98 



JAMIN ON METALLIC REFLEXION. 



Copper. — Angles and azimuths of polarization restored by 

 multiplied reflexions. 



The last experiments which we have to examine are those in 

 which the two planes of incidence make with each other a deter- 

 minate angle (w). Sir David Brewster caused the light to be re- 

 flected from the first surface at a determinate and constant angle, 

 then he sought by experiment for the incidence at which it was 

 necessary to reflect the light from the second plate in order to 

 restore the polarization : these are the experiments which Sir 

 David Brewster has represented by an empirical construction, 

 highly ingenious no doubt, but without any theoretical explana- 

 tion (the complements of the angles of incidence on the second 

 surface were made equal to the radii vectores of an ellipse) : it 

 will not be useless to show that in this latter case also, the theory 

 is perfectly accordant with the facts. 



The calculation made, pages 86 and following, applies here 

 without its being necessary to change anything in it. An inci- 

 dent ray polarized in the azimuth (90°— a) was reflected at the 

 first metallic plate at a given incidence ; it produces, after re- 

 flexion, two beams polarized in the principal azimuths, repre- 

 sented by the formulae 



