371 
ml the Optical System of Mineralogy . 
in the Iiands of Mr Brooke, were unable to distinguish these 
minerals from those already known, and even M. Haiiy failed 
in his examination of the last of them ; but by the application 
of the optical method, I have determined both of them to be 
new minerals, and the accuracy of these determinations has been 
completely established by chemical examination. 
Another argument in favour of the optical system may be de- 
rived from the recent determination of the primitive forms of 
nineteen artificial crystals, which we owe to Mr Brooke. The 
primitive forms of fifteen of these I had previously predicted 
by the optical method, as shewn in the following list : 
Ukomboidal. Pyramidal. 
Nitrate of Soda. Arseniate of Potash. 
Prismatic. 
Itochelle Salt. 
Acetate of Soda. 
Acetate of Zinc. 
Binacetate of Copper 
Sulphate of Magnesia * *. 
Tartrate of Potash, and 
Antimony. 
Bicarbonate of Potash, 
Tartaric Acid. 
Oxalic Acid. 
Citric Acid. 
Sulphate of Iron. 
Sulphate of Cobalt. 
Chromate of Potash. 
All these results are in perfect conformity with the more recent 
determinations of Mr Brooke and M. Levy. The last of these 
crystallographers has ranked the Prussiate of Potash under the 
Pyramidal System ; while the optical method places it in the 
Prismatic System. M. Levy will, we have no doubt, see reason 
to correct this determination. 
I shall now conclude these remarks, already too much extended, 
by a single observation. If all that I have now said is erroneous, 
—if Tesselite and Apophyllite are the same body; — and if the 
Sidphato-tri-carbonate erf lead is an exception to the optical 
singular substance, both in its structure and properties, and yet the most eminent 
of our crystallographers has not been able to distinguish it from the Iceland Meso - 
type. 
* By this result Mr Brooke has given a striking confirmation of the optical 
method. Haiiy made the Sulphate of Magnesia pyramidal ; the optical method 
made it prismatic , and both Professor Mohs and Mr Brooke have confirmed this 
last result. 
a a S5 
