III.— PHASE CHANGE BY REFLECTION— PRIMARILY 

 IN THE ULTRA-VIOLET* 



BY OLIVER H. GISH 



The first quantitative investigation of absolute phase change 

 was made by Quincke^ in 1872, This was followed by that of 

 Wernicke,- Wiener,^ Glan,* Hennig,^ Drude,*' Koenigsberger and 

 Bender.'^ All these investigations were confined to the visible 

 spectrum except that of Koenigsberger and Bender, who, in ad- 

 dition, measured for a few substances the phase change in the 

 infra-red. So far no measurements of this phenomenon have 

 been made in the ultra-violet. 



Quincke used a total reflecting prism, a portion of whose re- 

 flecting surface was silvered. Light from a point source, zvhen 

 reflected by this prism,, showed interference bands due to the 

 difference in phase of the waves reflected from the silver and 

 those reflected from the glass. He observed variations in these 

 bands with the angle of incidence, and also with the plane of polar- 

 ization. From measurements of the width of these bands he 

 arrived at values for the phase change from silver relative to that 

 from glass. The complexity of this method made it unsatisfactory. 



Wernicke devised a simpler method by which he measured the 

 phase change of silver and several dyes. In this method a thin, 

 plane, parallel plate of glass was so mounted that white light 

 reflected from it, entering a spectroscope, produced a spectrum 

 that showed vertical light and dark bands. The bands from the 



1 G. Quincke, Pogg. Ann., 142, p. 192, 1872. 



2 W. Wernicke, Pogg. Ann., 142, p. 192, 1876. 

 ^O. Wiener, Wied. Ann., 31, p. 629, 1887. 



* P. Glan, Wied. Ann., 7, p. 640, 1879; Wied. Ann., 47, p. 252, 1892. 



5 R. Hennig, Gott. Nachr., 13, p. 365, 1887. 



6 P. Drude, Wied. Ann., 50, p. 595, 1893; 51, p. 77, 1894. 



"^ J. Koenigsberger u. R. Bender, Ann. d. Phys., 26, p. 763, 1908. 



* Published also in The Physical Review. 



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