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'''Augustin-Jean Fresnel''' ({{IPAc-en|f|r|eɪ|ˈ|n|ɛ|l}} {{respell|fray|NEL|'}}; {{IPA-fr|ɔ.ɡy.stɛ̃ ʒɑ̃ fʁɛ.nɛl|lang}}; 10 May 1788 – 14 July 1827) was a [[France|French]] civil [[engineer]] and [[physicist]] whose research in [[optics]] led to the almost universal acceptance of the wave theory of light, and the rejection of any remnant of [[Isaac Newton|Newton]]'s [[corpuscular theory of light|corpuscular theory]], from the 1830s<ref>Darrigol, 2012, pp.{{nnbsp}}220–23</ref> until the end of the 19th century.
But he is perhaps better known for inventing the ''catadioptric'' (reflective/refractive) [[Fresnel lens]] and for pioneering the use of "stepped" lenses to extend the visibility of [[lighthouse
By expressing [[Christiaan Huygens|Huygens]]' principle of secondary waves and [[Thomas Young (scientist)|Young]]'s principle of [[interference (wave propagation)|interference]] in quantitative terms, and supposing that simple colors consist of ''[[sine wave|sinusoidal]]'' waves, Fresnel gave the first satisfactory explanation of [[diffraction]] by straight edges, including the first explanation of rectilinear propagation that would satisfy a modern physicist.<ref>Darrigol, 2012, p.{{hsp}}205</ref> By further supposing that light waves are purely ''[[transverse wave|transverse]]'', he explained the nature of [[polarization]] and lack thereof, the mechanism of ''chromatic polarization'' (the colors produced when polarized light is passed through a slice of doubly-refractive crystal followed by a second polarizer), and the [[transmission coefficient|transmission]] and [[reflection coefficient]]s at a boundary between transparent [[isotropy|isotropic]] media (including [[Brewster's angle]]). Then, by generalizing the relationship between wave speed and polarization for [[calcite]], he accounted for the directions and polarizations of the refracted rays in [[birefringence|doubly-refractive]] crystals of the ''biaxial'' class (those for which Huygens' secondary wavefronts are not axisymmetric). The period between the first publication of his pure-transverse-wave hypothesis and the presentation of his solution to the biaxial problem was less than a year. Later, by allowing the reflection coefficient to be ''[[complex number|complex]]'', he accounted for the change in polarization due to [[total internal reflection]], as exploited in the [[Fresnel rhomb]]. Defenders of the established corpuscular theory could not match his quantitative explanations of so many phenomena on so few assumptions.
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== Early life ==
[[File:Augustin Fresnel buste Broglie.jpg|thumb|Monument to Augustin Fresnel at his birthplace in [[Broglie, Eure|Broglie]]. The inscription, when translated, says:<br style="margin-bottom: 0.6ex;" />"Augustin Fresnel, Engineer of Bridges and Roads, member of the Academy of Sciences, creator of lenticular lighthouses, was born in this house on 10 May 1788. The theory of light owes to this emulator of Newton the highest concepts and the most useful applications."{{r|perchet-2011}}]]
=== Family ===
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Also in 1825, Fresnel extended his fixed design by adding a rotating array outside the fixed array.{{r|tag-fres}} Each panel of the rotating array refracted part of the fixed light from a horizontal fan into a narrow beam.
[[File:MuseeMarine-phareFresnel-p1000466.jpg|thumb|left|First-order rotating catadioptric Fresnel lens, dated 1870,
To reduce the loss of light in the reflecting elements, Fresnel proposed to replace the mirrors with ''catadioptric'' prisms, through which the light would pass by two refractions and one [[total internal reflection]].<ref>Levitt, 2013, pp.{{nnbsp}}79–80.</ref> The result was the lighthouse lens as we now know it. In 1826 he assembled a small model for use on the [[Canal Saint-Martin]],{{r|musee}} but he did not live to see a full-sized version.
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== Honors ==
[[File:Bust of Augustin Fresnel by David d'Angers-MnM 41 OA 256 D-IMG 8741.jpg|thumb|left|Bust of Fresnel by [[David d'Angers]] (1854), formerly in the lighthouse of [[Hourtin]], [[Gironde]], and now exhibited at the ''[[Musée national de la Marine]]''.]]
In 1823, Fresnel was unanimously elected a member of the [[French Academy of Sciences|Académie des sciences]].{{r|brock-1909}}{{r|chisholm-1911-fresnel}} In 1824<ref>Levitt, 2013, p.{{hsp}}77.</ref> he was made a ''chevalier de la Légion d'honneur'' (Knight of the [[Legion of Honour]]).{{r|academie}} On 9 June 1825, he was made a Foreign Member of the [[Royal Society|Royal Society of London]].{{r|royalS}} In 1827{{r|chisholm-1911-fresnel|rines-1919}} he was awarded the Society's [[Rumford Medal]] for the year 1824, "For his Development of the Undulatory Theory as applied to the Phenomena of Polarized Light, and for his various important discoveries in Physical Optics."{{r|royalS-rumford}}
But, as he wrote to Young in 1824, in him "that sensibility, or that vanity, which people call love of glory" had been blunted. "All the compliments," he says, "that I have received from Arago, Laplace and Biot never gave me so much pleasure as the discovery of a theoretic truth, or the confirmation of a calculation by experiment."{{r|chisholm-1911-fresnel}}▼
"{{smaller|FRESNEL}}" is among the [[List of the 72 names on the Eiffel Tower|72 names embossed on the Eiffel Tower]] — on the south-east side, 4th from the left. In the 19th century, as every lighthouse in France acquired a Fresnel lens, every one acquired a bust of Fresnel, seemingly watching over the coastline that he had made safer.<ref>Levitt, 2013, p.{{hsp}}233</ref>
{{clear}}▼
== Decline and death ==
[[File:Tombe d'Augustin Fresnel - Père Lachaise.JPG|thumb|Fresnel's grave at [[Père Lachaise Cemetery]], Paris, photographed in 2014.]]
▲But, as he wrote to Young in 1824, in him "that sensibility, or that vanity, which people call love of glory" had been blunted. "All the compliments," he says, "that I have received from Arago, Laplace and Biot never gave me so much pleasure as the discovery of a theoretic truth, or the confirmation of a calculation by experiment."{{r|chisholm-1911-fresnel}}
Rumford medal, which was
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and collaborator Arago.{{r|ripley-dana-1879}}
Fresnel is buried at [[Père Lachaise Cemetery]], Paris. The inscription on his headstone is partly [[commons:category:Grave of Augustin Fresnel (Père-Lachaise, division 14)|eroded away]]; the legible part says, when translated, "To the memory of Augustin Jean FRESNEL, member of the [[Institut de France|Institute of France]]."
{{clear}}
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* [[William Whewell]], in all three editions of his ''History of the Inductive Sciences'' (1837, 1847, and 1857), at the end of Book IX, compared the histories of physical astronomy and physical optics and concluded:{{quote|It would, perhaps, be too fanciful to attempt to establish a parallelism between the prominent persons who figure in these two histories. If we were to do this, we must consider Huyghens and Hooke as standing in the place of Copernicus, since, like him, they announced the true theory, but left it to a future age to give it development and mechanical confirmation; Malus and Brewster, grouping them together, correspond to [[Tycho Brahe]] and [[Johannes Kepler|Kepler]], laborious in accumulating observations, inventive and happy in discovering laws of phenomena; and Young and Fresnel combined, make up the Newton of optical science.{{r|whewell-1857|p=370-71}} }}
▲{{clear}}
What Whewell called the "true theory" has since undergone two major revisions. The first, by Maxwell, specified the physical fields whose variations constitute the waves of light. The second, initiated by Einstein's explanation of the [[photoelectric effect]], supposed that the energy of light waves was divided into [[quantum|quanta]], which were eventually identified with particles called [[photon|photons]]. But photons did not exactly correspond to Newton's corpuscles; for example, Newton's explanation of ordinary refraction required the corpuscles to travel faster in media of higher refractive index, which photons do not. Nor did photons displace waves; rather, they led to the paradox of [[wave–particle duality]].
Although Fresnel did not know that light waves are electromagnetic, he managed to construct the world's first coherent theory of light. In retrospect, this shows that his methods are applicable to multiple types of waves. And although light is now known to have both wavelike and particle-like aspects, it is the wavelike aspect that more easily explains the phenomena studied by Fresnel. In these respects, Fresnel's theory has stood the test of time, and Whewell's premature triumphalism contains an abiding truth.
== References ==
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<ref name=musee>Musée national de la Marine, [http://mnm.webmuseo.com/ws/musee-national-marine/app/collection/record/9067 "Appareil catadioptrique, Appareil du canal Saint-Martin"], accessed 26 August 2017; [https://web.archive.org/web/20170826030358/http://mnm.webmuseo.com/ws/musee-national-marine/app/collection/record/9067 archived] 26 August 2017.</ref>
<ref name=perchet-2011>D. Perchet, [https://e-monumen.net/patrimoine-monumental/monument-a-augustin-fresnel-broglie/ "Monument à Augustin Fresnel – Broglie"], e-monumen.net, 5 July 2011.</ref>
<ref name=pharedeC>Phare de Cordouan, [http://www.phare-de-cordouan.fr/lighting-systems.html "The lighting systems of the Cordouan Lighthouse"], accessed 26 August 2017; [https://web.archive.org/web/20160922153001/http://www.phare-de-cordouan.fr/lighting-systems.html archived] 22 September 2016.</ref>
<ref name=rines-1919>G.E. Rines (ed.), "Fresnel, Augustin Jean", ''Encyclopedia Americana'', 1918–20, v.12 (1919), [https://babel.hathitrust.org/cgi/pt?id=wu.89094370657;view=1up;seq=111 p.93]. (This entry inaccurately describes Fresnel as the "discoverer" of polarization of light and as a "Fellow" of the Royal Society, whereas in fact he ''explained'' polarization and was a "Foreign Member" of the Society; see text.)</ref>
<ref name=ripley-dana-1879>G. Ripley & C.A. Dana (ed.), "Fresnel, Augustin Jean", ''American Cyclopedia'', [https://archive.org/details/americancyclopae07ripluoft v.7], pp.486–9.</ref> (Contrary to this entry [p.486], calcite and quartz were ''not'' the only doubly refractive crystals known before Fresnel; see text.)
<ref name=royalS-2007>Royal Society, ''List of Fellows of the Royal Society 1660–2007'', A–J, July 2001, p.{{hsp}}130.</ref>
<ref name=royalS-rumford>Royal Society, [https://royalsociety.org/grants-schemes-awards/awards/rumford-medal/ "Rumford Medal"] (with link to full list of past winners), accessed 2 September 2017.</ref>
<ref name=silliman-2008>R.H. Silliman, "Fresnel, Augustin Jean", ''Complete Dictionary of Scientific Biography'', Detroit: Charles Scribner's Sons, 2008, v.5, pp. 165–71. (The [http://www.encyclopedia.com/people/science-and-technology/physics-biographies/augustin-jean-fresnel version at ''encyclopedia.com''] lacks the diagram and equations.)</ref>
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