Fresnel, Augustin Jean

Fresnel, Augustin Jean (1788—1827). A French physicist noted for his work on optics, such as aberration of light, interference, wave theory of light, etc. He constructed the first practical "interferometer", which is used at present in modified form in Ordnance, such as "interferometric analysis of air flow about projectiles In free flight"... 

In 1813 Jean Baptiste Biot (1774-1862) had discovered that quartz crystals could rotate the plane of plane-polarised light, and two years later he found that the same property was displayed by various natural organic products such as the liquids oil of turpentine and oil of lemon, and also by a solution of camphor in ethanol. This property, known as optical activity was found to disappear in the case of quartz when the crystals were fused. Augustin Jean Fresnel (1788-1827) suggested that the optical activity of the quartz was due to a helical arrangement of the molecules in the crystal, but it was evident that when the property was displayed by substances in the liquid or solution phase the explanation must reside in the structure of the molecule itself. 

This can be re-expressed in terms of the incident intensity, /<, and the reflectivity of the soap film, is the fraction of the incident intensity reflected by the soap film and depends on the angle of incidence and the refractive index of the film. It can be obtained from classical electromagnetic theory and was first derived by Augustin Jean Fresnel in 1823. Expressing (2.24) in terms of and /i,... 

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