On this day in 1904, the electrical Vacuum Tube was patented. It revolutionized the world, allowing electrical (as opposed to mechanical) switching. Forty years later, it was the core technology of ENIAC, the world's first computer.
I remember Gray Beards who called these by their old name, "valves". That is a great way to think about them, with electrical current representing flowing water in pipes, and vacuum tubes acting as valves to open and close the pipe. And I remember listening to baseball on our old 5 tube superhet radio.