252 A new system of Crystallographic Symbols. 
priety be expressed by a union of the letters of each. Another ad- 
vantage of these letters, manifest to the English reader, (one of 
secondary importance however,) consists in their being the initials of 
the words angle and edge, to planes on which, they are respectively 
applied. 
In all the primitive forms, except the cube and regular octahedron, 
it becomes necessary to distinguish the dissimilar primitive planes, 
solid angles, and edges from one another. ‘This may be done by 
means of Italic, and Roman letters, with the occasional use of dashes 
according to the following rule. In its full extent it is to be applied 
only to the oblique rhomboidal prism. Modifications of it for the 
other primitive forms, resulting from the similarity of some of their 
parts, will afterwards be pointed out. 
The crystal being in position; name the superior base P, the 
right lateral face P’, the dash inclining to the right ; the left lateral 
face P', the dash inclining to the left. (See fig. 1, which isa full 
application of the law about to be given.) Designate the front late- 
ral edge and the two superior basal edges by the Roman e, the side 
lateral and the two inferior basal edges by the italic e. ‘To distin- 
euish the superior basal edges from one another, give to the right, 
the right inclining dash, to the left, the left mclinmg dash; thus é 
and €: the same with the inferior basal edges. Thus half the edges 
of the crystals are named. ‘The remaining half beimg precisely sim- _ 
ilar to these, will receive the names of their opposites. ‘To letter 
the angles, apply the Roman a to the dominant or front superior sol- 
id angle, the italic a to the supplemental dominant or front inferior 
solid angle. Also the same italic @ to the superior lateral angles, 
distinguishing them by a dash inclining to the right or left according 
to the situation of the angle to the right or left hand. Thus a, a. 
In this way the angles and edges may receive their respective sym- 
bols, which will be used in naming planes situated on them. 
But it is farther necessary to specify the primitive plane on which 
a secondary inclines. ‘This may be concisely done by placing be- 
low its symbol, the dash belonging to this primitive plane. ‘Thus 
if it inclines on the right lateral face, plane P’, the dash inclin- 
ing to the right is to be placed below, and the contrary for an inclin- 
ation on the left lateral face. ‘Thus a plane on edge é inclining on 
plane P’ will be named é, &c. ‘To express the intermediary planes, 
we have but to combine the letters belonging to the angle and edge 
between which they are situated, and to place below, the dash of the 
