l effect occurred at the
galvanometer. No other deflection than that due to the thermo-electric
current was observable the whole time. Hence, though a conductor, and one
capable of exerting chemical action on the tin, was used, yet, not being an
_electrolyte_, not the slightest effect of an electrical current could be
observed (947.).

923. From this it seems apparent that the peculiar character and condition
of an electrolyte is _essential_ in one part of the voltaic circuit; and
its nature being considered, good reasons appear why it and it alone should
be effectual. An electrolyte is always a compound body: it can conduct, but
only whilst decomposing. Its conduction depends upon its decomposition and
the _transmission of its particles_ in directions parallel to the current;
and so intimate is this connexion, that if their transition be stopped, the
current is stopped also; if their course be changed, its course and
direction change with them; if they proceed in one direction, it has no
power to proceed in any other than a direction invariably dependent on
them. The particles of an electrolytic body are all so mutually connected,
are in such relation with each other through their whole extent in the
direction of the current, that if the last is not disposed of, the first is
not at liberty to take up its place in the new combination which the
powerful affinity of the most active metal tends to produce; and then the
current itself is stopped; for the dependencies of the current and the
decomposition are so mutual, that whichsoever be originally determined,
i.e. the motion of the particles or the motion of the current, the other is
invariable in its concomitant production and its relation to it.

924. Consider, then, water as an electrolyte and also as an oxidizing body.
The attraction of the zinc for the oxygen is greater, under the
circumstances, than that of the oxygen for the hydrogen; but in combining
with it, it tends to throw into circulation a current of electricity in a
certain direction. This direction is consistent (as is found by innumerable
experiments) with the transfer of the hydrogen from the zinc towards the
platina, and the transfer in the opposite direction of fresh oxygen from
the platina towards the zinc; so that the current _can pass_ in that one
line, and, whilst it passes, can consist with and favour the renewal of the
conditions upon the surface of the zinc, which at first determined both the
com