54 
DR. A. E. H. TUTTON ON THE 
Molecular Refraction (Gladstone and Dale). 
Salt. 
> -—j— M for ray C. 
Mean molecular 
refraction for ray C. 
'(a + jS + y). 
CL. 
A 
7- 
RbCd sulphate. 
AmCd „ . 
CsCd „ . 
102-70 
104-19 
112-74 
103-71 
105-03 
113-31 
105- 83 
106- 59 
114-73 
104- 08 
105- 27 
113-59 
Optic Axial Angle .—Three pairs of section-plates perpendicular to the two median 
lines were, after much trouble, obtained by grinding, which were adequately 
transparent to enable a complete series of measurements to be obtained of 2Ha and 
2Ho in bromonapbthalene, and the measurement in two cases of 2E for the most 
brilliant sodium light wave-length. Observations of the dispersion of the median 
lines between Li and F light were also successfully carried out. The results are 
shown in the next two tables. 
Apparent Optic Axial Angle in Air, 2E, of AmCd Sulphate for Sodium Light. 
Plate 1 . . . 124° 33' Plate 2 . . . 124° 31' 
Mean 2E . . . 124° 32' 
Determination of True Optic Axial Angle in Bromonaphthalene. 
No. of plate 
perp. 1 M.L. 
Observed 
2 H ( „ 
No. of plate 
perp. 2 M.L. 
Observed 
2 H 0 . 
Calculated 
2 V a . 
Mean 
2Y„. 
1 
o / 
64 29 
la 
o / 
92 48 
o / 
72 46" 
o / 
2 
64 27 
2 a 
92 57 
72 40 
72 45 
3 
64 32 
3 a 
92 44 
72 50, 
1 
1 
64 28 
la 
92 43 
72 477 
2 
64 25 
2 a 
92 53 
72 41 
72 46 
3 
64 30 
3a 
92 38 
72 51 J 
1 
1 
64 16 
la 
92 18 
72 507 
2 
64 11 
2 a 
92 20 
72 45 
72 51 
3 
64 16 
3a 
91 58 
72 58J 
1 
64 0 
la 
91 43 
72 537 
2 
63 57 
2 a 
91 46 
72 50 
72 56 
3 
64 2 
3 a 
91 22 
73 4 J 
1 
63 48 
la 
91 22 
72 547 
2 
63 50 
2 a 
91 23 
72 54 
> 
72 58 
3 
63 54 
3a 
91 4 
73 7 J 
1 
63 35 
la 
90 58 
72 567 
2 
63 40 
2 a 
91 3 
72 57 
> 
73 1 
3 
63 44 
3 a 
90 40 
73 10J 
