42 
DR. A. E. H. TUTTON ON THE 
Axial Ratios of the Optical Ellipsoid .—The calculated values of these ratios, both 
for the ammonium salt now described and for the analogous salts of the alkali metals 
previously studied, are collated comparatively in the next table. 
Axial Ratios of the Optical Indicatrix. 
oc : p 
7 
CC 
P 
7 
KCu sulphate 
. 0T981 : 1 
: 1-0105 
0-9981 
: 1 
1-0105 
RbCu ,, 
. 0-9987 : 1 
L0087 
1 "0015 
: 1-0028 
L0116 
NH 4 Cu „ 
. 0-9936 : 1 
1-0031 
1-0031 
L0096 
1-0128 
CsCu „ . 
. 0-9991 : 1 
1-0061 
1-0124 
1*0132 
1-0194 
Axial Ratios of the Optical Velocity Ellipsoid. 
a : b 
c 
a 
I) 
r 
KCu sulphate . 
. L0019 : 1 
0-9896 
1 "0019 
1 
0-9896 
RbCu ,, . . 
. 1 "0013 : 1 
0-9914 
0-9985 
0-9972 
0-9886 
NH 4 Cu „ . . 
. 1-0065 : 1 
0-9969 
0-9969 
0-9905 
0-9874 
CsCu ,, . 
. L0009 : 1 
0-9939 
0-9878 
0-9869 
0-9809 
Here again, as regards the absolute dimensions of the optical ellipsoid along its 
three axial directions, as indicated by the right-hand series of ratios, the ammonium 
salt stands just beyond the rubidium salt. In the left-hand series, in which the /3 
axis of each salt is the reference dimension for that salt, the copper group shows its 
individuality in the fact that the ratios for the ammonium salt are the lowest or 
highest, instead of, as in the other groups, being intermediate between the values for 
the rubidium and caesium salts. 
Molecular Optical Constants .—These are set forth in the next three tables, for all 
four salts, the new values now given for the densities having been employed in 
recalculating the values for the three salts containing the alkali metals. 
The specific refraction and dispersion of the ammonium salt stand out prominently 
higher than those of the three alkali-metal salts. The molecular dispersion for the 
ammonium salt is not, in this group by exception, the highest, but stands below, yet 
nearest to, that for the caesium salt. 
Table of Specific Refraction and Dispersion (Lorenz). 
Sulphate. 
Specific refractio 
ri 1 - 1 
Specific dispersion. 
n G - n c . 
{n* + 2)d 
For ray C (H 
“)• 
For ray Hy near G. 
CC. 
P- 
7- 
CC. 
P- 
7- 
CC. 
* P- 
7- 
AmCu . 
0-1497 
0-1521 
0-1534 
0-1533 
0-1558 
0-1571 
0-0036 
0-0037 
0-0037 
KCu.... 
0-1275 
0-1281 
0-1316 
0-1305 
0-1312 
0-1347 
0-0030 
0-0031 
0-0031 
RbCu . . . 
0-1116 
0-1120 
0-1145 
0-1141 
0-1145 
0-1171 
0-0025 
0-0025 
0-0026 
CsCu 
0-1033 
0-1035 
0-1051 
0-1057 
0-1059 
0-1075 
0-0024 
0-0024 
0-0024 
