2 Lord Rayleigh on Reflexion from Liquid Surfaces 



itself, the point corresponding to the polarizing angle, at 

 which the reflexion vanishes, and in passing which there is a 

 sudden change of phase of 180°. If the reflexion remains 

 finite at all angles, the curve in question meets the axis Y Y' 

 at some point P, not coincident with 0, and the correspond- 

 ing phase differs by a quarter-period from the phases met 



IT 



X 



with at a distance from this angle. So far as experiment 

 can yet show, this curve may be a straight line parallel to 

 X X', and at a short distance from it. If it lie above X X' 

 the reflexion is what Jamin characterizes as positive ; if below, 

 the reflexion is negative. 



To this order of approximation the behaviour of a trans- 

 parent body reflecting light of given wave-length is determined 

 by two constants, (1) the refractive index /jl, and (2) the 

 intensity of reflexion at the angle tan~V when the light is 

 polarized perpendicularly to the plane of incidence. The 

 most convenient form of the second constant for experimental 

 purposes is the ratio of reflected amplitudes for the two prin- 

 cipal planes w r hen the light, incident at the angle tan -1 //,, is 

 polarized at 45° to these planes. It may be called the 

 ellipticity, and, after Jamin, will be denoted by k. According 

 to Fresnel k = Q ; but Jamin found for water k= —'00577, and 

 for absolute alcohol k= +'00208. Contrasting liquids with 

 solids, he remarks*, u on vient de voir que leur polarisation 

 est elliptique, et qu'il est impossible d'en trouver la cause 

 dansune constitution moleculaire anormale." And, again: — 

 " II est jusqu'a present impossible de constater une relation 

 simple entre la valeur du coefficient h et l'indice de refraction ; 

 tout porte a croire, au contraire, que ces deux constantes sont 

 independentes, Fune de l'autre. Mais, a defaut de loi pre- 



* " Memoire sur la reflexion de la Lumiere a la surface des Liquides." 

 Ann. Chim. xxxi. p. 16-5 (1851). 



