Saturday, March 14, 2009

Augustin-Jean Fresnel

Did you ever see that thing called an "overhead projector"? You put a clear sheet of plastic on it, turn it on, and whatever you write on the plastic gets projected onto a screen. If you've examined it, you may have noticed that the glass plate where you put the transparency has a kind of circular design in it... That is called a Fresnel Lens. It "revolutionized lighthouse illumination throughout the world" - it was devised by Augustin-Jean Fresnel, a great physicist of the 19th century. He was born in Normandy in 1788, died near Paris in 1827.

His particular branch of physics was optics and the nature of light: "The essays published by him during 1819-1827 on refraction, interference, and related subjects are few in number, but every one of them is a masterpiece. He also made many improvements in the apparatus used in lighthouses." [Kneller] The name of Fresnel is attached to several laws and devices related to the study of optics.

Jaki gives us some of his philosophy:
It was Fresnel's awareness of this pattern in scientific history that gave him confidence in the correctness of his wave theory of diffraction. In his famous memoir of 1819, Fresnel explicitly referred to the repeated triumphs of simple assumptions in the field of classical mechanics. Furthermore, Fresnel accorded the principle of simplicity a genuinely metaphysical sense. That the mathematics of the corpuscular theory was far simpler he readily admitted. But he warned in the same breath that it is not the simplicity of mathematical formalism that should have the final word when a choice among various hypotheses was to be made. The decision, he insisted, should rest rather on the conceptual simplicity. Therefore a hypothesis aiming at acceptance should respect not so much the simplicity of mathematics but rather the simplicity of nature, which, as he noted, was not conditioned on mathematical difficulties. Nature always achieved a maximum of effects with a minimum of causes, and therefore a hypothesis based on a minimum of assumptions was, in Fresnel's eyes, always the most productive step toward sighting the true simplicity of nature.
[Jaki, The Relevance of Physics 349]

In the article from the Catholic Encyclopedia, Brock notes that "Fresnel was a deeply religious man and remarkable for his keen sense of duty." Father Kneller goes into this in some detail:
The famous physicist came of a deeply religious family. Thus his mother writes in 1802 in reply to a letter from his elder brother asking news of Augustin, then at college: "I pray God to give my son the grace to employ the great talents, which he has received, for his own benefit, and for the God of all. Much will be asked from him to whom much has been given, and most will be required of him who has received most." Augustin inherited this religious habit of mind. During the early years of his life as an engineer he was almost friendless, and was cast wholly on his own resources. He sought distraction in study, and with all the greater ardour inasmuch as he had never any taste for the practical life. "But the first inclination of his life was by no means to optics. Under the influence of a home education in which religion had held the first place he began to reflect on philosophical problems, and endeavoured to reach a rigorously scientific proof of certain of those doctrines to which he adhered with an ardent belief. But he never opened his mind on these questions save to members of his family or to his most intimate friends."
The editor of Fresnel's scientific works shows little inclination to dwell on the religious side of his character, but in spite of this we find many proofs that the great scientist remained all his life an adherent of the "Spiritual School". We find notes for instance of an essay in defence of the doctrine of immortality forwarded by Fresnel to a sceptical uncle of his. Fresnel's piety of disposition remained unaltered down to the last moment of his life. His friend, the engineer Duleau, who nursed him in his last illness, tells us that the constant theme of his conversation was the greatness of God, Whose power and wisdom he saw manifested in every part of nature. He always regarded his own intellectual endowments as a gift from God, and held it a duty to employ them for the advance of knowledge and the benefit of his fellow men. The thought of his untimely death and of the works he was compelled to leave unfinished, in no way troubled his devotion; there was something higher, he said, for mankind than science and genius.
[Fr. Kneller, Christianity and the Leaders of Modern Science, emphasis added]
If I may interject my own thought here, I find that very powerful and touching... it is a grand thing to think that his work is still in use, protecting men at sea, and providing a tool for use in education...


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