Notes on some Points in the Theory of Light. 215 



cidence ; while for all less values of the refractive index the in- 

 tensity will be least at the perpendicular incidence. 



Let i and i' be the angles of incidence and refraction, and 

 put" 



, sin i cos i 



M = -T v,, p = r, ; 



sin i cos i 



then if / be the intensity of the reflected light, when common 

 light is incident, Fresnel's expression 



1 _ j ( sin 2 (i - i'} tan 2 (i - i'} 

 T j an' (* + **) + Fan 2 (i + i) 



in which the intensity of the incident light is taken for unity, 

 may be put under the form 



which has a minimum value when 



+ l = M+ _ 8 



*"M 



the value of / being in that case 



J = 





and the corresponding angle of incidence being given by the 

 formula 



, 



sm l = - /-r T > where B * 



6 + V 2 -l 



Since /u + - cannot be less than 2, it is easy to see that, when 



