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Fresnel at the Observatory
Extrait du Observatoire de Paris centre de recherche et enseignement en astronomie et
astrophysique relevant du Ministère de l'Enseignement supérieur et de la Recherche.
https://www.obspm.fr/fresnel-at-the-observatory.html
Fresnel at the Observatory
Date de mise en ligne : mardi 11 août 2015
Observatoire de Paris centre de recherche et enseignement en astronomie et
astrophysique relevant du Ministère de l'Enseignement supérieur et de la
Recherche.
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Fresnel at the Observatory
The great physicist Augustin Fresnel (1788-1827) worked at the Paris Observatory with
François Arago from 1816 to 1819. They did experiments on interference and diffraction, and
it was there that Fresnel developed the wave theory of light, a lasting monument to his fame.
In September 1815, François Arago received at the Observatory a letter from someone unknown to him : the letter
included the following words :
I think that I have found the explanation and the theory of the colored fringes which can be seen in the shade of
bodies illuminated by a point source of light. The results of my calculations are confirmed by observation. [However,
to confirm these observations, I need instruments which can only be found in Paris. Before engaging the funds, I
would like to be certain that the effort is not useless, and that the law of diffraction has not already been established
by sufficiently precise experiments.
Augustin Jean Fresnel : gravure et dessin d'Ambroise Tardieu d'après nature (1825) Observatoire de Paris
The name of the unknown person was Augustin Fresnel. He was a young engineer of the department of « Ponts et
Chaussées » : having expressed his hostility to Napoleon after the latter's return from Elba, was confined to house
arrest in a small village not far from Caen. He had the time to do whatever interested him, especially physical optics,
and he managed to explain diverse optical phenomena via the wave theory of light, which he was in the process of
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Fresnel at the Observatory
developing.
The law of colored fringes
A month later, Fresnel sent to the Academy of Sciences a note about this theory. Arago, who was assigned as
rapporteur, was very impressed. After Napoleon abdicated, Fresnel was freed and Arago wrote to his head, François
Marie Riche de Prony (1755-1839), asking him allows Fresnel to work with him at the Observatory. The request was
accorded, since Prony could refuse nothing to Arago who was famous for his work in optics.
The wave theory
And so Fresnel came to the Observatory, and began a very fruitful collaboration with Arago. Fresnel was both a very
creative theorist and an excellent experimenter. Arago was less theoretically inclined, but on the other hand had
considerable experimental skill. Fresnel was thus able to create his masterpiece. Arago did contribute, but
generously left all the credit to his young colleague.
Banc d'optique pour études de diffraction ou polarisation Observatoire de Paris
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