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

Sections 1 and 2.—Lord Rayleigh showed, in 1871, that when radiation travels through a medium containing small particles whose dimensions are small compared with the wave-length, each of these sets up a secondary disturbance which travels in all directions at the expense of the energy in the original direction. Various hypotheses of the æther and of the molecule agree in giving for the scattered radiation near an element of volume an expression of the form I (0, θ) - μ (θ) E = ½ π2(n2 ─ 1)2λ-4(1+cos2θ) E/N, (1) where ω I (0, θ) is the intensity contained in a small solid angle ω in a direction θ with the direction of the original beam E; n is the refractive index of the gas, N the number of molecules per unit volume, and λ the wave-length of the incident radiation.