III. The polarization fields and the resonance frequencies of the alkali halide crystals

This is the authors' abstract. We don't add key points for this paper.

The effect of the polarization field on the dielectric constant of a medium can be taken into account in two alternative ways, which are equivalent. It may be regarded as enhancing the actual field that produces the polarization, or as determining the resonance frequencies of the medium, which will be different from the frequencies of the individual oscillators that constitute the medium. The dispersions of the alkali halides are discussed from the latter point of view. Though the polarization factors defining the interactions between the infra-red oscillators have the Lorentz value 4π/3, those defining the interactions of the electronic oscillators are found to be zero. The electronic overlap between the neighbouring ions in their equilibrium positions seems to be just the one that corresponds to negligible interactions between the electronic oscillators.