284 Professor Mohs'' Reply to Professor Weiss - , 
The agreement between the system of crystallization of M« 
Weiss and my own, extends only to the exterior of the latter , 
and has no reference whatever to the arrangement in their inte- 
rior. To connect several things, according to characters com- 
mon to them all, does not produce a system , but only an aggre- 
gate. If there exist several characters of that kind, or several 
differences in one character, we obtain several similar aggregates, 
and effect a division. Thus, the systems of crystallization of 
Professor Weiss may be considered as divisions of the crystal- 
line forms, according to those characteristic terms to which he 
refers their geometrical character ; and he would have expressed 
this rigorously, if, instead of Systems of Crystallization in the 
title of his memoir, he had said Forms of Crystallization. To 
every division of that kind, it is necessary to refer all such forms 
as exhibit the same geometrical character ; but among these 
forms themselves there exists no connection, because such a 
connection cannot be a consequence of their aggregation. 
Under these circumstances, we are led immediately to that con- 
nection of the forms in the interior of the system, from which, 
as an immediate and necessary consequence , flows their aggre- 
gation ; or what Professor Weiss understands by his systems of 
crystallization. The systems of crystallization of my method, 
therefore, are not mere aggregates, but true systems ; and, for 
this reason, essentially different from the systems of Professor 
Weiss ; and although both of them refer to the same objects in 
nature, yet it. is only in my systems that every single form oc- 
cupies that particular place which is assigned to it by its rela- 
tions to all the others ; the very property upon which is founded 
the true character of every system. 
Upon this property depends also the most important use 
that can be made of the systems and series of crystallization,— 
which I consider to be that which refers to the natural history 
species in the mineral kingdom. If, with Haiiy, we confine the 
notion of the species to the agreement of the individuals in both 
their integral molecules and their chemical constitution, or if, 
in general, we confine it to the agreement in one or several cha- 
racters, that notion will be so very deficient in many re- 
spects, that it cannot become of any use in a. natural system ; 
for it does not contain any thing of that highly remarkable con - 
