AND TRANSMITTED BY CERTAIN KINDS OF GLASS, 
287 
Table XXIII.—Polarising Angles. 
Crown Glass. 
Not repolished. 
Repolished with rouge. 
Repolished witli putty powder. 
O f // 
O / 
o / u 
56 14 30 
56 22 30 
56 49 0 
56 21 30 
56 28 30 
56 49 30 
56 25 30 
56 42 30 
56 37 30 
56 52 0 
Mean 56 20 30 
56 32 45 
56 50 10 
Flint Glass. 
Not repolished. 
Repolished with putty powder. 
O / // 
58 14 0 
O / // 
58 48 0 
58 44 0 
Mean 58 14 0 
58 46 0 
Table XXIV. gives the values of the refractive indices of the two kinds of glass 
as determined directly, and as deduced from the amounts of the reflected and trans¬ 
mitted light, and from the values of the polarising angles, both before and after 
repolishing. The values obtained in these ways do not agree well together, those 
deduced from the amount of the transmitted light being considerably the lowest; 
they show, however, that repolishing increased the theoretical value of the index as 
determined by three independent methods. 
Table XXIV. 
Values of the Refractive Indices. 
Crown glass. 
Flint glass. 
Observed. 
Calculated from amount of ligbt reflected, 
determined directly. 
Calculated fi’om amount of light reflected, 
deduced from amount transmitted. 
Calculated from polarising angle. < 
Before repo] isliing. 
After repolisliing. 
Before repolishing. 
_ After rejjolishing. 
' Before repolishing. 
After repolishing with rouge . 
,, „ putty . . 
1-5145 
1-4830 
1-5220 
1-4676 
1-4928 
1-5017 
1-5136 
1-5293 
1-6330 
1-6280 
/ 1-6590* 
1 l-6290t 
1-5930 
1-6055 
1-6149 
1-6490 
* Immediately after repolishIng. 
t After an interval. 
