Editing X-ray (section)

=== Pre-Röntgen observations and research ===
[[File:Crookes' type discharge tubes Wellcome M0015832EA.jpg|thumb|upright|Example of a [[Crookes tube]], a type of [[discharge tube]] that emitted X-rays]]

X-rays were originally noticed in science as a type of unidentified [[radiation]] emanating from [[discharge tube]]s by experimenters investigating [[cathode ray]]s produced by such tubes, which are energetic [[electron]] beams that were first observed in 1869. Early researchers noticed effects that were attributable to them in many of the early [[Crookes tube]]s (invented around [[1875 in science|1875]]). Crookes tubes created free electrons by [[ionization]] of the residual air in the tube by a high [[Direct current|DC]] [[voltage]] of anywhere between a few [[kilovolt]]s and 100&nbsp;kV. This voltage accelerated the electrons coming from the [[cathode]] to a high enough velocity that they created X-rays when they struck the [[anode]] or the glass wall of the tube.<ref>{{cite journal |doi=10.1038/npre.2009.3267.4|title=The History, Development and Impact of Computed Imaging in Neurological Diagnosis and Neurosurgery: CT, MRI, and DTI|journal=Nature Precedings|date=2009| vauthors = Filler A |doi-access=free}}</ref>

The earliest experimenter thought to have (unknowingly) produced X-rays was [[William Morgan (actuary)|William Morgan]]. In 1785, he presented a paper to the [[Royal Society of London]] describing the effects of passing [[Electric current|electrical currents]] through a partially evacuated glass tube, producing a glow created by X-rays.<ref name="Morg1785">{{cite journal |title=Electrical Experiments Made in Order to Ascertain the Non-Conducting Power of a Perfect Vacuum, &c. | vauthors = Morgan W |journal=Philosophical Transactions of the Royal Society |volume=75 |pages=272–278 |publisher=Royal Society of London  |date=24 February 1785 |url=https://archive.org/details/philtrans00580668 |doi=10.1098/rstl.1785.0014|doi-access=free }}</ref><ref>{{cite journal | vauthors = Anderson JG |title=William Morgan and X-rays |journal=Transactions of the Faculty of Actuaries |volume=17 |pages=219–221 |date =January 1945 |url = https://www.actuaries.org.uk/documents/william-morgan-and-x-rays |doi=10.1017/s0071368600003001}}</ref> This work was further explored by [[Humphry Davy]] and his assistant [[Michael Faraday]].{{cn|date=December 2024}}

Starting in 1888, Philipp Lenard conducted experiments to see whether cathode rays could pass out of the Crookes tube into the air. He built a Crookes tube with a "window" at the end made of thin aluminium, facing the cathode so the cathode rays would strike it (later called a "Lenard tube"). He found that something came through, that would expose photographic plates and cause fluorescence. He measured the penetrating power of these rays through various materials. It has been suggested that at least some of these "Lenard rays" were actually X-rays.<ref name="Thomson182-186">{{cite book |last1=Thomson |first1=Joseph John |chapter=Leonard's Experiments |pages=182–186 |hdl=2027/uiug.30112112077497?urlappend=%3Bseq=196%3Bownerid=13510798903097783-200 |hdl-access=free |title=The Discharge of Electricity Through Gases |date=1900 |publisher=C. Scribner's Sons }}</ref>

Helmholtz formulated mathematical equations for X-rays. He postulated a dispersion theory before Röntgen made his discovery and announcement. He based it on the [[electromagnetic theory of light]].<ref>''Wiedmann's Annalen'', Vol. XLVIII.</ref>{{Full citation needed|date=October 2021}} However, he did not work with actual X-rays.

In early 1890, photographer [[William Nicholson Jennings|William Jennings]] and associate professor of the [[University of Pennsylvania]] Arthur W. Goodspeed were making photographs of coins with electric sparks. On 22 February after the end of their experiments two coins were left on a stack of photographic plates before Goodspeed demonstrated to Jennings the operation of [[Crookes tube]]s. While developing the plates, Jennings noticed disks of unknown origin on some of the plates, but nobody could explain them, and they moved on. Only in 1896 they realized that they accidentally made an X-ray photograph (they didn't claim a discovery).<ref>{{cite journal |last1=Walden |first1=T L |title=The first radiation accident in America: a centennial account of the x-ray photograph made in 1890. |journal=Radiology |date=December 1991 |volume=181 |issue=3 |pages=635–639 |doi=10.1148/radiology.181.3.1947073 |pmid=1947073 }}</ref>

Also in 1890, Roentgen's assistant [[Ludwig Zehnder]] noticed a flash of light from a fluorescent screen immediately before the covered tube he was switching on punctured.<ref>{{cite journal |last1=Peh |first1=W. C. |title=Part II - Controversies Surrounding and Following Rontgen's Discovery |journal=Singapore Medical Journal |date=October 1995 |volume=36 |issue=5 |pages=554–558 |pmid=8882548 |url=http://www.smj.org.sg/sites/default/files/3605/3605hdxray1.pdf }}</ref>

When [[Stanford University]] physics professor [[Fernando Sanford]] conducted his "electric photography" experiments in 1891–1893 by photographing coins in the light of electric sparks,<ref name=":2">{{Cite book |url=https://books.google.com/books?id=pjwiKBTJsQkC&pg=PA63 |title=Illustrated Electrical Review: A Journal of Scientific and Electrical Progress |date=1894 |publisher=Electrical Review Publishing Company |language=en}}</ref> like Jennings and Goodspeed, he may have unknowingly generated and detected X-rays. His letter of [[1893#January–March|6 January 1893]] to the ''[[Physical Review]]'' was duly published<ref name=":2" /> and an article entitled ''Without Lens or Light, Photographs Taken With Plate and Object in Darkness'' appeared in the ''[[San Francisco Examiner]]''.<ref>{{Cite journal |vauthors=Wyman T |date=Spring 2005 |title=Fernando Sanford and the Discovery of X-rays |journal="Imprint", from the Associates of the Stanford University Libraries |pages=5–15}}</ref>

In [[1894 in science|1894]], [[Nikola Tesla]] noticed damaged film in his lab that seemed to be associated with Crookes tube experiments and began investigating this invisible, [[radiant energy]].<ref name="Scenes from the past: Nikola Tesla">{{cite journal | vauthors = Hrabak M, Padovan RS, Kralik M, Ozretic D, Potocki K | title = Scenes from the past: Nikola Tesla and the discovery of X-rays | journal = Radiographics | volume = 28 | issue = 4 | pages = 1189–1192 | date = July 2008 | pmid = 18635636 | doi = 10.1148/rg.284075206 | doi-access = free }}</ref><ref>{{Cite book | vauthors = Chadda PK | title = Hydroenergy and Its Energy Potential | date = 2009 | publisher = Pinnacle Technology | isbn = 978-1-61820-149-2 | page = 88 }}</ref> After Röntgen identified the X-ray, Tesla began making X-ray images of his own using high voltages and tubes of his own design,<ref>Tesla's technical publications indicate that he invented and developed a single-electrode X-ray tube. Morton, William James and Hammer, Edwin W. (1896) ''American Technical Book Co.'', p. 68. {{US patent|514170}}, "Incandescent Electric Light". {{US patent|454622}} "System of Electric Lighting". These differed from other X-ray tubes in having no target electrode and worked with the output of a [[Tesla coil]].</ref> as well as Crookes tubes.