Editing Cathode ray (section)

===Vacuum tubes===
The gas ionization (or [[cold cathode]]) method of producing cathode rays used in Crookes tubes was unreliable, because it depended on the pressure of the residual air in the tube. Over time, the air was absorbed by the walls of the tube, and it stopped working.

A more reliable and controllable method of producing cathode rays was investigated by Hittorf and Goldstein,{{citation needed|date=November 2011}} and rediscovered by [[Thomas Edison]] in 1880. A cathode made of a wire filament heated red hot by a separate current passing through it would release electrons into the tube by a process called [[thermionic emission]]. The first true electronic vacuum tubes, invented in 1904 by [[John Ambrose Fleming]], used this [[hot cathode]] technique, and they superseded Crookes tubes. These tubes didn't need gas in them to work, so they were evacuated to a lower pressure, around 10<sup>−9</sup> atm (10<sup>−4</sup> Pa). The ionization method of creating cathode rays used in Crookes tubes is today only used in a few specialized [[gas discharge tube]]s such as [[krytron]]s.

In 1906, [[Lee De Forest]] found that a small voltage on a grid of metal wires between the cathode and anode could control a current in a beam of cathode rays passing through a vacuum tube. His invention, called the [[triode]], was the first device that could [[amplifier|amplify]] electric signals, and revolutionized electrical technology, creating the new field of ''[[electronics]]''. Vacuum tubes made [[radio broadcasting|radio]] and [[television broadcasting]] possible, as well as [[radar]], talking movies, audio recording, and long-distance telephone service, and were the foundation of consumer electronic devices until the 1960s, when the [[transistor]] brought the era of vacuum tubes to a close.

Cathode rays are now usually called electron beams. The technology of manipulating electron beams pioneered in these early tubes was applied practically in the design of vacuum tubes, particularly in the invention of the cathode-ray tube (CRT) by [[Ferdinand Braun]] in 1897, which was used in [[television set]]s and [[oscilloscope]]s. Today, electron beams are employed in sophisticated devices such as electron microscopes, [[electron beam lithography]] and [[particle accelerator]]s.