44 
DR. A. E. H. TUTTON ON THE 
A determination with Plate 3 at temperatures up to 65° indicated that 2E increases 
rapidly on rise of temperature, a fact which accords with the alteration of the 
refractive indices by rise of temperature. 
For Na light the angle at the ordinary temperature, 15°, was 114° 46', at 40° it 
had increased to 131 15', at 45° to 136°, at 50° to 138°, at 55° to 143°, and at 65° to 
158° 20'. The angle thus increases by 44° for 50° rise of temperature. 
Determination of True Optic Axial Angle in Bromonaphthalene. 
of plate 
1 M.L. 
Observed 
2H„. 
No. of plate 
perp. 2 M.L. 
Observed 
2H 0 . 
Calculal 
2V a . 
1 
o / 
61 56 
la 
O 1 
96 31 
o / 
69 11 
2 
61 25 
2a 
96 30 
68 47 
3 
61 45 
3a 
96 25 
69 5 
1 
61 52 
la 
96 30 
69 8 
2 
61 23 
2 a 
96 30 
68 46 
3 
61 35 
3 a 
96 25 
68 57 
1 
61 3 
lco 
96 26 
68 32 
2 
60 50 
2 a 
96 30 
68 20 
3 
60 50 
3 a 
96 25 
68 22 
1 
60 4 
la 
96 21 
67 46 
2 
59 58 
2ft 
96 30 
67 38 
3 
59 52 
3 a 
96 25 
67 35 
1 
59 42 
la 
96 18 
67 30 
2 
59 18 
2a 
96 30 
67 6 
3 
59 24 
3 a 
96 25 
67 13 
1 
59 18 
la 
96 14 
67 12 
2 
58 45 
2a . 
96 30 
66 39 
3 
59 0 
*&Ll 
96 25 
66 53 
Light. 
Li 
C 
Na 
T1 
Cd 
F 
Mean 
2 Ya. 
69 1 
68 57 
68 31 
67 40 
67 16 
66 55 
Section la showed clear although minute dispersion, but Sections 2« and 3 a 
showed no trace of dispersion, the brushes in white light being sharply black without 
trace of coloured borders. 
Murmann and Potter found by indirect observation 121° 39' for 2 E, and 71° 21' 
for 2V„. 
Dispersion of the Median Lines. —-The inclined dispersion is very minute. 
Measurements in toluene indicated that the first median line lies nearer to the 
axis c for red Li light by 7' (mean of 4', 10', and 6') than for greenish-blue 
F light. 
In the next table the optic axial angles of the four copper salts are compared. 
The ammonium salt is seen to display an essential difference from the alkali-metal 
salts as regards optic axial angle. 
