416 Dr. A. H. Bucherer on a New Principle 



Suppose a system A contains only magnets and B only 

 electric charges; then the observer, whom we imagine always 

 to be on the passive system, will interpret the action exerted 

 on his system as electric or magnetic according as he stays 

 on B or on A. Evidently the electric action must equal the 

 magnetic action, and we have the relation 



.i E PBdT=-jjHa„, A ^ (5) 



Of "particular interest are the forces which uniform mag- 

 netic and electric field exert on moving electrons. They are 

 different from those of the Maxwellian theory. Suppose an 

 electron moves between the poles of an electromagnet, then, 

 according to equation (3), the force on the passive electron 

 is 



V u r x sq <r m dg 



F = 



(l- r2 snr 7 ) 



Y gl u (6) 



Here g is the outward normal erected on the positive 

 surface of the pole. For 4W m we can put H , the field 

 intensity as measured by an observer at rest with the electro- 

 magnet. We then can write for the force exerted on the 

 electron : 



F = VH u- — *— -,.,... (7) 



whereas the Maxwellian theory furnishes 



</VH u. 



Equation (7) can be tested by the deviation of Becquerel 

 rays in a magnetic field. 



Equation (4) furnishes the force which an electron ex- 

 periences in a uniform electric field, for instance in that of a 

 condenser. Let the surface-density of electricity on the 

 condenser-plate be a, then evidently 



F= Cf ri 9 v*s<r dg 



Atti 



^(s^r l 



-{•.Jw-r}. • • (8) 



