Abstract
Schroedinger's theory of dispersion is applied to the symmetrical top. The dipole of the top is assumed to lie along the axis of symmetry, and the wave-length of the incident light to be large as compared with the dimensions of the top. An explicit expression is derived for the index of refraction of a gas composed of symmetrical tops, as a function of the frequency of the incident light. As the perturbed eigenfunction is a linear function of only 3 unperturbed eigenfunctions, the dispersion formula, for a given state, consists of only 2 terms.