4oo' Introduction to the Study of Mineralogy . 



to, not so mirth with respect to its greater or less intensity, 

 because in this respect it is too much subject to be modified 

 by'accidental causes, but relatively to a certain aspect less 

 susceptible of being disguised by the effect of the same 

 causes, and which is, as it were, unctuous in certain mine- 

 rals, and pearly in others, Sec. New characters will, ac- 

 cording to circumstances, be associated with the preceding, 

 such as electricity by heat, or phosphorescence by the action 

 of fire. 



(i I shall endeavour to define prcciselv the character which 

 is inferred from the mechanical division of a mineral ; and 

 instead of confining myself to announce in general if it has 

 taken place in one, two, or three senses, will add the 

 values of the angles which the natural joinings form among 

 tach other; — and these joinings being as the first data for 

 attaining th^e exact determination, either of the primitive 

 form, or of that of the integrant molecule, it will be ne- 

 cessary to indicate these forms, a knowledge of them being 

 important in order to form a just idea of the species, 



" Finally, I shall comprehend within the same view, the 

 character's, the verification of which is reserved. for agents 

 which, like the acids and caloric, change the nature of a 

 small part of the substance, in order to assist us in becoming 

 acquainted with the whole. 



" So much for what concerns the species in general. It 

 will afterwards be requisite to subdivide it; and in order to 

 this, first to consider the varieties relative to the forms, 

 as the most w r orthy of attention. Each of them will have 

 its peculiar denomination and definition: and if this form 

 is the produce of a regular crystallization, it will be cha- 

 racterized by an abridged sign * composed of letters and 

 indications of the laws of decrement upon which it depends, 

 which, added to an exact figure, will present the best of all 

 descriptions. I shall add the respective incidences of its 

 faces, determined by theoretical calculation, and m which 

 properly resides the impression borne by a crystal of.the spe- 

 cies to which it belongs. 



* I shall detail in the generalities the method of writing these signs ; and I 

 >>ope that it will be found simple, and easy of comprehension. 



3 " Iii 



