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LXII. Faraday's "Magnetic Lines " as Quanta. — Part I. 

 By H. Stanley Allen, M.A., D.Sc, Reader in Physics 

 in the University of Edinburgh *. 



Introduction. 



I^ARADAY, in tbe third volume of his ' Experimental 

 Researches in Electricity/ returns again and again to 

 the discussion of the physical character of the lines of 

 magnetic force. Starting from the consideration of such 

 lines in the abstract " as expressing accurately the nature, 

 condition, direction, and amount of the force in any given 

 region either within or outside of the bar [magnet]," he 

 passes on to the inquiry "of the possible and probable 

 physical existence of such lines" (p. 438). "I cannot con- 

 ceive curved lines of force without the conditions of a 

 physical existence in that intermediate space" (p. 414). 

 "'Again and again the idea of an electro-tonic state has been 

 forced on my mind ; such a "state would coincide and become 

 identified with that which would then constitute the physical 

 lines of magnetic force" (p. 420). He considers the 

 question of their existence as "likely to be answered 

 ultimately in the affirmative" (p. 437). In language similar 

 to that employed by some supporters of the principle of 

 relativity, Faraday " endeavours to dismiss the aether, but 

 not the vibration " of the lines of force. 



In the present communication I propose to develop the 

 suggestion made in a paper f read before the Royal Society 

 of Edinburgh, 22 November, 1920, that the existence of 

 discrete lines of magnetic force, or as we should now term 

 them tubes of magnetic induction, is in accordance with the 

 requirements of the u quantum" theory, so that the quantum 

 is itself essentially magnetic. We may, in fact, regard a 

 unit tube of magnetic induction as one quantum. 



This view had its origin in the work of the late Prof. S. B. 

 McLaren on the magneton, but it is desirable to emphasize 

 the fact that the results to be given are independent of the 

 magneton hypothesis. They conform in many respects to 

 the mode of representation suggested by Sir Joseph Larmor 

 in the Physical Society Discussion on the Ring Electron 

 (1918) — " One or more electrons constrained to move round 

 a channel would be like an amperean current. It is not 

 unlikely that constraint of this kind will have to be 



* Communicated by the Author. 



t II. S. Allen, Proc. Roy. Soe. Edin. vol. xli. p. 34 (1921), 



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