48 BELL SYSTEM TECHNICAL JOURNAL 



If .vi and .T3 are binary (15.3) reduces to 



/Hu \ 

 n = n22 1 (15.4) 



\o nss/ 



which described classes 6, 7 and 8. 

 For xz quarternary alternating: 



/ Hn ni2 \ 



n = -ni2 Hn (15.5) 



\ WzzI 



This is found to handle classes 9 and 10. If .T3 is quarternary alternating 

 and xi is binary: 



/nu \ 

 n = Hn I (15.6) 



\o n33/ 



which is found to cover classes 11, 12, 13, 14 and 15. For classes 16, 17, 

 19, 23 and 25 n reduces to the form (15.5). 



If .V3 is trigonal and .ti is binary the matrix is (15.5) which then handles 

 cases 18, 20, 21, 22, 24, 26 and 27. 



For cubic crystals, not only are .Vi.vo and .V3 binary as for matrix (15.4) 



/i\ /o 1 ON 



but the vector I 1 I is an .43, for which a = I 1 1 whence, for classes 



\1/ \1 0/ 



28, 29, 30 and 31 we find the matrix: 



/Hn \ 



n = (0 Hu ) (15.6) 



\0 nil/ 



Reports of a pyro electric efifect in quartz should probably be attributed 

 to nonuniform heating exciting the piezo electric effect. Reports of a pyro 

 electric effect in such crystals as topaz and colemanite which have a center 

 of symmetry and hence cannot be piezo electric should probably be at- 

 tributed to this thermo electric effect. 



SECTION 16 



The Propagation of Light in Crystalline Media 



Maxwell's equations are : 



CV X 5 = 47r/ 

 CV X £ = -5 



