35 



colours, &c. are known to be, but they may be described and 

 discriminated by assigning the general causes and effects that 

 characterise each ; and il" mixed and compound, as some of 

 them are, the ingredients of such compounds may be distin- 

 guished and developed. 



90. In forming such descriptions with accuracy and ele« 

 gance, Dr. Cogan has excelled all preceding writers. To him 

 I am principally, but not invariably indebted for the grounds 

 of those I attempted. His arrangement, though perfectly 

 just with respect to classification, I have not followed ; that 

 not being consistent with the end I had in view. 



t' 2 ^ 1. 



