272 Count de Bournon's Description of 
reflection of light, in the small intervals which remain between 
the small crystalline laminae, in those parts where these laminae 
are not in perfect contact; it is necessary, therefore, that the 
crystal, or fragment, which possesses this property, should be in 
the state most favourable to its deveiopement. On this account, 
it must not be completely transparent; there being, in that 
case, too perfect a contact between the laminas; so that the 
light, not meeting with any medium to reflect it, but being 
entirely refracted, cannot occasion any appearance of the pro- 
perty here spoken of. Neither must the crystal, or fragment, 
be quite opaque ; it being necessary that the light, in order to 
undergo the reflection which produces this pleasing phenome- 
non, should at least be able to pass through the exterior laminae 
of that part of the crystal against which it strikes. The above 
circumstances are, in fact, those which appear to take place 
with respect to corundum. The imperfect corundum of the 
Carnatic, the crystals of which are generally more or less 
opaque, show no trace of this property upon their terminal 
faces ; whereas, it is frequently observed upon the terminal faces 
of the crystals of imperfect corundum from China, and also of 
that from the coast of Malabar, because those crystals generally 
possess a slight degree of semi -transparency. This character is 
still more common in the perfect corundum, whether sapphire 
or oriental ruby. There is not, however, the smallest appear- 
ance of it, when these stones possess the beautiful transparency 
belonging to them in their highest degree of perfection ; where- 
as, on the contrary, it is frequently seen to take place in a very 
lively and brilliant manner, in such of the stones as have an 
inferior degree of transparency. It rarely happens, that the crys- 
tals of perfect corundum are prevented by opacity from exhibit- 
