Light scattered by Spherical Metal Particles. 481 



for t)< 1*5 and >1*25. The reason for the discrepancy is not 

 clear. The following points may be noted : — 



(1) The polarization is calculated for a single isolated 

 particle. In the experiments, we are dealing with a mass of 

 particles, there being usually about 10 6 particles per cubic 

 centimetre. 



fi\ 1 — — LK^) 



(2) A different selection of the value of m'—— — 



might have brought the theoretical curves nearer the experi- 

 mental ones. The values of n and n/c chosen for the calcu- 

 lation are those given by R. S. Minor, viz. n = 0*176, 

 uk — 3*305. Other values that might have been used are 

 those given by Hagen and Rubens, nic = 3*78 for chemically 

 prepared silver, with a reflecting power R = - 927, giving 

 w = 0-31 ; Shea gives n = 0*20 for \486, and ?i = 0*27 for 

 X589. There is obviously very great uncertainty in regard 

 to these data. 



(3) In the theory it is assumed that all the particles are 

 strictly spherical. With very small particles this condition 

 would no doubt be fulfilled, the forces of surface tension 

 completely overcoming forces tending to produce crystalline 

 structure. But as the particles increase in size a point must 

 be reached at which the surface-tension forces are no longer 

 capable of keeping the particle in a spherical form. 



6. Summary. 



The polarization of the light scattered by spherical par- 

 ticles whose circumferences measure between one and two 

 wave-lengths has been calculated. First, on the supposition 

 that the particles are perfectly electrical conductors ; and, 

 secondly, for the case of silver particles immersed in water, 

 the incident light having a wave-length of 550 up. Obser- 

 vations have been made on the polarization of the light 

 scattered by silver suspensions containing particles of known 

 size. The behaviour indicated by the theory is followed 

 except when the circumference of the particles approaches 

 two wave-lengths. In this case the theory indicates some 

 remarkable changes in the polarization, which have not been 

 observed in any experiment. 



I am deeply indebted to Professor A. W. Porter for 

 suggesting the subject of this investigation, and for the 

 unfailing interest which he has taken in its progress. 



University College, London, 

 May 1915. 



Phil. Mag. S. 6. Vol. 30. No. 178. Oct. 1915. 2 I 



