An Etymological Dictionary of Astronomy and Astrophysics

A measure of the ability of a medium to separate different colors of light. It is defined by: (n₂ - n₁)/(n - 1), where  n₁ and n₂ are refractive indices at two specified widely differing wavelengths, and n is the → index of refraction for the average of these wavelengths.

See also: → dispersive; → power.