100 



with a crystal-plate parallel to (1210) will show a single binary 



axis perpendicular to the photographic plate. 1 ) 

 In fact, our experiments completely confirm the conclusions drawn 

 here. In fig. 95 a c, 96 a c, and p/ a c the stereographical pro- 



Fig. 95 a-c. 



Stereographical Projection of the R 6 n t g e n-patterns of quartz, turmaline 

 and calcite. Plates parallel to (0001). 



jections of the Ron t gen-patterns are reproduced, as they were 

 obtained by H. Haga and the author 2 ) in the case of the three 



Fig 96 a c. 



Stereographical Projection of the R on t gen-patterns of quartz, turmaline, 

 and calcite. Plates parallel to (1010). 



minerals -discussed here. There can be no doubt whatever about 



J ) A binary axis perpendicular to the photographic plate, manifests itself 

 in the photographs as a centre of symmetry in it; a centre of symmetry in 

 the crystal is not manifested in the pattern itself. 



2 ) H. Haga and F. M. Jaeger, Proceed. Akad. v. Wetenschappen Amster- 

 dam, Vol. 17, 18, (1914 -'16). On accidental abnormalities of the patterns of 

 quartz caused by twinning, vid. the papers mentioned here. 



