12 
DR. A. E. H. TTJTTON ON THE 
Molecular Refraction (Gladstone and Dale). 
f—A M for ray C. 
Mean molecular 
Salt. 
refraction for ray C. 
a. 
A 
7- 
T (a + ft + y). 
KNi 
sulphate. 
93 • 37 
94-92 
97-50 
95-26 
RbNi 
99-11 
100-43 
102-26 
100-60 
AmNi 
100-34 
101-55 
103-00 
101-63 
CsNi 
,, ..... 
109-35 
110-19 
110-91 
110-15 
Optic Axial Angle .—-Three pairs of section plates were ground perpendicular to the 
first and second median lines. The optic axial angle is so large as to be invisible 
in air. The next table affords the results of the measurements of 2TI a and 2H W in 
monobromonaphthalene, the interference figures in which are very well defined. 
Murmann and Rotter obtained 86° 26' for the true angle 2V a , for the middle of 
the spectrum. 
Dispersion of the Median Lines .—The inclined dispersion of the median lines is 
small. Measurements in toluene, the refractive index of which (l'4955) is slightly 
lower, and in benzene, which possesses a slightly higher index (l‘5027), indicated that 
the dispersion is such that the first median line is nearer by 8 minutes to the axis a 
for red C-hydrogen light than for greenish-blue F-hydrogen light. 
Ammonium Nickel Sulphate. 
Determination of True Optic Axial Angle in Bromonaphthalene. 
No. of jjlate Observed No. of plate Observed Calculated Mean 
perp. 1 M.L. 2H a . perp. 2 M.L. 2H 0 . 2V a . 2V a . 
Light. 
Li . 
C . 
Na. 
T1 . 
Cd . 
1 
2 
3 
1 
2 
3 
1 
2 
3 
1 
2 
3 
1 
2 
3 
1 
2 
3 
o / 
76 33 
la 
82 35 
76 26 
2a 
82 18 
76 32 
3a 
82 20 
76 30 
la 
82 31 
76 23 
2 a 
82 13 
76 29 
3a 
82 15 
76 8 
la 
81 55 
76 7 
2a 
81 50 
76 10 
3a 
81 45 
75 51 
la 
81 29 
75 50 
2a 
81 23 
75 50 
3a 
81 19 
75 42 
la 
81 11 
75 39 
2a 
81 5 
75 38 
3a 
81 0 
75 33 
la 
80 56 
75 27 
2a 
80 50 
75 26 
3a 
80 45 
86 
86 
86 
86 
86 
86 
86 
86 
86 
86 
86 
86 
86 
86 
86 
86 
86 
86 
o / 
86 27 
86 28 
86 33 
86 37 
86 40 
86 43 
