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(Fresnel acknowledged the British lenses and Buffon's invention in a memoir published in 1822.{{r|fresnel-1822-phares|p=2–4}}. The date of that memoir may be the source of the claim that Fresnel's lighthouse advocacy began two years later than Brewster's;{{r|chisholm-1911-brewster}} but the text makes it clear that Fresnel's involvement began no later than 1819.{{r|fresnel-1822-phares|p=1}})
[[File:Fresnel lighthouse lens diagram.png|thumb|246px|Cross-section of a first-generation Fresnel lighthouse lens, with sloping mirrors ''m,n'' above and below the refractive panel ''RC'' (with central segment ''A''). If the cross-section in every vertical plane through the lamp ''L'' is the same, the light is spread evenly around the horizon.]]▼
=== Fresnel's innovations ===
▲[[File:Fresnel lighthouse lens diagram.png|thumb|246px|Cross-section of a first-generation Fresnel lighthouse lens, with sloping mirrors ''m,n'' above and below the refractive panel ''RC'' (with central segment ''A''). If the cross-section in every vertical plane through the lamp ''L'' is the same, the light is spread evenly around the horizon.]]
Fresnel's next lens was a rotating apparatus with eight "bull's-eye" panels made in annular arcs by [[Saint-Gobain]],<ref>Levitt, 2013, p.71.</ref>, giving eight rotating beams, to be seen by mariners as a periodic flash. Above and behind each main panel was a smaller, sloping bull's-eye panel of trapezoidal outline with trapezoidal elements.{{r|gombert-2017}} This refracted the light to a sloping plane mirror, which then reflected it horizontally, 7 degrees ahead of the main beam, increasing the duration of the flash.{{r|fresnel-1822-phares|p=13,25}} Below the main panels were 128 small mirrors arranged in four rings, stacked like the slats of a [[louver]] or [[Venetian blind]]. Each ring, shaped like a [[frustum]] of a [[cone]], reflected the light to the horizon, giving a fainter steady light between the flashes. The official test, conducted on the ''[[Arc de Triomphe]]'' on 20 August 1822, was witnessed by the Commission — and by [[Louis XVIII of France|Louis XVIII]] and his entourage — from 32km away. The apparatus was stored at [[Bordeaux]] for the winter, and then reassembled at [[Cordouan Lighthouse]] under Fresnel's supervision. On 25 July 1823, the world's first lighthouse Fresnel lens was lit.<ref>Levitt, 2013, pp. 72–3.</ref> It was about this time that Fresnel started coughing up blood.<ref>Levitt, 2013, p.97;}}{{r|watson-2016|p=146}}
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{{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}} }}
[[File:David d'Angers - Fresnel.jpg|thumb|upright|left|Bust of Fresnel by [[David d'Angers|David d'Angers]].]]
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]].
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* H. Crew (ed.), [https://archive.org/details/wavetheoryofligh00crewrich ''The Wave Theory of Light: Memoirs by Huygens, Young and Fresnel''], American Book Co., 1900.
* O. Darrigol, ''A History of Optics: From Greek
* A. Fresnel (ed. H. de Senarmont, E. Verdet, L. Frenel), ''Oeuvres complètes d'Augustin Fresnel'' (3 vols.), Paris: Imprimerie impériale, 1866–70; [https://books.google.com/books?id=1l0_AAAAcAAJ v.1 (1866)], [https://archive.org/details/oeuvrescompltes00fresgoog v.2 (1868)], [https://archive.org/details/oeuvrescompltes01fresgoog v.3 (1870)].
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