^5^4 Mohs' System of Crysialtography 
minerals, all the characters, excepting the forms, agree together 
with perfect exactness. These forms may be hexahedra, oc- 
tahedra, rhomboidal-dodecahedra, &c. or combinations of two 
or more of such figures. Now, if from any individual whose 
form is an octahedron, that figure were removed, so to speak, 
and a hexahedron substituted in its place, then would this indi- 
vidual no longer differ from one whose form was originally 
a hexahedron, and so in other cases. The combinations again 
shew’, that we are warranted to adopt this process, and to ad- 
mit nothing arbitrary in our application of it. If one of those 
individuals appear under the form of a combination of the 
hexahedron and octahedron, we are at liberty either to consider 
its form as a hexahedron joined with an octahedron, or as an 
octahedron joined with a hexahedron ; as a hexahedron with 
truncated angles ; or as an octahedron with truncated angles. 
19 . Individuals capable of being brought under the concep- 
tion of uniformity differ in the smallest degree. — The diffe- 
rences among individuals, whose forms, colours, or characters 
are terms of the same series, or constitute a series themselves, 
the state of the remaining properties being the same, are not so 
great as the differences of those which, under similar circum- 
stances, exhibit no such relation. For, in the first case, if we 
put the members of the series equal, or substitute one mem- 
ber in place of all the rest, the individuals (13. 19.) become 
uniform. But this state indicates the smallest degree of diffe- 
rence. With the other class, however, no such method can 
be followed, because nothing but such characters (forms, co- 
lours, &c.), as are terms of the same series, can be interchanged 
or put in the place one of another (19.) Minerals of this sort 
cannot, therefore, by any means (by any regular proceeding 
with their characters), be brought under the notion of uni- 
formity. The differences which occur among them are greater 
than those of the preceding. 
SO. Separation of some individuals from the rest, leads to 
no conceptions of use in Natural History. — By this process, 
individuals may be found and separated from every other 
which, though in themselves not uniform (because they shew 
differences in one character, whose steps or shades repre- 
sent terms of a series), may yet be brought under the concep- 
