of Newton's Rings. 419 



When the light is incident at the polarizing angle of the 

 glass, the rings, so far as I can see, vanish totally. Though 

 I have looked several times with the most scrutinizing attention, 

 I have not been able to see the least trace. If the angle or" 

 incidence is gradually increased till it exceeds the polarizing 

 angle, the black-centered rings disappear gradually without al- 

 tering their size (a considerable quantity of light being still re- 

 flected from the diamond) and white-centered rings of the same 

 size appear in their place, without any intermediate stage except 

 a total absence of rings. From the agreement of this with theory 

 I conclude that the polarization of light at the inner surface 

 of glass is (to the senses) complete. But at the polarizing angle 

 of the diamond the case is perfectly different. On increasing 

 the angle of incidence till it exceeds this angle, the white- 

 centered rings do not disappear, but the first black ring con- 

 tracts so as to leave no central white, and becomes itself the 

 black center. After this there is no material change : I find 

 however that the black center of the rings produced by light 

 polarized perpendicular to the plane of reflection is always 

 (beyond the polarizing angle of the diamond) sensibly larger 

 than the black center of the rings produced by light polarized 

 in the plane of reflection. 



The nature of this transition from rings of one character to 

 rings of the opposite character appears to me to be, theoretically, 

 extremely curious. As the rings do not disappear, it is plain 

 that if light polarized perpendicular to the plane of incidence 

 (or whose vibrations are entirely in that plane) is incident at 

 what is called the maximum polarizing angle of the diamond, 

 a portion of it is still reflected. Still however on increasing the 

 angle of incidence the character of the rings is changed : and 



Vol. IV. Part III. 3H 



