. DC. OF THE CONNEXION OF FORMS. 89 



the scalene four-sided pyramid, which does not afford ex- 

 amples of their occurrence. Prismatic and prismatoidal 

 Hal-baryte, prismatic Topaz, prismatic Chrysolite, may be 

 quoted as examples. Besides these, (P + n) G and (P + n) 8 

 occur in prismatic Hal-baryte, (Pr -f n) 7 in prismatoidal 

 Antimony-glance, (P + n)' J in prismatoidal Manganese- 



. 96. SUBORDINATE SERIES. 



There exist several series of forms, homogeneous 

 and of similar bases with that of . 90. and belonging 

 to it, in reference to which the latter is termed the 

 Principal or Fundamental Series, while the others 

 are said to be Subordinate. 



A Subordinate Series is a succession of homogeneous 

 forms, whose bases are equal and similar to those of the 

 members of the principal series, but possessing axes, 

 which, on account of their relative magnitude, are ex- 

 cluded from the principal series : these members, however, 

 may form another series among themselves, which follows 

 the law of progression of the principal one. 



The members of the subordinate series may be derived 

 from those of the principal series, either directly, or by the 

 interposition of certain other forms, which are produced 

 from that series. In the present case, the first of these 

 methods being more simple, will find its application. 



Let AX, Fig. 38., be the axis, BCB'C' the base of the 

 fundamental form, and the points A', A", &c., X 7 , X", &c., 

 be determined, as has been shewn in the preceding deriva- 

 tions. 



Through those points lay the two rhombs FGIH and 

 F'GTH', similar and parallel to the base C'B'CB : produce 

 the axis, so as to have a = m. AX; draw the lines 

 F3, G21, &c. F% G% &c. and lay planes into these in 

 such situations that they include a space by themselves. 

 This space will have the form of a scalene four-sided pyra. 



