STUDY OF ORES AND METALS. 



429 



region for which slight changes in refractive index or absorption 

 index produce the greatest difference in phase are for low refractive 

 indices w < 1.5 especially for n < i and for high absorption indices. 

 Substances, however, with such indices are rare ; the conclusion is 

 therefore generally valid that the phase difference between the two 

 components of a birefracting and biabsorbing substance for ver- 



.I8Cf 



on— <1 2 3 4 5 6 7 8 9 'C 



Fig. 6. In this figure is given the phase diflFerence (ordinates) between 

 one of the components of normally incident polarized light (azimuth € = 45°) 

 and the same component after reflection from a birefracting, biabsorbing 

 crystal plate of refractive index n (abscissae) and absorption index k (curves). 



tically incident light is not great and that the anisotropism finds 

 expression chiefly in the intensity differences of the two com- 

 ponents. This conclusion is important, since it enables the observer 

 to &pply the methods outlined above for non-absorbing media to 

 the detection of anisotropism in opaque substances. 



