J. C. Maxwell’s, ‘Dynamical theory of the electromagnetic field’

```                                p/P - q/Q - r/R + s/S + h(1/P - 1/Q) + k(1/R - 1/P) + l(1/R + 1/Q) - m(1/P + 1/S) + n(1/Q - 1/S) + o(1/S - 1/R) = [tau] (26)
we find Z/z = 2 sin[half][alpha]/tan[theta] T/[pi] = [tu]/1 - [rho] (27)
In determining [tau] by experiment it is best to make the alteration
of resistance in one of the arms by means of the arrangement
described by Mr Jenkin in the Report of the British Association
for 1863 by which any value of [rho] from 1 to 1.01 can be accurately
measured.

<s>If<\s> We observe [alpha], the greatest deflexion due to the impulse
of induction when the galvanometer is in circuit when the
as to give no permanent current.

We then observe [beta] the greatest deflexion produced by the
permanent current when the resistance of one of the arms is
increased in the ratio of 1 to [rho], the galvanometer not being
in circuit till a little while after the connexion is made with
the battery.

In order to eliminate the effects of resistance of the air, it
is best to vary [rho] till [beta] = 2[alpha] nearly then
[tau]= T 1/[pi](1 - [rho]) 2 sin[half][alpha] / tan[half][beta] (28)
If all the arms of the balance except P consist of resistance
coils of very fine wire of no great length and doubled before
being coiled, the induction coefficients belonging to these
coils will be insensible and [tau] will be reduced to
p/P. The electric balance therefore affords the means
of measuring the self induction of any circuit whose
resistance is known

(46) It may also be used to determine the coefficient of induction
between two circuits as for instance, m, but it would be more convenient to measure this by directly
measuring the current as in (37) without  using the balance
We may also ascertain the equality of p/P and q/Q by there being no

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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