68 



BELL SYSTEM TECHNICAL JOURNAL 



Inversion through the origin (a center of symmetry) 



fl 0^ 



10 



10 



a= , u -1 Ul «= 000 100 



10 

 ^000001 



A rotation of 180° about Xi'. 



A reflection in xi plane: 



(21.14) 



«. .. (21.15) 



(21.16) 



A reflection in the X2 plane: 



a — ac- 



(21.17) 



In computing the electro-optic and mechanico-optic effects we need a 

 transformation that will restore to diagonality a matrix that has very small 

 but symmetrical off diagonal terms. This transformation we call a small 

 transformation. Such a transformation has its matrix differing but slightly 

 from an idemfactor. 



If 



Aio A31 > 



+ A22 A23 

 A23 ^33 + A 33/ 



