Mineralogy, according to the Principles of Professor MOHS. 307 



bodies may differ more or less from each other in regard to their 

 properties. 



Experience shews, that, among the vast number of individuals 

 which may in this way be compared with each other, there are 

 some in which all the properties agree, except a single one. 

 Thus we find hexahedrons of Fluor agreeing in every respect, ex- 

 cept the colour, which is blue, or green, or yellow, or even some- 

 times perfectly white. This result of immediate observation may, 

 however, be obtained in a much more general and satisfactory 

 manner, by considering it in the regular forms of minerals. The 

 combination of the hexahedron and the octahedron, in an indivi- 

 dual of Fluor, may be considered as the product of the power 

 of crystallisation, which caused this individual to assume at 

 the same time the form of the hexahedron and that of the octa- 

 hedron. With each of these two forms, all the rest of the pro- 

 perties, to be observed in the individual, must be necessarily 

 connected. Every combination, however great the number of 

 simple forms which it contains, serves to demonstrate this pro- 

 position. We obtain thus a number of individuals, which belong 

 to the same series of crystallisation, and which, in regard to the 

 rest of their properties, are absolutely identical. The preceding 

 example shews, that if a number of individuals differ only in a 

 single one of their properties, the differences in this property 

 may be such as to allow them to be considered as the gradations 

 of a continuous series. This series may be the series of crystal- 

 lisation, as in the example ; but it may be every series that can 

 be possibly produced by gradations in the properties, as, for in- 

 stance, in colour, in lustre, in transparency, &c. ; nay, it may be 

 extended even to those properties which remain constant in 

 every instance, and which may be considered as producing a 

 series, all the members of which are equal. 



Every individual, not excepting those which appear in com- 

 pound forms, must necessarily be identical with itself. If, in an 



