524 THE POPULAR SCIENCE MONTHLY. 



Avitli surprise, the power wMcb uneducated miners frequently possess, 

 of recognizing many minerals at sight. This they have acquired by 

 long experience and close familiarity with such objects, and such i)ower 

 of observation is with them so purely a habit that they are frequently 

 unable to state clearly the grounds on which their conclusions are 

 based. They recognize the minerals by what in common language is 

 called their looks, and they notice delicate differences in the looks to 

 which most men are blind. It is, however, the business of the scien- 

 tific mineralogist to analyze these looks, and to point out in what the 

 differences consist; so that by fixing his attention on these points the 

 student may gain, by a few hours' study, the power which the miner 

 acquires only after long experience. The chief difliculty, however, 

 which we find in teaching mineralogy is, that the students do not read- 

 ily see the differences when they ax-e pointed out, or, if they see them, 

 do not remember them with sufiicient precision to render their subse- 

 quent observations conclusive and precise. This either arises from a 

 failure to cultivate the powers of observation in childhood, or the sub- 

 sequent blunting of them by disuse. The ladies will scout the idea 

 that a brooch of cut-glass is as ornamental as one of diamond, and yet 

 I venture to assert that there is not one person in fifty, at least of 

 those who have not made a study of the subject, who can tell the dif- 

 ference between the two. The external appearance depends simjjly 

 on what we call lustre. The lustre of glass is vitreous, that of the 

 diamond adamantine, and I know of no other distinction which it is 

 more difficult for students to recognize than this. Those of you who 

 study mineralogy will experience this difiiculty, and it can be over- 

 come only by giving careful attention to the subject. The teacher 

 can do nothing more than put in your bands the specimens which 

 illustrate the point, and you must study these specimens until you see 

 the difference. It is a question of sight, not of understanding, and 

 all the optical theories of the cause of the lustre will not help you in 

 the least toward seeing the difference between diamond and glass, or 

 anglesite and heavy spar. Another illustration of the same fact is the 

 constant failure of students to distinguish by the eye alone between 

 the two minerals called copper-glance and gray copper. There is a 

 difference of color and lustre which, although usually well marked, it 

 requires an educated eye to distinguish. 



Mineralogy undoubtedly demands a more careful cultivation of the 

 perceptions than the other branches of chemistry ; but still you will 

 find abundant practice for close observation in them all. I have often 

 known students to reach erroneous results in qualitative analysis by 

 mistaking a white precipitate in a colored liquid for a colored precipi- 

 tate ; or by not attending to similar broad distinctions which would 

 have been obvious to any careful observer; and so in quantitative 

 analysis, mere delicacy of touch or handling is a great element of 

 success. 



