10 
DR. A. E. H. TUTTON ON THE 
Comparison of the Refractive Indices. 
Index. 
Light 
IvNi 
sulphate 
RbNi 
sulphate. 
NH 4 Ni 
sulphate. 
CsNi 
sulphate. 
\ 
Li. 
1-4809 
1 
4868 
1-4916 
1-5061 
C. 
1-4813 
1 
4872 
1-4921 
1-5065 
cc .... \ 
1 j 
Na .... 
1-4836 
1 
4895 
1-4949 
1-5087 
T1. 
1-4860 
1 
4920 
1-4976 
1-5112 ' 
F . 
1-4889 
1 
4949 
1-5007 
1-5146 
1 
L 
G . . . 
1-4933 
1 
4996 
1•5060 
1-5192 
I r 
Li.... . 
1-4889 
1 
4933 
1-4975 
1-5100 
C. 
1-4893 
1 
4937 
1-4980 
1-5104 
£....{ 
Na . . . 
1-4916 
1 
4961 
1-5007 
1-5129 
T1. . . 
1-4941 
1 
4987 
1-5037 
1-5154 
F . 
1•4972 
1 
5017 
1-5069 
1-5187 
i 
G. 
1-5015 
1 
5062 
1-5123 
1-5235 
i 
i 
Li. 
1-5022 
1 
5023 
1-5046 
1-5133 
C . . . . . 
1-5026 
1 
5027 
1-5051 
1-5137 
r. ■ • d 
Na .... 
1-5051 
1 
5052 
1-5081 
1-5162 
T1 . . 
1-5077 
1 
5078 
1-5110 
1-5189 
F. 
1-5109 
1 
5110 
1-5142 
1-5221 
l 
G. 
1-5153 
1 
5156' 
1-5196 
1-5266 
Mean refractive 
index (a + [3 + 
7 ) 
1-4934 
1 
•4969 
1-5012 
1-5126 
for Na light 
Double refraction, Na y _ a . . . 
0-0215 
0 
•0157 
0-0132 
0-0075 
with rise of atomic weight of the alkali metal, the value is less than that for the 
rubidium salt. 
Axial Ratios of the Optical Indicatrix. 
a 
: P 
7 
CC 
P 
7 
KNi sulphate 
. 00946 
1 
10091 
0'9946 
1 
1*0091 
RbNi „ . 
. 0-9956 
1 
D0061 
0-9986 
1-0030 
R0091 
NH 4 Ni „ . 
. 0-9961 
1 
C0049 
1-0022 
1-0061 
1-0111 
CsNi 
. 0-9972 
1 
1-0022 
1-0115 
D0143 
1-0165 
Axial Ratios of the Optical Velocity 
Ellipsoid. 
a 
b 
r 
a 
b 
r 
KNi sulphate 
. 1‘0054 
1 
0-9910 
1-0054 
1 
0-9910 
RbNi ,, 
. 1-0044 
1 
0-9940 
1-0014 
0'9970 
0-9910 
NH 4 Ni „ . 
. D0039 
1 
0-9951 
0-9978 
0-9939 
0-9891 
CsNi 
. 1-0028 
1 
0-9978 
0'9887 
0-9859 
0-9838 
Axial Ratios oj the Optical Ellipsoid .—These have been calculated for ammonium 
nickel sulphate for either form of ellipsoid ; the values are given in the accompanying 
table, and are compared with the values for the three analogous salts of the alkali 
