290 Mr Haidinger on the Forms of Crystallisation 
The following table contains some of the most important an- 
gles, together with the crystallographic signs, referring to the 
simple forms, according to the method of Professor Mohs. 
Inclination 
of P - 
- CO (a) upon 
Angle at the 
edge contiguous 
1 to the 
plane of inclination 
in 
pS?— 
2 
- (*) 
r:: 147 ®52' 
PF— 2 
(0 = 
= 1220 20' 
2 
(/) 
r=128® 40^ 
PF— 1 
(m) = 
:84® 
' 30' 
p?+i 
2 
- {e) 
= 112“ O' 
iPF 
(n) = 
62® 
24' 
Pr -j- ( 
x(J) 
= 90<> 29' 
P — 1 
2 
(g) = 
94® 
18' 
Pr + l 
2 
- (^) 
= 111'’ IP 
P — 1 
2 
(g') = 
93'' 
52' 
P — 1 
2 
ig) 
1280 23' 
(P-2) 
2 
t(h) = 
142 
0 20' 
P — 1 
2 
(g') 
= 1280 5' 
111 
0 32' 
P 
2 
(P) 
= lll'> 42' 
(P + OO)' 
132 
0 54' 
P 
2 
(n 
=. IIP 18' 
P+00 
(c) = 
59" 
40'. 
P+x 
= 90“ 14'. 
The perfectly hemiprismatic appearance of a crystal similar 
to the given figures, would be alone sufficient for excluding the 
forms of axotomous lead-baryte from the rhombohedral system, 
even though the measures of the angles should have been found 
to approach still nearer to 120® and 90®. But one and the 
same individual seldom presents more than one or two of its six 
sides to the obselwer, being in most cases joined to other indivi- 
duals, according to the law of regular composition mentioned in 
the beginning of this paper. 
The planes of composition pass through a line nearly perpen- 
, dlcular to two sides of the six-sided tabular crystals, like AB, 
