is shown oscillating at right angles to the ray (F) and retarded Va wave- 

 length behind this ray. Because of this difference in transmission, a 

 birefrigent object is regarded as having two axes of transmission of 

 polarized light. The axis along which the slow or retarded ray (S) 

 travels has a maximal refractive index (slow axis) while the axis along 

 which the fast or nonretarded ray (F) travels has a minimal refractive 

 index (fast axis). 



Unpolari zed 

 Incident Light 



Vertical vibrations 

 only slightly absorbed 





Horizontal vibrations 

 entirely absorbed 



t \ 



Plane-polarized 

 Transmitted Light 



Figure 11-23. Schematic Diagram Showing the Production of Plane- 

 polarized Light by Passage of Ordinary White Light Through a Sheet of 

 Polaroid Film. The medium contains oriented electronic resonators which 

 transmit only those components of the incident light vibrating in a perpen- 

 dicular plane. (From Bennett, H. S.. 1950. "The Microscopical Investiga- 

 tion of Biological Materials with Polarized Light." /// Jones, R. M. (Ed.), 

 "McClung's Handbook of Microscopical Technique," 3rd ed.. Paul B. 

 Hoeber. Inc., Harper & Brothers, New York, N. Y.. Fig. 102, p. 614.) 



When placed on the stage of the polarizing microscope and rotated 

 between crossed polarizer and analyzer, a birefrigent object shows vary- 

 ing degrees of brightness and darkness depending on the poshion of its 

 axis with respect to those of the analyzer (Figure 11-25). This is the 

 usual test for birefrigence of an object. Brightness of the object is at a 

 maximum when its axes make a ±45° angle with those of the polarizer 

 and analyzer (Figure 11-25). Because the axes of the object are not in 

 line with those of the analyzer, neither of the two polarized components 



244 / CHAPTER 11 



