826 
of reversed lamellae greater than three: for it will be evident, that 
an accidental reversion of four lamellae, for example, will have’ 
the same effect as the turning through 180° of two lamellae, of 
five the same as if one were reversed, etc. These cases are, there- 
fore, already contained amongst the possibilities formerly deduced 
in turning one, two, or three lamellae respectively. 
A closer examination now taught us, that in the case of six 
muscovite-lamellae crossing at 60°, three kinds of diffraction-images 
might be produced: with respect to the intensities of the spots 
normal patterns (VV); or such as are symmetrical with respect to a 
single plane bisecting the angle between two subsequent lamellae 
(diagonally-symmetrical; D); or finally such of the same symmetry, 
but in which the symmetry-plane now coincides with the direction 
of the lamellae themselves (lamellar-symmetrical; Z). If one of the 
six lamellae be turned, there are siv possibilities; if two be reversed, 
fifteen cases must be considered; and if three lamellae be turned 
through 180°, twenty possible combinations must be accounted for. 
In the first mentioned six cases only images with the bilateral sym- 
metry D appear to be possible, as we found it just now in the 
case of fig. 26; in the case of two reversed lamellae, we may find 
three combinations of pure hexagonal, normal symmetry, siz combi- 
nations of diagonally-symmetrical character D, and siz of lamellar 
symmetry L. In the last mentioned case of three reversed lamellae, 
we may find two possible combinations of normal character, here, 
however, not with hexagonal, but with trigonal symmetry; and 
eighteen combinations, corresponding to diagonally symmetrical 
diffraction-images D: 
A Review of the Possible Types of Intensity-Distribution in the Diffraction-Patterns, |. 
Obtained by means of Mica-Complexes with Lamellae Crossing at 60°. 
If one lamella If two lamellae | If three lamellae 
be turned: be turned: be turned: 
Number of possible 
combinations: 6 5 20 
Normal images: 0. 3 (hexag.). 2 (trigon.). 
Asymmetrical Images: 0. 0. 0. 
Diag. symm. Images: 6. 6. 18. 
Lamell. symm. Images: 0. 6. 0. 
From this it appears, that a mica-complex piled-up arbitrarily 
and without special care, with lamellae crossing alt 60°, will 
