NIAGARA. 147 
not, as I am assured by Mr. Huxley, by ordinary weather- 
ing, but by the eroding action of the fine sand blown 
against it. In these cases Nature furnishes us with hints 
which may be taken advantage of in art; and this action 
of sand has been recently turned to extraordinary account 
in the United States. When in Boston, I was taken by 
my courteous and helpful friend, Mr. Josiah Quincey, to 
see the action of the sand-blast. A kind of hopper con- 
taining fine silicious sand was connected with a reservoir 
of compressed air, the pressure being variable at pleasure. 
The hopper ended in a long slit, from which the sand was 
blown. A plate of glass was placed beneath this slit, and 
caused to pass slowly under it; it came out perfectly 
depolished, with a bright opalescent glimmer, such as 
could only be produced by the most careful grinding. 
Every little particle of sand urged against the glass, having 
all its energy concentrated on the point of impact, formed 
there a little pit, the depolished surface consisting of in- 
numerable hollows of this description. 
But this was not all. By protecting certain portions of 
the surface, and exposing others, figures and tracery of any 
required form could be etched upon the glass. The figures 
of open iron-work could be thus copied; while wire-gauze 
placed over the glass produced a reticulated pattern. But 
it required no such resisting substance as iron to shelter 
the glass. The patterns of the finest lace could be thus 
reproduced; the delicate filaments of the lace itself offering 
a sufficient protection. All these effects have been obtained 
with a simple model of the sand-blast devised by my assist- 
ant. A fraction of a minute suffices to etch upon glass a 
rich and beautiful lace pattern. Any yielding substance 
may be employed to protect the glass. By diffusing the 
shock of the particle, such substances practically destroy 
the local erosive power. The hand can bear, without in- 
convenience, a sand-shower which would pulverize glass. 
Etchings executed on glass with suitable kinds of ink are 
accurately worked out by the sand-blast. In fact, within 
certain limits, the harder the surface, the greater is the 
concentration of the shock, and the more effectual is the 
erosion. It is not necessary that the sand should be the 
harder substance of the two; corundum, for example, is 
much harder than quartz; still, quartz-sand can not only 
depolish, but actually blow a hole through a plate of corun- 
