' 810 Mr HaicUnger’s Comparative Viero qftlte Series of 
(IP _ P) (5 + df 
cost/- ^2 ^ ^2) + c^(b + df . 
, (JP — P) — P (h—df 
cos y -g2 ^tP + £2) + p (6 _ df ’ 
ftS (£.2 _ JP) _ £2 (J2 _ d?) 
cos a; _ ^^2 ^JP £ 2 ) ^ ^ df O (a^ (V + c^) + (6 — j)« c*)] 
IP (P — a2) _ p (o^ 4- d^) 
cos X _ ^ £ 2 ) ^ (6 + d)^ C) (pP (6^ + c^) + (6 — dfP)] 
tang MAP = ^ ; tang BAP = ; tang B'AP = -~ ; 
t 
COS CAC' 
According to these formulae, and the ratio of the lines a:b: 
c: d = 105 : S16.8 : 66.6 : 1, as corresponding nearest to nature, 
the angles of the fundamental form are 
P= ; 15P3'; nrSS'. 
The angle MAP, or the inclination of the axis, is = 0° 33'.' 
The angle BAM, or the anterior part of the prism Pr, which is 
Pr Pr 
designated by — ’ is 63'' 43' ; the angle MAB', or — , is 
64° 36'. The species of epidote is another instance of a very 
slight inclination of the axis, of which the axotomous lead-baryte 
has already furnished an example. 
Fig. 3. shews a combination of the preceding forms with two 
P 
new ones, P ^ — x (1) and — ^ (:^). The relations of these 
forms are easily obtained from the parallelism of the edges be- 
tween Z, n, and z, and from that between z, n, and M. 
Fig. 2. represents a more complicated variety than the two 
preceding ones, in which, however, the development of the 
simple forms will likewise follow from the mode in which the 
edges of combination are situated. It appears immediately that 
the faces marked q, forming truncations on the obtuse terminal 
edges of P, must be = Pr, the angle of the terminal edge of 
which is = 64° 37. If we suppose all the faces of the combina- 
tion to disappear except n, z, r, and T, which are known, and 
o, which is to be developed, the latter will produce a rhombic 
