308 MR HAIDINGER on the Determination of the Species in 



individual of this kind, we enlarge the faces of one of the simple 

 forms, after the other, we obtain a series of individuals, each of 

 which is in exactly the same relation to the idea of identity as the 

 fundamental individual, and though they are not absolutely iden- 

 tical, yet they agree in respect to this idea. It is evident that 

 the forms may be arbitrarily exchanged with each other, without 

 in the least producing any change in respect to the idea of iden- 

 tity. But two or more individuals become absolutely identical, if 

 we suppose them to possess one and the same form ; and this is the 

 process by which individuals, though not identical by themselves, 

 may yet be brought under the idea of identity. In the example 

 of Fluor quoted above, the hexahedron and the octahedron, both 

 possessing the same cleavage, the same refractive and dispersive 

 powers, the same colour, the same degree of transparency, the 

 same hardness and specific gravity, &c., may be taken in so far 

 for identical, as every thing that may be found to be true of the 

 one, in respect to a more general consideration of natural histo- 

 ry, will hold equally true in regard to the other : we are entitled 

 to exchange the hexahedron for the octahedron, or, in general, 

 any two members of one and the same series of crystallisation, 

 without destroying the idea of identity. 



It is rare to find a number of individuals in nature which dif- 

 fer only in one of their properties. More generally we meet with 

 such as, at the same time, deviate more or less in one or several of 

 their other properties ; and, in order to be capable of drawing more 

 general inferences, it is necessary to join several series, like those 

 considered above, within one and the same idea. Let us suppose 

 a number of individuals of Fluor to be compared with each other, 

 all of them possessing the same colour, a dark violet-blue, but 

 various regular forms, as the octahedron (Aberdeenshire), the 

 dodecahedron (Ehrenfriedersdorf), the hexahedral trigonal-icosi- 

 tetrahedron (St Agnes), the second variety of tetragonal-icosi te- 

 trahedrons (Zinnwald), and various combinations of the same 



