4 The Subject Propounded. 



ing the truth or falfhood of any propofition. Nay, 

 even the very noting down the feveral circum- 

 ftances of a procefs muft be advantageous, by 

 affording a conftant directory for repeating the 

 experiments afterwards, without any fear of a 

 mifcarriage : and the comparing one truth or 

 axiom with another, cannot fail to yield us juft 

 and folid conclufions, as well as the befl materials 

 for laying the foundation of a folid natural know- 

 ledge. 



A principal motive to the prefent undertaking, 

 in which I could with to be imitated, is the im- 

 provement of natural hiftory. A perfon, con- 

 verfant with things, and not with books only, 

 muft needs experience the infufHciency of our 

 prefent philofophy, and how few fubjects are 

 treated by writers with accuracy and precifion 

 enough, to give full fatisfaclion to an inquifitive 

 mind. Inftances of their negligence, in this re- 

 fpec~t, are every where obvious •, but no where 

 more fo, than on the fubjecl: of the pyrites •, no 

 one author having hitherto fupplied us with any 

 clear defcription, or tolerably accurate diflinction 

 of this important and leading mineral body. I 

 fay not this merely with a view to find fault, 

 being rather inclined to commend the care and 

 diligence of thofe, who have gone before me : 

 nor do I prefumc to fet up my own performance 

 for faultlefs and finifhed •, but to expofe the in- 

 dolent methods of thofe writers of our days, who 

 content themfelves with being mere tranferibers. 

 In our enquiries after truth, we ought to ufe a free- 

 dom and opennefs in animadverting upon the im- 

 perfection of our knowledge : Nor mould we 

 ftop fhort with the ancients •, but taking up one 

 body after another, confider each with due at- 

 tention and leifure, and thus collect material* 

 for latcft poftexity to work upon, and there- 

 with 



