Philosophical Transattions. 341 



light ; bnt Dr. Brewster, by employing a different method of obser- 

 vation, 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 polar- 

 ized light. He afterwards discovered the curious property possessed 

 by silver and gold of dividing a polarized ray into complementary 

 colours by successive reflexions. Mr. 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 

 jnore 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 polar- 

 ized 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 ex- 

 amining 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 re- 

 flexion ; and that in several cases the whole incident pencil is com- 

 pletely polarized. 



The action of metals upon polarized light forms the subject of 

 the second section of this paper, in which he investigates the 

 changes which polarized light undergoes accordingly as it is re- 

 flected at different angles of incidence, and in different azimuths of 

 the plane of primitive polarization. The light experiences in these 

 cases a physical change of a nature intermediate between that of 

 completely polarized light, and light wholly unpolarized ; neither 

 does it possess the same characters as that which has passed 

 through thin crystallized plates. Its constitution is exceedingly 

 analogous to light which is circularly polarized ; that is, which 

 comports itself as if it revolved with a circular motion during its 

 transmission through particular media. But in the case of circular 



