Introduction to the Study of Mineralogy* 465 



our senses, every thing that is tangible is carefully defined, 

 in which all the different signs by which an attentive ob- 

 server may recognise it are given by so many expressions, 

 which are afterwards presented separately by themselves, in 

 order to form the picture of each species. 



This union of suffrages in favour of the system I have al- 

 luded to, the great reputation which it has so justly acquired 

 for its author,, would present powerful motives to prevent 

 me from- quitting the track he has pointed out. But the 

 plan to which I had referred the order of classification, by 

 only admitting into it species properly so called, susceptible 

 of a rigorous determination, led me, in order to establish 

 their distinct characters, to profit by what they have most 

 constant, most general, and most intimately connected with 

 the constitution of their integrant molecules : and I have 

 given way to the obligation of reconciling with the fixed 

 principles I had adopted, relative to the whole of the science, 

 the method of studying its details. 



I shall here briefly mention the reasoning which directed 

 me in the manner of arranging this method. " The picture 

 of a species,'* I said to myself, "ought to present : 1st, a 

 sum of characters, by the assistance of which an observer 

 can ascertain that a mineral, which he N endeavours to class, 

 belongs to this species : 2d, the series of the varieties which 

 Subdivide the species. - , 



" Now the specific characters being as the fixed points 

 whence proceeds the knowledge relative to the species, I 

 shall exclude colours, at least when we speak of an earthy 

 or acid substance, as fugitive variable modifications foreign 

 to the type of the species which is the integrant molecule. 



" But I shall point out among these characters the spe- 

 cific gravity expressed numerically according to the result 

 of experiments, and note the hardness estimated by the 

 power which the body has to scratch another well known 

 substance employed to serve as a term of comparison. Nor 

 will I omit the property of double or single refraction, 

 because it belongs to the very basis of substances, although 

 it can be observed but very rarely when these substances are 

 in their natural state. The lustre will be sometimes referred 

 Vol. 33. No. 134. June 1809- Gg to, 



