XII. On the scattering and absorption of light in gaseous media, with applications to the intensity of sky radiation

Abstract

1. On the Scattering of Parallel Radiation by Molecules and Small Particles . The effect of small particles in scattering incident radiation was first worked out by Lord Rayleigh. When a stream of parallel radiation falls on a particle whose dimensions are small compared with the wave-length the resulting secondary disturbance travels in all directions at the expense of the intensity in the original direction. In a later paper Lord Rayleigh gave reasons for believing that the molecules of a gas are themselves able to scatter radiation in this way. In a gaseous medium it is legitimate to sum up the intensities of the scattered radiation due to each molecule in an element of volume without a consideration of phase-difference in consequence of the continuous change in the relative positions of a molecule in a gas. The same remark applies to the case where the scattering is due to small particles of dust since these partake, to some extent at least, of the molecular agitation of the gas in which they are held in suspension.