350 R. W. G. Wyckoff— Crystal Structures of 



tunity that they give of testing these " laws''. Again 

 they are perhaps more certainly correct because they do 

 not have so empirical a basis. 



The more accurate determination of the reflections from 

 the (100) cleavage face has given the following ratio of 

 intensities : 29 



100 : 12.1 : 10.1 : 4.5. 







Fig. 16. 











-^jTX 







+ / ^4v 



M /////Y/ s 

 p ///yyy 

 L /£%/ 



1 \ \ a\ / 2 // 



vVyV 





\ 



u ^\ 







E 



\ ^~\ \ 4 \ 

 1 ^— ' 



8 A A /\ 







|JD i 



.1 '; 1.2 



1 1.3 ^l 



1.4 



1.5 







U — - 





- 



The expression proportional to the intensity of reflection 

 for the calcite arrangement becomes for any order n when 

 applied to the 211 (new axes) plane: 



A=2 O + 2 c7a + '2 O -f- 4 O cos tt mi. 

 B = 0. 



Intensity = / { (34 + 16 cos 2 tt nu) 2 | , if C, Ca, and O are 

 taken proportional to the atomic numbers of the respect- 

 ive elements. Assuming the normal decline of intensity 

 with order, the calculated ratio of intensities becomes for 

 ^ = 0.25, 



100 : 5.6 : 7.0 : 6.5. 



29 W. H. Bragg, op. tit. 



