428 Mr. WueweE t on the Selection of a Notation 
for another opportunity. That Professor Mohs’ method does offer 
remarkable and valuable facilities for the determination of crys- 
talline laws, is a fact which may be ascertamed by examining the 
applications which have been made of it. The object of the fol- 
lowing pages is to modify the notation, so that, besides answering 
this purpose, it may possess as much of the scientific beauties of 
simplicity and generality, as is consistent with the nature of the 
subject to which it is applied. 
In speaking formerly of the above four classes of crystals, the 
terms were mentioned by which previous authors have designated 
them, and others were suggested. It is, however, reasonable that 
those who first navigate these new shores of science, should have 
the privilege of giving the names to the objects they discover, and 
I shall, therefore, adopt the denominations of preceding writers, 
with some alterations, which analogy seems to demand. The four 
classes will be termed the Rhombohedral, the Oblong-Pyramidal, 
the Square-Pyramidal, the Octahedral.. And the fundamental 
forms which will be used in deducing the derived forms will 
be, in each instance, a pyramid. In the first class, an equilateral 
triangular pyramid; in the second, one with a rhombic base; in 
the third, one with a square base, and in the fourth, the half 
of a regular octahedron. The first class is called Rhombohedral 
both by Mohs, Weiss, and Breithaupt; the last, which I have 
called Octahedral, in order to refer it to a pyramid like the rest, 
is what is by these writers called Tessular, Hexahedral, &c. In 
the names of the second and third, Mohs and Breithaupt differ 
with each other, and neither appears to attend sufficiently to 
analogy. Mohs calls the square-pyramidal simply pyramidal, 
and the oblong-pyramidal, prismatic, in which nomenclature the 
two terms have in no way a relation corresponding to the rela- 
tion of the forms, and might, with equal propriety be permuted. 
Breithaupt calls these two classes rhombic and tetragonal, or 
