74 
DR. BREWSTER ON THE LAW OF 
Plate Glass. 
Inclination of Plane of Polarization 
Angle of 
Incidence. 
Angle of 
Refraction. 
to Plane of Reflexion. 
Observed. Computed. 
Difference. 
90° . 
0° 0' . 
o 
o 
lO 
Cn 
o 
O 
0° o' 
88 . 
. 42 23 . 
. . 43 4 . 
. 42 49 . 
. +0 35 
86 . 
. 42 17 • 
. . 40 43 . 
. 40 36 . 
• +0 7 
84 . 
. 42 8 . 
. . 38 47 . 
. 38 22 . 
. +0 25 
80 . 
. 41 37 • 
. . 33 13 . 
. 33 46 . 
. —0 33 
75 . 
. 40 40 . 
. . 28 45 . 
. 27 41 . 
. "T 1 4 
70 . 
. 39 20 . 
. . 22 6 . 
. 21 3 . 
. +1 3 
65 
. 37 41 . 
. . 14 40 . 
. 13 53 . 
• +0 47 
60 . 
. 35 45 . 
6 10 . 
6 16 . 
. -0 6 
56 . 
. 34 0 . 
. . 0 0. 
0 0 . 
0 0 
50 . 
. 31 22 . 
9 0. 
9 0 . 
0 0 
45 . 
. 28 29 . 
. . 16 55 . 
. 16 31 . 
. -f 0 24 
40 . 
. 25 42 . 
. . 22 37 . 
. 23 1 . 
. —0 24 
30 . 
. 19 43 . 
. . 32 25 . 
. 33 19 . 
. —0 54 
20 . 
. 13 20 . 
. . 39 0 . 
. 40 4 . 
.—14 
10 . 
6 44 . 
. . 44 0 . 
. 43 49 . 
. +0 11 
These results, obtained in every part of the quadrant, completely establish 
the accuracy of the formula. The differences are all within the limits of the 
errors of observation, and amount, at an average, to 32^' on each observation. 
It is a curious circumstance, which I believe has not before been remarked, 
that at an incidence of 45° the deviation produced by refraction, or i—i 1 , is, in 
every substance, the complement of the angle of refraction i to 45° ; and in the 
action of all substances upon polarized light at an incidence of 45°, the rotation 
of the plane of polarization of a pencil polarized + 45°, or — 45°, is equal to 
t he angle of refraction; while the inclination of the plane of polarization to 
the plane of reflexion, or <p, is equal to the deviation i—i. 
In order to establish the accuracy of the formula for different degrees of 
refractive power, I made the following experiments on Diamond, in ivhich the 
index of refraction was 2.440. 
