Refractivity of Nitrogen

The refractive index of nitrogen for sodium light is, according to Mascart, 1.0002973, and according to Ramsay and Travers, 1.0002971. These values refer to standard density. The constants in Cauchy's formula,

n-1=A(1+B/λ²)

are A =29.06 and B=7.7, where n and λ represent the refractive index and wave-length respectively.