58 M. J.-L. Soret on Polarization 



and the polarization by refraction experienced by the diffused 

 light in passing through the glass to arrive at the- eye*. 

 This fact involves as a consequence that, if we operate exactly 

 in the same manner, employing only a neutral incident pencil 

 instead of a polarized pencil, the diffused rays will be much less 

 polarized in the plane of vision than they are when the light 

 arrives at the lampblack without passing through the glass. 

 Phenomena of the same kind are generally produced when the 

 light has penetrated into the body ; and when the latter has 

 no homogeneity and is not polished (chalk), very sensitive ap- 

 paratus is requisite to discover a trace of polarization. 



In coloured bodies the course of things is the same as in white 

 bodies, except that, the body not being transparent to every kind 

 of ray, it is only by superficial reflection or diffusion that the 

 white light is sent back : all the light which penetrates into the 

 interior to emerge again is coloured ; and the colour is that of 

 the rays which it permits to pass. It is natural, then, that the 

 white light, diffused superficially, should be alone polarized, 

 according to the laws of diffusion by a black body, while the 

 coloured light, which has undergone internal reflection, is not 

 polarized, or only partially so. From this results the fact, ob- 

 served by several physicists, that if one views through an ana- 

 lyzer, under a visual angle of 90°, a coloured diffusing substance 

 illumined by a pencil of natural light, the colour of the body 

 appears very pure and saturated when the analyzer is turned so 

 as to intercept the rays polarized in the plane of vision, while it 

 is washed with white when the analyzer is in the reverse posi- 

 tion or when it is viewed without an analyzer f. The experiment 

 can also be made by illuminating the unpolished coloured surface 

 by a horizontal pencil previously polarized in a vertical plane ; 

 in a horizontal visual plane, and under a visual angle of 90°, 

 the colour then appears richer than in any other position J. M. 



* When the incident pencil falls perpendicularly on the anterior surface 

 of a plate of glass slightly smoked on its posterior surface, we may assure 

 ourselves that there is no perturbation in the phenomena of polarization of 

 the light diffused after its passage through the glass. In fact, in this case 

 refraction modifies neither the direction nor the plane of polarization of 

 the incident pencil, and, on the other hand, the diffused rays come direct 

 to the eye. 



\ MM. de la Prevostaye and Desains interpret this fact by saying (with 

 some reservation, it is true) : — " It may hence be concluded that rays of 

 different tints are not diffused in the same proportions and according to 

 the same laws." Other authors content themselves with accounting for 

 the colour of bodies by saying that they diffuse certain rays more than 

 others : this is the expression of a fact, not an explanation. 



% This experiment becomes very beautiful when it is effected in the 

 following manner. A large pencil of solar or electric light is caused to 

 enter a dark room, being concentrated by a lens of long focus; near the 



