Dr. Wollaston on the cutting diamond. 269 
a clean fissure. But notwithstanding the hardness of the ruby 
was such as to occasion a great deal of labour in giving it the 
form I wished, the edge of this stone was by no means pro« 
portionally lasting. I am inclined to ascribe this defect in 
part to the grain or position of its laminae having been un- 
luckily oblique. And it seems highly probable that the 
singular durability of the edge of the cutting diamond, is 
owing in some measure to this circumstance, that its hardness 
in the direction of the natural angle of its crystal, is greater 
than in any other direction, as we find to be the case in other 
crystals of which the various degrees of hardness in different 
directions can be more easily examined. 
Nns 
