# Lorentz-Lorenz

The Lorentz-Lorenz formula, also known as the Clausius-Mossotti equation and the Maxwell equation, relates the refractive index of a dilute gas to its temperature, pressure, and molar refractivity. The index of refraction [itex]n[itex] is given by

[itex]
 n \approx \sqrt{1 + \frac{3 A p}{R T}}


[itex]

where [itex]A[itex] is the molar refractivity, [itex]p[itex] is the pressure of the gas, [itex]R[itex] is the universal gas constant, and [itex]T[itex] is the (absolute) temperature.

## History

The Lorentz-Lorenz formula is named after the Danish mathematician and scientist Ludwig Valentine Lorenz, who published it in 1869, and the Dutch physicist Hendrik Lorentz, who discovered it independently in 1870.

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