Brewster on the Optical Andlym of Minerals. It 
folteW the chemical method alonejihe would coufound 
with and extinguish the brilliant reflexions of the 
diamond under the name of Mihertd Carbon, 
When the chemist determines that two bodies haive the same 
ingredients j he is ignorant of the manner in which these ingre- 
dients are combiiied. If the analysis of a quadruped and a bird 
indicated the same elements^ he could not discover that these 
elements formed hair and horn in the one, while in the other 
they displayed theraselyes in the finest plumage. The chemist, 
indeed, must fail in detecting structures, because he commences 
his process by destroying them. 
In these observations, we suppose the art of the chemist to 
be perfect, and that the .chemical composition of the two sub- 
stances which he compares is determined beyond a doubt. But 
as this is far from being the case, we are disposed to think 
that when either the crystallographic or the optical methods 
•point out new properties in minerals which the chemist has con- 
founded, he ought to consider these properties as affording at 
least strong presumptions that his art may be in fault. The 
history of Arragonite furnishes us with an excellent illustration 
of this remark;- and it is a fact not less important, that the late 
Reverend Mr Gregor discovered in the Brazilian Topaz * both 
Potash and Soda, although both these ingredients eluded the 
sagacity of Klaproth and Berzelius. 
M. Berzelius has remarked, that while the optical characters 
of minerals may be derived from the nature of their element, 
and the number of atoms of each element, they may arise also 
from casual mixtures and impurities, and that to employ optical 
phenomena, produced by such accidental circumstances, is to 
carry the use of this method to its maximum. In this opinion 
we heartily concur ; but we are not aware that any such optical 
phenomena have ever been proposed, even as subsidiary charac- 
• The optical properties of the Br^iliaii Topaz differ essentially from tho.se of 
Scotland, Saxony, and New Holland. See Dr Paris’s Memoir of the Rever<end 
W. Gregor, London 1818, p. 29. Note, and p. 31., for an account of his Analysis 
of the Brazilian Topaz, and a paper on the Topaz, which will appear in the 3d NOi.. 
of the Transactiona of the Cambridge Philosojihical 
VOL. VII. NO. 13 . JULY 1822 , B. 
