. 135. GENERAL IDEAS OF FORMS. 145 



to rhombohedrons. This requires, however, certain re- 

 strictions, which will be mentioned along with the results 

 of that process, in some of the paragraphs referring to the 

 Character of Combinations. 



GENEHAL IDEAS OP SIMPLE FORMS. 

 . 135. SYSTEM OF CRYSTALLISATION. 



The assemblage of simple forms derivable from 

 one fundamental form (. 87.), independent of all 

 consideration of its dimensions, is termed a System 

 of Crystallisation, and denominated after the fun- 

 damental form, from which it is derived. 



The term System of Crystallisation has often been made 

 use of in a sense different from that of the present defini- 

 tion. 



A System of Crystallisation is not a mere aggregation of 

 forms, according to their different kinds, or according to 

 certain properties peculiar to them ; but it is the Assemblage 

 of those Relations which take place among certain simple 

 forms, in as far as they are derived from one fundamental 

 form. 



From the above mentioned four fundamental forms, there 

 arise four different Systems of Crystallisation ; and no more 

 systems are possible, if there exist only four forms of this 

 kind. We have no reason to assume a new fundamental 

 form in Crystallography, unless we have discovered or ob- 

 served a form, which cannot be derived from any one of 

 those which are known. As this is the case with the sca- 

 lene four-sided pyramids with an inclined axis (. 90.), the 

 number of systems of crystallisation will be increased to 

 six, or perhaps to seven. In none of these systems can 

 there be any objection against considering all those forms 



VOL. i. K 



