Editing Electron diffraction (section)

=== Electrons in vacuum ===
{{See also|Cathode ray|Electron#History|label 2=History of the electron}}
{{anchor|Figure 3}}{{multiple image
| direction         = vertical
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| width             = 200
| image1            = Katódsugarak mágneses mezőben(1).jpg
| image2            = Katódsugarak mágneses mezőben(2).jpg
| footer            = Figure 3: A Crookes tube – without emission (top, grey background) and with emission and a shadow due to the [[cross pattée]] blocking part of the electron beam (bottom, black background); see also [[Cathode ray | cathode ray tube]]
| alt1              = Image of a Crookes tube when it is not actively being used.
| alt2              = Image of a Crookes tube when it is operating, showing luminescence when the electrons hit the glass walls.
}}

Experiments involving electron beams occurred long before the discovery of the electron; [[wiktionary:ἤλεκτρον|ēlektron]] (ἤλεκτρον) is the Greek word for [[amber]],<ref name="DictOrigins">
{{cite book
 | last = Shipley | first = J.T.
 | title = Dictionary of Word Origins
 | page = 133
 | publisher = [[The Philosophical Library]] | year = 1945
 | isbn = 978-0-88029-751-6
 | url = https://archive.org/details/dictionaryofword00ship/page/133
 | url-access = registration
}}</ref> which is connected to the recording of electrostatic charging<ref name="Lacks">{{Cite journal |last1=Iversen |first1=Paul |last2=Lacks |first2=Daniel J. |date=2012 |title=A life of its own: The tenuous connection between Thales of Miletus and the study of electrostatic charging |url=https://www.sciencedirect.com/science/article/pii/S0304388612000216 |journal=Journal of Electrostatics |language=en |volume=70 |issue=3 |pages=309–311 |doi=10.1016/j.elstat.2012.03.002 |issn=0304-3886|url-access=subscription }}</ref> by [[Thales of Miletus]] around 585 BCE, and possibly others even earlier.<ref name="Lacks"/>

In 1650, [[Otto von Guericke]] invented the [[vacuum pump]]<ref name="Harsch 2007">
{{cite journal
| last=Harsch
| first=Viktor
| date=2007
| title=Otto von Gericke (1602–1686) and his pioneering vacuum experiments
| url=https://pubmed.ncbi.nlm.nih.gov/18018443/
| journal=Aviation, Space, and Environmental Medicine
| volume=78| issue=11
| pages=1075–1077
| doi=10.3357/asem.2159.2007
| issn=0095-6562| pmid=18018443
}}</ref> allowing for the study of the effects of high voltage electricity passing through [[rarefied air]]. In 1838, [[Michael Faraday]] applied a high voltage between two metal [[electrode]]s at either end of a glass tube that had been partially evacuated of air, and noticed a strange light arc with its beginning at the [[cathode]] (negative electrode) and its end at the [[anode]] (positive electrode).<ref name=":1">Michael Faraday (1838) [https://books.google.com/books?id=ypNDAAAAcAAJ&pg=PA125 "VIII.  Experimental researches in electricity. — Thirteenth series.,"] ''Philosophical Transactions of the Royal Society of London'', '''128''' :  125–168.</ref> Building on this, in the 1850s, [[Heinrich Geissler]] was able to achieve a pressure of around 10<sup>−3</sup> [[Atmosphere (unit)|atmospheres]], inventing what became known as [[Geissler tube]]s. Using these tubes, while studying electrical conductivity in [[rarefied]] gases in 1859, [[Julius Plücker]] observed that the radiation emitted from the negatively charged cathode caused phosphorescent light to appear on the tube wall near it, and the region of the phosphorescent light could be moved by application of a magnetic field.<ref name=":3">{{Cite journal|last=Plücker|first=M.|date=1858|title=XLVI. Observations on the electrical discharge through rarefied gases|url=https://doi.org/10.1080/14786445808642591|journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science|volume=16|issue=109|pages=408–418|doi=10.1080/14786445808642591|issn=1941-5982|url-access=subscription}}</ref>

In 1869, Plücker's student [[Johann Wilhelm Hittorf]] found that a solid body placed between the cathode and the phosphorescence would cast a shadow on the tube wall, e.g. [[#Figure 3|Figure 3]].<ref name="Martin 1986">{{Citation |last=Martin |first=Andre |title=Advances in Electronics and Electron Physics, Volume 67 |pages=183–186 |year=1986 |editor-last=Hawkes |editor-first=Peter |contribution=Cathode Ray Tubes for Industrial and Military Applications |publisher=Academic Press |isbn=9780080577333}}
</ref> Hittorf inferred that there are straight rays emitted from the cathode and that the phosphorescence was caused by the rays striking the tube walls. In 1876 [[Eugen Goldstein]] showed that the rays were emitted perpendicular to the cathode surface, which differentiated them from the incandescent light. [[Eugen Goldstein]] dubbed them [[cathode ray]]s.<ref>{{Cite book |last=Goldstein |first=Eugen |url=https://books.google.com/books?id=7-caAAAAYAAJ&pg=PA279 |title=Monatsberichte der Königlich Preussischen Akademie der Wissenschaften zu Berlin |date=1876 |publisher=The Academy |pages=279–295, pp 286 |language=de}}</ref><ref name="Whittaker">
{{cite book
 |last=Whittaker
 |first=E.T.
 |author-link=E. T. Whittaker
 |title=[[A History of the Theories of Aether and Electricity]]
 |volume=1
 |publisher=Nelson |place=London
 |year=1951
}}</ref> By the 1870s [[William Crookes]]<ref name=":2">{{Cite journal |last=Crookes |first=William |date=1878 |title=I. On the illumination of lines of molecular pressure, and the trajectory of molecules |url=https://royalsocietypublishing.org/doi/10.1098/rspl.1878.0098 |journal=Proceedings of the Royal Society of London |language=en |volume=28 |issue=190–195 |pages=103–111 |doi=10.1098/rspl.1878.0098 |s2cid=122006529 |issn=0370-1662|url-access=subscription }}</ref> and others were able to evacuate glass tubes below 10<sup>−6</sup> atmospheres, and observed that the glow in the tube disappeared when the pressure was reduced but the glass behind the anode began to glow. Crookes was also able to show that the particles in the cathode rays were negatively charged and could be deflected by an electromagnetic field.<ref name=":2" /><ref name="Martin 1986" />

In 1897, [[J. J. Thomson|Joseph Thomson]] measured the mass of these cathode rays,<ref>{{Cite journal |last=Thomson |first=J. J. |date=1897 |title=XL. Cathode Rays |url=https://doi.org/10.1080/14786449708621070 |journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science |volume=44 |issue=269 |pages=293–316 |doi=10.1080/14786449708621070 |issn=1941-5982|url-access=subscription }}</ref> proving they were made of particles. These particles, however, were 1800 times lighter than the lightest particle known at that time – a [[hydrogen]] atom. These were originally called ''corpuscles'' and later named electrons by [[George Johnstone Stoney]].<ref>{{Cite journal |last=Stoney | first=George Johnstone |url=https://www.biodiversitylibrary.org/item/51466 |title=Cause of Double Lines in Spectra| journal=The Scientific Transactions of the Royal Dublin Society |year=1891 |volume=4 |location=Dublin |pages=563, pp 583}}</ref>

The control of electron beams that this work led to resulted in significant technology advances in electronic amplifiers and television displays.<ref name="Martin 1986" />