566-568] Examples 493 



We now see that the strengths of the molecular currents will be changed 

 by induction in such a way that the electrokinetic momentum of each remains 

 unaltered. If the molecule is placed in a magnetic field whose lines of force 

 run in the same direction as those from the molecule, then the effect of induc- 

 tion is to decrease the strength of the molecule until the aggregate number 

 of tubes of force which cross it is equal to the number originally crossing it. 

 This effect of induction is of the opposite kind from that required to explain 

 the phenomenon of induced magnetism in iron and other paramagnetic sub- 

 stances. It has, however, been suggested by Weber that it may account for 

 the phenomenon of diamagnetism. 



568. Modern views as to the structure of matter compel us to abandon 

 Ampere's conception of molecular currents, but this conception can be 

 replaced by another which is equally capable of accounting for magnetic 

 phenomena. On the modern view all electric currents are explained as the 

 motion of streams of electrons. The flow of Ampere's molecular current may 

 accordingly be replaced by the motion of rings of electrons. The rotation 

 of one or more rings of electrons would give rise to a magnetic field exactly 

 similar to that which would be produced by the flow of a current of electricity 

 in a circuit of no resistance. 



It is on these lines that it appears probable that an explanation of 

 magnetic phenomena will be found in the future. No complete explanation 

 has so far been obtained, for the simple and sufficient reason that the arrange- 

 ment and behaviour of the electrons in the molecule or atom is still unknown. 



REFERENCES. 



On the general dynamical theory of currents : 



MAXWELL. Electricity and Magnetism, Vol. n, Part iv, Chaps, vi and vn. 

 On rapidly alternating currents : 



J. J. THOMSON. Recent Researches in Electricity and Magnetism, Chap. vi. 

 On Ampere's theory of magnetism : 



MAXWELL. Electricity and Magnetism, Vol. n, Part iv, Chap. xxn. 



EXAMPLES. 



1. Two wires are arranged in parallel, their resistances being R and S, and their 

 coefficients of induction being L, M, N. Shew that for an alternating current of frequency 

 p the pair of wires act like a single conductor of resistance R and self-induction L, given by 



B 



RS (R+ S) +p* {R (N- M) Z +S (L - M ) 2 } 



L 



