Augustin-Jean Fresnel

Augustin-Jean Fresnel was a French civil engineer and physicist. Born on 10 May 1788 in Broglie, Normandy, he was the second of four sons of architect Jacques Fresnel and his wife Augustine. The family moved twice during his early childhood. His older brother Louis entered the École Polytechnique and became an artillery lieutenant, but was killed in action in Spain. Younger brother Léonor followed Augustin into civil engineering and later helped edit his works, while the youngest, Fulgence, became a linguist and diplomat. Their mother’s brother, Jean François Mérimée, was a painter and professor at the École Polytechnique. Fresnel’s parents were Jansenist Catholics, and religion dominated his early education at home. He was a sickly child, considered slow by his family, and a disputed story claims he could barely read until age eight. At nine or ten, he was known for making toy weapons from tree branches that worked too well, earning him the nickname “man of genius” from friends. In 1801 he was sent to the École Centrale at Caen, and in late 1804 he entered the École Polytechnique, placing 17th in the entrance exam. There he made few friends but excelled in drawing and geometry, winning a prize for solving a problem posed by Adrien-Marie Legendre. After graduating in 1806, he studied at the École Nationale des Ponts et Chaussées, finishing in 1809 and joining the Corps des Ponts et Chaussées, where he would work for the rest of his life. Fresnel remained a Jansenist throughout his life. He saw his intellectual gifts as divine and felt obligated to use them for others. A fellow engineer who nursed him in his final illness noted that Fresnel viewed the study of nature as part of studying God’s power and goodness, placing virtue above science. He prayed for strength of soul not only against death but against the interruption of discoveries from which he hoped to derive useful applications. His Jansenist faith may have prevented him from obtaining a permanent academic post; his only teaching role was at the Athénée in the winter of 1819–20. Fresnel’s research in optics led to widespread acceptance of the wave theory of light, replacing Newton’s corpuscular theory from the late 1830s through the end of the 19th century. He is best known for inventing the catadioptric Fresnel lens, which uses both reflection and refraction, and for pioneering stepped lenses that greatly extended lighthouse visibility, saving many lives. The simpler dioptric stepped lens, first proposed by Count Buffon and independently reinvented by Fresnel, is used in screen magnifiers and overhead projector condensers. He gave the first satisfactory explanation of diffraction by straight edges, including a wave-based account of why light travels in straight lines. By proposing that light waves are purely transverse, he explained polarization, and later worked on double refraction. Fresnel battled tuberculosis throughout his life and died from it on 14 July 1827 at age 39. He lived just long enough to receive recognition, including the Rumford Medal from the Royal Society on his deathbed. His name appears throughout modern optics and wave terminology. After Maxwell’s electromagnetic theory absorbed the wave theory of light in the 1860s, some attention shifted away from Fresnel’s contributions.