380 Mr Bevan , The Influence on Light reflected from and 
The Influence on Light reflected from and transmitted through 
a Metal of a Current in the Metal. By P. V. Bevan, B.A., Trinity 
College, Cambridge. 
[ Received 19 February 1902.] 
The equations applicable to metallic media under the influence 
of light vibrations may be written 
(a + ob^ + ic + cd) [EH] 
d H 
dt 
V curl H, 
— -V curl E, 
taking g = 1 as we only deal with vibrations of such rapidity 
that the magnetic properties of the metals become lost. 
The constants in the first equation are obtained by considering 
the effect of corpuscles in the metal which are of two types, those 
which are confined to a certain region and can perform oscillations 
about an equilibrium position, and others which can move more 
or less freely from one region to another in the metal. (Cf. Drude, 
Reports presented to the International Congress on Physics, Paris 
1900.) I propose to consider the case of light reflected at the 
surface of a metal carrying a current. 
The first of the above equations must be modified since we 
have a constant external force E x which is steady, as we are only 
considering the case of a steady current. This produces in the 
plate a steady flow of ions 
Ei X r n 
- + - e.h,], 
( t cr 
where the first term is the ordinary conduction term according to 
Ohm’s Law and the second term represents the Hall effect, a 
representing the specific resistance of the metal. 
The state of the metal is now different from its state when 
no current passes, since the force E x may be sufficient to dislodge 
some of the ions which before the current was flowing were per- 
forming oscillations and the freely moving corpuscles have now on 
the average a velocity in the direction of the force E x . 
Leaving out of account the constants c, d since they involve 
the ratio of the velocity of a corpuscle to that of light, we confine 
ourselves to the consideration of the constants a and b. 
