C 3 
XIV. On the 'cutting diamond. By W. H. Wollaston, M. D. 
Sec. R. S. 
Read May 2, 1816. 
When we consider how long the diamond has been in 
common use for the purpose of cutting glass, it is rather sur- 
prising that no adequate explanation has been given of that 
remarkable property, and that even the conditions on which 
the effect depends have not been duly investigated. 
Many persons, indeed, are not aware of the distinction 
that is to be drawn between scratching and cutting. In the 
former, the surface is irregularly torn into a rough furrow ; 
in the latter a smooth fissure, or superficial crack, is made, 
which should be continued without interruption from one end 
to the other of the line in which the glass is intended to be cut. 
The skilful workman then applies a small force solely at one 
extremity of this line, and the crack which he forms is led by 
the fissure almost with certainty to the other. 
Any other substance harder than glass, possesses the 
power of scratching in common with the diamond. But the 
power of cutting has been thought confined to the diamond ; 
and it is true that its peculiar hardness certainly contributes 
to the duration of that power. 
I was informed that persons employed in setting diamonds 
for the use of the glazier, always select natural diamonds dis~ 
tinctly crystallized, which they term sparks ; but upon what 
