STUDY OF ORES AND METALS. 427 



because it shows that high reflecting power (metalHc or sub-nietalHc 

 luster) may arise either from high absorption index as in Na, Ag; 

 or from high refractive index, as in Si and galena ; or from both 

 high refractive index and high absorption index, as in Ir, Zn. The 

 curves of these figures show that in general an increase in the ab- 

 sorption index is much more efifective in increasing the reflecting 

 power of the substance than the same amount of increase in the re- 

 fractive index. 



The ratio of the amplitude components Rs, Rp is (equation 27) 



Rl _ _Ep 

 Rp~ ~ Ep' 



For Ep = Es this reduces to — i and indicates a phase difference 

 of TT between the incident and reflected waves. The phase difference 

 between the two components is (equation 29) 



tan (A. — Aj^o. 



Therefore plane-polarized, vertically incident light is still plane- 

 polarized after reflection from an isotropic absorbing body. 



Birefractmg , Biabsorbing Media. — The intensity ratio of the 

 reflected components from a birefracting, biabsorbing crystal plate 

 is stated by equation (28) which can be written for £.? = £/> or 

 tan e ^ I 



Irs _ 4[(wi — no)(i ■+■ W 1W2) + Uin^in^K^^ — Wifi^) 



lrp~^ [(«x + 1)2 + n,'Kmn2 - lY + n,^KiV~ ' ^^^^ 



This equation shows that for weakly birefracting substances {n-^ 

 approximately equal to Wo) the intensity ratio depends on the dif- 

 ference of the squares of the absorption indices. For substances 

 with weak biabsorption the intensity ratio depends primarily on the 

 difiference of the refractive indices. This indicates that an increase 

 in the biabsorption is more effective in increasing the degree of 

 anisotropism than the same amount of increase in birefringence. 



The phase difference between one of the components and that 

 of the incident beam is given by equation (23). Series of values 

 computed by means of this equation are listed in Table 7 and are 

 presented in graphical form in Fig. 6 in which the refractive indices 



