Editing Visible spectrum (section)

==History==
[[File: Newton's color circle.png|thumb|Newton's color circle, from ''Opticks'' of 1704, showing the colors he associated with [[musical note]]s. The spectral colors from red to violet are divided by the notes of the musical scale, starting at D. The circle completes a full [[octave]], from D to D. Newton's circle places red, at one end of the spectrum, next to violet, at the other. This reflects the fact that non-spectral [[purple]] colors are observed when red and violet light are mixed.]]

In the 13th century, [[Roger Bacon]] theorized that [[rainbow]]s were produced by a similar process to the passage of light through glass or crystal.<ref>{{cite book|url=https://archive.org/details/thescienceoflogi01coffuoft|page=[https://archive.org/details/thescienceoflogi01coffuoft/page/185 185]|quote=roger bacon prism.|title=The Science of Logic: An Inquiry Into the Principles of Accurate Thought |first=Peter|last=Coffey|year=1912|publisher=Longmans}}</ref>

In the 17th century, [[Isaac Newton]] discovered that prisms could disassemble and reassemble white light, and described the phenomenon in his book ''[[Opticks]]''. He was the first to use the word ''spectrum'' ([[Latin]] for "appearance" or "apparition") in this sense in print in 1671 in describing his [[experiment]]s in [[optics]]. Newton observed that, when a narrow beam of [[sunlight]] strikes the face of a glass [[Dispersive prism|prism]] at an angle, some is [[reflected]] and some of the beam passes into and through the glass, emerging as different-colored bands. Newton hypothesized light to be made up of "corpuscles" (particles) of different colors, with the different colors of light moving at different speeds in transparent matter, red light moving more quickly than violet in glass. The result is that red light is bent ([[refracted]]) less sharply than violet as it passes through the prism, creating a spectrum of colors.

[[File:Newton prismatic colours.JPG|thumb|upright=1.35|Newton's observation of prismatic colors ([[David Brewster]] 1855)]] Newton originally divided the spectrum into six named colors: [[red]], [[Orange (color)|orange]], [[yellow]], [[green]], [[blue]], and [[Violet (color)|violet]]. He later added [[indigo]] as the seventh color since he believed that seven was a perfect number as derived from the [[Ancient Greece|ancient Greek]] [[sophists]], of there being a connection between the colors, the musical notes, the known objects in the [[Solar System]], and the days of the week.<ref name="Isacoff2009">{{cite book|last=Isacoff|first=Stuart|title=Temperament: How Music Became a Battleground for the Great Minds of Western Civilization|url=https://books.google.com/books?id=2kasFeTRcf4C&pg=PA12|access-date=18 March 2014|date=16 January 2009|publisher=Knopf Doubleday Publishing Group|isbn=978-0-307-56051-3|pages=12–13|archive-date=4 October 2024|archive-url=https://web.archive.org/web/20241004082506/https://books.google.com/books?id=2kasFeTRcf4C&pg=PA12#v=onepage&q&f=false|url-status=live}}</ref> The human eye is relatively insensitive to indigo's frequencies, and some people who have otherwise-good vision cannot distinguish indigo from blue and violet. For this reason, some later commentators, including [[Isaac Asimov]],<ref>{{cite book|last=Asimov|first=Isaac|title=Eyes on the universe : a history of the telescope|year=1975|publisher=Houghton Mifflin|location=Boston|isbn=978-0-395-20716-1|page=[https://archive.org/details/eyesonuniverse00isaa/page/59 59]|url-access=registration|url=https://archive.org/details/eyesonuniverse00isaa/page/59}}</ref> have suggested that indigo should not be regarded as a color in its own right but merely as a shade of blue or violet. Evidence indicates that what Newton meant by "indigo" and "blue" does not correspond to the modern meanings of those color words. Comparing Newton's observation of prismatic colors with a color image of the visible light spectrum shows that "indigo" corresponds to what is today called blue, whereas his "blue" corresponds to [[cyan]].<ref>{{cite book|last=Evans|first=Ralph M.|title=The perception of color|year=1974|publisher=Wiley-Interscience|location=New York|isbn=978-0-471-24785-2|edition=null}}</ref><ref>{{cite journal|last=McLaren|first=K.|title=Newton's indigo|journal=Color Research & Application|date=March 2007|volume=10|issue=4|pages=225–229|doi=10.1002/col.5080100411}}</ref><ref>{{cite book|last=Waldman|first=Gary|title=Introduction to light : the physics of light, vision, and color|year=2002|publisher=Dover Publications|location=Mineola|isbn=978-0-486-42118-6|pages=193|url=https://books.google.com/books?id=PbsoAXWbnr4C&q=Newton+color+Indigo&pg=PA193|edition=Dover|access-date=2020-10-29|archive-date=2024-10-04|archive-url=https://web.archive.org/web/20241004082617/https://books.google.com/books?id=PbsoAXWbnr4C&q=Newton+color+Indigo&pg=PA193#v=snippet&q=Newton%20color%20Indigo&f=false|url-status=live}}</ref>

In the 18th century, [[Johann Wolfgang von Goethe]] wrote about optical spectra in his ''[[Theory of Colours]]''. Goethe used the word ''spectrum'' (''Spektrum'') to designate a ghostly optical [[afterimage]], as did [[Schopenhauer]] in ''[[On Vision and Colors]]''. Goethe argued that the continuous spectrum was a compound phenomenon. Where Newton narrowed the beam of light to isolate the phenomenon, Goethe observed that a wider aperture produces not a spectrum but rather reddish-yellow and blue-cyan edges with [[white]] between them. The spectrum appears only when these edges are close enough to overlap.

In the early 19th century, the concept of the visible spectrum became more definite, as light outside the visible range was discovered and characterized by [[William Herschel]] ([[infrared]]) and [[Johann Wilhelm Ritter]] ([[ultraviolet]]), [[Thomas Young (scientist)|Thomas Young]], [[Thomas Johann Seebeck]], and others.<ref>{{cite book
 | title = The Cambridge History of Science: The Modern Physical and Mathematical Sciences
 | volume = 5
 | editor = Mary Jo Nye
 | publisher = Cambridge University Press
 | year = 2003
 | isbn = 978-0-521-57199-9
 | page = 278
 | url = https://books.google.com/books?id=B3WvWhJTTX8C&q=spectrum+%22thomas+young%22+herschel+ritter&pg=PA278
 | access-date = 2020-10-29
 | archive-date = 2024-10-04
 | archive-url = https://web.archive.org/web/20241004082507/https://books.google.com/books?id=B3WvWhJTTX8C&q=spectrum+%22thomas+young%22+herschel+ritter&pg=PA278#v=snippet&q=spectrum%20%22thomas%20young%22%20herschel%20ritter&f=false
 | url-status = live
 }}</ref>
Young was the first to measure the wavelengths of different colors of light, in 1802.<ref>{{cite book
 | title = Lines of light: the sources of dispersive spectroscopy, 1800–1930
 | author = John C. D. Brand
 | publisher = CRC Press
 | year = 1995
 | isbn = 978-2-88449-163-1
 | pages = 30–32
 | url = https://books.google.com/books?id=sKx0IBC22p4C&q=light+wavelength+color++young+fresnel&pg=PA30
 | access-date = 2020-10-29
 | archive-date = 2024-10-04
 | archive-url = https://web.archive.org/web/20241004082507/https://books.google.com/books?id=sKx0IBC22p4C&q=light+wavelength+color++young+fresnel&pg=PA30#v=snippet&q=light%20wavelength%20color%20%20young%20fresnel&f=false
 | url-status = live
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The connection between the visible spectrum and [[color vision]] was explored by Thomas Young and [[Hermann von Helmholtz]] in the early 19th century. Their [[Young–Helmholtz theory|theory of color vision]] correctly proposed that the eye uses three distinct receptors to perceive color.
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