the Corundum Stone, audits Varieties, &c. 275 
The imperfect corundum may likewise be cut in such a man- 
ner as to produce the starry reflection ; but it is more rare than in 
the perfect kind, to meet with pieces which have all the qualities 
requisite for this purpose. There is, in Mr. Grevillf/s collec- 
tion, a large piece of imperfect corundum, of a brown colour, 
which has been cut en cabochon, with the above-mentioned in- 
tention ; but, the cutting not having been made in the proper 
direction, the starry reflection is exhibited in a very imperfect 
manner, as it proceeds from a point near the plane of the base 
of the stone. The effect produced, however, is sufficient to 
remove all doubts respecting the existence of the property here 
spoken of, in this kind of corundum. 
CHARACTER AFFORDED BY ANALYSIS. 
In order to complete the proofs I have already given, that all 
the stones which form the subject of this Paper are of one and 
the same nature, I shall borrow this last mentioned character 
from the analyses made by Mr. Chenevix, which will hereafter 
be described at length by that able chemist; and it may be 
observed, that few instances can be met with where the chemist 
and the mineralogist, after having jointly employed themselves 
in their different provinces, upon the same substance, have 
arrived at a more satisfactory and correspondent result. 
According to Mr. Chenevix's analyses, the constituent parts 
of the various substances here treated of, are as follows. 
