Transparent Plates upon Light. 31 
Fig. 3. 
_ Tn order to demonstrate these views by an analysis of the changes 
which the intromitted light experiences from the two refractions and 
the intermediate reflexion of a transparent plate, I took a plate of 
glass.of the shape MN (Fig. 3.) having an oblique face Md cut upon 
one of its ends. A ray of light RA, polarized + 45° and — 45°, 
was made to fall upon it at A, at an angle of incidence of nearly 83°, 
so that the inclination of the planes of polarization of the reflected 
ray A P was about 364°. Now the ray AC after reflexion in the 
direction C S, without any refraction at B, where it emerges perpen- 
dicularly to Md, would also have had the inclination of its planes of 
polarization equal to 364° if there had been no intermediate refrac- 
tion at A; but this refraction alone being capable of producing an 
inclination of 53° or a rotation of 53°—45°=8°, and this rotation 
being in an opposite direction from that produced by the second re- 
- flexion at C, the inclination of the planes of polarization for the ray - 
CS is nearly 444°, the reflexion at C having brought back the ray 
A C almost exactly into the state of natural light. 
Without changing either the light or the angle, I éemented 1 a prism 
Med onthe face Md, so that cd was parallel to dN, and I found 
that the second refraction at 6, equal to that at A, changed the incli- 
nation of the planes of polarization to 53°; that is, the two refrac- 
tive actions at A and b had overcome the action of reflexion at C, 
and the pencil }s actually contained light polarized perpendicular to 
the plane of reflexion. 
In order to to put this result to another test, I took a plate McNQ 
(Fig. 3.) of the same glass, which separated the pencil b s reflected 
at the second surface, from the parallel pencil A P reflected from the 
first surface, and [ found that at an angle of 83° the value of the 
inclination I or 9 for the ray was about 374°, while the value of I for 
the ray bs was nearly 55°, an effect almost equal to the refractive 
action of a plate at 83° of incidence. 
