SOME OBSERVATIONS ON NIAGARA. 221 



You know that the Sphinx of Egypt is nearly covered up by the 

 sand of the desert. The neck of the Sphinx is partly cut across, not, 

 as I am assured by Mr. Huxley, by ordinary weathering, but by the 

 eroding action of the fine sand blown against it. In these cases Na- 

 ture furnishes us with hints which may be taken advantage of in art ; 

 and this action of sand has been recently turned to extraordinary ac- 

 count in the United States. When in Boston, I was taken by Mr. Jo- 

 siah Quincy to see the action of the sand-blast. A kind of hopper 

 containing fine silicious sand was connected with a reservoir of com- 

 pressed 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 con- 

 centrated on the point of impact, formed there a little pit, the depol- 

 ished surface consisting of innumerable 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 reticu- 

 lated pattern. But it required no such resisting substance as iron 

 to shelter the glass. The patterns of the finest lace could be thus re- 

 produced, the delicate filaments of the lace itself offering a sufficient 

 protection. 



All these effects have been obtained with a simple model of the 

 sand-hlast devised for me by my assistant. 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 imme- 

 diately diffusing the shock of the particle, such substances practically 

 destroy the local erosive power. The hand can bear without incon- 

 venience a sand-shower which would pulverize glass. Etchings exe- 

 cuted on glass, with suitable kinds of ink, are accurately worked out 

 by the sand-blast. In fact, within certain limits, the harder the sur- 

 face, 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 act 

 ually blow a hole through a plate of corundum. Nay, glass may be 



ties of form are produced, and referred to the effect which the erosive action thus indi- 

 cated would hare on railway and other works executed on sandy tracts. 



" Dr. Hector stated that, although, as a group, the specimens on the table could not 

 well be mistaken for artificial productions, still the forms are so peculiar, and the edges, 

 in a few of them, so perfect, that, if they were discovered associated with human works, 

 there is no doubt that they would have been referred to the so-called ' stone period.' " 

 Extracted from the Minutes of the Wellington Philosophical Society, February 9, 18C9. 



