Fresnel, Augustin Jean

French physicist who refined the theory of polarized light. Fresnel realized in 1821 that light waves do not vibrate like sound waves longitudinally, in the direction of their motion, but transversely, at right angles to the direction of the propagated wave.

Fresnel first had to confirm the wave theory of light. He demonstrated mathematically that the dimensions of light and dark bands produced by diffraction could be related to the wavelength of the light producing them if light consisted of waves. To explain double refraction, he then arrived at the theory of transverse waves.