AND TRANSMITTED BY THIN PLATES. 169 



led to detect some curious phenomena of the rings, when the light 

 is polarized perpendicularly to the plane of incidence, which had 

 escaped the notice of preceding observers. 



In applying his theory, however, to light polarized in any 

 plane, M. Jamin disregards, as insensible, the additional terms 

 which depend upon the Cauchian phase. His formulas, thus 

 simplified, should therefore accord with those obtained in the 

 present paper for a plate bordered on both sides by the same 

 medium. Such, however, is not the case : the results, in fact, are 

 entirely at variance, M. Jamin's formulas giving plane-polarized 

 light at the extreme incidence, where (according to the theory 

 above given) the departure from plane polarization is greatest. 

 I believe that this discrepancy is accounted for by an error, into 

 which M. Jamin seems to have fallen, in computing the maximum 

 difference of phase of the two components of the light, which are 

 polarized respectively in the two principal planes. 



