plate
similar to those formerly used (101.), but of interminable length; the
inner and outer edges were amalgamated, and the conductors applied one to
each edge, at the place of the magnetic poles. The current of electricity
evolved did not appear by the galvanometer to be stronger, if so strong, as
that from the circular plate (88.).

136. In the other, small thick discs of copper or other metal, half an inch
in diameter, were revolved rapidly near to the poles, but with the axis of
rotation out of the polar axis; the electricity evolved was collected by
conductors applied as before to the edges (86.). Currents were procured,
but of strength much inferior to that produced by the circular plate.

137. The latter experiment is analogous to those made by Mr. Barlow with a
rotating iron shell, subject to the influence of the earth[A]. The effects
obtained by him have been referred by Messrs. Babbage and Herschel to the
same cause as that considered as influential in Arago's experiment[B]; but
it would be interesting to know how far the electric current which might be
produced in the experiment would account for the deflexion of the needle.
The mere inversion of a copper wire six or seven times near the poles of
the magnet, and isochronously with the vibrations of the galvanometer
needle connected with it, was sufficient to make the needle vibrate through
an arc of 60 deg. or 70 deg.. The rotation of a copper shell would perhaps decide
the point, and might even throw light upon the more permanent, though
somewhat analogous effects obtained by Mr. Christie.

[A] Philosophical Transactions, 1825. p. 317.

[B] Ibid. 1825. p. 485.

138. The remark which has already been made respecting iron (66.), and the
independence of the ordinary magnetical phenomena of that substance and the
phenomena now described of magneto-electric induction in that and other
metals, was fully confirmed by many results of the kind detailed in this
section. When an iron plate similar to the copper one formerly described
(101.) was passed between the magnetic poles, it gave a current of
electricity like the copper plate, but decidedly of less power; and in the
experiments upon the induction of electric currents (9.), no difference in
the kind of action between iron and other metals could be perceived. The
power therefore of an iron plate to drag a magnet after it, or to intercept
magnetic action, should be carefully distinguished from the similar p