PROFESSOR POWELL ON A THEORY OF THE DISPERSION OF LIGHT, 
Topaz. Rudberg. 
First Axis of elasticity. 
Ray. 
Observed value 
of f l. 
( 4 )- 
Ratio (~\ 
\sine/ 
Calculated va- 
lue of /. c 
. / arc \ 
= const, x ( - — ) 
\sine / 
B 
1-6084 
O / // 
10 5 0 
1-0051 
1-6085 
C 
1-6093 
10 34 42 
1-0056 
1-6092 
D 
1-6116 
11 46 48 
1-0070 
1-6114 
E 
1-6145 
13 10 22 
1-0089 
1-6145 
F 
1-6170 
14 16 53 
1-0104 
1-6172 
G 
1-6215 
16 8 40 
1-0133 
1-6216 
H 
1-6254 
17 30 2 
1-0157 
1-6254 
const. = 1-6003 
Second Axis. 
O / ✓/ 
B 
1-6105 
10 7 o 
1-00515 
1-6105 
C 
1-6114 
10 36 47 
1-0058 
1-6115 
D 
1-6137 
11 49 10 
1-0071 
1-6136 
E 
1-6167 
13 12 58 
1-0090 
1-6165 
F 
1-6191 
14 19 45 
1-0104 
1-6189 
G 
1-6236 
16 11 53 
1-0133 
1-6236 
H 
1-6274 
17 33 29 
1-0158 
1-6275 
const. = 1-6022 
Third Axis. 
B 
1-6180 
O 11 / 
10 7 0 
1-00515 
1-6180 
c 
1-6188 
10 36 47 
1-0058 
1-6189 
D 
1-6211 
11 49 10 
1-0071 
1-6209 
E 
1-6241 
13 12 58 
1-0090 
1-6240 
F 
1-6265 
14 19 45 
1-0104 
1-6264 
G 
1-6312 
16 11 53 
1-0133 
1-6310 
H 
1-6351 
17 33 29 
1-0158 
1-6351 
const. = 1-60955 
