OF THE DOUBLE SELEXATES OF THE SEPJES rt,M(Se04)2,6IL0. 
281 
at tlie oi'diuaiy temperature itself for blue light of wave-length 4G6. For G-light 
intersection has occurred, and the curve hitherto called a has })assed to the y side of 
the /3 straight line. 
This unusual optical character of csesium magnesium selenate is similar to a 
remarkable extent to that of cmsium magnesium sulphate (p. 475 of the double 
suljDhate memoir*) ; in the case of the latter salt, the wave-length for uniaxiality 
is 450. 
Comparison of the Molecular Optical Constants. 
Ilf* 1 ^ 
Specihc Refraction, 7-^5 -—, = it. 
^ {m -1- 'l)d 
For ray C (Ha). For ray Hy near Ct. 
a. 
h- 
7- 
a. 
fi. 
7- 
KMg sel. . . 
. 0-1232 
0-1237 
0-1267 
0-1264 
0-1269 
0-1300 
138 
139 
150 
142 
144 
151 
sel. . . 
. 0-1091 
0-1098 
0-1117 
0-1122 
0-1125 
0-1146 
68 
72 
82 
70 
73 
81 
CsMg sel. . . 
. 0-1026 
0-1026 
0-1035 
0-1052 
0-1052 
0 106 2 
Molecular 
Refraction, 
a- - 1 
n~ + 2 
For ray C (Ha). 
For ray Hy near G. 
a 
h 
7 
7.. 
h. 
7 - 
KMg sel. . . 
. 61 
■07 
61 
■30 
62- 
81 
62' 
■64 
CO 
*0 
64 
41 
3- 
26 
3 
■24 
2 ■ 85 
3' 
•32 3 
■30 
2 ■ 
94 
RbMg sel. . 
. 64 
■33 
64 
■54 
65- 
66 
65 
■96 
66-17 
67 
■38 
5 ■ 
73 
5 - 
54 
5-06 
5 ■ 
00 
00 
' 68 
5 
■13 
CsMgsel. . . 
. 70- 
■06 
70- 
•08 
70- 
72 
71 
■84 
71-85 
72 
■51 
Specihc Dispersion, Hg 11^. 
/4 
7- 
KMg sel. 
. 0'0032 
0-0032 
0-0033 
RbMg sel. 
. ()-0028 
0-0027 
0-0029 
CsMg sel. 
. O-OO'JG 
0-002G 
0-0027 
Mulecular 
Dispersion, lUo 
“ lUc. 
KMg sel. 
CC. 
. . 1-57 
h- 
f57 
7- 
1-G3 
RbMg sel. 
. , 1-G3 
1-G3 
1-72 
CsMg sel. ... 
. . 1-78 
1-77 
1-79 
‘ JoUrn. Clieni. Soe., Trairs.,’ 18'J6. 
2 
VOL. CXCVII.—A. 
