(39. 50.); and is a strong proof in addition to those advanced by M.
Ampere, of the identity of the agents concerned in these several
operations. It probably occurs, momentarily, during the passage of the
common electric spark (24.), and may perhaps be obtained hereafter in bad
conductors by weak electrical currents or other means (74. 76).

68. The state appears to be instantly assumed (12.), requiring hardly a
sensible portion of time for that purpose. The _difference_ of time between
volta-electric and magneto-electric induction, rendered evident by the
galvanometer (59.), may probably be thus explained. When a voltaic current
is sent through one of two parallel wires, as those of the hollow helix
(34.), a current is produced in the other wire, as brief in its continuance
as the time required for a single action of this kind, and which, by
experiment, is found to be inappreciably small. The action will seem still
more instantaneous, because, as there is an accumulation of power in the
poles of the battery before contact, the first rush of electricity in the
wire of communication is greater than that sustained after the contact is
completed; the wire of induction becomes at the moment electro-tonic to an
equivalent degree, which the moment after sinks to the state in which the
continuous current can sustain it, but in sinking, causes an opposite
induced current to that at first produced. The consequence is, that the
first induced wave of electricity more resembles that from the discharge of
an electric jar, than it otherwise would do.

69. But when the iron cylinder is put into the same helix (31.), previous
to the connexion being made with the battery, then the current from the
latter may be considered as active in inducing innumerable currents of a
similar kind to itself in the iron, rendering it a magnet. This is known by
experiment to occupy time; for a magnet so formed, even of soft iron, does
not rise to its fullest intensity in an instant, and it may be because the
currents within the iron are successive in their formation or arrangement.
But as the magnet can induce, as well as the battery current, the combined
action of the two continues to evolve induced electricity, until their
joint effect is at a maximum, and thus the existence of the deflecting
force is prolonged sufficiently to overcome the inertia of the galvanometer
needle.

70. In all those cases where the helices or wires are advanced towards or