the Corundum Stone, mid its Varieties, &c. 2.73 
ing the property here treated of ; but, as I have already said, the 
terminal faces which, by their position, replace the solid angles 
of the summit of the primitive rhomboid, are absolutely the 
only ones which can in any degree possess it : no appearance 
of it can be seen in any other part. This is not surprising ; 
for, as the effect here spoken of proceeds from the reflection 
of light, in the spaces between the crystalline laminae, the 
plane which may be considered as produced by a section which 
would expose the edges of all these laminae, must necessarily 
be the most proper to occasion it. This effect also takes place 
when the crystals are broken, by chance, in a direction more 
or less approaching to that which is parallel to the abovemen- 
tioned plane, notwithstanding the fracture then exhibits a very 
rugged appearance. It even happens sometimes, that this frac- 
ture is such that the edges of the laminae protrude, in the manner 
observed in the fibres of wood when it is broken across the 
grain ; yet the property here treated of is not less evident; 
and, in this last case, it is often very distinctly seen proceeding 
from between the laminae. 
To the above property must also be referred, that beautiful 
reflection of light, in the form of a star with six rays, which 
is frequently given, by cutting, to oriental rubies, sapphires, &c. 
and which causes those stones to be then called by the name 
of star-stones. The manner of cutting which brings the per- 
fect corundum into this state is, most commonly, on the part 
of the lapidary, rather the result of chance, than the conse- 
quence of any determined theory respecting the cause of the 
effect he means to produce. Accordingly, in the greater number 
of the stones which have this property, the point from whence 
the starry reflection proceeds, instead of being in the middle; 
