OF ELLIPTIC POLARIZATION. 
299 
but in silver, where the polarization approaches nearly to circular, the oscilla- 
tions diminish very slowly in amplitude, as the following Table shows. 
No. of Reflexions 
from Silverat73° 
of Incidence. 
State of the Reflected Light. 
Inclination of the Plane of 
Polarization, or <p. 
Observed. Calculated. 
1 . . 
Elliptically polarized. 
2 
Restored to light polarized . 
. —38 15 . 
. —38 
15 
3 . . 
Elliptically polarized. 
4 . . 
Restored to light polarized . 
. +31 15 . , 
. +31 
52 
5 . . 
Elliptically polarized. 
6 . . 
Restored to light polarized . 
. -26 0 . 
. —26 
6 
12 . . 
Restored to light polarized . 
. +13 
30 
18 . . 
Restored to light polarized . 
. — 6 
42 
36 . . 
Restored to light polarized . 
• + o 
47 
Owing to the high dispersive power of silver, I found it difficult to carry the 
comparison any further with white light, as the colours closed in upon the 
points of evanescence, and rendered it impossible to determine with any pre- 
cision the inclination of the plane of polarization. 
The preceding results afford the clearest explanation of the phenomena which 
steel and silver exhibit in the reflexion of common light. As common light is 
similar to two equal pencils polarized +45° and —45°, and as steel brings two 
such pencils into a state of parallelism with the plane of reflexion, common 
light must therefore be wholly polarized in the plane of reflexion after 8 reflex- 
ions. In like manner we see why the same effect is not produced by silver, 
because after 8 reflexions the two planes of the pencils are inclined 42°, so as to 
form a partially polarized pencil. 
The same results also furnish us with a method of computing the proportion 
of polarized light in any pencil of common light, reflected from metals at 
angles at which the restoration of the elliptical polarized pencil is effected. In 
order to determine this proportion for steel after two reflexions at 75°, we must 
consider that a pencil polarized +45° is restored by these two reflexions to 
light polarized — 17°, and consequently a pencil polarized —45° to light pola- 
rized + 17°. Hence a beam of common light will consist after two reflexions of 
two pencils +17° and —17° of equal intensity, and consequently in the same 
