— 201 — 
perhaps in the nature of things, it seems at least inevitable 
that the nomenclature of elementary properties should be 
vague and unsatisfactory. The properties of solids : — hard, 
soft, brittle, tough, tenacious, elastic, malleable do not stand 
in any definite relation to one another. Even the hardnes, 
which resists abraison, the hardness which resists penetration, 
the hardness which resists crushing are by no means identical ; 
so that one body may possess more of the one sort of hard- 
ness than a second body does, while the second body exceeds 
the first in another sort of hardness. Nor do any of the 
above mentioned properties of solids stand in any simple 
relation to that resistance to the separation of contiguous 
parts which is called cohesion. 
By no attribution of this single property of cohesion, could 
we define shell-lac or ice, bodies which are at the same time 
tough, brittle, elastic and soft. 
There appear to be two kinds of solid cohesion, which may 
be called stubborn and persistent. These may coexist but are 
not identical. The one is strong to assert the other pertina- 
cious to maintain. The four following substances may serve 
to illustrate the possession of these two cohesions in various 
quantity : — 
Talc has little stubborn and little persistent cohesion. 
Glass „ much „ „ „ „ „ 
Gold ,,' little ,, ,, much „ ,, 
Iron ,, much „ „ much ,, „ ■ 
The necessity for this discrimination exists in a yet higher 
degree in liquids. If we conceive two liquids of different 
nature dropping from the same substance which they both 
wet, and if there be only one kind of cohesion : the one 
which has the greatest cohesion will tend most strongly to 
assume the spherical form : and this would tend to cause it 
to drop sooner or have a smaller drop size than the other. 
On the other hand the liquid of stronger cohesion will 
cling most strongly to the film of liquid adhering to the 
solid: this will keep it longer from falling and thereby in- 
