant, from moon landings to coronations, sharing an experience that no earlier technology could deliver.

Electronic scanning — a beam of electrons painting an image line by line under magnetic control — became the cathode-ray tube, the display of nearly every screen, oscilloscope, and radar set until flat panels arrived. The camera tube taught engineers to turn light into a timed electrical signal, the ancestor of the video sensor in every phone. And the discipline of slicing a picture into a scanned raster of discrete points is exactly the logic that digital imaging and video compression inherited whole.