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 carne 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- 



