1204 
views, a molecular formula of four times the single one, to the 
pyroxenes such of twice the single chemical formula of the resp. 
metasilicates would have to be attributed. Furthermore the crystal- 
forms themselves of this dimorphous series are related to each other 
in a close and well known way. The composition of amphibole 
and augite can be expressed as that of mixed crystals of Ca(Mg,Fe) 
(SiO,), and MgAl,SiO,; their parameters are: 
Of amphibole: a:b: ¢ = 0,5318 : 8 : 0,29386; 8 = 75%. 
Of augie: abe 1.05820). 0/5925 NRS 89°38’. 
If now for augite a somewhat different choice of the axes *) than 
the ones here adopted is made, its parameters become: a: 6: ¢ = 
= 1,0921: 1: 0,5893; 8 = 74°10’. In this form the analogy with 
amphibole immediately comes to the fore: the values for a and c 
in the case of augite are evidently twice those of amphibole, while 
the angle of inclination 8 is about the same. It may be remarked 
furthermore, that if the conclusions of Brace, according to whose 
investigations the conception of “molecular weight” for the solid 
crystal is losing its significance, were right, appreciable differences 
in the structures of the RöNraeN-patterns of amphibole and augite 
could hardly be expected any more, if the above mentioned great 
analogy between the structure of the two minerals is taken into account. 
Indeed, experiment shows this analogy in the RöNrGrN-patterns of 
augite and amphibole for sections parallel to (100) in a striking 
manner; moreover it is quite well discernible for sections parallel 
to (O01). It is more difficult to distinguish in the patterns obtained 
parallel to (010), which fact partially may be explained by the not 
completely similar orientation of the two images with respect to each 
other, and the accompanying suppression of some spots and unequal 
distribution of the intensities of the other ones; a direct comparison 
is here much more difficult than in cases, where the images possess 
one or more planes of symmetry. 
The plates of amphibole had a thickness of respectively 1,08, 1,11, 
and 0,84 mm.; those of augite: of 1,02 1,08, and 1,00 mm. Both 
minerals came from Bohemia; the photos are reproduced in fig. 15 
and 16 of Plate [V, and in fig. 17 to 20 on Plate V; the stereo- 
graphical projections in fig. 18 to 23 on Plate VI. 
In every case also these patterns show a symmetry quite in 
concordance with the conclusions drawn from the proposed theory 
of the diffraction-phenomenon. 
1) In the first choice of parameters, the pyramid o had the symbol {122}. We 
simply take 0 = {111}, which symbols are also given by Naumann-ZirxeL, according 
to the measurements of Von Koxscuarow. 
