of the Sulphato-tri-Carbonate of Lead' 223 



undef consideration m is n 4 ; but the axis of P' is equal to one- 

 fourth of the axis of P; the former pyramid consequently 



P 2, and the sign of the derived form becomes ~^- ) 

 the divisor 2 being added, because the pyramid occurs in the 

 crystal only at that side of the axis which corresponds to |. The 

 angle formed by the intersection of h and h is = 142 26'. The 

 prism d being the limit on one side of that series to which 







( p ~ 2 )- belongs, will be represented by ( p -f- oo ) 4 . It is evi- 

 dent that/ which appears with parallel edges of combination in 

 the place of the terminal edge AB of P, must on that account be 



o 



_ . The inclination of this face to P co or is 



= 128 40'. From immediate measurement, and from their 

 situation between a and P or P', the faces g and g belong to 



p i p i 



- , and g' and g' to ^ The edge produced by the in- 

 tersection of g and g is 94 18' ; and that produced by g r 

 and g' - 93 52'. 



The inclination of c to a is = 90 14' ; 



Pa 111 42V 



P' a = 111 18'; 



g a 128 23'; 



g' a - 128 5'. 



The representation of the whole form by crystallographic 

 signs is : 



p_ 00 PJ . Pr + 1 Pj-1 (P )* P , Pr+j. P 1 _ P 



f e g h P ef P 



P + oo . (P + oo)* . Pr + co . 

 c d b 



VOL. X. P. I. F f 



