Editing Refractive index (section)

==History==
[[File:Thomas Young (scientist).jpg|thumb|120px|alt=Stipple engraving of Thomas Young|[[Thomas Young (scientist)|Thomas Young]] coined the term ''index of refraction'' in 1807.]]

[[Thomas Young (scientist)|Thomas Young]] was presumably the person who first used, and invented, the name "index of refraction", in 1807.<ref>{{cite book |last= Young |first= Thomas |year= 1807 |title= A course of lectures on natural philosophy and the mechanical arts |publisher= J. Johnson |page= [https://archive.org/details/lecturescourseof01younrich/page/413 413] |url= https://archive.org/details/lecturescourseof01younrich}}</ref>
At the same time he changed this value of refractive power into a single number, instead of the traditional ratio of two numbers. The ratio had the disadvantage of different appearances. [[Isaac Newton|Newton]], who called it the "proportion of the sines of incidence and refraction", wrote it as a ratio of two numbers, like "529 to 396" (or "nearly 4 to 3"; for water).<ref name=Newton>{{cite book |last= Newton |first= Isaac |date= 1730 |title= Opticks: Or, A Treatise of the Reflections, Refractions, Inflections and Colours of Light |publisher= William Innys at the West-End of St. Paul's |page= [https://archive.org/details/opticksoratreat00newtgoog/page/n273 247] |url= https://archive.org/details/opticksoratreat00newtgoog}}</ref>  [[Francis Hauksbee|Hauksbee]], who called it the "ratio of refraction", wrote it as a ratio with a fixed numerator, like "10000 to 7451.9" (for urine).<ref name=Hauksbee>{{cite journal |last= Hauksbee |first= Francis |date= 1710 |title= A Description of the Apparatus for Making Experiments on the Refractions of Fluids |page= 207 |journal= Philosophical Transactions of the Royal Society of London |volume= 27 |issue= 325–336 |s2cid= 186208526 |doi= 10.1098/rstl.1710.0015 }}</ref> [[Charles Hutton|Hutton]] wrote it as a ratio with a fixed denominator, like 1.3358 to 1 (water).<ref name=Hutton>{{cite book |last= Hutton |first= Charles |year= 1795 |title= Philosophical and mathematical dictionary |page= 299 |url= https://books.google.com/books?id=lsdJAAAAMAAJ&pg=PA299 |url-status= live |archive-url= https://web.archive.org/web/20170222031446/https://books.google.com/books?id=lsdJAAAAMAAJ&pg=PA299 |archive-date= 2017-02-22}}</ref>

Young did not use a symbol for the index of refraction, in 1807. In the later years, others started using different symbols: {{mvar|n}}, {{mvar|m}}, and {{mvar|µ}}.<ref name=Fraunhofer>{{cite journal |last= von Fraunhofer |first= Joseph |date= 1817 |title= Bestimmung des Brechungs und Farbenzerstreuungs Vermogens verschiedener Glasarten |language= de |trans-title= Determination of the Refraction and Color Scattering Power of Different Types of Glass |journal= Denkschriften der Königlichen Akademie der Wissenschaften zu München |trans-journal= Journal of the Royal Academy of Sciences in Munich |volume= 5 |page= 208 |url= https://books.google.com/books?id=lMRSAAAAcAAJ&pg=PA208 |url-status= live |archive-url= https://web.archive.org/web/20170222074213/https://books.google.com/books?id=lMRSAAAAcAAJ&pg=PA208 |archive-date= 2017-02-22 |author-link= Joseph von Fraunhofer }} {{lang|de|Exponent des Brechungsverhältnisses}} is index of refraction</ref><ref name=Brewster>{{cite journal |last= Brewster |first= David |date= 1815 |title= On the structure of doubly refracting crystals |journal= Philosophical Magazine |volume= 45 |issue= 202 |page= 126 |url= https://books.google.com/books?id=GhpRAAAAYAAJ&pg=PA124 |doi= 10.1080/14786441508638398 |url-status= live |archive-url= https://web.archive.org/web/20170222103726/https://books.google.com/books?id=GhpRAAAAYAAJ&pg=PA124 |archive-date= 2017-02-22 |author-link= David Brewster}}</ref><ref name=Herschel>{{cite book |last= Herschel |first= John F. W. |date= 1828 |title= On the Theory of Light |page= 368 |url= https://books.google.com/books?id=Lo4_AAAAcAAJ |url-status= live |archive-url= https://web.archive.org/web/20151124000212/https://books.google.com/books?id=Lo4_AAAAcAAJ&printsec=frontcover |archive-date= 2015-11-24 |author-link= John Herschel }}</ref> The symbol {{mvar|n}} gradually prevailed.