Augustin-Jean Fresnel
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Augustin-Jean Fresnel (pronounced [freɪ'nel] or fray-NELL in American English, [fʁɛ'nɛl] in French) (May 10, 1788 – July 14, 1827), was a French physicist who contributed significantly to the establishment of the theory of wave optics. He invented an improved lense that was used to intensify the light in lighthouses.
Biography
Fresnel was the son of an architect, born at Broglie (Eure). His early progress in learning was slow, and he still could not read when he was eight years old. At thirteen he entered the École Centrale in Caen, and at sixteen and a half the École Polytechnique, where he acquitted himself with distinction. From there he went to the École des Ponts et Chaussées. He served as an engineer successively in the departments of Vendée, Drôme and Ille-et-Vilaine; but having supported the Bourbons in 1814 he lost his appointment on Napoleon's return to power.
On the second restoration of the monarchy, he obtained a post as engineer for the roads of Paris. His researches in optics, continued until his death, appear to have been begun about the year 1814, when he prepared a paper on the aberration of light, which, however, was not published. In 1818 he wrote a memoir on diffraction for which in the ensuing year he received the prize of the Académie des Sciences at Paris. In 1820, he came upon the idea of creating a large lense as a composite of smaller lenticular cells. This was the fresnel lense, the main application for which Fresnel saw as the intensification of light for lighthouses. Fresnel and Francois Arago developed a brighter light to use in conjunction with the improved lense, and the two elements were combined in an installation at a lighthouse in 1823, the construction of which was underwritten by the French government. Fresnel's work on the improvement of lighthouses led to his appointment as the Secretary of Lighthouses for the French government, which he held concurrently with his engineering post. In the same year, Fresnel was unanimously elected a member of the academy, and in 1825 he became a member of the Royal Society of London. In Fresnel's later years, he suffered both economically and physically. In order to enhance his meager income, he took a job as temporary examiner for the Ecole Polytechnic, but was forced to relinquish this work in 1824 because of poor health. He retired to Ville-d'Avray and refrained from scientific work. His interest in the practical application of science is evident from his words spoken not long before his death:
"I could have wished to live longer, because I percieve that there are in the inexhaustible range of science, a great number of questions of public utility, of which, perhaps, I might have had the happiness of finding the solution."
The Royal Society of London presented him with the Rumford Medal, which he received on his deathbed. He died of tuberculosis.
His labours in the cause of optical science received during his lifetime only scant public recognition, and some of his papers were not printed by the Académie des Sciences until many years after his decease. But, as he wrote to Young in 1824, in him "that sensibility, or that vanity, which people call love of glory" had been blunted. "All the compliments," he says, "that I have received from Arago, Laplace and Biot never gave me so much pleasure as the discovery of a theoretic truth, or the confirmation of a calculation by experiment."
Researches
His discoveries and mathematical deductions, building on experimental work by Thomas Young, extended the wave theory of light to a large class of optical phenomena. In 1817, Young had proposed a small transverse component to light, while yet retaining a far larger longitudinal component. Fresnel, by the year 1821, was able to show via mathematical methods that polarization could be explained only if light was entirely transverse, with no longitudinal vibration whatsoever.
His use of two plane mirrors of metal, forming with each other an angle of nearly 180°, allowed him to avoid the diffraction effects caused (by the apertures) in the experiment of FM Grimaldi on interference. This allowed him to conclusively account for the phenomena of interference in accordance with the wave theory.
With François Arago he studied the laws of the interference of polarized rays. He obtained circularly polarized light by means of a rhombus of glass, known as "Fresnel's rhomb," having obtuse angles of 126° and acute angles of 54°.
He is perhaps best known as the inventor of the Fresnel lens, first adopted in lighthouses while he was a French commissioner of lighthouses, and found in many applications today.
See also
- Fresnel equations
- Fresnel diffraction
- Fresnel integral
- Fresnel lantern
- Fresnel lens
- Fresnel rhomb
- Fresnel zone
- Zone plate
- Fresnel number
- Aether drag hypothesis
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External links
- John J. O'Connor and Edmund F. Robertson. Augustin-Jean Fresnel at the MacTutor archive
- This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.
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