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 



r/E 

 (a + ib) =j- + (o + id) [EH] = V curl H, 



^ = -FcurlB, 



taking /x = 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 Ej which is steady, as we are only 

 considering the case of a steady current. This produces in the 

 plate a steady flow of ions 



-5 + -PBXHJ, 

 a 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! 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 Ej. 



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. 



