Mr. W. J. Lewis's CrystallograpMc Notes. 123 



The planes observed on these two crystals are given by the 

 stereographic projection (fig. 5). 



Mr. Thomas Davies, of the British Museum, lent me a 

 crystal which showed a very prominent plane below the s 

 plane, as also some narrow ones, looking somewhat like stria- 

 tions, between them. The distribution of the faces on this 

 crystal is shown by the stereographic projection (fig. 6). It 

 is a combination of b (2 1 f), r (1 0),j (2 2 l\ s=a(4 1 2), 

 g =«(3 2 4), t (5 3 6), s' (7 2 4), a (4 1 2), % (15 8 8). 



Direct observations of t and / in the zone [b y/ s] were 

 too little reliable to be of any service. These planes were 

 therefore determined by observations of the angles they make 

 with b and z jr The plane &' is somewhat doubtful. The faces 

 w and n are very rounded, and no reliable measurement could 

 be made. 



_ The planes (50 19 19), (3 2 I), (5 3 6), (7 2 4) are not 

 given by M. DesCloizeaux ; and this is possibly the first time 

 that their existence has been recorded. The following table 

 gives the observed and calculated angles for these planes: — 





Calculated. 



Observed. 



ry ... 



30 25J;- 



f 30 231 on the 1 



| 30 20i on the si 



z% • • • 



36 15 



36 1 



~r t s ... 

 Tjl (310 6) 



28 54 



28 53 



33 47 



33 57 not good 



r,w(6 17 12) 



38 9 



37 52 „ „ 



Lr,w(5 1410) 



38 29 



ry 



~b n g . . . 



10 19 



10 16 



h n t . . . 



13 41i 





$j,Sj • . . 



34 33 



35 near. 



h • • ■ 



52 39 



52 43 



6^(5 3 6) . 



50 44 



50 29 



6 s' (7 2 4) . 



39 lOi 



39 101 



z u i . . . 



30 42 



30 28i 



z //S > . . . 



27 44 



28 



