256 ON THE REFLEXION AND REFRACTION OF LIGHT. 



But the part of the equation (3) belonging to this surface, 

 and which yet remains to be satisfied, is 



dv 



ff 

 JJ 



do. dw n 



- dy 



j/ j; 73 , s . 



dydz 5 ( + - 8,, 4- B, - + 



and as 8^ = 8^, &c., we obtain, as before, 



.. /du dv dw\ fdo dw\ 

 \dx dy dz) \dy dzl 



and these belong to the particular value cc = 0. 



The six particular conditions (5) and (6), belonging to the 

 surface of junction of the two media, combined with the six 

 general -equations before obtained, are necessary and sufficient 

 for the complete determination of the motion of the two media, 

 supposing the initial state of each given. We shall not here 

 attempt their general solution, but merely consider the propa- 

 gation of a plan6 wave of infinite extent, accompanied by its 

 reflected and refracted waves, as in the preceding paper on 

 Sound. 



Let the direction of the axis of 0, which yet remains arbi- 

 trary, be taken parallel to the intersection of the plane of the 

 incident wave with the surface of junction, and suppose the dis- 



