In Some of the Plots of the Interstellar Polarization (for example, fig. 1 of first paper by Gehrels in the present compilation) a striking feature is noted in a discontinuity that frequently occurs near λ-1 = 1.3. The following explanation of the shape of the curve of interstellar polarization as a function of wavelength is proposed in terms of physical optics.

Far in the infrared, light passes the particle with relatively little interaction. At shorter wavelengths (red light), scattering by the molecules at the particle skin increases and consequently the amount of polarization rises. The rise with increasing values of λ-1 is steep (although not necessarily with λ-4 for polarization).

Prediction of the wavelength at which the rise becomes evident would necessitate a knowledge of the optical depth or scattering cross sections. These factors have not yet been evaluated. Qualitatively, the larger the particles, the larger the wavelength at which the polarization rise becomes manifest because of greater molecular optical depth near the skin.