S12 Mr Haidinger’s Compm'ative View of the Series 
ratio of a ! : 6', is = « : 5, on account of the parallelism of the 
edges between 5 ;, and r ; but, as appears more distinctly in 
a projection, the intersection of u and M would be parallel to 
the edge of combination between u and z/, and the ratio of a' : 
is therefore = | a : c. The sign of the half of the pyramid, as 
(Pr — lf 
occurring in the combination, is = — ^ 
of a! : b' : (f may also be expressed by : b:^c. 
lographic sign of the whole combination is 
Pr 
P — X. 
I 
z 
r 
{Py 
d 
2 ’ 
Pr— 1. 
oc y q 
(Pr+x)^ P]^ + x. 
o M, 
, since the ratio 
The crystal- 
2 
u 
Pf _i_ 1 — Pr-l-2^ 
The horizontal prisms • — ^ — (<?) = 45° 37', and — — ^ ^ 
(i) = 34° 21', in Fig. 4., are obtained from immediate measure- 
ment. The rest of the forms are known from the preceding 
combination. 
All these varieties have been observed in crystals from Aren- 
dal ; those from Dauphiny are commonly less complicated, but 
require perhaps more attention on the part of the observer, be- 
cause they are so very deeply streaked in a direction parallel to 
the edges of combination between P — - x and Pr -f x . They 
are besides, in most cases, subject to regular composition. One 
of these crystals is represented in Fig. 6. It is a combination 
Pr Pr P 
-T 
(“)• Pr + ao(il/), 
and Pr + X (P). Only the last of these faces is not comprised 
in any of the preceding varieties. 
It is not the purpose of this paper to give a full account of 
all the simple forms which occur in epidote, far less of the nu- 
merous combinations in which they appear, and of the regular 
o 
• A variety from Piedmont, in the collection of Mr Allan, contains — - i — 
39', corresponding to % on the opposite side of the fundamental form. 
