Augustin FRESNEL Culture

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Augustin FRESNEL Culture

Postby Stephane_14 » Fri Apr 15, 2022 11:20 pm

“Clumsy” user of Thea Render, I decided to give the developers a little nod. I can make them suffer a little (each in turn) by reading this little moment of local scientific history. I live in a village called "Mathieu" located in Normandy between the city of Caen and the Channel Sea. It was here at “Mathieu” that Augustin Fresnel began these experiments on light and polarization. On this building, still inhabited, there is a plaque on which is written:
In this house Inhabited by his family for three centuries AUGUSTIN FRESNEL Member of the Academy of Sciences began in 1815 his research and experiments on the properties of light and founded the science of modern optics.

In 1804, at the age of 16, Augustin passed the entrance exam to Polytechnique. At Polytechnique, he receives lessons from the best teachers of this rapidly changing era, Monge, Fourier, Poisson, Legendre... and befriends Arago, his senior by one year. In 1806, Fresnel was admitted to the School of Bridges and Roads. At the end of his studies, in 1809, he was appointed engineer in the corps des Ponts et Chaussées. He spends his free time filling his notebooks with “daydreams” wondering about subjects as diverse as hydraulic machines, India ink, star gazing and... the nature of light.
The hundred days
March 1815. Napoleon's return from the island of Elba will change his life. He was then stationed in the department of Drôme. Faithful to his liberal convictions, he enlisted in the royal army which opposed the Emperor's march on Paris. This choice is worth to Fresnel to be relieved. However, he is authorized to go into exile in Mathieu in the family home. He took advantage of his visit to Paris to find out from Arago about the latest discoveries concerning light.
The learned founder of modern optics
It was therefore in Mathieu, during the year 1815, that Fresnel really undertook his research on light, in particular on the phenomenon of diffraction. He drills a small hole in a shutter, illuminates a hair using the beam obtained and observes the shadow: alternately dark and shiny fringes appear on the screen. His means are artisanal, but his observations are already precise: he builds himself a quality micrometer with the help of the locksmith of the village; he has the idea of observing the fringes without a screen, by aiming with a magnifying glass, which facilitates their observation.

From October 15, then November 10, 1815, Fresnel sent his first memoirs to the Academy of Sciences. Criticizing Newton's corpuscular theory then in vogue, he used the wave model of light to interpret the results obtained.
Reintegrated in July 1815 into the body of engineers, he was first appointed to Rennes, then to Paris in 1818. His stay in the capital and the scientific and friendly protection of Arago facilitated his research. In a few years, despite failing health, his discoveries followed one another at a breathtaking pace.

In 1816, he designed and carried out the famous experiment called Fresnel mirrors.
In 1818, as part of the competition organized by the Academy of Sciences on the nature of light, he submitted his thesis on the diffraction of light "Natura est simplex fecunda" (nature is simple and fertile). In this thesis where he combines scientific rigor and experimental precision, he opposes the ideas of Newton. It demonstrates that only the wave model can explain diffraction phenomena. This memory is fundamental. It is hotly debated; on March 15, 1819, the Academy of Sciences finally awarded him the prize, thus consecrating Fresnel's undulatory theses.

In collaboration with Arago and Young, he deepens the study of interference and the polarization of light. The results observed allow him to affirm that the light vibration is transverse, that is to say perpendicular to the direction of propagation. Within a few years, he created modern crystal optics as it is still taught today.
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The genius of the headlights
On June 21, 1819, Augustin Fresnel was appointed to the lighthouse commission.
In a few months, it invents the lenses with levels or lens, of Fresnel; intended to replace the parabolic mirrors used until then. This original optical system is a clever combination of several thin lenses, which are therefore easy to manufacture, and reflective prisms. This assembly, placed in front of the headlight lamp, forms a very long-range parallel beam of light. Several Fresnel lenses placed around the lamp make it possible to recover practically all the light produced by it. The Cordouan lighthouse, at the mouth of the Gironde, is the first equipped. The intensity of the beam is multiplied by nine
Died at 40
On May 12, 1823, by unanimous vote - an exceptional fact - Fresnel was elected to the Academy of Sciences. But the workload is too heavy. Its many functions exhaust it. His fragile health is deteriorating. At a time when his genius was finally recognized, tuberculosis carried him away on July 14, 1827. He was just 39 years old! A week before his death, Arago had come to present him with Rumford's medal; the Royal Society of London, had just awarded it to him.
Partial excerpts from the book “Regard sur Mathieu” June 2001
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Stéphane HENRY
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