Mr Levy on Enchase 
Mod. 
i 
= (cPb h gl) 
'm, 
i 
= 143°. 58' 
Mod. 
i! 
m, 
i‘ 
= 147°. 24' 
Mod. 
V 
= («* digl) 
m. 
i" 
= 99°.53' 
Mod. 
i!" 
- (V H 
m, 
m 
■= 153° 
Mod. 
m 
= (b 3 dig') 
m. 
£//// 
= 116° 
132 
i, i . = 134°.18' 
i', V = 99°. 44" 
2 7/ , i" = 11 3°. 42' 
£% = 122 ° 
i ////l , ^ = 105°.20' 
Art. XXI. — 0?i the modes of Notation of Weiss, Mohs, and 
Hauy. By A. Levy, Esq. M. A. &c. Communicated by 
the Author. 
Xn the number of the Edinburgh Philosophical Journal for 
January 1825, I have given general formulae to determine the 
law of decrement by which a Rhomboid, the incidence of the fa- 
ces of which is known, may be supposed to be derived from an- 
other rhomboid, whose angle is also known, and which is consi- 
dered as the primitive form with respect to the first. I have 
also begun to explain other formulae relative to a particular case 
of the dodecaedrons, which are derivable from a rhomboid. In- 
stead of proceeding now with the successive examination of the 
different decrements which may produce dodecaedrons, I shall 
consider at once the most general case, and deduce, afterwards, 
from it the particular ones. 
Let dd', Plate VI. Fig. 6., be a dodecaedron, derived by an in- 
termediary decrement from the rhomboid rr'. Fig. 7. Let the 
axis of the rhomboid and dodecaedron be parallel, and the prin- 
cipal section r o r' of the first be parallel to the section dbd' of the 
second ; then the plane add'. Fig. 6., will be parallel to the plane 
mrr'. Fig. 7. Let the plane fgh , Fig. 7., be parallel to one of 
the faces adb of the dodecaedron ; if we suppose the edge of the 
rhomboid to be one, and the linesjfr, h r , g r, to be respectively 
b y, b the crystallographical sign of the dodecaedron would be 
by b *) ; and the problem to be resolved, is to determine the 
indices b y> b or at least the ratios of the two last to the first, 
when the incidences of the faces of the dodecaedron are known. 
Not to repeat too often the crystallographical sign of the dode- 
caedron, I shall represent the faces by the letter i ; the angle of 
i 2 
