AND DISPERSION IN ICELAND SPAR, 
445 
Table XIII.—Results of Theory for C. 
e. 
From Theory. 
From Experiment. | 
Excess of 
Experiment. 
I. 
0 20 35 
1-65435 
1-65438 
+ 3 
II. 
4 5 7 
1-65335 
1-65335 
0 
I. 
7 39 25 
1-65082 
1-65078 
- 4 
I. 
11 34 51 
1-64635 
1-64627 
- 8 
I. 
17 23 14 
1-63678 
1-63684 
+ 6 
I. 
20 42 48 
1-62989 
1-62991 
+ 2 
II. 
23 34 21 
1-62326 
1-62341 
+ 15 
I. 
24 33 38 
1-62085 
1-62095 
+ 10 
I. 
25 28 23 
1-61855 
1-61862 
+ 7 
II. 
29 6 1 
1-60897 
1-60906 
+ 11 
II. 
34 38 36 
1-59326 
1-59336 
+ 10 
II. 
38 51 23 
1-58083 
1-58091 
+ 12 
II. 
41 0 26 
1-57443 
1-57449 
+ 6 
III. 
45 51 25 
1-56151 
1 56163 
+ 12 
II. 
46 59 20 
1-55677 
1-55692 
+ 15 
III. 
49 11 23 
1-55044 
1-55058 
+ 14 
III. 
52 31 57 
1-54113 
1-54116 
+ 3 
nr. 
58 31 47 
1-52560 
1-52567 
+ 7 
hi. 
61 47 0 
1-51797 
1-51805 
+ 8 
in. 
63 3 25 
1-51516 
1-51523 
+ 7 
hi. 
66 23 19 
1-50830 
1-50833 
+ 3 
Til. 
72 29 31 
1-49782 
1-49786 
+ 4 
hi. 
75 49 4 
1-49331 
1-49331 
0 
hi. 
79 19 19 
1-48955 
1-48962 
+ 7 
IV. 
80 6 35 
1-48885 
1-48887 
+ 2 
IV. 
87 1 19 
1-48495 
1-48499 
+ 4 
IV. 
89 42 4 
1-48457 
1-48457 
0 
Table XIII. gives the results for the ray C for the same values of the angle of 
incidence as those given in Tables XI. and XII. for F and g. This enables a com¬ 
parison of the results to be more easily made for the three rays than if it were 
requisite to refer to X. In each case the results are similar. 
The differences are least near the axes, being negative for F near the minor axis, 
and for g near both major and minor. 
For C the errors are positive throughout, so that a small increase of the axes of 
the curve given by theory would, on the whole, bring theory and experiment into 
closer agreement. 
For F the differences near the minor axis being negative, we should require to 
decrease the minor axis of the ellipse. This would increase slightly the positive 
errors, and render, on the whole, the variation from Fresnel’s spheroid more marked, 
and greater than the variation of the red ray. 
MDCCCLXXX, 3 M 
