The Refractive Index of Sodium Vapor and the Width of theDLines in Absorption

Employing classical methods, a theoretical relation is developed between the refractivity of sodium vapor near the $D$ lines and their observed width in absorption. A preliminary experimental test of this relation is described. The method involved observation of the wave-lengths of interference fringes produced by sodium vapor when a Michelson interferometer was used in conjunction with a spectroscope and a source of white light. This is a convenient means of determining refractivity in cases where it varies rapidly with wave-length. The approximate observations verify the classical theory, and serve to give a determination of $\frac{e^2}{m{c}^2}$ which is correct in order of magnitude. As regards the scattering of radiation, therefore, sodium atoms may be considered as behaving in a manner analogous to Hertzian oscillators. Further experimental study is planned.