REFORM OF MINERALOGICAL SYSTEMS. 265 



into account all the resemblances and differences of 

 the objects classified. It is obvious that to execute 

 such a work, implied a most intimate and universal 

 acquaintance with minerals ; a power of combin- 

 ing in one vivid survey the whole mineral kingdom. 

 To illustrate the spirit in which Professor Mohs per- 

 formed his task, I hope I may be allowed to refer 

 to my own intercourse with him. At an early 

 period of my miner alogical studies, when the very 

 conception of a Natural System was new to me, he, 

 with great kindliness of temper, allowed me habi- 

 tually to propose to him the scruples which arose 

 in my mind, before I could admit principles which 

 appeared to me then so vague and indefinite ; and 

 answered my objections with great patience and 

 most instructive clearness. Among other difficulties, 

 I one day propounded to him this ; " You have 

 published a Treatise on Mineralogy, in which you 

 have described all the important properties of all 

 known minerals. On your principles, then, it ought 

 to be possible, merely by knowing the descriptions 

 in your book, and without seeing any minerals, to 

 construct a natural system ; and this natural system 

 ought to turn out identical with that which you 

 have produced, by so careful an examination of the 

 minerals themselves." He pondered a moment, and 

 then he answered, "It is true; but what an enormous 

 imagination (einbildungskraft, power of inward 

 imagining,} a man must have for such a work." 

 Vividness of conception of sensible properties, and 



