On Crystallography, 69 



The description of every determinable variety presents 

 successively the name which it bears, conformably to the 

 principles of the method of nomenclature which has been 

 above explained, the indication of its representative sign, 

 that of its figure, its synonymy, according to Korae de 

 1'Isle or other crystallographers; and lastly, the measure- 

 ments of its principal angles. When the structure of the 

 variety is complex, we add to its description explanations 

 proper for better understanding the results of the laws upon 

 which it depends. 



The indications relative to colour and to transparency 

 compose the second section, under the title of Effects of 

 light*. It is proper to remark on this subject, that any- 

 given form may offer successively all the varieties of co- 

 lour and transparency, and that, in return, evary colour 

 and every degree of transparency may be met with in every 

 kind of form. But it is unnecessary to overload the me- 

 thod with all these combinations. It is sufficient, if it 

 presents a method of indicating that which exists in any 

 given variety, to describe' this variety completely. Thus 

 the table of the characters of telesie contains implicitly all 

 the following combinations : primitive limpid telesie; unit 

 tary red transparent telesie ; amorphous translucid telesie. 



When the name which we have adopted for ori£ species 

 of mineral has been applied to different species, from a de- 

 lusive resemblance, such as colour, we indicate these doable 

 applications in a particular table placed at the end of that 

 of the varieties ; and I hope I shall be applauded for the 

 tedious task whrch I have entered upon, in order to clear 

 up the confusion which arose from these communications 

 of one and the same name to substances so ill adapted to 

 be associated with each other. 



Each article is terminated by annotations relative to the 

 situation of the substanees'in the ground, to the researches 

 which have made us acquainted with them, to its physical 

 properties, its uses in the arts, medicine, &c. I have even 

 thought it right to present most of these objects more in 

 detail than has been generally done, so as to avoid the 

 dryness of too concise indications, without however giving 

 myself up to a multiplicity of details which would appear 

 to be misplaced in a treatise upon mineralogy. 



[To be continued.] 



* We have placed the word limpid at the head of effects of colours, be- 

 cause it seemed natural to commence here by the privation of character, 

 jince it indicates that the substance is in the greatest possible state of purity. 



E3 X. Pro- 



