( 31T ) 
Art. XVI. — Outline of Professor Mohs'" New System of Cry- 
stallography and Mineralogy. (Continued from page 176.) 
65. Specific gravity. — Specific gravity and hardness are 
the most important of these characters. With regard to 
the former, we need only observe that an instrument is neces- 
sary for estimating it, and of these the most convenient is the 
Hydrometer of Nicolson. In giving the characters of orders, 
genera and species, it is proper to lay down the limits with- 
in which the specific gravities of the several varieties are inclu- 
ded. 
66. Hardness. Scale of it. — The methods hitherto employ- 
ed to estimate the hardness of minerals, are all inadequate ; 
first, because they have no proper' scale ; and, secondly, because 
the process followed is not sufficiently uniform. The scale 
now employed is a series of minerals that consists of ten mem- 
bers, and includes the whole range of hardness displayed in the 
mineral kingdom. The minerals are (a) Common talc, a 
straight schistose variety of a white colour, =r: 1 . Foliated gyp’^ 
sum (5), or Fraueneis, with straight foliated fracture, and in 
coarse granular concretions (crystals are too soft) = % Calca- 
reous spar (c), a white moderately transparent variety, of a 
specific gravity below 2.8 ; = 3, Fluor-spar (d), any variety 
whose colour is not too dark, and whose distinct concretions 
are not too small ; 4. Apatite (e), or asparagus-stone (we 
employ the asparagus green variety, imbedded in apple-green 
talc, from Salzburg) ; — 5. Felspar (y), any cleavable var- 
riety of common felspar or adularia ; = 6. Common quartz 
(^•), or rock-crystal, if possible compact and semi-transpa- 
rent ; 7. Topaz (Ji) from Schneckenstein ; == 8. Corun- 
dum (?) ; m 9. Diamond (k) ; —10. The zero of our scale is 
fluidity. 
67. Farther division. Expression hy Ni^mhers.^lihe defi- 
ciencies of this scale are not unknown to us, but numerous 
experiments have convinced us of its applicability. Though 
the distances between two consecutive degrees are not in all 
VOT,. ITT. NO. 6. OCTOBF.r 1820. 
Y 
