OF ELLIPTIC POLARIZATION. 
293 
circularly polarized when it has suffered two total reflexions from glass at an 
angle of 54^° ; and when such a ray is made to suffer other two reflexions at 
the same angle, it is restored to the state of light polarized — 45° to the plane 
of reflexion, whatever be the azimuth of the second plane of reflexion in rela- 
tion to the first. In like manner I shall proceed to show that a ray of light 
polarized +45°, and reflected once at the maximum polarizing angle from 
metals and certain metallic ores, has an analogous polarization, viz. a polari- 
zation hitherto unrecognized, and intermediate between circular and rectilineal 
polarization. 
Let the ray polarized +45° be reflected at ~b 0 from steel, and let a second 
plate of steel be made to turn round the ray thus reflected. At the azimuths 
of 45°, 135°, 225°, and 315°, with the plane of primitive polarization, that is, 
when the planes of the two reflexions are either coincident or rectangular, the 
first reflected ray will be restored to polarized light at an incidence of 75°. At 
azimuths of 0° and 1 80° the restoration will be effected at an incidence of 80°, 
while at azimuths of 90° and 270° it will take place at an incidence of 70°, and 
at intermediate azimuths it will take place at intermediate incidences. Hence 
the ray of light reflected from steel, though it has the general properties of a 
circularly polarized ray, differs from it in this remarkable particular, that it 
requires different angles of incidence in different azimuths to restore the po- 
larized light. 
In circular polarization, as we have seen, the ray has the same properties in 
all its sides ; and the angles of reflexion at which it is restored to polarized 
light in different azimuths are all equal, like the radii of a circle described 
round the ray. Hence, without any theoretical reference, the term circular 
polarization is from this and other facts experimentally appropriate. In like 
manner, without referring to the theoretical existence of elliptic vibrations pro- 
duced by the interference of two rectilineal vibrations of unequal amplitudes, 
we may give to the new phenomena the name of elliptic polarization, because 
the angles of reflexion at which this kind of light is restored to polarized light 
may be represented by the variable radius of an ellipse. 
In circular polarization the restored ray has its plane of polarization always 
inclined — 45° to the plane of the second system of reflexions. In elliptic 
polarization the difference is remarkable. The inclination of the plane of the 
