66 



Article III. 

 Memoir on Metallic Reflexion. By M. J. Jamin*. 



[From the Annates de Chimie et de Physique for March 1847.] 



T N a remarkable memoir published in the Philosophical Trans- 

 actions for April 1830, Sir David Brewster called the atten- 

 tion of scientific men to the phrenomena presented by the reflexion 

 of metals ; and without endeavouring to determine the nature of 

 the modifications produced on light by metals, he performed 

 experiments which led him to the discovery of some isolated 

 laws, of which he gave no theoretical explanation. Since that 

 period, metallic reflexion has become the object of continued 

 researches ; some mathematical, of which we shall often have 

 occasion to speak in the sequel ; the others experimental, too 

 few in number for the complete solution of the problem, often 

 destitute of the necessary precision, and employing very com- 

 plicated methods of measurement. It is with the intention of 

 simplifying these methods and extending these researches, that 

 I have undertaken the following experiments. Before proceeding 

 to them I shall recapitulate the most simple and general laws 

 discovered by Sir David Brewster. 



1. If a ray of light, polarized in azimuths of 0° or 90°, be 

 reflected from a metal any number of times, it always remains 

 polarized in the same plane after reflexion. 



2. Every ray, which before reflexion is polarized in any other 

 azimuth, becomes partially depolarized after having undergone 

 the action of the metal. 



3. If we cause a beam of natural light to fall on a metallic 

 mirror, it is not polarized by reflexion at any incidence ; and 

 when examined by a polariscope, presents the appearances of a 

 partially polarized ray. Sir David Brewster has also remarked, 

 and this is an important observation, that there exists a particular 

 incidence for which the proportion of light polarized by reflexion 

 is greater than for any other ; this incidence has been called the 

 angle of maximum polarization. 



* The Editor has to acknowledge his obligations to Alfred W. Hobson, B, A., 

 St. John's College, Cambridge, who kindly undertook the translation of this 

 paper. 



