OPTIC AXES IN HARMOTOME AND WOHLERITE. 
575 
crystal the red axes undergo an apparent separation in air equal to 170° 53'. while the 
blue axes undergo a total reflexion. If we cast our eyes over the Table of the inclina- 
tions of the planes, it is easy to see that the crystals of Wohlerite, besides the faces indi- 
cated above, as making angles almost equal in front and in rear with the vertical axis, 
present, furthermore, modifications with inclinations which are very nearly identical in 
two zones at right angles to each other. These crystals being rarely sufficiently good 
to furnish very precise measurements, it is almost impossible to distinguish crystallogra- 
phically between the one and the other of the forms to, o\ and a\ ; rf, p, and a 1 ; 
d\ and a z ; e 1 and ; e\ and <p : one can only do this by looking out for the facile 
cleavage that runs parallel to g l and the orientation of the plane of the optic axes. At 
the time of my first publications on the subject of Wohlerite'*, it was almost impossible 
to employ these two methods, in consequence of the scarcity of isolated crystals. This 
scarcity having become less felt in consequence of Professor Nordenskiold having been 
so kind as to send me some specimens, and from my having sacrificed one fine specimen 
upon its gangue, I have been enabled to obtain the precise interpretation of all the crystals 
I have figured in Plate XXXIV. accompanying my new investigation. The greater part 
of these crystals have been described in my two former memoirs and in my ‘ Manual’^; 
and as there has been confusion between the zones A 1 mg 1 and A 1 dp, on several of them, 
it may be useful that I should show here how my new symbols correspond with those of 
Dauber and with those which are introduced in my ‘Manual,’ or in the figures 234, 
235, 236, plate 40 of my ‘Atlas.’ 
New symbols. 
Dauber. 
Manual. 
Eig. 234, pi. 40. 
Fig. 235, pi. 40. 
Fig. 236, pi. 40. 
h 1 
a 
m, 
m 
m central. 
ff l 
b 
in 
P 
m 
m lateral. 
k% 
„ 
,, 
,, 
h 3 
n 
bj\ 
id 
h 2 and g % 
m 
m 
b io 
h 1 and g 1 
h l and g 1 
9 Z 
9 
bio 
„ 
h? and g 2 
h 2 and g‘ 
9 2 
h 
b l 
b l 
h 3 and g 3 
A 3 and g 3 
p and a 1 
k 
b 1 
h 3 and g 3 
„ 
b l 
o 1 and a\ 
d 
H 
h x and g 1 
„ 
e 2 and x=(V b\li \ ) 
X 
a 1 and e 1 
„ 
„ 
a 1 and e 1 
e 1 and b\ 
0 
a 2 and e 2 
,, 
a 2 and e 2 
a 2 and e 2 
e\ and f = (b l d^g 1 ') 
,, 
a i and e 4 
„ 
„ 
d\ and a 3 
p 
Jt and % 
„ 
k and ^ 
y=(c9 b g 1 ) and b^ 
i 
s and <r 
” 
” 
and a 
The faces formerly (v and <p) were erroneously placed upon my figure 236 ; they belong 
to the zone g l e x p (new symbols), and are the same as a 4 and e 4 . The former prism, 
Af g\, having only been met with once and having yielded but one, and that a very 
imperfect measurement, must, it seems to me, be abandoned. 
* Annales de Cliimie et de Physique, 3rd series, vol. si. 
t Annales des Mines, 5th series, t. xvi. 1859. Manuel de Mineralogie, vol. i. 1862. 
4 K 
MDCCCLXVIII. 
