189 



a consequence of isomorphous admixture, etc.; cf.: Hrauns. 

 :o cit., p. 358, (1891). The truth may lie in the middle in this matter 

 too, the two views separately being perhaps both too exclusive and 

 >ne-sitle<l. It is quite possible and even probable, that in many cases 

 iternal stresses are in fact the direct cause of the optical anomalies; 

 nit our experience 

 the study of the 

 lomalous crystals 

 >v means of Ront- 

 jen-rays seems to in- 

 irate, that there is 

 many cases a grea- 

 ter probability of the 

 )rrectness of Mal- 

 lard's view. 



In the course of 

 mr studies on the 

 symmetry of the 

 R 6 n t g e n-patterns 



general 1 ), a series 

 )f optical anomalous 



Fig. 154. 



Stereographical Projection of the Rontgen-pattern 

 of pseudo- tetragonal Strychnine-sulphate. 



:rystals were also in- 

 stigated : besides 

 racite and leucite al- 



?ady mentioned, po- 

 ssium-ferrocyanide, apophyllite, sodium-chlorate, benitoite' racanic 



n-ethylenediamine-cobalti-bromide, benzile, brucite, etc. were studied, 



id also some crystals endowed with rotatory power, like quartz, 

 innabar, strychnine-sulphate, etc. Although in the last mentioned 



ises faultless patterns were obtained (fig. 154}, - - a fact which 

 lemonstratcs to what high degree of perfection this supposed lamellar 



itercalation can go, we observed in the case of apophyllite, potas- 

 sium- f err ocyanide, benzile, benitoite, and the complex co6a//i-salt 

 just mentioned, that even from apparently homogeneous and fault- 

 less plates, patterns of a lower symmetry were obtained, than should 

 be the case with respect to their proper symmetry. 



In particular, images were obtained which posessed only a single 



i) ( f. H. Haga and F. M. Jaeger, Proceed. Kon. Akad. v. Wet. Amsterdam, 

 Vol. 16, 17, 18, (19141916); 17. 438. (1914); 18. 1355, 1552. (1915). 



