382 Mr Bevan , The Influence on Light reflected from and 
Now in the second term H 2 is not very large and E' is small 
compared with Ej so that the second term is to the fourth in the 
ratio E' : Ej and can be neglected, both terms being small com- 
pared to the other terms in this expression. 
The equation is therefore 
✓Jin' ■p 
(a + ib) =- + 1 + - [E 1? H x + H'] = V curl (H, + H'), 
at or a 
E \ 
and as — 4- - [EjHd = V curl H 1; 
cr a 
r/E r A 
(a + ib) jr + - [EjH'] = V curl H , 
dt <r L J 
as the first equation connecting the electric and magnetic forces 
due to the light vibrations. 
We have also 
dU' 
dt 
= - V curl E'. 
For convenience we write the equations 
r7E 
a + ly [PH] = V curl H, 
f/H ir 
- = - V curl E, 
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 we have 
a pX = V mN — nM)\ 
apY — yPN = V ( nL -IN) l (1), 
apZ + 7 PJf - V ( IM - mL) J 
and p(L, M, N) = - V(mZ-nY, nX - IZ , IY - ml) (2). 
We have therefore 
apZIX + yP (. Mn - Nm) = 0, 
tLl = 0, 
2ZX = 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. 
