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) in Normandy. His early progress in learning was slow, and he could barely read when he was eight years old. But at age nine, he is said to have made improvements to some toy armaments that made them dangerous, and which were, as a result, proscribed by the elders of the community in which he lived. At thirteen he entered the École Centrale in Caen, where he was instructed by an illustrious and well-qualified roster of instructors. At sixteen and a half he transferred to the École Polytechnique, where he attracted the attention of famed mathematician Adrien-Marie Legendre, who as an examiner, noticed a novel solution for a geometric problem provided by Fresnel on an exam. This encouraged Fresnel in his studies and his approach. From there he went to the École des Ponts et Chaussées.
Professional life
After graduation, Fresnel served as an engineer successively in the departments of Vendée, Drôme and Ille-et-Vilaine, primarly involved in the details of road construction. In 1814, because he was a supporter of the French monarchy, he lost his appointment on Napoleon's return to power. n 1815 he joined the armed services of the royalist forces, but the strain on his constitution did not permit him to stay long in that capacity.
On the second restoration of the monarchy, Fresnel obtained a post as engineer for the roads of Paris. His researches in optics appear to have been begun about the year 1814, when he prepared a paper on the aberration of light, which, however, was not published because its details appeared to have already been brought to light by earlier investigators. At that time, he began studying the phenomenon called polarized light, which would be the subject of many of his later researches and discoveries. 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. Two years later, 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 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 while in the last stages of tuberculosis. He died in 1827.
Character
Freznel was of a frail constitution, and had a meek manner that was never overbearing. It was said that if one of his colleagues was shown to have committed a transgression as a public servant, his mild manner would be replaced by swift outrage. He was generally self-effacing, and far more interested in the pursuit of science and the public welfare. 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
The wave theory of light, which stretches back to antiquity, holds that light is a continuous series of impulses transmitted in the same manner as sound is transmitted in air. Some scientists, including Isaac Newton, believed that light was composed of moving particles. Waves interfere with each other in a distinct way that can be detected. Fresnel's use of two plane mirrors of metal, forming with each other an angle of nearly 180°, allowed him to conclusively account for the phenomena of interference in accordance with the wave theory.
Fresnel's 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, who had already pointed out that light produces patterns that can be accounted for by wave interference, had proposed a small transverse component to light, while yet retaining a far larger longitudinal component similar to the way sound is transmitted. Fresnel, by the year 1821, was able to show via mathematical methods that polarization could be explained only if light was entirely transverse (the modulations being perpendicular to the motion of the waves, as are waves in the sea), with no longitudinal vibration whatsoever. Fresnel's research partner, Francois Arago, did not want to give his full support to this conclusion, thus leaving the credit with Fresnel, who published his findings.
Fresnel's research showed further that the transverse nature of lightwaves could explain a phenomenon called double refraction, which splits light into two images. This double-image effect was well known as a property of icelandic feldspar, a crystalline mineral, but Fresnel showed the same property was exhibited by compressed glass.
"I had convinced myself," said Fresnel, "by a pure contemplation of the facts, that it was not possible to discover the true explanation of double refraction, without explaining, at the same time, the phenomena of polarization, which always goes along with it; and accordingly, it was after having found what mode of vibration constituted polarization, that I caught sight of the mechanical causes of double refraction."<<<An. Ch.
With Arago, Fresnel studied the laws of the interference of polarized rays. He predicted the existence of, and 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°.
Fresnel 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
ReferencesISBN links support NWE through referral fees
- Arago, F. 1859. Biographies of Distinguished Scientific Men. Tr. W. Smyth, B. Powell, R. Grant. Boston: Ticknor and Fields. 171-273.
- Whewell, William. 1857. History of the Inductive Sciences From the Earliest to the Present Time. 3 Vols. London: John W. Parker and Son. 2:330-339.
- Stevenson, Alan. 1850. A Rudimentary Treatise on the History, Construction and Illumination of Lighthouses. J. Weale.
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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