hy Means of GrajpMcal Methods. 



277 



protractor, were found to be ^5° 10^ and 79° 20', calculated 

 i5° 20' and 79° 10'. By means of the stereographic scale c/\ d 

 was determined as 31° 10', calculated 31° 20'. The poles of 

 the 2:)Yramid o were located by means of the measurement 

 mA(9 = 35° 30', a small circle from ?/i, 110, being used. The 

 great circle ao made an angle, ;r', of 1:9° 45' at a, which, when 

 plotted from 5, was found to intersect the vertical radius at 



Xa=^uod3 



I'lSO, practically 2<?, the calculated value being 1*178 ; hence 

 the axial relation of o is —a :h : 2c, the indices being 221. 

 The poles of o could also have been located by constructing a 

 great circle through m and s, 110 and 111, thus determining 

 201, and then a second great circle through h and 201. 



For the purpose of showing the adaptability of the stereo- 

 graphic projection to measurements made with the two-circle 

 goniometer, and also for illustrating another method of treat- 

 ing the monoclinic system, a problem encountered in the study 

 of azurite crystals from Broken Hills, New South Wales, will 

 be presented. The crystals, which are exceptionally beautiful, 

 were measured and figured b}^ Mr. Kalph G. YanName. 

 They are lengthened in the direction of the ortho axis, like the 

 ordinary development of epidote, and the habit is well illus- 

 trated by figure 26, drawn in clinographic projection with the 

 h axis to the front. The crystal was orientated on the goni- 

 ometer with the orthodome zone horizontal and the pinacoid a, 

 100, vertical, thus making an imaginary clino-pinacoid the 

 polar face, although the form was not present on the crystal. 



