Fr.: équation de Cauchy
A relationship between the → refractive index (n) and the wavelength of light (λ) passing through a medium. It is commonly stated in the following form: n = A + B/λ2 + C/λ4, where A, B, and C are constants characterizing the medium. The two-component Cauchy equation is n = A + B/λ2, from which the dispersion becomes dn/dλ = -2B/λ3 showing that dispersion varies approximately as the inverse cube of the wavelength. The dispersion at 4000 A will be about 8 times as large as at 8000 Å.
Named after Augustin Louis Cauchy (1789-1857), French mathematician and physicist who found the first equation of dispersion in 1836; → equation.