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Dispersal --> dispersion

(Science: microscopy) The variation of refractive index with colour (or wave-length) of light. The spreading of white light into its component colours when passing through a glass prism is due to dispersion which, in turn, is due to the fact that the refractive index of transparent substances is lower for long wavelengths than for-short wavelengths. A measure of dispersion is defined as: nd - 1 v= nf-nC where nd = refractlve index at 589 nm (yellow), nf = 486 nm (blue), nC = 656 nm (red). The act of dispersing or diffusing something; the dispersion of the troops; the diffusion of knowledge.