126 



From the fact that of C, Si, Ge and Sn we know inodifieations 

 with the same striictiii'e as diamond, while this is not the case for 

 Ti, Zr and Th, we might conclude that C and Si are somewhat 

 more intimately connected with the elements of group \Vb than 

 with those of group lY(f. 



To Prof. Dr. W. H. Keksom I am much indebted for his interest 

 and his kind help in this investigation. 



.1) In the calculation of the intensities, only llie structure factor, the Lorentz- 

 factor and the number of planes factor have been used, not the polarisation factor 

 and the temperature factor. 



