SPECIFYING QUARTZ CRYSTAL ORIENTATION 



245 



90° the field is dark; if a 7^ or 90° the field is bright. In Fig. 2.26 we illus- 

 trate how, for one color of light the polarization starts out as plane at the 



Fig. 2.25 — Recombination more generally- 

 crystal boundary, passes through elliptical to circular polarization, then flat- 

 tens out the other way through elliptical to plane polarization at a distance 



