(1039) 
- . Noa TT 
in which y= ~/CK =u — > 
= ra T 
«=the angle between WP and the projection-plane =» + 
so that 
F a ke 
cos 6 col (> i >) + sin 6 sin (¢ — u + =) 
col h mk — Z 
JT 
cos (¢ —uw-+ =) 
cos 6 ty — sin 6 cos (y— u) x 
= ———— ony Ns Ai Sa Lax etek. cee 
The angle between the long ellipse-axis and the trace of J is 
consequently given by ie 
ZPOE= 7 HOF — / HOE yah . « . (6) 
Fig. 3. 
Fig. 3 gives the projection of a triclinic crystal, oligoclase of 
Bamle *). If one measures v along the great circle ROQ from the 
plane MOM, positively opposite to the hands of a clock, o from 
ROQ positively to the right, then the optic-axes A and B and 
their biseetrices are determined by: 
@ oO 
A — 67°58’ — 44°58’ 
B — 83°53’ + 47°9’ 
a — 75°36’ + 1°6’ 
c + 6°35’ — 82°28’ 
1) RosenBusch, Mikrosk. Physiogr. I. 2, 342. 
HR* 
