865 
on the Optical System of Mineralogy. 
lite resembles the analysis of a bird, the feathers, flesh and bones 
of which are all pounded together in a mortar, and submitted 
in a mass to the action of destructive agents. Mr Herschel, 
whose opinion on this subject must have great weight, observes, 
when speaking of Apophyllite, “ The specimen I am now de- 
6C scribing presents the hitherto unique combination of no less 
u than three distinct substances , uniting to form a single crys- 
u tab” “ It would certainly be in the highest degree interest - 
“ mg to subject them all three to chemical analysis ; but as the 
“ total weight of the specimen presenting these anomalies did 
not exceed 60 grains, of which nearly one-half consisted of 
“ the ordinary variety, I have not sufficient confidence in my 
61 c own chemical dexterity to enter on so very delicate an in- 
a quiry, which would obviously call for a degree of precision at- 
(c tainable only by consummate masters in the art of mine- 
u ral analysis.” “ It remains , therefore , to be ascertained , 
a whether their different actions on light be owing to a differ- 
6i ence in composition, or merely in their state of aggregation.” 
Cambridge Transactions , vol. i. When M. Berzelius, there- 
fore, or Mr Herschel, who is perfectly capable of executing 
what he too modestly shrinks from, shall have performed this 
interesting analysis , it will be competent for Mr Brooke to say, 
that Tesselite either is or is not chemically the same with Apo- 
phyllite. If the analysis of each part shall turn out similar to 
that of the whole, philosophers who know what Tesselite actual- 
ly is, may perhaps still decide that two bodies may be chemi- 
cally the same, and yet mineralogically different. 
Let us now follow Mr Brooke into his own stronghold of 
crystallography. 
“ A few days (he continues) before Dr Brewster’s paper was pub- 
lished, it happened that I had been measuring the angles of apophyb 
lites from most of the localities in which they occur, all of which I 
found to agree with each other more nearly than different minerals of 
the same species frequently do. The Tesselite is not , therefore, crys - 
tallographically a new species *. But when chemistry and crystallo- 
“ Note by Mr Brooke — “ I have found several crystals of this substance, cor- 
responding in a remarkable manner in their general form, of flattened four-sided 
prisms, terminated by four-sided pyramids with truncated summits, but with their 
corresponding planes dissimilar • the planes which appear as the summits of some of 
the prisms, being only the lateral planes of very short , and otherwise disproportioned 
