REFLEXION AND INFRACTION OF POLARIZED LIGHT. 175 



the incidence, being least when the light is incident perpen- 

 dicularly, and greatest when it is most oblique. On the 

 other hand, the value of 0', for light polarized perpendicu- 

 larly to the plane of incidence, diminishes from the perpen- 

 dicular incidence to the polarizing angle, at which it va- 

 nishes, and afterwards increases with the incidence up to 

 t = 90. 



"When i = 0, the values of v and v' are each equal to 



- =-, fj, being the refractive index ; and the intensity of the 

 light reflected perpendicularly is 



This remarkable expression was first given by Young. 



On the other hand, when i = 90, or when the ray grazes 

 the surface, the intensity of the reflected light is equal to 

 that of the incident ; or the whole of the light is reflected, 

 whatever be the reflecting substance. 



(188J We have seen that a ray of common light is equiva- 

 lent to two polarized rays of equal intensity, whose planes of 

 polarization are at right angles. Now, let such a ray, whose 

 intensity = 1, be incident upon the surface of a transparent 



medium ; and let it be resolved into two, each equal to -, po- 



Z 



larized respectively in the plane of incidence, and in the per- 

 pendicular plane. Each of these polarized rays will give 

 rise to a reflected and refracted ray; so that the actual 

 reflected and refracted rays will consist of two portions, 

 one polarized in the plane of incidence, and the other in 

 the perpendicular plane. If these portions were of equal 

 intensity, as they are in the incident light, the reflected and 



