Mohs’’ System of' Crystallography 
11, Preparation f err forming the notion (^'Homogeneity. 
in two individuals, two forms, either similar or belonging 
io the same series^ present themselves, one of the following 
things must be the case : Either those individuals completely 
agree with each other ^ in regard to their remaining charac- 
teristics ; or else, in this respect they differ more or less. 
12. Idea of uniformity. Examples. — As to the first case 
(12), namely, when the forms are similar, it is clear that mi- 
nerals in which all the other characters likewise agree, can- 
not be different in any point of view that regards natural his- 
tory. Such minerals are named uniform. Similarly coloured 
hexahedra of calcareous-spar, pentagonal dodecahedra of py- 
rites, differing merely in their size or other casual circumstan- 
ces (which are not objects contemplated by natural history), af- 
ford examples of this. 
IS. Individuals xohieh are not uniform. Examples. — If, 
whilst the forms are .nmilar^ differences exist among the re- 
maining characters, minerals of this sort undoubtedly admit 
a natural historical distinction, and consequently are at least not 
uniform. Examples of this are to be found in the octahedron 
of diamond and magnetic iron-ore ; the pentagonal dodeca- 
hedron of pyrites and glance-cobalt ; red, green, blue hexahe- 
dra of fiuor ; black, red, green rhomboidal dodecahedra of gar- 
net, &c. 
14. In dissimilar foi’ms, proof is requisite only for the 
first of those statements. — As to the second case (12.) namely, 
when the forms are not similar^ but simply members of one 
series (I. 60.) ; it is required of us only to produce evidence 
for the first of those statements (12.), that such being their mu- 
iual relation., the individuals may completely agree., so far 
as concerns their remaining characters'., for, with regard to 
the other statement, that they may happen not to agree com- 
pletely, no farther proof is necessary ; nor can any of the con- 
sequences which result from that fact, be of use in the present 
inquiry, 
15. Tlu proofs are deduced by nuans of the combinations. 
Forms which constitute members of the same series are capable 
of entering into combination with each other (I. 39. 49. 51. 
54.) Consider noAv a combination of two, three, or more 
