404 
DR. A. E. H. TUTTON ON THE 
Crystal Plate 1, Parallel c {001}. 
Circle reading for normal (N in fig. 3) to c(00l), determined by coincidence of 
spider-lines with their own reflections . . . 214° 18'. 
Plate Arranged with Crystal Behind (as in fig. 3). 
Light. 
Observed left 
vertex. 
Calculated 
2 M.L.* 
Observed right 
vertex. 
2V 0 . 
Li ....... . 
o / 
276 1 
o / 
217 36 
159 11 
o r 
116 50 
C. 
276 0 
217 35-5 
159 11 
116 49 
Na. 
275 59 
217 37 
159 15 
116 44 
T1. 
275 58 
217 37-5 
159 17 
116 41 
Cd. 
275 57 
217 38-5 
159 20 
116 37 
F. 
275 55 
217 39-5 
159 24 
116 31 
Dispersion (Li F) . 
0 6 
0 3-5 
0 13 
* The midway position between the observed left and right vertex readings. 
Plate Arranged with Crystal in Front. 
Light. 
Observed left 
vertex. 
Calculated 
2 M.L. 
Observed right 
vertex. 
2Y 0 . 
Li ....... . 
o 
96 
, 
3 
o 
37 
. 
38 
o 
339 
/ 
13 
o / 
116 50 
C. 
96 
3 
37 
38-5 
339 
14 
116 49 
Na. 
96 
2 
37 
41-5 
339 
21 
116 41 
T1. 
96 
0 
37 
43-5 
339 
27 
116 33 
Cd. 
95 
57 
37 
43 
339 
29 
116 28 
F. 
95 
55 
37 
42-5 
339 
30 
116 25 
Dispersion (Li ~ F) . 
0 
8 
0 
4-5 
0 
17 
Light. 
Mean 2V 0 . 
Mean 2V a . Mean 2 M.L. 
Li. 
o / 
116 50 
or or 
63 10 217 37 
C.. 
116 49 
63 11 217 37 
Na. 
116 43 
63 17 217 39 
T1. 
116 37 
63 23 217 40 
Cd. 
116 33 
63 27 217 41 
F. 
116 28 
63 32 217 41 
Dispersion (Li ~ F) . . . 0 4 
1 
