I)R. A. E. H. TUTTON ON THE 
30 
Murmann and Rotter obtained for in red light 1'482, in yellow light L '484, 
and in green light I’485. 
9 
General Formula for /3, corrected to a vacuum :— 
1*469.1 + 
633 924 
A 2 
3 568 840 000 000 
A 4 
The index a is also reproduced hy the formula if the constant 1'4691 is diminished 
by 0'0039, and the y index if the constant is increased by 0'0073. 
Observations at 70° showed that the refractive indices of ammonium manganese 
sulphate diminish by about 0'0019 (for a) to 0'0021 (for y) for 55° rise of temperature. 
In the next table the refractive indices of the three salts containing manganese are 
O c3 
compared. 
Comparison of the Refractive Indices. 
Index. 
Light. 
RbMn 
sulphate. 
NH,Mn 
sulphate. 
CsMn 
sulphate. 
( 
Li. 
1-4741 
1-4770 
1-4918 
C. 
1-4745 
1-4775 
1-4922 
i 
a J 
j . . . . • ] 
Na. 
1-4767 
1-4801 
1-4946 
T1. 
1-4791 
1-4827 
1-4972 
I 
F. 
1-4821 
1-4858 
1-5003 
l 
G. 
1-4864 
1-4912 
1•5046 
r 
Li. 
1-4781 
1-4810 
1-4936 
C. 
1-4785 
1-4815 
1-4940 
ft.... \ 
Na. 
1-4807 
1-4840 
1-4966 
T1. 
1-4831 
1-4865 
1-4991 
1 
F. 
1-4860 
1-4897 
1-5022 
l 
G. 
1-4907 
1-4951 
1-5066 
f 
Li. 
1-4880 
1-4882 
1-4995 
C. 
1-4884 
1-4887 
1-4999 
y < 
Na. 
1-4907 
1-4913 
1•5025 
T1. 
1-4933 
1-4940 
1-5051 
1 
F. 
1-4965 
1-4971 
1-5083 
l 
G. 
1-5015 
1-5025 
1-5129 
Mean refractive 
Na light 
index i (a + /3 + y) for 
1-4827 
1-4851 
1•4979 
. 
Double refraction, Na y _ a . 
0-0140 
0-0112 
0-0079 
The position of the ammonium salt as regards refractive indices is precisely similar 
to that in the nickel and cobalt groups already dealt with, namely, just beyond that 
of the rubidium salt, the indices of which are only very slightly lower. The 
ammonium salt also occupies an intermediate position between the rubidium and 
