REFLEXION AND REFRACTION OF POLARIZED LIGHT. 97 



will be complementary to that which it was before. Professor 

 Airy was led to anticipate this result from the consideration of 

 Fresnel's expressions, and afterwards verified it on trial,* appa- 

 rently without any knowledge of the facts observed by M. Arago. 

 A similar confirmation of the same principles may be obtained by 

 combining, in Fresnel's experiment, a metallic reflector with one 

 of glass. The light being polarized perpendicularly to the plane 

 of reflexion, the central band will be white, when the angle of inci- 

 dence is below the polarizing angle of the glass ; at the polarizing 

 angle, the interference bars will vanish altogether ; and beyond 

 that incidence they will reappear with a dark centre, instead of a 

 white one. This .method of observation would seem to be pecu- 

 liarly adapted to the investigation of the change of phase produced 

 by metallic reflexion at various incidences. 



By the same considerations Professor Airy was led to expect 

 that when Newton's rings were formed between two transparent 

 substances of different refractive powers the light being polarized 

 perpendicularly to the plane of incidence, the rings should be 

 black-centred, when the incidence was less than the polarizing 

 angle of the low-refracting substance, or greater than that of the 

 high-refracting substance ; while they should appear with a white 

 centre, when it was intermediate to these angles ; the vibrations 

 of the waves reflected from the two surfaces being of opposite signs 

 in the former case, and of the same sign in the latter. All these 

 expectations were fully confirmed by experiment.! The sub- 

 stances selected by Professor Airy for these observations were 

 plate-glass and diamond, these substances differing very widely 

 in their refractive powers ; and in the course of his experiments 

 he has noticed certain peculiarities in the phenomena, from which 

 he has drawn some highly interesting conclusions respecting the 

 nature of reflexion from diamond. Had this been subjected to 

 the ordinary laws, the reflexion should cease, and the rings dis- 

 appear, at the polarizing angles of both substances. This however 

 was not the case. The rings did not vanish at the polarizing 

 angle of the diamond ; but the first black ring contracted, as the 

 incidence was gradually increased, and finally usurped the place 



* "On a Remarkable Modification of Newton's Rings." Cambridge Trans. 1832. 

 t " On the Phenomena of Newton's Kings, when formed between two tram-parcn 

 substances of different refractive powers." Cambridge Trans. 1832. 



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