to designate the Planes of Crystals. 439 
P’ is used to designate the fundamental pyramid of the oblong 
pyramidal system when the derivation is made from the ¢ransverse 
angle of the base. 
Derivatives of R’ and P’ are obtained and designated in the 
same manner as for R and P. 
In cases of hemihedral combinations, we have also the symbols 
r 
h, 7 > oe &ec. as explained in paragraph 10. 
W. WHEWELL. 
Trinity CoLLece, 
Feb. 11, 1827. 
Vol. Il. Part II. sL 
