822 
such as polassium-ferrocyanide, always manifested in their most 
complete and undisturbed form an axis of fourfold symmetry at the 
highest, and the same appeared to be the case with all true tetra- 
gonal crystals hitherto investigated. But in such complexes of lamellae, 
an axis of fourfold symmetry of the diffraction-image results only, 
when the composing subsequent lamellae include an angle of 90°, 
instead of 45°, as could be demonstrated e.g. by the pattern repro- 
duced in fig. 4, obtained with a system of muscovite-lamellae, care- 
fully arranged at 90°. 
Fig. 4. Stereographical Projection of the Rönrtaen-pattern of a Compiex of 
Muscovite-lamellae crossing at 90°. 
It must be concluded, therefore, that, if pseudo-tetragonal crystals 
be of the nature of polysynthetical intergrowths at all, the composing 
lamellae cannot cross at other angles than 90°. But from the mathe- 
matical theory of optical superposition’) it follows necessarily, — 
and the early experiments of NöRREMBERG and others are in full 
agreement with this conclusion, — that such systems of lamellae 
!) In 1906, at my request, professor LoreNrz was kind enough to develop once 
more the theory of the optical phenomena in systems of regularly piled-up lamellae. 
His results agree, although not quantitatively, yet in their principal features with 
those obtained by Marrarp and others. 
