Editing Augustin-Jean Fresnel (section)

=== Reception ===

For the supplement to Riffault's translation of [[Thomas Thomson (chemist)|Thomson]]'s ''System of Chemistry'', Fresnel was chosen to contribute the article on light. The resulting 137-page essay, titled ''De la Lumière'' (''On Light''),<ref>Fresnel, 1822a.</ref> was apparently finished in June 1821 and published by February 1822.<ref name=gg-p884>Grattan-Guinness, 1990, p.&nbsp;884.</ref> With sections covering the nature of light, diffraction, thin-film interference, reflection and refraction, double refraction and polarization, chromatic polarization, and modification of polarization by reflection, it made a comprehensive case for the wave theory to a readership that was not restricted to physicists.<ref>Cf. Frankel, 1976, p.&nbsp;169.</ref>

To examine Fresnel's first memoir and supplements on double refraction, the Académie des Sciences appointed Ampère, Arago, [[Joseph Fourier|Fourier]], and Poisson.<ref>Fresnel, 1866–70, vol.&nbsp;2, pp.&nbsp;261n,{{px2}}369n.</ref> Their report,<ref>Printed in Fresnel, 1866–70, vol.&nbsp;2, pp.&nbsp;459–464.</ref> of which Arago was clearly the main author,<ref>Buchwald, 1989, p.&nbsp;288.</ref> was delivered at the meeting of 19 August 1822. Then, in the words of [[Émile Verdet]], as translated by [[Ivor Grattan-Guinness]]:
{{blockquote|Immediately after the reading of the report, Laplace took the floor, and… proclaimed the exceptional importance of the work which had just been reported: he congratulated the author on his steadfastness and his sagacity which had led him to discover a law which had escaped the cleverest, and, anticipating somewhat the judgement of posterity, declared that he placed these researches above everything that had been communicated to the Académie for a long time.<ref>Fresnel, 1866–70, vol.&nbsp;1, pp.&nbsp;lxxxvi–lxxxvii; Grattan-Guinness, 1990, p.&nbsp;896.</ref>}}
Whether Laplace was announcing his conversion to the wave theory—at the age of 73—is uncertain. Grattan-Guinness entertained the idea.<ref>Grattan-Guinness, 1990, p.&nbsp;898.</ref> Buchwald, noting that Arago failed to explain that the "ellipsoid of elasticity" did not give the correct planes of polarization, suggests that Laplace may have merely regarded Fresnel's theory as a successful generalization of Malus's ray-velocity law, embracing Biot's laws.<ref>Buchwald, 1989, pp.&nbsp;289–390.</ref>

[[File:Beugungsscheibchen.k.720.jpg|thumb|Airy diffraction pattern 65{{nbsp}}mm from a 0.09{{nbsp}}mm circular aperture illuminated by red laser light. Image size: 17.3{{nbsp}}mm{{tsp}}×{{tsp}}13{{nbsp}}mm]]

In the following year, Poisson, who did not sign Arago's report, disputed the possibility of transverse waves in the aether. Starting from assumed equations of motion of a fluid medium, he noted that they did not give the correct results for partial reflection and double refraction—as if that were Fresnel's problem rather than his own—and that the predicted waves, even if they were initially transverse, became more longitudinal as they propagated. In reply Fresnel noted, ''inter alia'', that the equations in which Poisson put so much faith did not even predict [[viscosity]]. The implication was clear: given that the behavior of light had not been satisfactorily explained except by transverse waves, it was not the responsibility of the wave-theorists to abandon transverse waves in deference to pre-conceived notions about the aether; rather, it was the responsibility of the aether modelers to produce a model that accommodated transverse waves.<ref>Frankel, 1976, pp.&nbsp;170–171; cf.&nbsp;Fresnel, 1827, tr.&nbsp;Hobson, pp.&nbsp;243–244,{{tsp}}262.</ref> According to Robert H.&nbsp;Silliman, Poisson eventually accepted the wave theory shortly before his death in 1840.<ref>Silliman, 1967, pp.&nbsp;284–285, citing Fresnel, 1866–70, vol.&nbsp;1, p.&nbsp;lxxxix, note&nbsp;2.&nbsp; Frankel (1976, p.&nbsp;173) agrees. Worrall (1989, p.&nbsp;140) is skeptical.</ref>

Among the French, Poisson's reluctance was an exception. According to Eugene Frankel, "in Paris no debate on the issue seems to have taken place after 1825. Indeed, almost the entire generation of physicists and mathematicians who came to maturity in the 1820s—Pouillet, [[Félix Savart|Savart]], [[Gabriel Lamé|Lamé]], [[Claude-Louis Navier|Navier]], [[Joseph Liouville|Liouville]], Cauchy—seem to have adopted the theory immediately." Fresnel's other prominent French opponent, Biot, appeared to take a neutral position in 1830, and eventually accepted the wave theory—possibly by 1846 and certainly by 1858.<ref>Frankel, 1976, pp.&nbsp;173–174.</ref><!-- On Biot's later views, Silliman (1967, p. 284) cites no sources and is clearly mistaken. -->

In 1826, the British astronomer [[John Herschel]], who was working on a book-length article on light for the ''[[Encyclopædia Metropolitana]]'', addressed three questions to Fresnel concerning double refraction, partial reflection, and their relation to polarization. The resulting article,{{r|herschel-light}} titled simply "Light", was highly sympathetic to the wave theory, although not entirely free of selectionist language. It was circulating privately by 1828 and was published in 1830.<ref>Buchwald, 1989, pp.&nbsp;291–296; Darrigol, 2012, pp.&nbsp;220–221,{{tsp}}303.</ref> Meanwhile, Young's translation of Fresnel's ''De la Lumière'' was published in installments from 1827 to 1829.<ref>Fresnel, 1822a; Kipnis, 1991, pp.&nbsp;227–228.</ref> [[George Biddell Airy]], the former [[Lucasian Professor of Mathematics|Lucasian Professor]] at [[University of Cambridge|Cambridge]] and future [[Astronomer Royal]], unreservedly accepted the wave theory by 1831.<ref>Buchwald, 1989, p.&nbsp;296.</ref> In 1834, he famously calculated the diffraction pattern of a circular aperture from the wave theory,{{r|airy-1834}} thereby explaining the limited [[angular resolution]] of a perfect [[telescope]] {{crossreference|(see [[Airy disk]])}}. By the end of the 1830s, the only prominent British physicist who held out against the wave theory was [[David Brewster|Brewster]], whose objections included the difficulty of explaining [[photochemistry|photochemical]] effects and (in his opinion) [[dispersion (optics)|dispersion]].<ref>Darrigol, 2012, pp.&nbsp;222–223,{{tsp}}248.</ref>

A German translation of ''De la Lumière'' was published in installments in 1825 and 1828. The wave theory was adopted by [[Joseph von Fraunhofer|Fraunhofer]] in the early 1820s and by [[Franz Ernst Neumann]] in the 1830s, and then began to find favor in German textbooks.<ref>Kipnis, 1991, pp.&nbsp;225,{{px2}}227; Darrigol, 2012, pp.&nbsp;223,{{px2}}245.</ref>

The economy of assumptions under the wave theory was emphasized by [[William Whewell]] in his ''History of the Inductive Sciences'', first published in 1837. In the corpuscular system, "every new class of facts requires a new supposition," whereas in the wave system, a hypothesis devised in order to explain one phenomenon is then found to explain or predict others. In the corpuscular system there is "no unexpected success, no happy coincidence, no convergence of principles from remote quarters"; but in the wave system, "all tends to unity and simplicity."{{hsp}}<ref>Whewell, 1857, pp.&nbsp;340–341; the quoted paragraphs date from the 1st Ed.&nbsp;(1837).</ref>

Hence, in 1850, when [[Léon Foucault|Foucault]] and [[Hippolyte Fizeau|Fizeau]] found by experiment that light travels more slowly in water than in air, in accordance with the wave explanation of refraction and contrary to the corpuscular explanation, the result came as no surprise.<ref>Whewell, 1857, pp.&nbsp;482–483; Whittaker, 1910, p.&nbsp;136; Darrigol, 2012, p.&nbsp;223.</ref>
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