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PROFESSOR MILLER ON THE POSITION OF THE AXES 



(5). In Acetate of Oxide of Zinc, ZnAH\ the cleavage being parallel 

 to the face p, ph = 46°. 30', pc = 79°. 55', "mm' = 67°.24', pm = 67°.33', 

 pg = 7 '5". 30', g-g-' = 58°. 43'. The symbols of the simple forms are, 

 c {10 0}, j» {0 01$, h {101}, m |H 1}, g fill}- 



The optic axes lie in a plane perpendicular to 

 the faces p, h, c. The apparent direction of the 

 optic axis a, seen in air through the faces p, 

 makes an angle of 50°. 15', with a normal to p. 

 When the crystal is immersed in oil, the apparent 

 directions of the optic axes seen through the 

 faces p, make with each other an angle of 79°. 15'. 

 P- 1.494. Hence p£= 11°. 16', A£=35°. 14', a/3 = 84°.30'. 



(6). In Bicarbonate of Potash, KC 2 H, me = 

 53°. 15', ra* = 76°.35', mf= 127°.52', rf</'=42°.0'. 

 The symbols of the simple forms are, m {10 0}, 

 t {0 1}, / {TO 1}, e {2 3}, d \\ 1 0}. 



The apparent direction of the optic axis a seen 

 in air through the faces e, makes an angle of 56°. 45', 

 with a normal to e. The apparent directions of the optic axes seen in oil 

 through the faces e make with each other an angle of 83°. /x = 1.482. 

 Hence ea = 48°. 21', e& = 47°. 53', e% = 6 '.28', a/3 = 81°. 38'. 



(7). In Tartaric Acid, TH, mm' = 88°.30', ee'= 76°.30', pm = 97°. 10', 

 ph = 80°. 3'. The symbols of the simple forms are, h {100}, p {001}, 

 m {1 1 0}, a {1 1}, e {Toi}, e {0 1 1}. 



The apparent directions of the optic axes seen in 

 oil through artificial sections perpendicular to the faces 

 p, h, lie in a plane inclined at an angle of 69°. 30' to 

 the face p, and make with each other an angle of 1 03°. 

 /u= 1.542 nearly. Hence pi = 20°. 30', />£ = 10°. 33', 

 a/3= 96°. 36'. 



