The action of metals upon light has always presented a remarkable, and hitherto inexplicable, anomaly in the science of polarization. Malus, to whom this branch of optics owes its origin, had at first announced that metals exerted no polarizing influence on light; but Dr. Brewster, by employing a different method of observation, ascertained that the light reflected from metallic surfaces was modified in such a manner as to exhibit, when transmitted through thin crystallized plates, the complementary colours of polarized light. He afterwards discovered the curious property possessed by silver and gold, of dividing a polarized ray into complementary colours by successive reflexions. M. Biot, to whom the author communicated this discovery, pursued the inquiry to which it led, and arrived at the same conclusions as to the mode in which this class of phenomena should be explained. Subsequent researches, however, convinced the author that these generalizations had been too hastily formed; and the study of Fresnel’s curious discoveries' respecting circular polarization enabled him to advance still further in the inquiry, and he now presents to the Royal Society in this paper, a complete analysis of the singular phenomena exhibited in the action of metals upon light. The first section of the paper treats of the action of metals upon common light. A ray of common light reflected from a metallic surface when analysed by a rhomb of calcareous spar, exhibits a defalcation of light in one of the images, as if a portion of the light was polarized in the plane of reflexion. This effect will be still more distinctly seen on examining the system of polarized rings formed round the axes of crystals by means of the light reflected from metals. If the light had suffered no modification by reflexion, or if the metal reflected in equal quantities the light polarized in opposite planes, the rings would not be visible at all, whereas it is found that they are easily visible in the light reflected from all metals. They are most distinctly perceived at an incidence of about 74°, and become more and more faint as the incidence succeeds or falls short of that angle. They appear best defined in light reflected from galena, and from metallic lead, and with least distinctness in light reflected from silver and gold. On examining the effect of successive reflexion of the same ray by metallic surfaces, the author found that the quantity of light which each polarizes in the plane of reflexion, increases with every reflexion, and that in several cases the whole incident pencil is completely polarized.
X. On the elliptic polarization of light by reflexion from metallic surfaces