Of the Rays of Light. 177 
greater than 90°, or the angle of incidence below or above the polarizing angle. For 
very oblique reflexion, then, both displacements are negative ; and, therefore, whether 
the plane of polarization coincides with, or is perpendicular to, the plane of reflexion, 
the wave will undergo a change of half a phase at the instant of reflexion. 
From Sir Davip Brewsrter’s important researches on the nature of metallic reflexion, 
it appears that a plane-polarized ray, which is incident upon a metallic reflector, be- 
comes elliptically-polarized after reflexion ; a result which indicates a difference in the 
phases of the two resolved vibrations. But it appears further, from the same researches, 
that this difference of phase varies with the incidence, and vanishes altogether at the 
extreme incidences; so that at the limiting incidence of 90°, there is either no alteration 
in the phase of vibration, whether parallel or perpendicular to the plane of reflexion, 
or that alteration is the same for the two vibrations. From some observation of the 
fringes produced by the interference of direct light with that reflected from speculum 
metal, I conclude that the former is the case. 
