260 A new system of Crystallographic Symbols. 
Thesameby Hay. M M’P(A? B: G')(A® B? G') (A? B?G?) 
AB C) (AB Or), (Be C+) CA GC") GAG? C’) 
(AGC! )BBCCG! 2G (A? GB? (AB Cs)(?AC'G2)A. 
15.5 
3), == lA AS 
a i= 2 ae oto ed # 
a? = 1449 44’ 91” e2 = 1580 ganar 
242 = 150° 47 39” e214), 146° Isis6e 
6.3 
ID) a MLAS) Ihe ot 
In writing the description, the symbol of that plane is loonie first, 
which gives the character to the form of the crystal. In this case 
evidently, the faces of the cube should precede, as is the case above. 
As a general rule, the lateral planes of a prism should be first notic- 
ed, next the bases, and lastly the planes on the angles and basal edges. 
By an examination of the figure, it appears that in five instances, 
there is but half the number of planes that perfect regularity would 
require. This is expressed by the figure 2, under the symbols of 
these five planes. 
It will be observed that the figures of the numerator, in some in- 
stances, change places with one another. ‘This results from the dif- 
ferent situations of the same plane. Were this change not made, the 
inference with regard to the face on which the secondary inclines, 
would be incorrect. It may be well to look for a moment at the 
manner in which the face on which a plane inclines, may be de- 
termined from its symbol. ‘Take for instance the plane gia situated 
between the superior base and the left lateral face. It is to be deci- 
ded on which of these planes it inclines. Suppose it to be on the 
latter—consequently the numerator should express the decrement 
along its edges, and the denominator, that in the direction of the 
right superior basal edge. ‘This being placed towards the observer, 
15 the left hand figure, should express the decrement on the left 
edge, (front lateral,) and 5 the same on the right edge, the left su- 
perior basal. But the number to the left, 15, being the greatest, 
the plane ought to be situated to the left of a plane, on the solid an- 
gle, (not intermediary,) which inclines on the same face—which is 
not the case with the plane under consideration. But if we sup- 
