168 Magnetic Held produced by Charged Condenser. 



We thus see that the part of the flux represented by 



— ■iirvdy J Nda? 



is just such as to annul the other portion represented by 



V ^dy [f C K 1 F^+ r D K 2 F^+ jKiFdff], 



the equivalent o£ which we found for the total flux 

 on page 154. If we prefer a rather less exact but more 

 vivid picture of the phenomenon, we may say that the total 

 magnetic flux produced by the motion of the tubes of force 

 between the elements of individual doublets, is just equal 

 and opposite to the magnetic flux produced by the motion of 

 the tubes joining different doublets. Considering the second 

 view in which the doublets exist, but are orientated at a. 

 haphazard manner in the absence of the electric force, we 

 must look upon them as being turned on the application of 

 the electric force so that their axes tend to point on the 

 average in one direction, to an extent depending on the 

 electric force. It is easy to see that the effect of this orien- 

 tation of the doublets is to reduce the potential difference 

 which would exist between the opposite faces of the dielectric 

 for the same distribution of charge on the charged plates, 

 and to the extent that this reduction AV is proportional to V, 

 we may write 



V VI 



, T — rr== = ■== — =-=-_ = = constant = K. 



V — AV V— pV 1—p 



The argument showing the absence of any magnetic flux 

 through a strip joining two points at the same potential 

 follows in a manner exactly similar to that given above. 

 On any conceivable view, in which dielectric action is to be 

 explained entirely by the presence of electric charges in the 



f E 1 f B 



dielectric, the expression | Yds must equal -7 — 5 1 fds, 



where the integral is taken along any path between A and B, 

 and the quantities P and / represent the components of the 

 polarization and of the true electric intensity at a point 

 within the dielectric respectively, and as we have seen this 

 latter integral vanishes when A and B are at the same 

 potential, so that on no theory of this kind can we obtain 

 any resultant magnetic flux through the closed circuit referred 

 to on page 154, due to the motion through space of a system 

 of charged bodies along with the circuit. 



