388 Mr Bevan, The Influence on Light reflected from and 
And again with v = v 1 — tv 2 , a being — a + ih, this ratio 
_ na — v l + i (nh + vfl 
na + v i + t ( nb — v 2 ) ’ 
so that in this case the change of phase on reflection is 
m _ 1 2 (av i + bv 1 )n 
p n 2 (a 2 + h 2 ) — v j 2 — v 2 ' 
And for the additional change of phase due to the current 
dT x 
VL = Ol/j +=- 0 v 2 , 
VV\ OV 2 
where Bvi, $v 2 ns before, are equal to 
v 2 
Vi 
Vi* + V 2 ' 
We get the change of phase in this case as a fraction of the 
wave-length 
XPtan^.r 1-3 k* 
4ttV n' s (l + k 2 f } 
for incidences not very far removed from the normal, so that again 
the change is too small to be measured. 
Consider now the effect of the current on the velocity of the 
light transmitted through the metal. In the metal the velocity 
of the light is 
r= p 
flVPfl 2 ’ 
and this 
P 
flap 4- v 2 * 
The velocity V' will therefore be different when the current 
flows in the metal from its value in the metal without any current. 
The change in the velocity is 
and is therefore 
dVf 
dv 9 
Sv. 2 , 
pv 2 &V 2 
(af 2 + v 2 fl \ 
# 
which is 
yv\v 2 </> 
(ap + v 2 2 fl (v 2 +vp’ 
Let us now consider the case of light passing through a thin 
metal plate, and then find the effect on the emergent light of 
