829 
of 120°, but each following lamella was turned with respect to the 
“preceding through 180° about an axis perpendicular to its plane of 
cleavage. It will be easily understood that in this way the symmetry 
of the intensity-distribution in the two patterns must be essentially the 
same; it is remarkable, moreover, that also the patterns themselves 
appeared identical, notwithstanding the fact, that the sequence of 
Fig. 6. Stereographical Projection (schematical) of the Rönreenpatterns of 
two Mica-piles, the Lamellae of which crossed at angles of 60° 
and 120° respectively, with a partial reversion of some of them. 
subsequent lamellae was different in the two mica-piles: both dif- 
fraction-images show a senary axis and. six planes of symmetry 
passing through it. 
§ 7. Regarding the results obtained in the above, hardly any doubt 
can remain as to the principal justification of our former view, 
according to which the observed abnormalities in the R6nreunpatterns 
of pseudo-symmetrical uniaxial crystals are in reality caused by a 
simple reversion of the position of the composing lamellae. Rotations 
of this kind may, for example, occur in some cases of tvin-formation 
between those lamellae, if the axis of rotation or twinning be only 
no real symmetry-element of the crystallographical structure of the 
