268 Dr. Wollaston on the cutting diamond. 
on that side to which the greater pressure was directed, and 
the cut completely fails. 
It might be thought that the weakness of the glass in this 
part would nevertheless occasion it to break in the desired 
direction ; but the bottom of a flaw is in fact of very great 
breadth when compared to the simple crack produced in a 
proper cut. In one case the force applied to break the glass 
is dispersed over a space of some extent, and may be di- 
verted from its course; in the other the whole force is 
confined successively to the mere points of a mathematical 
line, which may be conceived the bottom of the fissure, and 
is directed onward by the facility with which the adhesion of 
each particle in succession yields to its progress. - 
The depth to which the fissure made by the diamond pe- 
netrates, need not be greater than of an inch, for I found 
that the fracture might be completely turned from its course, 
at any part of the intended line, by grinding away a portion 
of the surface ; and by an average of several experiments 
the thickness of the glass was not found to be diminished so 
much as Troths of an inch. 
Since the form of the cutting edge appeared from the 
above trials to be the principal circumstance on which the 
property of cutting depends, I thought it not improbable that 
other stones possessed of the requisite hardness, might be 
found to produce the same effect, if brought to a similar 
curvilinear edge. By a little pains I succeeded in giving this 
form to a sapphire, a ruby, a spinell ruby, to rock crystal, 
and some other substances, and found that each of these 
bodies has |the power of cutting glass for a short time with 
