A formula for the index of refraction of air,
where is the wavelength. More generally, Cauchy's formula states
where and are constants (Born and Wolf 1999, p. 95).
References
Born, M. and Wolf, E. Principles of Optics: Electromagnetic Theory of Propagation, Interference, and Diffraction of Light, 7th ed. Cambridge, England: Cambridge University Press, 1999.
