93 
the angles of crystals, 
what symbols, according to the notation here proposed, cor- 
respond to the different laws in the old system. Thus 
A decrement on the superior angle is expressed by (^, g, ^), 
A 
which corresponds to Hauy's symbol p_, 
9 J_ 
On a lateral angle by ( — corresponding to ; 
± 
On an inferior angle by [p, — g, — q) corresponding to ^ ^ : 
r 
On a terminal edge by (o, q, r) corresponding to ; 
On a lateral edge by (^, — o) corresponding to G ^ • 
An intermediary decrement thus (/>, gr, r), corresponding 
to |a^B^C-^| and (/>, — q, — r) corresponding to 
(O^’D^F^). 
The symbols of the faces of the primary form are (/>, o, o). 
7. There is in fact, however, no necessity to suppose the 
secondary forms to be produced either by truncation of a 
primary one, or by addition to it. If we suppose that the 
small rhomboids, of which A a was assumed to be made up, 
are continued through all the space round the point A, we 
may conceive a plane to pass among these, parallel to PQR. 
And this plane will be represented by {p ; q ; r) indepen- 
dently of any consideration of the rhomboid A a or the point 
A ; for if we take a?iy pointy and from it draw lines to the 
plane, parallel to the three edges Ax,Ay,Az, these three 
lines will be asy,y, And any other plane may simi- 
larly pass among the small rhomboids, and be represented 
by {p' \ q' 9 ^)- And if we obtain any solid figure contained 
by such planes, we may, by supposing those of the small 
