Editing Augustin-Jean Fresnel (section)

== Engineering assignments ==

Fresnel was initially posted to the western département of [[Vendée]]. There, in 1811, he anticipated what became known as the [[Solvay process]] for producing [[sodium carbonate|soda&nbsp;ash]], except that recycling of the [[ammonia]] was not considered.{{r|reilly-1951}} That difference may explain why leading chemists, who learned of his discovery through his uncle Léonor, eventually thought it uneconomic.<ref>Cf.{{tsp}} Silliman, 1967, pp.&nbsp;28–33; Levitt, 2013, p.&nbsp;29; Buchwald, 1989, pp.&nbsp;113–114.&nbsp; The surviving correspondence on soda ash extends from August 1811 to April 1812; see Fresnel, 1866–70, vol.&nbsp;2, pp.&nbsp;810–817.</ref>

[[File:028_album_dauphiné,_Nyons,_Drome,_by_AD_cropped.jpg|thumb|left|<div style="text-align: center;">Nyons, France, 19th century, drawn by Alexandre Debelle (1805–1897) </div>]]

About 1812, Fresnel was sent to [[Nyons]], in the southern département of [[Drôme]], to assist with the imperial highway that was to connect Spain and Italy.<ref name=silliman-p166 /> It is from Nyons that we have the first evidence of his interest in optics. On 15 May 1814, while work was slack due to [[Napoleon]]'s defeat,<ref>Boutry, 1948, pp.&nbsp;593–594.</ref> Fresnel wrote a "''P.S.''" to his brother Léonor, saying in part:
{{blockquote|I would also like to have papers that might tell me about the discoveries of French physicists on the polarization of light. I&nbsp;saw in the ''Moniteur'' of a few months ago that [[Jean-Baptiste Biot|Biot]] had read to the Institute a very interesting memoir on the ''polarization of light''. Though I&nbsp;break my head, I&nbsp;cannot guess what that is.<ref>Fresnel, 1866–70, vol.&nbsp;2, p.&nbsp;819; emphasis in original.</ref>}}
As late as 28 December he was still waiting for information, but by 10 February 1815 he had received Biot's memoir.<ref>Boutry, 1948, p.&nbsp;593; Arago, 1857, pp.&nbsp;407–408; Fresnel, 1815a.</ref> (The ''[[Institut de France]]'' had taken over the functions of the French ''[[French Academy of Sciences|Académie des Sciences]]'' and other ''académies'' in 1795. In&nbsp;1816 the ''Académie des Sciences'' regained its name and autonomy, but remained part of the institute.{{r|academie-hist}})

In March 1815, perceiving Napoleon's return from [[Elba]] as "an attack on civilization",<ref>Arago, 1857, p.&nbsp;405; Silliman, 2008, p.&nbsp;166.&nbsp; Arago does not use quotation marks.</ref> Fresnel departed without leave, hastened to [[Toulouse]] and offered his services to the royalist resistance, but soon found himself on the sick list. Returning to Nyons in defeat, he was threatened and had his windows broken. During the [[Hundred Days]] he was placed on suspension, which he was eventually allowed to spend at his mother's house in Mathieu. There he used his enforced leisure to begin his optical experiments.<ref>Levitt, 2013, pp.&nbsp;38–39; Boutry, 1948, p.&nbsp;594; Arago, 1857, pp.&nbsp;405–406; Kipnis, 1991, p.&nbsp;167.</ref>