Editing Cosmic ray (section)

===Discovery===
[[File:Pacini measurement.jpg|thumb|left|Pacini makes a measurement in 1910.|upright=0.8]]
In 1909, [[Theodor Wulf]] developed an [[electrometer]], a device to measure the rate of ion production inside a hermetically sealed container, and used it to show higher levels of radiation at the top of the [[Eiffel Tower]] than at its base.<ref>{{cite journal |last1=Wulf |first1=Theodor |title=Beobachtungen über die Strahlung hoher Durchdringungsfähigkeit auf dem Eiffelturm |journal=Physikalische Zeitschrift |date=1910 |volume=11 |pages=811–813 |url=https://babel.hathitrust.org/cgi/pt?id=njp.32101054770845&view=1up&seq=349&skin=2021 |trans-title=Observations of radiation of high penetration power at the Eiffel tower |language=German}}</ref> However, his paper published in ''[[Physikalische Zeitschrift]]'' was not widely accepted. In 1911, [[Domenico Pacini]] observed simultaneous variations of the rate of ionization over a lake, over the sea, and at a depth of 3 metres from the surface. Pacini concluded from the decrease of radioactivity underwater that a certain part of the ionization must be due to sources other than the radioactivity of the Earth.<ref>{{cite journal|author=Pacini, D.|year=1912|title=La radiazione penetrante alla superficie ed in seno alle acque|journal=[[Il Nuovo Cimento]]|volume=3|issue=1|pages=93–100|doi=10.1007/BF02957440|arxiv=1002.1810|bibcode=1912NCim....3...93P|s2cid=118487938}}: Translated with commentary in
{{cite journal|author=de Angelis, A.|year=2010|title=Penetrating Radiation at the Surface of and in Water|journal=[[Il Nuovo Cimento]]|volume=3|issue=1|pages=93–100|arxiv=1002.1810|bibcode=1912NCim....3...93P|doi=10.1007/BF02957440|s2cid=118487938}}</ref>

In 1912, [[Victor Francis Hess|Victor Hess]] carried three enhanced-accuracy Wulf electrometers<ref name=HessNobelPresSp>{{cite web|url=http://nobelprize.org/nobel_prizes/physics/laureates/1936/press.html|title=Nobel Prize in Physics 1936 – Presentation Speech|publisher=Nobelprize.org|date=10 December 1936|access-date=27 February 2013}}</ref> to an altitude of 5,300&nbsp;metres in a [[hot air balloon|free balloon]] flight. He found the ionization rate increased to twice the rate at ground level.<ref name=HessNobelPresSp/> Hess ruled out the Sun as the radiation's source by making a balloon ascent during a near-total eclipse. With the moon blocking much of the Sun's visible radiation, Hess still measured rising radiation at rising altitudes.<ref name=HessNobelPresSp/> He concluded that "The results of the observations seem most likely to be explained by the assumption that radiation of very high penetrating power enters from above into our atmosphere."<ref>{{cite journal|author=Hess, V.F. |author-link=Victor Francis Hess |year=1912 |title=Über Beobachtungen der durchdringenden Strahlung bei sieben Freiballonfahrten |trans-title=On observations of penetrating radiation during seven free balloon flights |language=de |journal=Physikalische Zeitschrift |volume=13 |pages=1084–1091 |arxiv=1808.02927}}</ref> In 1913–1914, [[Werner Kolhörster]] confirmed Victor Hess's earlier results by measuring the increased ionization enthalpy rate at an altitude of 9&nbsp;km.<ref>{{cite journal |last1=Kolhörster |first1=Werner |title=Messungen der durchdringenden Strahlung im Freiballon in größeren Höhen |journal=Physikalische Zeitschrift |date=1913 |volume=14 |pages=1153–1156 |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015021268936&view=1up&seq=1285&skin=2021 |trans-title=Measurements of the penetrating radiation in a free balloon at high altitudes |language=German}}</ref><ref>{{cite journal |last1=Kolhörster |first1=W. |title=Messungen der durchdringenden Strahlungen bis in Höhen von 9300 m. |journal=Verhandlungen der Deutschen Physikalischen Gesellschaft |date=1914 |volume=16 |pages=719–721 |url=https://babel.hathitrust.org/cgi/pt?id=coo.31924056112083&view=1up&seq=741&skin=2021 |trans-title=Measurements of the penetrating radiation up to heights of 9300 m. |language=German}}</ref>[[File:HessKol.jpg|thumb|Increase of ionization with altitude as measured by Hess in 1912 (left) and by Kolhörster (right)]] Hess received the [[Nobel Prize in Physics]] in 1936 for his discovery.<ref>{{cite web|author=Hess, V.F.|author-link=Victor Francis Hess|year=1936|title=The Nobel Prize in Physics 1936|publisher=[[The Nobel Foundation]]|url=http://nobelprize.org/nobel_prizes/physics/laureates/1936/index.html|access-date=11 February 2010}}</ref><ref>{{cite web|author=Hess, V.F.|author-link=Victor Francis Hess|year=1936|title=Unsolved Problems in Physics: Tasks for the Immediate Future in Cosmic Ray Studies|series=Nobel Lectures|publisher=The Nobel Foundation|url=http://nobelprize.org/nobel_prizes/physics/laureates/1936/index.html|access-date=11 February 2010}}</ref>
[[File:Hessballon.jpg|thumb|Hess lands after his balloon flight in 1912.]]