Editorial Note. 105 
Now for some facts a another kind. I touch 7 only half a 
dozen points out of many in the memoir of Prof. Hinrichs. 
In the “ Atom Mochanies ” there are the following penn ate : 
§ 253. Chrysoberyl has its prism 119° 46’, or 14’ less than 120°; 
the other angle is 120° 7’, instead of 120°. The vertical axis is 
given a="81 (Dana) ; but shes form admits of a’=8a=1°21 quite as 
well. In this case, however, 1°21 is only 0°01 smaller than 1°22= 
/3. So that chrysoberyl must be referred to a fundamental form 
differing very little from the tesseral form in a rhombohedral posi- 
tion. With this view the formula Be Al, also coincides; by whic 
. it is placed with the Spinel group. Dana, it is true, gives Be Al, 
: which allies it to corundum; but in the latter a=1°361, which is 
very different. 
§ 254. We could cite very many such forms; our space however 
will not permit it. The two exceptions above given are sufficient 
to show that whoever bases a classification upon erystal-systems, 
builds a purely artificial edifice, which must give way before the 
first earnest investigation. One might quite as well classify asses 
_ according to the lengths of their caudal appendages expressed in. 
centimeters, as minerals by their systems of crystallization. Brook- 
: ite, eo rutile, are essentially alike; in Dana’s system, these 
ident y similar substances are inden 3 in three different groups. 
us ag a in innumerable cases. 
Prof. Hinrichs here attributes to me, in the first place, views I do 
not hold, and, _ secondly, presents, as his own, ideas which were pub- 
lished by m ein the last edition of my Mineralogy, and the vyol- 
umes of this Journal for 18 
On pages 196 to 205 of sie Mineralogy, after general observa- 
tions on Isomorphism ps homeomorphism as I there term the 
talline forms to the tesseral or iso ometri¢ ‘erecea) iter, at 
these pages T a ot: use the foreible and clegant compar- 
ison to asses tails; but have the idea in this fo " 
morphism m [meaning ordinary isomorphism], as Laurent. ‘has observ- 
ed, is not confined to forms of the same system alone.’ 
_t afterward show that rutile and anatase, although made to 
differ widely in st in the ordinary statements of the a 
autho ical i aie 
