ssing through it, and yet the spark on breaking
contact was scarcely visible. The experiment was repeated with a wire
one-ninth of an inch in diameter and thirty-six feet long with the same
results.

1069. That the effects, and also the action, in all these forms of the
experiment are identical, is evident from the manner in which the former
can be gradually raised from that produced by the shortest wire to that of
the most powerful electro-magnet: and this capability of examining what
will happen by the most powerful apparatus, and then experimenting for the
same results, or reasoning from them, with the weaker arrangements, is of
great advantage in making out the true principles of the phenomena.

1070. The action is evidently dependent upon the wire which serves as a
conductor; for it varies as that wire varies in its length or arrangement.
The shortest wire may be considered as exhibiting the full effect of spark
or shock which the electromotor can produce by its own direct power; all
the additional force which the arrangements described can excite being due
to some affection of the current, either permanent or momentary, in the
wire itself. That it is a _momentary_ effect, produced only at the instant
of breaking contact, will be fully proved (1089. 1100.).

1071. No change takes place in the quantity or intensity of the current
during the time the latter is _continued_, from the moment after contact is
made, up to that previous to disunion, except what depends upon the
increased obstruction offered to the passage of the electricity by a long
wire as compared to a short wire. To ascertain this point with regard to
_quantity_, the helix i (1053.) and the galvanometer (1055.) were both made
parts of the metallic circuit used to connect the plates of a small
electromotor, and the deflection at the galvanometer was observed; then a
soft iron core was put into the helix, and as soon as the momentary effect
was over, and the needle had become stationary, it was again observed, and
found to stand exactly at the same division as before. Thus the quantity
passing through the wire when the current was continued was the same either
with or without the soft iron, although the peculiar effects occurring at
the moment of disjunction were very different in degree under such
variation of circumstances.

1072. That the quality of _intensity_ belonging to the constant current did
not vary with the circumstances favouring the pecul