Who was Augustin Jean Fresnel?

   Augustin Jean Fresnel was a French engineer and physicist, was born in Broglie, Normandy, and studied at the École Polytechnique and the École des Ponts et Chaussées. After spending several years as a government engineer in various parts of France, Fresnel lost his post because he declared his allegiance to the Bourbons when Napoleon escaped from Elba. Through the influence of Dominique Arago, he subsequently became secretary of the government's lighthouse department in Paris. There he invented the lighthouse lens which bears his name, introduced revolving lights, and designed the Fresnel concentric wick, which greatly enhanced the brilliancy of lighthouse lamps.
   Fresnel extended his researches to the kinematics and the dynamics of light and, independently of the investigations conducted by Thomas Young, discovered the phenomenon of interference, or effect caused by the meeting of two beams of monochromatic light. Fresnel insured acceptance of the undulatory theory of light when he introduced the idea that the vibrations of the ether are transverse to the directions of the beams of light.
   The validity of the undulatory theory was further confirmed by Fresnel's investigations of the modifications in interference brought about by polarized light.