144 On the Equivalent Shell of a Circular Current. 



and v is equal to unity. Forces between rings of the same 

 kind alone come in, forces between electric and magnetic 

 rinos cancelling each other if the displacement is very smalh 

 Equating the two expressions 



e () 2 _W_ JV»o_ 



from which we immediately get 



" i 

 and 



e () = VKm 

 nt — Vfie . 



Comparing these with our equivalence formulae we see 

 A=V. Also, 



or 



fo 



m * ~ 



K 



e 



m 



VK~ 



y/fi 



(vi.) 



which is the ultimate equivalence formula*. 



§ 6. Conclusion, 



If the above be true we may develop our conception of the 

 system of electromagnetic ring doublets of which the electric 

 and magnetic currents are relative aspects. We may con- 

 ceive the two rings as elastic and as spinning round opposite 

 to each other and continually threading each other. The 

 spinning supplies the motive power for the threading, the 

 distance apart between two corresponding portions of the 

 two rings pursuing each other depending on the velocity. 



It appears the pole may be taken as the fundamental 

 physical entity just as the electron. The diameter of the 

 electron from Fleming's formula comes out to be of the 

 order 10 _4 ' 3xl ° n cm. The electron or the magnetic pole 

 may be an u electromagnetic doublet" of corpuscles of this 

 diameter. 



If we assume an electric and a magnetic fluid to fill all 

 space, the a electromagnetic doublet" may be regarded as 

 an electric and a magnetic vortex, having the same recti- 

 linear and circular axes and spinning in opposite directions, 

 superposed on one another. These two vortical motions 



* See Lodge's ' Electrons,' Appendix C. 



