REFLEXION OF POLARIZED LIGHT. 



251 



pointing out how they are connected with the two theo- 

 ries of light ; how in the theory of emission I do not 



values very much resembling the last yet differing from them; 

 viz: 



sin (i r) . sin 2 i 



(7.) 



(8.) 



sin. (i+ r) sin (i + r) 



If we draw lines perpendicular to the directions of these rays, they 



will also form a similar triangle, among whose sides the same rela- 

 tions will subsist. Hence, Professor Maccullagh inferred that these 

 would represent the directions of the vibrations in the plane of inci- 

 dence ; and as the lengths or amplitudes of these vibrations are un- 

 known, but are dependent upon, as they are the measures of, the 

 vibratory forces acting, so if one of the sides of the triangle be 

 assumed to represent the magnitude of the incident vibration, the 

 others will represent those of the reflected and refracted rays, they 

 being the mechanical components of which the former is the resul- 

 tant. 



On this construction, and by assuming the hypothesis of equal 

 density within and without the medium, he deduced the above form- 

 ulas (7.) (8.) for vibrations parallel to the plane of incidence, and 

 others resembling (3.) and (4.) for vibrations perpendiciilar to that 



