ON THE POLARIZATION OF LIGHT. 



247 



SO comprehensive, the author has been induced to copy it 

 verbatim. 



E p 



H 



Fig. 157. 





f*"^\; 



" A B, C D, represent the rectangular vibrations by which 

 a ray of common light is supposed to be propagated. 



" E, a plate of tourmaline, called in this situation the 

 polarizer, and so turned that A B may vibrate in the plane of 

 its crystallographical axis. 



" F, light polarized by E, by stopping the vibrations C D, 

 and transmitting those of A B. 



" G, a piece of selenite of such a thickness as to produce 

 red light and its complementary colour, green. 



" H, the polarized light F bifurcated, or divided into ordi- 

 nary and extraordinary rays, and thus said to be dipolarized 

 by the double refractor Gr, and forming two planes of polarized 

 light o and e, vibrating at right angles to each other. 



" I, a second plate of tourmaline, here called the analyzer, 

 with its axis in the same direction as that of E, through which 

 the several systems of waves of the ordinary and extraordinary 

 rays H, not being inclined at a greater angle to the axis of the 

 analyzer than that of 45", are transmitted and brought together 

 under conditions that may produce interferences. 



" K, the waves E," and E-' for red light of the ordinary and 

 extraordinary systems meeting in the same state of vibration, 

 occasioned by a difference of an even number of half undu- 

 lations, and thus forming a wave of doubled Intensity for 

 red light. 



" L, M, the waves Y° and Y' and B" and B^ for yeUow and 



