The separation of waves of different wavelengths due to a dependence of sound velocity on wave length in a medium. The process in which radiation is separated into its component wavelengths. Huygen's principle explains this action by considering the continued formation and propagation of "wavelets" of all wavelengths within the radiation field. Refractive dispersion also may be considered the result of a differential change in velocity according to wavelength as the radiation passes through a refractive interface. (1) This principle is applied to wave propagation in a fluid, wherein the speed of a wave disturbance depends upon its wavelength. Any disturbance that can be analyzed into two or more harmonic wave trains will undergo dispersion, each component being propagated at its own group velocity, provided this velocity is not zero. (2) The rate of change with wavelength of the index of refraction of any refractive interface or discontinuity. The dispersion increases toward shorter wavelengths, and varies approximately inversely with the cube of the wavelength. In general, large refractive indices tend to produce correspondingly large dispersions. The dependence of dispersion on wavelength exhibits irregularities (called anomalous dispersion) near any absorption lines or absorption bands. (3) In statistics, the scattering of the values of a frequency distribution from their average