REFLECTING POWER OF CRYSTALS L79 



OX THE VARIATION IX THE REFLECTING POWER OF 



ISOLATED CRYSTALS OF SELENIUM AND OF 



TELLURIUM WITH A VARIATION IN THE 



AZIMUTH OF THE INCIDENT PLANE 



POLARIZED LIGHT. 



L. P. SIEG. 



The reflecting power of a surface is defined as the ratio of 

 the intensity of the light, reflected at perpendicular incidence ( 

 to the intensity of the incident light. There are two ways of 

 determining the reflecting power of a metallic surface. One is 

 by a direct, or photometric (dioptric) method. The other is 

 by an indirect (katoptric) method. In the latter an analysis 

 is made of the elliptic-ally polarized light coming from the sur- 

 face in question, upon which plane polarized light is incident. 

 This analysis yields what are called the optical constants of 

 the substance. These constants are the index of refraction, the 

 absorption index, and the reflecting power. Both methods have 

 been used repeatedly and the concordance of the results gives 

 us such faith in the indirect method, that, in view of the fact 

 that the absorption index and index of refraction of the metal 

 constituting the surface arc much more easily determined by 

 the second method, we generally employ this indirect method. 

 Nevertheless it is always desirable when possible to check the 

 results by some direct experimental attack. 



Most of the work done on metallic surfaces has been done, 

 not only by the indirect method, but also on rather large 

 polished surfaces of the metals in question. In view of the 

 fact that metals are essentially crystalline, it becomes at once 

 en open question as to whether the optical constants determined 

 from large polished surfaces represent the real facts. For unless 

 the crystals constituting the metal belong to the cubic system, 

 one should certainly expect a set of optical constants depend- 

 ing on the orientation of the crystalline axis. In this view, 

 then, the constants ordinarily determined can represenl only. 

 except in the case of metals of the eubic system, certain mean 

 values of the actual constants. 



