STUDY OF ORES AND METALS. 



405 



For a wave length Ao = . 0005458 mm. (near the mercury green hne) 

 this expression reduces to 



1 ^° 



(2b) 



Fig. I. In this figure the curves are equi-intensity curves indicating the 

 ratio of the intensity of the transmitted light to that of the (normally) inci- 

 dent light for a plate o.ooi mm. thick, for greenish yellow hght (^o = 0.0005458 

 mm.), and for different refractive indices (ordinates) and absorption indices 

 (abscissae). The pronounced effect of even a small absorption index in cut- 

 ting down the transmission is evident from the curves. 



A series of vakies computed by means of this equation on the 

 basis of thickness / = 0.001 mm. (i micron about %o the thickness of 

 an ordinary rock thin-section) are Hsted in Table I. and represented 



