with such rapidity as to present the appearance of a continued
discharge. If a long wire or an electro-magnet be used as the connecting
conductor instead of a short wire, a similar appearance may be produced by
tapping the vessel containing the mercury and making it vibrate; but the
sparks do not usually follow each other so rapidly as to produce an
apparently continuous spark, because of the time required, when the long
wire or electro-magnet is used, both for the full development of the
current (1101. 1106.) and for its complete cessation.

[A] Quarterly Journal of Science, vol. xii, p. 420.

1077. Returning to the phenomena in question, the first thought that arises
in the mind is, that the electricity circulates with something like
_momentum or inertia_ in the wire, and that thus a long wire produces
effects at the instant the current is stopped, which a short wire cannot
produce. Such an explanation is, however, at once set aside by the fact,
that the same length of wire produces the effects in very different
degrees, according as it is simply extended, or made into a helix, or forms
the circuit of an electro-magnet (1069.). The experiments to be adduced
(1089.) will still more strikingly show that the idea of momentum cannot
apply.

1078. The bright spark at the electromotor, and the shock in the arms,
appeared evidently to be due to _one_ current in the long wire, divided
into two parts by the double channel afforded through the body and through
the electromotor; for that the spark was evolved at the place of
disjunction with the electromotor, not by any direct action of the latter,
but by a force immediately exerted in the wire of communication, seemed to
be without doubt (1070.). It followed, therefore, that by using a better
conductor in place of the human body, the _whole_ of this extra current
might be made to pass at that place; and thus be separated from that which
the electromotor could produce by its immediate action, and its _direction_
be examined apart from any interference of the original and originating
current. This was found to be true; for on connecting the ends of the
principal wire together by a cross wire two or three feet in length,
applied just where the hands had felt the shock, the whole of the extra
current passed by the new channel, and then no better spark than one
producible by a short wire was obtained on disjunction at the electromotor.

1079. The _current_ thus separated was ex