( 728 ) 
= 1 3 8445 _ 1 ra ss a3) 1 € 5 JQ 
hee eT Vo at py ae a ar ane oes 
1 
To Tl (8 corresponds 
o = + 54°448" 
of these two values only 6 = — 54448" cooresponds to (18). 
A further investigation shows that the pole of the secant plane SS 
is represented bv 
o = — 54°44'8", G—= — 54PM48!, 
whereas the other values of @ and o do not correspond. The secant 
plane is the octahedronplane (111) as appears clearly from fig. 2; 6 
corresponds to the angle between (O01): (111) the cosinus of which 
is represented by 
COS A = = hohe thy ky Tht a i aa i V3 
ANNEN ARES A 
If the planes £, I’, and V, (vide fig. 1) lie in one zone the form- 
ulas (10) and (6) obtain a much less complicate form. Because 
y = 0 the coefficients (3), (5) and (8) change into 
=== COL a, cot h, — (Ot ce cot h, \ 
b = cot h, — cot h, (19) 
j= 0G, — ch a, \ 
=de gh 
so that: 
Ee ee 
20 
Gi: OOF eae 
i h° 5 hb: 
—0. . . (20) 
a 
te) See Ee BSE 0 AEO rk ale 
In an amphibole erystal the planes (110), 110 and (010) are lying 
in one zone; (110) may serve as equator plane. Whilst the real 
angles between (110): 410) and (010): (410) are resp. @, = 55°50! 
and «a, =-—-62°5' the apparent angles, measured in a rock slide, 
amounted to h, = 43° and h, = — 79°. 
(19) gives: 
a = 0,43625 > a =9).19032 
b= — 1.26674 be 
f—=—1,20858 ; #2? =1,46070 
from which: 
rat) 
EE 2875. os 
- fo i 
— 0,58074 
