543 



To derlnce the symmetry of the RoNTGEN-patlenis of these orystal- 

 sections, as it may be expected after tlie theory of the phenomenon, 

 it must be kept in mind, tliat this symmetry will be the same, as 

 in the case of the correspoiniing sections of a Active crystal, whose 

 symmetry would be that of the investigated crystal after addition of the 

 symmetry-centre ihere-to. Indeed, for the piienonienon of the Röntgen- 

 radiation tlie symmetry-centre would play the role of "addilive" 

 symmetry-element; and inversely this supposition may be judged 

 satisfactorily proved, if the experiments will show on the olher 

 hand a complete concordance between the facts and the theoretical 

 deduction. 



In the accompanying table iheiefore the theoretically expected sym- 

 metry of the RöNTGEN-patierns, as deduced from the now adopted 

 theory, is summerized for ail the optically uniaxial crystals from ihe 

 classes 9 to 27. Prom lids table the expected symmetry of the 

 diffraction-image for all urdaxial crystals can immediately be seen. 



§ 2. In the fuilowing pages we pul)iisii the results obtained in 



A 



