Ill \.\CO\AI. SYSTMM 



107 



tennin.-itions of the intermediate axes, a new form, Fig. 205, the 

 pri-m of the third order, will result. When the pole is to 



FIG. 204. The Positive Trigonal Pyramid of 

 the Second Order, (hhaEl). 



FIG. 205. The Negative Left 

 Trigonal Prism of the Third 

 Order, (iEHl). 



the right of the point p, it is a right form ; when to the left of p, 

 it is a left form; when between a and a 3 , a plus, and between a 3 and 

 a 2 , a minus form. 



/ '2 3*23*3" 00 C ^ 



IV. Trigonal prisms of the second order, f ' 

 (hhiho), (2hhho). 



When the poles are at the points a, Fig. 201, a new form, Fig. 

 206, the trigonal prism of the second order, will result, in which the 

 lateral axes terminate in the central point of the face and bisect 

 the opposite edges, as illustrated in Fig. 206. 

 The relation of the trigonal pyramids and 

 prisms to the lateral axes is shown in Fig. 

 202, which is a plan of the equatorial plane. 



Other forms. All other positions of 

 the poles will yield forms of the ditrigonal 

 equatorial type. 



The possible forms to combine in this 

 type will be : 



Right and left plus and minus trigonal 

 pyramids_of the third order, (hkil), (khil), 



(ihkl), (ikhl). 



T>i j , , ., ,,, FIG. 206. The Plus Trig- 



Plus and minus_tngonal_pyramids of the ona , prism of the gecond 



second order, (hh2hl), (2hhhl). Order, (hhafio). 



