angement passed between the poles
of the magnet, in the direction parallel to these edges, a current was
urged through the wires attached to the outer angles, and the galvanometer
became strongly affected; but when a single film of paper was interposed,
and the experiment repeated, no sensible effect could be produced.

128. A section of this kind could not interfere much with the induction of
magnetism, supposed to be of the nature ordinarily received by iron.

129. The effect of rotation or deflection of the needle, which M. Arago
obtained by ordinary magnets, M. Ampere succeeded in procuring by
electro-magnets. This is perfectly in harmony with the results relative to
volta-electric and magneto-electric induction described in this paper. And
by using flat spirals of copper wire, through which electric currents were
sent, in place of ordinary magnetic poles (Ill.), sometimes applying a
single one to one side of the rotating plate, and sometimes two to opposite
sides, I obtained the induced currents of electricity from the plate
itself, and could lead them away to, and ascertain their existence by, the
galvanometer.

130. The cause which has now been assigned for the rotation in Arago's
experiment, namely, the production of electrical currents, seems abundantly
sufficient in all cases where the metals, or perhaps even other conductors,
are concerned; but with regard to such bodies as glass, resins, and, above
all, gases, it seems impossible that currents of electricity, capable of
producing these effects, should be generated in them. Yet Arago found that
the effects in question were produced by these and by all bodies tried
(81.). Messrs. Babbage and Herschel, it is true, did not observe them with
any substance not metallic, except carbon, in a highly conducting state
(82.). Mr. Harris has ascertained their occurrence with wood, marble,
freestone and annealed glass, but obtained no effect with sulphuric acid
and saturated solution of sulphate of iron, although these are better
conductors of electricity than the former substances.

131. Future investigations will no doubt explain these difficulties, and
decide the point whether the retarding or dragging action spoken of is
always simultaneous with electric currents.[A] The existence of the action
in metals, only whilst the currents exist, i.e. whilst motion is given (82.
88.), and the explication of the repulsive action observed by M. Arago (82.
125.), are powerful re