How does the vacuum tube work?

Clear those pesky gas particles out of the way, and negatively charged electrons will leap straight for a positively charged metal plate.
In other words, an electrical current will flow more efficiently through a vacuum, a space free of matter.
This is the basis for the key invention of the early twentieth century: the vacuum tube.
It consists of a glass bulb emptied off air.
On one side is a metal filament, on the other a metal plate.
An electrical charge heats the filament, freezing its electrons, which are attracted to the metal plate.
Applying a current to a small grid placed between the filament and the plate makes it possible to not only transmit but also amplify electrical signals along their path.
This elaboration on the vacuum tube, known as a triode vacuum tube, revolutionized communication in the early twentieth century, enabling long-distance telephony, radio, and TV.