123 
In fig. 2 a and the full lines have the same meaning as in fig. 1. 
The nucleus Q is surrounded by 4 nuclei, one of which is P. 
R is another one and S and 7’ have not been drawn. Let QS and 
QT rotate about PQ until they coincide with QR. Then the binding 
rings about QR, QS and QT coincide too. The above mentioned 
relation between the phases is now so, that in those coinciding 
rings the pairs of electrons form a regular hexagon. The positions 
of the planes 6' and 6" into which the planes 6 of fig. 1 are split 
up are not changed by this rotation. In fig. 2 the phase has been 
chosen in such a way that those 6 planes form pairs that coincide 
and so give the three planes 6’ and 6", the construction of which 
needs no further explanation. In reality the hexagon pgqrstu is 
perpendicularto QR and at equal distances from Q and R. In the 
fig. it has been represented as shifted downwards and clapped down 
on the plane of drawing by a rotation about a diameter perpen- 
dicular to QR. The hexagon ABCD EF is the projection of the 
former on a plane perpendicular to the plane of drawing through 
PQ and clapped down on this plane by a rotation about this line. 
When now the radius of the rings has been chosen so, that 
6" falls halfway between 4' and a, the structure factor of (222) in 
the phase represented in the figure will become zero. From the 
ENE i 1 
construction it is evident that the radius must be chosen ee 245 
times the distance between two nuclei. It is found that in that 
