101 



full agreement between the experimental result and the theo- 

 tiial deductions. 



That in all cases of crystalline symmetry this agreement really 

 Ces place, and that therefore reversely it maybe safely concluded, 

 it the Ront gen-radiation is in all circumstances actually a 

 trie ally-symmetrical phenomenon, was demonstrated for the first 

 le by the same authors l ) in a series of papers, in which were 



ribid experiments with crystals of almost all the 32 classes 

 crystallography. 



It accidental abnormalities caused by occasional irregularities 



the molecular structure, or by twinning-phenomena, be leaved 



t of account here, we can say that the centrically-symmetrical nature 



the radiation considered, as well as the agreement of theoretically 











vr. 





Fig. 97 a-c. 



Stereographical Projection of the Ront gen-patterns of quartz, turmaline, 

 and calcite. Plates parallel to (1210). 



Reeled and experimentally found symmetry of the Ront gen-patterns, 



now been exactly stated in all cases. 



14. The same thesis about the increase of symmetry of a 

 stalline medium, in which a phenomenon of a special symmetry 

 :urs, appears to be true for all other physical phenomena in crys- 

 >. In the same way we find that the 32 possible symmetry-classes 

 of crystallography are reduced to the following eleven: 



I, C H 2 , D 3 ,, C H 4 , Df , Cl C D 3 , C H 6 , Df , T B , and K u . 

 for all phenomena which have likewise a centrically-symmetrical 

 character. 



We may also ask: to which and to how many classes will the 

 phenomena of Pyro- and piezo-electricity appear to be restricted, - 

 phenomena for which the absence of a symmetry-centre appears 

 to be precisely the striking feature? 



