hy Means of GrajpMcal Methods. 



275 



the perpendicular from x' at a distance equal to the length of 

 the G axis; hence the symbol of ^ is 111. The pyramid y, in 

 the zone o :^, was determined by the angle 6»Ay=26° 42', 

 from which <r*^A2/ = 63° 18' ; hence a small circle sc^ drawn at 

 63° 18' from c?, iignre 23, fixes the position of y. A radius 

 through y was found to intersect the divided circle at 57° 30' 

 from (7, 100, which corresponds with the pole of . the prism n, 

 and a chord from ^, at right angles to this line, intersects the 

 front radius at a distance equal to 2<2. The intercepts on the 

 first and second axes of n^ y, and a third face in the zone, /i, 

 are therefore 2a : ^, the indices of n being 120. The slope 



of y, measured with the stereographic scale, was found to be 

 56° 45', calculated 56° 48', and a line at this angle intersects 

 the perpendicular from y' at a distance equal to the length of 

 the c axis ; hence the parameter relation of y \^ ^a : h : c, the 

 indices being 122. The pyramid [i was located by the meas- 

 urement cA/>«=37° 23', and a line at this angle meets the 

 perpendicular from y' at a distance equal to ^c ; hence the 

 parameter relation of fx is ^a '.h : Jc, the indices being 124. 

 The pyramid z, in the zone cl \ p, was located by the measure- 

 ment Sa2 = 24° 49'. This was done by first determining the 

 zone n, ^, d, {i and o by means of the great circle protractor, 



