406 Mr green, on THE REFLEXION AND 



_ ds cP(f) <P(p, 



^^) rff - ^ to + df) • 



Similarly, in the lower medium 



^ ' df ^' \dx' dfj' 

 where 



y,dt A, 



The above are the known general equations of fluid motion, which 

 must be satisfied for all the internal points of both fluids ; but at the 

 surface of separation, the velocities of the particles perpendicular to this 

 surface and the pressure there must be the same for both fluids. Hence 

 we have the particular conditions 



d(p _ d<p, \ 



dx dx \ (where x = 0), 



As = A,s, ) 



neglecting such quantities as are very small compared with those retained, 

 or by eliminating .9 and s\, we get 



d(p _ d(p, ' 



dx dx 



{A) 



dt " ' dt] 



r (when X = 0). 



The general equations (1) and (2), joined to the particular conditions 

 {A) which belong to the surface of separation {y%), only, are sufficient 



