Cathode ray
They were first observed in 1859 by German physicist Julius Plücker and Johann Wilhelm Hittorf,[1] and were named in 1876 by Eugen Goldstein Kathodenstrahlen, or cathode rays.
[2][3] In 1897, British physicist J. J. Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, which was later named the electron.
Cathode-ray tubes (CRTs) use a focused beam of electrons deflected by electric or magnetic fields to render an image on a screen.
Modern vacuum tubes use thermionic emission, in which the cathode is made of a thin wire filament which is heated by a separate electric current passing through it.
After the invention of the vacuum pump in 1654 by Otto von Guericke, physicists began to experiment with passing high voltage electricity through rarefied air.
[4] In 1857, German physicist and glassblower Heinrich Geissler sucked even more air out with an improved pump, to a pressure of around 10−3 atm and found that, instead of an arc, a glow filled the tube.
The explanation of these effects was that the high voltage accelerated free electrons and electrically charged atoms (ions) naturally present in the air of the tube.
When they struck atoms in the glass wall, they excited their orbital electrons to higher energy levels.
Later researchers painted the inside back wall with fluorescent chemicals such as zinc sulfide, to make the glow more visible.
In 1869, German physicist Johann Hittorf was first to realize that something must be traveling in straight lines from the cathode to cast the shadows.
German scientists Eilhard Wiedemann, Heinrich Hertz and Goldstein believed they were "aether waves", some new form of electromagnetic radiation, and were separate from what carried the electric current through the tube.
The debate was resolved in 1897 when J. J. Thomson measured the mass of cathode rays, showing they were made of particles, but were around 1800 times lighter than the lightest atom, hydrogen.
Philipp Lenard also contributed a great deal to cathode-ray theory, winning the Nobel Prize in 1905 for his research on cathode rays and their properties.
A more reliable and controllable method of producing cathode rays was investigated by Hittorf and Goldstein,[citation needed] 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.
Ernest Rutherford demonstrated that rays could pass through thin metal foils, behavior expected of a particle.
This was evidence that the beams were composed of particles because scientists knew it was impossible to deflect electromagnetic waves with an electric field.
(Alexander Reid, who was Thomson's graduate student, performed the first experiments but he died soon after in a motorcycle accident[8] and is rarely mentioned.)
