Secrion III, 1912 [131] Trans. R.S. C. 
Scattering and Attenuation of Light in Gaseous Media with Applications 
to the Intensity of Sky Radvation.* 
By Louis Vessot Kine, B.A., (Cantab.), Lecturer in Physics, McGill 
University, Montreal. 
Presented by Dr. A. 8. Eve, F.R.S.C. 
(Read May 15th, 1912.) 
Abstract. 
1. When radiation travels through a medium containing small 
particles whose linear dimensions are small compared with a wave- 
length of light, Lord Rayleigh? showed in 1871 that 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 to the scattered radiation in the 
neighbourhood of an element of volume an expression of the form, 
T2 (n? — 1)? 
Le(O;O)) = t2(O) hy Re 
2 XN 
(1 + cos?0) E, (i) 
leading to the well-known exponential law of attenuation 
9 9 e 
Bios | n° — 1)° a 
EE ect). wherex= 27 ( = (1) 
MN 

I (0.6) denotes the intensity of the scattered radiation from an 
element of volume in a direction © with the incident radiation of in- 
tensity E and wave-length À: n denotes the refractive index of the 
gas and N the number of molecules per unit volume. 
Expressions (i) and (11) embody what is generally known as Ray- 
leigh’s Law which expresses the scattered radiation in tems. of the : 
properties of the medium. In a later paper Rayleigh*® gave reasons 
for believing that the molecules of a gas were themselves able to scatter 
radiation in this way and that both the attenuation of light by the earth’s 

! The complete memoir will be found in the Philosophical Transactions of the 
Royal Society of London, Vol. 213A, 1913, pp. 1-60. 
? Rayleigh, Phil. Mag., xli, pp. 107, 274, 447 (1871). Collected Works, Vol. 1, 
pp. 87, 104, 518. 
3 Rayleigh, Phil. Mag., xlvii, p. 375 (1899). Collected Works, Vol. IV, p. 397. 
