12 A POPULAR EXPOSITION OF THE 
obtained. The degree of hardness of the mineral is then said to be 
equal to that of the member of the scale with which it agrees the 
nearest. Thus, if the mineral agrees in hardness with Fluor-spar 
we say, in its description, H (or hardness) =4. If, on the other 
hand, it be somewhat softer than fluor-spar, but harder than caleare- 
ous spar, we say, H=3.5. Finally, if, as frequently happens, the 
hardness of a mineral vary slightly in different specimens, the limits 
of the hardness are always stated. Thus, if in some specimens, a 
mineral agree in hardness with calc-spar, and in others with fluor- 
spar, we say, H = 38 to 4; or, more commonly, H =3—4. Ifthe 
hardness be very rigorously tested, it will frequently be found to 
differ slightly on different faces of a crystallized specimen, or on the 
broad faces and the edges of the lamine of foliated specimens,—but 
this, so far as regards the simple determination of minerals, is prac - 
tically of little moment. 
As the minerals of which the scale of Méhs consists, may not 
be in all places obtainable, vr always at hand when required, the 
author of this paper contrived some years ago another scale, agreeing 
closely enough for practical purposes with that of Mohs, and exact- 
ing for its application only such objects as are always to be met with. 
The following is the scale in question ; its use explains itself: 
Chapman's Convenient Scale of Hardness, to correspond with that 
of Méhs. 
. Yields easily to the nail. 
» Does not yield to the nail. Does not scratch a copper coin. 
3. Scratches a copper coin, but is also scratched by one, being 
of about the same degree of hardness. 
4. Not scratched by a copper coin. Does not scratch glass 
(ordinary window-glass). 
5. Scratches glass very feebly. Yields easily to the knife. 
6. Scratches glass easily. Yields with difficulty to the knife. 
7. Does not yield to the knife. Yields with difficulty to the 
edge of a file. 
8, 9, 10. Harder than flint or rock-erystal. 
b — 
Convenient terms of comparison for ‘degrees of hardness above 
No. 7 cannot be easily obtained ; but that is of little consequence, 
as there are but few minerals of common occurrence which exhibit 
a higher degree ; and these are readily distinguished by other char- 
