422 Professor Airy on the Phenomena 



while the angle of incidence is a few degrees less than the maxi- 

 mum polarizing- angle of the diamond, the phase of light polar- 

 ized perpendicular to the plane of reflexion is more retarded than 

 the phase of light polarized in that plane. 



I have not found any variation in these results from changing 

 the position of the plane of reflexion on the diamond surface. 



The result of these experiments and reasonings may be thus 

 stated. 



1. When the angle of incidence is less than the maximum 

 polarizing angle of the diamond, the nature of its reflexion is 

 similar to that of metallic reflexion : the phase of vibrations in 

 the plane of reflexion being more retarded than that of vibrations 

 perpendicular to the plane of reflexion, but perhaps by a smaller 

 quantity than in reflexion from metals. 



2. In the neighbourhood of the polarizing angle, the nature of 

 the reflexion is different from any that has hitherto been de- 

 scribed. The vibrations in the plane of reflexion do not vanish, 

 but on increasing the angle of incidence by three or four degrees 

 the phase of vibration is gradually retarded by nearly 180°. In 

 the reflexion of light whose vibrations are perpendicular to the 

 plane of reflexion there is no striking difference between the ef- 

 fects of diamond and those of glass. 



3. For angles of incidence greater than the polarizing angle, 

 there is no sensible difference between the effects of diamond 

 and those of glass. 



I may remark that the extent of vibration in the plane of 

 reflexion may be represented thus (the formula being purely 

 empirical and given only for illustration). The vibration in the 



incident light being asm — (vt-x) that in the reflected lisrht is 



A 



