Editing Cathode ray (section)

{{Short description|Beam of electrons observed in vacuum tubes}}
{{More citations needed|date=February 2011}}
[[File:Cyclotron motion smaller view.jpg|thumb|upright=1.2|A beam of cathode rays in a vacuum tube bent into a circle by a [[magnetic field]] generated by a [[Helmholtz coil]]. Cathode rays are normally invisible; in this demonstration [[Teltron tube]], enough gas has been left in the tube for the gas atoms to [[luminescence|luminesce]] when struck by the fast-moving electrons.]]

'''Cathode rays''' are streams of [[electron]]s observed in [[vacuum tube|discharge tube]]s. If an evacuated glass tube is equipped with two [[electrode]]s and a [[voltage]] is applied, glass behind the positive electrode is observed to glow, due to electrons emitted from the [[cathode]] (the electrode connected to the negative terminal of the voltage supply). They were first observed in 1859 by German physicist [[Julius Plücker]] and [[Johann Wilhelm Hittorf]],<ref>{{Citation
 | first =Andre
 | last =Martin
 | contribution =Cathode Ray Tubes for Industrial and Military Applications
 | editor-last =Hawkes
 | editor-first =Peter
 | title =Advances in Electronics and Electron Physics, Volume 67
 | publisher =Academic Press
 | year =1986
 | isbn =9780080577333
 | page =183
 | quote ="Evidence for the existence of "cathode-rays" was first found by Plücker and Hittorf ..."
}}</ref> and were named in 1876 by [[Eugen Goldstein]] ''Kathodenstrahlen'', or cathode rays.<ref>E. Goldstein (May 4, 1876) [https://books.google.com/books?id=7-caAAAAYAAJ&pg=PA279 "Vorläufige Mittheilungen über elektrische Entladungen in verdünnten Gasen"] (Preliminary communications on electric discharges in rarefied gases), ''Monatsberichte der Königlich Preussischen Akademie der Wissenschaften zu Berlin'' (Monthly Reports of the Royal Prussian Academy of Science in Berlin), 279-295. From page 286:  "''13. Das durch die Kathodenstrahlen in der Wand hervorgerufene Phosphorescenzlicht ist höchst selten von gleichförmiger Intensität auf der von ihm bedeckten Fläche, und zeigt oft sehr barocke Muster.''"  (13. The phosphorescent light that's produced in the wall by the cathode rays is very rarely of uniform intensity on the surface that it covers, and [it] often shows very baroque patterns.)</ref><ref>Joseph F. Keithley ''The story of electrical and magnetic measurements: from 500 B.C. to the 1940s'' John Wiley and Sons, 1999 {{ISBN|0-7803-1193-0}}, page  205</ref> 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 tube]]s (CRTs) use a focused beam of electrons deflected by electric or magnetic fields to render an image on a screen.