Editing Isaac Newton (section)

=== Optics ===
[[File:Newton telescope replica 1668.jpg|thumb|A replica of the reflecting telescope Newton presented to the [[Royal Society]] in 1672 (the first one he made in 1668 was loaned to an instrument maker but there is no further record of what happened to it).<ref>{{Cite book |last=King |first=Henry |url=https://books.google.com/books?id=KAWwzHlDVksC&pg=PA74 |title=The History of the Telescope |publisher=Charles Griffin & Co. |year=1955|page=74}} Reprinted, Dover Publications, 1979 & 2003, {{isbn|978-0-486-43265-6}} </ref>]]

In 1666, Newton observed that the spectrum of colours exiting a [[Triangular prism (optics)|prism]] in the position of [[minimum deviation]] is oblong, even when the light ray entering the prism is circular, which is to say, the prism refracts different colours by different angles.<ref>{{Cite book |last=Whittaker |first=E. T. |author-link=E. T. Whittaker |url=https://archive.org/details/historyoftheorie00whitrich/page/14/mode/2up |title=A History of the Theories of Aether and Electricity: From the Age of Descartes to the Close of the Nineteenth Century |publisher=Longmans, Green, and Co. |year=1910 |pages=15–16 }}</ref><ref>{{Cite book |last=Darrigol |first=Olivier |url=https://books.google.com/books?id=Ye_1AAAAQBAJ&pg=PAPA81 |title=A History of Optics from Greek Antiquity to the Nineteenth Century |date=2012 |publisher=Oxford University Press |isbn=978-0-19-964437-7 |page=81 |access-date=}}</ref> This led him to conclude that colour is a property intrinsic to light – a point which had, until then, been a matter of debate.

From 1670 to 1672, Newton lectured on optics.<ref>{{Cite web |last=Newton |first=Isaac |title=Hydrostatics, Optics, Sound and Heat |url=http://cudl.lib.cam.ac.uk/view/MS-ADD-03970/ |url-status=live |archive-url=https://web.archive.org/web/20120108215515/http://cudl.lib.cam.ac.uk/view/MS-ADD-03970/ |archive-date=8 January 2012 |access-date=10 January 2012 |publisher=Cambridge University Digital Library}}</ref> During this period he investigated the [[refraction]] of light, demonstrating that the multicoloured image produced by a prism, which he named a [[spectrum]], could be recomposed into white light by a [[lens (optics)|lens]] and a second prism.{{sfn|Ball|1908|p=324}} Modern scholarship has revealed that Newton's analysis and resynthesis of white light owes a debt to [[Corpuscularianism|corpuscular]] alchemy.<ref>[[William R. Newman]], "Newton's Early Optical Theory and its Debt to Chymistry", in Danielle Jacquart and Michel Hochmann, eds., ''Lumière et vision dans les sciences et dans les arts'' (Geneva: Droz, 2010), pp. 283–307. {{Cite web |url=http://webapp1.dlib.indiana.edu/newton/html/Newton_optics-alchemy_Jacquart_paper.pdf |title=Archived copy |access-date=1 June 2012 |archive-date=28 May 2016 |archive-url=https://web.archive.org/web/20160528020600/http://webapp1.dlib.indiana.edu/newton/html/Newton_optics-alchemy_Jacquart_paper.pdf |url-status=bot: unknown }} (PDF)</ref>

In his work on [[Newton's rings]] in 1671, he used a method that was unprecedented in the 17th century, as "he ''averaged'' all of the differences, and he then calculated the difference between the average and the value for the first ring", in effect introducing a now [[Least squares#Founding|standard method]] for reducing noise in measurements, and which does not appear elsewhere at the time.<ref>{{Cite web |last=Drum |first=Kevin |date=2013-05-10 |title=The Groundbreaking Isaac Newton Invention You've Never Heard Of |url=https://www.motherjones.com/kevin-drum/2013/05/groundbreaking-isaac-newton-invention-youve-never-heard/ |access-date=2024-12-21 |website=Mother Jones |language=en-US}}</ref> He extended his "error-slaying method" to studies of equinoxes in 1700, which was described as an "altogether unprecedented method" but differed in that here "Newton required good values for each of the original equinoctial times, and so he devised a method that allowed them to, as it were, self-correct."<ref name=":11">{{Cite book |last1=Buchwald |first1=Jed Z. |url=https://books.google.com/books?id=QdT7xGlZvPUC&pg=PA103 |title=Newton and the Origin of Civilization |last2=Feingold |first2=Mordechai |date=2013 |publisher=[[Princeton University Press]] |isbn=978-0-691-15478-7 |location= |pages=90–93, 101–103}}</ref> Newton wrote down the first of the two 'normal equations' known from [[ordinary least squares]], and devised an early form of regression analysis, as he averaged a set of data, 50 years before [[Tobias Mayer]] and also "summing the residuals to zero he ''forced'' the regression line to pass through the average point". Newton also differentiated between two uneven sets of data and may have considered an optimal solution regarding bias, although not in terms of effectiveness.<ref name=":18">{{Cite journal |last1=Belenkiy |first1=A. |last2=Echague |first2=E. V. |date=2016-02-01 |title=Groping toward linear regression analysis: Newton's analysis of Hipparchus' equinox observations |url=https://ui.adsabs.harvard.edu/abs/2016Obs...136....1B/abstract |journal=The Observatory |volume=136 |pages=1–22 |bibcode=2016Obs...136....1B |issn=0029-7704}}</ref>

He showed that coloured light does not change its properties by separating out a coloured beam and shining it on various objects, and that regardless of whether reflected, scattered, or transmitted, the light remains the same colour. Thus, he observed that colour is the result of objects interacting with already-coloured light rather than objects generating the colour themselves. This is known as [[Early life of Isaac Newton#Newton's theory of colour|Newton's theory of colour]].{{sfn|Ball|1908|p=325}} His 1672 paper on the nature of white light and colours forms the basis for all work that followed on colour and colour vision.<ref>{{cite book |last=Marriott |first=F.H.C. |chapter=Colour Vision: Introduction |date=1962 |title=The Visual Process |pages=219–229  |publisher=Academic Press |language=en |doi=10.1016/b978-1-4832-3089-4.50021-2}}</ref>

[[File:Dispersive Prism Illustration.jpg|thumb|Illustration of a [[dispersive prism]] separating white light into the colours of the spectrum, as discovered by Newton]]

From this work, he concluded that the lens of any [[refracting telescope]] would suffer from the [[dispersion (optics)|dispersion]] of light into colours ([[chromatic aberration]]). As a proof of the concept, he constructed a telescope using reflective mirrors instead of lenses as the [[objective (optics)|objective]] to bypass that problem. Building the design, the first known functional reflecting telescope, today known as a [[Newtonian telescope]], involved solving the problem of a suitable mirror material and shaping technique.<ref name="White 1997, p170" /> He grounded his own mirrors out of a custom composition of highly reflective [[speculum metal]], using Newton's rings to judge the [[quality (philosophy)|quality]] of the optics for his telescopes. In late 1668,<ref>{{Cite book |last=Hall |first=Alfred Rupert |author-link=Alfred Rupert Hall |url=https://archive.org/details/isaacnewtonadven0000hall/page/67 |title=Isaac Newton: Adventurer in thought |date=1996 |publisher=[[Cambridge University Press]] |isbn=978-0-521-56221-8 |series= |location= |pages=67}}</ref> he was able to produce this first reflecting telescope. It was about eight inches long and it gave a clearer and larger image. In 1671, he was asked for a demonstration of his reflecting telescope by the Royal Society.{{sfn|White|1997|p=168}} Their interest encouraged him to publish his notes, ''Of Colours'',<ref>{{Cite web |last=Newton |first=Isaac |title=Of Colours |url=http://www.newtonproject.sussex.ac.uk/view/texts/normalized/NATP00004 |url-status=live |archive-url=https://web.archive.org/web/20141009051407/http://www.newtonproject.sussex.ac.uk/view/texts/normalized/NATP00004 |archive-date=9 October 2014 |access-date=6 October 2014 |website=The [[Newton Project]]}}</ref> which he later expanded into the work ''[[Opticks]]''. When [[Robert Hooke]] criticised some of Newton's ideas, Newton was so offended that he withdrew from public debate. However, the two had brief exchanges in 1679–80, when Hooke, who had been appointed Secretary of the Royal Society,<ref>{{Cite book |last=Inwood |first=Stephen |url=https://archive.org/details/forgottengeniusb00inwo/page/246 |title=The Forgotten Genius |publisher=MacAdam/Cage Pub. |year=2003 |isbn=978-1-931561-56-3 |location=San Francisco |pages=246–247 |oclc=53006741}}</ref> opened a correspondence intended to elicit contributions from Newton to Royal Society transactions,<ref name="hooke1679nov24" /> which had the effect of stimulating Newton to work out a proof that the elliptical form of planetary orbits would result from a centripetal force inversely proportional to the square of the radius vector.<ref>{{Cite web |date=2025-03-05 |title=Isaac Newton |url=https://www.britannica.com/biography/Isaac-Newton/The-Principia |access-date=2025-03-15 |website=www.britannica.com |language=en}}</ref>

[[File:Newton-letter-to-briggs 03.jpg|thumb|upright|Facsimile of a 1682 letter from Newton to [[William Briggs (physician)|William Briggs]], commenting on Briggs' ''A New Theory of Vision'']]

Newton argued that light is composed of particles or corpuscles, which were refracted by accelerating into a denser medium. He verged on soundlike waves to explain the repeated pattern of reflection and transmission by thin films (''Opticks'' Bk. II, Props. 12), but still retained his theory of 'fits' that disposed corpuscles to be reflected or transmitted (Props.13). Physicists later favoured a purely wavelike explanation of light to account for the [[interference (wave propagation)|interference]] patterns and the general phenomenon of [[diffraction]]. Despite his known preference of a particle theory, Newton in fact noted that light had both particle-like and wave-like properties in ''Opticks'', and was the first to attempt to reconcile the two theories, thereby anticipating later developments of [[Wave–particle duality|wave-particle duality]], which is the modern understanding of light.<ref name=":22">{{Cite book |last=Finkelstein |first=David Ritz |author-link=David Finkelstein |url=https://books.google.com/books?id=OvjsCAAAQBAJ&pg=PA156 |title=Quantum Relativity |date=1996 |publisher=Springer Berlin Heidelberg |isbn=978-3-642-64612-6 |location= |pages=156, 169–170 |language=en |doi=10.1007/978-3-642-60936-7}}</ref><ref>{{Cite book |last1=Bacciagaluppi |first1=Guido |url=https://books.google.com/books?id=EAPX3JfQAgIC&pg=PA31 |title=Quantum Theory at the Crossroads: Reconsidering the 1927 Solvay Conference |last2=Valentini |first2=Antony |author-link2=Antony Valentini |date=2009 |publisher=[[Cambridge University Press]] |isbn=978-0-521-81421-8 |location= |pages=31–32 |oclc=227191829}}</ref> Physicist [[David Finkelstein]] called him "the first quantum physicist" as a result.<ref name=":22" />

In his ''Hypothesis of Light'' of 1675, Newton posited the existence of the [[luminiferous aether|ether]] to transmit forces between particles. The contact with the [[Cambridge Platonists|Cambridge Platonist]] philosopher [[Henry More]] revived his interest in alchemy.<ref name="More" /> He replaced the ether with occult forces based on [[Hermeticism|Hermetic]] ideas of attraction and repulsion between particles. His contributions to science cannot be isolated from his interest in alchemy.<ref name="More" /> This was at a time when there was no clear distinction between alchemy and science.<ref>{{cite book |author1=Allison B. Kaufman |url=https://books.google.com/books?id=ZLT4DwAAQBAJ&pg=PA9 |title=Pseudoscience: The Conspiracy Against Science |author2=James C. Kaufman |publisher=MIT Press |year=2019 |isbn=978-0-262-53704-9 |edition= |page=9}}</ref><ref>{{cite book |author1=Márcia Lemos |url=https://books.google.com/books?id=6xNUDgAAQBAJ&pg=PA83 |title=Exchanges between Literature and Science from the 1800s to the 2000s: Converging Realms |publisher=Cambridge Scholars Publishing |year=2017 |isbn=978-1-4438-7605-6 |edition= |page=83}}</ref>

In 1704, Newton published ''Opticks'', in which he expounded his corpuscular theory of light, and included a set of queries at the end, which were posed as unanswered questions and positive assertions. In line with his corpuscle theory, he thought that normal matter was made of grosser corpuscles and speculated that through a kind of alchemical transmutation, with query 30 stating "Are not gross Bodies and Light convertible into one another, and may not Bodies receive much of their Activity from the Particles of Light which enter their Composition?"<ref name="Newton's Alchemy and His Theory of Matter" /> Query 6 introduced the concept of a [[black body]].<ref>{{Cite book |last=Bochner |first=Salomon |url=https://books.google.com/books?id=naH_AwAAQBAJ&pg=PA221 |title=Role of Mathematics in the Rise of Science |date=1981 |publisher=[[Princeton University Press]] |isbn=978-0-691-08028-4 |edition= |location= |pages=221, 347 |language=en}}</ref><ref>{{Cite book |last=Rowlands |first=Peter |url=https://books.google.com/books?id=u0NBDwAAQBAJ&pg=PA69 |title=Newton – Innovation And Controversy |publisher=[[World Scientific Publishing]] |year=2017 |isbn=9781786344045 |pages=69}}</ref> 

Newton investigated [[electricity]] by constructing a primitive form of a frictional [[electrostatic generator]] using a glass globe,<ref>Opticks, 2nd Ed 1706. Query 8.</ref> and detailed an experiment in 1675 that showed when one side of a glass sheet is rubbed to create an electric charge, it attracts "light bodies" to the opposite side. He interpreted this as evidence that electric forces could pass through glass.<ref>{{Cite journal |last=Sanford |first=Fernando |year=1921 |title=Some Early Theories Regarding Electrical Forces – The Electric Emanation Theory |url=https://www.jstor.org/stable/6312 |journal=The Scientific Monthly |volume=12 |issue=6 |pages=544–550 |bibcode=1921SciMo..12..544S |issn=0096-3771}}</ref> His idea in ''Opticks'' that optical [[Reflection (physics)|reflection]] and [[refraction]] arise from interactions across the entire surface is regarded as the beginning of the field theory of electric force.<ref name=":16" /> He recognized the crucial role of electricity in nature, believing it to be responsible for various phenomena, including the emission, reflection, refraction, inflection, and heating effects of light. He proposed that electricity was involved in the sensations experienced by the human body, affecting everything from muscle movement to brain function.<ref>{{Cite book |last=Home |first=R. W. |title=Contemporary Newtonian Research |date=1982 |publisher=Springer Netherlands |isbn=978-94-009-7715-0 |editor-last=Bechler |editor-first=Zev |series= |location= |pages=191 |chapter=Newton on Electricity and the Aether}}</ref> His mass-dispersion model, ancestral to the successful use of the [[Action principles|least action principle]], provided a credible framework for understanding refraction, particularly in its approach to refraction in terms of momentum.<ref name=":16">{{Cite book |last=Rowlands |first=Peter |url=https://books.google.com/books?id=u0NBDwAAQBAJ&pg=PA109 |title=Newton – Innovation And Controversy |publisher=[[World Scientific Publishing]] |year=2017 |isbn=9781786344045 |pages=109}}</ref>

In ''Opticks'', he was the first to show a diagram using a prism as a beam expander, and also the use of multiple-prism arrays. Some 278 years after Newton's discussion, [[beam expander#Multiple-prism beam expanders|multiple-prism beam expanders]] became central to the development of [[laser linewidth|narrow-linewidth]] [[tunable laser]]s. The use of these prismatic beam expanders led to the [[multiple-prism dispersion theory]].<ref name=OPN1 />

Newton was also the first to propose the [[Goos–Hänchen effect]], an [[optical phenomenon]] in which [[Linear polarization|linearly polarized]] light undergoes a small lateral shift when [[Total internal reflection|totally internally reflected]]. He provided both experimental and theoretical explanations for the effect using a mechanical model.<ref>{{Cite journal |last1=Ul Haq |first1=Iqra Zia |last2=Syed |first2=Aqeel A. |last3=Naqvi |first3=Qaisar Abbas |date=2020 |title=Observing the Goos–Hänchen shift in non-integer dimensional medium |url=https://linkinghub.elsevier.com/retrieve/pii/S0030402619319709 |journal=Optik |language=en |volume=206 |pages=164071 |doi=10.1016/j.ijleo.2019.164071|bibcode=2020Optik.20664071U }}</ref>

Science came to realise the difference between perception of colour and mathematisable optics. The German poet and scientist, [[Johann Wolfgang von Goethe]], could not shake the Newtonian foundation but "one hole Goethe did find in Newton's armour,&nbsp;... Newton had committed himself to the doctrine that refraction without colour was impossible. He, therefore, thought that the object-glasses of telescopes must forever remain imperfect, achromatism and refraction being incompatible. This inference was proved by [[John Dollond|Dollond]] to be wrong."<ref>Tyndall, John. (1880). ''Popular Science Monthly'' Volume 17, July. [[s:Popular Science Monthly/Volume 17/July 1880/Goethe's Farbenlehre: Theory of Colors II]]</ref>
[[File:Portrait of Sir Isaac Newton (4670220).jpg|thumb|upright|Engraving of ''Portrait of Newton'' by [[John Vanderbank]]]]