SOME ACCESSORIES AND THEIR USES 41 



piece. The second prism is called the " analyzer." 

 Very often the analyzer is made to rotate instead 

 of the polarizer. Lighting is effected by the mirror. 

 The polariscope spUts light in such a way that certain 



Fig. 14. — Polarizer. 



objects illuminated by it display most wonderful 

 colour effects, which are varied as the rotating 

 prism is turned. Films of selenite interposed 

 between the polarizer and the object produce 

 variations of tints and colour backgrounds. The 



Fi& 15 — Analyzer 



polariscope is commonly used in examining rock 

 sections, crystals, starches, etc., and it is valuable 

 in such examinations because of the remarkable 

 way in which it reveals structure. The modern 



6 



