Oscillatory Theory of Light. 413 



Angle of Relative 



incidence. acceleration. 



o 



Perpendicular incidence . J undulation. 



Principal incidence \ undulation. 



Grazing incidence ... 90 



In the case of total reflexion, light polarized in planes per- 

 pendicular to the plane of incidence has its phase more accele- 

 rated than light polarized in that plane, by an amount to which 

 the formulae of Fresnel give a close approximation. 



The proposed hypothesis has not yet been applied to reflexion 

 from doubly refracting crystals ; but there can be little doubt 

 that it will be found to represent the phenomena correctly. 



6. Of Circular and Elliptic Polarization. 



Light polarized in a plane oblique to the angle of incidence 

 is, generally speaking, elliptically polarized after reflexion, the 

 plane-polarized components of the disturbance being in different 

 phases. 



According to the hypothesis of oscillations, circularly and 

 elliptically polarized light, being compounded of oscillations in 

 different phases round two transverse axes, consist in a sort of 

 nutation of the longitudinal axis of each luminiferous atom. The 

 direction of this nutation, and the form of the circle or ellipse 

 described by the ends of the longitudinal axes, serve to define 

 the character of the light. The ellipse of nutation has its axes 

 in the same proportion with, but perpendicular in position to, 

 those of the elliptic orbit supposed to be described by each atom 

 according to the hypothesis of vibrations. 



The molecular mechanism by which certain media transmit 

 right- and left-handed circularly or elliptically polarized light 

 with different velocities, is still problematical according to either 

 hypothesis. The laws of the phsenomena, however, may be 

 represented by means of the assumption, that in the substances 

 in question the extraneous load on the luminiferous atoms is a 

 function of the direction of nutation. 



7. Of Dispersion. 



If we assume the extent of sensible direct action of the polarity 

 of the luminiferous atoms to be appreciable as compared with 

 the length of a wave, the velocity of propagation (precisely as 

 with the vibratory hypothesis) is found to consist of a constant 

 quantity, diminished by the sum of a series in terms of the 

 reciprocal of the square of the length of a wave. 



It may be doubted, however, whether this supposition is of 

 itself adequate to explain the phsenomena of dispersion ; and 



