6 John Mills 



larized. If, however, the plane polarized portions of the two 

 beams which go to form the fringes have been rotated through 

 an angle of an odd multiple of 90 ° with respect to each other, 

 the fringes previously due to them will disappear. Interference 

 phenomena due to the natural light portions of the same beams 

 would still be observable unless these also had suffered a similar 

 rotation. 



w 



N 



U— ^ 



In the form in which the observations given above were taken 

 each tube was susceptible at the point of a minimum of rotation 

 of an odd multiple of 45°. Of the light entering the interferom- 

 eter (see the accompanying figure) a portion of that reaching 

 tube EW is plane polarized by reflection from the dividing sur- 

 face 1 ab and by transmission through the compensating plate cd, 



1 In the present form of the interferometer the dividing surface of ad was 

 used uusilvered. 



T50 



