l)y Means of Grajpliical Methods. 



25Y 



56° 19' 

 29 49 



a/Kl, lOOAOlO = 94° 26' ar\p, lOOAlU 

 f^Ac, IOOaOOI = 72 36i cAi>, OOlAlU 

 lf\c, OIOaOOI = 78 421- 



The lengths and inclinations of the axes derived from the 

 foregoing measurements are as follows : 



a : 5 : c = 1-07285 : 1 : 0-62127 ; 

 a = 103° 18'; /9 = 108° 44' ; ;- = 81° 39' 



From the measurements given above the poles a, 5, c and ]) 

 of rhodonite have been accurately located in the stereographic 

 projection, figure 8, and through the poles the j^rincipal zones, 

 corresponding to those of figure 5, have been drawn. The 



relation between figures 6 and 8 is a most important one. 

 The angles «, tz and ^o, made by the meeting of the great circles 

 at the pole a^ figure 8, are identical with a, tz and p of figure 6, 

 and a like correspondence holds true at the poles h and c of 

 figure 8, as indicated by similarity in the lettering. In order 

 to make clear that the angles «, tz and p of the stereographic 

 projection, figure 8, are identical with «, ti and p of the rhodo- 

 nite axes, which, it must be remembered, are shown in cliuo- 

 graphic projection in figure 6 and therefore somewhat dis- 

 torted, let it be assumed that a model corresponding to figure 5, 

 but constructed so as to represent the triclinic system, is at 

 hand. Since the front pinacoid a of figure 7 is parallel to the 

 h 'and o axes, its normal is at right angles to the plane of these 

 axes ; hence if we imagine ourselves as looking at the h and c 

 axes of a triclinic crvstal in the direction of the normal to the 



