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Art. XX. — Remarks on the subjects connected with Dr Brew- 
sters 44 Reply to Mr Brooke's Observations on the Optical 
System of Mineralogy? By H. J. Brooke, F.R.S. 
D r Brewster lias published in No. 18. of this Journal 44 a 
Reply” to what he terms my 44 observations on the connexion 
between the optical structure of minerals and their primitive 
forms? Dr Brewster must allow me to say, that, as I disap- 
prove the phrases optical structure and primitive forms , I have 
not used either of them, except in quoting a paragraph of his. 
Dr Brewster states, that, unwilling to occupy his time with 
such discussion, he would have addressed me privately on the 
subject, if the learned Editor of the Annals of Philosophy had 
not inserted my observations in that work. On this matter, I 
have only to remark, that I was ignorant even of the learned 
editor’s intention of giving any account of my volume, until af- 
ter the number which contained his notice was published. 
As a matter of mere feeling, I can assure Dr Brewster, that 
an object of greater indifference scarcely exists, than whether 
Tesselite be or be not Apophyllite, or whether the present systems 
of mineralogy shall or shall not be superseded by Dr Brewster's 
optical system. I cannot, however, suffer Dr Brewster's hasty 
44 reply" to pass unnoticed. 
The reader who has perused this 44 reply j will have seen that 
the opinions which have operated so powerfully upon the feel- 
ings of Dr Brewster, relate to these points. 
1. Whether the mineral which Dr Brewster has named Tes- 
selite, be really a distinct species from the Apophy llite, considered 
either chemically or crystallographically- 
2. Whether the crystalline form of the sulphate- tri-carbonate 
of lead be a rhomboid. 
3. Whether the use of optical characters can at present be re- 
lied upon for the determination of a mineral species. 
Before I proceed to justify the opinions I have expressed on 
these points, it will be necessary to consider for a moment the 
meaning of the term primitive form, and what Dr Brewster's 
ideas are of a mineral species. 
A primary form of a crystal is a simple figure, bearing cer- 
tain known and demonstrable relations to other figures, belong- 
