438 Mr. WuHEWELL on the Selection of a Notation 
This law may be thus expressed. 
A diametef is drawn to the base of any pyramid; (MC in 
Figs. 1, 2, 3.) 
This diameter is increased (or diminished) in the. ratio of the 
index m (producing MC’). 
Through the angle (B,) and the extremity of this diameter, 
parallel to the edge of the origmal pyramid, (CV,) is drawn a 
plane (BC'V’). 
The figure bounded by all such planes is taken. 
By symbols thus constructed, we can represent any plane 
whatever, and it has been seen in a preceding Paper that the 
mode of intersection of different planes will afford us the means 
of recognizing their origin and law. 
For the sake of convenience, two other symbols are introduced. 
ist. The letter r after the fundamental letter. 
For —- Ro, we have put Rr, 
3@ 
LS plata 2 sce ORE Nees 5 25 
@ 
for Q 
or oS jae c a ane outa ane male's ow ae Ve 
Oreo 0 
or = Oe) Re oo oosisaccasoon) ry 
The letter r is added to the fundamental letter, when m, the second 
index, becomes infinite, and the axis of the fundamental pyramid 
remains unaltered. - 
2d. An accent added to the fundamental letter in two cases. 
R’ is used to designate the fundamental pyramid of the rhombo- 
hedral system, its base being turned through two right angles, 
or placed in a éransverse position. 
