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BELL SYSTEM TECHNICAL JOURNAL 



tion of an electric axis is taken as the positive x axis of a right-hand xyz 

 rectangular coordinate system. The z axis is taken along the axis of the 

 hexagonal prism, and since the .v axis is an axis of two-fold symmetry we 



Fig. 2.2 — An idealized quartz crj-stal 



can take either end of the prism as the direction of +s. We then choose y 

 to form a right-handed coordinate system. (In a right-handed system if a 

 right-handed screw turns about the z axis in the sense x to y it would ad- 



