polarisation of light by reflexion from transparent bodies. 145 
of A, the same effect being produced at angles equidistant 
from the maximum polarising angle. 
In order to apply the formulas with facility in ascertaining 
the number of reflexions necessary to polarise a pencil of light, 
I have calculated the following Table containing values of A 
and a for various values of N and n, the reflexions being sup- 
posed to be made from glass, whose index of refraction is 
equal to 1.525. 
Table showing the angles at which a pencil of light is polarised by 
any number of reflexions at the same angle. 
When the angles are greater than the 
maximum polarising angle, or 56° 45'. 
When the angles are less than the maxi- 
mum polarising angle, or 56° 45'. 
Angles at which the 
Angles at which the 
Number of reflexions 
incident light is 
Number of reflexions 
incident light is 
necessary to polarise 
wholly polarised by 
necessary to polarise 
wholly polarised by 
the incident light. 
the number of re 
the incident light. 
the number of reflex- 
flexions in Col. 1. 
ions in Col. 3. 
1 
O 
56 
45 
1 
O 
5 6 
45 
2 
62 
30 
2 
50 
26 
3 
% 
33 
3 
46 
30 
4 
67 
33 
4 
43 
5i 
5 
6 9 
1 
5 
41 
43 
6 
70 
9 
6 
40 
0 
7 
7i 
5 
7 
38 
33 ! 
8 
7i 
5i 
8 
37 
20 
9 
72 
30 
9 
36 
15 
10 
73 
4 
10 
35 
18 
27 
77 
4° 
27 
26 
39 
64 
80 
4 1 
64 
20 
52 
100 
81 
57 
100 
18 
11 i 
125 
82 
3 2 
125 
16 
58 
1000 
86 
15 
1000 
8 
4 6 1 
mdcccxv. U 
