i6a Introduction to the Study of Mineralogy. 



daccd at the same instant. By these traits he will also recog- 

 nise a phosphated lime ; and on examining in detail, upon the 

 picture of this substance, the varieties relative to indetermi- 

 nable forms, he will learn that the name which he should 

 give to the substance under inspection, will be thatofp/zos- 

 phated, earthy, whitish lime. 



I shall only add one reflection. We can easily conceive 

 that a pupil, when studying with specimens in his hands, 

 and a system founded upon external characters, can suc- 

 ceed in ascertaining all other specimens which may present 

 themselves to him under the same aspect. But his sy- 

 stem having accustomed him to examine objects by the 

 eye and touch, custom has produced an impression upon 

 his mind; which is awakened by their presence, and the 

 cause of which he would be much embarrassed to explain 

 clearly by the help of language. A similar exercise will 

 produce an analogous effect with a person who has at first 

 employed more precise characters ; the object which he 

 has considered attentively, after having once determined it, 

 has only occasion to appear : it says enough to his organs, 

 and enables him to dispense with referring to experiment, or 

 to the use of an instrument, unless it has ceased to be fa- 

 miliar to him. But when an unknown object conceals the 

 same intimate composition under an aspect quite different, 

 the student who is accustomed to take as his guide a method 

 purely descriptive, (confined to the circle of bodies, which 

 its author had under his eyes,) may commit a mistake, 

 while another, with the assistance of the first methods, will 

 not be imposed on by a false appearance : and this is a new 

 proof of the preeminence of these characters, which, be- 

 longing more closely to the nature of substances, and mark- 

 ing those points which are least likely to escape a common 

 observer, are susceptible of a much greater latitude, and 

 have the double advantage of being applied to our acquired 

 knowledge, and, as it were, to go before those which will 

 subsequently present themselves*. 



After 



* It would be desirable to endeavour to add new physical and chemical 

 characters, simple, and easy to be determined, to those which we already 



know. 



