382 Mr Bevan, The Influence on Light reflected from and 



Now in the second term H x is not very large and E' is small 

 compared with E x so that the second term is to the fourth in the 

 ratio E' : E 1 and can be neglected, both terms being small com- 

 pared to the other terms in this expression. 



The equation is therefore 



( a + t b) ^ + - 1 + - [E 1} H x + H'] = V curl (H, + H'), 



dt <T <T 



E \ 



and as — + - [EiHj] = V curl H 1} 



d"R' "X 

 (a + ib)^ + - [BjHI = V curl H', 

 at o" 



as the first equation connecting the electric and magnetic forces 

 due to the light vibrations. 

 We have also 



^5=-FcurlE'. 

 dt 



For convenience we write the equations 



a^ + *7[P.H]=FcurlH, 



^ H = _FcurlE, 

 dt 



and we suppose the current parallel to Ox so that P representing 

 the current E. M. F. is (P, 0, 0). 



If then the forces in a disturbance propagated in the metal 

 vary as c<fc+»»+«*+p0 we h ave 



apX =V{mN-nM)\ 



apY- 7 PN=V(nL-lN) \ (1), 



apZ + yPM =V(IM- ml) J 



and p(L, M, N) = - V(mZ-nY, nX-lZ, IY - mX) (2). 



We have therefore 



apXIX + yP (Mn - Nm) = 0, 



tLl = 0, 



2LX = 0. 



And therefore the magnetic force is in the wave front, the 

 electric force is perpendicular to the magnetic force but not 

 accurately in the wave front. 



