in -regard to Discoveries in Crystallography . 28¥ 
forms of the whole series of crystallization, in which it must be 
considered, if we wish to acquire a distinct and satisfactory know- 
ledge of it. The signs of Professor Weiss represent single 
faces, and nothing of that connection which distinguishes my 
method of designation. As to the perspicuity and facility in the 
employment of my signs, in comparison with those of M. Weiss* 
1 leave this to your own judgment, and to that of all who may 
choose to occupy themselves with the matter. I am far from 
supposing these designations, or, in fact, any part of my method 
already brought to such a degree of perfection, as to be inca- 
pable of any improvement or simplification. But I believe, that 
although M. Weiss means to intimate as much of his own, yet 
he will find considerable difficulties, in the way he now pursues, 
in conferring upon his denominations and signs those advan- 
tages which mine already possess. 
I have, in the second edition of my Characteristic, adopted 
the angles given by Professor Weiss, of felspar (prismatic 
felspar), in preference to all others, because this species is one 
of those which have, from the earliest period, been the particular 
object of his inquiries, in which he was assisted by an exquisite 
collection of its varieties, formed by himself with much zeal and 
knowledge. The reason why his name has not been mention- 
ed is,, that I had reserved all similar citations for the second vo- 
lume of my Treatise. Yet these demonstrations have been 
found incorrect, by the measurements instituted by M. Ilaidin- 
ger, with perfect individuals of the species, through means of 
the reflecting goniometer. The terminal edge of the funda- 
mental form, given by M. Weiss as —126° 52' 11 ".5, has 
been found — 126° 12' ; the more obtuse angle of the vertical 
prism, which he assumes as =■ 120', = 118° 52'. A third da- 
tum to be depended upon for calculating the inclination of the 
axis is still wanted ; for this reason, in the mean time, the incli- 
nation has been supposed — 0. In this manner you will find 
the indication of the forms of prismatic felspar in the first 
volume of my Treatise. 
This seems to me a proper place for mentioning a fact re- 
specting what has hitherto been called Felspar, which is still 
more important than the accurate estimation of the angles. 
This species, besides prismatic felspar, contains the varieties of 
at least two or three other species, differing in several of their 
