26 Professor Mohs’s General Reflections on 
of Nature, or a Natural System, in the above acceptation of the 
phrase, because nature produces only bodies, and not ideas ; and 
if we yet intend to make application of the expression in ques- 
tion, it must be in another signification, to be explained after- 
wards. 
From the preceding considerations, it appears, that the idea 
of the species also, as well as every thing that refers to this idea, 
must be founded exclusively on the natural-historical properties, 
and must not contain any characteristic marks that are not natu- 
ral-historical properties. We may suppose for the present, that 
these properties have been demonstrated to be sufficiently appli- 
cable and secure for the purpose. Whenever we introduce a 
chemical property, or in general any which is not a natural-his- 
torical one, we cease to be consistent, because we transgress the 
limits of Natural History itself. In fact, it is only pureness of 
principle in producing the natural-history species, that can ren- 
der this species the foundation of all other sciences which treat 
of mineral productions, and it ceases to be useful for this pur- 
pose whenever we permit the results of these sciences to enter 
into the determination of the species. If, in Chemistry, we wish 
to refer the results of analysis to the mineral kingdom, we must 
compare them with the natural- historical species, without regard 
to any other properties, and for this end we must employ a suffi- 
cient number of correctly determined varieties, which, in parti- 
cular, should be simple, and not intermixed with foreign sub- 
stances. The results obtained by this kind of comparison with 
the natural-historical species, will afford the idea of a chemical 
species. It is sufficiently demonstrated by experience, that the 
different varieties of one and the same species often do not ex- 
actly agree in their mixture ; and this remarkable phenomenon 
has given rise to many ingenious hypotheses, of which the idea 
of isomorphous bodies is the most interesting. It is important 
to observe, in respect to this subject, that these substances may 
be exchanged for one another in the mixture of a certain spe- 
cies, without having any influence on the natural-history spe- 
cies ; their difference does not produce the slightest alteration 
in the forms, or in the other natural-historical properties, par- 
ticularly in hardness and specific gravity. If this be the 
case, then also, in a chemical sense, individuals differing on- 
