166 Dr. W. F. G. Swann on the Magnetic Field jirodnced 



quantity whose line integral across the dielectric is K times- 

 the potential difference between A and B. 



"Viewing the matter from the standpoint we have adopted,, 

 we are driven to the conclusion, that though the dielectric 

 acts at all points outside it or at a point in a hole inside it 

 as though the tubes did actually pass continually through it,, 

 nevertheless, they do not run continuously in this way ; in 

 fact, between the elements of a doublet the tubes actually 

 pass in the opposite direction to the ordinarily defined polari- 

 zation. At each point inside the material of the dielectric, 

 we must look upon the number of tubes of force per square 

 centimetre as being algebraically made up of two parts : 



(1) the number ordinarily defined as the polarization, and 



(2) the number contributed in the opposite direction by the 

 separation of the two kinds of electricity in the doublets.. 

 At any point outside the dielectric the second set is of course 



T7"T}V 



absent. The ifirst set is equal to -r — 2 , where F' is the 



electric intensity as ordinarily understood, at a point within 

 the dielectric. The second set N' is such that 



f s K ^, f\ TJ 1 /Potential difference \ 1 f ^ 7 



J R W F ^-J R N ^ = W( between R and S ) = wj/^ 



so that K-lf* f» 



where F and N are the resolved portions of F' and N' along 

 the path RS, along which the integral is taken, for it is to 

 be remembered that we are admitting no mysterious method 

 of modifying the force in the dielectric other than that due 

 to the charges. The physical effect of the doublets is to 

 reduce the work which we should do in taking a unit of 

 electricity from R to S, since when between the elements 

 of a doublet we should be assisted in our journey, the effect 

 being greater, the greater the moments of the doublets ; and 

 to the extent that we may assume the effect produced by the 

 doublets to be proportional to the potential difference V 

 which would exist between the planes of opposite faces of 

 the dielectric if the dielectric were absent and the charges 

 on C and D were the same as at present, we may write AV 

 (the lowering of the potential difference between the faces) 

 as AV=pV, where p is a constant. The specific inductive 



V 1 



capacity will then be ^-ry or 1 _ • 



