242 Count de Bournon's Description of 
in my opinion, occasions greater obstacles to the progress of 
a science, than making a change in its nomenclature, especially 
when that change is made without a general agreement. For, 
by this means there exists no fixed basis; and, consequently, 
every one thinks he has a right to exercise an arbitrary power 
in this respect, and to reject the name given to a substance by 
those who first observed and described it, for the purpose of 
giving it one more suitable to his own ideas. And thus, at last, 
it becomes necessary, (in order that the labours of our prede- 
cessors may not be wholly useless,) to fill the new works on 
the subject with a tedious list of synonyms, which too often 
becomes in the end a mass of uncertainty, and a subject of 
everlasting discussion. 
COLOUR. 
Although the colour of stones, strictly speaking, may be 
considered as a very variable circumstance, and as one which 
can by no means be included among those fixed characters 
which determine the nature of the stone, it is nevertheless cer- 
tain, that many stones seem disposed to assume some colours in 
preference to others ; and, therefore, the colour of a stone, though 
an uncertain character, may sometimes serve as a secondary 
mark of distinction ; particularly, if we are cautious not to draw 
any inferences from it, except in conjunction with other cha- 
racters. As its chief use is, to fix the value of precious stones, 
and as, in those here treated of, it has served as a basis for the 
former classification of them, it becomes more necessary to 
give a minute description of it in this substance than in any 
other. 
I have already said, that the colour of common corundum, 
