408 Mr green, on THE REFLEXION AND 



media. But these by substitution give 



af{hy + ct) - aF{hy + ct) = a,f:{J>y + c/), 

 l^\f{hy + ct) + F'{hy + cf)} = AX(6y + c^, 

 because a' = — a, and a; = 0. 



Hence by writing, to abridge, the characteristics only of the functions 



(7) 



or if we introduce Q, 6^, the angles of incidence and refraction, since 



cot ^ = T . 



cot 0,= ^, 



/A, cote N 



•^ Ma cot^y" 



^,^^/A, _COt^N 



^ Va cote/"^'' 



A, _ cote^ 



, ,, » 7^ A cote 

 and therefore -^ = —■ , 



A cot e 

 which exhibits under a very simple form, the ratio between the intensities 

 of the disturbances, in the incident and reflected wave. 



But the equations (6) give 



and hence 



7 _ 7, 



sin 9 sin 9/ 

 the ordinary law of sines. 



