A new system of Crystallographic Symbols. 251 
planes. Conciseness therefore must necessarily be a peculiarity of 
any method that will accomplish the desired object. In fact, it will 
be found that the expressions following from the system about to be 
proposed, are frequently not one quarter the length usual in other 
systems. 
Before proceeding to the details of the plan, it will be necessa- 
ry to explain what the situation of a crystal is when im position ; 
that is, so situated that the following laws may be correctly ap- 
plied in lettering its different parts. In general, the prisms are 
supposed to be on their bases with a lateral edge towards the ob- 
server. It is immaterial which lateral edge of the cube or right 
Square prism is in front, as they are similar to one another, (formed 
by the meeting of equal and equally inclined planes.) In the nght 
rectangular and right rhomboidal* prisms, the smallest of the lateral 
faces must be to the right, with any edge of the former, but an ob- 
tuse one of the latter in front. An obtuse edge is also to be made 
the anterior one in the right rhombic prism. In the oblique rhombic 
and rhomboidal prisms,} let the dominant solid angle be the superior 
and anterior one. Hence if itis obtuse, an obtuse edge, if acute, 
an acute edge, will be before the observer. The position of the 
rhombohedron may be the same that is usually given to that solid ; 
that is with the axis—the line connecting the vertices of the domi- 
nant solid angles—placed perpendicularly. ‘The above positions are 
those in which the figures of crystals are commonly given in works on 
Mineralogy. 
With regard to the octahedra, the base must be placed horizental- 
ly. Their positions in other respects may be inferred from those of 
the prisms of the same bases. ‘Thus that of the mght square octa- 
hedron from that of the right square prism; the right rectangular 
octahedron from the right rectangular prism; and the right rhombic 
octahedron from the right rhombic prism. 
In lettering the planes of crystals, the letter a, as a general rule is 
to be applied to those on the angles, e, to those on the edges, and 2, 
to the intermediary planes. ‘The letters a and e are selected because 
of the ease with which they may be combined to express the inter- 
mediary planes, which, correctly speaking, being neither on the an- 
gles nor edges, but rather intermediary between them, may with pro- 
* Usually termed the right oblique-angled prism. 
+ Usually called the doubly oblique prism, but the base of this and of the so call- 
ed right oblique angled prism, being the rhomboid, (as this term is used in geome- 
try,) the names 1 adopt seem preferable. 
