438 Mr Bevan, Reflexion and Transmission of Light 



Reflexion and transmission of Light by a Charged Metal 

 Surface. By P. V. Bevan, 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 cau 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 £, n, £ 

 represent its displacement, 



m\ = eX, 



mi) =eY, 



mfc, = eZ — a 2 £, 



