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be attributed to the specifie secondary radiation of the sulphur-, and 
selenium-atoms, all other circumstances being the same. 
§ 6. Anhydrite, Coelestine and Baryte. 
As till now we did not succeed in getting suitable patterns of 
anglesite: PbSO,, — especially because no good crystals were at 
our disposition, — we will compare here only the minerals anhy- 
drite: CaSO,, coelestine: SrSO,, and baryte: BaSO, more in detail. 
Again the degree of analogy between these three substances can 
be seen from the following values of their parameters and topical 
axes: 
Anhydrite: CaSO,. a:b:ec=— 0,8932:1:1,0008; spec. gravity: 2,96; 
fA) == OOD RD 
Coelestine : Sr ERO: 6:c=0,7790:1:1,2800; spec. gravity: SIDE 
yo bew = 2/80: ae 4,60. 
Baryte : BaSO,. a:b:¢ 8152 :1:1,3136; spec. gravity: 4,486, 
En 4,79 
Evidently CaSO, cannot be considered to be isomorphous with 
the Sr-, and the Ba-salt in the true sense of the word, notwith- 
standing its close relation to them; indeed, also the comparison of 
the corresponding Röntgen-patterns will show immediately, that the 
anhydrite gives images, which are strongly different from those of 
both the other salts’). (Vid. the projections 16, 19 and 22 on 
Plate IV). 
Of baryte we got patterns suitable for reproduction only from 
plates parallel to (100) and (001), reproduced in fig. 9 and 10 on 
Plate II. Neither the images obtained with coelestine, nor those of 
baryte parallel to (O10), could be reproduced. Therefore from 
these we have published on Plate IV only the corresponding stereo- 
graphical projections, side by side with those of the plates of baryte; 
they are reproduced in fig. 17, 20; 18, 21, and 23 on Plate IV. 
Although the images of baryte and coelestine parallel to (100), 
and in the same way those parallel to (010), appear to be highly 
analogous, these also are differing in minor details and especially 
in the intensity-distribution of the spots. Also in this case there can 
be given hardly any other explanation, — if the similarity of all 
other circumstances is taken into account, — than that it is the 
specific secondary radiation of the mutually. substituting atoms Sr 
and Ba, which produces these differences. 
1) In our former drawings an interchange of the 6- and c-axes has occurred, 
as Prof. Rinne was kind enough to indicate. Therefore we have reproduced the 
figures once more in tlie right positions, and with the corresponding indices. 
