278 Penfield — Solution of Problems in Crystallography 



In the stereograph] c projection, figure 27, the angles ^, deter- 

 mined bj the readings of the vertical circle, were laid off on 

 the divided circle, starting from a, 100, and the angles ^o, given 

 bj the readings of the horizontal circle, were plotted on their 

 respective diameters by means of the stereographic scale. The 

 angles for making the projection shown in figure 27 are as 

 follows : 



27 





9 



P 







9 



p 



a, 100, 



00° 00' 



90° 



00' 



P. 



104, 



102° 15' 



90°* 00' 



m, 110, 



u 



49 



39 



Q. 



134, 



(( 



57 10 



w, 120, 



a 



30 



29 



K 



2-18'3, 



122 59 



12 43 



A, 221, 



25 18 



53 



02 



0. 



101, 



134 51 



90 00 



p. 111, 



42 50 



59 



06 



V, 



302, 



146 32 



(( 



c, 001, 



87 36 



90 



00 



V, 



201, 



153 47 



(( 



I, 023, 



a 



59 



37 



l\ 



221, 



u 



52 08 



/; on. 



(( 



48 



40 



0, 



241, 



li 



32 44 



s, 021, 



u 



29 



36 











Having located the poles of the several faces, the zones 

 shown in figure 27 were easily found by means of the great 

 circle protractor. Starting, then, with the assumption that the 

 symbols of two poles are known, for example, m, 110, and^, 

 111, it is possible to determine the symbols of the remaining 

 forms by no other means than that afforded by zonal relations. 

 As it is the object of this paper, however, to indicate the 

 methods of graphical solution, the problem may be dealt with 

 in a manner analogous to that employed in the orthorhombic 

 system, since the h axis is at right angles to the plane of the a 



