24 Of the dißinähe Charakters of I perceived that natnes having been given to dif ferent mineral fubftances, lonietimes by reafon of their external properties, fometimes by realbn of their internal, and the bufinefs of the mine- u °r g ,-i eing t0 diftin g ui ^ the fubjedts to which thoie different names have been given from each other, he muft in fome cafes rely chiefly on the external, and in others chiefly on the internal, charatters; but, if any ambiguity remain, the decifion mufl: reft with thefe. Thus diamonds, rubies, emeralds, and other precious ftones, received their names, and were well diftinguifhed from each other, long before their internal properties were known, if even at prefent they can be faid to be fo: there mufl: furely then be fome means of diftinguifhing them, and thefe means can be no other than their exter nal properties: it were indeed a melancholy cir- cumftance to a jeweller if there were no other certain way of diftinguifhing diamonds than their internal properties; for, the only one of that kind with which we are at prefent acquainted is their deftrudtibility by heat; he fhould therefore deftroy the ftone before he could know it. What I have faid of precious ftones mav be underftood of far the greater number of ftony fubftances; either they have not been analyzed, or the analyfes given of them prefent different refults, ard confequently are undecifive; yet, fince they can be diflinguifhed, it is plain this diftin&ion may be made by external charadters. It muft be remarked, howevtr, that, in diftin guifhing earths and ftones which have never been analyzed, or which, independently of any ar.a- lyfis, have received their denomination from mere external charadlers, ambiguities frequently arile;