of the current due to induction, is sometimes called the counter current. (36) If an additional resistance v is suddenly thrown into the circuit, as by breaking contact, so as to force the current to pass through a thin wire of resistance v, then the original current is u =[xi]/R and the final current is b = [xi]/R + v. The current of induction is then [half][xi] 2R + v / R(R + v) and continues for a time 2 L / R + v. This current is greater than that which the battery can maintain in the two wires R and r and may be sufficient to ignite the thin wire v. When contact is broken by separating the <s>parts<\s> wires in air this additional resistance is given by the interposed air and since the electromotive force across the new resistance may be estimated equal to [half][xi} v / R a spark will be force across If the elctromotive force is of th form E sin pt as in the case of a coil revolving in a magnetic field then x = E/[rho] sin (pt  [alpha]) where [rho]<sup>2<\sup> = R<sup>2<\sup> + L<sup>2<\sup>p<sup>2<\sup> and tan [alpha] = L p/R
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Manuscript details
 Author
 James Clerk Maxwell
 Reference
 PT/72/7
 Series
 PT
 Date
 1864
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Cite as
J. C. Maxwell’s, ‘Dynamical theory of the electromagnetic field’, 1864. From The Royal Society, PT/72/7
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