or _giving direction to the
ordinary chemical affinity_ of the bodies present. The body under
decomposition may be considered as a mass of acting particles, all those
which are included in the course of the electric current contributing to
the final effect; and it is because the ordinary chemical affinity is
relieved, weakened, or partly neutralized by the influence of the electric
current in one direction parallel to the course of the latter, and
strengthened or added to in the opposite direction, that the combining
particles have a tendency to pass in opposite courses.

519. In this view the effect is considered as _essentially dependent_ upon
the _mutual chemical affinity_ of the particles of opposite kinds.
Particles _aa_, fig. 53, could not be transferred or travel from one pole N
towards the other P, unless they found particles of the opposite kind _bb_,
ready to pass in the contrary direction: for it is by virtue of their
increased affinity for those particles, combined with their diminished
affinity for such as are behind them in their course, that they are urged
forward: and when any one particle _a_, fig. 54, arrives at the pole, it is
excluded or set free, because the particle _b_ of the opposite kind, with
which it was the moment before in combination, has, under the superinducing
influence of the current, a greater attraction for the particle _a'_, which
is before it in its course, than for the particle _a_, towards which its
affinity has been weakened.

520. As far as regards any single compound particle, the case may be
considered as analogous to one of ordinary decomposition, for in fig. 54,
_a_ may be conceived to be expelled from the compound _ab_ by the superior
attraction of _a'_ for _b_, that superior attraction belonging to it in
consequence of the relative position of _a'b_ and _a_ to the direction of
the axis of electric power (517.) superinduced by the current. But as all
the compound particles in the course of the current, except those actually
in contact with the poles, act conjointly, and consist of elementary
particles, which, whilst they are in one direction expelling, are in the
other being expelled, the case becomes more complicated, but not more
difficult of comprehension.

521. It is not here assumed that the acting particles must be in a right
line between the poles. The lines of action which may be supposed to
represent the electric currents passing through a decomposing liquid, hav