(1042) 
mv 
Ma =de 
furnishes for g, = “AaM =172°58’ and 6, = 
about the value y—-+ 89°50’. Thereby the value wu=y—h= 
= 12 MW, isc tound: 
Per contra the axial angle 2 1” can be determined, if one knows 
the secant-plane S(v,o), the extinction w with regard to the trace 
of a known plane JV (u,r) and the direction of the extreme ray- 
velocities. 
In fig. 5 the amphibole-crystal is represented, of which in the 
previous communication’) with the help ef the apparent angles 
between the prism-planes and the clinopinakoid the orientation was 
determined. The angles «@, = 55°50' and a, = — 62°5’ are here 
inclosed either by the “planes msn, (= «,) anid”05\2 ni, == Gi vee 
taken as equatorplane, or by m,:m,(—=a,) and 6,:m,(=a,), m, 
considered as equatorplane*). For the place of the poles of the 
secant-planes S, and S, found, it does not make any difference, 
whether m, with its pole D, or m, with its pole / is taken as 
equatorplane, as this oecasions only an interchange of s, and xs,. If 
one takes m, as equatorplane, then lies 
Ss, with v' S= ORD: 
Oes — 80553, 
s, with: il! == 290K 39 
Oe ee SO 
1) These Proc. XIII, p. 728. 
2) The complications resulting for the orientation from the crystal-symmetry will 
be treated in a further communication. 
