ning round that
helix should be rendered visible as a spark; and in this manner a spark was
obtained from ii when the junction of i with the electromotor was broken,
in place of appearing at the disjoined extremity of i itself.

1091. By introducing a galvanometer or decomposing apparatus into the
circuit formed by the helix ii, I could easily obtain the deflections and
decomposition occasioned by the induced current due to the breaking contact
at helix i, or even to that occasioned by making contact of that helix with
the electromotor; the results in both cases indicating the contrary
directions of the two induced currents thus produced (26.).

1092. All these effects, except those of decomposition, were reproduced by
two extended long wires, not having the form of helices, but placed close
to each other; and thus it was proved that the _extra current_ could be
removed from the wire carrying the original current to a neighbouring wire,
and was at the same time identified, in direction and every other respect,
with the currents producible by induction (1089.). The case, therefore, of
the bright spark and shock on disjunction may now be stated thus: If a
current be established in a wire, and another wire, forming a complete
circuit, be placed parallel to the first, at the moment the current in the
first is stopped it induces a current in the _same_ direction in the
second, the first exhibiting then but a feeble spark; but if the second
wire be away, disjunction of the first wire induces a current in itself in
the same direction, producing a strong spark. The strong spark in the
single long wire or helix, at the moment of disjunction, is therefore the
equivalent of the current which would be produced in a neighbouring wire if
such second current were permitted.

1093. Viewing the phenomena as the results of the induction of electrical
currents, many of the principles of action, in the former experiments,
become far more evident and precise. Thus the different effects of short
wires, long wires, helices, and electro-magnets (1069.) may be
comprehended. If the inductive action of a wire a foot long upon a
collateral wire also a foot in length, be observed, it will be found very
small; but if the same current be sent through a wire fifty feet long, it
will induce in a neighbouring wire of fifty feet a far more powerful
current at the moment of making or breaking contact, each successive foot
of wire adding to the sum of act