1360 
images of such isomorphous crystals, would appear to be quite identical. 
Even if this supposition most favourable for the older conception 
of the structure-analogy of isomorphous crystals were held up, 
— a very remarkable phenomenon still remains in these cases, 
which always and with all isomorphous crystal-species hitherto 
investigated, was observed: i.e. the fact, that the distribution of the 
relative intensities of homologous spots in the corresponding patterns 
of such isomorphous crystals, appears to be very different with the 
different members of every series; while also the total number of the 
spots, which appear in every corresponding zone, seems to be variable 
in the case of every substance in particular. 
If now a close analogy in the structure of the space-lattices is 
supposed, it will appear hardly possible to explain this remarkable 
fact in any other way, than by accounting for the mentioned differences 
by the very different specific secondary radiation of the atoms, which 
in the space-lattices will be substituted for each other isomorphously. 
If e.g. the /ead-atom under the influence of the incident primary 
RöÖNTGEN-rays will indeed radiate in a specifie way, different from 
the radiation of calcium-, or barium-atoms under the same circum- 
stances, — than it is at least comprehensible, that even in the case of 
a completely analogous spacial arrangement of such atoms in the different 
space-lattices of the studied crystals, the Röntgen-patterns obtained 
can differ in the number as well as in the intensity-distribution of 
the diffraction-spots as strongly, as was really observed. Further, 
that these pecularities, which were found by us in a// investigated 
cases, cannot be accidental, is sufficiently proved thereby, but is 
in favour of the supposition, that they are connected with the special 
nature of the atoms substituted for each other. 
It seems unnecessary to illustrate the mentioned fact by demon- 
stration of a particular Röntgenpattern or by discussing special values 
of the indices: an immediate comparison of corresponding stereo- 
graphical projections can show this in a sufficiently evident way. 
§ 4. Rhodochrosite and Calcite. 
The used erystal-plates of rhodochrosite: MnCO, were cut from 
a beautiful’ pink erystal from Colorado (The Lake Co). The corre- 
sponding photogrammes are reproduced in figs. 7 and 8 on Plate II, 
and in stereographical projection in figs. 11 and 13 on Plate IV. 
The Röntgen-patterns of calcite have already been described by us ’), 
as regards those from plates cut parallel to 11010) and 1210), while 
1) H. Haes and F. M. Jagcer, These Proceed. 18, 548. (1915). 
