438 Mr Bevan, Reflexion and Transmission of Light 
Reflexion and transmission of Light by a Charged Metal- 
Surface. By P. V. Bey an, B.A., Trinity College. 
\Read 5 May 1902.] 
As there appears to be an essential difference between positive 
and negative charges of electricity with regard to the matter 
associated with the charges, it seems probable that some differ- 
ence should be observable in the effect of charging a metal mirror 
positively and negatively on light reflected from the mirror. 
We can suppose that a charged metal consists of the metal 
itself in the ordinary condition with a layer on its surface of 
corpuscles which are associated with the electrical charge. In 
the case of negatively charged metals these corpuscles would be 
of the nature of cathode particles, while with positively charged 
surfaces the corpuscles would be molecules from which a negative 
particle had been abstracted. The equations for the metallic 
medium will now be altered as this layer will consist of these 
corpuscles in greater abundance than throughout the substance 
of the metal, so that for the case of reflected light we have to 
consider three media, the air, the layer containing the charge and 
the body of the metal itself. 
We can consider the layer with the' charge to be very thin 
indeed, as compared with the wave-length of light, so that in our 
equations we can finally put the thickness of this layer = 0, keep- 
ing the surface density finite. 
Suppose in the charge layer we have n' charges per unit 
volume, which we cao suppose freely moveable in the direction 
parallel to the surface, but not in the direction normal to the 
surface. Let the axis of Z be normal to the metal, Ox and Oy 
in the surface. 
Then the equations we may take for a corpuscle are, if f, rj, f 
represent its displacement, 
= eX, 
mi) =eY, 
m% = eZ — a 2 f, 
