821 
The character of the whole pattern as that of an original figure 
repeated regularly a number of times, equal to the number of lamellae 
contained in a full turn of 360° (here, therefore 6 or 8), — was 
observed in all cases of normal diffraction-images ; it can be considered 
as the normal character of the diffraction-patterns of such complex 
systems of lamellae. 
Basing ourselves upon the experience gained in these and other cases, 
we may, therefore, safely enunciate as a general rule: [7 the central 
part of a regular complex of crystalline lamellae, cut perpendicular 
to a plane of symmetry of the crystals, and crossing at angles 
22 
a=—, be radiated through by Rontexnrays, then the normal dif- 
n 
fraction-pattern thus obtained, will exhibit an axis of n-fold sym- 
metry, showing, therefore the image of an original pattern repeated 
n-tumes. The diffraction-image of the dextro- and laevogyratory com- 
plexes of this kind are always identical. 
§ 4. From what has been said, it must be concluded directly, 
that pseudo-tetragonal, circularly polarizing crystals can not be con- 
sidered as built up in the way supposed by Marrarp, namely, if 
they do not consist of a substance, the molecules of which are them- 
selves endowed with rotatory power. For it may be easily foreseen, 
that even in the case where the composing lamellae possessed no 
symmetry-plane whatever, the final diffraction-image will at least 
show an axis of octogonal symmetry, the eight planes of symmetry 
in fig. 3a then having disappeared. In this most general case of 
lamellae crossing at 45°, therefore, the pattern should all the same 
show an octogonal symmetry-axis, which, however, is impossible 
in crystallography, and which, in agreement with this fact, wasnever found 
by us in any diffraction-image of real or apparent tetragonal crystals. 
The RonxtceNnpatierns of any optically-inactive, pseudo-tetragonal erys- 
tal-species'), or those of optically-inactive, pseudo-tetragonal crystals 
stance, conf. the paper of R. Grocker, Ann. der Physik, (4) 47, 337, (1915). We 
have now started the systematical investigation of the phenomenon stated in the 
above, according to which the special character of the diffraction-image of such 
crossed lamellae varies with the angle 9, at which subsequent lamellae cross. 
From the fact, that the text figures 2—7 are drawn on the same scale as fig. 1, 
it will immediately be clear, that there can be not a mere superposition of images 
here, as e.g. a considerable number of the outer spots of fig, 1 have completely 
disappeared, even in so simple a case as that of fig. 4. 
') Conf. the pattern of strychnine-sulphate, in: E‚ M. Jaranr, Lectwres on the 
Principle of Symmetry and ils Application in all natural Sciences, 2nd Edition, 
Amsterdam, (1920), p. 194, 195. However, in this case the molecules of the sub- 
stance have a rotatory power in solution also. 
