"1% Mr Levy on the. modes of Notation 
bedroll with a rhombic base, wit'h the occurrence of only half 
the number of faces which symmetry would require. 
The method of Professor Mohs may be shortly stated to be 
this: — For each of his five or six systems of crystallisation, there 
are series of secondary forms, the terms of each series having to 
one another some simple relation, founded on properties which 
have been found to obtain among crystals ; and the sign he uses 
to designate any modification, indicates the scries to which that 
modification belongs, and its rank in that series *. 
Each of these two methods may be contended to have over 
Haiiy^s the advantage of not being based upon a theory of the 
formation of crystals; but should that be thought an important 
objection to Haiiy's designation, it appears to me that his signs 
might be retained, without any reference to decrements: they 
would not designate, then, the number of rows in breadth and in 
height, by the subtraction of which, in the superimposed laminae, 
some secondary face is supposed to be produced ; but they would 
indicate in what ratio the edges of the primitive are cut by a 
plane parallel to the secondary. 
The method of Professor Weiss is not yet adapted to two of 
the most frequently occurring forms, the oblique rhombic prism, 
^nd the doubly oblique prism ; and whatever modifications are 
made to fit it to those cases, it does not appear that it will be pos- 
sible to use three rectangular axes, consequently all its geome- 
trical simplicity and the facility it may now alford for calculation, 
of no avail. 
The method of Professor Mohs has the advantage of expressihg 
some very curious geometrical properties of the secondary forms, 
most of which had, I believe, been noticed by Haiiy, in treating 
of what he denominates hypothetical primitive form. Thus^ 
the sign by which Professor Mohs designates the dodecahedron 
of the variety paradoocate of carbonate of lime, shews at once 
that the inferior edges of this dodecahedron are parallel to the 
inferior edges of the rhomboid inverse^, and that its axis is 
three times that of the rhomboid, the inferior edges of which 
would coincide with the inferior edges of the dodecahedron. 
* Se No. V. of this Journal^ and the several papers published by Mr Haidln- 
gcr, where this mode of designation is used. 
