On some Phenomena of Polarization by Diffusion of Light. 205 



If the direction of the original vibration be inclined at an 

 angle 6 to Z, and that of the scattered ray at an angle <j>, we 

 have on resolution 



tan<£>=cosa tan 0, 



which expresses the important law enunciated by Stokes*. 



The preceding investigation depends upon the smallness of 

 D'— D as well as of A; but where the original vibrations are 

 parallel to the bar, the result is correct to all powers of D f — D. 

 I find that, if the bar be circular and composed of material for 

 which the density is D' and rigidity n' (the corresponding quan- 

 tities for the rest of the medium being D and n), the expression 

 for the scattered vibration is 



27rArD'-D n'-n \ 2tt/ 1x „ \\ 



7— — s — rS -TTri 1 c o sa r xcos — I bt—K — o I, 



\ f R* L 2D n' + n J \\ 8/' 



corresponding to 



y— cos — bt 



A, 



for the incident light at the centre of the bar. Tf we suppose 

 that n' = n, this agrees with the result already found; and it is 

 correct if the bar be small enough, whatever may be the magni- 

 tude of — p- 



XXVI. On some Phenomena of Polarization by Diffusion of Light. 

 By J. L. SoRETf. 



IN a recent memoir of great interest J, M. G.-A. Hirn has 

 occupied himself with the optical properties of flames ; and, 

 for the explanation of the whole of the phenomena, he suggests 

 the hypothesis that the solid incandescent particles to which the 

 flame owes its brightness become transparent at that high tem- 

 perature and have no longer any sensible reflecting-power. A 

 section of the memoir is devoted to the phenomena of polariza- 

 tion in, or rather to their absence from, the light of flames, and 

 contains the account of some experiments on the effect obtained 

 by causing the light of the sun to fall on a flame and on the 

 smoke which may escape from it §. 



* "■ Dynamical Theory of Diffraction," Camb. Trans, vol. ix. 



t Translated from the Bibliotheque Universelle, Archives des Sciences 

 for November 1873, vol. xlviii. pp. 231-241. 



X " Memoire sur les proprietes optiques de la flamme des corps en com- 

 bustion et sur la temperature du Soleil," Annates de Chimie etde Physique, 

 November 1873. 



§ We will quote the following passage : — 



" One of Arago's first observations in optics demonstrated that the light 



